Previous studies have investigated family structure and serotonergic genes as separate risk factors for depression. An Italian research team has now reported findings on the interplay between these risk factors. To investigate this interplay, Nobile et al. (2009) tested the effects of two-parent vs. one-parent family structure and two serotonergic polymorphisms (TPH2 G-703T and 5-HTTLPR) on CBCL DSM-oriented Affective Problems scale scores in Italian 10- to 14-year-olds. One sample (N = 441) was from the Italian Project on Pre-adolescent Mental Health (PrISMA). The second sample (N = 166) was from a longitudinal study of emotional and behavioral problems. For both samples, parents completed the CBCL and a sociodemographic form that included information about marital status. Genomic DNA was extracted from mouthwash samples. Nobile et al. found that one-parent family structure, the “G” variant of the TPH2 G-703T gene, and the “short” allele of the 5-HTTLPR gene were each associated with significantly elevated scores on the Affective Problems scale.
Consistent with genetic theory, each genetic effect was small, whereas the family structure effect was larger than either of the genetic effects. In testing interactions between effects of genes and family structure, Nobile et al. found that children obtained significantly higher Affective Problem scores if they had the G variant of the TPH2 gene or if they had the 5-HTTLPR short allele only if they lived in one-parent rather than two-parent families. These findings were confirmed even after taking account of SES, Internalizing scores, and an alternative definition of the 5-HTTLPR gene. The authors pointed out that one-parent families may not represent exclusively environmental risk factors, as they could be associated with genetic risk factors The authors also pointed out that the findings could differ in populations having different proportions of one-parent families, which would argue for replicating the research in additional populations.
Nevertheless, the findings certainly suggest important interactions between effects of genes and of family structure on the problems measured by the CBCL DSM-oriented Affective Problems scale.
Reference: Nobile, M., Rusconi, M., Bellina, M., Marino, C., Giorda, R., Carlet, O., Vanzin, L., Molteni, M., & Battaglia, M. (2009). The influence of family structure, the TPH2 G-703T and the 5-HTTLPR serotonergic genes upon affective problems in children aged 10-14 years. Journal of Child Psychology and Psychiatry, 50, 317-325.