KL and major depressive disorder: This hypothesis is supported by the KL-VS heterozygous genotype only favorable for survival in old people, not in centenarian (27) or young controls (21).While limited investigations focused on the anti-aging factor of Klotho and treatment response in MDD, whether the Klotho SNPs distribution contribute α-Klotho protein expression and disease severity in MDD patients of different ages is still unknown.