The genetic contribution to radiographic hip osteoarthritis in women - Results of a classic twin study

Objective, To assess the genetic contribution to radiographic hip osteoarth ritis (OA) by measuring the distribution of disease features in monozygotic (MZ) and dizygotic (DZ) twins, Methods. A population-based, cross-sectional study was conducted of 135 MZ and 277 DZ healthy female twin pairs, 50 years of age and older, who were r ecruited into the St. Thomas' UK Adult Twin Registry. Pelvic radiographs we re read by a single observer who was blinded to the pairing and zygosity of the twins. The films were assessed for overall OA grade using a modificati on of the Kellgren and Lawrence scheme, and assessed for individual radiogr aphic features. Results. There was evidence of significant familial clustering for grade I and grade II OA changes, with an excess concordance in MZ twins compared wi th DZ twins, suggesting a genetic effect. The MZ versus DZ excess was also apparent for those classified as having more severe disease, although the n umber of pairs with these disease features was small. Familial clustering a ttributable to genetic factors was evident for joint space narrowing of <2. 5 mm, Familial, but not genetic, clustering was seen for subchondral sclero sis, The number of pairs concordant for definite osteophytes in the sample was too low to assess this feature alone, These results translate into a si gnificant heritability of 58% for OA overall and 64% for joint space narrow ing. The heritability estimates decreased a little when the potential confo unding influences of age, body mass index, and hip bone density were taken into account. Conclusion. Genetic factors have a significant contribution to OA at the hi p in women and account for <similar to>60% of the variation in population l iability to the disease.