Odds ratios for subjects with different numbers of risk alleles for knee OA. Effects of the number of ASPN, GDF5, and DVWA susceptibility risk alleles on knee osteoarthritis (OA) risk. Odds ratios (ORs) and their 95% confidence intervals according to the number of risk alleles were calculated by using a logistic regression model adjusted for gender, age, and body mass index. We set the control group as subjects who have zero or one risk allele. Each additional risk allele increased the OR by 1.22 (95% CI, 1.11 to 1.34), which indicated the cumulative effects of the three alleles on knee OA.