SLC6A4 and Menkes disease: Interestingly, the outcome of GWAS evidenced that the classical serotonergic and dopaminergic candidate genes, like transporters (SLC6A3 and SLC6A4) and receptors are not significantly associated with any psychiatric disorder (https://www.ebi.ac.uk/gwas/home), with one exception, DRD2, that was found associated with both MD and SCZ [25–27].