A case of autosomal dominant osteopetrosis type II with a novel TCIRG1 gene mutation

Osteopetrosis is a rare genetic disorder characterized by increased bone mineral density (BMD) due to osteoclast failure. T-cell immune regulator 1 (TCIRG1) plays crucial roles on osteoclast function, and its mutation causes autosomal recessive osteopetorosis. However, mutations in TCIRG1 have never been identified in autosomal dominant osteopetrosis (ADO). A 3-year-old boy was first presented to the clinic because of spontaneous radius and femur fractures. He has optic atrophy. The areal BMD at the lumbar spine was 1274 g/cm (233% of normal). Laboratory tests revealed no remarkable abnormal findings, including anemia, except for extremely elevated serum tartrate-resistant acid phosphatase-5b (14,600 mU/dL). Radiographically, the skull base, pelvis, and vertebrae showed a focal sclerosis. Genetic analysis revealed a novel heterozygous missense mutation (His242Arg). Taken together with the mutation, his mild clinical features were diagnosed as ADO. This case implies that TCIRG1 could become a genetic candidate for ADO in addition to malignant forms such as ARO.