Other studies have also found increased levels of pituitary, adrenal, thyroid and gonadal axis hormones (adrenocorticotropic hormone (ACTH), cortisol, and thyroid stimulating hormone (TSH), corticotropin-releasing hormone (CRH), thyrotropin-releasing hormone (TRH), Gonadotropin-releasing hormone (GnRH), total thyroxine 3 and 4 (TT4, and TT3)) and catecholamines (norepinephrine and epinephrine) in chronic insomnia patients, which seem to be correlated with insomnia severity [72, 64, 73]. This evidence concerns the gene POMC and insomnia.