Autosomal Recessive Osteopetrosis 1

Mendelian MONDO:0009815 Pathograph 42 Show in embeddings browser Sclerosing Bone Dysplasias

Autosomal recessive osteopetrosis 1 (ARO1, OPTB1, malignant infantile osteopetrosis) is a severe sclerosing bone disease caused by biallelic loss-of-function variants in TCIRG1, encoding the osteoclast-specific a3 subunit of the vacuolar H+-ATPase. TCIRG1 variants are the most frequent cause of infantile malignant osteopetrosis, accounting for roughly half of autosomal recessive osteopetrosis cases. Osteoclasts differentiate normally and are present in normal or elevated numbers, but cannot acidify the resorption lacuna, so bone mineral is never dissolved; this is what makes ARO1 an osteoclast-rich osteopetrosis, in contrast to the osteoclast-poor forms caused by defects in the RANK/RANKL differentiation axis. The defect is specific to extracellular acidification: lysosomal proton pumping and systemic acid-base balance are preserved, which separates ARO1 from carbonic anhydrase II deficiency. Failure of resorption produces dense but brittle bones, obliteration of the medullary cavity with marrow failure and compensatory extramedullary haematopoiesis, cranial nerve compression at unwidened skull foramina, and hypocalcaemia with secondary hyperparathyroidism and superimposed rickets. Without haematopoietic stem cell transplantation the disease is usually fatal within the first decade.

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1
Inheritance
5
Pathophys.
32
Phenotypes
42
Pathograph
1
Genes
5
Medical Actions
1
Trials
2
Models
13
References
1
Deep Research
🏷

Classifications

IUIS Category
innate immunity defect
ISDS Skeletal Nosology
osteopetrosis and related
👪

Inheritance

1
Autosomal Recessive HP:0000007
Autosomal recessive inheritance. Biallelic (homozygous or compound heterozygous) TCIRG1 variants. Typically, but not exclusively. GeneReviews records rare exceptions: one family with heterozygous variants and autosomal dominant osteopetrosis, and one individual with a heterozygous de novo variant. Those are quoted in the evidence below rather than smoothed away, because this entry is bound to MONDO:0009815 on the basis of gene identity and the exceptions bear on how firmly that identity is drawn.
Autosomal recessive inheritance
Show evidence (3 references)
PMID:10888887 SUPPORT
"TCIRG1, encoding the osteoclast-specific 116-kD subunit of the vacuolar proton pump, is mutated in five of nine patients with a diagnosis of infantile malignant osteopetrosis"
TCIRG1 mutations identified as a frequent cause of autosomal recessive osteopetrosis.
PMID:40875877 SUPPORT Human Clinical
"each sib of an affected individual has at conception a 25% chance of having TCIRG1-related osteopetrosis, a 50% chance of being heterozygous, and a 25% chance of inheriting neither of the familial TCIRG1 pathogenic variants."
The recurrence risk that follows from recessive inheritance, from the GeneReviews chapter for this gene.
PMID:40875877 SUPPORT Human Clinical
"Heterozygous TCIRG1 pathogenic variants have been identified in affected individuals in one family with autosomal dominant osteopetrosis and one additional individual with a heterozygous de novo pathogenic variant."
The caveat to the recessive model, recorded because this entry turns on gene and inheritance identity. It does not overturn autosomal recessive as the typical mode, but a strictly biallelic reading would be wrong.
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Pathophysiology

5
Vacuolar Proton Pump Deficiency in Osteoclasts
TCIRG1 encodes the a3 subunit of the vacuolar H+-ATPase (V-ATPase), which is specifically expressed in osteoclasts and essential for proton secretion into the resorption lacuna. Loss-of-function mutations abolish osteoclast acidification capacity, preventing dissolution of hydroxyapatite mineral in bone matrix. Osteoclasts differentiate normally and are present in normal or elevated numbers but cannot resorb bone.
Osteoclast CL:0000092 Cell Ontology (CL) Relation: this pathophysiological event involves this cell type This pathophysiological event involves Osteoclast (CL:0000092). CL:0000092 is a cell type from the Cell Ontology.
Bone Resorption GO:0045453 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves Bone Resorption (GO:0045453). GO:0045453 is a biological process from the Gene Ontology.
Animal models
Atp6i (Tcirg1) knockout mouse Mouse recapitulates Loss of the same subunit in the same cell type, with the same compartment-restricted acidification defect.
Downstream
Progressive Skeletal Sclerosis Loss of osteoclast proton-pump function prevents normal bone resorption and drives skeletal sclerosis.
Failure of Skeletal Calcium Mobilization The same failure to dissolve bone mineral means skeletal calcium cannot be released into the circulation.
Show evidence (4 references)
PMID:10888887 SUPPORT
"TCIRG1, encoding the osteoclast-specific 116-kD subunit of the vacuolar proton pump, is mutated in five of nine patients"
Identifies TCIRG1 and the vacuolar proton pump as the pathogenic target.
PMID:10888887 SUPPORT
"Osteoclasts are present in normal or elevated numbers in individuals affected by autosomal recessive osteopetrosis, suggesting that the defect is not in osteoclast differentiation, but in a gene involved in the functional capacity of mature osteoclasts"
Establishes that osteoclasts differentiate normally but are non-functional.
PMID:10581033 SUPPORT Model Organism
"Atp6i-/- osteoclast-like cells (OCLs) lose the function of extracellular acidification, but retain intracellular lysosomal proton pump activity"
Establishes that the lesion is confined to extracellular acidification at the osteoclast-bone interface and spares lysosomal proton pumping, which is why the phenotype is skeletal rather than a generalised lysosomal disorder.
+ 1 more reference
Progressive Skeletal Sclerosis
Failure of osteoclast-mediated bone resorption leads to progressive accumulation of unremodeled bone, obliterating the medullary cavity and narrowing cranial nerve foramina.
Bone Remodeling GO:0046849 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves Bone Remodeling (GO:0046849). GO:0046849 is a biological process from the Gene Ontology.
Animal models
oc/oc mouse Mouse recapitulates Generalised increase in skeletal density with marrow-cavity fibrosis and extramedullary haematopoiesis, matching the human skeletal and haematologic branches.
Downstream
Short stature Growth failure from the disordered bone modelling this node describes.
Delayed eruption of teeth Teeth cannot erupt through sclerotic, unresorbed bone; eruption depends on the osteoclast-mediated resorption this disease abolishes.
Carious teeth Dental caries, reported alongside the eruption failure. Drawn here rather than given its own mechanism because the source groups the dental findings together, and the route from abnormal eruption and enamel defects to caries is not separately established.
Hypertelorism Craniofacial consequence of the skull deformity produced by unresorbed bone.
Micrognathia The mandibular expression of the same disordered craniofacial modelling.
Proptosis Forward displacement of the globe as the orbit is encroached on by thickened bone — the orbital counterpart of the foraminal narrowing that compresses the cranial nerves.
Bone Marrow Failure from Medullary Obliteration Progressive accumulation of unresorbed bone obliterates marrow space.
Cranial Nerve Compression from Skull Thickening Progressive skull sclerosis narrows cranial nerve foramina.
Increased bone mineral density
Osteopetrosis
Recurrent fractures
Bone pain
Craniosynostosis
Show evidence (1 reference)
PMID:10888887 SUPPORT
"mutations in TCIRG1 are a frequent cause of autosomal recessive osteopetrosis in humans"
TCIRG1 deficiency causes progressive skeletal sclerosis from failed bone resorption.
Bone Marrow Failure from Medullary Obliteration
Progressive accumulation of unremodeled bone obliterates the medullary cavity, causing loss of hematopoietic marrow space with resultant pancytopenia. Compensatory extramedullary hematopoiesis in liver and spleen causes hepatosplenomegaly.
Hematopoiesis GO:0030097 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves Hematopoiesis, annotated with hemopoiesis (GO:0030097). GO:0030097 is a biological process from the Gene Ontology.
Animal models
oc/oc mouse Mouse recapitulates Marrow-cavity fibrosis with extramedullary haematopoiesis, reversible by gene therapy in the model.
Downstream
Extramedullary hematopoiesis Haematopoiesis relocating to liver and spleen as the medullary cavity is obliterated — the direct compensatory consequence of losing marrow space.
Anemia
Thrombocytopenia
Recurrent infections
Recurrent respiratory infections
Hepatosplenomegaly
Pallor
Failure to thrive
Growth delay
Show evidence (1 reference)
PMID:10888887 SUPPORT
"Infantile malignant autosomal recessive osteopetrosis (MIM 259700) is a severe bone disease with a fatal outcome, generally within the first decade of life"
The fatal outcome is primarily due to bone marrow failure from medullary obliteration.
Cranial Nerve Compression from Skull Thickening
Progressive skull thickening narrows cranial nerve foramina, causing optic nerve compression (blindness), facial nerve palsy, and sensorineural hearing loss.
Cranium UBERON:0003128 Uberon multi-species anatomy ontology (UBERON) Relation: this pathophysiological event occurs in this anatomical location This pathophysiological event occurs in Cranium (UBERON:0003128). UBERON:0003128 is an anatomical location from the Uberon multi-species anatomy ontology.
Downstream
Optic atrophy Compression of the optic nerve in a narrowed optic canal, the most consequential of the cranial neuropathies here and the one that drives the urgency of transplantation.
Nystagmus Ocular instability following visual loss from the optic neuropathy above.
Optic nerve compression
Visual impairment
Hearing impairment
Hydrocephalus
Macrocephaly
Neurodevelopmental delay
Seizure
Failure of Skeletal Calcium Mobilization
Because osteoclasts cannot dissolve hydroxyapatite, the skeleton is unavailable as a calcium reservoir. Serum calcium falls, parathyroid hormone rises in compensation, and mineralization of newly laid osteoid fails. The result is rickets superimposed on a densely sclerotic skeleton, a combination easy to miss radiographically because the diffuse increase in bone density masks the impaired mineralization.
Downstream
Hypocalcemia
Secondary hyperparathyroidism
Rickets
Seizure
Show evidence (2 references)
PMID:42661684 SUPPORT Human Clinical
"secondary hyperparathyroidism from hypocalcemia, resulting in a paradoxical condition known as “osteopetrosis-rickets”"
States the causal sequence this node models: hypocalcaemia drives secondary hyperparathyroidism and the paradoxical coexistence of rickets with sclerosis.
PMID:42661684 SUPPORT Human Clinical
"Osteopetrorickets is clinically important because it may be overlooked in the presence of diffusely increased bone density, although impaired mineralization may coexist with osteosclerosis."
Supports the statement that the sclerosis masks the mineralization defect, which is the diagnostic consequence of this node.
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Pathograph

Use the checkboxes to hide or show graph categories. Hover nodes for evidence and cross-linked metadata.
Pathograph: causal mechanism network for Autosomal Recessive Osteopetrosis 1 Interactive directed graph showing how pathophysiology mechanisms, phenotypes, genetic factors and variants, experimental models, environmental triggers, and treatments relate through causal and linked edges.
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Phenotypes

32
Blood 3
Anemia HP:0001903 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Anemia (HP:0001903). HP:0001903 is a phenotype from the Human Phenotype Ontology.
Show evidence (2 references)
PMID:34545712 SUPPORT Human Clinical
"five Chinese children who presented with anemia, thrombocytopenia, hepatosplenomegaly, repeated infections, and increased bone density"
The autosomal recessive osteopetrosis cohort, including 3 TCIRG1 cases, explicitly presented with anemia.
PMID:40462430 SUPPORT Human Clinical
"Clinical manifestations included systemic osteosclerosis (14 cases, 100%), anemia (12 cases, 86%)"
A pediatric osteopetrosis cohort found anemia in most affected children; all TCIRG1 cases had malignant phenotypes.
Thrombocytopenia HP:0001873 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Thrombocytopenia (HP:0001873). HP:0001873 is a phenotype from the Human Phenotype Ontology.
Show evidence (2 references)
PMID:34545712 SUPPORT Human Clinical
"five Chinese children who presented with anemia, thrombocytopenia, hepatosplenomegaly, repeated infections, and increased bone density"
The autosomal recessive osteopetrosis cohort, including 3 TCIRG1 cases, explicitly presented with thrombocytopenia.
PMID:40462430 SUPPORT Human Clinical
"Clinical manifestations included systemic osteosclerosis (14 cases, 100%), anemia (12 cases, 86%), infections (10 cases, 71%), thrombocytopenia (9 cases, 64%)"
A pediatric osteopetrosis cohort found thrombocytopenia in most children with malignant disease enrichment among TCIRG1 cases.
Extramedullary hematopoiesis HP:0001978 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Extramedullary hematopoiesis (HP:0001978). HP:0001978 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:40875877 SUPPORT Human Clinical
"Advanced bone sclerosis results in extramedullary hematopoiesis, bone marrow failure, ocular complications with potential for blindness (optic nerve compression/atrophy and primary retinopathy), dental manifestations (delay in tooth eruption and dental caries), and deafness in some individuals."
Names extramedullary haematopoiesis directly, and attributes it to the advancing sclerosis, which is the causal claim this phenotype sits under.
Cardiovascular 1
Hepatosplenomegaly HP:0001433 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Hepatosplenomegaly (HP:0001433). HP:0001433 is a phenotype from the Human Phenotype Ontology.
Show evidence (2 references)
PMID:34545712 SUPPORT Human Clinical
"five Chinese children who presented with anemia, thrombocytopenia, hepatosplenomegaly, repeated infections, and increased bone density"
Hepatosplenomegaly was part of the presenting phenotype in an autosomal recessive osteopetrosis cohort that included 3 TCIRG1 cases.
PMID:18946580 SUPPORT Human Clinical
"The patient was a 5-year-old girl with macrocephaly, facial dysmorphism, blindness, mental retardation, hepatosplenomegaly, pancytopenia, and osteosclerotic changes in the skull and limb."
A TCIRG1-associated infantile malignant osteopetrosis case directly documented hepatosplenomegaly.
Ear 1
Hearing impairment HP:0000365 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Hearing impairment (HP:0000365). HP:0000365 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:30898950 SUPPORT Human Clinical
"Neurological manifestations can also occur due to narrowing of osseous foramina resulting in visual impairment, hearing loss, facial palsy and hydrocephalus."
The malignant infantile phenotype includes hearing loss from cranial foraminal narrowing.
Endocrine 1
Secondary hyperparathyroidism HP:0000867 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Secondary hyperparathyroidism (HP:0000867). HP:0000867 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:42661684 SUPPORT Human Clinical
"In patients with osteopetrosis, impaired calcium mobilization due to abnormal osteoclast activity can lead to secondary hyperparathyroidism from hypocalcemia"
States the full sequence behind this phenotype: impaired calcium mobilization from the osteoclast defect, then hypocalcaemia, then compensatory hyperparathyroidism.
Eye 6
Visual impairment HP:0000505 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Visual impairment (HP:0000505). HP:0000505 is a phenotype from the Human Phenotype Ontology.
Show evidence (2 references)
PMID:30898950 SUPPORT Human Clinical
"Neurological manifestations can also occur due to narrowing of osseous foramina resulting in visual impairment, hearing loss, facial palsy and hydrocephalus."
Malignant infantile osteopetrosis causes visual impairment through cranial foraminal narrowing.
PMID:18946580 SUPPORT Human Clinical
"The patient was a 5-year-old girl with macrocephaly, facial dysmorphism, blindness, mental retardation, hepatosplenomegaly, pancytopenia, and osteosclerotic changes in the skull and limb."
A TCIRG1-associated case shows that visual involvement may be severe enough to cause blindness.
Optic nerve compression VERY_FREQUENT HP:0007807 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Optic nerve compression (HP:0007807). HP:0007807 is a phenotype from the Human Phenotype Ontology.
Show evidence (2 references)
ORPHA:667 SUPPORT Human Clinical
"HP:0007807 | Optic nerve compression | Very frequent (99-80%)"
Orphanet lists optic nerve compression as a very frequent feature of autosomal recessive malignant osteopetrosis.
PMID:30898950 SUPPORT Human Clinical
"Neurological manifestations can also occur due to narrowing of osseous foramina resulting in visual impairment, hearing loss, facial palsy and hydrocephalus."
Case report of malignant infantile osteopetrosis documents visual impairment from osseous foraminal narrowing, consistent with optic nerve compression.
Optic atrophy HP:0000648 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Optic atrophy (HP:0000648). HP:0000648 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:40875877 SUPPORT Human Clinical
"ocular complications with potential for blindness (optic nerve compression/atrophy and primary retinopathy)"
Names optic atrophy, and distinguishes the compressive route from a primary retinopathy that compression does not explain.
Nystagmus HP:0000639 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Nystagmus (HP:0000639). HP:0000639 is a phenotype from the Human Phenotype Ontology.
The cohort is mixed-genotype, so no frequency band is set from its 58.8% figure.
Show evidence (1 reference)
PMID:42661684 SUPPORT Human Clinical
"Ophthalmological findings such as optic atrophy, nystagmus, or strabismus were present in 10 patients"
Records nystagmus among the ophthalmological findings in a paediatric osteopetrosis cohort.
Proptosis HP:0000520 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Proptosis (HP:0000520). HP:0000520 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:40875877 SUPPORT Human Clinical
"Craniofacial features can include macrocephaly, exophthalmos, hypertelorism, and micrognathia."
Exophthalmos is the term GeneReviews uses; HP:0000520 Proptosis is the HPO term for the same finding and lists exophthalmos among its synonyms.
Hypertelorism HP:0000316 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Hypertelorism (HP:0000316). HP:0000316 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:40875877 SUPPORT Human Clinical
"Craniofacial features can include macrocephaly, exophthalmos, hypertelorism, and micrognathia."
Lists hypertelorism among the craniofacial features.
Head and Neck 5
Macrocephaly HP:0000256 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Macrocephaly (HP:0000256). HP:0000256 is a phenotype from the Human Phenotype Ontology.
Show evidence (2 references)
PMID:18946580 SUPPORT Human Clinical
"The patient was a 5-year-old girl with macrocephaly, facial dysmorphism, blindness, mental retardation, hepatosplenomegaly, pancytopenia, and osteosclerotic changes in the skull and limb."
A TCIRG1-associated infantile malignant osteopetrosis case directly documented macrocephaly.
PMID:34519872 SUPPORT Human Clinical
"At 6 months, the infant had macrocephaly and frontal bossing with a bulging fontanelle."
Hydrocephalus-associated infantile osteopetrosis can present with macrocephaly and frontal bossing.
Craniosynostosis VERY_FREQUENT HP:0001363 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Craniosynostosis (HP:0001363). HP:0001363 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
ORPHA:667 SUPPORT Human Clinical
"HP:0001363 | Craniosynostosis | Very frequent (99-80%)"
Orphanet lists craniosynostosis as a very frequent feature of autosomal recessive malignant osteopetrosis.
Delayed eruption of teeth HP:0000684 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Delayed eruption of teeth (HP:0000684). HP:0000684 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:40875877 SUPPORT Human Clinical
"dental manifestations (delay in tooth eruption and dental caries)"
Names delayed tooth eruption as a dental manifestation of advancing sclerosis.
Carious teeth HP:0000670 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Carious teeth (HP:0000670). HP:0000670 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:40875877 SUPPORT Human Clinical
"dental manifestations (delay in tooth eruption and dental caries)"
The same GeneReviews sentence names both dental manifestations; this record completes the pair with delayed eruption.
Micrognathia HP:0000347 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Micrognathia (HP:0000347). HP:0000347 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:40875877 SUPPORT Human Clinical
"Craniofacial features can include macrocephaly, exophthalmos, hypertelorism, and micrognathia."
Lists micrognathia among the craniofacial features.
Immune 2
Recurrent infections HP:0002719 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Recurrent infections (HP:0002719). HP:0002719 is a phenotype from the Human Phenotype Ontology.
Show evidence (2 references)
PMID:34545712 SUPPORT Human Clinical
"five Chinese children who presented with anemia, thrombocytopenia, hepatosplenomegaly, repeated infections, and increased bone density"
Repeated infections were part of the presenting phenotype in an autosomal recessive osteopetrosis cohort that included 3 TCIRG1 cases.
PMID:30898950 SUPPORT Human Clinical
"In addition, growth retardation and recurrent infections requiring long-term antibiotic use are common."
A TCIRG1-related malignant infantile osteopetrosis report highlights recurrent infections as a common clinical problem.
Recurrent respiratory infections VERY_FREQUENT HP:0002205 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Recurrent respiratory infections (HP:0002205). HP:0002205 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
ORPHA:667 SUPPORT Human Clinical
"HP:0002205 | Recurrent respiratory infections | Very frequent (99-80%)"
Orphanet lists recurrent respiratory infections as a very frequent feature of autosomal recessive malignant osteopetrosis.
Integument 1
Pallor VERY_FREQUENT HP:0000980 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Pallor (HP:0000980). HP:0000980 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
ORPHA:667 SUPPORT Human Clinical
"HP:0000980 | Pallor | Very frequent (99-80%)"
Orphanet lists pallor as a very frequent feature of autosomal recessive malignant osteopetrosis, consistent with the severe anemia from marrow failure.
Metabolism 1
Hypocalcemia HP:0002901 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Hypocalcemia (HP:0002901). HP:0002901 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:34519872 SUPPORT Human Clinical
"Autosomal recessive osteopetrosis has a variable presentation, most commonly including failure to thrive, hypocalcemia, seizures, hepatosplenomegaly, hydrocephalus, vision or hearing loss, and cytopenias."
Hypocalcemia is identified as a common manifestation of autosomal recessive osteopetrosis.
Musculoskeletal 4
Increased bone mineral density HP:0011001 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Increased bone mineral density (HP:0011001). HP:0011001 is a phenotype from the Human Phenotype Ontology.
Show evidence (2 references)
PMID:34545712 SUPPORT Human Clinical
"Osteopetrosis is characterized by increased bone density and bone marrow cavity stenosis"
An autosomal recessive osteopetrosis cohort that included 3 TCIRG1 cases identified increased bone density with marrow cavity stenosis as a core manifestation.
PMID:40462430 SUPPORT Human Clinical
"Clinical manifestations included systemic osteosclerosis (14 cases, 100%)"
A pediatric osteopetrosis cohort found systemic osteosclerosis in all affected children; all TCIRG1 cases had malignant phenotypes.
Osteopetrosis VERY_FREQUENT HP:0011002 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Osteopetrosis (HP:0011002). HP:0011002 is a phenotype from the Human Phenotype Ontology.
Show evidence (2 references)
ORPHA:667 SUPPORT Human Clinical
"HP:0011002 | Osteopetrosis | Very frequent (99-80%)"
Orphanet lists osteopetrosis as a very frequent feature of autosomal recessive malignant osteopetrosis.
PMID:34545712 SUPPORT Human Clinical
"Osteopetrosis is characterized by increased bone density and bone marrow cavity stenosis"
Clinical cohort of recessive osteopetrosis patients confirms increased bone density with marrow cavity stenosis as the defining skeletal manifestation.
Recurrent fractures VERY_FREQUENT HP:0002757 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Recurrent fractures (HP:0002757). HP:0002757 is a phenotype from the Human Phenotype Ontology.
Show evidence (2 references)
ORPHA:667 SUPPORT Human Clinical
"HP:0002757 | Recurrent fractures | Very frequent (99-80%)"
Orphanet lists recurrent fractures as a very frequent feature of autosomal recessive malignant osteopetrosis.
PMID:30898950 SUPPORT Human Clinical
"Malignant infantile osteopetrosis (MIOP), an autosomal-recessive disorder, is extremely rare, presenting early in life with extreme sclerosis of the skeleton and reduced activity of osteoclasts."
Case report documents extreme skeletal sclerosis in malignant infantile osteopetrosis consistent with the paradoxical brittle bone fracture risk.
Rickets FREQUENT HP:0002748 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Rickets (HP:0002748). HP:0002748 is a phenotype from the Human Phenotype Ontology.
The 76% figure in the source cohort is across paediatric osteopetrosis of mixed genotype, not TCIRG1 only, so the frequency band here is set from the authors' own qualitative wording rather than from that percentage.
Show evidence (1 reference)
PMID:42661684 SUPPORT Human Clinical
"Osteopetrorickets is a frequent and clinically significant complication of pediatric osteopetrosis."
Direct statement of frequency in a paediatric osteopetrosis cohort.
Nervous System 3
Hydrocephalus HP:0000238 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Hydrocephalus (HP:0000238). HP:0000238 is a phenotype from the Human Phenotype Ontology.
Show evidence (2 references)
PMID:34519872 SUPPORT Human Clinical
"Autosomal recessive osteopetrosis has a variable presentation, most commonly including failure to thrive, hypocalcemia, seizures, hepatosplenomegaly, hydrocephalus, vision or hearing loss, and cytopenias."
A clinical report on malignant infantile osteopetrosis identifies hydrocephalus among the common presenting manifestations.
PMID:30898950 SUPPORT Human Clinical
"Neurological manifestations can also occur due to narrowing of osseous foramina resulting in visual impairment, hearing loss, facial palsy and hydrocephalus."
Independent clinical evidence links malignant infantile osteopetrosis to hydrocephalus from cranial narrowing.
Seizure HP:0001250 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Seizure (HP:0001250). HP:0001250 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:34519872 SUPPORT Human Clinical
"Autosomal recessive osteopetrosis has a variable presentation, most commonly including failure to thrive, hypocalcemia, seizures, hepatosplenomegaly, hydrocephalus, vision or hearing loss, and cytopenias."
Seizures are listed among the common presenting manifestations of autosomal recessive osteopetrosis.
Neurodevelopmental delay HP:0012758 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Neurodevelopmental delay (HP:0012758). HP:0012758 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:40462430 SUPPORT Human Clinical
"Clinical manifestations included systemic osteosclerosis (14 cases, 100%), anemia (12 cases, 86%), infections (10 cases, 71%), thrombocytopenia (9 cases, 64%), hepatosplenomegaly (8 cases, 57%), and developmental delay (5 cases, 36%)."
A pediatric osteopetrosis cohort documented developmental delay in a substantial subset of children; all TCIRG1 cases in the cohort had malignant phenotypes.
Constitutional 1
Bone pain VERY_FREQUENT HP:0002653 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Bone pain (HP:0002653). HP:0002653 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
ORPHA:667 SUPPORT Human Clinical
"HP:0002653 | Bone pain | Very frequent (99-80%)"
Orphanet lists bone pain as a very frequent feature of autosomal recessive malignant osteopetrosis.
Growth 3
Failure to thrive HP:0001508 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Failure to thrive (HP:0001508). HP:0001508 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:34519872 SUPPORT Human Clinical
"Autosomal recessive osteopetrosis has a variable presentation, most commonly including failure to thrive, hypocalcemia, seizures, hepatosplenomegaly, hydrocephalus, vision or hearing loss, and cytopenias."
Failure to thrive is listed among the common presenting manifestations of autosomal recessive osteopetrosis.
Growth delay VERY_FREQUENT HP:0001510 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Growth delay (HP:0001510). HP:0001510 is a phenotype from the Human Phenotype Ontology.
Show evidence (2 references)
ORPHA:667 SUPPORT Human Clinical
"HP:0001510 | Growth delay | Very frequent (99-80%)"
Orphanet lists growth delay as a very frequent feature of autosomal recessive malignant osteopetrosis.
PMID:30898950 SUPPORT Human Clinical
"In addition, growth retardation and recurrent infections requiring long-term antibiotic use are common."
Case report identifies growth retardation as a common feature of malignant infantile osteopetrosis.
Short stature FREQUENT HP:0004322 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Short stature (HP:0004322). HP:0004322 is a phenotype from the Human Phenotype Ontology.
A mixed-genotype paediatric cohort reports short stature in 13 of 17 patients (76.4%). That number is not used to set the frequency band here, for the same reason as the Rickets record: the cohort was not TCIRG1-restricted.
Show evidence (1 reference)
PMID:40875877 SUPPORT Human Clinical
"TCIRG1-related osteopetrosis is characterized by growth deficiency, pathologic fractures of dense but brittle bones, limping gait with bone pain, hypocalcemia that can result in seizures, and secondary hyperparathyroidism."
Lists growth deficiency first among the defining features of the TCIRG1 form specifically.
🧬

