The genetic relationship between cannabis and tobacco cigarette use in European and African American female twins and siblings.
BACKGROUND Use 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. METHODS Data 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. RESULTS Cigarette 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. CONCLUSION Heritability 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.
Drug and alcohol dependence