RARE DISEASE
Osteopetrosis and related disorders
Osteopetrosis and related disorders
Osteopetrosis and related disorders
Drug discovery
1
drug
With orphan designation
Overview
Osteopetrosis is a group of rare genetic disorders characterized by defective osteoclast-mediated bone resorption, leading to abnormally dense, brittle bones and complications such as fractures, bone marrow failure, and cranial nerve compression. Major types include autosomal dominant (ADO, Albers-Schönberg disease), autosomal recessive (ARO), and intermediate forms, with severity ranging from asymptomatic to life-threatening manifestations in infancy [1][3][7][12].
Burden
Mortality: Untreated ARO is fatal in infancy/early childhood due to marrow failure or infections [3][7].
Morbidity: Chronic pain, recurrent fractures, vision/hearing loss, and growth retardation [1][12].
Healthcare costs: High due to complex management, HSCT, and lifelong multidisciplinary care [5][15].
Therapies
Severe ARO: Hematopoietic stem cell transplantation (HSCT) to address bone marrow failure and metabolic defects; limited efficacy in neurodegenerative subtypes [5][9].
Mild/ADO: Supportive care (fracture management, physical therapy), calcium/vitamin D supplementation, interferon gamma-1b to enhance osteoclast activity [2][9][15].
Complications: Surgery for fractures/deformities, antibiotics for osteomyelitis, and multidisciplinary care for neurological, dental, and hematological issues [2][12].
Categories: rare bone diseases, rare developmental anomalies during embryogenesis, rare genetic diseases, rare transplant-related disorders
Research Papers
1,709 drug discovery papers about Osteopetrosis and related disorders, with 3 first-in-class emerging drug candidates forecasted to outperform the average preclinical success rate. Recent publications:
1,709 drug discovery papers about Osteopetrosis and related disorders, with 3 first-in-class emerging drug candidates forecasted to outperform the average preclinical success rate. Recent publications:
2026-06-29 | A Novel Homozygous T-Cell Immune Regulator 1 (TCIRG1) Stop-Gain Variant Causing Malignant Infantile Osteopetrosis
Malignant infantile osteopetrosis (MIOP) is a rare life-threatening autosomal recessive disorder characterized by defective osteoclast-mediated bone resorption, most commonly caused by pathogenic variants in the TCIRG1 gene. Without hematopoietic stem cell transplantation (HSCT), the disease is associated with severe morbidity and early mortality. We report a 15-month-old Moroccan girl born to first-cousin consanguineous parents who initially presented during infancy with failure to thrive, persistent bicytopenia, developmental delay, axial hypotonia, divergent strabismus with nystagmus, and facial dysmorphism. Skeletal radiographs demonstrated diffuse osteosclerosis, obliteration of medullary cavities, and characteristic Erlenmeyer flask deformities, strongly suggestive of MIOP. Whole-exome sequencing identified a novel homozygous pathogenic variant in T-cell immune regulator 1 (TCIRG1) (NM_006019.4:c.1897C>T; p.Gln633Ter). The variant is absent from the gnomAD database and was classified as pathogenic according to the American College of Medical Genetics and Genomics/Association for Molecular Pathology (ACMG/AMP) criteria. To the best of our knowledge, this variant has not previously been reported in affected individuals. The patient is currently undergoing evaluation for HSCT. This case expands the mutational spectrum of TCIRG1-associated MIOP and highlights the importance of early genomic testing in infants from consanguineous families presenting with unexplained cytopenias, growth failure, and characteristic skeletal abnormalities.
2026-06-25 | Subtype-specific bone mineralization defects and early treatment amelioration in murine models of autosomal recessive osteopetrosis revealed by Raman spectroscopy.