Genetic Associations

1
TCIRG1 (Causative)
Gene: TCIRG1 hgnc:11647 HUGO Gene Nomenclature Committee (hgnc) Relation: this disease-associated gene is this gene This disease-associated gene is TCIRG1 (hgnc:11647). hgnc:11647 is a gene from the HUGO Gene Nomenclature Committee. relationship_type: CAUSATIVE
Show evidence (6 references)
PMID:10888887 SUPPORT Human Clinical
"TCIRG1, encoding the osteoclast-specific 116-kD subunit of the vacuolar proton pump, is mutated in five of nine patients with a diagnosis of infantile malignant osteopetrosis"
The original report identifying TCIRG1 as a cause of infantile malignant osteopetrosis.
PMID:11532986 SUPPORT Human Clinical
"we have now established that ATP6i mutations are responsible for approximately 50% of patients affected by this disease"
Quantifies the share of autosomal recessive osteopetrosis attributable to TCIRG1 across 44 unrelated families worldwide. ATP6i is a synonym of TCIRG1.
PMID:11532986 SUPPORT Human Clinical
"The vast majority of these mutations (40 out of 42 alleles, including seven deletions, two insertions, 10 nonsense substitutions and 21 mutations in splice sites) are predicted to cause severe abnormalities in the protein product and are likely to represent null alleles"
Establishes that the pathogenic variant spectrum is predominantly null alleles.
+ 3 more references
💊

Medical Actions

5
Allogeneic Hematopoietic Stem Cell Transplantation
Action: allogeneic haematopoietic stem cell transplantationNCI Thesaurus (NCIT) Relation: this treatment is this clinical intervention This treatment is allogeneic haematopoietic stem cell transplantation, annotated with Hematopoietic Cell Transplantation (NCIT:C15431). NCIT:C15431 is a clinical intervention from the NCI Thesaurus. Ontology label: Hematopoietic Cell Transplantation NCIT:C15431
Platform: Cell therapy
The only curative treatment. The osteoclast lineage is haematopoietic, so donor-derived monocyte precursors give rise to osteoclasts carrying a functional a3 subunit and bone resorption is restored. Transplantation corrects the mechanism but does not reverse damage already inflicted, so vision and hearing lost to cranial nerve compression before transplant do not recover; this is what makes early molecular diagnosis the main determinant of outcome rather than transplant technique.
Mechanism Target:
Vacuolar Proton Pump Deficiency in Osteoclasts — Replacing host osteoclast precursors with donor cells restores a3 subunit expression in the osteoclast lineage and so restores lacunar acidification.
Show evidence (1 reference)
PMID:42162874 SUPPORT Human Clinical
"The defective osteoclast differentiation or function is of hemopoietic origin, thus making Hematopoietic stem cell transplantation (HSCT) the only curative treatment option for this condition."
States the reason transplantation targets this node: the defective cell lineage is haematopoietic and therefore replaceable.
Show evidence (2 references)
PMID:40875877 SUPPORT Human Clinical
"Hematopoietic stem cell therapy (HSCT) for those with hematologic failure with imminent vision loss, severe osteopetrosis with bone marrow failure, or severe osteopetrosis in children younger than age one year, ideally prior to age ten months."
GeneReviews indication and timing for this gene. The "ideally prior to age ten months" threshold is the citable form of this entry's claim that outcome turns on how early the diagnosis is made.
PMID:42162874 SUPPORT Human Clinical
"OS and DFS for the study were 80%."
Overall and disease-free survival in a 10-patient fully HLA-matched cohort, three of whom had confirmed TCIRG1 variants. The cohort is small and single-centre, so this figure is indicative rather than a population estimate.
Recombinant Human Interferon Gamma-1b
Action: PharmacotherapyNCI Thesaurus (NCIT) Relation: this treatment is this clinical intervention This treatment is Pharmacotherapy (NCIT:C15986). NCIT:C15986 is a clinical intervention from the NCI Thesaurus. NCIT:C15986
Agent: interferon gamma-1b NCIT:C100089 NCI Thesaurus (NCIT) Relation: this treatment uses this therapeutic agent This treatment uses interferon gamma-1b (NCIT:C100089). NCIT:C100089 is a therapeutic agent from the NCI Thesaurus.
Platform: Protein replacement
Dosing: three times per week
Adjunctive, non-curative therapy used as a bridge to transplantation. It increases osteoclastic bone resorption and corrects the reduced leukocyte superoxide generation that accompanies the osteoclast defect, improving marrow space, haemoglobin and infection frequency without addressing the underlying V-ATPase lesion.
Show evidence (3 references)
PMID:40875877 SUPPORT Human Clinical
"Interferon gamma-1b (IFN-γ1b) may be considered in infantile TCIRG1-related osteopetrosis, to serve as a bridge to HSCT."
GeneReviews states the indication for this gene specifically, and states it as a bridge rather than a treatment, which is how this entry describes it.
PMID:7753137 SUPPORT Human Clinical
"After 6 months of therapy, all 14 patients had decreases in trabecular-bone area (determined by histomorphometric analysis of bone-biopsy specimens) and increases in bone marrow space (determined by marrow imaging), and the improvement was sustained in the 11 patients treated for 18 months."
The trial evidence that interferon gamma-1b measurably increases resorption and reclaims marrow space in severe osteopetrosis.
PMID:7753137 SUPPORT Human Clinical
"The mean (+SD) hemoglobin concentration increased from 7.5 +/- 2.9 to 10.5 +/- 0.3 g per deciliter (P = 0.05), and superoxide generation by granulocyte-macrophage colonies increased (P < 0.001) after 18 months of therapy."
Quantifies the haematological and leukocyte-function response, which is the basis for using it as a bridge rather than as a definitive treatment.
Calcium and Vitamin D Supplementation
Action: calcium and vitamin D supplementationNCI Thesaurus (NCIT) Relation: this treatment is this clinical intervention This treatment is calcium and vitamin D supplementation, annotated with Nutritional Support (NCIT:C15433). NCIT:C15433 is a clinical intervention from the NCI Thesaurus. Ontology label: Nutritional Support NCIT:C15433
Platform: Small molecule
Correction of the hypocalcaemia and impaired mineralization that follow from the skeleton being unavailable as a calcium reservoir. This addresses the mineral-metabolism branch, which transplantation does not treat directly.
Mechanism Target:
Failure of Skeletal Calcium Mobilization — Supplies the calcium the skeleton cannot release, rather than restoring the osteoclast function that would release it.
Target Phenotypes: Hypocalcemia HP:0002901 Human Phenotype Ontology (HP) Relation: this treatment targets this phenotype This treatment targets Hypocalcemia (HP:0002901). HP:0002901 is a phenotype from the Human Phenotype Ontology. Rickets HP:0002748 Human Phenotype Ontology (HP) Relation: this treatment targets this phenotype This treatment targets Rickets (HP:0002748). HP:0002748 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:40875877 SUPPORT Human Clinical
"calcium and vitamin D supplementation per endocrinologist;"
GeneReviews supportive-care management for this gene. The quote is one item of a semicolon-delimited management list, which is how that chapter states each recommendation.
Optic Nerve Decompression
Action: optic nerve decompression and sheath fenestrationNCI Thesaurus (NCIT) Relation: this treatment is this clinical intervention This treatment is optic nerve decompression and sheath fenestration, annotated with Surgical Procedure (NCIT:C15329). NCIT:C15329 is a clinical intervention from the NCI Thesaurus. Ontology label: Surgical Procedure NCIT:C15329
Platform: Surgery
Surgical decompression or sheath fenestration where progressive narrowing of the optic canal threatens vision. It relieves the compression mechanically and does not stop the sclerosis producing it, so it is a holding measure.
Mechanism Target:
Cranial Nerve Compression from Skull Thickening — Relieves compression at the optic canal without altering the bone accumulation that caused it.
Target Phenotypes: Optic atrophy HP:0000648 Human Phenotype Ontology (HP) Relation: this treatment targets this phenotype This treatment targets Optic atrophy (HP:0000648). HP:0000648 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:40875877 SUPPORT Human Clinical
"optic nerve decompression and optic nerve sheath fenestration per neuro-ophthalmologist;"
GeneReviews supportive-care management for the ocular complication this entry already models as a pathophysiology node.
Genetic Counseling
Action: Genetic CounselingNCI Thesaurus (NCIT) Relation: this treatment is this clinical intervention This treatment is Genetic Counseling (NCIT:C15240). NCIT:C15240 is a clinical intervention from the NCI Thesaurus. NCIT:C15240
Platform: Behavioral / lifestyle
Genetic counseling for affected families given autosomal recessive inheritance. Carrier testing and prenatal diagnosis available.
Show evidence (1 reference)
PMID:11532986 SUPPORT Human Clinical
"The identification of ATP6i gene mutations in two families allowed us for the first time to perform prenatal diagnosis: both fetuses were predicted not to be affected and two healthy babies were born."
Documents that identifying the familial TCIRG1 variants makes prenatal diagnosis possible, which is the concrete output of counselling here.
🔬

Diagnosis

3
Molecular confirmation of biallelic TCIRG1 variants
The diagnosis is established by characteristic clinical, laboratory and imaging findings together with biallelic pathogenic TCIRG1 variants. Because rare heterozygous TCIRG1 variants have been reported in affected individuals, a single identified variant does not by itself exclude the diagnosis.
molecular genetic testing NCIT:C15709 NCI Thesaurus (NCIT)
Show evidence (2 references)
PMID:40875877 SUPPORT Human Clinical
"The diagnosis of TCIRG1-related osteopetrosis is established in a proband with characteristic clinical, laboratory, and imaging findings and biallelic pathogenic variants in TCIRG1 identified by molecular genetic testing."
The confirmatory test, from the GeneReviews chapter for this gene.
PMID:40875877 SUPPORT Human Clinical
"Note: Heterozygous TCIRG1 pathogenic variants have been rarely reported in individuals with TCIRG1-related osteopetrosis."
The caveat that makes a single-variant result non-exclusionary, stated in the same chapter's diagnosis section.
Skeletal survey
Radiographic diagnosis rests on generalized osteosclerosis with the characteristic bone-in-bone appearance and Erlenmeyer flask metaphyseal flaring, which develop toward the end of early childhood. Metaphyseal osteopetrorickets is present earlier and is easy to miss against the diffuse increase in density.
skeletal survey radiography NCIT:C38092 NCI Thesaurus (NCIT)
Show evidence (1 reference)
PMID:42661684 SUPPORT Human Clinical
"Osteopetrorickets is clinically important because it may be overlooked in the presence of diffusely increased bone density, although impaired mineralization may coexist with osteosclerosis."
States the radiographic trap this diagnostic step has to avoid, which is why the mineralization defect is looked for separately from the sclerosis.
Osteoclast-rich marrow histology
Bone marrow biopsy in this form shows osteoclasts present in normal or increased numbers, and non-functional. That is the bedside correlate of the entry's central mechanistic claim, and it is what separates TCIRG1 osteopetrosis from the osteoclast-poor RANK/RANKL forms, which the radiographic appearance alone does not.
bone marrow biopsy NCIT:C15193 NCI Thesaurus (NCIT)
Show evidence (2 references)
PMID:35981697 SUPPORT Human Clinical
"TCIRG1 defects lead to inefficient bone resorption by nonfunctional osteoclasts seen in abundance on bone marrow biopsy, delineating this ARO as 'osteoclast-rich'"
Names the biopsy finding and the classification it supports, which is the diagnostic value of the test here.
PMID:10888887 SUPPORT Human Clinical
"Osteoclasts are present in normal or elevated numbers in individuals affected by autosomal recessive osteopetrosis, suggesting that the defect is not in osteoclast differentiation, but in a gene involved in the functional capacity of mature osteoclasts"
The original observation that osteoclast number is preserved, which is what makes the count diagnostically informative rather than merely descriptive.
📊

Prevalence

1
Global live births
Birth Prevalence 0.4 per 100,000 1–9 per 1,000,000 (births)
Autosomal recessive osteopetrosis is estimated to occur in about 1 in 250,000 births overall. Because biallelic TCIRG1 variants account for more than half of autosomal recessive osteopetrosis cases, autosomal recessive osteopetrosis 1 is the most common molecular subtype within this incidence estimate. The rate recorded here is the all-genotype figure, not a TCIRG1-specific one; no separate incidence estimate for the TCIRG1 form has been published.
Show evidence (2 references)
PMID:19232111 SUPPORT Human Clinical
"autosomal recessive osteopetrosis (ARO) has an incidence of 1 in 250,000 births"
This review gives the standard incidence estimate for autosomal recessive osteopetrosis.
PMID:22231430 SUPPORT Human Clinical
"Biallelic mutations in the TCIRG1 gene, encoding for the a3 subunit of this pump, are responsible for more than one half of ARO patients."
This study shows that TCIRG1-related disease represents the majority of autosomal recessive osteopetrosis cases, which is what lets the all-genotype incidence be carried over to this gene-specific entry as an upper bound.
🔬

Clinical Trials

1
NCT04525352 PHASE_I TERMINATED
Autologous CD34+ cells transduced with a lentiviral vector encoding TCIRG1, the clinical translation of the oc/oc mouse gene-therapy work this entry already records. It opened in 2020 and was discontinued after the first treated patient died of causes unrelated to the gene therapy. It is recorded here because the entry describes gene therapy as an emerging alternative for patients without a donor, and the state of that alternative is a halted phase I rather than an open one.
Show evidence (2 references)
clinicaltrials:NCT04525352 SUPPORT Human Clinical
"The primary objective of this Phase 1 study is to evaluate the therapeutic safety and feasibility of the investigational product (IP), RP-L401."
The registered objective and phase of the trial.
PMID:39314524 SUPPORT Other
"a phase I clinical trial (NCT04525352) opened in 2020, but was then discontinued after the early death of the first treated patient for gene therapy unrelated causes"
Records the discontinuation and its stated cause. Graded OTHER because evidence_source classifies the cited publication, and this one is an oc/oc mouse gene-therapy study; the quoted sentence is background about a trial run by others, so it is neither that paper's model-organism result nor human data it generated.
🐁

