TCIRG1 and Bone marrow hypocellularity: The incidence rate is 1:200,000.[3] Approximately 50% of cases are due to double allele mutations in T-cell immune regulator 1 (TCIRG1).[4] The gene encoding the A3 subunit of osteoclast V-ATPase is the basis for the establishment of an acidic environment in the resorption region of osteoclasts.[5] The typical clinical manifestations of IMO are generalized osteosclerosis, pathologic fractures, cranial nerve entrapment (predominantly the optic nerve), bone marrow failure, hepatosplenomegaly, and recurrent infections.