Autosomal dominant osteopetrosis type Ⅱ resulting from a de novo mutation in the CLCN7 gene: A case report

BACKGROUND Osteopetrosis is a family of extremely rare diseases caused by failure of osteoclasts and impaired bone resorption. Among them, autosomal dominant osteopetrosis type Ⅱ(ADO Ⅱ), related to the chloride channel 7(CLCN7) gene, is the most frequent form of osteopetrosis. In this study, we report a de novo mutation of CLCN7 in a patient without the family history of ADO Ⅱ.CASE SUMMARY A 5-year-old Chinese boy with ADO Ⅱ was found to have a de novo mutation in the CLCN7 gene [c.746 C>T(p.P249 L)]. Typical clinical manifestations, including thickening of the cortex of spinal bones and long bones, non-traumatic fracture of the femoral neck, and femoral head necrosis, were found in this patient. The patient is the first reported case of ADO Ⅱ with the missense mutation c.746 C>T(p.P249 L) of the CLCN7 gene reported in China. We also review the available literature on ADO Ⅱ-related CLCN7 mutations, including baseline patient clinical features, special clinical significance, and common mutations.CONCLUSION Our report will enrich the understanding of mutations in ADO Ⅱ patients. The possibility of a de novo mutation should be considered in individuals who have no family history of osteopetrosis.