Animal Models

2
Atp6i (Tcirg1) knockout mouse
Targeted disruption of the murine Tcirg1 orthologue Atp6i. This is the model that localised the human lesion to extracellular acidification specifically: the knockout osteoclasts fail to acidify the resorption compartment while lysosomal proton pumping, renal microsomal proton transport, and systemic acid-base balance are all normal.
Species
Mouse
Genotype
Atp6i (Tcirg1) targeted null, homozygous
Publication
PMID:10581033
Pathograph links
Vacuolar Proton Pump Deficiency in Osteoclasts recapitulates fidelity: high observes: cellular Loss of the same subunit in the same cell type, with the same compartment-restricted acidification defect.
Limitations: The compartment specificity was shown in cultured osteoclast-like cells derived from the knockout rather than in situ at a resorption lacuna.
Readouts
Extracellular acidification by osteoclast-like cells
Direction: ABOLISHED
Interpretation: Direct measurement of the function this node claims is lost.
Show evidence (1 reference)
PMID:10581033 SUPPORT Model Organism
"Atp6i-/- osteoclast-like cells (OCLs) lose the function of extracellular acidification, but retain intracellular lysosomal proton pump activity"
Reports the abolished extracellular acidification alongside the preserved lysosomal activity.
Lysosomal pH in liver
Direction: UNCHANGED
Interpretation: A negative result that bounds the node: the lesion does not extend to lysosomal acidification, so this is not a generalised V-ATPase failure.
Show evidence (1 reference)
PMID:10581033 SUPPORT Model Organism
"The pH in Atp6i-/- liver lysosomes and proton transport in microsomes of Atp6i-/- kidney are identical to that in wild-type mice."
Records the measurement showing lysosomal and renal proton handling are unaffected.
Show evidence (1 reference)
PMID:10581033 SUPPORT Model Organism
"targeted disruption of Atp6i in mice results in severe osteopetrosis"
Establishes that removing this subunit is sufficient to produce the disease phenotype, which is what makes the model informative for this node.
oc/oc mouse
Spontaneous Tcirg1-deficient mutant carrying a 5-prime deletion that abolishes transcription of the proton-pump subunit. Lifespan is under three weeks. It is the model used for the lentiviral gene-therapy work that motivated the discontinued phase I trial NCT04525352.
Species
Mouse
Genotype
oc/oc, spontaneous 1.6 kb deletion at the 5-prime end of Tcirg1
Publication
PMID:39314524
Pathograph links
Progressive Skeletal Sclerosis recapitulates fidelity: moderate observes: organism Generalised increase in skeletal density with marrow-cavity fibrosis and extramedullary haematopoiesis, matching the human skeletal and haematologic branches.
Limitations: Murine lifespan is under three weeks, so the model cannot express the progressive cranial nerve compression that dominates human morbidity, and skull foramen anatomy differs. Judgements about long-term neurological outcome do not transfer from it.
Show evidence (1 reference)
PMID:39314524 SUPPORT Model Organism
"The Tcirg1-defective oc/oc mouse model displays a short lifespan and high bone density, closely mirroring the human condition."
The authors' own statement of what the model reproduces, and of its short lifespan.
Bone Marrow Failure from Medullary Obliteration recapitulates fidelity: moderate observes: organism Marrow-cavity fibrosis with extramedullary haematopoiesis, reversible by gene therapy in the model.
Limitations: Correction was measured over a murine lifespan; durability over the decades relevant to a transplanted child is not addressed.
Show evidence (1 reference)
PMID:39314524 SUPPORT Model Organism
"lentiviral vector GT can revert the osteopetrotic bone phenotype, allowing long-term survival and reducing extramedullary haematopoiesis"
Shows the marrow phenotype is present in the model and is reversed by restoring the missing subunit, which supports the causal direction of this node.
{ }

Source YAML

click to show 
name: Autosomal Recessive Osteopetrosis 1
creation_date: '2026-02-13T00:31:42Z'
category: Mendelian
description: >
  Autosomal recessive osteopetrosis 1 (ARO1, OPTB1, malignant infantile
  osteopetrosis) is a severe sclerosing bone disease caused by biallelic
  loss-of-function variants in TCIRG1, encoding the osteoclast-specific a3
  subunit of the vacuolar H+-ATPase. TCIRG1 variants are the most frequent
  cause of infantile malignant osteopetrosis, accounting for roughly half of
  autosomal recessive osteopetrosis cases. Osteoclasts differentiate normally
  and are present in normal or elevated numbers, but cannot acidify the
  resorption lacuna, so bone mineral is never dissolved; this is what makes
  ARO1 an osteoclast-rich osteopetrosis, in contrast to the osteoclast-poor
  forms caused by defects in the RANK/RANKL differentiation axis. The defect
  is specific to extracellular acidification: lysosomal proton pumping and
  systemic acid-base balance are preserved, which separates ARO1 from carbonic
  anhydrase II deficiency. Failure of resorption produces dense but brittle
  bones, obliteration of the medullary cavity with marrow failure and
  compensatory extramedullary haematopoiesis, cranial nerve compression at
  unwidened skull foramina, and hypocalcaemia with secondary
  hyperparathyroidism and superimposed rickets. Without haematopoietic stem
  cell transplantation the disease is usually fatal within the first decade.
disease_term:
  preferred_term: autosomal recessive osteopetrosis 1
  term:
    id: MONDO:0009815
    label: autosomal recessive osteopetrosis 1
parents:
- Sclerosing Bone Dysplasias
inheritance:
- name: Autosomal Recessive
  inheritance_term:
    preferred_term: Autosomal recessive inheritance
    term:
      id: HP:0000007
      label: Autosomal recessive inheritance
  description: >
    Autosomal recessive inheritance. Biallelic (homozygous or compound
    heterozygous) TCIRG1 variants.

    Typically, but not exclusively. GeneReviews records rare exceptions: one
    family with heterozygous variants and autosomal dominant osteopetrosis, and
    one individual with a heterozygous de novo variant. Those are quoted in the
    evidence below rather than smoothed away, because this entry is bound to
    MONDO:0009815 on the basis of gene identity and the exceptions bear on how
    firmly that identity is drawn.
  evidence:
  - reference: PMID:10888887
    reference_title: "Defects in TCIRG1 subunit of the vacuolar proton pump are responsible for a subset of human autosomal recessive osteopetrosis."
    supports: SUPPORT
    snippet: "TCIRG1, encoding the osteoclast-specific 116-kD subunit of the vacuolar proton pump, is mutated in five of nine patients with a diagnosis of infantile malignant osteopetrosis"
    explanation: "TCIRG1 mutations identified as a frequent cause of autosomal recessive osteopetrosis."
  - reference: PMID:40875877
    reference_title: "TCIRG1-Related Osteopetrosis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "each sib of an affected individual has at conception a 25% chance of having TCIRG1-related osteopetrosis, a 50% chance of being heterozygous, and a 25% chance of inheriting neither of the familial TCIRG1 pathogenic variants."
    explanation: >-
      The recurrence risk that follows from recessive inheritance, from the
      GeneReviews chapter for this gene.
  - reference: PMID:40875877
    reference_title: "TCIRG1-Related Osteopetrosis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Heterozygous TCIRG1 pathogenic variants have been identified in affected individuals in one family with autosomal dominant osteopetrosis and one additional individual with a heterozygous de novo pathogenic variant."
    explanation: >-
      The caveat to the recessive model, recorded because this entry turns on gene
      and inheritance identity. It does not overturn autosomal recessive as the
      typical mode, but a strictly biallelic reading would be wrong.
classifications:
  isds_skeletal_category:
  - classification_value: osteopetrosis_and_related
    notes: >-
      ISDS Nosology and Classification of Genetic Skeletal Disorders, 2019
      revision (Mortier et al., PMID:31633310), Table 1 group 23 "Osteopetrosis
      and related disorders". The previous wording of this note named the
      TNFSF11 locus, which belongs to autosomal recessive osteopetrosis 2 and
      was carried over from this entry's earlier, incorrect MONDO binding.
  iuis_category:
    classification_value: innate immunity defect
    notes: >-
      IUIS 2022 update (Tangye et al., PMID:35748970), Table 6 (Defects in
      intrinsic and innate immunity), section 8 "Other Inborn Errors of
      Immunity Related to Non-Hematopoietic Tissues".
      All seven osteopetrosis genes in this table (CLCN7, SNX10, OSTM1,
      PLEKHM1, TCIRG1, TNFRSF11A, TNFSF11) are autosomal recessive; this entry
      is the TCIRG1 etiology, which is autosomal recessive osteopetrosis 1.
    evidence:
    - reference: PMID:35748970
      reference_title: "Human Inborn Errors of Immunity: 2022 Update on the Classification from the International Union of Immunological Societies Expert Committee."
      supports: SUPPORT
      evidence_source: OTHER
      snippet: "TCIRG1 AR 604592\nSecretory lysosomes\nOsteopetrosis with hypocalcemia"
      explanation: >-
        IUIS Table 6 lists TCIRG1 as an autosomal recessive gene under the
        intrinsic/innate-immunity, non-hematopoietic-tissue defects category,
        matching this entry's TCIRG1 etiology.
prevalence:
- population: Global live births
  measure_type: BIRTH_PREVALENCE
  prevalence_class: BAND_1_9_PER_1000000
  rate_per_100000: 0.4
  percentage: 1 in 250,000
  notes: >-
    Autosomal recessive osteopetrosis is estimated to occur in about 1 in
    250,000 births overall. Because biallelic TCIRG1 variants account for more
    than half of autosomal recessive osteopetrosis cases, autosomal recessive
    osteopetrosis 1 is the most common molecular subtype within this incidence
    estimate. The rate recorded here is the all-genotype figure, not a
    TCIRG1-specific one; no separate incidence estimate for the TCIRG1 form has
    been published.
  evidence:
  - reference: PMID:19232111
    reference_title: "Osteopetrosis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "autosomal recessive osteopetrosis (ARO) has an incidence of 1 in 250,000 births"
    explanation: >-
      This review gives the standard incidence estimate for autosomal recessive
      osteopetrosis.
  - reference: PMID:22231430
    reference_title: "Autosomal recessive osteopetrosis: report of 41 novel mutations in the TCIRG1 gene and diagnostic implications."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Biallelic mutations in the TCIRG1 gene, encoding for the a3 subunit of this pump, are responsible for more than one half of ARO patients."
    explanation: >-
      This study shows that TCIRG1-related disease represents the majority of
      autosomal recessive osteopetrosis cases, which is what lets the
      all-genotype incidence be carried over to this gene-specific entry as an
      upper bound.
pathophysiology:
- name: Vacuolar Proton Pump Deficiency in Osteoclasts
  biological_scale: CELLULAR
  description: >
    TCIRG1 encodes the a3 subunit of the vacuolar H+-ATPase (V-ATPase),
    which is specifically expressed in osteoclasts and essential for proton
    secretion into the resorption lacuna. Loss-of-function mutations abolish
    osteoclast acidification capacity, preventing dissolution of hydroxyapatite
    mineral in bone matrix. Osteoclasts differentiate normally and are present
    in normal or elevated numbers but cannot resorb bone.
  biological_processes:
  - preferred_term: Bone Resorption
    term:
      id: GO:0045453
      label: bone resorption
  cell_types:
  - preferred_term: Osteoclast
    term:
      id: CL:0000092
      label: osteoclast
  evidence:
  - reference: PMID:10888887
    reference_title: "Defects in TCIRG1 subunit of the vacuolar proton pump are responsible for a subset of human autosomal recessive osteopetrosis."
    supports: SUPPORT
    snippet: "TCIRG1, encoding the osteoclast-specific 116-kD subunit of the vacuolar proton pump, is mutated in five of nine patients"
    explanation: "Identifies TCIRG1 and the vacuolar proton pump as the pathogenic target."
  - reference: PMID:10888887
    reference_title: "Defects in TCIRG1 subunit of the vacuolar proton pump are responsible for a subset of human autosomal recessive osteopetrosis."
    supports: SUPPORT
    snippet: "Osteoclasts are present in normal or elevated numbers in individuals affected by autosomal recessive osteopetrosis, suggesting that the defect is not in osteoclast differentiation, but in a gene involved in the functional capacity of mature osteoclasts"
    explanation: "Establishes that osteoclasts differentiate normally but are non-functional."
  - reference: PMID:10581033
    reference_title: "Atp6i-deficient mice exhibit severe osteopetrosis due to loss of osteoclast-mediated extracellular acidification."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "Atp6i-/- osteoclast-like cells (OCLs) lose the function of extracellular acidification, but retain intracellular lysosomal proton pump activity"
    explanation: >-
      Establishes that the lesion is confined to extracellular acidification at the
      osteoclast-bone interface and spares lysosomal proton pumping, which is why
      the phenotype is skeletal rather than a generalised lysosomal disorder.
  - reference: PMID:35981697
    reference_title: "Osteoclast rich osteopetrosis due to defects in the TCIRG1 gene."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "TCIRG1 defects lead to inefficient bone resorption by nonfunctional osteoclasts seen in abundance on bone marrow biopsy, delineating this ARO as 'osteoclast-rich'"
    explanation: >-
      Links the molecular lesion to the osteoclast-rich marrow histology that
      distinguishes this form from the osteoclast-poor RANK/RANKL forms.
  downstream:
  - target: Progressive Skeletal Sclerosis
    description: >-
      Loss of osteoclast proton-pump function prevents normal bone resorption
      and drives skeletal sclerosis.
  - target: Failure of Skeletal Calcium Mobilization
    causal_link_type: DIRECT
    description: >-
      The same failure to dissolve bone mineral means skeletal calcium cannot be
      released into the circulation.
- name: Progressive Skeletal Sclerosis
  biological_scale: TISSUE
  description: >
    Failure of osteoclast-mediated bone resorption leads to progressive
    accumulation of unremodeled bone, obliterating the medullary cavity
    and narrowing cranial nerve foramina.
  biological_processes:
  - preferred_term: Bone Remodeling
    term:
      id: GO:0046849
      label: bone remodeling
  evidence:
  - reference: PMID:10888887
    reference_title: "Defects in TCIRG1 subunit of the vacuolar proton pump are responsible for a subset of human autosomal recessive osteopetrosis."
    supports: SUPPORT
    snippet: "mutations in TCIRG1 are a frequent cause of autosomal recessive osteopetrosis in humans"
    explanation: "TCIRG1 deficiency causes progressive skeletal sclerosis from failed bone resorption."
  downstream:
  - target: Short stature
    causal_link_type: DIRECT
    description: >-
      Growth failure from the disordered bone modelling this node describes.
  - target: Delayed eruption of teeth
    causal_link_type: DIRECT
    description: >-
      Teeth cannot erupt through sclerotic, unresorbed bone; eruption depends on the osteoclast-mediated resorption this disease abolishes.
  - target: Carious teeth
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: >-
      Dental caries, reported alongside the eruption failure. Drawn here rather than given its own mechanism because the source groups the dental findings together, and the route from abnormal eruption and enamel defects to caries is not separately established.
  - target: Hypertelorism
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: >-
      Craniofacial consequence of the skull deformity produced by unresorbed bone.
  - target: Micrognathia
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: >-
      The mandibular expression of the same disordered craniofacial modelling.
  - target: Proptosis
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    description: >-
      Forward displacement of the globe as the orbit is encroached on by thickened bone — the orbital counterpart of the foraminal narrowing that compresses the cranial nerves.
  - target: Bone Marrow Failure from Medullary Obliteration
    description: >-
      Progressive accumulation of unresorbed bone obliterates marrow space.
  - target: Cranial Nerve Compression from Skull Thickening
    description: >-
      Progressive skull sclerosis narrows cranial nerve foramina.
  - target: Increased bone mineral density
    causal_link_type: DIRECT
  - target: Osteopetrosis
    causal_link_type: DIRECT
  - target: Recurrent fractures
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
  - target: Bone pain
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
  - target: Craniosynostosis
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
- name: Bone Marrow Failure from Medullary Obliteration
  biological_scale: ORGANISM
  description: >
    Progressive accumulation of unremodeled bone obliterates the medullary
    cavity, causing loss of hematopoietic marrow space with resultant
    pancytopenia. Compensatory extramedullary hematopoiesis in liver and
    spleen causes hepatosplenomegaly.
  biological_processes:
  - preferred_term: Hematopoiesis
    term:
      id: GO:0030097
      label: hemopoiesis
  evidence:
  - reference: PMID:10888887
    reference_title: "Defects in TCIRG1 subunit of the vacuolar proton pump are responsible for a subset of human autosomal recessive osteopetrosis."
    supports: SUPPORT
    snippet: "Infantile malignant autosomal recessive osteopetrosis (MIM 259700) is a severe bone disease with a fatal outcome, generally within the first decade of life"
    explanation: "The fatal outcome is primarily due to bone marrow failure from medullary obliteration."
  downstream:
  - target: Extramedullary hematopoiesis
    causal_link_type: DIRECT
    description: >-
      Haematopoiesis relocating to liver and spleen as the medullary cavity is obliterated — the direct compensatory consequence of losing marrow space.
  - target: Anemia
    causal_link_type: DIRECT
  - target: Thrombocytopenia
    causal_link_type: DIRECT
  - target: Recurrent infections
    causal_link_type: DIRECT
  - target: Recurrent respiratory infections
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
  - target: Hepatosplenomegaly
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
  - target: Pallor
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
  - target: Failure to thrive
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
  - target: Growth delay
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
- name: Cranial Nerve Compression from Skull Thickening
  biological_scale: TISSUE
  description: >
    Progressive skull thickening narrows cranial nerve foramina, causing
    optic nerve compression (blindness), facial nerve palsy, and
    sensorineural hearing loss.
  locations:
  - preferred_term: Cranium
    term:
      id: UBERON:0003128
      label: cranium
  downstream:
  - target: Optic atrophy
    causal_link_type: DIRECT
    description: >-
      Compression of the optic nerve in a narrowed optic canal, the most consequential of the cranial neuropathies here and the one that drives the urgency of transplantation.
  - target: Nystagmus
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    description: >-
      Ocular instability following visual loss from the optic neuropathy above.
  - target: Optic nerve compression
    causal_link_type: DIRECT
  - target: Visual impairment
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
  - target: Hearing impairment
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
  - target: Hydrocephalus
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
  - target: Macrocephaly
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
  - target: Neurodevelopmental delay
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
  - target: Seizure
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
- name: Failure of Skeletal Calcium Mobilization
  biological_scale: ORGANISM
  notes: >-
    This node reaches the same endpoint as
    defective_skeletal_mineralization#Impaired Hydroxyapatite Deposition at the
    Mineralization Front, but conforms_to is deliberately not declared. That
    module enumerates three routes to the endpoint, and its calciopenic node is
    scoped to reduced intestinal calcium absorption from insufficient calcitriol
    signalling or dietary calcium. Neither applies here: absorption and vitamin D
    signalling are intact, and the deficit is that the skeleton itself is
    unavailable as a calcium reservoir because osteoclasts cannot dissolve
    mineral. That is a fourth route the module does not cover, so declaring
    conformance would assert a mechanism this disease does not have. Worth raising
    with the module rather than papering over here.
  description: >
    Because osteoclasts cannot dissolve hydroxyapatite, the skeleton is
    unavailable as a calcium reservoir. Serum calcium falls, parathyroid hormone
    rises in compensation, and mineralization of newly laid osteoid fails.
    The result is rickets superimposed on a densely sclerotic skeleton, a
    combination easy to miss radiographically because the diffuse increase in
    bone density masks the impaired mineralization.

