Having this in mind, we first conducted a systematic search in the PubMed database by including the complete name of each PD: “Schizophrenia”, “Depression”, “Bipolar Disorder”, “Borderline Personality Disorder”, “Obsessive Compulsive Disorder”, “Autism Spectrum Disorder”, and “Attention Deficit and Hyperactivity Disorder”, followed by insulin-like growth factor “IGF”. This evidence concerns the gene IGF1 and major depressive disorder.