On the paradoxically high relative prevalence of osteogenesis imperfecta type III in the black population of South Africa.

In a survey of Black patients with osteogenesis imperfecta (OI) attending the Baragwanath Hospital, Johannesburg, the severe autosomal recessive OI type III was recognized in 21, of whom 18 lived in the Johannesburg area. By contrast only 5 had the ostensibly common mild autosomal dominant OI type I. The estimated minimum population frequency is 0.6 per hundred thousand for OI type III in this group and 0.1 per hundred thousand for OI type I. These figures are the reverse of those calculated for White Australians, where the ratio between OI type I and III is of the order of 7 to 1. This anomalous situation has important genetic and practical implications.