Since their identification in 1958 (2), continuing efforts have been undertaken to advance the understanding of PDE biology and function, and PDE have been considered pharmacological targets in various diseases, such as pulmonary diseases like COPD and asthma, depression, schizophrenia, erectile dysfunction, and autoimmune disease like psoriasis/psoriasis arthritis and rheumatoid arthritis (8, 100, 121–125). The gene discussed is ALDH7A1; the disease is major depressive disorder.