This study examined whether the 5-HTTLPR polymorphism in the SLC6A4 gene is associated with self-reported symptoms of depressed mood in first-year university students with a persistent pattern of short sleep.
Students provided DNA samples and completed on-line sleep diaries and a mood scale during the first semester. A priori phenotypes for nocturnal sleep and mood scores were compared for the distribution of genotypes.
Brown University, Providence, Rhode Island.
A sample of 135 first-year students, 54 male, 71 Caucasian, mean age 18.1 (± 0.5) yr.
Students completed on-line sleep diaries daily across the first term (21-64 days; mean = 51 days ± 11) and Center for Epidemiologic Studies-Depression (CES-D) mood scale after 8 wk. DNA was genotyped for the triallelic 5-HTTLPR polymorphism. Low-expressing S and LGpolymorphisms were designated S′, and high-expressing LA was designated L′. Phenotype groups were identified from a combination of CES-D (median split: high > 12; low < 13) and mean nocturnal total sleep time (TST) from diaries: (shorter ≤ 7 hr; longer ≥ 7.5 hr). Three genotypes were identified (S′S′, S′L′, L′L′); the S′S′ genotype was present in a higher proportion of Asian than non-Asian students.
Four phenotype groups were compared: 40 students with shorter TST/high CES-D; 34 with shorter TST/low CES-D; 29 with longer TST/high CES-D; 32 with longer TST/low CES-D. Female:male distribution did not vary across phenotype groups (chi-square = 1.39; df = 3; P = 0.71). S′S′ participants (n = 23) were overrepresented in the shorter TST/high CES-D group (chi- square = 15.04; df = 6; P < 0.02). This association was sustained after removing participants with preexisting evidence of depressed mood (chi-square = 12.90; df = 6; P = 0.045).
These data indicate that young adults who reported shorter nocturnal sleep and higher depressed mood are more likely than others to carry a variant of the SLC6A4 gene associated with low expression of the serotonin transporter.
Carskadon MA; Sharkey KM; Knopik VS; McGeary JE. Short sleep as an environmental exposure: a preliminary study associating 5-HTTLPR genotype to self-reported sleep duration and depressed mood in first-year university students. SLEEP 2012;35(6):791-796.