RARE DISEASE
Atypical Rett syndrome
Atypical Rett syndrome
Atypical Rett syndrome
Synonyms: Atypical RTT, Rett syndrome variant
Synonyms: Atypical RTT, Rett syndrome variant
Synonyms: Atypical RTT, Rett syndrome variant
Drug discovery
0
drugs
With orphan designations
Overview
Atypical Rett syndrome is a neurodevelopmental disorder caused by MECP2 mutations or other genetic variants (e.g., CDKL5), characterized by partial loss of acquired skills (e.g., hand use, language), gait abnormalities, and stereotypic hand movements. Diagnosis requires ≥2 core symptoms, ≥5 supportive criteria (e.g., scoliosis, sleep disturbances), and exclusion of brain injury. It presents with variable severity, later onset, or incomplete regression compared to classic RTT, affecting ~1/45,000 females. Management focuses on symptom relief and supportive care [7][9][11].
Burden
Progressive motor-behavioral decline: 48.5% pediatric patients require hospitalization/ER visits; adults face higher rates of scoliosis (73.9%) and seizures (56.5%) [4][14].
Lifelong dependency: 80% require assistive devices; 40–60% need gastrostomy feeds or respiratory support [1][4][7].
Economic/emotional strain: High caregiving demands and unmet therapeutic needs despite symptom management [4][7].
Therapies
Multidisciplinary care: Physical/occupational therapy (87% pediatric use), speech-language therapy, and behavioral interventions [1][4].
Medications: Antiepileptics (e.g., carbamazepine), prokinetics for GI motility, melatonin for sleep, and scoliosis management (bracing/surgery) [3][4][7].
Emerging therapies: Gene replacement and RNA/DNA editing in clinical trials [8][13][18].
Categories: rare genetic diseases, rare neurological diseases
Research Papers
279 drug discovery papers about Atypical Rett syndrome, with 4 first-in-class emerging drug candidates forecasted to outperform the average preclinical success rate. Recent publications:
279 drug discovery papers about Atypical Rett syndrome, with 4 first-in-class emerging drug candidates forecasted to outperform the average preclinical success rate. Recent publications:
categories:
Small molecules
oligonucleotides
2024-03-14 | Synthetic dosage-compensating miRNA circuits for quantitative gene therapy
A longstanding challenge in gene therapy is expressing a dosage-sensitive gene within a tight therapeutic window. For example, loss of MECP2 function causes Rett syndrome, while its duplication causes MECP2 duplication syndrome. Viral gene delivery methods generate variable numbers of gene copies in individual cells, creating a need for gene dosage-invariant expression systems. Here, we introduce a compact miRNA-based, incoherent feed-forward loop circuit that achieves precise control of Mecp2 expression in cells and brains, and improves outcomes in an AAV-based mouse model of Rett syndrome gene therapy. Single molecule analysis of endogenous and ectopic Mecp2 mRNA revealed precise, sustained expression across a broad range of gene dosages. Delivered systemically in a brain-targeting AAV capsid, the circuit strongly suppressed Rett behavioral symptoms for over 24 weeks, outperforming an unregulated gene therapy. These results demonstrate that synthetic miRNA-based regulatory circuits can enable precise in vivo expression to improve the safety and efficacy of gene therapy.
2023-01-20 | Site-directed A → I RNA editing as a therapeutic tool: moving beyond genetic mutations
Adenosine deamination by the ADAR family of enzymes is a natural process that edits genetic information as it passes through messenger RNA. Adenosine is converted to inosine in mRNAs, and this base is interpreted as guanosine during translation. Realizing the potential of this activity for therapeutics, a number of researchers have developed systems that redirect ADAR activity to new targets, ones that are not normally edited. These site-directed RNA editing (SDRE) systems can be broadly classified into two categories: ones that deliver an antisense RNA oligonucleotide to bind opposite a target adenosine, creating an editable structure that endogenously expressed ADARs recognize, and ones that tether the catalytic domain of recombinant ADAR to an antisense RNA oligonucleotide that serves as a targeting mechanism, much like with CRISPR-Cas or RNAi. To date, SDRE has been used mostly to try and correct genetic mutations. Here we argue that these applications are not ideal SDRE, mostly because RNA edits are transient and genetic mutations are not. Instead, we suggest that SDRE could be used to tune cell physiology to achieve temporary outcomes that are therapeutically advantageous, particularly in the nervous system. These include manipulating excitability in nociceptive neural circuits, abolishing specific phosphorylation events to reduce protein aggregation related to neurodegeneration or reduce the glial scarring that inhibits nerve regeneration, or enhancing G protein-coupled receptor signaling to increase nerve proliferation for the treatment of sensory disorders like blindness and deafness.
2022-04-01 | Loss of neurodevelopmental-associated miR-592 impairs neurogenesis and causes social interaction deficits
Abstract microRNA-592 (miR-592) has been linked to neurogenesis, but the influence of miR-592 knockout in vivo remains unknown. Here, we report that miR-592 knockout represses IPC-to-mature neuron transition, impairs motor coordination and reduces social interaction. Combining the RNA-seq and tandem mass tagging-based quantitative proteomics analysis (TMT protein quantification) and luciferase reporter assays, we identified MeCP2 as the direct targetgene of miR-592 in the mouse cortex. In Tg (MECP2) mice, lipofection of miR-592 efficiently reduced MECP2 expression in the brains of Tg (MECP2) mice at E14.5. Furthermore, treatment with miR-592 partially ameliorated the autism-like phenotypes observed in adult Tg( MECP2 ) mice. The findings demonstrate that miR-592 might play a novel role in treating the neurodevelopmental-associated disorder.
2019-04-30 | Enhancing Neuronogenesis and Counteracting Neuropathogenic Gene Haploinsufficiencies by RNA Gene Activation.
Small activating RNAs (saRNAs), targeting endogenous genes and stimulating their transcription, are a promising tool for implementing a variety of neurotherapeutic strategies. Among these there is the stimulation of select histogenetic subroutines for purposes of cell-based brain repair, as well as the therapeutic treatment of gene expression deficits underlying severe neurological disorders.We employed RNA activation (RNAa) to transactivate the Emx2 transcription factor gene in embryonic cortico-cerebral precursor cells. This led to enhanced self-renewal, delayed differentiation, and reduced death of neuronally committed precursors, resulting in a remarkable expansion of the neuronogenic precursors pool. These results are of paramount interest for purposes of gene-promoted brain repair. As such, RNAa makes therapeutic stimulation of neuronogenesis via Emx2 overexpression a feasible goal, preventing the drawbacks of exogenous gene copies introduction.Moreover, we employed RNAa to achieve a gentle transactivation of the Foxg1 transcription factor gene, specifically in cortico-cerebral cells. This manipulation led to an appreciable biological outcome, while complying with endogenous gene tuning linked to early central nervous system regionalization and late activity of neocortical projection neurons. Foxg1-activating miRNAs stimulated RNApolII recruitment, possibly via Ago1. One of them worked promisingly in vivo. As such, RNAa can be a valuable approach for therapeutic treatment of the FOXG1-haploinsufficiency-linked variant of the Rett syndrome. Remarkably, hemizygosity for specific genes and polygenic chromosomal segments underlies a huge number of neuropathological entities for which no cure is presently available. Based on the results reported above, RNAa might be a simple and scalable approach for fixing this class of problems.
2019-01-04 | MicroRNAs and Long Non-coding RNAs in Genetic Diseases
Since the discovery and classification of non-coding RNAs, their roles have gained great attention. In this respect, microRNAs and long non-coding RNAs have been firmly demonstrated to be linked to regulation of gene expression and onset of human diseases, including rare genetic diseases; therefore they are suitable targets for therapeutic intervention. This issue, in the context of rare genetic diseases, is being considered by an increasing number of research groups and is of key interest to the health community. In the case of rare genetic diseases, the possibility of developing personalized therapy in precision medicine has attracted the attention of researchers and clinicians involved in developing "orphan medicinal products" and proposing these to the European Medicines Agency (EMA) and to the Food and Drug Administration (FDA) Office of Orphan Products Development (OOPD) in the United States. The major focuses of these activities are the evaluation and development of products (drugs, biologics, devices, or medical foods) considered to be promising for diagnosis and/or treatment of rare diseases or conditions, including rare genetic diseases. In an increasing number of rare genetic diseases, analysis of microRNAs and long non-coding RNAs has been proven a promising strategy. These diseases include, but are not limited to, Duchenne muscular dystrophy, cystic fibrosis, Rett syndrome, and β-thalassemia. In conclusion, a large number of approaches based on targeting microRNAs and long non-coding RNAs are expected in the field of molecular diagnosis and therapy, with a facilitated technological transfer in the case of rare genetic diseases, in virtue of the existing regulation concerning these diseases.
small molecules
2026-06-15 | Reduction in Seizure Generalization Associated With Long-Term Low-Dose Immunomodulatory Therapy Using Prednisolone and Methotrexate in Rett Syndrome: A Case Report.
