5-HTTLPR genotype, asthma, diabetes and late-life depression in an older French population

Associations between environmental risk factors and depression have been reported to be stronger in people with the S allele of the S/L polymorphism in the serotonin transporter gene-linked promoter region (5-HTTLPR); however, most studies have focused on adverse life events as a general exposure, and interactions with physical disorders have been less investigated. We therefore investigated associations of asthma and diabetes with depression in an older community population and compared these by 5-HTTLPR genotype.

A sample of 1617 people aged 65 years and over, from Montpellier, France, were examined for depression, using the Center for Epidemiologic Studies Depression Scale and Mini International Neuropsychiatric Interview assessments, and a standardised interview was conducted to establish physical health status. Blood samples were also taken for 5-HTTLPR genotype.

Depression was significantly associated with asthma and diabetes but not with 5-HTTLPR genotype. After adjustment for age, sex, education and co-residency, the association between asthma and depression did increase in strength and significance across genotype groups (odds ratios in LL, SL and SS genotypes: 1.59 (0.66-3.82), 1.88 (1.05-3.36) and 3.00 (1.26-7.13), respectively) although the interaction term fell below statistical significance (p = 0.29). No modification was observed for diabetes as an exposure.

The findings provided some support for effect modification by 5-HTTLPR genotype for asthma but for not diabetes as risk factors for depression.