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).

Osteosclerotic metaphyseal dysplasia (OSMD) is a rare condition characterized by distinctive radiographic changes, including osteosclerosis localized predominantly to the metaphyses of the long bones. The shafts of the long bones are osteopenic. Laboratory abnormalities include elevated alkaline phosphatase levels in some, but not all, patients. Elevated urinary pyridinoline and deoxypyridinoline levels, markers of osteoclastic activity, have also been reported (Nishimura and Kozlowski, 1993; Kasapkara et al., 2013; Guo et al., 2017). Patients with OSMD have been described who also show hypotonia, developmental delay, seizures, and later-onset spastic paraplegia; however, OSMD resulting from mutation in the LRRK1 gene does not appear to include these neurologic features (Nishimura and Kozlowski, 1993; Kasapkara et al., 2013; Guo et al., 2017). Reviews Howaldt et al. (2020) reviewed published reports of LRRK1-associated OSMD, and noted that patients typically present with recurrent pathologic fractures and osteosclerosis at multiple skeletal sites, predominantly at the metaphyses and vertebral bodies. Variable degrees of osteosclerosis of ribs and skull and of Erlenmeyer flask deformity of the femurs have been observed.