MTHFR and psychotic disorder: Evidence from recent meta-analyses on schizophrenia suggested that MTHFR 677T, in particular the TT genotype (Lewis et al., 2005; Gilbody et al., 2007), confers susceptibility to psychosis, although there appears to be considerable study heterogeneity (Allelic odds ratio (OR): I2 = 52% to 57%; Allen et al., 2008; Shi et al., 2008).