GENETIC INFLUENCES ON OSTEOARTHRITIS IN WOMEN - A TWIN STUDY

Objectives-To assess the relative contribution of genetic and environm ental factors to common forms of osteoarthritis of the hands and knees . Design-Classic twin study with unselected twins who were screened ra diologically for osteoarthritis. Subjects-130 identical and 120 non-id entical female twins aged 48-70 recruited from a London based twin reg ister and through a national media campaign. Main outcome measures-Sim ilarity in identical compared with non-identical twin pairs for radiog raphic changes at the interphalangeal and first carpometacarpal joints of the hands and the tibiofemoral joint and patellofemoral joint of t he knee expressed as intraclass correlations. Results-The intraclass c orrelations of radiographic osteophytes and narrowing at most sites an d the presence of Heberden's nodes and knee pain were higher in the id entical pairs. The intraclass correlation of the total radiographic os teoarthritis score in identical pairs (rMZ) was 0.64 (SE 0.05) compare d with 0.38 (0.08) in non-identical pairs. The proportion of genetic v ariance of total osteoarthritis score (osteophytes and narrowing) with modelling techniques was estimated at 0.54 (95% confidence interval 0 .43 to 0.65) and ranged from 0.39 to 0.65 for different sites and feat ures (P<0.001) after adjustment for age and weight. Conclusions-These results demonstrate for the first time a clear genetic effect for radi ographic osteoarthritis of the hand and knee in women, with a genetic influence ranging from 39-65%, independent of known environmental or d emographic confounders. The results of this study should lead to furth er work on isolating the gene or genes involved in the pathogenesis of this common disabling disease.