Vice versa, it has also been suggested that mood disorders affect the functioning of the hypothalamic-pituitary-thyroid (HPT) axis, as illustrated by a blunted thyrotropin (TSH) response to thyrotropin-releasing hormone (TRH) stimulation, and a decreased amplitude of the nocturnal TSH surge in patients with MDD (15–17). This evidence concerns the gene TRH and mood disorder.