The genetic relationship between cannabis and tobacco cigarette use in European- and African-American female twins and siblings

Abstract

BackgroundUse of cigarettes and cannabis frequently co-occurs. We examine the role of genetic and environmental influences on variation in and covariation between tobacco cigarette and cannabis use across European-American (EA) and African-American (AA) women. MethodsData on lifetime cannabis and cigarette use were drawn from interviews of 956 AA and 3557 EA young adult female twins and non-twin same sex female full siblings. Twin modeling was used to decompose variance in and covariance between cigarette and cannabis use into additive genetic, shared, special twin and non-shared environmental sources. ResultsCigarette use was more common in EAs (75.3%, 95% C.I. 73.8–76.7%) than AAs (64.2%, 95% C.I. 61.2–67.2%) while cannabis use was marginally more commonly reported by AAs (55.5%, 95% C.I. 52.5–58.8%) than EAs (52.4%, 95% C.I. 50.7–54.0%). Additive genetic factors were responsible for 43–66% of the variance in cigarette and cannabis use. Broad shared environmental factors (shared+special twin) played a more significant role in EA (23–29%) than AA (2–15%) women. In AA women, the influence of non-shared environment was more pronounced (42–45% vs. 11–19% in EA women). There was strong evidence for the same familial influences underlying use of both substances (rA=0.82–0.89; rC+T=0.70–0.75). Non-shared environmental factors were also correlated but less so (rE=0.48–0.66). No racial/ethnic differences were apparent in these sources of covariation. ConclusionHeritability of cigarette and cannabis use is comparable across racial/ethnic groups. Differences in the contribution of shared and non-shared environmental influences indicate that different factors may shape substance use in EA and AA women.