OPRM1 and migraine disorder: Second, other pain-related genetic polymorphisms, such as BDNF rs2049046 and G-712A reported in migraine studies (Azimova et al., 2013; Sutherland et al., 2014) or OPRM1 A118G reported in PDM study (Wei et al., 2017), might also be potential candidates of genetic modulators of chronic pain-sculpted brain complexity.