Autosomal recessive osteopetrosis-6 (OPTB6) is a bone disorder of intermediate severity characterized by radiologic findings in childhood or adolescence of cortical sclerosis of the pelvic bones, and band-like sclerosis in metaphyses and metadiaphyses of femora, tibiae, and fibulae, and in vertebral endplates ('rugger jersey spine'). 'Erlenmeyer flask' deformity of distal femora may be present (van Wesenbeeck et al., 2007). For a general phenotypic description and a discussion of genetic heterogeneity of autosomal recessive osteopetrosis, see OPTB1 (259700).