Genetic risks in Perthes' disease.

A population study of Perthes' disease in South Wales over a 25-year period has shown a low risk of the disorder in relatives. The risk of Perthes' disease in sibs is under 1% (2 in 323), while the risk to children of an children of an affected parent is about 3% (1 in 35) when adjusted for age of onset. No increased risk was found in relatives of patients with bilateral as compared with unilateral Perthes' disease. A mating between two affected individuals resulted in monozygotic twins concordant for Perthes' disease, but no familial concentration to suggest the action of a single major gene was found. The importance of excluding generalised disorders which may mimic Perthes' disease and may show Mendelian inheritance is emphasised, but it is concluded that true Perthes' disease has a relatively minor genetic component.