MTHFR and schizophrenia: Finally, single nucleotide polymorphisms (SNPs) can be also implicated in the etiology of schizophrenia: two SNPs in the promoter region of the α1A-adrenergic receptor (ADRA1A) gene [101], or interactive effect of α2A-adrenergic receptor (ADRA2A) gene polymorphism and methylenetetrahydrofolate reductase (MTHFR) gene polymorphism [102], which may additionally aggravate the low-dopamine state [103].