TPH2 and depressive disorder: In addition, several single nucleotide polymorphisms in the human TPH2 gene have been associated with major depression (e.g., R441H; [40,41]) and alcoholism (e.g., intron variant rs1386496; [42,43]); however, other investigators have failed to find the link between TPH2 gene variants and depression (for review [41]) or alcohol dependence [44,45].