Investigating the aspartic acid (D) repeat of asporin as a risk factor for osteoarthritis in a UK Caucasian population

Objective. A compelling genetic association with osteoarthritis (OA) of 2 functional alleles in the aspartic acid (D) repeat of the asporin gene was recently reported in a Japanese population. Allele D13 of the repeat encoded OA protection, whereas allele D14 encoded OA susceptibility. The 2 alleles mediate differences in the capacity of asporin to inhibit the cartilage growth factor transforming growth factor 6, with the D14 allele being a particularly potent inhibitor. Our objective was to assess whether the D repeat is associated with OA in UK Caucasians. Methods. The repeat was genotyped in 1,247 patients who had undergone elective joint replacement of the hip or the knee due to end-stage primary OA and in 748 age-matched controls. Results. The D13 allele was more common in controls, and the D14 allele was more common in patients. However, this trend was significant only for men who had undergone hip replacement (P = 0.016, odds ratio 1.48, 95% confidence interval 1.09-2.01). Conclusion. Our data suggest that the asporin polymorphism is not a major influence on OA etiology in Caucasians. The results of our study do not question the veracity of the Japanese report. Instead, our study highlights the complex, heterogeneous nature of OA genetic susceptibility.