Osteogenesis imperfecta type III: an ancient mutation in Africa?

In a survey of institutions for crippled persons in Zimbabwe, 58 patients with osteogenesis imperfecta (OI) were identified; 42 had the rare OI Type III. The Shona and Ndebele people, who comprise the major tribal groups in Zimbabwe, both had a similar and relatively high gene frequency for this disorder. Both tribes were derived from common progenitors, but until 150 years ago had been geographically separated for 2 millenia. Subsequently, they have remained culturally and socially distinct. The implications are that the mutation for OI III in Africa occurred at least 2,000 years ago.