Autosomal recessive osteopetrosis is a rare genetic disorder caused by impaired osteoclast function, leading to excessive bone mass, defective remodeling, and fragility fractures. While bone density alterations are well recognized, compositional parameters remain poorly characterized. Here, we applied Raman spectroscopy to characterize bone defects in two murine models, the RANKL-deficient Rankl-/- (mild form) and the TCIRG1-deficient oc/oc (severe form), compared with healthy controls. Raman analysis revealed a gradient in mineral-to-matrix ratio, progressively showing lower values from healthy to Rankl-/- and to oc/oc (skull: 2.93 ± 0.02 vs. 2.19 ± 0.31 vs. 1.72 ± 0.15, p < 0.05; long bone: 3.59 ± 0.56 vs. 2.60 ± 0.53 vs. 1.86 ± 0.17, p < 0.05 for all pairs except Rankl-/- vs oc/oc). Crystallinity showed overall lower values in osteopetrotic bones compared to WT, with partially overlapping distributions between Rankl-/- and oc/oc mice (skull: 0.050 ± 0.001 vs. 0.046 ± 0.001 vs. 0.048 ± 0.001; long bone: 0.050 ± 0.001 vs. 0.047 ± 0.001 vs. 0.048 ± 0.001 for WT, Rankl-/- and oc/oc, respectively). Multivariate analysis achieved 95% classification accuracy under exploratory animal-level cross-validation. In oc/oc mice treated with bone marrow transplantation, Raman analysis detected a significantly higher mineral-to-matrix ratio at day 18 compared to untreated oc/oc mice (2.668 ± 0.124 vs. 2.207 ± 0.311; p = 0.040, respectively). These findings identify genotype-specific compositional alterations in ARO models and provide proof-of-concept that Raman spectroscopy can characterize mineralization defects in intact bones ex vivo, suggesting that further development of non-invasive or minimally invasive Raman-based approaches may enable future studies of ARO progression and therapeutic response in clinically relevant settings.
2026-06-25 | Expression of Phosphomimetic OSTM1-T328E/S329D Variant Partially Restores Bone Resorption Defect in LRRK1-Deficient Mice.
LRRK1 is essential for osteoclast-mediated bone resorption, and loss of LRRK1 function causes osteopetrosis in mice and humans. However, the mechanisms by which LRRK1 regulates osteoclast activity remain incompletely defined. We previously identified that phosphorylation of OSTM1 at threonine 328 and serine 329 was compromised in LRRK1-deficient osteoclasts. To test the role for OSTM1 phosphorylation in LRRK1 regulation of osteoclast functions, we expressed a phosphomimetic OSTM1 variant in LRRK1-null osteoclasts. Overexpression of phosphomimetic, but not a dephosphomimetic variant, partially restored resorptive activity in LRRK1-deficient osteoclasts in vitro. To test OSTM1's role in rescuing defective bone resorption in Lrrk1-null mice, we generated Ostm1-T328E/S329D knock-in (KI) mice and crossed them onto the Lrrk1-deficient background. Ostm1-T328E/S329D KI mice displayed normal skeletal development and bone remodeling. When crossed to the Lrrk1-deficient background, OSTM1-T328E/S329D expression increased osteoclast resorptive activity and bone formation and partially improved trabecular architecture, although bone volume remained unchanged. These findings demonstrate that OSTM1 phosphorylation contributes to LRRK1-dependent regulation of osteoclast function and identify the LRRK1-OSTM1 pathway as a mechanistic node controlling bone resorption. Our work provides new insight into the molecular basis of LRRK1-mediated osteoclast function and highlights OSTM1 phosphorylation as a potential therapeutic target for metabolic bone diseases.
2026-06-29 | A Novel Homozygous T-Cell Immune Regulator 1 (TCIRG1) Stop-Gain Variant Causing Malignant Infantile Osteopetrosis
Malignant infantile osteopetrosis (MIOP) is a rare life-threatening autosomal recessive disorder characterized by defective osteoclast-mediated bone resorption, most commonly caused by pathogenic variants in the TCIRG1 gene. Without hematopoietic stem cell transplantation (HSCT), the disease is associated with severe morbidity and early mortality. We report a 15-month-old Moroccan girl born to first-cousin consanguineous parents who initially presented during infancy with failure to thrive, persistent bicytopenia, developmental delay, axial hypotonia, divergent strabismus with nystagmus, and facial dysmorphism. Skeletal radiographs demonstrated diffuse osteosclerosis, obliteration of medullary cavities, and characteristic Erlenmeyer flask deformities, strongly suggestive of MIOP. Whole-exome sequencing identified a novel homozygous pathogenic variant in T-cell immune regulator 1 (TCIRG1) (NM_006019.4:c.1897C>T; p.Gln633Ter). The variant is absent from the gnomAD database and was classified as pathogenic according to the American College of Medical Genetics and Genomics/Association for Molecular Pathology (ACMG/AMP) criteria. To the best of our knowledge, this variant has not previously been reported in affected individuals. The patient is currently undergoing evaluation for HSCT. This case expands the mutational spectrum of TCIRG1-associated MIOP and highlights the importance of early genomic testing in infants from consanguineous families presenting with unexplained cytopenias, growth failure, and characteristic skeletal abnormalities.
