Primary osteoarthritis of the hip in monozygotic and dizygotic male twins.

Population and total hip replacement surveys show that primary osteoarthritis of the hip is uncommon in African Americans and rare in Asians, suggesting a genetic basis for this disease. We studied genetic influences on primary osteoarthritis of the hip by estimating monozygotic (MZ) and dizygotic (DZ) twin correlations using a two-stage data collection. A total of 6419 male veteran twins of the NAS-NRC Twin Registry, born between 1917 and 1927, were contacted by telephone (first stage). Telephone interview determined that 2% reported a total hip replacement for arthritis rather than fracture. X-rays of twin pairs in which one twin had undergone total hip replacement were sought and reviewed (second stage), and concordance for primary arthritis was determined based on x-ray diagnosis. Heritability of primary osteoarthritis, Kellgren & Lawrence Grade II and higher, was estimated using a covariance structure analysis for 2-stage data. The best-fitting model included only components for additive genetics and for unique environment. Additive genetics accounted for 53% (95% confidence interval 30-72%) in the liability for self reported hip replacement surgery and unique environment for the remaining 47% (95% confidence interval 28-70%). Additive genetics accounted for 61% (95% confidence interval 18-86%) of the variance in liability for x-ray determined primary osteoarthritis with unique environment accounting for the remaining 39%. These data establish a genetic influence on primary osteoarthritis of the hip in male twins and suggest that further work is indicated to isolate the genes responsible for this disease.