The mixed evidence for methylation of dopamine transporter genes in SZ – including hypermethylation of DAT1 [30], hypomethylation of SCL6A3 [37] and differential methylation of SLC18A2 [27], is interesting in the context of previous evidence of genome-wide differential methylation of GFRA2 in SZ [28], a receptor for glial cell-derived neurotrophic factor (GDNF) which manages dopaminergic neuronal maintenance while also being implicated in SZ and BD [57, 58]. Here, GDNF is linked to Behcet disease.