Allan-Herndon-Dudley syndrome: Research & Drug Discovery Data

Drug discovery

drugs

With orphan designations

Overview

Allan-Herndon-Dudley syndrome (AHDS) is a rare X-linked genetic disorder caused by mutations in the SLC16A2 gene, which disrupts thyroid hormone transport into the brain. This results in severe intellectual disability, motor dysfunction (hypotonia progressing to spasticity), and abnormal thyroid hormone levels (elevated T3, low T4). Affected males exhibit developmental delays, muscle hypoplasia, and characteristic facial features. Neurological deficits arise from cerebral hypothyroidism, while peripheral tissues experience thyrotoxicosis. Diagnosis relies on clinical findings, thyroid function tests, and genetic confirmation [1][6][12].

Population

Exclusively affects males (X-linked recessive inheritance) with neonatal/infantile onset [1][6].
Estimated prevalence: ~1 in 70,000 males, though underdiagnosis is suspected [17].
Over 320 confirmed cases across 132 families worldwide [1][7].

Burden

Severe disability: Most patients never walk or speak, requiring lifelong caregiver assistance [6][12].
Medical complications: Failure to thrive, respiratory infections, scoliosis, and cardiac arrhythmias [9][12].
Reduced lifespan: Mortality risk increases due to malnutrition and recurrent infections, though some survive into their 60s [1][12].
Economic impact: High costs associated with 24/7 care, specialized therapies, and frequent hospitalizations [4][19].

Therapies

Supportive care: Physical/occupational therapy, antispasmodics (e.g., baclofen), and seizure management [1][12].
Hormonal modulation: PTU/levothyroxine to reduce peripheral thyrotoxicosis [8]; thyroid hormone analogs (TRIAC, DITPA) bypass MCT8 to improve brain T3 availability [3][8].
Emerging therapies: AAV9-MCT8 gene therapy restored motor/cognitive function in preclinical models [2][18]; prenatal DITPA trials aim to mitigate developmental deficits [8].

Categories: rare endocrine diseases, rare genetic diseases, rare neurological diseases

Research Papers

120 drug discovery papers about Allan-Herndon-Dudley syndrome, with 2 first-in-class and 5 next-in-class emerging drug candidates forecasted to outperform the average preclinical success rate. Recent publications:

2026-04-01 | Allan-Herndon-Dudley Syndrome

Abstract This chapter provides pictures and clinical details of Allan-Herndon-Dudley syndrome, an XLID with generalized muscle hypoplasia, childhood hypotonia, ataxia, athetosis, dysarthria, and spastic paraplegia. The gene (SLC16A2) is responsible for transporting triiodothyronine into neurons. Marked hypotonia and paucity of skeletal muscle mass permit diagnosis in infancy. Although the facies do not appear distinctive in childhood, there is a tendency in adult life toward elongation of the face, cupping or abnormal folding of the ears, and large ears. Spastic paraplegia and contractures of the small and large joints become evident in adult life. Shallow pectus excavatum, ulnar deviation of the hand, scoliosis, and valgus position of the great toe may be seen. Excessive drooling and dysarthria continue into adult life, deep tendon reflexes become hyperactive, and clonus and Babinski signs may be seen. Fungal infections appear common.

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2026-01-23 | Delineating the role of monocarboxylate transporter 8 (MCT8) in the context of neuroinflammation–mediated oligodendrocytopathy

Oligodendrocytes (OLs) myelinate central nervous system (CNS) axons and provide metabolic support to maintain axonal integrity. Thyroid hormone (TH) is a mitogen for oligodendroglial precursor cells (OPCs) maturation into myelinating OLs. Cellular uptake of TH is mediated by monocarboxylate transporter 8 (MCT8; encoded by slc16a2 ), and its dysfunction results in intracellular triiodothyronine (T3) deprivation, leading to hypomyelination and myelin degeneration during neuroinflammation. We showed that MCT8 expression is maintained in OPCs residing within the sub–ventricular zone (SVZ) throughout CNS development, suggesting a role during OL development. We identified MCT8 deficiency during neuroinflammatory and cuprizone demyelination models, as well as in secondary progressive multiple sclerosis (SPMS). These conditions were associated with dysregulated AKT–mTOR–PANK2 signaling and abrogated Co Enzyme A and lipid synthesis pathways in the CNS during myelin degeneration. Hence, neuroprotection during SPMS maybe achieved by overcoming MCT8 deficiencies in OLs.