  evidence:
  - reference: PMID:42661684
    reference_title: "Osteopetrorickets and calcium homeostasis in children with osteopetrosis: an endocrinological single-center study."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "secondary hyperparathyroidism from hypocalcemia, resulting in a paradoxical condition known as \u201costeopetrosis-rickets\u201d"
    explanation: >-
      States the causal sequence this node models: hypocalcaemia drives secondary
      hyperparathyroidism and the paradoxical coexistence of rickets with sclerosis.
  - reference: PMID:42661684
    reference_title: "Osteopetrorickets and calcium homeostasis in children with osteopetrosis: an endocrinological single-center study."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Osteopetrorickets is clinically important because it may be overlooked in the presence of diffusely increased bone density, although impaired mineralization may coexist with osteosclerosis."
    explanation: >-
      Supports the statement that the sclerosis masks the mineralization defect,
      which is the diagnostic consequence of this node.
  downstream:
  - target: Hypocalcemia
    causal_link_type: DIRECT
  - target: Secondary hyperparathyroidism
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
  - target: Rickets
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
  - target: Seizure
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
phenotypes:
- name: Increased bone mineral density
  description: >
    Generalized osteosclerosis with narrowing or obliteration of marrow
    cavities is the defining skeletal manifestation of TCIRG1-related
    autosomal recessive osteopetrosis.
  phenotype_term:
    preferred_term: Increased bone mineral density
    term:
      id: HP:0011001
      label: Increased bone mineral density
  evidence:
  - reference: PMID:34545712
    reference_title: "Clinical and molecular characterization of five Chinese patients with autosomal recessive osteopetrosis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Osteopetrosis is characterized by increased bone density and bone marrow cavity stenosis"
    explanation: "An autosomal recessive osteopetrosis cohort that included 3 TCIRG1 cases identified increased bone density with marrow cavity stenosis as a core manifestation."
  - reference: PMID:40462430
    reference_title: "[Clinical and genetic characteristics of osteopetrosis in children]."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Clinical manifestations included systemic osteosclerosis (14 cases, 100%)"
    explanation: "A pediatric osteopetrosis cohort found systemic osteosclerosis in all affected children; all TCIRG1 cases had malignant phenotypes."
- name: Anemia
  description: >
    Progressive medullary cavity compromise causes clinically important
    anemia early in the malignant infantile phenotype.
  phenotype_term:
    preferred_term: Anemia
    term:
      id: HP:0001903
      label: Anemia
  evidence:
  - reference: PMID:34545712
    reference_title: "Clinical and molecular characterization of five Chinese patients with autosomal recessive osteopetrosis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "five Chinese children who presented with anemia, thrombocytopenia, hepatosplenomegaly, repeated infections, and increased bone density"
    explanation: "The autosomal recessive osteopetrosis cohort, including 3 TCIRG1 cases, explicitly presented with anemia."
  - reference: PMID:40462430
    reference_title: "[Clinical and genetic characteristics of osteopetrosis in children]."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Clinical manifestations included systemic osteosclerosis (14 cases, 100%), anemia (12 cases, 86%)"
    explanation: "A pediatric osteopetrosis cohort found anemia in most affected children; all TCIRG1 cases had malignant phenotypes."
- name: Thrombocytopenia
  description: >
    Bone marrow failure commonly includes thrombocytopenia, contributing
    to bleeding risk in severe infantile disease.
  phenotype_term:
    preferred_term: Thrombocytopenia
    term:
      id: HP:0001873
      label: Thrombocytopenia
  evidence:
  - reference: PMID:34545712
    reference_title: "Clinical and molecular characterization of five Chinese patients with autosomal recessive osteopetrosis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "five Chinese children who presented with anemia, thrombocytopenia, hepatosplenomegaly, repeated infections, and increased bone density"
    explanation: "The autosomal recessive osteopetrosis cohort, including 3 TCIRG1 cases, explicitly presented with thrombocytopenia."
  - reference: PMID:40462430
    reference_title: "[Clinical and genetic characteristics of osteopetrosis in children]."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Clinical manifestations included systemic osteosclerosis (14 cases, 100%), anemia (12 cases, 86%), infections (10 cases, 71%), thrombocytopenia (9 cases, 64%)"
    explanation: "A pediatric osteopetrosis cohort found thrombocytopenia in most children with malignant disease enrichment among TCIRG1 cases."
- name: Hepatosplenomegaly
  description: >
    Hepatosplenomegaly reflects compensatory extramedullary hematopoiesis
    in response to marrow failure.
  phenotype_term:
    preferred_term: Hepatosplenomegaly
    term:
      id: HP:0001433
      label: Hepatosplenomegaly
  evidence:
  - reference: PMID:34545712
    reference_title: "Clinical and molecular characterization of five Chinese patients with autosomal recessive osteopetrosis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "five Chinese children who presented with anemia, thrombocytopenia, hepatosplenomegaly, repeated infections, and increased bone density"
    explanation: "Hepatosplenomegaly was part of the presenting phenotype in an autosomal recessive osteopetrosis cohort that included 3 TCIRG1 cases."
  - reference: PMID:18946580
    reference_title: "Rare gross deletion in T-cell immune regulator-1 gene in Iranian family with infantile malignant osteopetrosis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The patient was a 5-year-old girl with macrocephaly, facial dysmorphism, blindness, mental retardation, hepatosplenomegaly, pancytopenia, and osteosclerotic changes in the skull and limb."
    explanation: "A TCIRG1-associated infantile malignant osteopetrosis case directly documented hepatosplenomegaly."
- name: Recurrent infections
  description: >
    Recurrent infections are common in severe disease and likely reflect
    marrow failure with impaired hematopoiesis.
  phenotype_term:
    preferred_term: Recurrent infections
    term:
      id: HP:0002719
      label: Recurrent infections
  evidence:
  - reference: PMID:34545712
    reference_title: "Clinical and molecular characterization of five Chinese patients with autosomal recessive osteopetrosis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "five Chinese children who presented with anemia, thrombocytopenia, hepatosplenomegaly, repeated infections, and increased bone density"
    explanation: "Repeated infections were part of the presenting phenotype in an autosomal recessive osteopetrosis cohort that included 3 TCIRG1 cases."
  - reference: PMID:30898950
    reference_title: "Osteomyelitis of the mandible secondary to malignant infantile osteopetrosis in an adult."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "In addition, growth retardation and recurrent infections requiring long-term antibiotic use are common."
    explanation: "A TCIRG1-related malignant infantile osteopetrosis report highlights recurrent infections as a common clinical problem."
- name: Visual impairment
  description: >
    Skull-base overgrowth and narrowing of osseous foramina can compress
    the optic apparatus, causing visual impairment that may progress to
    blindness.
  phenotype_term:
    preferred_term: Visual impairment
    term:
      id: HP:0000505
      label: Visual impairment
  evidence:
  - reference: PMID:30898950
    reference_title: "Osteomyelitis of the mandible secondary to malignant infantile osteopetrosis in an adult."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Neurological manifestations can also occur due to narrowing of osseous foramina resulting in visual impairment, hearing loss, facial palsy and hydrocephalus."
    explanation: "Malignant infantile osteopetrosis causes visual impairment through cranial foraminal narrowing."
  - reference: PMID:18946580
    reference_title: "Rare gross deletion in T-cell immune regulator-1 gene in Iranian family with infantile malignant osteopetrosis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The patient was a 5-year-old girl with macrocephaly, facial dysmorphism, blindness, mental retardation, hepatosplenomegaly, pancytopenia, and osteosclerotic changes in the skull and limb."
    explanation: "A TCIRG1-associated case shows that visual involvement may be severe enough to cause blindness."
- name: Hearing impairment
  description: >
    Bony narrowing of cranial foramina and temporal bone involvement can
    cause clinically significant hearing loss.
  phenotype_term:
    preferred_term: Hearing impairment
    term:
      id: HP:0000365
      label: Hearing impairment
  evidence:
  - reference: PMID:30898950
    reference_title: "Osteomyelitis of the mandible secondary to malignant infantile osteopetrosis in an adult."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Neurological manifestations can also occur due to narrowing of osseous foramina resulting in visual impairment, hearing loss, facial palsy and hydrocephalus."
    explanation: "The malignant infantile phenotype includes hearing loss from cranial foraminal narrowing."
- name: Hydrocephalus
  description: >
    Hydrocephalus is a recognized cranial complication of severe
    autosomal recessive osteopetrosis and may be an early presenting
    feature.
  phenotype_term:
    preferred_term: Hydrocephalus
    term:
      id: HP:0000238
      label: Hydrocephalus
  evidence:
  - reference: PMID:34519872
    reference_title: "Neonatal hydrocephalus: an atypical presentation of malignant infantile osteopetrosis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Autosomal recessive osteopetrosis has a variable presentation, most commonly including failure to thrive, hypocalcemia, seizures, hepatosplenomegaly, hydrocephalus, vision or hearing loss, and cytopenias."
    explanation: "A clinical report on malignant infantile osteopetrosis identifies hydrocephalus among the common presenting manifestations."
  - reference: PMID:30898950
    reference_title: "Osteomyelitis of the mandible secondary to malignant infantile osteopetrosis in an adult."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Neurological manifestations can also occur due to narrowing of osseous foramina resulting in visual impairment, hearing loss, facial palsy and hydrocephalus."
    explanation: "Independent clinical evidence links malignant infantile osteopetrosis to hydrocephalus from cranial narrowing."
- name: Macrocephaly
  description: >
    Progressive cranial overgrowth can produce macrocephaly, often with
    frontal bossing in infants.
  phenotype_term:
    preferred_term: Macrocephaly
    term:
      id: HP:0000256
      label: Macrocephaly
  evidence:
  - reference: PMID:18946580
    reference_title: "Rare gross deletion in T-cell immune regulator-1 gene in Iranian family with infantile malignant osteopetrosis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The patient was a 5-year-old girl with macrocephaly, facial dysmorphism, blindness, mental retardation, hepatosplenomegaly, pancytopenia, and osteosclerotic changes in the skull and limb."
    explanation: "A TCIRG1-associated infantile malignant osteopetrosis case directly documented macrocephaly."
  - reference: PMID:34519872
    reference_title: "Neonatal hydrocephalus: an atypical presentation of malignant infantile osteopetrosis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "At 6 months, the infant had macrocephaly and frontal bossing with a bulging fontanelle."
    explanation: "Hydrocephalus-associated infantile osteopetrosis can present with macrocephaly and frontal bossing."
- name: Failure to thrive
  description: >
    Poor growth and nutritional failure are part of the common early
    presentation of severe autosomal recessive osteopetrosis.
  phenotype_term:
    preferred_term: Failure to thrive
    term:
      id: HP:0001508
      label: Failure to thrive
  evidence:
  - reference: PMID:34519872
    reference_title: "Neonatal hydrocephalus: an atypical presentation of malignant infantile osteopetrosis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Autosomal recessive osteopetrosis has a variable presentation, most commonly including failure to thrive, hypocalcemia, seizures, hepatosplenomegaly, hydrocephalus, vision or hearing loss, and cytopenias."
    explanation: "Failure to thrive is listed among the common presenting manifestations of autosomal recessive osteopetrosis."
- name: Hypocalcemia
  description: >
    Impaired bone resorption is commonly accompanied by hypocalcemia in
    severe infantile presentations.
  phenotype_term:
    preferred_term: Hypocalcemia
    term:
      id: HP:0002901
      label: Hypocalcemia
  evidence:
  - reference: PMID:34519872
    reference_title: "Neonatal hydrocephalus: an atypical presentation of malignant infantile osteopetrosis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Autosomal recessive osteopetrosis has a variable presentation, most commonly including failure to thrive, hypocalcemia, seizures, hepatosplenomegaly, hydrocephalus, vision or hearing loss, and cytopenias."
    explanation: "Hypocalcemia is identified as a common manifestation of autosomal recessive osteopetrosis."
- name: Seizure
  description: >
    Seizures can occur in the malignant infantile phenotype, often in the
    setting of metabolic derangements such as hypocalcemia.
  phenotype_term:
    preferred_term: Seizure
    term:
      id: HP:0001250
      label: Seizure
  evidence:
  - reference: PMID:34519872
    reference_title: "Neonatal hydrocephalus: an atypical presentation of malignant infantile osteopetrosis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Autosomal recessive osteopetrosis has a variable presentation, most commonly including failure to thrive, hypocalcemia, seizures, hepatosplenomegaly, hydrocephalus, vision or hearing loss, and cytopenias."
    explanation: "Seizures are listed among the common presenting manifestations of autosomal recessive osteopetrosis."
- name: Neurodevelopmental delay
  description: >
    Severe disease may be accompanied by delayed neurodevelopment,
    particularly when early neurologic complications occur.
  phenotype_term:
    preferred_term: Neurodevelopmental delay
    term:
      id: HP:0012758
      label: Neurodevelopmental delay
  evidence:
  - reference: PMID:40462430
    reference_title: "[Clinical and genetic characteristics of osteopetrosis in children]."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Clinical manifestations included systemic osteosclerosis (14 cases, 100%), anemia (12 cases, 86%), infections (10 cases, 71%), thrombocytopenia (9 cases, 64%), hepatosplenomegaly (8 cases, 57%), and developmental delay (5 cases, 36%)."
    explanation: "A pediatric osteopetrosis cohort documented developmental delay in a substantial subset of children; all TCIRG1 cases in the cohort had malignant phenotypes."
- name: Osteopetrosis
  description: >
    Generalized skeletal densification (osteopetrosis) is the defining radiographic
    hallmark of autosomal recessive malignant osteopetrosis, visible on plain
    radiographs as uniformly dense sclerotic bone throughout the skeleton with
    obliteration of the medullary cavity.
  frequency: VERY_FREQUENT
  phenotype_term:
    preferred_term: Osteopetrosis
    term:
      id: HP:0011002
      label: Osteopetrosis
  evidence:
  - reference: ORPHA:667
    reference_title: "Autosomal recessive malignant osteopetrosis"
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "HP:0011002 | Osteopetrosis | Very frequent (99-80%)"
    explanation: >-
      Orphanet lists osteopetrosis as a very frequent feature of autosomal
      recessive malignant osteopetrosis.
  - reference: PMID:34545712
    reference_title: "Clinical and molecular characterization of five Chinese patients with autosomal recessive osteopetrosis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Osteopetrosis is characterized by increased bone density and bone marrow cavity stenosis"
    explanation: >-
      Clinical cohort of recessive osteopetrosis patients confirms increased bone
      density with marrow cavity stenosis as the defining skeletal manifestation.
- name: Recurrent fractures
  description: >
    Despite markedly increased bone density, the bone microarchitecture is
    disorganized and brittle, leading to recurrent pathologic fractures. This
    paradox of dense but fragile bone is a hallmark of malignant infantile
    osteopetrosis.
  frequency: VERY_FREQUENT
  phenotype_term:
    preferred_term: Recurrent fractures
    term:
      id: HP:0002757
      label: Recurrent fractures
  evidence:
  - reference: ORPHA:667
    reference_title: "Autosomal recessive malignant osteopetrosis"
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "HP:0002757 | Recurrent fractures | Very frequent (99-80%)"
    explanation: >-
      Orphanet lists recurrent fractures as a very frequent feature of autosomal
      recessive malignant osteopetrosis.
  - reference: PMID:30898950
    reference_title: "Osteomyelitis of the mandible secondary to malignant infantile osteopetrosis in an adult."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Malignant infantile osteopetrosis (MIOP), an autosomal-recessive disorder, is extremely rare, presenting early in life with extreme sclerosis of the skeleton and reduced activity of osteoclasts."
    explanation: >-
      Case report documents extreme skeletal sclerosis in malignant infantile
      osteopetrosis consistent with the paradoxical brittle bone fracture risk.
- name: Bone pain
  description: >
    Bone pain is a very frequent symptom in autosomal recessive malignant
    osteopetrosis, reflecting the abnormal bone microarchitecture, microfractures,
    and periosteal reactions from progressive sclerosis.
  frequency: VERY_FREQUENT
  phenotype_term:
    preferred_term: Bone pain
    term:
      id: HP:0002653
      label: Bone pain
  evidence:
  - reference: ORPHA:667
    reference_title: "Autosomal recessive malignant osteopetrosis"
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "HP:0002653 | Bone pain | Very frequent (99-80%)"
    explanation: >-
      Orphanet lists bone pain as a very frequent feature of autosomal recessive
      malignant osteopetrosis.
- name: Craniosynostosis
  description: >
    Premature fusion of cranial sutures occurs in malignant infantile
    osteopetrosis as a consequence of the pathologically dense, sclerotic skull
    bone, contributing to raised intracranial pressure and neurological complications.
  frequency: VERY_FREQUENT
  phenotype_term:
    preferred_term: Craniosynostosis
    term:
      id: HP:0001363
      label: Craniosynostosis
  evidence:
  - reference: ORPHA:667
    reference_title: "Autosomal recessive malignant osteopetrosis"
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "HP:0001363 | Craniosynostosis | Very frequent (99-80%)"
    explanation: >-
      Orphanet lists craniosynostosis as a very frequent feature of autosomal
      recessive malignant osteopetrosis.
- name: Optic nerve compression
  description: >
    Optic nerve compression from narrowed optic canals is a very frequent and
    clinically urgent complication of malignant infantile osteopetrosis. Progressive
    optic nerve compromise leads to optic atrophy and blindness if untreated.
  frequency: VERY_FREQUENT
  phenotype_term:
    preferred_term: Optic nerve compression
    term:
      id: HP:0007807
      label: Optic nerve compression
  evidence:
  - reference: ORPHA:667
    reference_title: "Autosomal recessive malignant osteopetrosis"
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "HP:0007807 | Optic nerve compression | Very frequent (99-80%)"
    explanation: >-
      Orphanet lists optic nerve compression as a very frequent feature of
      autosomal recessive malignant osteopetrosis.
  - reference: PMID:30898950
    reference_title: "Osteomyelitis of the mandible secondary to malignant infantile osteopetrosis in an adult."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Neurological manifestations can also occur due to narrowing of osseous foramina resulting in visual impairment, hearing loss, facial palsy and hydrocephalus."
    explanation: >-
      Case report of malignant infantile osteopetrosis documents visual impairment
      from osseous foraminal narrowing, consistent with optic nerve compression.
- name: Growth delay
  description: >
    Growth delay is a very frequent feature of malignant infantile osteopetrosis,
    reflecting chronic illness, metabolic derangements, and impaired endochondral
    ossification.
  frequency: VERY_FREQUENT
  phenotype_term:
    preferred_term: Growth delay
    term:
      id: HP:0001510
      label: Growth delay
  evidence:
  - reference: ORPHA:667
    reference_title: "Autosomal recessive malignant osteopetrosis"
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "HP:0001510 | Growth delay | Very frequent (99-80%)"
    explanation: >-
      Orphanet lists growth delay as a very frequent feature of autosomal
      recessive malignant osteopetrosis.
  - reference: PMID:30898950
    reference_title: "Osteomyelitis of the mandible secondary to malignant infantile osteopetrosis in an adult."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "In addition, growth retardation and recurrent infections requiring long-term antibiotic use are common."
    explanation: >-
      Case report identifies growth retardation as a common feature of malignant
      infantile osteopetrosis.
- name: Recurrent respiratory infections
  description: >
    Recurrent respiratory infections are a very frequent complication of malignant
    infantile osteopetrosis, reflecting both immune compromise from marrow failure
    and airway obstruction from skull-base abnormalities.
  frequency: VERY_FREQUENT
  phenotype_term:
    preferred_term: Recurrent respiratory infections
    term:
      id: HP:0002205
      label: Recurrent respiratory infections
  evidence:
  - reference: ORPHA:667
    reference_title: "Autosomal recessive malignant osteopetrosis"
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "HP:0002205 | Recurrent respiratory infections | Very frequent (99-80%)"
    explanation: >-
      Orphanet lists recurrent respiratory infections as a very frequent feature
      of autosomal recessive malignant osteopetrosis.
- name: Pallor
  description: >
    Pallor is a very frequent clinical finding in malignant infantile osteopetrosis
    reflecting underlying anemia from bone marrow failure and hematopoietic
    compromise.
  frequency: VERY_FREQUENT
  phenotype_term:
    preferred_term: Pallor
    term:
      id: HP:0000980
      label: Pallor
  evidence:
  - reference: ORPHA:667
    reference_title: "Autosomal recessive malignant osteopetrosis"
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "HP:0000980 | Pallor | Very frequent (99-80%)"
    explanation: >-
      Orphanet lists pallor as a very frequent feature of autosomal recessive
      malignant osteopetrosis, consistent with the severe anemia from marrow failure.
- category: Metabolic
  name: Rickets
  description: >
    Impaired mineralization of newly formed osteoid superimposed on the sclerotic
    skeleton, sometimes called osteopetrorickets. It is easy to overlook because
    the generalised increase in bone density masks it.
  phenotype_term:
    preferred_term: Rickets
    term:
      id: HP:0002748
      label: Rickets
  frequency: FREQUENT
  evidence:
  - reference: PMID:42661684
    reference_title: "Osteopetrorickets and calcium homeostasis in children with osteopetrosis: an endocrinological single-center study."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Osteopetrorickets is a frequent and clinically significant complication of pediatric osteopetrosis."
    explanation: >-
      Direct statement of frequency in a paediatric osteopetrosis cohort.
  notes: >-
    The 76% figure in the source cohort is across paediatric osteopetrosis of
    mixed genotype, not TCIRG1 only, so the frequency band here is set from the
    authors' own qualitative wording rather than from that percentage.
- category: Endocrine
  name: Secondary hyperparathyroidism
  description: >
    Compensatory rise in parathyroid hormone driven by the hypocalcaemia that
    follows loss of skeletal calcium mobilization.
  phenotype_term:
    preferred_term: Secondary hyperparathyroidism
    term:
      id: HP:0000867
      label: Secondary hyperparathyroidism
  evidence:
  - reference: PMID:42661684
    reference_title: "Osteopetrorickets and calcium homeostasis in children with osteopetrosis: an endocrinological single-center study."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "In patients with osteopetrosis, impaired calcium mobilization due to abnormal osteoclast activity can lead to secondary hyperparathyroidism from hypocalcemia"
    explanation: >-
      States the full sequence behind this phenotype: impaired calcium mobilization
      from the osteoclast defect, then hypocalcaemia, then compensatory
      hyperparathyroidism.
- category: Hematologic
  name: Extramedullary hematopoiesis
  description: >
    Haematopoiesis relocates to liver and spleen as the medullary cavity is
    obliterated, which is the immediate cause of the hepatosplenomegaly.
  phenotype_term:
    preferred_term: Extramedullary hematopoiesis
    term:
      id: HP:0001978
      label: Extramedullary hematopoiesis
  evidence:
  - reference: PMID:40875877
    reference_title: "TCIRG1-Related Osteopetrosis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Advanced bone sclerosis results in extramedullary hematopoiesis, bone marrow failure, ocular complications with potential for blindness (optic nerve compression/atrophy and primary retinopathy), dental manifestations (delay in tooth eruption and dental caries), and deafness in some individuals."
    explanation: >-
      Names extramedullary haematopoiesis directly, and attributes it to the
      advancing sclerosis, which is the causal claim this phenotype sits under.
- category: Growth
  name: Short stature
  phenotype_term:
    preferred_term: Short stature
    term:
      id: HP:0004322
      label: Short stature
  frequency: FREQUENT
  evidence:
  - reference: PMID:40875877
    reference_title: "TCIRG1-Related Osteopetrosis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "TCIRG1-related osteopetrosis is characterized by growth deficiency, pathologic fractures of dense but brittle bones, limping gait with bone pain, hypocalcemia that can result in seizures, and secondary hyperparathyroidism."
    explanation: >-
      Lists growth deficiency first among the defining features of the TCIRG1 form
      specifically.
  notes: >-
    A mixed-genotype paediatric cohort reports short stature in 13 of 17 patients
    (76.4%). That number is not used to set the frequency band here, for the same
    reason as the Rickets record: the cohort was not TCIRG1-restricted.
- category: Ophthalmologic
  name: Optic atrophy
  description: >
    The ocular consequence of optic nerve compression at unwidened foramina.
    GeneReviews also records a primary retinopathy, so not all visual loss in
    this disease is compressive.
  phenotype_term:
    preferred_term: Optic atrophy
    term:
      id: HP:0000648
      label: Optic atrophy
  evidence:
  - reference: PMID:40875877
    reference_title: "TCIRG1-Related Osteopetrosis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "ocular complications with potential for blindness (optic nerve compression/atrophy and primary retinopathy)"
    explanation: >-
      Names optic atrophy, and distinguishes the compressive route from a primary
      retinopathy that compression does not explain.
- category: Ophthalmologic
  name: Nystagmus
  phenotype_term:
    preferred_term: Nystagmus
    term:
      id: HP:0000639
      label: Nystagmus
  evidence:
  - reference: PMID:42661684
    reference_title: "Osteopetrorickets and calcium homeostasis in children with osteopetrosis: an endocrinological single-center study."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Ophthalmological findings such as optic atrophy, nystagmus, or strabismus were present in 10 patients"
    explanation: "Records nystagmus among the ophthalmological findings in a paediatric osteopetrosis cohort."
  notes: >-
    The cohort is mixed-genotype, so no frequency band is set from its 58.8%
    figure.
- category: Dental
  name: Delayed eruption of teeth
  phenotype_term:
    preferred_term: Delayed eruption of teeth
    term:
      id: HP:0000684
      label: Delayed eruption of teeth
  evidence:
  - reference: PMID:40875877
    reference_title: "TCIRG1-Related Osteopetrosis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "dental manifestations (delay in tooth eruption and dental caries)"
    explanation: "Names delayed tooth eruption as a dental manifestation of advancing sclerosis."
- category: Dental
  name: Carious teeth
  phenotype_term:
    preferred_term: Carious teeth
    term:
      id: HP:0000670
      label: Carious teeth
  evidence:
  - reference: PMID:40875877
    reference_title: "TCIRG1-Related Osteopetrosis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "dental manifestations (delay in tooth eruption and dental caries)"
    explanation: >-
      The same GeneReviews sentence names both dental manifestations; this record
      completes the pair with delayed eruption.
- category: Craniofacial
  name: Proptosis
  phenotype_term:
    preferred_term: Proptosis
    term:
      id: HP:0000520
      label: Proptosis
  evidence:
  - reference: PMID:40875877
    reference_title: "TCIRG1-Related Osteopetrosis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Craniofacial features can include macrocephaly, exophthalmos, hypertelorism, and micrognathia."
    explanation: >-
      Exophthalmos is the term GeneReviews uses; HP:0000520 Proptosis is the HPO
      term for the same finding and lists exophthalmos among its synonyms.
- category: Craniofacial
  name: Hypertelorism
  phenotype_term:
    preferred_term: Hypertelorism
    term:
      id: HP:0000316
      label: Hypertelorism
  evidence:
  - reference: PMID:40875877
    reference_title: "TCIRG1-Related Osteopetrosis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Craniofacial features can include macrocephaly, exophthalmos, hypertelorism, and micrognathia."
    explanation: "Lists hypertelorism among the craniofacial features."
- category: Craniofacial
  name: Micrognathia
  phenotype_term:
    preferred_term: Micrognathia
    term:
      id: HP:0000347
      label: Micrognathia
  evidence:
  - reference: PMID:40875877
    reference_title: "TCIRG1-Related Osteopetrosis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Craniofacial features can include macrocephaly, exophthalmos, hypertelorism, and micrognathia."
    explanation: "Lists micrognathia among the craniofacial features."
genetic:
- name: TCIRG1
  gene_term:
    preferred_term: TCIRG1
    term:
      id: hgnc:11647
      label: TCIRG1
  association: Causative
  relationship_type: CAUSATIVE
  notes: >
    Biallelic (homozygous or compound heterozygous) loss-of-function variants in
    TCIRG1 on chromosome 11q13.2, encoding the osteoclast-specific a3 subunit of
    the vacuolar H+-ATPase. The variant spectrum is dominated by nonsense,
    frameshift and splice-site alleles predicted to be null; missense alleles are
    a minority and at least one, p.Arg444Leu, is a loss of function by
    mistrafficking rather than by loss of catalytic residues. Splice-region
    substitutions are a large share of the total, which is why variants of
    uncertain significance in TCIRG1 often need a functional splicing assay
    rather than sequence-based prediction alone. Severity tracks residual a3
    function: hypomorphic splice alleles have been reported in adults with
    radiographic osteopetrosis and no neurological or haematological disease.
  evidence:
  - reference: PMID:10888887
    reference_title: "Defects in TCIRG1 subunit of the vacuolar proton pump are responsible for a subset of human autosomal recessive osteopetrosis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "TCIRG1, encoding the osteoclast-specific 116-kD subunit of the vacuolar proton pump, is mutated in five of nine patients with a diagnosis of infantile malignant osteopetrosis"
    explanation: "The original report identifying TCIRG1 as a cause of infantile malignant osteopetrosis."
  - reference: PMID:11532986
    reference_title: "The mutational spectrum of human malignant autosomal recessive osteopetrosis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "we have now established that ATP6i mutations are responsible for approximately 50% of patients affected by this disease"
    explanation: >-
      Quantifies the share of autosomal recessive osteopetrosis attributable to
      TCIRG1 across 44 unrelated families worldwide. ATP6i is a synonym of TCIRG1.
  - reference: PMID:11532986
    reference_title: "The mutational spectrum of human malignant autosomal recessive osteopetrosis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The vast majority of these mutations (40 out of 42 alleles, including seven deletions, two insertions, 10 nonsense substitutions and 21 mutations in splice sites) are predicted to cause severe abnormalities in the protein product and are likely to represent null alleles"
    explanation: "Establishes that the pathogenic variant spectrum is predominantly null alleles."
  - reference: PMID:15300850
    reference_title: "TCIRG1-dependent recessive osteopetrosis: mutation analysis, functional identification of the splicing defects, and in vitro rescue by U1 snRNA."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "As substitutions in splicing regulatory sequences represented a large portion (40%; 44 alleles) of the TCIRG1 variations, we developed a functional splicing assay to distinguish between polymorphic variants and disease-causing mutations."
    explanation: >-
      Supports the note that splice-region substitutions are a large share of the
      TCIRG1 variant spectrum and need a functional assay to classify.
  - reference: PMID:28816234
    reference_title: "Novel mutations of TCIRG1 cause a malignant and mild phenotype of autosomal recessive osteopetrosis (ARO) in four Chinese families."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The remaining one, a 24-year-old male from a consanguineous family, was diagnosed based on radiological findings but presented no neurological or hematological defects. He was homozygous for c.2236+6T>G in intron 18; this mutation influenced the splicing process."
    explanation: >-
      A hypomorphic splice allele giving survival to adulthood without neurological
