CLOCK and major depressive disorder: There is also a strong genetic component underlying many mood disorders,9, 10 and there have been a few tantalizing suggestions of links between clock gene polymorphisms and bipolar disorder.11, 12, 13 Nevertheless, most association studies to date have concluded that genetic associations between circadian clock gene variants and MDD are weak at best.4, 11, 12, 13, 14, 15 However, in psychiatric disorders such as MDD, bipolar disorder, schizophrenia and so on, phenotyping the overt manifestations of the disorder may lead to misleading interpretations of etiology.