Rett syndrome is a severe neurodevelopmental disorder most commonly associated with pathogenic variants of the MECP2 gene and frequently accompanied by epilepsy. Seizures occur in a substantial proportion of patients and may be resistant to conventional antiepileptic therapy. Emerging evidence suggests that neuroinflammatory processes may contribute to seizure propagation and represent a potential therapeutic target. A girl born at term with initially normal early development is described. At approximately 2 years of age, she developed regression of speech and stereotypic hand movements, accompanied by seizures and other neurological features consistent with Rett syndrome. The patient received long-term therapy consisting of low-dose prednisolone and methotrexate in addition to anticonvulsant treatment. During follow-up, a reduction in seizure generalization and a shift in seizure pattern were observed, with generalized seizures becoming less frequent and replaced by brief focal seizures without secondary generalization. In this single case, long-term low-dose prednisolone and methotrexate therapy was associated with a reduction in seizure generalization. Although a causal relationship cannot be established, this observation supports the hypothesis that immunomodulatory mechanisms may influence seizure propagation in pharmacoresistant epilepsy.
2026-06-01 | Heat shock factor 1 signaling: A novel pathway implicated in Rett syndrome pathophysiology
Rett syndrome (RTT) is a neurodevelopmental disorder that is associated with loss-of-function mutations in the methyl CpG binding protein 2 ( MECP2 ) gene. MECP2 regulates transcription both locally and globally, making it challenging to distinguish between genes that are pathogenic and those that constitute transcriptional noise. A rare subpopulation of patients lack MECP2 mutations despite presenting with sufficient symptoms to warrant a clinical diagnosis of RTT. These patients are classified as having atypical and MEPC2 mutation-negative forms of the disorder. We hypothesized that identifying pathways with conserved disruption between typical and atypical forms of RTT would be a viable mechanism to reduce transcriptional noise and identify which genes are most critical to their shared clinical presentation. To test this theory, we conducted differential RNA sequencing using five atypical RTT, six typical RTT (R255X), and nine neurotypical control temporal cortex autopsy samples. Pathways associated with heat shock factor 1 (HSF1) signaling were among the most enriched in both RTT populations. Validation studies using 37 patient temporal cortex samples showed that increased HSF1 signaling was enriched in those with classically severe MECP2 mutations. To investigate whether increased HSF1 signaling is compensatory or pathogenic, we conducted in vivo hyperthermia experiments complemented by cellular stress array analyses. These experiments established that RTT model mice exhibit faster and larger induction of cellular stress-associated proteins. Pharmacological induction of HSF1 in Mecp2 +/- mice was consistent with hyperthermia experiments, showing seizure-like phenotypes and lethality. Conversely, chronic inhibition of HSF1 signaling improved RTT-like phenotypes in domains of motor learning and general health. Together, these data suggest that promiscuous HSF1 signaling is likely a pathogenic amplifier of severe phenotypes and provide a rationale that inhibiting this pathology may hold therapeutic potential in RTT and related disorders. Significance statement Rett syndrome (RTT) is a devastating neurodevelopmental disorder with limited therapeutic options. This manuscript identifies Heat shock factor 1 (HSF1)-signaling a novel therapeutic target and proposes a molecular mechanism by which cellular stress responses are regulated in RTT.
2025-12-18 | Mesodermal-specific MECP2 expression in Drosophila induces visceral and skeletal muscle defects rescued by butyrate supplementation
Abstract Background Patients affected by Rett syndrome (RTT) and MECP2 duplication syndrome (MDS) experience disabling muscle weakness and gastrointestinal dysmotility of unclear origin. Whether these defects arise cell-autonomously, rather than secondarily to neural dysfunction, and which developmental windows are most vulnerable to MeCP2 disfunction remains unresolved. MeCP2 is a dosage-sensitive transcriptional regulator, whose functions are tightly linked to chromatin states. Because short-chain fatty acids (SCFAs) are known to inhibit histone deacetylases (HDACs), a tractable in vivo model is needed to test the effect of HDAC modulation on muscle defects. Methods We misexpressed human MECP2 in the Drosophila melanogaster mesoderm that gives rise to skeletal and visceral muscles. We analyzed quantitatively their morphology and function. To assess the effects of SCFA supplementation, we also supplemented diets with sodium butyrate (NaB), Lalbaay®, a NaB-containing supplement, acetate (AcOH), and valproate (VPA). Findings MECP2 misexpression caused pre-eclosion lethality, thinning of larval skeletal fibers with nuclear mispositioning and altered mitochondria. Functionally, it reduced locomotion, decreased food transit and gut peristalsis. Phenotypes were strongest when expression began during development. NaB and VPA supplementation rescue most of these phenotypes, consistent with their histone-deacetylase (HDAC) activity. Defects were not observed upon comparable misexpression of an RTT-associated MeCP2 loss-of-function variant, indicating that they might be relevant to pathogenesis of MECP2-related disorders. Interpretation Our genetic in vivo analysis models peripheral effects of MeCP2 dysregulation and their amelioration, supporting the possibility of HDAC-targeted strategies for MECP2-related muscle and gastrointestinal dysfunction.
2025-11-26 | Epigenetic Dysregulation in Rett Syndrome: Multisystem Pathophysiology, MECP2 Isoform-Specific Mechanisms, and Targeted Therapeutic Strategies
Rett syndrome (RTT), an X-linked neurodevelopmental disorder predominantly arising from de novo MECP2 mutations, manifests with psychomotor regression, stereotypic hand movements, gait apraxia, and expressive aphasia, driven by dosage-sensitive epigenetic dysregulation via MeCP2's methyl-CpG-binding domain (MBD) and transcriptional repression domain (TRD). Isoform-specific expression (MeCP2-E1 neuronal predominance) and X-chromosome inactivation mosaicism underpin phenotypic variability, with missense (R133C, T158M) and nonsense (R168X, R255X) variants correlating to severity gradients. Multisystem pathophysiology encompasses brainstem-mediated respiratory dysrhythmias, QTc prolongation via ion channel perturbations, enteric hypomotility, osteopenic fractures, and mitochondrial bioenergetic deficits, exacerbated by glial-neuronal crosstalk and oxidative stress. Preclinical platforms, including Mecp2-null rodents, patient-derived iPSCs, and cerebral organoids, elucidate synaptic hyperexcitability, dendritic arborization deficits, and reversibility upon Mecp2 reactivation. Therapeutic modalities span supportive multidisciplinary interventions, FDA-approved trofinetide (IGF-1 analog modulating neurotrophic cascades), AAV-mediated gene replacement (NGN-401, TSHA-102 with miRARE autoregulation), ASOs for dosage normalization, and emerging PPAR-γ agonists targeting metabolic homeostasis. Prioritized research agendas emphasize validated biomarkers (BDNF/IGF-1 axes, miRNA signatures), combinatorial regimens, and equitable global access to mitigate caregiver burden and phenotypic heterogeneity.
2025-11-20 | Butyrate modifies epigenetic and immune pathways in peripheral mononuclear cells from children with neurodevelopmental disorders associated with chromatin dysregulation.
Pathogenic DNA variants in chromatin-related genes constitute an important minority of neurodevelopmental disorders (NDDs). Epigenetic mechanisms, including chromatin regulation driven by genetic or environmental factors, are increasingly recognised as key contributors to pathogenesis of diverse NDDs. We hypothesise that therapeutic strategies targeting chromatin dysregulation, such as histone deacetylase inhibition with butyrate, may be a potential disease modifying therapy for NDDs. We first performed peripheral blood bulk RNA sequencing (RNA-seq) to explore baseline gene regulation in children with chromatin-related NDDs (Kabuki syndrome (KMT2D, n = 4), CHARGE syndrome (CHD7, n = 2), and Rett syndrome (MECP2, n = 5), and children with NDDs but without a monogenic diagnosis (non-monogenic, n = 8), compared with sex-matched healthy controls (total n = 21). Next, to explore the effects of butyrate, single-cell RNA sequencing (scRNA-seq) was performed on 101,539 peripheral immune cells from four selected patients (one per condition) and two controls, before and after butyrate treatment. At baseline, dysregulation of ribosomal and immune pathways was seen in all four NDD cohorts (KMT2D, CHD7, MECP2, non-monogenic) compared to controls. Butyrate largely reversed these pathways, normalising ribosomal and immune pathways in patient and control cells. Butyrate induced up-regulation of ribosome, GTPase, cytoskeletal, mitochondrial pathways, and down-regulation of epigenetic and immune pathways. In conclusion, we identified a common ribosomal-immune RNA signature in chromatin-related NDDs, and a similar signature in non-monogenic NDDs. We showed that butyrate modulates epigenetic and immune gene networks in monogenic and non-monogenic NDDs, positioning butyrate as a promising therapeutic modulator across diverse NDDs.
proteins
2026-05-11 | Toward an NGF-based therapy for Rett syndrome.
Rett syndrome (RTT) is a severe neurodevelopmental disorder primarily caused by mutations in the MECP2 gene. Although recent therapeutic advances, such as the approval of Trofinetide, offer partial relief, no comprehensive curative treatment is currently available. Among the emerging strategies, nerve growth factor (NGF) has gained attention due to its neurotrophic and immunomodulatory properties. This review, in addition to discussing the key features of RTT and the role of growth factors, also highlights recent evidence supporting NGF-based strategies for RTT, focusing on two independent studies that tested intranasal administration of NGF-like molecules in Mecp2-mutant mice. Both recombinant human NGF (rhNGF) and a modified, "painless" variant (hNGFp) improved behavioral (cognitive and motor) symptoms. While rhNGF primarily restored mitochondrial function, hNGFp restored neuroinflammatory responses through microglial regulation. Despite differences in molecular mechanisms and dosages, both molecules demonstrated efficacy without adverse effects, especially when administered intranasally, preventively, and over longer periods. These findings suggest that NGF may act through dual mechanisms, by supporting energy homeostasis and regulating immune responses. The use of intranasal delivery further enhances translational potential by overcoming blood-brain barrier limitations. Together, these studies provide a strong rationale for pursuing NGF-based therapies in RTT and encourage further investigations to optimize dosing, timing, and safety in preclinical and clinical settings.
