“…Furthermore, one case-only study (Alioglu et al, 2009) and two family-based studies (McGlinchey et al, 2004;Kim et al, 2007) were also excluded. Finally, 21 studies (Szalai et al, 2001;Simeoni et al, 2004;Cermakova et al, 2005;McDermott et al, 2005;Bjarnadottir et al, 2006;Iwai et al, 2006;Cam et al, 2008;Bucova et al, 2008;Jemaa et al, 2008;Bucova et al, 2009a;Bucova et al, 2009b;Zhang et al, 2009;Zhong et al, 2010;van Wijk et al, 2010;El Mahgoub et al, 2011;Lin et al, 2012;Wang & Zhang, 2012;Yang et al, 2012;Xu et al, 2013;Kaur et al, 2013;Nasibullin et al, 2014) with a total of 8,735 cases and 12,300 controls were included in this meta-analysis. The process of the study selection and exclusion is shown in Figure 1.…”