[Circadian rhythm and mood disorder].

Mood disorders show a common feature of distorted cycling of biological systems, manifesting, for example, as diurnal mood variation in depression, phasic time course in bipolar disorder, and seasonal mood swing in seasonal affective disorder. Accordingly, circadian dysfunction has been supposed to play an etiological role in mood disorders. Increasing evidence indicates that circadian misalignment between neuroendocrinological rhythm and the timing of sleep correlates with the severity of symptoms. In addition, several genetic studies have suggested that certain clock gene variants play a role in vulnerability to these disorders, and especially bipolar disorders. However, the role of circadian phenotypes and circadian genes in mood spectrum disorders remains unclear, although currently seem to have a pathoplastic rather than a pathogenetic effect.