2026-05-11 | Clinical experience using trofinetide in Rett syndrome and related MECP2 diagnosis at the children's hospital of Philadelphia post approval.
Rett syndrome (RTT) is a rare neurodevelopmental disorder primarily caused by pathogenic variants in the MECP2 gene. Trofinetide (Daybue) became the first FDA-approved medication for RTT in March 2023. This study evaluates the real-world effectiveness and side effect profile of Trofinetide in 55 individuals (50 females, 5 males) with RTT or MECP2-related neurodevelopmental disorders over a 12-month period. Data was collected through clinic assessments and caregiver reports. Results demonstrated that 75.9% of individuals experienced some improvement in RTT symptoms by caregiver report, particularly in engagement, communication, and motor skills. The side effect profile was better than the phase 3 trials with only 48.1% reporting diarrhea and 16.7% experiencing vomiting. Overall, the findings support the effectiveness of trofinetide in the RTT population and suggests potential effectiveness in the broader MECP2 population including males and those with atypical presentations. The data highlights the need for further work to determine long-term benefits in the full spectrum of MECP2 related disorders. Finally, the study highlights the importance of titration, individualized dosing and side effect management to improve retention and outcomes.
2026-01-01 | THE GENE THAT SILENCES CHILDHOOD: INSIGHTS INTO RETT SYNDROME
Rett syndrome (RS) is an uncommon, degenerative neurodevelopmental disorder that affects around 1 in 10,000-15,000 female children and occurs primarily as a result of mutations in the MECP2 gene on the X chromosome. Children with RS appear to develop normally until the first six to eighteen months, when they begin to regress and experience characteristic symptoms, including loss of the ability to use their hands purposefully, inability to develop spoken language, abnormal walking abilities, and stereotyped hand movement patterns. The atypical variants of RS are the result of mutations in the CDKL5 and FOXG1 genes and may present with earlier onset of seizure activity or no normal developmental period. Dysfunction of the MECP2 gene disrupts transcriptional regulation of genes involved with synaptic connectivity (how the neurons talk to each other), neuronal maturation, and the balance between excitatory and inhibitory actions on the nervous system resulting in seizure activity, impairment of movement, irregular respiratory function, dysregulation of the autonomic nervous system (which controls the automatic processes of the body), and severe cognitive impairment. Diagnosis is based upon patterns of clinical regression and is confirmed through genetic testing. Current treatment for RS is supportive and done by a team of medical professionals. Goals for supportive treatment are to provide individuals with seizure control, nutrition, physical therapy, and behavioral management. While there is no cure for RS, advances in molecular research have led to the approval of Trofinetide, and ongoing research studies using gene therapy, RNA correction, and neurotrophic modulation for RS are showing promise as disease-modifying treatments. Early diagnosis, coordination of care across the continuum of care, and the advancement of research will continue to improve the quality of life and outcomes for individuals with Rett syndrome.
2025-10-23 | Pediatric intestinal pseudo‐obstruction found in 3‐year‐old male with Rett‐related mutation of methyl‐CpG binding protein 2
Abstract A 3‐year‐old male with chronic abdominal distention, constipation, and severe malnutrition is diagnosed with pediatric intestinal pseudo‐obstruction (PIPO) after extensive evaluation that excluded mechanical, malabsorptive, metabolic, inflammatory, and infectious causes. Aside from speech delay, he has a normal neurologic exam. Whole exome sequencing reveals a pathogenic methyl‐CpG binding protein 2 (MECP2) variant, suggesting atypical Rett syndrome. Management includes promotility agents and a gastrostomy tube with cyclic feedings of peptide‐based formula, leading to resolution of symptoms. This case highlights the diagnostic complexity of PIPO and the need to consider genetic etiologies, including MECP2‐related disorders, even in patients with mild neurologic findings. Early genetic testing and multidisciplinary care are essential for diagnosis and management in this atypical presentation of Rett syndrome with manifestation of PIPO.
2025-07-21 | Altered oscillatory coupling reflects possible inhibitory interneuron dysfunction in Rett syndrome
Rett syndrome is a rare neurodevelopmental disorder caused primarily by pathogenic variants in the MECP2 gene, leading to lifelong cognitive impairments. To understand the broad neural disruptions in Rett syndrome, it is essential to examine large-scale brain dynamics at the level of neural oscillations. Phase-amplitude coupling, a form of cross-frequency interaction that supports information integration across temporal and spatial scales, is a promising candidate measure for capturing such widespread neural dysfunction. Phase-amplitude coupling depends on the coordinated activity of specific neuronal subtypes, and while multiple subtypes are implicated in different aspects of the Rett syndrome phenotype, their role in shaping large-scale oscillatory dynamics in Rett syndrome is not well understood. To investigate this, we utilized a multi-level approach, combining EEG recordings with computational modeling to identify alterations in phase-amplitude coupling in Rett syndrome and probe their underlying cellular and circuit-level mechanisms. We recorded resting-state EEG from 38 individuals with Rett syndrome and 30 age- and sex-matched typically developing individuals. Phase-amplitude coupling was quantified: modulation index was obtained to determine coupling strength, and phase bias was assessed to examine the preferred phase of coupling. We characterized phase-amplitude coupling across all low and high frequency combinations and electrodes, as well as within canonical theta-gamma and alpha-gamma frequency pairs across four predefined cortical regions. Finally, we modeled a biophysically-constrained Layer 4 cortical network to propose a possible mechanism underlying changes to oscillatory dynamics. We found significantly stronger phase-amplitude coupling in Rett syndrome across widespread cortical regions and frequency pairs, with a pronounced increase in theta-gamma and alpha-gamma coupling in anterior, posterior, and whole-brain regions (P < 0.05). Individuals with Rett syndrome also exhibited a more positive alpha-gamma phase bias in anterior and whole-brain regions (P < 0.05). Biophysically constrained modelling demonstrated that reduced VIP-expressing interneuron activity alone could recapitulate the pattern of increased theta-gamma and alpha-gamma phase-amplitude coupling observed in Rett syndrome (P < 0.001). These findings identify alterations in awake-state phase-amplitude coupling in Rett syndrome and propose a mechanistic link to VIP+ interneuron dysfunction. Elevated phase-amplitude coupling may serve as a promising biomarker of cortical dysfunction and a translational bridge from neural circuitry to clinically observable EEG signatures. By implicating VIP+ interneurons, our results open new avenues for testing interventions in preclinical models to identify potential novel therapeutic targets for individuals with Rett syndrome.
gene therapies
2026-08-10 | Translational reading frame predicts the pathogenicity of C-terminal frameshift deletions in MeCP2.
Mutations in the MECP2 gene cause the severe neurological disorder Rett syndrome. A cluster of frameshift-causing C-terminal deletions (CTDs) removes ~100 amino acids and accounts for approximately 10% of RTT-causing mutations. Their pathogenicity is unexpected because this C-terminal domain is dispensable in mice. Analysis of pathogenic and benign human MECP2 variants reveals that some individuals with apparently typical CTDs do not develop Rett syndrome, confirming that C-terminal truncations are not intrinsically pathogenic. Using human sequence data and mouse models we show that pathogenicity results from a marked reduction in MeCP2 levels and depends on the presence of a proline proline stop motif (-PPX) generated by a shift to the +2 reading frame. CTDs that shift to the +1 frame avoid this motif and are benign. Replacing the stop codon of the PPX motif with tryptophan restores MeCP2 expression and rescues RTT-like phenotypes in a CTD mouse model. An adenine base editor efficiently introduces this substitution in cultured cells. These findings define a reliable prognostic distinction between benign and pathogenic CTDs and establish a potential editing strategy for correcting disease-causing CTD mutations.
2026-07-11 | Cellular, electrophysiological and behavioral improvements in a mouse model of Rett syndrome following gene therapy combined with focused ultrasound-mediated blood-brain barrier opening.
Rett syndrome (RTT) is a severe X-linked neurodevelopmental disorder due to pathogenic variants in the methyl CpG binding protein 2 gene (MECP2). The discovery that deficits resulting from Mecp2 loss are reversible in mice has increased interest in gene therapy as a potential cure for RTT. We have previously evaluated the efficacy of a self-complementary AAV9 vector expressing a codon-optimized version of Mecp2 (scAAV9-MCO) delivered via a systemic approach in early symptomatic Mecp2-knock-out male (KO) mice. In the present study, focused ultrasound (FUS) was used to transiently disrupt the blood-brain barrier (BBB) in a RTT mouse model, thereby facilitating enhanced AAV delivery to the central nervous system (CNS). Our findings demonstrate that scAAV9-MCO administration, when combined with FUS, significantly improves survival, body weight, respiratory function, and locomotor activity, while restoring the excitatory-inhibitory synaptic balance in hippocampal neurons in treated KO mice relative to untreated animals. Quantification of the brain infection level revealed that 20-40% of cells are Mecp2-positive in the brain of KO mice following the treatment with scAAV9-MCO and FUS. This is a significant improvement compared to prior results without FUS. The evaluation of the protein levels indicates a possible overdose of Mecp2 protein in the brain cells. Nevertheless, these results demonstrate that using FUS following systemic administration of an AAV9 vector represents a significant improvement over classical gene therapy protocol for RTT.
