↓ α-Klotho levels in MDD ↔ α-Klotho levels in elderly recurrent and young MDD patients (vs. control)Earlier onset age, higher plasma α-Klotho levels, and lower HAMD scores in young MDD↑ α-Klotho levels in rs9315202 T alleles carrier regardless age or sexNegative correlation between the rs9315202 T allele and disease severity in the elderly MDD patients. This evidence concerns the gene KL and major depressive disorder.