Rees et al. (1995) described the cases of a female infant who died at 9 months of age and her infant brother who died at the age of 1 month with features combining those of infantile osteopetrosis (see ... Rees et al. (1995) described the cases of a female infant who died at 9 months of age and her infant brother who died at the age of 1 month with features combining those of infantile osteopetrosis (see OPTB1, 259700) and infantile neuroaxonal dystrophy (256600). The sibs were born of nonconsanguineous Caucasian parents. Infantile osteopetrosis was diagnosed in the first child shortly after delivery. CT scan of the head revealed agenesis of the corpus callosum. Postmortem examination demonstrated cerebral atrophy, absence of the corpus callosum, and a small hippocampus. Neuroaxonal spheroids were found in parts of the central nervous system and in peripheral nerves. The second child was delivered at 36 weeks' gestation because of intrauterine fetal distress. The diagnosis of osteopetrosis and partial agenesis of the corpus callosum was made shortly after delivery. Cases combining axonal dystrophy and osteopetrosis were reported by Ambler et al. (1983), Fitch et al. (1973), and Jagadha et al. (1988). This may represent a distinct single-gene disorder inherited as an autosomal recessive. Alternatives are that it is a pleiotropic manifestation of the gene responsible for either infantile neuroaxonal dystrophy or infantile osteopetrosis or that it represents a contiguous gene syndrome combining features of the 2 recessive disorders.