2026-04-01 | Crossing the blood–brain barrier: Advances and frontiers of AAV gene therapy in central nervous system disorders
Adeno-associated virus (AAV) vectors have emerged as a leading platform for gene therapy targeting central nervous system (CNS) disorders; however, efficient, safe, and scalable delivery across the blood-brain barrier (BBB) remains a central challenge for clinical translation. This review provides a comprehensive and forward-looking synthesis of recent advances in AAV-based CNS gene therapy, focusing on delivery strategies, disease applications, and genome editing technologies, while highlighting key translational factors influencing clinical outcomes. We first outline the biological properties of AAV vectors, including capsid diversity, genome packaging constraints, and regulatory elements that govern transgene expression and durability. We then compare major routes of administration—direct intracranial delivery, cerebrospinal fluid (CSF)-mediated approaches, and systemic intravenous injection—highlighting their advantages and limitations in achieving brain-wide versus region-specific transduction. In addition, we discuss key parameters affecting in vivo performance, including dose, distribution, and tissue tropism. Special emphasis is placed on recent advances in capsid engineering, including in vivo directed evolution, receptor-guided rational design, and cross-species validation strategies that aim to bridge long-standing translational gaps between rodent models and nonhuman primates or humans. We next summarize therapeutic progress across major CNS disorders, including neurodegenerative diseases such as Alzheimer’s disease and Parkinson’s disease, as well as monogenic neurodevelopmental and lysosomal storage disorders exemplified by Rett syndrome and mucopolysaccharidosis, together with emerging clinical insights from ongoing trials. In parallel, we describe the integration of AAV delivery with genome editing modalities—particularly base and prime editing—which offer precise and potentially safer alternatives to conventional gene replacement strategies, especially for diseases driven by defined genetic variants. Finally, we outline key translational bottlenecks, including host immune responses, dose-dependent toxicity, limited packaging capacity, and the need for improved cell-type specificity and regulatory control. We propose a framework for next-generation CNS gene therapy centered on “human receptor-guided capsid design, multi-layered transcriptional regulation, and precision genome editing”. Together with advances in scalable manufacturing, quality control, and regulatory standardization, these developments are expected to improve safety, enhance delivery efficiency, and support more durable therapeutic outcomes. This review provides an integrated perspective to guide future research and facilitate clinical translation of AAV-based therapeutics for CNS disorders.
2026-03-18 | mPFC pyramidal neuron synchrony during social competition to form social rankings is disrupted in male Mecp2 knockout mice.
Altered social behaviors are prevalent in neurodevelopmental disorders like monogenic Rett syndrome, which is caused by pathogenic variants in the gene encoding the methylated DNA binding transcriptional regulator MeCP2. Monosynaptic projections from the ventral hippocampus to the medial prefrontal cortex (mPFC) modulate social memory, and are altered in male Mecp2 knockout (KO) mice. The standard tube test was used to define the social hierarchy between age- and genotype-matched triads over six consecutive days of round-robin competitions, and revealed that male Mecp2 KO mice form social ranks but display more submissive behaviors than those observed between similarly aged triads of male wild-type (WT) littermate controls. The same triads of each genotype performed similarly in the warm spot test, where mice of each genotype compete to stand on a single warm spot in a cage with a cooled floor. The dominant WT mouse from the prior tube test had preferential and active access to the beneficial place in the competition test (warm spot) showing more dominant behaviors than the other two WT mice. On the contrary, all three Mecp2 KO mice shared the warm spot equally, showing more submissive behaviors than those observed between the three WT mice. In vivo Ca2+ imaging from pyramidal neurons in the prelimbic mPFC during the warm spot test confirmed the presence of socially sensitive neurons, i.e., neurons that either increase or decrease their spiking activity during social interactions. mPFC pyramidal neurons in male Mecp2 KO mice showed fewer and smaller Ca2+ transients during baseline, as well as during each social interaction in the warm spot test, when their activity is less synchronous than in those of WT mice. In addition, chronically inhibiting the activity of mPFC-projecting excitatory neurons of the ventral hippocampus using an intersectional DREADD approach restored behavioral deficits in male Mecp2 KO mice. Together, these results demonstrate that male Mecp2 mice show a low behavioral engagement during social competition tests that alters their social hierarchy and is reflected in altered activity and synchrony between mPFC pyramidal neurons. Our observations also underscore the potential relevance of this long-range projection for altered social behaviors in other mouse models of neurodevelopmental disorders associated with autism.
2026-03-12 | MECP2-Associated Rett Syndrome Without Developmental Regression—A Case Series
Clinical phenotype expansion of neurodevelopmental disorders is increasingly important. With accessibility and diagnostic ability of genetic testing expanding, new clinical criteria will continue to be elucidated. Here we describe a case series of 4 female pediatric patients seen for global developmental delay in non-genetic, specialty clinics who received unexpected genetic diagnoses of MECP2 -associated Rett syndrome (RS). These results highlight broadening clinical presentation for RS. None of the patients in this cohort met clinical RS diagnostic criteria at the time of genetic testing, as there was no period of typical development or developmental regression. These cases demonstrate both the importance of broad genomic sequencing for patients with global developmental delay and that increasing understanding of atypical and mild presentations of syndromes like RS will continue to evolve as genetic testing becomes standard of care for clinical features like developmental delay.
other
2024-01-20 | Counter-balancing X-linkedMecp2hypofunction by hyperfunction ameliorates disease features in a model of Rett syndrome: implications for genetic therapies
Treating monogenic neurodevelopmental disorders remains challenging and mostly symptomatic. X-linked disorders affecting women such as the postnatal neurodevelopmental disorder Rett syndrome caused by mutations in the gene MECP2 have additional challenges due to dosage sensitivity and to cellular mosaicism caused by random X-chromosome inactivation. An approach to augment MECP2 expression from wild-type cells in RTT may be feasible and simpler than gene replacement but has never been tested due to known toxicity of MECP2 over-expression, as evidenced by the distinct neurological condition known as MECP2 Duplication Syndrome. Here, using genetic techniques, we find that counter-balancing Mecp2-null cells in female Mecp2 -null/+ mice by a complementary population of cells harboring an X-linked transgene associated with 3X normal levels of MECP2 leads to normalization of multiple whole animal phenotypic outcomes without noticeable toxicity. In addition, in vivo LFP recordings demonstrate that counter-balancing Mecp2 loss-of-function improves select within-region and between-region abnormalities. By comparing the counter-balance approach with an approach based on cell autonomous restoration of MeCP2 using an autosomal transgene expressing 2X normal levels of MECP2 in all cells (mimicking gene replacement), we identify neurobehavioral and electrographic features best suited for preclinical biomarkers of a therapeutic response to cell autonomous versus non-cell autonomous correction. Notably, these proof-of-concept findings demonstrate how non-cell autonomous suppression of MeCP2 deficiency by boosting overall wild-type MeCP2 levels may be a viable disease-modifying therapy for RTT, with potential implications for genetic-based therapies of monogenic X-linked disorders.
2017-03-02 | Novel therapeutic approaches: Rett syndrome and human induced pluripotent stem cell technology
Recent advances in induced pluripotent stem cell (iPSC) technology target screening and discovering of therapeutic agents for the possible cure of human diseases. Human induced pluripotent stem cells (hiPSC) are the right kind of platform for testing potency of specific active compounds. Ayurveda, the Indian traditional system of medicine developed between 2,500 and 500 BC, is a science involving the intelligent formulations of herbs and minerals. It can serve as a "goldmine" for novel neuroprotective agents used for centuries to treat neurological disorders. This review discusses limitations in screening drugs for neurological disorders and the advantages offered by hiPSC integrated with Indian traditional system of medicine. We begin by describing the current state of hiPSC technology in research on Rett syndrome (RTT) followed by the current controversies in RTT research combined with the emergence of patient-specific hiPSC that indicate an urgent need for researchers to understand the etiology and drug mechanism. We conclude by offering recommendations to reinforce the screening of active compounds present in the ayurvedic medicines using the human induced pluripotent neural model system for research involving drug discovery for RTT. This integrative approach will fill the current knowledge gap in the traditional medicines and drug discovery.
2016-09-28 | A review of Rett syndrome (RTT) with induced pluripotent stem cells
Human induced pluripotent stem cells (hiPSCs) are pluripotent stem cells generated from somatic cells by the introduction of a combination of pluripotency-associated genes such as OCT4, SOX2, along with either KLF4 and c-MYC or NANOG and LIN28 via retroviral or lentiviral vectors. Most importantly, hiPSCs are similar to human embryonic stem cells (hESCs) functionally as they are pluripotent and can potentially differentiate into any desired cell type when provided with the appropriate cues, but do not have the ethical issues surrounding hESCs. For these reasons, hiPSCs have huge potential in translational medicine such as disease modeling, drug screening, and cellular therapy. Indeed, patient-specific hiPSCs have been generated for a multitude of diseases, including many with a neurological basis, in which disease phenotypes have been recapitulated in vitro and proof-of-principle drug screening has been performed. As the techniques for generating hiPSCs are refined and these cells become a more widely used tool for understanding brain development, the insights they produce must be understood in the context of the greater complexity of the human genome and the human brain. Disease models using iPS from Rett syndrome (RTT) patient's fibroblasts have opened up a new avenue of drug discovery for therapeutic treatment of RTT. The analysis of X chromosome inactivation (XCI) upon differentiation of RTT-hiPSCs into neurons will be critical to conclusively demonstrate the isolation of pre-XCI RTT-hiPSCs in comparison to post-XCI RTT-hiPSCs. The current review projects on iPSC studies in RTT as well as XCI in hiPSC were it suggests for screening new potential therapeutic targets for RTT in future for the benefit of RTT patients. In conclusion, patient-specific drug screening might be feasible and would be particularly helpful in disorders where patients frequently have to try multiple drugs before finding a regimen that works.
