Influence of familial factors on radiologic disease progression over two years in siblings with osteoarthritis at multiple sites: A prospective longitudinal cohort study

Objective The contribution of genetics to osteoarthritis (OA) progression is not known. To gain more insight into whether familial factors play a role in disease progression of OA, we analyzed familial aggregation of radiologic OA progression in a study of sibling pairs (the Genetics, Arthrosis, and Progression [GARP] study). Methods A total of 105 white probands and their 105 siblings with OA at multiple joint sites were included in a prospective cohort study. Radiologic progression of OA was defined as a 1‐point score increase in total scores for severity of joint space narrowing (JSN) or osteophytes on standardized radiographs of the hands, knees, and hips obtained at baseline and after 2 years. Odds ratios were calculated for siblings and probands sharing radiologic disease progression. Results A total of 100 probands and 93 siblings were followed for 2 years (median age 60 years, 80% women). In 92 sibling pairs both the proband and sibling had complete radiographic followup. Radiologic progression of JSN and osteophytes was present in 47% and 42% of the probands and 34% and 37% of the siblings, respectively. The odds ratios (95% confidence intervals), adjusted for age, sex, and body mass index, of a sibling having radiologic progression if the proband had progression were 3.0 (1.2–7.8) for JSN progression and 1.5 (0.6–3.6) for osteophyte progression. A dose‐response relationship was found between the amount of increase in JSN total scores among probands and the progression of JSN in siblings. Conclusion Familial factors played a role in the radiologic progression of JSN over 2 years in patients with OA at multiple sites.