[Malignant infantile osteopetrosis: Case report of a 5-month-old boy].

Malignant infantile osteopetrosis is a rare congenital disease characterized by a dysfunction of osteoclasts followed by an abnormal bone densification. We report the case of a 5-month-old infant in whom this disease was suspected because of the clinical (hepatosplenomegaly, gingival hypertrophy), hematological (pancytopenia and hypocalcemia), and radiological criteria (abnormal bone density, periosteal reaction). The genetic investigation confirmed the diagnosis. Compound heterozygous mutations in the CLCN7 gene were identified, including an as yet undescribed mutation. The second mutation had already been described as being responsible for severe and irreversible neurological damage in patients with osteopetrosis. Since this patient presented severely delayed development, he was not eligible for bone marrow transplantation.