2012-06-19 | Modeling neurodevelopmental disorders using human neurons
The cellular and molecular mechanisms of neurodevelopmental conditions such as autism spectrum disorders have been studied intensively for decades. The unavailability of live patient neurons for research, however, has represented a major obstacle in the elucidation of the disease etiologies. Recently, the development of induced pluripotent stem cell (iPSC) technology allows for the generation of human neurons from somatic cells of patients. We review ongoing studies using iPSCs as an approach to model neurodevelopmental disorders, the promise and caveats of this technique and its potential for drug screening. The reproducible findings of relevant phenotypes in Rett syndrome iPSC-derived neurons suggest that iPSC technology offers a novel and unique opportunity for the understanding of and the development of therapeutics for other autism spectrum disorders.
oligonucleotides
2024-03-14 | Synthetic dosage-compensating miRNA circuits for quantitative gene therapy
A longstanding challenge in gene therapy is expressing a dosage-sensitive gene within a tight therapeutic window. For example, loss of MECP2 function causes Rett syndrome, while its duplication causes MECP2 duplication syndrome. Viral gene delivery methods generate variable numbers of gene copies in individual cells, creating a need for gene dosage-invariant expression systems. Here, we introduce a compact miRNA-based, incoherent feed-forward loop circuit that achieves precise control of Mecp2 expression in cells and brains, and improves outcomes in an AAV-based mouse model of Rett syndrome gene therapy. Single molecule analysis of endogenous and ectopic Mecp2 mRNA revealed precise, sustained expression across a broad range of gene dosages. Delivered systemically in a brain-targeting AAV capsid, the circuit strongly suppressed Rett behavioral symptoms for over 24 weeks, outperforming an unregulated gene therapy. These results demonstrate that synthetic miRNA-based regulatory circuits can enable precise in vivo expression to improve the safety and efficacy of gene therapy.
2023-01-20 | Site-directed A → I RNA editing as a therapeutic tool: moving beyond genetic mutations
Adenosine deamination by the ADAR family of enzymes is a natural process that edits genetic information as it passes through messenger RNA. Adenosine is converted to inosine in mRNAs, and this base is interpreted as guanosine during translation. Realizing the potential of this activity for therapeutics, a number of researchers have developed systems that redirect ADAR activity to new targets, ones that are not normally edited. These site-directed RNA editing (SDRE) systems can be broadly classified into two categories: ones that deliver an antisense RNA oligonucleotide to bind opposite a target adenosine, creating an editable structure that endogenously expressed ADARs recognize, and ones that tether the catalytic domain of recombinant ADAR to an antisense RNA oligonucleotide that serves as a targeting mechanism, much like with CRISPR-Cas or RNAi. To date, SDRE has been used mostly to try and correct genetic mutations. Here we argue that these applications are not ideal SDRE, mostly because RNA edits are transient and genetic mutations are not. Instead, we suggest that SDRE could be used to tune cell physiology to achieve temporary outcomes that are therapeutically advantageous, particularly in the nervous system. These include manipulating excitability in nociceptive neural circuits, abolishing specific phosphorylation events to reduce protein aggregation related to neurodegeneration or reduce the glial scarring that inhibits nerve regeneration, or enhancing G protein-coupled receptor signaling to increase nerve proliferation for the treatment of sensory disorders like blindness and deafness.
2022-04-01 | Loss of neurodevelopmental-associated miR-592 impairs neurogenesis and causes social interaction deficits
Abstract microRNA-592 (miR-592) has been linked to neurogenesis, but the influence of miR-592 knockout in vivo remains unknown. Here, we report that miR-592 knockout represses IPC-to-mature neuron transition, impairs motor coordination and reduces social interaction. Combining the RNA-seq and tandem mass tagging-based quantitative proteomics analysis (TMT protein quantification) and luciferase reporter assays, we identified MeCP2 as the direct targetgene of miR-592 in the mouse cortex. In Tg (MECP2) mice, lipofection of miR-592 efficiently reduced MECP2 expression in the brains of Tg (MECP2) mice at E14.5. Furthermore, treatment with miR-592 partially ameliorated the autism-like phenotypes observed in adult Tg( MECP2 ) mice. The findings demonstrate that miR-592 might play a novel role in treating the neurodevelopmental-associated disorder.
2019-04-30 | Enhancing Neuronogenesis and Counteracting Neuropathogenic Gene Haploinsufficiencies by RNA Gene Activation.
Small activating RNAs (saRNAs), targeting endogenous genes and stimulating their transcription, are a promising tool for implementing a variety of neurotherapeutic strategies. Among these there is the stimulation of select histogenetic subroutines for purposes of cell-based brain repair, as well as the therapeutic treatment of gene expression deficits underlying severe neurological disorders.We employed RNA activation (RNAa) to transactivate the Emx2 transcription factor gene in embryonic cortico-cerebral precursor cells. This led to enhanced self-renewal, delayed differentiation, and reduced death of neuronally committed precursors, resulting in a remarkable expansion of the neuronogenic precursors pool. These results are of paramount interest for purposes of gene-promoted brain repair. As such, RNAa makes therapeutic stimulation of neuronogenesis via Emx2 overexpression a feasible goal, preventing the drawbacks of exogenous gene copies introduction.Moreover, we employed RNAa to achieve a gentle transactivation of the Foxg1 transcription factor gene, specifically in cortico-cerebral cells. This manipulation led to an appreciable biological outcome, while complying with endogenous gene tuning linked to early central nervous system regionalization and late activity of neocortical projection neurons. Foxg1-activating miRNAs stimulated RNApolII recruitment, possibly via Ago1. One of them worked promisingly in vivo. As such, RNAa can be a valuable approach for therapeutic treatment of the FOXG1-haploinsufficiency-linked variant of the Rett syndrome. Remarkably, hemizygosity for specific genes and polygenic chromosomal segments underlies a huge number of neuropathological entities for which no cure is presently available. Based on the results reported above, RNAa might be a simple and scalable approach for fixing this class of problems.
2019-01-04 | MicroRNAs and Long Non-coding RNAs in Genetic Diseases
Since the discovery and classification of non-coding RNAs, their roles have gained great attention. In this respect, microRNAs and long non-coding RNAs have been firmly demonstrated to be linked to regulation of gene expression and onset of human diseases, including rare genetic diseases; therefore they are suitable targets for therapeutic intervention. This issue, in the context of rare genetic diseases, is being considered by an increasing number of research groups and is of key interest to the health community. In the case of rare genetic diseases, the possibility of developing personalized therapy in precision medicine has attracted the attention of researchers and clinicians involved in developing "orphan medicinal products" and proposing these to the European Medicines Agency (EMA) and to the Food and Drug Administration (FDA) Office of Orphan Products Development (OOPD) in the United States. The major focuses of these activities are the evaluation and development of products (drugs, biologics, devices, or medical foods) considered to be promising for diagnosis and/or treatment of rare diseases or conditions, including rare genetic diseases. In an increasing number of rare genetic diseases, analysis of microRNAs and long non-coding RNAs has been proven a promising strategy. These diseases include, but are not limited to, Duchenne muscular dystrophy, cystic fibrosis, Rett syndrome, and β-thalassemia. In conclusion, a large number of approaches based on targeting microRNAs and long non-coding RNAs are expected in the field of molecular diagnosis and therapy, with a facilitated technological transfer in the case of rare genetic diseases, in virtue of the existing regulation concerning these diseases.
small molecules
2026-06-15 | Reduction in Seizure Generalization Associated With Long-Term Low-Dose Immunomodulatory Therapy Using Prednisolone and Methotrexate in Rett Syndrome: A Case Report.
Rett syndrome is a severe neurodevelopmental disorder most commonly associated with pathogenic variants of the MECP2 gene and frequently accompanied by epilepsy. Seizures occur in a substantial proportion of patients and may be resistant to conventional antiepileptic therapy. Emerging evidence suggests that neuroinflammatory processes may contribute to seizure propagation and represent a potential therapeutic target. A girl born at term with initially normal early development is described. At approximately 2 years of age, she developed regression of speech and stereotypic hand movements, accompanied by seizures and other neurological features consistent with Rett syndrome. The patient received long-term therapy consisting of low-dose prednisolone and methotrexate in addition to anticonvulsant treatment. During follow-up, a reduction in seizure generalization and a shift in seizure pattern were observed, with generalized seizures becoming less frequent and replaced by brief focal seizures without secondary generalization. In this single case, long-term low-dose prednisolone and methotrexate therapy was associated with a reduction in seizure generalization. Although a causal relationship cannot be established, this observation supports the hypothesis that immunomodulatory mechanisms may influence seizure propagation in pharmacoresistant epilepsy.
