Many human traits exhibit sexual dimorphism, where the prevalence and perhaps etiology differs between men and women. When the effect of a genetic risk factor on a trait or disease is significantly different in men and women, gene by sex interaction exists. The McCarthy lab is involved in characterizing gene by sex interaction in the etiology of lipid disturbances and metabolic syndrome. Using a combination of epidemiological and genomic approaches applied to human populations, we are studying the genome-wide occurrence of gene by sex interaction for dyslipidemias, and the mediating effects of sex hormones on these interactions. A major focus of our work is the dyslipidemia associated with chronic hepatitis C virus (HCV) infection, where infected individuals experience a decline in all lipids, especially ApoB-containing lipoproteins. We have found that lipid response to HCV infection is a sexually dimorphic trait and are working closely with Duke GI/Hepatologist John McHutchison to explore the link between host genetic variation, HCV dyslipidemia and clinical outcomes of HCV, and the underlying basis of observed sexual dimorphism of HCV outcomes.