Postpartum depressive symptoms and the BDNF Val66Met functional polymorphism: effect of season of delivery

Postpartum depression (PPD) is an often underdiagnosed and undertreated mood disorder, with negative impact on the mother's and infant's health. Seasonal variation has been discussed as a risk factor for PPD. Candidate genes, such as those encoding for the brain-derived neurotrophic factor (BDNF), serotonin transporter (5-HTT), and Period2 (PER2), have been associated with depression and seasonal disorders. The present study is aimed to examine whether functional polymorphic variants, BDNF Val66Met, 5-HTTLPR, or PER2 SNP 10870, are associated with PPD symptoms and whether these genetic polymorphisms interact with season in predicting PPD symptoms. This case-control study comprised of 275 women from a population-based cohort of delivering women in Sweden, who completed a questionnaire containing the Edinburgh postnatal depression scale (EPDS) at 6 weeks and 6 months postpartum. Stressful life events (SLEs) and maternity stressors were also assessed. The results did not reveal any statistically significant overall association between the studied genetic polymorphisms and PPD symptoms. However, a significant association between BDNF Met66 carrier status and development of PPD symptoms at 6 weeks postpartum, even when controlling for prepartum and postpartum environmental risk factors, was evident among mothers delivering during autumn/winter. No gene-gene interactions were found but a cumulative effect was detected with carriers of a greater number of 5-HTTLPR S and BDNFVal66Met Met alleles reporting higher EPDS scores, if delivered during autumn/winter. Our findings propose a role of the BDNF gene in the development of PPD symptoms, potentially mediated by season of delivery.