2026-06-01 | Heat shock factor 1 signaling: A novel pathway implicated in Rett syndrome pathophysiology
Rett syndrome (RTT) is a neurodevelopmental disorder that is associated with loss-of-function mutations in the methyl CpG binding protein 2 ( MECP2 ) gene. MECP2 regulates transcription both locally and globally, making it challenging to distinguish between genes that are pathogenic and those that constitute transcriptional noise. A rare subpopulation of patients lack MECP2 mutations despite presenting with sufficient symptoms to warrant a clinical diagnosis of RTT. These patients are classified as having atypical and MEPC2 mutation-negative forms of the disorder. We hypothesized that identifying pathways with conserved disruption between typical and atypical forms of RTT would be a viable mechanism to reduce transcriptional noise and identify which genes are most critical to their shared clinical presentation. To test this theory, we conducted differential RNA sequencing using five atypical RTT, six typical RTT (R255X), and nine neurotypical control temporal cortex autopsy samples. Pathways associated with heat shock factor 1 (HSF1) signaling were among the most enriched in both RTT populations. Validation studies using 37 patient temporal cortex samples showed that increased HSF1 signaling was enriched in those with classically severe MECP2 mutations. To investigate whether increased HSF1 signaling is compensatory or pathogenic, we conducted in vivo hyperthermia experiments complemented by cellular stress array analyses. These experiments established that RTT model mice exhibit faster and larger induction of cellular stress-associated proteins. Pharmacological induction of HSF1 in Mecp2 +/- mice was consistent with hyperthermia experiments, showing seizure-like phenotypes and lethality. Conversely, chronic inhibition of HSF1 signaling improved RTT-like phenotypes in domains of motor learning and general health. Together, these data suggest that promiscuous HSF1 signaling is likely a pathogenic amplifier of severe phenotypes and provide a rationale that inhibiting this pathology may hold therapeutic potential in RTT and related disorders. Significance statement Rett syndrome (RTT) is a devastating neurodevelopmental disorder with limited therapeutic options. This manuscript identifies Heat shock factor 1 (HSF1)-signaling a novel therapeutic target and proposes a molecular mechanism by which cellular stress responses are regulated in RTT.
2025-12-18 | Mesodermal-specific MECP2 expression in Drosophila induces visceral and skeletal muscle defects rescued by butyrate supplementation
Abstract Background Patients affected by Rett syndrome (RTT) and MECP2 duplication syndrome (MDS) experience disabling muscle weakness and gastrointestinal dysmotility of unclear origin. Whether these defects arise cell-autonomously, rather than secondarily to neural dysfunction, and which developmental windows are most vulnerable to MeCP2 disfunction remains unresolved. MeCP2 is a dosage-sensitive transcriptional regulator, whose functions are tightly linked to chromatin states. Because short-chain fatty acids (SCFAs) are known to inhibit histone deacetylases (HDACs), a tractable in vivo model is needed to test the effect of HDAC modulation on muscle defects. Methods We misexpressed human MECP2 in the Drosophila melanogaster mesoderm that gives rise to skeletal and visceral muscles. We analyzed quantitatively their morphology and function. To assess the effects of SCFA supplementation, we also supplemented diets with sodium butyrate (NaB), Lalbaay®, a NaB-containing supplement, acetate (AcOH), and valproate (VPA). Findings MECP2 misexpression caused pre-eclosion lethality, thinning of larval skeletal fibers with nuclear mispositioning and altered mitochondria. Functionally, it reduced locomotion, decreased food transit and gut peristalsis. Phenotypes were strongest when expression began during development. NaB and VPA supplementation rescue most of these phenotypes, consistent with their histone-deacetylase (HDAC) activity. Defects were not observed upon comparable misexpression of an RTT-associated MeCP2 loss-of-function variant, indicating that they might be relevant to pathogenesis of MECP2-related disorders. Interpretation Our genetic in vivo analysis models peripheral effects of MeCP2 dysregulation and their amelioration, supporting the possibility of HDAC-targeted strategies for MECP2-related muscle and gastrointestinal dysfunction.
2025-11-26 | Epigenetic Dysregulation in Rett Syndrome: Multisystem Pathophysiology, MECP2 Isoform-Specific Mechanisms, and Targeted Therapeutic Strategies
Rett syndrome (RTT), an X-linked neurodevelopmental disorder predominantly arising from de novo MECP2 mutations, manifests with psychomotor regression, stereotypic hand movements, gait apraxia, and expressive aphasia, driven by dosage-sensitive epigenetic dysregulation via MeCP2's methyl-CpG-binding domain (MBD) and transcriptional repression domain (TRD). Isoform-specific expression (MeCP2-E1 neuronal predominance) and X-chromosome inactivation mosaicism underpin phenotypic variability, with missense (R133C, T158M) and nonsense (R168X, R255X) variants correlating to severity gradients. Multisystem pathophysiology encompasses brainstem-mediated respiratory dysrhythmias, QTc prolongation via ion channel perturbations, enteric hypomotility, osteopenic fractures, and mitochondrial bioenergetic deficits, exacerbated by glial-neuronal crosstalk and oxidative stress. Preclinical platforms, including Mecp2-null rodents, patient-derived iPSCs, and cerebral organoids, elucidate synaptic hyperexcitability, dendritic arborization deficits, and reversibility upon Mecp2 reactivation. Therapeutic modalities span supportive multidisciplinary interventions, FDA-approved trofinetide (IGF-1 analog modulating neurotrophic cascades), AAV-mediated gene replacement (NGN-401, TSHA-102 with miRARE autoregulation), ASOs for dosage normalization, and emerging PPAR-γ agonists targeting metabolic homeostasis. Prioritized research agendas emphasize validated biomarkers (BDNF/IGF-1 axes, miRNA signatures), combinatorial regimens, and equitable global access to mitigate caregiver burden and phenotypic heterogeneity.
2025-11-20 | Butyrate modifies epigenetic and immune pathways in peripheral mononuclear cells from children with neurodevelopmental disorders associated with chromatin dysregulation.
Pathogenic DNA variants in chromatin-related genes constitute an important minority of neurodevelopmental disorders (NDDs). Epigenetic mechanisms, including chromatin regulation driven by genetic or environmental factors, are increasingly recognised as key contributors to pathogenesis of diverse NDDs. We hypothesise that therapeutic strategies targeting chromatin dysregulation, such as histone deacetylase inhibition with butyrate, may be a potential disease modifying therapy for NDDs. We first performed peripheral blood bulk RNA sequencing (RNA-seq) to explore baseline gene regulation in children with chromatin-related NDDs (Kabuki syndrome (KMT2D, n = 4), CHARGE syndrome (CHD7, n = 2), and Rett syndrome (MECP2, n = 5), and children with NDDs but without a monogenic diagnosis (non-monogenic, n = 8), compared with sex-matched healthy controls (total n = 21). Next, to explore the effects of butyrate, single-cell RNA sequencing (scRNA-seq) was performed on 101,539 peripheral immune cells from four selected patients (one per condition) and two controls, before and after butyrate treatment. At baseline, dysregulation of ribosomal and immune pathways was seen in all four NDD cohorts (KMT2D, CHD7, MECP2, non-monogenic) compared to controls. Butyrate largely reversed these pathways, normalising ribosomal and immune pathways in patient and control cells. Butyrate induced up-regulation of ribosome, GTPase, cytoskeletal, mitochondrial pathways, and down-regulation of epigenetic and immune pathways. In conclusion, we identified a common ribosomal-immune RNA signature in chromatin-related NDDs, and a similar signature in non-monogenic NDDs. We showed that butyrate modulates epigenetic and immune gene networks in monogenic and non-monogenic NDDs, positioning butyrate as a promising therapeutic modulator across diverse NDDs.
proteins
2026-05-11 | Toward an NGF-based therapy for Rett syndrome.
Rett syndrome (RTT) is a severe neurodevelopmental disorder primarily caused by mutations in the MECP2 gene. Although recent therapeutic advances, such as the approval of Trofinetide, offer partial relief, no comprehensive curative treatment is currently available. Among the emerging strategies, nerve growth factor (NGF) has gained attention due to its neurotrophic and immunomodulatory properties. This review, in addition to discussing the key features of RTT and the role of growth factors, also highlights recent evidence supporting NGF-based strategies for RTT, focusing on two independent studies that tested intranasal administration of NGF-like molecules in Mecp2-mutant mice. Both recombinant human NGF (rhNGF) and a modified, "painless" variant (hNGFp) improved behavioral (cognitive and motor) symptoms. While rhNGF primarily restored mitochondrial function, hNGFp restored neuroinflammatory responses through microglial regulation. Despite differences in molecular mechanisms and dosages, both molecules demonstrated efficacy without adverse effects, especially when administered intranasally, preventively, and over longer periods. These findings suggest that NGF may act through dual mechanisms, by supporting energy homeostasis and regulating immune responses. The use of intranasal delivery further enhances translational potential by overcoming blood-brain barrier limitations. Together, these studies provide a strong rationale for pursuing NGF-based therapies in RTT and encourage further investigations to optimize dosing, timing, and safety in preclinical and clinical settings.
2026-05-11 | Clinical experience using trofinetide in Rett syndrome and related MECP2 diagnosis at the children's hospital of Philadelphia post approval.
Rett syndrome (RTT) is a rare neurodevelopmental disorder primarily caused by pathogenic variants in the MECP2 gene. Trofinetide (Daybue) became the first FDA-approved medication for RTT in March 2023. This study evaluates the real-world effectiveness and side effect profile of Trofinetide in 55 individuals (50 females, 5 males) with RTT or MECP2-related neurodevelopmental disorders over a 12-month period. Data was collected through clinic assessments and caregiver reports. Results demonstrated that 75.9% of individuals experienced some improvement in RTT symptoms by caregiver report, particularly in engagement, communication, and motor skills. The side effect profile was better than the phase 3 trials with only 48.1% reporting diarrhea and 16.7% experiencing vomiting. Overall, the findings support the effectiveness of trofinetide in the RTT population and suggests potential effectiveness in the broader MECP2 population including males and those with atypical presentations. The data highlights the need for further work to determine long-term benefits in the full spectrum of MECP2 related disorders. Finally, the study highlights the importance of titration, individualized dosing and side effect management to improve retention and outcomes.
