Serotonergic mechanisms are thought to play an important role in the pathogenesis of seasonal affective disorder (SAD). The expression of the serotonin transporter (5-HTT) is regulated in part by an insertion/deletion polymorphism in the serotonin transporter gene promoter region (5-HTTLPR). The 5-HTTLPR short allele (s) has been associated with anxietyrelated personality traits and depression, and one study observed an association between the 5-HTTLPR s-allele and SAD and the trait of seasonality. We genotyped 138 SAD patients and 146 healthy volunteers with low seasonality for 5-HTTLPR. No difference between patients and controls was found for genotype distribution and s-allele frequency. However, genotype distribution and allele frequencies were strongly associated with DSM-IV depression subtypes. Melancholic depression was associated with the 5-HTTLPR long (l) allele and atypical depression with the 5-HTTLPR s-allele (two-sided Fisher's exact test: genotype distribution: P¼0.0038; allele frequencies: P¼0.007). Our data are compatible with the hypothesis of a disease process that is not causally related to 5-HTTLPR, but involves 5-HT neurotransmission and 5-HTTLPR somewhere on its way to phenotypic disease expression. Molecular Psychiatry (2003) 8, 942-946. doi:10.1038/sj.mp.4001392Keywords: melancholic; atypical; mood disorders; nosology; genetics Although the impact of seasons on the incidence of mood disorders has been known since ancient times, only in the 1980s of our century seasonal affective disorder (SAD) has been described as a distinct nosologic entity. 1 Typically, patients with SAD, winter type, fulfill the diagnostic criteria for recurrent major depressive or bipolar disorder according to DSM-IV criteria and suffer from depressive episodes during fall and winter, alternating with remission or hypomania/mania in spring and summer. Common symptoms in SAD include depressed mood and the so-called atypical or reverse neurovegetative symptoms, such as hypersomnia, hyperphagia, fatigue, carbohydrate craving, and subsequent weight gain. The tendency to experience seasonal variations in mood, feeding behavior, energy, and social activity has been termed seasonality and can be measured using the global seasonality score (GSS). Although the etiology of SAD is still unclear, a substantial heritable component in seasonality has been shown in twin studies.2,3 A solid body of literature suggests involvement of serotonin (5-HT) in the pathogenesis of SAD. 4 Serotonergic parameters, including central 5-HTT availability, 5 hypothalamic 5-HT concentrations, and peripheral serotonergic parameters 6 show seasonal fluctuations. A variety of research parameters, such as the tryptophan depletion paradigm, 7 hormonal challenge studies, 8 and in vivo imaging of central 5-HTT availability 9 have shown alterations in serotonergic parameters in depressed patients with SAD. Some studies also suggest that serotonergic alterations may be trait markers in SAD.7 Genes involved in serotonergic neurotransmission are thus good cand...

Decreased synaptic serotonin during depressive episodes is a central element of the monoamine hypothesis of depression. The serotonin transporter (5-HTT, SERT) is a key molecule for the control of synaptic serotonin levels. Here we aimed to detect state-related alterations in the efficiency of 5-HTT-mediated inward and outward transport in platelets of drug-free depressed patients suffering from seasonal affective disorder (SAD). 5-HTT turnover rate, a measure for the number of inward transport events per minute, and tyramineinduced, 5-HTT-mediated outward transport were assessed at baseline, after 4 weeks of bright light therapy, and in summer using a case-control design in a consecutive sample of 73 drug-free depressed patients with SAD and 70 nonseasonal healthy controls. Patients were drug-naive or medication-free for at least 6 months prior to study inclusion, females patients were studied in the follicular phase of the menstrual cycle. All participants were genotyped for a 5-HTT-promoter polymorphism (5-HTTLPR) to assess the influence of this polymorphism on 5-HTT parameters. Efficiency of 5-HTT-mediated inward (p ¼ 0.014) and outward (p ¼ 0.003) transport was enhanced in depressed patients. Both measures normalized toward control levels after therapy and in natural summer remission. Changes in outward transport showed a clear correlation with treatment response (r ¼ 0.421, p ¼ 0.001). Changes in inward transport were mediated by changes in 5-HTT transport efficiency rather than affinity or density. 5-HTTLPR was not associated with any of the 5-HTT parameters. In sum, we conclude that the 5-HTT is in a hyperfunctional state during depression in SAD and normalizes after light therapy and in natural summer remission.

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