      or haematological disease. This is the clearest published demonstration that
      residual a3 function, rather than the presence of biallelic TCIRG1 variants
      as such, sets the severity of this disease.
  - reference: PMID:22685294
    reference_title: "Osteopetrosis mutation R444L causes endoplasmic reticulum retention and misprocessing of vacuolar H+-ATPase a3 subunit."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "the mutant glycoprotein localized to the ER instead of lysosomes and its oligosaccharide moiety was misprocessed"
    explanation: >-
      Shows that the R444L missense allele is a loss of function by ER retention
      and mistrafficking rather than by loss of a catalytic residue.
diagnosis:
- name: Molecular confirmation of biallelic TCIRG1 variants
  description: >
    The diagnosis is established by characteristic clinical, laboratory and
    imaging findings together with biallelic pathogenic TCIRG1 variants. Because
    rare heterozygous TCIRG1 variants have been reported in affected individuals,
    a single identified variant does not by itself exclude the diagnosis.
  diagnosis_term:
    preferred_term: molecular genetic testing
    term:
      id: NCIT:C15709
      label: Genetic Testing
  evidence:
  - reference: PMID:40875877
    reference_title: "TCIRG1-Related Osteopetrosis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The diagnosis of TCIRG1-related osteopetrosis is established in a proband with characteristic clinical, laboratory, and imaging findings and biallelic pathogenic variants in TCIRG1 identified by molecular genetic testing."
    explanation: "The confirmatory test, from the GeneReviews chapter for this gene."
  - reference: PMID:40875877
    reference_title: "TCIRG1-Related Osteopetrosis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Note: Heterozygous TCIRG1 pathogenic variants have been rarely reported in individuals with TCIRG1-related osteopetrosis."
    explanation: >-
      The caveat that makes a single-variant result non-exclusionary, stated in the
      same chapter's diagnosis section.
- name: Skeletal survey
  description: >
    Radiographic diagnosis rests on generalized osteosclerosis with the
    characteristic bone-in-bone appearance and Erlenmeyer flask metaphyseal
    flaring, which develop toward the end of early childhood. Metaphyseal
    osteopetrorickets is present earlier and is easy to miss against the diffuse
    increase in density.
  diagnosis_term:
    preferred_term: skeletal survey radiography
    term:
      id: NCIT:C38092
      label: Skeletal Survey X-Ray
  evidence:
  - reference: PMID:42661684
    reference_title: "Osteopetrorickets and calcium homeostasis in children with osteopetrosis: an endocrinological single-center study."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Osteopetrorickets is clinically important because it may be overlooked in the presence of diffusely increased bone density, although impaired mineralization may coexist with osteosclerosis."
    explanation: >-
      States the radiographic trap this diagnostic step has to avoid, which is why
      the mineralization defect is looked for separately from the sclerosis.
- name: Osteoclast-rich marrow histology
  description: >
    Bone marrow biopsy in this form shows osteoclasts present in normal or
    increased numbers, and non-functional. That is the bedside correlate of the
    entry's central mechanistic claim, and it is what separates TCIRG1
    osteopetrosis from the osteoclast-poor RANK/RANKL forms, which the
    radiographic appearance alone does not.
  diagnosis_term:
    preferred_term: bone marrow biopsy
    term:
      id: NCIT:C15193
      label: Bone Marrow Biopsy
  evidence:
  - reference: PMID:35981697
    reference_title: "Osteoclast rich osteopetrosis due to defects in the TCIRG1 gene."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "TCIRG1 defects lead to inefficient bone resorption by nonfunctional osteoclasts seen in abundance on bone marrow biopsy, delineating this ARO as 'osteoclast-rich'"
    explanation: >-
      Names the biopsy finding and the classification it supports, which is the
      diagnostic value of the test here.
  - reference: PMID:10888887
    reference_title: "Defects in TCIRG1 subunit of the vacuolar proton pump are responsible for a subset of human autosomal recessive osteopetrosis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Osteoclasts are present in normal or elevated numbers in individuals affected by autosomal recessive osteopetrosis, suggesting that the defect is not in osteoclast differentiation, but in a gene involved in the functional capacity of mature osteoclasts"
    explanation: >-
      The original observation that osteoclast number is preserved, which is what
      makes the count diagnostically informative rather than merely descriptive.
treatments:
- name: Allogeneic Hematopoietic Stem Cell Transplantation
  description: >
    The only curative treatment. The osteoclast lineage is haematopoietic, so
    donor-derived monocyte precursors give rise to osteoclasts carrying a
    functional a3 subunit and bone resorption is restored. Transplantation
    corrects the mechanism but does not reverse damage already inflicted, so
    vision and hearing lost to cranial nerve compression before transplant do
    not recover; this is what makes early molecular diagnosis the main
    determinant of outcome rather than transplant technique.
  therapeutic_modality: CELL_THERAPY
  treatment_term:
    preferred_term: allogeneic haematopoietic stem cell transplantation
    term:
      id: NCIT:C15431
      label: Hematopoietic Cell Transplantation
  target_mechanisms:
  - target: Vacuolar Proton Pump Deficiency in Osteoclasts
    description: >-
      Replacing host osteoclast precursors with donor cells restores a3 subunit
      expression in the osteoclast lineage and so restores lacunar acidification.
    evidence:
    - reference: PMID:42162874
      reference_title: "Hematopoietic Stem Cell Transplantation in Infantile Osteopetrosis: Lessons from a Resource-Limited Setting."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "The defective osteoclast differentiation or function is of hemopoietic origin, thus making Hematopoietic stem cell transplantation (HSCT) the only curative treatment option for this condition."
      explanation: >-
        States the reason transplantation targets this node: the defective cell
        lineage is haematopoietic and therefore replaceable.
  evidence:
  - reference: PMID:40875877
    reference_title: "TCIRG1-Related Osteopetrosis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Hematopoietic stem cell therapy (HSCT) for those with hematologic failure with imminent vision loss, severe osteopetrosis with bone marrow failure, or severe osteopetrosis in children younger than age one year, ideally prior to age ten months."
    explanation: >-
      GeneReviews indication and timing for this gene. The "ideally prior to age ten
      months" threshold is the citable form of this entry's claim that outcome turns
      on how early the diagnosis is made.
  - reference: PMID:42162874
    reference_title: "Hematopoietic Stem Cell Transplantation in Infantile Osteopetrosis: Lessons from a Resource-Limited Setting."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "OS and DFS for the study were 80%."
    explanation: >-
      Overall and disease-free survival in a 10-patient fully HLA-matched cohort,
      three of whom had confirmed TCIRG1 variants. The cohort is small and
      single-centre, so this figure is indicative rather than a population estimate.
  notes: >-
    The survival figure quoted here is from a 10-patient single-centre cohort
    that was not restricted to TCIRG1 and included one RANK case, so it should
    not be read as a TCIRG1-specific outcome.
- name: Recombinant Human Interferon Gamma-1b
  description: >
    Adjunctive, non-curative therapy used as a bridge to transplantation. It
    increases osteoclastic bone resorption and corrects the reduced leukocyte
    superoxide generation that accompanies the osteoclast defect, improving
    marrow space, haemoglobin and infection frequency without addressing the
    underlying V-ATPase lesion.
  therapeutic_modality: PROTEIN_REPLACEMENT
  treatment_term:
    preferred_term: Pharmacotherapy
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
    therapeutic_agent:
    - preferred_term: interferon gamma-1b
      term:
        id: NCIT:C100089
        label: Interferon Gamma-1b
  dosing_interval: three times per week
  evidence:
  - reference: PMID:40875877
    reference_title: "TCIRG1-Related Osteopetrosis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Interferon gamma-1b (IFN-γ1b) may be considered in infantile TCIRG1-related osteopetrosis, to serve as a bridge to HSCT."
    explanation: >-
      GeneReviews states the indication for this gene specifically, and states it as
      a bridge rather than a treatment, which is how this entry describes it.
  - reference: PMID:7753137
    reference_title: "Long-term treatment of osteopetrosis with recombinant human interferon gamma."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "After 6 months of therapy, all 14 patients had decreases in trabecular-bone area (determined by histomorphometric analysis of bone-biopsy specimens) and increases in bone marrow space (determined by marrow imaging), and the improvement was sustained in the 11 patients treated for 18 months."
    explanation: >-
      The trial evidence that interferon gamma-1b measurably increases resorption
      and reclaims marrow space in severe osteopetrosis.
  - reference: PMID:7753137
    reference_title: "Long-term treatment of osteopetrosis with recombinant human interferon gamma."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The mean (+SD) hemoglobin concentration increased from 7.5 +/- 2.9 to 10.5 +/- 0.3 g per deciliter (P = 0.05), and superoxide generation by granulocyte-macrophage colonies increased (P < 0.001) after 18 months of therapy."
    explanation: >-
      Quantifies the haematological and leukocyte-function response, which is the
      basis for using it as a bridge rather than as a definitive treatment.
  notes: >-
    This trial predates routine molecular diagnosis and enrolled "severe
    osteopetrosis" rather than genotyped TCIRG1 patients, so the response cannot
    be attributed to the TCIRG1 form specifically. Note also that the trial
    reports increased osteoclastic resorption in cells that, in ARO1, cannot
    acidify at all; how much benefit is achievable through a null a3 subunit is
    not resolved by this study.
  review_notes: >-
    Dosing is 1.5 micrograms per kilogram per dose subcutaneously, three times
    per week, in the cited trial. dosing_interval_days is deliberately left
    unset because the schedule is three doses per week rather than one dose every
    N days, and forcing it to 2.33 would misrepresent the regimen.
- name: Calcium and Vitamin D Supplementation
  description: >
    Correction of the hypocalcaemia and impaired mineralization that follow from
    the skeleton being unavailable as a calcium reservoir. This addresses the
    mineral-metabolism branch, which transplantation does not treat directly.
  therapeutic_modality: SMALL_MOLECULE
  treatment_term:
    preferred_term: calcium and vitamin D supplementation
    term:
      id: NCIT:C15433
      label: Nutritional Support
  target_mechanisms:
  - target: Failure of Skeletal Calcium Mobilization
    description: >-
      Supplies the calcium the skeleton cannot release, rather than restoring the
      osteoclast function that would release it.
  target_phenotypes:
  - preferred_term: Hypocalcemia
    term:
      id: HP:0002901
      label: Hypocalcemia
  - preferred_term: Rickets
    term:
      id: HP:0002748
      label: Rickets
  evidence:
  - reference: PMID:40875877
    reference_title: "TCIRG1-Related Osteopetrosis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "calcium and vitamin D supplementation per endocrinologist;"
    explanation: >-
      GeneReviews supportive-care management for this gene. The quote is one item of
      a semicolon-delimited management list, which is how that chapter states each
      recommendation.
- name: Optic Nerve Decompression
  description: >
    Surgical decompression or sheath fenestration where progressive narrowing of
    the optic canal threatens vision. It relieves the compression mechanically
    and does not stop the sclerosis producing it, so it is a holding measure.
  therapeutic_modality: SURGERY
  treatment_term:
    preferred_term: optic nerve decompression and sheath fenestration
    term:
      id: NCIT:C15329
      label: Surgical Procedure
  target_mechanisms:
  - target: Cranial Nerve Compression from Skull Thickening
    description: >-
      Relieves compression at the optic canal without altering the bone
      accumulation that caused it.
  target_phenotypes:
  - preferred_term: Optic atrophy
    term:
      id: HP:0000648
      label: Optic atrophy
  evidence:
  - reference: PMID:40875877
    reference_title: "TCIRG1-Related Osteopetrosis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "optic nerve decompression and optic nerve sheath fenestration per neuro-ophthalmologist;"
    explanation: >-
      GeneReviews supportive-care management for the ocular complication this entry
      already models as a pathophysiology node.
- name: Genetic Counseling
  description: >
    Genetic counseling for affected families given autosomal recessive
    inheritance. Carrier testing and prenatal diagnosis available.
  therapeutic_modality: BEHAVIORAL
  treatment_term:
    preferred_term: Genetic Counseling
    term:
      id: NCIT:C15240
      label: Genetic Counseling
  evidence:
  - reference: PMID:11532986
    reference_title: "The mutational spectrum of human malignant autosomal recessive osteopetrosis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The identification of ATP6i gene mutations in two families allowed us for the first time to perform prenatal diagnosis: both fetuses were predicted not to be affected and two healthy babies were born."
    explanation: >-
      Documents that identifying the familial TCIRG1 variants makes prenatal
      diagnosis possible, which is the concrete output of counselling here.
clinical_trials:
- name: NCT04525352
  phase: PHASE_I
  status: TERMINATED
  description: >
    Autologous CD34+ cells transduced with a lentiviral vector encoding TCIRG1,
    the clinical translation of the oc/oc mouse gene-therapy work this entry
    already records. It opened in 2020 and was discontinued after the first
    treated patient died of causes unrelated to the gene therapy. It is recorded
    here because the entry describes gene therapy as an emerging alternative for
    patients without a donor, and the state of that alternative is a halted
    phase I rather than an open one.
  evidence:
  - reference: clinicaltrials:NCT04525352
    reference_title: "A Phase I Clinical Trial for Gene Therapy in Infantile Malignant Osteopetrosis (IMO) to Evaluate the Safety and Preliminary Efficacy of Autologous CD34+ Enriched Cells Transduced With a LV Vector Encoding the TCIRG1 Gene"
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The primary objective of this Phase 1 study is to evaluate the therapeutic safety and feasibility of the investigational product (IP), RP-L401."
    explanation: "The registered objective and phase of the trial."
  - reference: PMID:39314524
    reference_title: "Correction of osteopetrosis in the neonate oc/oc murine model after lentiviral vector gene therapy and non-genotoxic conditioning."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "a phase I clinical trial (NCT04525352) opened in 2020, but was then discontinued after the early death of the first treated patient for gene therapy unrelated causes"
    explanation: >-
      Records the discontinuation and its stated cause. Graded OTHER because
      evidence_source classifies the cited publication, and this one is an oc/oc
      mouse gene-therapy study; the quoted sentence is background about a trial
      run by others, so it is neither that paper's model-organism result nor human
      data it generated.
animal_models:
- name: Atp6i (Tcirg1) knockout mouse
  species: Mouse
  genotype: Atp6i (Tcirg1) targeted null, homozygous
  publication: PMID:10581033
  description: >
    Targeted disruption of the murine Tcirg1 orthologue Atp6i. This is the model
    that localised the human lesion to extracellular acidification specifically:
    the knockout osteoclasts fail to acidify the resorption compartment while
    lysosomal proton pumping, renal microsomal proton transport, and systemic
    acid-base balance are all normal.
  modeled_mechanisms:
  - target: Vacuolar Proton Pump Deficiency in Osteoclasts
    relationship: RECAPITULATES
    fidelity: HIGH
    model_scale: CELLULAR
    description: >-
      Loss of the same subunit in the same cell type, with the same
      compartment-restricted acidification defect.
    limitations: >-
      The compartment specificity was shown in cultured osteoclast-like cells
      derived from the knockout rather than in situ at a resorption lacuna.
    readouts:
    - name: Extracellular acidification by osteoclast-like cells
      target: Vacuolar Proton Pump Deficiency in Osteoclasts
      direction: ABOLISHED
      interpretation: >-
        Direct measurement of the function this node claims is lost.
      evidence:
      - reference: PMID:10581033
        reference_title: "Atp6i-deficient mice exhibit severe osteopetrosis due to loss of osteoclast-mediated extracellular acidification."
        supports: SUPPORT
        evidence_source: MODEL_ORGANISM
        snippet: "Atp6i-/- osteoclast-like cells (OCLs) lose the function of extracellular acidification, but retain intracellular lysosomal proton pump activity"
        explanation: "Reports the abolished extracellular acidification alongside the preserved lysosomal activity."
    - name: Lysosomal pH in liver
      target: Vacuolar Proton Pump Deficiency in Osteoclasts
      direction: UNCHANGED
      interpretation: >-
        A negative result that bounds the node: the lesion does not extend to
        lysosomal acidification, so this is not a generalised V-ATPase failure.
      evidence:
      - reference: PMID:10581033
        reference_title: "Atp6i-deficient mice exhibit severe osteopetrosis due to loss of osteoclast-mediated extracellular acidification."
        supports: SUPPORT
        evidence_source: MODEL_ORGANISM
        snippet: "The pH in Atp6i-/- liver lysosomes and proton transport in microsomes of Atp6i-/- kidney are identical to that in wild-type mice."
        explanation: "Records the measurement showing lysosomal and renal proton handling are unaffected."
    evidence:
    - reference: PMID:10581033
      reference_title: "Atp6i-deficient mice exhibit severe osteopetrosis due to loss of osteoclast-mediated extracellular acidification."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "targeted disruption of Atp6i in mice results in severe osteopetrosis"
      explanation: >-
        Establishes that removing this subunit is sufficient to produce the disease
        phenotype, which is what makes the model informative for this node.
- name: oc/oc mouse
  species: Mouse
  genotype: oc/oc, spontaneous 1.6 kb deletion at the 5-prime end of Tcirg1
  publication: PMID:39314524
  description: >
    Spontaneous Tcirg1-deficient mutant carrying a 5-prime deletion that abolishes
    transcription of the proton-pump subunit. Lifespan is under three weeks. It is
    the model used for the lentiviral gene-therapy work that motivated the
    discontinued phase I trial NCT04525352.
  modeled_mechanisms:
  - target: Progressive Skeletal Sclerosis
    relationship: RECAPITULATES
    fidelity: MODERATE
    model_scale: ORGANISM
    description: >-
      Generalised increase in skeletal density with marrow-cavity fibrosis and
      extramedullary haematopoiesis, matching the human skeletal and haematologic
      branches.
    limitations: >-
      Murine lifespan is under three weeks, so the model cannot express the
      progressive cranial nerve compression that dominates human morbidity, and
      skull foramen anatomy differs. Judgements about long-term neurological
      outcome do not transfer from it.
    evidence:
    - reference: PMID:39314524
      reference_title: "Correction of osteopetrosis in the neonate oc/oc murine model after lentiviral vector gene therapy and non-genotoxic conditioning."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "The Tcirg1-defective oc/oc mouse model displays a short lifespan and high bone density, closely mirroring the human condition."
      explanation: "The authors' own statement of what the model reproduces, and of its short lifespan."
  - target: Bone Marrow Failure from Medullary Obliteration
    relationship: RECAPITULATES
    fidelity: MODERATE
    model_scale: ORGANISM
    description: >-
      Marrow-cavity fibrosis with extramedullary haematopoiesis, reversible by
      gene therapy in the model.
    limitations: >-
      Correction was measured over a murine lifespan; durability over the decades
      relevant to a transplanted child is not addressed.
    evidence:
    - reference: PMID:39314524
      reference_title: "Correction of osteopetrosis in the neonate oc/oc murine model after lentiviral vector gene therapy and non-genotoxic conditioning."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "lentiviral vector GT can revert the osteopetrotic bone phenotype, allowing long-term survival and reducing extramedullary haematopoiesis"
      explanation: >-
        Shows the marrow phenotype is present in the model and is reversed by
        restoring the missing subunit, which supports the causal direction of this node.
references:
- reference: PMID:40875877
  title: "TCIRG1-Related Osteopetrosis."
  tags:
  - GeneReviews
- reference: DOI:10.1093/stcltm/szab019
  title: Alterations in Hematopoietic and Mesenchymal Stromal Cell Components of the Osteopetrotic Bone Marrow Niche
  found_in:
  - Autosomal_Recessive_Osteopetrosis-deep-research-falcon.md
  findings:
  - statement: Osteopetrosis is a rare inherited disease characterized by impaired osteoclast activity causing defective bone resorption and bone marrow aplasia.
    supporting_text: Osteopetrosis is a rare inherited disease characterized by impaired osteoclast activity causing defective bone resorption and bone marrow aplasia.
    evidence:
    - reference: DOI:10.1093/stcltm/szab019
      reference_title: Alterations in Hematopoietic and Mesenchymal Stromal Cell Components of the Osteopetrotic Bone Marrow Niche
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: Osteopetrosis is a rare inherited disease characterized by impaired osteoclast activity causing defective bone resorption and bone marrow aplasia.
      explanation: Deep research cited this publication as relevant literature for Autosomal Recessive Osteopetrosis.
- reference: DOI:10.1182/blood-2015-01-625541
  title: Hematopoietic stem cell transplantation for infantile osteopetrosis
  found_in:
  - Autosomal_Recessive_Osteopetrosis-deep-research-falcon.md
  findings:
  - statement: Key PointsHematopoietic cell transplantation results in long-term survival.
    supporting_text: Key PointsHematopoietic cell transplantation results in long-term survival.
    evidence:
    - reference: DOI:10.1182/blood-2015-01-625541
      reference_title: Hematopoietic stem cell transplantation for infantile osteopetrosis
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: Key PointsHematopoietic cell transplantation results in long-term survival.
      explanation: Deep research cited this publication as relevant literature for Autosomal Recessive Osteopetrosis.
- reference: DOI:10.1186/s13023-021-01955-6
  title: 'Haploidentical haematopoietic stem cell transplantation for malignant infantile osteopetrosis and intermediate osteopetrosis: a retrospective analysis of a single centre'
  found_in:
  - Autosomal_Recessive_Osteopetrosis-deep-research-falcon.md
  findings:
  - statement: To evaluate the clinical efficacy of haploidentical haematopoietic stem cell transplantation (haplo-HSCT) for the treatment of malignant infantile osteopetrosis (MIOP) and intermediate osteopetrosis.
    supporting_text: To evaluate the clinical efficacy of haploidentical haematopoietic stem cell transplantation (haplo-HSCT) for the treatment of malignant infantile osteopetrosis (MIOP) and intermediate osteopetrosis.
    evidence:
    - reference: DOI:10.1186/s13023-021-01955-6
      reference_title: 'Haploidentical haematopoietic stem cell transplantation for malignant infantile osteopetrosis and intermediate osteopetrosis: a retrospective analysis of a single centre'
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: To evaluate the clinical efficacy of haploidentical haematopoietic stem cell transplantation (haplo-HSCT) for the treatment of malignant infantile osteopetrosis (MIOP) and intermediate osteopetrosis.
      explanation: Deep research cited this publication as relevant literature for Autosomal Recessive Osteopetrosis.
- reference: DOI:10.1242/dmm.048940
  title: 'Autosomal recessive osteopetrosis: mechanisms and treatments'
  found_in:
  - Autosomal_Recessive_Osteopetrosis-deep-research-falcon.md
  findings:
  - statement: Autosomal recessive osteopetrosis (ARO) is a severe inherited bone disease characterized by defective osteoclast resorption or differentiation.
    supporting_text: Autosomal recessive osteopetrosis (ARO) is a severe inherited bone disease characterized by defective osteoclast resorption or differentiation.
    evidence:
    - reference: DOI:10.1242/dmm.048940
      reference_title: 'Autosomal recessive osteopetrosis: mechanisms and treatments'
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: Autosomal recessive osteopetrosis (ARO) is a severe inherited bone disease characterized by defective osteoclast resorption or differentiation.
      explanation: Deep research cited this publication as relevant literature for Autosomal Recessive Osteopetrosis.
- reference: DOI:10.18699/vjgb-23-46
  title: Clinical, genetic aspects and molecular pathogenesis of osteopetrosis
  found_in:
  - Autosomal_Recessive_Osteopetrosis-deep-research-falcon.md
  findings:
  - statement: Osteopetrosis (“marble bone”, ICD-10-78.2) includes a group of hereditary bone disorders distinguished by clinical variability and genetic heterogeneity.
    supporting_text: Osteopetrosis (“marble bone”, ICD-10-78.2) includes a group of hereditary bone disorders distinguished by clinical variability and genetic heterogeneity.
    evidence:
    - reference: DOI:10.18699/vjgb-23-46
      reference_title: Clinical, genetic aspects and molecular pathogenesis of osteopetrosis
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: Osteopetrosis (“marble bone”, ICD-10-78.2) includes a group of hereditary bone disorders distinguished by clinical variability and genetic heterogeneity.
      explanation: Deep research cited this publication as relevant literature for Autosomal Recessive Osteopetrosis.
- reference: DOI:10.2106/jbjs.19.00558
  title: TCIRG1 Transgenic Rescue of Osteoclast Function Using Induced Pluripotent Stem Cells Derived from Patients with Infantile Malignant Autosomal Recessive Osteopetrosis
  found_in:
  - Autosomal_Recessive_Osteopetrosis-deep-research-falcon.md
  findings:
  - statement: Osteoclasts are hematopoietic stem cell-derived multinucleated cells necessary for bone remodeling and resorption.
    supporting_text: Osteoclasts are hematopoietic stem cell-derived multinucleated cells necessary for bone remodeling and resorption.
    evidence:
    - reference: DOI:10.2106/jbjs.19.00558
      reference_title: TCIRG1 Transgenic Rescue of Osteoclast Function Using Induced Pluripotent Stem Cells Derived from Patients with Infantile Malignant Autosomal Recessive Osteopetrosis
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: Osteoclasts are hematopoietic stem cell-derived multinucleated cells necessary for bone remodeling and resorption.
      explanation: Deep research cited this publication as relevant literature for Autosomal Recessive Osteopetrosis.
- reference: DOI:10.3324/haematol.2019.238261
  title: Expanded circulating hematopoietic stem/progenitor cells as novel cell source for the treatment of TCIRG1 osteopetrosis
  found_in:
  - Autosomal_Recessive_Osteopetrosis-deep-research-falcon.md
  findings:
  - statement: Allogeneic hematopoietic stem cell transplantation is the treatment of choice for autosomal recessive osteopetrosis caused by defects in the TCIRG1 gene.
    supporting_text: Allogeneic hematopoietic stem cell transplantation is the treatment of choice for autosomal recessive osteopetrosis caused by defects in the TCIRG1 gene.
    evidence:
    - reference: DOI:10.3324/haematol.2019.238261
      reference_title: Expanded circulating hematopoietic stem/progenitor cells as novel cell source for the treatment of TCIRG1 osteopetrosis
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: Allogeneic hematopoietic stem cell transplantation is the treatment of choice for autosomal recessive osteopetrosis caused by defects in the TCIRG1 gene.
      explanation: Deep research cited this publication as relevant literature for Autosomal Recessive Osteopetrosis.
- reference: DOI:10.3389/fendo.2024.1450349
  title: Correction of osteopetrosis in the neonate oc/oc murine model after lentiviral vector gene therapy and non-genotoxic conditioning
  found_in:
  - Autosomal_Recessive_Osteopetrosis-deep-research-falcon.md
  findings:
  - statement: Autosomal recessive osteopetrosis (ARO) is a rare genetic disease, characterized by increased bone density due to defective osteoclast function.
    supporting_text: Autosomal recessive osteopetrosis (ARO) is a rare genetic disease, characterized by increased bone density due to defective osteoclast function.
    evidence:
    - reference: DOI:10.3389/fendo.2024.1450349
      reference_title: Correction of osteopetrosis in the neonate oc/oc murine model after lentiviral vector gene therapy and non-genotoxic conditioning
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: Autosomal recessive osteopetrosis (ARO) is a rare genetic disease, characterized by increased bone density due to defective osteoclast function.
      explanation: Deep research cited this publication as relevant literature for Autosomal Recessive Osteopetrosis.
- reference: DOI:10.3389/fped.2023.1096770
  title: 'Case report: Gene mutations and clinical characteristics of four patients with osteopetrosis'
  found_in:
  - Autosomal_Recessive_Osteopetrosis-deep-research-falcon.md
  findings:
  - statement: 'Case report: Gene mutations and clinical characteristics of four patients with osteopetrosis'
    supporting_text: Osteopetrosis is characterized by increased bone density caused by decreased osteoclasts or dysfunction of their differentiation and absorption properties, usually caused by biallelic variants of the TCIRG1(OMIM:604592)and CLCN7(OMIM:602727) genes.
    evidence:
    - reference: DOI:10.3389/fped.2023.1096770
      reference_title: 'Case report: Gene mutations and clinical characteristics of four patients with osteopetrosis'
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: Osteopetrosis is characterized by increased bone density caused by decreased osteoclasts or dysfunction of their differentiation and absorption properties, usually caused by biallelic variants of the TCIRG1(OMIM:604592)and CLCN7(OMIM:602727) genes.
      explanation: Deep research cited this publication as relevant literature for Autosomal Recessive Osteopetrosis.
- reference: DOI:10.3389/fped.2023.978879
  title: A novel compound heterozygous mutation of the CLCN7 gene is associated with autosomal recessive osteopetrosis
  found_in:
  - Autosomal_Recessive_Osteopetrosis-deep-research-falcon.md
  findings:
  - statement: Osteopetrosis is a genetic condition of the skeleton characterized by increased bone density caused by osteoclast formation and function defects.
    supporting_text: Osteopetrosis is a genetic condition of the skeleton characterized by increased bone density caused by osteoclast formation and function defects.
    evidence:
    - reference: DOI:10.3389/fped.2023.978879
      reference_title: A novel compound heterozygous mutation of the CLCN7 gene is associated with autosomal recessive osteopetrosis
      supports: SUPPORT
      evidence_source: OTHER
      snippet: Osteopetrosis is a genetic condition of the skeleton characterized by increased bone density caused by osteoclast formation and function defects.
      explanation: Deep research cited this publication as relevant literature for Autosomal Recessive Osteopetrosis.
- reference: DOI:10.3390/genes14040900
  title: Outlining the Clinical Profile of TCIRG1 14 Variants including 5 Novels with Overview of ARO Phenotype and Ethnic Impact in 20 Egyptian Families
  found_in:
  - Autosomal_Recessive_Osteopetrosis-deep-research-falcon.md
  findings:
  - statement: TCIRG1 gene mutations underlie osteopetrosis, a rare genetic disorder impacting osteoclast function with consequent brittle bones prone to fracture, in spite of being characterized by increased bone density.
    supporting_text: TCIRG1 gene mutations underlie osteopetrosis, a rare genetic disorder impacting osteoclast function with consequent brittle bones prone to fracture, in spite of being characterized by increased bone density.
    evidence:
    - reference: DOI:10.3390/genes14040900
      reference_title: Outlining the Clinical Profile of TCIRG1 14 Variants including 5 Novels with Overview of ARO Phenotype and Ethnic Impact in 20 Egyptian Families
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: TCIRG1 gene mutations underlie osteopetrosis, a rare genetic disorder impacting osteoclast function with consequent brittle bones prone to fracture, in spite of being characterized by increased bone density.
      explanation: Deep research cited this publication as relevant literature for Autosomal Recessive Osteopetrosis.
- reference: DOI:10.59213/tp.2025.249
  title: 'The clinical and genetic spectrum of infantile osteopetrosis: a single-center experience including a novel TCIRG1 mutation'
  found_in:
  - Autosomal_Recessive_Osteopetrosis-deep-research-falcon.md
  findings:
  - statement: Osteopetrosis (OP) is a rare, severe inherited disorder of bone metabolism caused by impaired osteoclast function.
    supporting_text: Osteopetrosis (OP) is a rare, severe inherited disorder of bone metabolism caused by impaired osteoclast function.
    evidence:
    - reference: DOI:10.59213/tp.2025.249
      reference_title: 'The clinical and genetic spectrum of infantile osteopetrosis: a single-center experience including a novel TCIRG1 mutation'
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: Osteopetrosis (OP) is a rare, severe inherited disorder of bone metabolism caused by impaired osteoclast function.
      explanation: Deep research cited this publication as relevant literature for Autosomal Recessive Osteopetrosis.
📚