2026-01-01 | THE GENE THAT SILENCES CHILDHOOD: INSIGHTS INTO RETT SYNDROME
Rett syndrome (RS) is an uncommon, degenerative neurodevelopmental disorder that affects around 1 in 10,000-15,000 female children and occurs primarily as a result of mutations in the MECP2 gene on the X chromosome. Children with RS appear to develop normally until the first six to eighteen months, when they begin to regress and experience characteristic symptoms, including loss of the ability to use their hands purposefully, inability to develop spoken language, abnormal walking abilities, and stereotyped hand movement patterns. The atypical variants of RS are the result of mutations in the CDKL5 and FOXG1 genes and may present with earlier onset of seizure activity or no normal developmental period. Dysfunction of the MECP2 gene disrupts transcriptional regulation of genes involved with synaptic connectivity (how the neurons talk to each other), neuronal maturation, and the balance between excitatory and inhibitory actions on the nervous system resulting in seizure activity, impairment of movement, irregular respiratory function, dysregulation of the autonomic nervous system (which controls the automatic processes of the body), and severe cognitive impairment. Diagnosis is based upon patterns of clinical regression and is confirmed through genetic testing. Current treatment for RS is supportive and done by a team of medical professionals. Goals for supportive treatment are to provide individuals with seizure control, nutrition, physical therapy, and behavioral management. While there is no cure for RS, advances in molecular research have led to the approval of Trofinetide, and ongoing research studies using gene therapy, RNA correction, and neurotrophic modulation for RS are showing promise as disease-modifying treatments. Early diagnosis, coordination of care across the continuum of care, and the advancement of research will continue to improve the quality of life and outcomes for individuals with Rett syndrome.
2025-10-23 | Pediatric intestinal pseudo‐obstruction found in 3‐year‐old male with Rett‐related mutation of methyl‐CpG binding protein 2
Abstract A 3‐year‐old male with chronic abdominal distention, constipation, and severe malnutrition is diagnosed with pediatric intestinal pseudo‐obstruction (PIPO) after extensive evaluation that excluded mechanical, malabsorptive, metabolic, inflammatory, and infectious causes. Aside from speech delay, he has a normal neurologic exam. Whole exome sequencing reveals a pathogenic methyl‐CpG binding protein 2 (MECP2) variant, suggesting atypical Rett syndrome. Management includes promotility agents and a gastrostomy tube with cyclic feedings of peptide‐based formula, leading to resolution of symptoms. This case highlights the diagnostic complexity of PIPO and the need to consider genetic etiologies, including MECP2‐related disorders, even in patients with mild neurologic findings. Early genetic testing and multidisciplinary care are essential for diagnosis and management in this atypical presentation of Rett syndrome with manifestation of PIPO.
2025-07-21 | Altered oscillatory coupling reflects possible inhibitory interneuron dysfunction in Rett syndrome
Rett syndrome is a rare neurodevelopmental disorder caused primarily by pathogenic variants in the MECP2 gene, leading to lifelong cognitive impairments. To understand the broad neural disruptions in Rett syndrome, it is essential to examine large-scale brain dynamics at the level of neural oscillations. Phase-amplitude coupling, a form of cross-frequency interaction that supports information integration across temporal and spatial scales, is a promising candidate measure for capturing such widespread neural dysfunction. Phase-amplitude coupling depends on the coordinated activity of specific neuronal subtypes, and while multiple subtypes are implicated in different aspects of the Rett syndrome phenotype, their role in shaping large-scale oscillatory dynamics in Rett syndrome is not well understood. To investigate this, we utilized a multi-level approach, combining EEG recordings with computational modeling to identify alterations in phase-amplitude coupling in Rett syndrome and probe their underlying cellular and circuit-level mechanisms. We recorded resting-state EEG from 38 individuals with Rett syndrome and 30 age- and sex-matched typically developing individuals. Phase-amplitude coupling was quantified: modulation index was obtained to determine coupling strength, and phase bias was assessed to examine the preferred phase of coupling. We characterized phase-amplitude coupling across all low and high frequency combinations and electrodes, as well as within canonical theta-gamma and alpha-gamma frequency pairs across four predefined cortical regions. Finally, we modeled a biophysically-constrained Layer 4 cortical network to propose a possible mechanism underlying changes to oscillatory dynamics. We found significantly stronger phase-amplitude coupling in Rett syndrome across widespread cortical regions and frequency pairs, with a pronounced increase in theta-gamma and alpha-gamma coupling in anterior, posterior, and whole-brain regions (P < 0.05). Individuals with Rett syndrome also exhibited a more positive alpha-gamma phase bias in anterior and whole-brain regions (P < 0.05). Biophysically constrained modelling demonstrated that reduced VIP-expressing interneuron activity alone could recapitulate the pattern of increased theta-gamma and alpha-gamma phase-amplitude coupling observed in Rett syndrome (P < 0.001). These findings identify alterations in awake-state phase-amplitude coupling in Rett syndrome and propose a mechanistic link to VIP+ interneuron dysfunction. Elevated phase-amplitude coupling may serve as a promising biomarker of cortical dysfunction and a translational bridge from neural circuitry to clinically observable EEG signatures. By implicating VIP+ interneurons, our results open new avenues for testing interventions in preclinical models to identify potential novel therapeutic targets for individuals with Rett syndrome.
gene therapies
2026-08-10 | Translational reading frame predicts the pathogenicity of C-terminal frameshift deletions in MeCP2.
Mutations in the MECP2 gene cause the severe neurological disorder Rett syndrome. A cluster of frameshift-causing C-terminal deletions (CTDs) removes ~100 amino acids and accounts for approximately 10% of RTT-causing mutations. Their pathogenicity is unexpected because this C-terminal domain is dispensable in mice. Analysis of pathogenic and benign human MECP2 variants reveals that some individuals with apparently typical CTDs do not develop Rett syndrome, confirming that C-terminal truncations are not intrinsically pathogenic. Using human sequence data and mouse models we show that pathogenicity results from a marked reduction in MeCP2 levels and depends on the presence of a proline proline stop motif (-PPX) generated by a shift to the +2 reading frame. CTDs that shift to the +1 frame avoid this motif and are benign. Replacing the stop codon of the PPX motif with tryptophan restores MeCP2 expression and rescues RTT-like phenotypes in a CTD mouse model. An adenine base editor efficiently introduces this substitution in cultured cells. These findings define a reliable prognostic distinction between benign and pathogenic CTDs and establish a potential editing strategy for correcting disease-causing CTD mutations.
2026-07-11 | Cellular, electrophysiological and behavioral improvements in a mouse model of Rett syndrome following gene therapy combined with focused ultrasound-mediated blood-brain barrier opening.
Rett syndrome (RTT) is a severe X-linked neurodevelopmental disorder due to pathogenic variants in the methyl CpG binding protein 2 gene (MECP2). The discovery that deficits resulting from Mecp2 loss are reversible in mice has increased interest in gene therapy as a potential cure for RTT. We have previously evaluated the efficacy of a self-complementary AAV9 vector expressing a codon-optimized version of Mecp2 (scAAV9-MCO) delivered via a systemic approach in early symptomatic Mecp2-knock-out male (KO) mice. In the present study, focused ultrasound (FUS) was used to transiently disrupt the blood-brain barrier (BBB) in a RTT mouse model, thereby facilitating enhanced AAV delivery to the central nervous system (CNS). Our findings demonstrate that scAAV9-MCO administration, when combined with FUS, significantly improves survival, body weight, respiratory function, and locomotor activity, while restoring the excitatory-inhibitory synaptic balance in hippocampal neurons in treated KO mice relative to untreated animals. Quantification of the brain infection level revealed that 20-40% of cells are Mecp2-positive in the brain of KO mice following the treatment with scAAV9-MCO and FUS. This is a significant improvement compared to prior results without FUS. The evaluation of the protein levels indicates a possible overdose of Mecp2 protein in the brain cells. Nevertheless, these results demonstrate that using FUS following systemic administration of an AAV9 vector represents a significant improvement over classical gene therapy protocol for RTT.
