This hypothesis is based on: a) the association of gender-specific social behavior with sexual hormones in healthy individuals [2]–[4]; b) the hypogonadal state caused by depression via HPA axis hyperactivity and suppression of GnRH secretion [52]; and c) these behavioral changes are more pronounced in the presence of SI, which supports a dose-response relationship with depression severity. This evidence concerns the gene GNRH1 and major depressive disorder.