Serum lipids, such as triglycerides (TG) and high- and low-density lipoprotein cholesterol (HDL and LDL), are influenced by both genetic and lifestyle factors. Over 250 lipid loci have been identified,1-6 yet, it is unclear to what extent lifestyle factors modify the effects of these variants, or those yet to be identified. Smoking is associated with an unfavorable lipid profile,7,8 warranting its investigation as a lifestyle factor that potentially modifies genetic associations with lipids. Identifying interactions using traditional 1 degree of freedom (1df) tests of SNP x smoking terms may have low power, except in very large sample sizes. To enhance the detection of loci, a 2 degree of freedom (2df) test that jointly evaluates the interaction and main effects was developed.9
The Gene-Lifestyle Interactions Working Group, under the aegis of the Cohorts for Heart and Aging Research in Genomic Epidemiology (CHARGE) Consortium10, was formed to conduct analyses of lifestyle interactions in the genetic basis of cardiovascular traits. As both genetic and lifestyle factors differ across populations with different ancestry backgrounds, and to address the underrepresentation of non-European populations in genomic research, great effort went into creating a large, multi-ancestry resource for these investigations.11 Here, we report a genome-wide interaction study that uses both the 1df test of interaction and the 2df joint test of main and interaction effects to test the hypothesis that genetic associations of serum lipids differ by smoking status.