Serotonin transporter polymorphism modifies the association between depressive symptoms and sleep onset latency complaint in elderly people: results from the 'InveCe.Ab' study

Previous studies have documented the involvement of the central nervous system serotonin in promoting wakefulness. There are few and conflicting results over whether there is an actual association between bearing the short allele of serotonin transporter promoter polymorphism (5-HTTLPR) and worse sleep quality. This study examined whether sleep onset latency complaint is associated with the 5-HTTLPR triallelic polymorphism in the SLC6A4 gene promoter and whether this polymorphism influences the relationship between sleep onset latency complaint and depressive symptoms in elderly people. A total of 1321 community-dwelling individuals aged 70-74 years were interviewed for sleep onset latency complaint and for sleep medication consumption. Participants' genomic DNA was typed for 5-HTTLPR and rs25531 polymorphisms. Depressive symptoms were evaluated with the Geriatric Depression Scale Short form and general medical comorbidity was assessed by the Cumulative Illness Rating Scale. The presence of a past history of depression was recorded. The S' allele of the 5-HTTLPR triallelic polymorphism was associated with sleep onset latency complaint. This association was maintained after adjusting for depressive symptoms, sex, age, history of depression and medical comorbidity. After stratification for 5-HTTLPR/rs25531, only in S'S' individuals high depressive symptoms were actually associated with sleep onset latency complaint. These data indicate that the low-expressing 5-HTTLPR triallelic polymorphism is an independent risk factor for sleep onset latency disturbance. Furthermore, the 5-HTTLPR genotype influences the association between depressive symptoms and sleep onset latency complaint.