In addition to sensitivity to estrogen and progesterone fluctuations, biological theories have demonstrated that other changes, such as those of gonadal hormones but also neuroactive steroid levels after birth, altered cytokines and hypothalamic–pituitary–adrenal (HPA) axis hormones fluctuations, acid-altered fats, and oxytocin and arginine vasopressin levels are involved in the production of PPD onset in predisposed women [21,22]. This evidence concerns the gene OXT and progressive pseudorheumatoid arthropathy of childhood.