References & Deep Research

References

13
PMID:40875877
TCIRG1-Related Osteopetrosis.
No top-level findings curated for this source.
DOI:10.1093/stcltm/szab019
Alterations in Hematopoietic and Mesenchymal Stromal Cell Components of the Osteopetrotic Bone Marrow Niche
1 finding
Osteopetrosis is a rare inherited disease characterized by impaired osteoclast activity causing defective bone resorption and bone marrow aplasia.
"Osteopetrosis is a rare inherited disease characterized by impaired osteoclast activity causing defective bone resorption and bone marrow aplasia."
Show evidence (1 reference)
DOI:10.1093/stcltm/szab019 SUPPORT Human Clinical
"Osteopetrosis is a rare inherited disease characterized by impaired osteoclast activity causing defective bone resorption and bone marrow aplasia."
Deep research cited this publication as relevant literature for Autosomal Recessive Osteopetrosis.
DOI:10.1182/blood-2015-01-625541
Hematopoietic stem cell transplantation for infantile osteopetrosis
1 finding
Key PointsHematopoietic cell transplantation results in long-term survival.
"Key PointsHematopoietic cell transplantation results in long-term survival."
Show evidence (1 reference)
DOI:10.1182/blood-2015-01-625541 SUPPORT Human Clinical
"Key PointsHematopoietic cell transplantation results in long-term survival."
Deep research cited this publication as relevant literature for Autosomal Recessive Osteopetrosis.
DOI:10.1186/s13023-021-01955-6
Haploidentical haematopoietic stem cell transplantation for malignant infantile osteopetrosis and intermediate osteopetrosis: a retrospective analysis of a single centre
1 finding
To evaluate the clinical efficacy of haploidentical haematopoietic stem cell transplantation (haplo-HSCT) for the treatment of malignant infantile osteopetrosis (MIOP) and intermediate osteopetrosis.
"To evaluate the clinical efficacy of haploidentical haematopoietic stem cell transplantation (haplo-HSCT) for the treatment of malignant infantile osteopetrosis (MIOP) and intermediate osteopetrosis."
Show evidence (1 reference)
DOI:10.1186/s13023-021-01955-6 SUPPORT Human Clinical
"To evaluate the clinical efficacy of haploidentical haematopoietic stem cell transplantation (haplo-HSCT) for the treatment of malignant infantile osteopetrosis (MIOP) and intermediate osteopetrosis."
Deep research cited this publication as relevant literature for Autosomal Recessive Osteopetrosis.
DOI:10.1242/dmm.048940
Autosomal recessive osteopetrosis: mechanisms and treatments
1 finding
Autosomal recessive osteopetrosis (ARO) is a severe inherited bone disease characterized by defective osteoclast resorption or differentiation.
"Autosomal recessive osteopetrosis (ARO) is a severe inherited bone disease characterized by defective osteoclast resorption or differentiation."
Show evidence (1 reference)
DOI:10.1242/dmm.048940 SUPPORT Human Clinical
"Autosomal recessive osteopetrosis (ARO) is a severe inherited bone disease characterized by defective osteoclast resorption or differentiation."
Deep research cited this publication as relevant literature for Autosomal Recessive Osteopetrosis.
DOI:10.18699/vjgb-23-46
Clinical, genetic aspects and molecular pathogenesis of osteopetrosis
1 finding
Osteopetrosis (“marble bone”, ICD-10-78.2) includes a group of hereditary bone disorders distinguished by clinical variability and genetic heterogeneity.
"Osteopetrosis (“marble bone”, ICD-10-78.2) includes a group of hereditary bone disorders distinguished by clinical variability and genetic heterogeneity."
Show evidence (1 reference)
DOI:10.18699/vjgb-23-46 SUPPORT Human Clinical
"Osteopetrosis (“marble bone”, ICD-10-78.2) includes a group of hereditary bone disorders distinguished by clinical variability and genetic heterogeneity."
Deep research cited this publication as relevant literature for Autosomal Recessive Osteopetrosis.
DOI:10.2106/jbjs.19.00558
TCIRG1 Transgenic Rescue of Osteoclast Function Using Induced Pluripotent Stem Cells Derived from Patients with Infantile Malignant Autosomal Recessive Osteopetrosis
1 finding
Osteoclasts are hematopoietic stem cell-derived multinucleated cells necessary for bone remodeling and resorption.
"Osteoclasts are hematopoietic stem cell-derived multinucleated cells necessary for bone remodeling and resorption."
Show evidence (1 reference)
DOI:10.2106/jbjs.19.00558 SUPPORT Human Clinical
"Osteoclasts are hematopoietic stem cell-derived multinucleated cells necessary for bone remodeling and resorption."
Deep research cited this publication as relevant literature for Autosomal Recessive Osteopetrosis.
DOI:10.3324/haematol.2019.238261
Expanded circulating hematopoietic stem/progenitor cells as novel cell source for the treatment of TCIRG1 osteopetrosis
1 finding
Allogeneic hematopoietic stem cell transplantation is the treatment of choice for autosomal recessive osteopetrosis caused by defects in the TCIRG1 gene.
"Allogeneic hematopoietic stem cell transplantation is the treatment of choice for autosomal recessive osteopetrosis caused by defects in the TCIRG1 gene."
Show evidence (1 reference)
DOI:10.3324/haematol.2019.238261 SUPPORT Human Clinical
"Allogeneic hematopoietic stem cell transplantation is the treatment of choice for autosomal recessive osteopetrosis caused by defects in the TCIRG1 gene."
Deep research cited this publication as relevant literature for Autosomal Recessive Osteopetrosis.
DOI:10.3389/fendo.2024.1450349
Correction of osteopetrosis in the neonate oc/oc murine model after lentiviral vector gene therapy and non-genotoxic conditioning
1 finding
Autosomal recessive osteopetrosis (ARO) is a rare genetic disease, characterized by increased bone density due to defective osteoclast function.
"Autosomal recessive osteopetrosis (ARO) is a rare genetic disease, characterized by increased bone density due to defective osteoclast function."
Show evidence (1 reference)
DOI:10.3389/fendo.2024.1450349 SUPPORT Model Organism
"Autosomal recessive osteopetrosis (ARO) is a rare genetic disease, characterized by increased bone density due to defective osteoclast function."
Deep research cited this publication as relevant literature for Autosomal Recessive Osteopetrosis.
DOI:10.3389/fped.2023.1096770
Case report: Gene mutations and clinical characteristics of four patients with osteopetrosis
1 finding
Case report: Gene mutations and clinical characteristics of four patients with osteopetrosis
"Osteopetrosis is characterized by increased bone density caused by decreased osteoclasts or dysfunction of their differentiation and absorption properties, usually caused by biallelic variants of the TCIRG1(OMIM:604592)and CLCN7(OMIM:602727) genes."
Show evidence (1 reference)
DOI:10.3389/fped.2023.1096770 SUPPORT Human Clinical
"Osteopetrosis is characterized by increased bone density caused by decreased osteoclasts or dysfunction of their differentiation and absorption properties, usually caused by biallelic variants of the TCIRG1(OMIM:604592)and CLCN7(OMIM:602727) genes."
Deep research cited this publication as relevant literature for Autosomal Recessive Osteopetrosis.
DOI:10.3389/fped.2023.978879
A novel compound heterozygous mutation of the CLCN7 gene is associated with autosomal recessive osteopetrosis
1 finding
Osteopetrosis is a genetic condition of the skeleton characterized by increased bone density caused by osteoclast formation and function defects.
"Osteopetrosis is a genetic condition of the skeleton characterized by increased bone density caused by osteoclast formation and function defects."
Show evidence (1 reference)
DOI:10.3389/fped.2023.978879 SUPPORT Other
"Osteopetrosis is a genetic condition of the skeleton characterized by increased bone density caused by osteoclast formation and function defects."
Deep research cited this publication as relevant literature for Autosomal Recessive Osteopetrosis.
DOI:10.3390/genes14040900
Outlining the Clinical Profile of TCIRG1 14 Variants including 5 Novels with Overview of ARO Phenotype and Ethnic Impact in 20 Egyptian Families
1 finding
TCIRG1 gene mutations underlie osteopetrosis, a rare genetic disorder impacting osteoclast function with consequent brittle bones prone to fracture, in spite of being characterized by increased bone density.
"TCIRG1 gene mutations underlie osteopetrosis, a rare genetic disorder impacting osteoclast function with consequent brittle bones prone to fracture, in spite of being characterized by increased bone density."
Show evidence (1 reference)
DOI:10.3390/genes14040900 SUPPORT Human Clinical
"TCIRG1 gene mutations underlie osteopetrosis, a rare genetic disorder impacting osteoclast function with consequent brittle bones prone to fracture, in spite of being characterized by increased bone density."
Deep research cited this publication as relevant literature for Autosomal Recessive Osteopetrosis.
DOI:10.59213/tp.2025.249
The clinical and genetic spectrum of infantile osteopetrosis: a single-center experience including a novel TCIRG1 mutation
1 finding
Osteopetrosis (OP) is a rare, severe inherited disorder of bone metabolism caused by impaired osteoclast function.
"Osteopetrosis (OP) is a rare, severe inherited disorder of bone metabolism caused by impaired osteoclast function."
Show evidence (1 reference)
DOI:10.59213/tp.2025.249 SUPPORT Human Clinical
"Osteopetrosis (OP) is a rare, severe inherited disorder of bone metabolism caused by impaired osteoclast function."
Deep research cited this publication as relevant literature for Autosomal Recessive Osteopetrosis.

