Perthes' disease: a new genetic hypothesis.

We describe the sex and age distributions of the onset of Perthes' disease in our own and six other large published series. The mathematical features of these distributions, together with the evidence for familial aggregations, agree with the theory that the disease is autoaggressive in aetiology and that two genetically-distinctive groups are at risk. We consider the frequency of affected sides - left, right, bilateral - in our own and other series: concordance for affected side(s) within sibships suggests that laterality might be genetically determined. Following Gray et al. we believe that predisposition to the disease is polygenic and we propose a simple scheme - involving an X-linked "recessive" factor and an autosomal homozygous allele in each genotype - that is reasonably consistent with the slender evidence.