CVS: cyclic vomiting syndrome; WPW: Wolff-Parkinson-Wight syndrome; CFS: chronic fatigue syndrome; DSM-5: Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition; ACTH: adrenocorticotropic hormone; MSH: melanocyte-stimulating hormone. The gene discussed is POMC; the disease is myalgic encephalomeyelitis/chronic fatigue syndrome.