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2026-01-01 | P215: Real world data-driven insights into the patient journey and diagnostic delays in MCT8 deficiency (Allan-Herndon-Dudley syndrome)

MCT8 deficiency (Allan-Herndon-Dudley syndrome) is a rare, X-linked disorder caused by loss-of-function variants in the SLC16A2 gene that encodes the thyroid hormone transporter MCT8. This condition presents primarily with hypotonia, failure to thrive, neurodevelopmental impairment, and symptoms related to thyrotoxicosis. Low physician awareness, nonspecific early symptoms, and lack of specific diagnostic codes contribute to delays in diagnosis and appropriate management. Diagnosis in the context of recognition and raised suspicion of MCT8 deficiency can be made on the basis of symptomology, a unique thyroid hormone profile (elevated T3, normal or low T4, normal or slightly elevated TSH) and genetic testing.

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2026-04-01 | Allan-Herndon-Dudley Syndrome

Open article ↗

2026-01-23 | Delineating the role of monocarboxylate transporter 8 (MCT8) in the context of neuroinflammation–mediated oligodendrocytopathy

Open article ↗

2026-01-01 | P215: Real world data-driven insights into the patient journey and diagnostic delays in MCT8 deficiency (Allan-Herndon-Dudley syndrome)

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Drug Discovery Landscape

6 orphan drug designations for Allan-Herndon-Dudley syndrome, including 1 approved therapy.

Drug	Therapy type	Regulator	Orphan designation	Approval	Sponsor
3,5-diiodothyropropionic acid	small molecules	EMA	2021-07-19	—	Dexcel Pharma GmbH
3,5-diiodothyropropionic acid	small molecules	FDA	2020-07-28	—	Dexcel Pharma Technologies Ltd.
tiratricol	small molecules	FDA	2019-01-16	—	Rare Thyroid Therapeutics
Tiratricol [Emcitate]	small molecules	EMA	2017-11-08	2025-02-17	Rare Thyroid Therapeutics International AB
3,5-diiodothyropropionic acid	small molecules	EMA	2013-10-07	—	CATS Consultants GmbH
3,5-diiodothyropropionic acid	small molecules	FDA	2013-05-14	—	Zarion Pharmaceuticals P/L

Allan-Herndon-Dudley syndrome

Allan-Herndon-Dudley syndrome

Allan-Herndon-Dudley syndrome

Overview

Population

Burden

Therapies

Categories: rare endocrine diseases, rare genetic diseases, rare neurological diseases

Research Papers

2026-04-01 | Allan-Herndon-Dudley Syndrome

2026-01-23 | Delineating the role of monocarboxylate transporter 8 (MCT8) in the context of neuroinflammation–mediated oligodendrocytopathy

2026-01-01 | P215: Real world data-driven insights into the patient journey and diagnostic delays in MCT8 deficiency (Allan-Herndon-Dudley syndrome)

2026-04-01 | Allan-Herndon-Dudley Syndrome

2026-01-23 | Delineating the role of monocarboxylate transporter 8 (MCT8) in the context of neuroinflammation–mediated oligodendrocytopathy

2026-01-01 | P215: Real world data-driven insights into the patient journey and diagnostic delays in MCT8 deficiency (Allan-Herndon-Dudley syndrome)

Drug Discovery Landscape

Updated: Aug 27, 2026