Association of allelic and genotypic frequencies in TPH2 in MDD patients [37,41], a study related to gender base do not show a significant result in TPH2 gene effect on susceptibility of MDD [42,43], another study target single locus and haplotype analysis didn’t show any association while targeting SNP rs7305115 in Japanese population [44]. This evidence concerns the gene TPH2 and major depressive disorder.