2026-04-01 | Crossing the blood–brain barrier: Advances and frontiers of AAV gene therapy in central nervous system disorders
Adeno-associated virus (AAV) vectors have emerged as a leading platform for gene therapy targeting central nervous system (CNS) disorders; however, efficient, safe, and scalable delivery across the blood-brain barrier (BBB) remains a central challenge for clinical translation. This review provides a comprehensive and forward-looking synthesis of recent advances in AAV-based CNS gene therapy, focusing on delivery strategies, disease applications, and genome editing technologies, while highlighting key translational factors influencing clinical outcomes. We first outline the biological properties of AAV vectors, including capsid diversity, genome packaging constraints, and regulatory elements that govern transgene expression and durability. We then compare major routes of administration—direct intracranial delivery, cerebrospinal fluid (CSF)-mediated approaches, and systemic intravenous injection—highlighting their advantages and limitations in achieving brain-wide versus region-specific transduction. In addition, we discuss key parameters affecting in vivo performance, including dose, distribution, and tissue tropism. Special emphasis is placed on recent advances in capsid engineering, including in vivo directed evolution, receptor-guided rational design, and cross-species validation strategies that aim to bridge long-standing translational gaps between rodent models and nonhuman primates or humans. We next summarize therapeutic progress across major CNS disorders, including neurodegenerative diseases such as Alzheimer’s disease and Parkinson’s disease, as well as monogenic neurodevelopmental and lysosomal storage disorders exemplified by Rett syndrome and mucopolysaccharidosis, together with emerging clinical insights from ongoing trials. In parallel, we describe the integration of AAV delivery with genome editing modalities—particularly base and prime editing—which offer precise and potentially safer alternatives to conventional gene replacement strategies, especially for diseases driven by defined genetic variants. Finally, we outline key translational bottlenecks, including host immune responses, dose-dependent toxicity, limited packaging capacity, and the need for improved cell-type specificity and regulatory control. We propose a framework for next-generation CNS gene therapy centered on “human receptor-guided capsid design, multi-layered transcriptional regulation, and precision genome editing”. Together with advances in scalable manufacturing, quality control, and regulatory standardization, these developments are expected to improve safety, enhance delivery efficiency, and support more durable therapeutic outcomes. This review provides an integrated perspective to guide future research and facilitate clinical translation of AAV-based therapeutics for CNS disorders.
2026-03-18 | mPFC pyramidal neuron synchrony during social competition to form social rankings is disrupted in male Mecp2 knockout mice.
Altered social behaviors are prevalent in neurodevelopmental disorders like monogenic Rett syndrome, which is caused by pathogenic variants in the gene encoding the methylated DNA binding transcriptional regulator MeCP2. Monosynaptic projections from the ventral hippocampus to the medial prefrontal cortex (mPFC) modulate social memory, and are altered in male Mecp2 knockout (KO) mice. The standard tube test was used to define the social hierarchy between age- and genotype-matched triads over six consecutive days of round-robin competitions, and revealed that male Mecp2 KO mice form social ranks but display more submissive behaviors than those observed between similarly aged triads of male wild-type (WT) littermate controls. The same triads of each genotype performed similarly in the warm spot test, where mice of each genotype compete to stand on a single warm spot in a cage with a cooled floor. The dominant WT mouse from the prior tube test had preferential and active access to the beneficial place in the competition test (warm spot) showing more dominant behaviors than the other two WT mice. On the contrary, all three Mecp2 KO mice shared the warm spot equally, showing more submissive behaviors than those observed between the three WT mice. In vivo Ca2+ imaging from pyramidal neurons in the prelimbic mPFC during the warm spot test confirmed the presence of socially sensitive neurons, i.e., neurons that either increase or decrease their spiking activity during social interactions. mPFC pyramidal neurons in male Mecp2 KO mice showed fewer and smaller Ca2+ transients during baseline, as well as during each social interaction in the warm spot test, when their activity is less synchronous than in those of WT mice. In addition, chronically inhibiting the activity of mPFC-projecting excitatory neurons of the ventral hippocampus using an intersectional DREADD approach restored behavioral deficits in male Mecp2 KO mice. Together, these results demonstrate that male Mecp2 mice show a low behavioral engagement during social competition tests that alters their social hierarchy and is reflected in altered activity and synchrony between mPFC pyramidal neurons. Our observations also underscore the potential relevance of this long-range projection for altered social behaviors in other mouse models of neurodevelopmental disorders associated with autism.
2026-03-12 | MECP2-Associated Rett Syndrome Without Developmental Regression—A Case Series
Clinical phenotype expansion of neurodevelopmental disorders is increasingly important. With accessibility and diagnostic ability of genetic testing expanding, new clinical criteria will continue to be elucidated. Here we describe a case series of 4 female pediatric patients seen for global developmental delay in non-genetic, specialty clinics who received unexpected genetic diagnoses of MECP2 -associated Rett syndrome (RS). These results highlight broadening clinical presentation for RS. None of the patients in this cohort met clinical RS diagnostic criteria at the time of genetic testing, as there was no period of typical development or developmental regression. These cases demonstrate both the importance of broad genomic sequencing for patients with global developmental delay and that increasing understanding of atypical and mild presentations of syndromes like RS will continue to evolve as genetic testing becomes standard of care for clinical features like developmental delay.
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2024-01-20 | Counter-balancing X-linkedMecp2hypofunction by hyperfunction ameliorates disease features in a model of Rett syndrome: implications for genetic therapies
Treating monogenic neurodevelopmental disorders remains challenging and mostly symptomatic. X-linked disorders affecting women such as the postnatal neurodevelopmental disorder Rett syndrome caused by mutations in the gene MECP2 have additional challenges due to dosage sensitivity and to cellular mosaicism caused by random X-chromosome inactivation. An approach to augment MECP2 expression from wild-type cells in RTT may be feasible and simpler than gene replacement but has never been tested due to known toxicity of MECP2 over-expression, as evidenced by the distinct neurological condition known as MECP2 Duplication Syndrome. Here, using genetic techniques, we find that counter-balancing Mecp2-null cells in female Mecp2 -null/+ mice by a complementary population of cells harboring an X-linked transgene associated with 3X normal levels of MECP2 leads to normalization of multiple whole animal phenotypic outcomes without noticeable toxicity. In addition, in vivo LFP recordings demonstrate that counter-balancing Mecp2 loss-of-function improves select within-region and between-region abnormalities. By comparing the counter-balance approach with an approach based on cell autonomous restoration of MeCP2 using an autosomal transgene expressing 2X normal levels of MECP2 in all cells (mimicking gene replacement), we identify neurobehavioral and electrographic features best suited for preclinical biomarkers of a therapeutic response to cell autonomous versus non-cell autonomous correction. Notably, these proof-of-concept findings demonstrate how non-cell autonomous suppression of MeCP2 deficiency by boosting overall wild-type MeCP2 levels may be a viable disease-modifying therapy for RTT, with potential implications for genetic-based therapies of monogenic X-linked disorders.
2017-03-02 | Novel therapeutic approaches: Rett syndrome and human induced pluripotent stem cell technology
Recent advances in induced pluripotent stem cell (iPSC) technology target screening and discovering of therapeutic agents for the possible cure of human diseases. Human induced pluripotent stem cells (hiPSC) are the right kind of platform for testing potency of specific active compounds. Ayurveda, the Indian traditional system of medicine developed between 2,500 and 500 BC, is a science involving the intelligent formulations of herbs and minerals. It can serve as a "goldmine" for novel neuroprotective agents used for centuries to treat neurological disorders. This review discusses limitations in screening drugs for neurological disorders and the advantages offered by hiPSC integrated with Indian traditional system of medicine. We begin by describing the current state of hiPSC technology in research on Rett syndrome (RTT) followed by the current controversies in RTT research combined with the emergence of patient-specific hiPSC that indicate an urgent need for researchers to understand the etiology and drug mechanism. We conclude by offering recommendations to reinforce the screening of active compounds present in the ayurvedic medicines using the human induced pluripotent neural model system for research involving drug discovery for RTT. This integrative approach will fill the current knowledge gap in the traditional medicines and drug discovery.
2016-09-28 | A review of Rett syndrome (RTT) with induced pluripotent stem cells
Human induced pluripotent stem cells (hiPSCs) are pluripotent stem cells generated from somatic cells by the introduction of a combination of pluripotency-associated genes such as OCT4, SOX2, along with either KLF4 and c-MYC or NANOG and LIN28 via retroviral or lentiviral vectors. Most importantly, hiPSCs are similar to human embryonic stem cells (hESCs) functionally as they are pluripotent and can potentially differentiate into any desired cell type when provided with the appropriate cues, but do not have the ethical issues surrounding hESCs. For these reasons, hiPSCs have huge potential in translational medicine such as disease modeling, drug screening, and cellular therapy. Indeed, patient-specific hiPSCs have been generated for a multitude of diseases, including many with a neurological basis, in which disease phenotypes have been recapitulated in vitro and proof-of-principle drug screening has been performed. As the techniques for generating hiPSCs are refined and these cells become a more widely used tool for understanding brain development, the insights they produce must be understood in the context of the greater complexity of the human genome and the human brain. Disease models using iPS from Rett syndrome (RTT) patient's fibroblasts have opened up a new avenue of drug discovery for therapeutic treatment of RTT. The analysis of X chromosome inactivation (XCI) upon differentiation of RTT-hiPSCs into neurons will be critical to conclusively demonstrate the isolation of pre-XCI RTT-hiPSCs in comparison to post-XCI RTT-hiPSCs. The current review projects on iPSC studies in RTT as well as XCI in hiPSC were it suggests for screening new potential therapeutic targets for RTT in future for the benefit of RTT patients. In conclusion, patient-specific drug screening might be feasible and would be particularly helpful in disorders where patients frequently have to try multiple drugs before finding a regimen that works.
2012-06-19 | Modeling neurodevelopmental disorders using human neurons
The cellular and molecular mechanisms of neurodevelopmental conditions such as autism spectrum disorders have been studied intensively for decades. The unavailability of live patient neurons for research, however, has represented a major obstacle in the elucidation of the disease etiologies. Recently, the development of induced pluripotent stem cell (iPSC) technology allows for the generation of human neurons from somatic cells of patients. We review ongoing studies using iPSCs as an approach to model neurodevelopmental disorders, the promise and caveats of this technique and its potential for drug screening. The reproducible findings of relevant phenotypes in Rett syndrome iPSC-derived neurons suggest that iPSC technology offers a novel and unique opportunity for the understanding of and the development of therapeutics for other autism spectrum disorders.
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