Chotai et al. [71] investigating three SNPs—one in the tryptophan hydroxylase 1 (TPH1) gene (A218C), 5-HTTLPR L/S polymorphism, and the dopamine D4 receptor (DRD4) 7-repeat allele polymorphism—demonstrated that the frequency of the DRD4 7-repeat allele showed one-cyclic season of birth variation in women with schizophrenia. Here, DRD4 is linked to schizophrenia.