OSTM1 and autosomal recessive osteopetrosis: The earliest examples of this were spontaneous mutations, such as the gray-lethal osteopetrotic mouse described in 1935 (27), which led some 60 years later to defining OSTM1 (Osteoclastogenesis Associated Transmembrane Protein 1) loss-of-function autosomal recessive osteopetrosis (28).