Some of the susceptibility genes, such as cAMP responsive element binding protein 1 (CREB1) in males, affect the core component of depressive disorder with depressive mood and anhedonia (unrelated to sleep disturbance), whereas others, such as tryptophan hydroxylase 2 (TPH2) or glutamate decarboxylase 1 (GAD1) in females, are more strongly associated with mood disorder only when accompanied with disturbed sleep [56]. Here, GAD1 is linked to depressive disorder.