Chunk #9 — Three examples of misspecified models in the G×E literature — Kaufman et al., 2004: A gene-by-environment or an ethnicity-by-environment interaction?
Using a mixed-ethnicity sample (32% African American, 22% biracial, and 46% non-African American; n=104), Kaufman et al. (20) reported results showing that the depressogenic effect of a repeat polymorphism (short/long [s/l]) at the serotonin-transporter- linked polymorphic region (5HTTLPR) depended on childhood maltreatment and on social support. I focus first on the two-way 5HTTLPR-by-maltreatment interaction they describe. The investigators included ethnicity (the ancestral proportion score), age, and gender in the regression equation “given the relevance of these potential confounding variables in interpreting the study results,” (p. 17318). The test of the 5HTTLPR-by-maltreatment interaction was significant (p=.007), and this effect was primarily due to maltreated individuals with the s/s allele having significantly higher depression scores. However, as noted by the investigators, African Americans have a significantly higher frequency of the long repeat allele compared to non-African Americans. If, due to cultural norms, maltreated African Americans are less likely to report depression than maltreated non-African Americans, some or all of the detected G×E interaction may have been due to ethnicity moderating the effect of maltreatment. Somewhat less plausibly, it is also possible that