Deep Research

1

Deep research results are used as seeds for research; they do not undergo the same validation as the main records and may contain errors. How we use deep research.

Evaluations and curation notes (1)

Repoint to MONDO:0009815 and expand TCIRG1 osteopetrosis curation · 2026-09-09T19:23:47Z · View source

Curation for claim #11552 (autosomal recessive osteopetrosis 1, MONDO:0009815). Preflight found the KB already held this disease's content under the wrong identifier: kb/disorders/Autosomal_Recessive_Osteopetrosis.yaml was named 'Autosomal Recessive Osteopetrosis Type 2' and bound to MONDO:0009816, whose MONDO definition is the TNFSF11 disease, while its description, all four pathophysiology nodes, its prevalence record and every phenotype explanation were about TCIRG1. Rather than add a second TCIRG1 entry, the existing file was renamed to Autosomal_Recessive_Osteopetrosis_1.yaml and repointed to MONDO:0009815; issue #11558 records the defect and the validation gap that let it through. The TNFSF11 genetic record, which a ClinGen sweep had matched to the entry by its (wrong) MONDO ID, was removed, and stubs/Autosomal_Recessive_Osteopetrosis_2.yaml was added so the TNFSF11 disease returns to the curation queue rather than disappearing with the rename. Enhancement used one OpenScientist deep-research report (research/Autosomal_Recessive_Osteopetrosis_1-deep-research-openscientist.md; 17/17 references resolved, 19/19 quotes verified) plus the TCIRG1-Related Osteopetrosis GeneReviews chapter (PMID:40875877) as the phenotype baseline. Added: an HGNC-bound TCIRG1 genetic record with the variant-spectrum evidence; a fifth pathophysiology node for the failure of skeletal calcium mobilization that produces hypocalcaemia, secondary hyperparathyroidism and osteopetrorickets; biological_scale tags on all five nodes; three phenotypes (Rickets, Secondary hyperparathyroidism, Extramedullary hematopoiesis); two animal models (Atp6i knockout and oc/oc) with modeled_mechanisms, readouts and limitations; and a rewritten treatments block. The report's suggested HP:0002690 for pathological fractures is Large sella turcica and was not used; every HP, GO, CL and NCIT CURIE in the entry was resolved through OLS at the point of writing. The report's NCIT suggestions for interferon gamma-1b (C1032) and calcitriol (C328) were also wrong and were replaced by lookups. The HSCT treatment term was corrected from NCIT:C15289 (Organ Transplantation, modality SURGERY) to NCIT:C15431 (Hematopoietic Cell Transplantation, modality CELL_THERAPY). Validated with just validate, just validate-terms, just check-entity-refs, just check-causal-targets and just validate-disorders.

OpenScientist ▸
Autosomal Recessive Osteopetrosis 1 (ARO1 / TCIRG1-Related Malignant Infantile Osteopetrosis): A Comprehensive Disease Characteristics Report
openscientist-autonomous 15 citations 2026-09-09T19:14:07.844100

Autosomal Recessive Osteopetrosis 1 (ARO1 / TCIRG1-Related Malignant Infantile Osteopetrosis): A Comprehensive Disease Characteristics Report

Disease: Autosomal Recessive Osteopetrosis 1 (ARO1) Identifiers: OMIM 259700 · MONDO:0009815 · Orphanet ORPHA:667 (osteopetrosis, malignant infantile) · MeSH D010022 (Osteopetrosis) · ICD-10 Q78.2 · ICD-11 LD24.K0 Category: Mendelian, autosomal recessive Causal gene: TCIRG1 (HGNC:11647; chr11q13.2; also Atp6i, OC116, ATP6V0A3)

Summary

Autosomal Recessive Osteopetrosis 1 (ARO1) is the classic malignant infantile osteopetrosis caused by biallelic loss-of-function variants in TCIRG1, the gene encoding the a3 subunit of the vacuolar H⁺-ATPase (V-ATPase) proton pump. The a3 subunit is essential for acidification of the osteoclast resorption lacuna. When it is lost, osteoclasts differentiate and are present in normal or increased numbers but cannot dissolve bone mineral—hence the pathological hallmark of an "osteoclast-rich" osteopetrosis with abundant, non-functional osteoclasts on marrow biopsy. TCIRG1 mutations account for roughly 50% of malignant infantile osteopetrosis cases, making it the single most common cause of the disease.

The consequence of failed osteoclastic bone resorption is a cascade of clinical problems: dense but mechanically fragile bones (pathological fractures), progressive obliteration of marrow cavities producing bone marrow failure with pancytopenia and extramedullary hematopoiesis (hepatosplenomegaly), narrowing of cranial nerve foramina causing blindness and deafness, hypocalcemia with tetanic seizures, and, because the high resorption-lacuna pH also impairs dietary calcium mobilization, a co-occurring "osteopetrorickets." The disease presents in the neonatal period or early infancy (incidence ~1 in 250,000 births) and, untreated, is frequently fatal within the first decade of life.

The only curative therapy is allogeneic hematopoietic stem cell transplantation (HSCT), since the osteoclast defect is of hematopoietic origin; early HLA-matched transplant yields roughly 80% overall survival, but it does not reverse established neurologic damage—underscoring the urgency of early molecular diagnosis. Adjunctive medical measures (recombinant human interferon gamma-1b, calcitriol, calcium/vitamin D) provide bridging or supportive benefit but are not curative. Tcirg1/Atp6i-deficient mouse models faithfully recapitulate the disease and have enabled ex-vivo lentiviral gene therapy proof-of-concept, an emerging alternative for patients lacking a suitable donor.

Section 1 — Disease Information

Overview. ARO1 is a genetically determined skeletal dysplasia in which defective osteoclast-mediated bone resorption leads to a generalized increase in bone density with paradoxical bone fragility. It is the most severe ("malignant") form of osteopetrosis, typically manifesting at birth or in early infancy. The information in this report is derived predominantly from aggregated disease-level resources (OMIM, Orphanet, GeneReviews-style syntheses) and from individual patient case reports/case series, rather than from large EHR-based cohorts; the rarity of the disease means most quantitative data come from single-center pediatric cohorts and multi-family molecular studies.

Key identifiers.

Resource Identifier
OMIM 259700 (osteopetrosis, autosomal recessive 1, OPTB1)
Gene OMIM 604592 (TCIRG1)
MONDO MONDO:0009815
Orphanet ORPHA:667 (malignant infantile osteopetrosis)
MeSH D010022 (Osteopetrosis)
ICD-10 Q78.2
ICD-11 LD24.K0
HGNC (gene) HGNC:11647 (TCIRG1)

Synonyms / alternative names. Malignant infantile osteopetrosis (MIOP); infantile malignant osteopetrosis (IMO/IMOP); osteopetrosis autosomal recessive 1 (OPTB1); "marble bone disease" (a historical umbrella term); Albers-Schönberg disease is a related but distinct autosomal dominant form and should not be conflated with ARO1. TCIRG1 gene synonyms include Atp6i, ATP6V0A3, OC116, and TIRC7.

Section 2 — Etiology

Primary cause. ARO1 is a monogenic disorder caused by biallelic (homozygous or compound heterozygous) loss-of-function mutations in TCIRG1. There is no environmental, infectious, or lifestyle cause; the etiology is entirely genetic. TCIRG1 encodes the a3 subunit of the V-ATPase; loss of function abolishes acidification of the osteoclast resorption lacuna, producing the osteoclast-rich phenotype (Finding F001).

"TCIRG1 encodes the a3 subunit, an essential isoform of the vacuolar ATPase proton pump involved in acidification of the osteoclast resorption lacuna and in secretory lysosome trafficking. TCIRG1 defects lead to inefficient bone resorption by nonfunctional osteoclasts seen in abundance on bone marrow biopsy, delineating this ARO as 'osteoclast-rich'." — PMID: 35981697

Genetic risk factors. The causal variants are the biallelic TCIRG1 mutations themselves. The dominant risk factor at the population level is consanguinity: most reported index families are first-cousin consanguineous with homozygous "private" variants (Finding F010). No common susceptibility loci or modifier genes have been definitively established for ARO1; disease severity is largely determined by the residual function of the specific alleles (e.g., hypomorphic splice variants give milder disease).

Environmental / lifestyle / infectious risk factors. None apply. ARO1 is not caused or triggered by toxins, radiation, diet, occupation, or pathogens. (Notably, congenital CMV infection can mimic the presentation—see Diagnostics—but is not causal.)

Protective factors. No environmental or dietary protective factors are known. The only "protective" genetic circumstance is possession of a hypomorphic (partially functional) allele, which attenuates severity (e.g., the intron 18 c.2236+6T>G splice variant associated with a mild adult phenotype; Finding F006).

Gene–environment interactions. Not applicable in a causal sense. The one clinically relevant interaction is dietary calcium × osteoclast dysfunction: because bone-derived calcium cannot be mobilized and high lacunar pH impairs dietary calcium uptake, nutritional calcium status modulates the hypocalcemia/rickets phenotype (osteopetrorickets, Finding F003).

Section 3 — Phenotypes

The phenotype is a multisystem consequence of failed osteoclast function. Quantitative frequencies below come primarily from a single-center pediatric osteopetrosis cohort (n=17; Finding F008) and from case series.

Phenotype Type HPO term (suggested) Frequency Onset Severity/course
Generalized osteosclerosis / increased bone density Radiographic/physical HP:0011002 (Osteopetrosis) ~100% (defining) Congenital/neonatal Progressive
Short stature Physical HP:0004322 13/17 (76.4%) Infancy/childhood Progressive
Ophthalmologic abnormalities (optic atrophy, nystagmus, visual impairment) Clinical sign HP:0000648 (Optic atrophy), HP:0000639 (Nystagmus) 10/17 (58.8%) Infancy Progressive, often irreversible
Hearing loss Clinical sign HP:0000365 7/17 (41.1%) Infancy/childhood Progressive
Hepatosplenomegaly (extramedullary hematopoiesis) Clinical sign HP:0001433 7/17 (41.1%) Infancy Progressive
Pancytopenia / bone marrow failure (anemia, thrombocytopenia) Lab abnormality HP:0001876, HP:0001903, HP:0001873 Common Neonatal/infancy Progressive, life-threatening
Hypocalcemia (± tetanic seizures) Lab abnormality HP:0002901 Common Neonatal Episodic/progressive
Pathological fractures Physical HP:0002690 Common Infancy/childhood Recurrent
Osteopetrorickets (metaphyseal rickets) Radiographic/lab HP:0002748 (Rickets) Frequent (all ARO in one cohort had metaphyseal osteopetrorickets) Infancy —
Macrocephaly / frontal bossing Physical HP:0000256, HP:0002007 Recurrent Infancy —
Hydrocephalus Clinical sign HP:0000238 Occasional Infancy Progressive
Dental anomalies / delayed eruption Physical HP:0000684, HP:0000682 Recurrent Childhood —
Recurrent infections Clinical HP:0002719 Recurrent Infancy —
Developmental delay Behavioral/neuro HP:0001263 Recurrent Infancy —
Hypotonia / spasticity Neuro sign HP:0001252 / HP:0001257 Recurrent Infancy —
Seizures Neuro sign HP:0001250 Occasional (incl. hypocalcemic tetany) Neonatal/infancy Episodic

"The median age at diagnosis was 14 months (range, 15 days-130 months), and short stature was observed in 13 of 17 patients (76.4%). Ophthalmologic abnormalities were present in 10 patients (58.8%), hearing loss in 7 patients (41.1%), and hepatosplenomegaly in 7 patients (41.1%)." — PMID: 42661684

"Classic ARO is characterised by fractures, short stature, compressive neuropathies, hypocalcaemia with attendant tetanic seizures, and life-threatening pancytopaenia." — PMID: 19232111

Quality of life. ARO1 imposes severe QoL impact: visual and hearing impairment compromise sensory development; recurrent fractures and short stature limit mobility; marrow failure requires transfusion support and confers infection/bleeding risk; and the disease is life-limiting without HSCT. Disease-specific QoL instrument data (EQ-5D/SF-36/PROMIS) are not available for this ultra-rare pediatric condition; QoL is inferred from the clinical severity and treatment burden.

Section 4 — Genetic / Molecular Information

Causal gene. TCIRG1 (HGNC:11647; gene OMIM 604592), located at chr11q13.2, encodes the a3 subunit of the V-ATPase V0 domain—the membrane-embedded proton-translocating sector. The a3 isoform is highly expressed in osteoclasts and is essential for pumping protons into the resorption lacuna and for secretory lysosome trafficking (Finding F001).

Variant spectrum. Pathogenic TCIRG1 variants are predominantly loss-of-function: nonsense/stop-gain, frameshift indels, and canonical splice-site variants, with a minority of missense alleles (Finding F006). Representative variants:

Variant (cDNA / protein) Type Notes
c.1897C>T (p.Gln633Ter) Nonsense Homozygous; absent from gnomAD; ACMG "pathogenic"
c.676G>T (p.E226*) Nonsense Compound het
c.909C>A (p.Y303*) Nonsense Known pathogenic
c.2008C>T (p.R670*) Nonsense Known pathogenic
c.624delC (p.P208PfsX1) Frameshift Pakistani consanguineous family
c.1191del (p.P398Sfs*5) Frameshift Compound het
c.1370del (p.T457Tfs*71); c.66delC; c.692delA Frameshift Reported
c.1554+2T>C; c.2236+6T>G; c.1020+1_1020+5dup Splice c.2236+6T>G (intron 18) is hypomorphic → mild phenotype
p.R444L Missense ER retention/misprocessing of a3 → LOF via mistrafficking

Classification & allele frequency. Most variants are private to individual consanguineous families, absent from gnomAD, and classified pathogenic/likely pathogenic per ACMG/AMP criteria.

"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 ... ACMG/AMP criteria." — PMID: 42529563

Functional consequence. The mechanism is loss of function. Truncating/frameshift/splice variants abolish a3 protein or produce nonfunctional protein; the R444L missense causes ER retention and misprocessing of the glycoprotein, preventing its lysosomal/membrane localization:

"the mutant glycoprotein localized to the ER instead of lysosomes and its oligosaccharide moiety was misprocessed" — PMID: 22685294

A rare hypomorphic splice variant demonstrates genotype–phenotype correlation—partial function → mild disease:

"He was homozygous for c.2236+6T>G in intron 18; this mutation influenced the splicing process." — PMID: 28816234

Modifier genes / epigenetics / chromosomal abnormalities. No established modifier genes, disease-specific epigenetic changes, or recurrent chromosomal abnormalities. ARO1 is a single-gene disorder; large structural changes are not a typical mechanism (variants are point mutations/small indels detectable by SNP-array homozygosity mapping and sequencing).

Section 5 — Environmental Information

Not applicable as a cause. ARO1 has no environmental, lifestyle, or infectious etiology. The only clinically relevant environmental modifier is dietary calcium/vitamin D status, which interacts with the impaired calcium mobilization to influence hypocalcemia and rickets severity. Congenital CMV infection is an important differential/mimic (not a cause) because it can reproduce the cytopenia and hepatosplenomegaly (Finding F007).

Section 6 — Mechanism / Pathophysiology

Ordered causal chain

  1. Biallelic loss-of-function mutation in TCIRG1 leads to absent or nonfunctional a3 subunit of the osteoclast V-ATPase. (demonstrated)
  2. Loss of a3 results in failure to assemble a functional proton pump at the osteoclast ruffled border. (demonstrated in vitro/model)
  3. This leads to failure to acidify the resorption lacuna (the sealed extracellular compartment between osteoclast and bone). (demonstrated — Atp6i knockout loses extracellular but not intracellular lysosomal acidification)
  4. Failure of acidification results in inability to dissolve hydroxyapatite bone mineral and to activate acid-dependent collagenolytic enzymes → osteoclasts are abundant but non-resorptive ("osteoclast-rich" osteopetrosis). (demonstrated)
  5. Non-resorption leads to accumulation of dense, disorganized bone and obliteration of the medullary cavity. (demonstrated)

Branch A → Skeletal: Dense but poorly remodeled bone results in mechanical fragility → pathological fractures, short stature, macrocephaly, and dental anomalies. (demonstrated)

Branch B → Hematologic: Medullary obliteration leads to bone marrow failure → pancytopenia and compensatory extramedullary hematopoiesis → hepatosplenomegaly. (demonstrated)

Branch C → Neurologic: Failure to widen skull foramina with growth results in cranial nerve compression → optic atrophy/blindness, deafness, and, when CSF outflow is obstructed, hydrocephalus. (demonstrated)

Branch D → Mineral metabolism: Inability to mobilize skeletal calcium plus high lacunar pH impairing dietary calcium uptake leads to hypocalcemia → secondary hyperparathyroidism → poor osteoid mineralization ("osteopetrorickets") and hypocalcemic tetanic seizures. (demonstrated) 6. The combined skeletal, hematologic, neurologic, and metabolic failure results in the malignant infantile clinical syndrome, frequently fatal in the first decade if untreated. (demonstrated)

Detail by category

  • Molecular pathway / biochemical defect: Failure of V-ATPase–mediated H⁺ transport (proton pumping) at the ruffled-border plasma membrane. GO: proton transmembrane transport (GO:1902600), vacuolar proton-transporting V-type ATPase complex (GO:0016471), extracellular acidification. The pump is specifically required for extracellular acidification—Atp6i-null cells retain intracellular lysosomal proton-pump activity and mice keep normal systemic acid–base balance, unlike carbonic anhydrase II deficiency (Finding F005).

"targeted disruption of Atp6i in mice results in severe osteopetrosis. Atp6i-/- osteoclast-like cells (OCLs) lose the function of extracellular acidification, but retain intracellular lysosomal proton pump activity." — PMID: 10581033

  • Cellular process: Osteoclast (CL:0000092) bone resorption (GO:0045453) is abolished; osteoclast differentiation is intact (RANK/RANKL signaling normal), distinguishing this from osteoclast-poor ARO (RANK/RANKL defects).
  • Protein dysfunction: Loss of function through truncation, or (for R444L missense) ER retention and misprocessing (protein mistrafficking).
  • Metabolic changes: Systemic hypocalcemia, elevated PTH, disordered calcium/phosphate balance → rickets. Systemic acid–base balance is preserved (contrast CA2 deficiency).
  • Immune involvement: Osteoclasts share the granulocyte-macrophage lineage with phagocytes; defective leukocyte superoxide production is documented and is corrected by interferon gamma-1b (relevant to therapy).
  • Tissue damage: Mechanical bone fragility, marrow fibrosis, compressive neuropathy.
  • Subcellular compartments: Ruffled-border plasma membrane, secretory lysosomes (GO:0005765 lysosomal membrane; GO:0005886 plasma membrane; GO:0016471 V-ATPase complex).

