Nature vs nurture in knee osteoarthritis - the importance of age, sex and body mass index.

OBJECTIVE

(1) To estimate the life-time genetic contribution for knee osteoarthritis (OA) surgery and (2) to explore any differences in the genetic contribution across age, sex and body mass index (BMI).

METHODS

We studied the sex-specific genetic contribution to knee OA surgery in a prospective cohort study of 62,490 twins aged 35 years or older with a follow-up period of up to 47 years (10,092 identical and 21,153 non-identical twin pairs, 54% women). To study interactions with age, we graphed the heritabilities over the lifespan for men and women. We also studied the sex-specific heritability across strata of the median BMI to explore any interactions with BMI.

RESULTS

The overall heritability of knee OA surgery was 0.53 (95% confidence intervals [CI] = 0.31-0.75), with higher heritability among women (H = 0.80 (95% CI = 0.73-0.87)) than men (H = 0.39 (95% CI = 0.10-0.69)). For men, the heritability started to rise after age 68. The genetic contribution was particularly low in men above median BMI (H = 0.08, 95% CI = -0.32-0.48). For women, the heritability was consistently high from age 50 to death, independently of BMI (H = 0.77, 95% CI = 0.66-0.87).

CONCLUSION

There is a higher and more consistent genetic contribution for knee OA surgery in women than men. In men the genetic contribution was relatively low and varied with age and BMI.