COMT and myalgic encephalomeyelitis/chronic fatigue syndrome: It has been reported that subjects with CFS were distinguished by SNP markers in candidate genes that were involved in hypothalamic-pituitary-adrenal (HPA) axis function and neurotransmitter systems, including catechol-O-methyltransferase (COMT), 5-hydroxytryptamine receptor 2A (HTR2A), monoamine oxidase A (MAOA), monoamine oxidase B (MAOB), nuclear receptor subfamily 3; group C, member 1 glucocorticoid receptor (NR3C1), proopiomelanocortin (POMC) and tryptophan hydroxylase 2 (TPH2) genes [8-11].