[Diagnostic features, epidemiology, and pathophysiology of seasonal affective disorder]

Seasonal Affective Disorder (SAD) is characterized by patterns of major depressive episodes that occur and remit with the change of seasons. Two seasonal patterns have been identified: summer-type depression with typical depressive signs and symptoms, and winter-type depression with atypical features of depression. In the subsyndromal form of SAD (S-SAD) symptoms are milder, although vegetative symptoms are clinically significant. SAD needs to be differentiated from atypical depression, cyclothymic disorder, and dysthymia or chronic MDD which may be characterized by a winter worsening of symptoms. Full remission of symptoms must occur after the passing of the season for the disorder to merit the diagnosis of SAD. The mean prevalence of SAD in the temperate zone is 3 to 10%, while that of S-SAD is 6 to 20%. In Hungarian general population the occurrence of SAD is 4.6%, and S-SAD is 7.2%. The pathophysiology of SAD seems to be heterogeneous, studies suggest abnormal circadian rhythm and neurotransmitter function (phase shift hypothesis, role of serotonin, dopamin and norepinephrine). Genetic studies focusing on candidate genes involve 5-HTR2A, 5-HTR2C, DRD4, G protein, and clock-related genes.