Partial replication of two rumination-related candidate gene studies.

Two recent papers associated candidate genes with brooding rumination, a possible cognitive endophenotype for depression, in children ages 8-14 years. Stone et al. reported that BDNF val66met polymorphism predicted brooding in adolescence. Woody et al. reported that children carrying at least one copy of a CRHR1 TAT haplotype reported less brooding than their peers in the presence of maternal depression. We attempted to replicate and extend these findings in a sample of twins aged 12-16 years. We analyzed the BDNF val66met (rs6265) polymorphism and two (rs242924 and rs7209436) out of three single nucleotide polymorphisms (SNPs) that Woody et al. used to create a CRHR1 haplotype. We controlled for maternal history of depression and clustering within families. Unlike Stone et al., we found higher brooding among BDNF Met carriers. This main effect was qualified by an interaction with pubertal status, with the effect driven by more physically mature participants. Similar to Woody et al., we found an interaction between CRHR1 SNPs and maternal depression, with the homozygous minor genotype acting as a protective factor against brooding in the presence of maternal depression. Findings provide partial support for the influence of candidate genes in two environmentally sensitive systems on brooding.