2026-06-25 | Subtype-specific bone mineralization defects and early treatment amelioration in murine models of autosomal recessive osteopetrosis revealed by Raman spectroscopy.
Autosomal recessive osteopetrosis is a rare genetic disorder caused by impaired osteoclast function, leading to excessive bone mass, defective remodeling, and fragility fractures. While bone density alterations are well recognized, compositional parameters remain poorly characterized. Here, we applied Raman spectroscopy to characterize bone defects in two murine models, the RANKL-deficient Rankl-/- (mild form) and the TCIRG1-deficient oc/oc (severe form), compared with healthy controls. Raman analysis revealed a gradient in mineral-to-matrix ratio, progressively showing lower values from healthy to Rankl-/- and to oc/oc (skull: 2.93 ± 0.02 vs. 2.19 ± 0.31 vs. 1.72 ± 0.15, p < 0.05; long bone: 3.59 ± 0.56 vs. 2.60 ± 0.53 vs. 1.86 ± 0.17, p < 0.05 for all pairs except Rankl-/- vs oc/oc). Crystallinity showed overall lower values in osteopetrotic bones compared to WT, with partially overlapping distributions between Rankl-/- and oc/oc mice (skull: 0.050 ± 0.001 vs. 0.046 ± 0.001 vs. 0.048 ± 0.001; long bone: 0.050 ± 0.001 vs. 0.047 ± 0.001 vs. 0.048 ± 0.001 for WT, Rankl-/- and oc/oc, respectively). Multivariate analysis achieved 95% classification accuracy under exploratory animal-level cross-validation. In oc/oc mice treated with bone marrow transplantation, Raman analysis detected a significantly higher mineral-to-matrix ratio at day 18 compared to untreated oc/oc mice (2.668 ± 0.124 vs. 2.207 ± 0.311; p = 0.040, respectively). These findings identify genotype-specific compositional alterations in ARO models and provide proof-of-concept that Raman spectroscopy can characterize mineralization defects in intact bones ex vivo, suggesting that further development of non-invasive or minimally invasive Raman-based approaches may enable future studies of ARO progression and therapeutic response in clinically relevant settings.
2026-06-25 | Expression of Phosphomimetic OSTM1-T328E/S329D Variant Partially Restores Bone Resorption Defect in LRRK1-Deficient Mice.
LRRK1 is essential for osteoclast-mediated bone resorption, and loss of LRRK1 function causes osteopetrosis in mice and humans. However, the mechanisms by which LRRK1 regulates osteoclast activity remain incompletely defined. We previously identified that phosphorylation of OSTM1 at threonine 328 and serine 329 was compromised in LRRK1-deficient osteoclasts. To test the role for OSTM1 phosphorylation in LRRK1 regulation of osteoclast functions, we expressed a phosphomimetic OSTM1 variant in LRRK1-null osteoclasts. Overexpression of phosphomimetic, but not a dephosphomimetic variant, partially restored resorptive activity in LRRK1-deficient osteoclasts in vitro. To test OSTM1's role in rescuing defective bone resorption in Lrrk1-null mice, we generated Ostm1-T328E/S329D knock-in (KI) mice and crossed them onto the Lrrk1-deficient background. Ostm1-T328E/S329D KI mice displayed normal skeletal development and bone remodeling. When crossed to the Lrrk1-deficient background, OSTM1-T328E/S329D expression increased osteoclast resorptive activity and bone formation and partially improved trabecular architecture, although bone volume remained unchanged. These findings demonstrate that OSTM1 phosphorylation contributes to LRRK1-dependent regulation of osteoclast function and identify the LRRK1-OSTM1 pathway as a mechanistic node controlling bone resorption. Our work provides new insight into the molecular basis of LRRK1-mediated osteoclast function and highlights OSTM1 phosphorylation as a potential therapeutic target for metabolic bone diseases.
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Drug Discovery Landscape
1 orphan drug designation for Osteopetrosis and related disorders.
1 orphan drug designation for Osteopetrosis and related disorders.
Drug | Therapy type | Regulator | Orphan designation | Approval | Sponsor |
|---|---|---|---|---|---|
Autologous haematopoietic stem and progenitor cell population containing CD34+ cells transduced with a lentiviral vector encoding the TCIRG1 cDNA ex vivo expanded | gene therapies | EMA | 2021-10-15 | — | Fondazione Telethon Ets |
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