Heritabilities of radiologic osteoarthritis in peripheral joints and of disc degeneration of the spine

Objective. To estimate the genetic influence on the occurrence of radiologi c osteoarthritis (ROA) in the knees, hips, and hands and disc degeneration of the spine in the general population. Methods. A random sample of 1,583 individuals was drawn to estimate the pre valence of ROA and disc degeneration in the general population. Of 118 prob ands with multiple affected joint sites who were derived from this sample, we were able to recruit 257 siblings. The variance of ROA and disc degenera tion within sibling pairs was compared with the variance between sibling pa irs. Heritability estimates for ROA in the knees, hips, and hands and for d isc degeneration of the spine were calculated. OA was defined according to radiologic criteria, using the Kellgren/Lawrence grading system. Results. We observed that hand ROA and disc degeneration of the spine were statistically significantly more frequent in siblings than in the random sa mple, whereas the prevalence of knee and of hip ROA was similar and lower, respectively. Heritability estimates for hand ROA and disc degeneration wer e statistically significant, P = 0.56 (95% confidence interval [95% CI] 0.3 4-0.76) and P = 0.75 (95% CI 0.30-1.00), respectively. For knee and hip ROA , no evidence of a genetic effect in the general population was found. Fina lly, the heritability estimate for a score that summed the number of joints affected in the knees, hips, hands, and spine was 0.78 (95% CI 0.52-0.98). All heritability estimates were adjusted for age, sex, body mass index, an d bone mineral density. Conclusion. The present study shows that in the general population, there i s a strong genetic effect for hand ROA and disc degeneration of the spine. The findings on the total number of joints affected at multiple sites sugge st genetic susceptibility to generalized OA.