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



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.



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.



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.
Washington University School of Medicine, Department of Psychiatry, 660 S. Euclid, CB 8134, Saint Louis, MO 63110, USA. Electronic address: arpana@wustl.edu.
Arpana
A
Agrawal
Washington University School of Medicine, Department of Psychiatry, 660 S. Euclid, CB 8134, Saint Louis, MO 63110, USA.
Julia D
JD
Grant
King's College, Department of Addictions, London, UK.
Michael T
MT
Lynskey
Washington University School of Medicine, Department of Psychiatry, 660 S. Euclid, CB 8134, Saint Louis, MO 63110, USA.
Pamela A F
PA
Madden
Washington University School of Medicine, Department of Psychiatry, 660 S. Euclid, CB 8134, Saint Louis, MO 63110, USA.
Andrew C
AC
Heath
Washington University School of Medicine, Department of Psychiatry, 660 S. Euclid, CB 8134, Saint Louis, MO 63110, USA.
Kathleen K
KK
Bucholz
Yale University School of Medicine, Department of Psychiatry, New Haven, CT, USA.
Carolyn E
CE
Sartor
D000293:Adolescent; D001741:Black or African American / Q000235:genetics* / Q000523:psychology; D002188:Cannabis; D005260:Female; D006801:Humans; D008137:Longitudinal Studies; D008385:Marijuana Smoking / Q000235:genetics* / Q000523:psychology; D035781:Siblings / Q000523:psychology; D012907:Smoking / Q000235:genetics* / Q000523:psychology; D014029:Tobacco Use Disorder / Q000235:genetics / Q000523:psychology; D014427:Twins / Q000235:genetics* / Q000523:psychology; D044465:White People / Q000235:genetics* / Q000523:psychology; D055815:Young Adult; D062789:Tobacco Products
Cannabis; Cigarette; Heritability; Initiation; Tobacco; Twin