Cell types (CL): osteoclast (CL:0000092). Biological processes (GO): bone resorption (GO:0045453), proton transmembrane transport (GO:1902600), ossification/bone remodeling. Chemical entities (CHEBI): proton/hydron (CHEBI:15378), calcium(2+) (CHEBI:29108), hydroxyapatite.

Section 7 — Anatomical Structures Affected

  • Primary organ/system: Skeletal system / bone (UBERON:0002481 bone tissue; UBERON:0001474 bone element). Generalized involvement, bilateral and symmetric.
  • Secondary organ involvement:
  • Bone marrow (UBERON:0002371) → marrow failure.
  • Liver (UBERON:0002107) and spleen (UBERON:0002106) → extramedullary hematopoiesis, hepatosplenomegaly.
  • Cranial nerves — optic nerve (UBERON:0000941), vestibulocochlear nerve → compression → blindness/deafness.
  • Brain / ventricular system → hydrocephalus.
  • Teeth (UBERON:0001091) → dental anomalies.
  • Hematopoietic/immune system → cytopenias, recurrent infection.
  • Tissue/cell level: Bone (connective tissue); target cell is the osteoclast (CL:0000092). Osteoblasts are not primarily defective.
  • Subcellular level: V-ATPase complex at ruffled-border plasma membrane and secretory lysosomes.
  • Lateralization: Bilateral, symmetric, generalized (a systemic skeletal dysplasia).

Section 8 — Temporal Development

  • Onset: Congenital / neonatal to early infancy. Median age at diagnosis in one cohort was 14 months (range 15 days–130 months), though signs often begin earlier (Finding F008). Onset pattern is chronic/progressive from birth.
  • Progression: Progressive without treatment. Characteristic radiographic features (Erlenmeyer flask deformity, bone-in-bone appearance) develop toward the end of early childhood, while metaphyseal osteopetrorickets is present in infancy (Finding F007).
  • Course: Progressive, non-remitting. Disease duration is lifelong; untreated malignant infantile disease is frequently fatal in the first decade (Finding F009).
  • Critical intervention window: HSCT is most effective before irreversible neurologic (cranial-nerve) damage—this defines the therapeutic time window. Remission is treatment-induced (via HSCT); spontaneous remission does not occur.

"typical skeletal features such as Erlenmeyer flask deformity and bone-in-bone appearance that developed toward the end of early childhood" — PMID: 37704070

Section 9 — Inheritance and Population

  • Inheritance: Autosomal recessive; 25% recurrence risk for carrier couples. High penetrance; the classic malignant form has consistently early, severe expression, while rare hypomorphic alleles give milder disease (variable expressivity by genotype) (Finding F010).
  • Epidemiology: ARO overall incidence ~1 in 250,000 births (Finding F002). TCIRG1 accounts for ~50% of malignant infantile cases, so TCIRG1-ARO1 incidence is on the order of ~1 in 500,000 births. Prevalence is low given high early mortality without treatment.
  • Penetrance / expressivity: Complete penetrance for biallelic LOF; expressivity varies with residual allele function.
  • Genetic anticipation / mosaicism: Not applicable (not a repeat-expansion disorder; germline mosaicism not a described feature).
  • Consanguinity & founder effects: Consanguinity is a major driver; many index families are first-cousin consanguineous with homozygous private variants identifiable by SNP-array homozygosity mapping (e.g., ~4 Mb chr11 region harboring TCIRG1). Population-specific recurrent alleles exist in some communities.

"DNA samples from five family members were subjected to genome-wide SNP array genotyping and homozygosity mapping which identified ~4 Mb region on chr11 harboring the TCIRG1 gene." — PMID: 29237407

  • Demographics: No strong sex predilection (autosomal). Higher observed burden in populations with high consanguinity rates (Middle East, North Africa, South Asia). Age distribution: overwhelmingly infants/young children.

Section 10 — Diagnostics

Imaging (first-line). Skeletal radiographs show generalized osteosclerosis, obliteration of medullary cavities, Erlenmeyer flask (metaphyseal) deformity, and "bone-in-bone" appearance (Finding F007).

"Skeletal radiographs demonstrated diffuse osteosclerosis, obliteration of medullary cavities, and characteristic Erlenmeyer flask deformities, strongly suggestive of MIOP." — PMID: 42529563

Laboratory. Anemia, thrombocytopenia/bicytopenia (marrow failure); hypocalcemia with elevated PTH; poor osteoid mineralization (osteopetrorickets). Systemic acid–base balance is normal (helps distinguish CA2 deficiency). Bone marrow biopsy shows abundant osteoclasts ("osteoclast-rich").

Genetic testing (confirmatory). Targeted single-gene or gene-panel analysis and whole-exome sequencing (WES) covering the osteopetrosis genes—TCIRG1, CLCN7, OSTM1, SNX10, TNFRSF11A, TNFSF11, PLEKHM1, CA2—are the confirmatory standard. Homozygosity mapping via SNP array is useful in consanguineous families. WGS may be used when panel/WES is negative; note that a molecular diagnosis is not always obtained, yet the clinical/radiographic picture can suffice to proceed to HSCT.

Differential diagnosis. Other osteopetrosis subtypes (CLCN7, OSTM1, RANK/RANKL, SNX10, FERMT3); CA2 deficiency (osteopetrosis with renal tubular acidosis and cerebral calcification—absent in TCIRG1 ARO, whose acid–base balance is normal); pycnodysostosis (CTSK); and congenital CMV infection, which mimics the cytopenia/hepatosplenomegaly (Finding F007).

"It may have similar clinical manifestations with congenital cytomegalovirus infection." — PMID: 41204604

Screening. Carrier and cascade testing of relatives once the familial variants are known; prenatal molecular diagnosis and preimplantation genetic testing are available for at-risk families.

Section 11 — Outcome / Prognosis

  • Untreated: Malignant infantile osteopetrosis is frequently fatal during the first decade of life due to marrow failure, hemorrhage, infection, and neurologic complications (Finding F009).

"The disease is frequently fatal during the first decade of life." — PMID: 7753137

  • With early HSCT: Overall and disease-free survival of ~80% in an HLA-matched cohort (Finding F004). Prognosis is markedly worse when advanced neurologic involvement is already present, because HSCT does not reverse established cranial-nerve damage.

"Some genetic subtypes may be potentially curable with hematopoietic stem cell transplantation, but the results are overall poor in patients with advanced neurologic involvement or adverse genetic mutations." — PMID: 40625472

  • Morbidity: Irreversible blindness/deafness, growth failure, fracture-related disability, and transplant-related complications drive long-term morbidity.
  • Prognostic factors: Age at HSCT, presence/absence of neurologic damage at transplant, donor HLA match, and genotype (hypomorphic alleles = milder disease).

Section 12 — Treatment

Curative — allogeneic HSCT (NCIT: Hematopoietic Cell Transplantation, C15431). Because the osteoclast defect is hematopoietic in origin, HSCT can replace defective osteoclast precursors with functional donor-derived cells and is the only curative option (Finding F004).

"The defective osteoclast differentiation or function is of hemopoietic origin, thus making Hematopoietic stem cell transplantation (HSCT) the only curative treatment option for this condition." — PMID: 42162874

"OS and DFS for the study were 80%." — PMID: 42162874

HSCT complications observed in a 10-patient cohort: cyclosporine-induced hypertension (100%), neutropenic fever (90%), mucositis (60%), veno-occlusive disease (30%), acute GVHD (30%), and post-HSCT hypercalcemia/rebound hypercalcemia (20%). Myeloablative conditioning (fludarabine/busulfan) was used.

Adjunctive / medical (not curative). - Recombinant human interferon gamma-1b (NCIT: Interferon Gamma-1b, C1032) — 1.5 µg/kg SC three times weekly. In a 14-patient trial, 6 months of therapy decreased trabecular-bone area, increased marrow space, raised mean hemoglobin from 7.5±2.9 to 10.5±0.3 g/dL (P=0.05), and increased leukocyte superoxide generation (P<0.001), sustained to 18 months. It acts by enhancing osteoclastic bone resorption and correcting defective leukocyte superoxide production (Finding F009).

"After 6 months of therapy, all 14 patients had decreases in trabecular-bone area (determined by histomorphometric analysis of bone-biopsy specimens) and increases in bone marrow space" — PMID: 7753137

"IFNγ-1b has been demonstrated to increase osteoclastic bone resorption and leucocytic function." — PMID: 18031077

  • Calcitriol (NCIT: Calcitriol, C328) and PTH can stimulate residual osteoclast activity; calcium and vitamin D supplementation correct hypocalcemia/osteopetrorickets. Supportive measures include transfusions, infection prophylaxis, seizure control, and management of hydrocephalus (ventriculoperitoneal shunt).

Emerging — gene therapy. HSC-targeted ex-vivo lentiviral gene therapy corrects osteopetrosis in Tcirg1/oc/oc mouse models (Finding F005), offering an autologous alternative for patients without a suitable donor (see below).

"lentiviral vector GT can revert the osteopetrotic bone phenotype, allowing long-term survival and reducing extramedullary haematopoiesis" — PMID: 39314524

Personalized medicine. Genotype guides prognosis (hypomorphic vs null alleles) and family counseling; adjunctive medical therapy is used to bridge to transplant and to manage calcium metabolism peri-transplant.

Section 13 — Prevention

  • Primary prevention: None exists (the disease is neither environmental nor infectious). Prevention is reproductive/genetic.
  • Genetic counseling & carrier/cascade testing: Essential for at-risk and consanguineous families; 25% recurrence risk per pregnancy for carrier couples.
  • Prenatal & preimplantation diagnosis: Once the familial biallelic variants are known, prenatal molecular testing and PGT are available.
  • Secondary prevention: Early molecular diagnosis is the key measure—it enables HSCT before irreversible neurologic damage, the single most important determinant of outcome (Finding F010).
  • Tertiary prevention: Management of complications (transfusion, infection prophylaxis, ophthalmologic/audiologic monitoring, hydrocephalus surveillance, calcium/vitamin D management).

Section 14 — Other Species / Natural Disease

  • Mouse (NCBI Taxon 10090): The ortholog is Tcirg1 / Atp6i (NCBI Gene 27060). Two key models: the targeted Atp6i knockout and the spontaneous oc/oc mouse, both Tcirg1-deficient (Finding F005).
  • Natural disease / veterinary relevance: Osteopetrosis occurs naturally in several species (cattle, mice); TCIRG1-orthologous forms are documented in animal genetics resources (OMIA). Comparative pathology shows conserved osteoclast dysfunction.
  • Evolutionary conservation: The V-ATPase a3 subunit and its role in osteoclast extracellular acidification are conserved across mammals, which is why murine models faithfully recapitulate the human disease.
  • Transmission: Not applicable (non-infectious, non-zoonotic).

Section 15 — Model Organisms

Model Type Genetic basis Recapitulation Key use
Atp6i (Tcirg1) knockout mouse Mammalian, in vivo Targeted null Severe osteopetrosis; loss of osteoclast extracellular acidification with retained intracellular lysosomal pump activity; normal systemic acid–base Established the acidification-specific mechanism
oc/oc mouse Mammalian, spontaneous mutant Tcirg1 deficiency Severe infantile-type osteopetrosis Preclinical gene-therapy testing
Osteoclast-like cell cultures (OCLs) In vitro Atp6i−/− Loss of extracellular acidification Cellular mechanism dissection

"targeted disruption of Atp6i in mice results in severe osteopetrosis. Atp6i-/- osteoclast-like cells (OCLs) lose the function of extracellular acidification, but retain intracellular lysosomal proton pump activity." — PMID: 10581033

Applications: mechanism of osteoclast acidification; HSC-targeted neonatal lentiviral gene therapy proof-of-concept, which reverted the osteopetrotic phenotype, allowed long-term survival, and reduced extramedullary hematopoiesis (Finding F005). Limitations: murine skull/cranial-nerve foramen anatomy and lifespan differ from humans, limiting modeling of cranial-nerve compression and long-term neurologic outcomes. Resources: MGI, IMSR.

Mechanistic Model / Interpretation

TCIRG1 biallelic LOF mutation
│  (absent/nonfunctional V-ATPase a3 subunit)
▼
No proton pump at osteoclast ruffled border
│
▼
Failure to acidify resorption lacuna  ── (extracellular only; lysosomes spared)
│
▼
Osteoclasts present but CANNOT resorb bone  ("osteoclast-rich" ARO)
│
├──► SKELETAL: dense fragile bone → fractures, short stature, macrocephaly, dental defects
│
├──► HEMATOLOGIC: medullary obliteration → pancytopenia
│                 + extramedullary hematopoiesis → hepatosplenomegaly
│
├──► NEUROLOGIC: unwidened foramina → optic/auditory nerve compression
│                 → blindness, deafness; ± hydrocephalus
│
└──► MINERAL: no Ca mobilization + high lacunar pH impairs dietary Ca uptake
               → hypocalcemia → ↑PTH → poor mineralization ("osteopetrorickets")
               → tetanic seizures
│
▼
Malignant infantile syndrome → death in first decade if untreated
│
▼
HSCT (donor osteoclast precursors) = CURE (~80% OS) IF before neurologic damage
Gene therapy (ex-vivo lentiviral, autologous HSC) = emerging alternative

The unifying theme is that a single biochemical lesion—failure of extracellular proton pumping by osteoclasts—produces the entire multisystem phenotype. All downstream branches (skeletal, hematologic, neurologic, metabolic) are second-order consequences of one primary defect, which is why a hematopoietic replacement strategy (HSCT) that restores functional osteoclast precursors is curative for the disease's mechanism—yet cannot undo damage (blindness, deafness) already inflicted before treatment. This dictates the clinical imperative: diagnose and transplant early.

Evidence Base

PMID Title (abbrev.) Role
35981697 Osteoclast-rich osteopetrosis due to defects in the TCIRG1 gene Defines gene product, acidification function, osteoclast-rich pathology, osteopetrorickets, cranial-nerve/marrow features
29237407 Novel p.P208PfsX1 mutation in V-ATPase a3 TCIRG1 = ~50% of MIOP; homozygosity mapping in consanguineous family
19232111 Osteopetrosis (review) Incidence 1/250,000; core clinical features
25673572 Osteopetrosis with superimposed rickets Rickets mechanism (Ca/P balance)
42529563 Homozygous TCIRG1 stop-gain Nonsense variant, gnomAD absence, ACMG; radiographic hallmarks; consanguinity
34545712 Five Chinese ARO patients Biallelic nonsense/frameshift spectrum
28816234 Novel TCIRG1 mutations, malignant & mild Hypomorphic splice variant → mild phenotype
22685294 R444L ER retention Missense LOF via mistrafficking
10581033 Atp6i-deficient mice Knockout phenotype; acidification-specific defect
39314524 Gene therapy in neonate model Lentiviral GT reverts phenotype
42162874 HSCT in infantile osteopetrosis HSCT is only cure; 80% OS/DFS; complication profile
40625472 MIOP with neuro/hematologic complications Poor HSCT outcomes with advanced neuro involvement
37704070 Turkish osteopetrosis spectrum Radiographic feature timing
41204604 Misdiagnosed as CMV CMV differential/mimic
42661684 Osteopetrorickets & Ca homeostasis cohort Quantitative phenotype frequencies, median dx age
7753137 IFN-γ long-term treatment Untreated prognosis; IFN-γ-1b trial efficacy
18031077 Pathogenesis & rationale for IFN-γ-1b IFN-γ mechanism

Evidence source types: human clinical (case reports/series, cohort studies, IFN-γ trial), model organism (Atp6i/oc mice, gene therapy), and in vitro (OCL acidification assays, R444L trafficking).

Limitations and Knowledge Gaps

  1. Small, heterogeneous cohorts. Quantitative phenotype frequencies (Section 3) derive from a single 17-patient center that included multiple genetic subtypes, not TCIRG1-only patients; TCIRG1-specific frequencies may differ.
  2. No formal QoL data. Standardized QoL instrument data (EQ-5D/SF-36/PROMIS) are unavailable for this ultra-rare pediatric disease.
  3. Genotype–phenotype resolution is incomplete. Beyond the null-vs-hypomorphic dichotomy, fine correlations between specific TCIRG1 variants and organ-specific severity are not established.
  4. HSCT survival figures come from limited cohorts. The ~80% OS reflects small, HLA-matched cohorts; outcomes vary substantially with donor type, conditioning, and neurologic status at transplant.
  5. Gene therapy is preclinical. Lentiviral correction is demonstrated in mice only; no human ARO1 gene-therapy outcomes are yet available.
  6. Precise prevalence unknown. Only incidence estimates exist; true prevalence is uncertain given high early mortality and underdiagnosis in low-resource settings.

Proposed Follow-up Experiments / Actions

  1. TCIRG1-restricted natural-history cohort. Aggregate multi-center, genetically-confirmed TCIRG1 patients to derive organ-specific phenotype frequencies, age-of-onset distributions, and validated genotype–phenotype correlations.
  2. Neurologic-outcome timing study. Correlate age/neurologic status at HSCT with long-term visual/auditory recovery to define the precise "window of opportunity" quantitatively.
  3. First-in-human gene therapy trial design. Translate the ex-vivo lentiviral HSC approach to a phase I/II trial for TCIRG1-ARO1 patients lacking matched donors, with engraftment, osteoclast-function, and safety endpoints.
  4. Newborn/expanded carrier screening evaluation. Assess cost-effectiveness of TCIRG1 inclusion in carrier panels for high-consanguinity populations to enable pre-symptomatic diagnosis and earlier HSCT.
  5. Adjunctive-therapy RCT. Formally test interferon gamma-1b (± calcitriol) as a bridge-to-transplant in TCIRG1-ARO1 with bone-resorption and hematologic endpoints, since existing evidence is from small/older trials and ADO2 models.
  6. Biomarker development. Validate circulating markers of osteoclast function (e.g., resorption markers, superoxide indices) to monitor disease activity and treatment response peri-HSCT.

Report compiled from 10 confirmed findings across 5 investigation iterations and 28 reviewed papers. Evidence prioritizes primary literature with verified abstract quotations.

Artifacts

Reference Validation

Checked with linkml-reference-validator 0.2.1.

Outcome Count
References checked 17
Resolved 17
Unresolved (possible confabulation) 0
Unverifiable 0
Quoted claims checked 19
Quoted claims found in source 19
Quoted claims not found in source 0
References weighed for topical relevance 17
On topic 17
Off topic 0

All extracted references resolved successfully.

Term Validation

Checked with linkml-term-validator 0.4.5, through the ols: adapter.

Outcome Count
Terms checked 40
Resolved 38
Unresolved (possible confabulation) 0
Obsolete 0
Unverifiable 2
Terms whose name was checked 17
Terms named correctly 4
Terms named as a different term 10
Terms whose name is worth a second look 3

Terms the report names something else

These identifiers resolve, so nothing about them looks wrong, and the ontology calls them something unrelated to what the report calls them. That usually means the identifier is not the one the sentence needs:

  • MONDO:0009815 (2 mentions) - the report calls it "MONDO"; MONDO calls it autosomal recessive osteopetrosis 1
  • HP:0004322 (1 mention) - the report calls it "Physical"; HP calls it Short stature
  • HP:0000365 (1 mention) - the report calls it "Clinical sign"; HP calls it Hearing impairment
  • HP:0001433 (1 mention) - the report calls it "Clinical sign"; HP calls it Hepatosplenomegaly
  • HP:0002901 (1 mention) - the report calls it "Lab abnormality"; HP calls it Hypocalcemia
  • HP:0002690 (1 mention) - the report calls it "Physical"; HP calls it Large sella turcica
  • HP:0000238 (1 mention) - the report calls it "Clinical sign"; HP calls it Hydrocephalus
  • HP:0002719 (1 mention) - the report calls it "Clinical"; HP calls it Recurrent infections
  • HP:0001263 (1 mention) - the report calls it "Behavioral/neuro"; HP calls it Global developmental delay
  • HP:0001250 (1 mention) - the report calls it "Neuro sign"; HP calls it Seizure

Terms whose name is worth a second look

The report's name for these is recognisably related to the term's own name without being one of them. A loose paraphrase reads the same way as a citation of the wrong sibling term - and so does a related synonym, which the ontology records precisely because it names something adjacent rather than the same thing - so these are listed rather than judged:

  • CL:0000092 (3 mentions) - the report calls it "Cellular process: Osteoclast"; CL calls it osteoclast**
  • UBERON:0000941 (1 mention) - the report calls it "Cranial nerves — optic nerve"; UBERON calls it cranial nerve II
  • UBERON:0001091 (1 mention) - the report calls it "Teeth"; UBERON calls it calcareous tooth, and lists "tooth" among its other names

Terms named inconsistently

The report gives these identifiers more than one name of its own:

  • ORPHA:667 - called "osteopetrosis, malignant infantile", "malignant infantile osteopetrosis"

Prefixes with no resolver

Terms carrying these prefixes were not checked either way, because no configured ontology covers them. An unrecognised prefix may name an ontology this run could not reach as easily as one that does not exist, so nothing here is evidence of fabrication: ORPHA.