Association between DAZL polymorphisms and susceptibility to male infertility: systematic review with meta-analysis and trial sequential analysis

Several studies have investigated the association between polymorphisms in the Deleted in AZoospermia-Like (DAZL) gene and male infertility risk, but with inconsistent results. We aimed to derive a more precise estimation of the relationship, therefore a meta-analysis was performed. A total of 13 case-control studies, including 2556 cases and 1997 controls, were selected. Two polymorphisms in DAZL were investigated, namely T12A (Thr12 -> Ala) and T54A (Thr54 -> Ala). Our meta-analysis showed that A > G is a risk factor for male infertility (P = 0.047, OR = 1.262, 95% CI = 1.003-1.587). However, when using trial sequential analysis (TSA) to confirm, we found that A > G risk effect turned out to be false positive. In addition, significant association was found between the T54A polymorphism and male infertility under co-dominant model (AG vs. AA: OR = 4.364, 95% CI = 2.207-8.630, P < 0.001) and dominant model (OR = 4.584, 95% CI = 2.320-9.058, P < 0.001). Stratified analysis showed that significantly strong association between T54A polymorphism and male infertility was present only in Asians, but not in Caucasians. Further studies of T12A and T54A with their biological functions are needed to understand the role of these polymorphisms in the development of male infertility.