SLC6A3 and schizophrenia: There was a highly significant 45% decrease in DAT mRNA levels (F=17.73; df=55; P<0.0001) and also a significant 37% decrease in the levels of VMAT2 mRNA (F=6.54; df=54; P=0.014) in the substantia nigra of schizophrenia cases when compared with controls (Figures 3a and b).