Mood and anxiety disorders are common psychiatric illnesses and epidemiological and clinical data point to high comorbidity between depression and anxiety disorders that may reflect shared pathophysiological mechanisms (Kessler et al., 2008; Lamers et al., 2011), including dysfunctional regulation of circadian clock gene expression (Gouin et al., 2010; Lavebratt et al., 2010; Valenzuela et al., 2016). The gene discussed is CLOCK; the disease is major depressive disorder.