A Genetic Epidemiological Mega Analysis of Smoking Initiation in Adolescents.
BACKGROUND
Previous studies in adolescents were not adequately powered to accurately disentangle genetic and environmental influences on smoking initiation (SI) across adolescence.


METHODS
Mega-analysis of pooled genetically informative data on SI was performed, with structural equation modeling, to test equality of prevalence and correlations across cultural backgrounds, and to estimate the significance and effect size of genetic and environmental effects according to the classical twin study, in adolescent male and female twins from same-sex and opposite-sex twin pairs (N = 19 313 pairs) between ages 10 and 19, with 76 358 longitudinal assessments between 1983 and 2007, from 11 population-based twin samples from the United States, Europe, and Australia.


RESULTS
Although prevalences differed between samples, twin correlations did not, suggesting similar etiology of SI across developed countries. The estimate of additive genetic contributions to liability of SI increased from approximately 15% to 45% from ages 13 to 19. Correspondingly, shared environmental factors accounted for a substantial proportion of variance in liability to SI at age 13 (70%) and gradually less by age 19 (40%).


CONCLUSIONS
Both additive genetic and shared environmental factors significantly contribute to variance in SI throughout adolescence. The present study, the largest genetic epidemiological study on SI to date, found consistent results across 11 studies for the etiology of SI. Environmental factors, especially those shared by siblings in a family, primarily influence SI variance in early adolescence, while an increasing role of genetic factors is seen at later ages, which has important implications for prevention strategies.


CONCLUSIONS
This is the first study to find evidence of genetic factors in liability to SI at ages as young as 12. It also shows the strongest evidence to date for decay of effects of the shared environment from early adolescence to young adulthood. We found remarkable consistency of twin correlations across studies reflecting similar etiology of liability to initiate smoking across different cultures and time periods. Thus familial factors strongly contribute to individual differences in who starts to smoke with a gradual increase in the impact of genetic factors and a corresponding decrease in that of the shared environment.
Department of Human and Molecular Genetics, Virginia Institute for Psychiatric and Behavioral Genetics, Virginia Commonwealth University, Richmond, VA.|Department of Psychiatry, Virginia Institute for Psychiatric and Behavioral Genetics, Virginia Commonwealth University, Richmond, VA.|Massey Cancer Center, Virginia Commonwealth University, Richmond, VA.|Department of Kinesiology, KU Leuven, Leuven, Belgium.
Hermine H
HH
Maes
Department of Human and Molecular Genetics, Virginia Institute for Psychiatric and Behavioral Genetics, Virginia Commonwealth University, Richmond, VA.|Division of Epidemiology, Department of Family Medicine and Population Health, Virginia Commonwealth University, Richmond, VA.
Elizabeth
E
Prom-Wormley
Department of Human and Molecular Genetics, Virginia Institute for Psychiatric and Behavioral Genetics, Virginia Commonwealth University, Richmond, VA.|Department of Psychiatry, Virginia Institute for Psychiatric and Behavioral Genetics, Virginia Commonwealth University, Richmond, VA.
Lindon J
LJ
Eaves
Institute for Behavioral Genetics, University of Colorado, Boulder, CO.
Soo Hyun
SH
Rhee
Institute for Behavioral Genetics, University of Colorado, Boulder, CO.
John K
JK
Hewitt
Institute for Behavioral Genetics, University of Colorado, Boulder, CO.|Department of Psychiatry, University of Colorado, Denver, CO.
Susan
S
Young
Institute for Behavioral Genetics, University of Colorado, Boulder, CO.
Robin
R
Corley
Department of Psychology, University of Minnesota, Minneapolis, MN.
Matt
M
McGue
Department of Psychology, University of Minnesota, Minneapolis, MN.
William G
WG
Iacono
Department of Psychology, University of Minnesota, Minneapolis, MN.
Lisa
L
Legrand
Department of Psychology, University of Minnesota, Minneapolis, MN.|Human Development and Family Studies Department, Auburn University, Auburn, AL.
Diana R
DR
Samek
Venebio Group, LLC, Richmond, VA.
E Lenn
EL
Murrelle
Department of Human and Molecular Genetics, Virginia Institute for Psychiatric and Behavioral Genetics, Virginia Commonwealth University, Richmond, VA.|Department of Psychiatry, Virginia Institute for Psychiatric and Behavioral Genetics, Virginia Commonwealth University, Richmond, VA.
Judy L
JL
Silberg
Carolina Population Center, University of North Carolina at Chapel Hill, Chapel Hill, NC.
Donna R
DR
Miles
Department of Pediatric Cardiology, Virginia Commonwealth University, Richmond, VA.
Richard M
RM
Schieken
Department of Kinesiology, KU Leuven, Leuven, Belgium.
Gaston P
GP
Beunen
Department of Kinesiology, KU Leuven, Leuven, Belgium.
Martine
M
Thomis
Department of Psychological and Brain Sciences, Indiana University, Bloomington, IN.
Richard J
RJ
Rose
Department of Psychiatry, Virginia Institute for Psychiatric and Behavioral Genetics, Virginia Commonwealth University, Richmond, VA.|Department of Psychology, Virginia Commonwealth University, Richmond, VA.
Danielle M
DM
Dick
Department of Biological Psychology, VU University, Amsterdam, The Netherlands.
Dorret I
DI
Boomsma
Behavioural Science Institute, Radboud University, Nijmegen, The Netherlands.
Meike
M
Bartels
Department of Biological Psychology, VU University, Amsterdam, The Netherlands.|Behavioural Science Institute, Radboud University, Nijmegen, The Netherlands.
Jacqueline M
JM
Vink
Department of Medical Epidemiology and Biostatistics, Karolinska Institutet, Stockholm, Sweden.
Paul
P
Lichtenstein
Centre for Behavioural Research in Cancer, Cancer Council Victoria, Melbourne, Australia.
Victoria
V
White
Department of Public Health and Institute for Molecular Medicine (FIMM), University of Helsinki, Helsinki, Finland.|Department of Health, National Institute for Health and Welfare, Helsinki, Finland.
Jaakko
J
Kaprio
Department of Human and Molecular Genetics, Virginia Institute for Psychiatric and Behavioral Genetics, Virginia Commonwealth University, Richmond, VA.|Department of Psychiatry, Virginia Institute for Psychiatric and Behavioral Genetics, Virginia Commonwealth University, Richmond, VA.
Michael C
MC
Neale
D000293:Adolescent; D000328:Adult; D001315:Australia / Q000453:epidemiology; D002648:Child; D005060:Europe / Q000453:epidemiology; D005260:Female; D006801:Humans; D008297:Male; D012907:Smoking / Q000453:epidemiology* / Q000235:genetics*; D018433:Twin Studies as Topic; D014427:Twins / Q000235:genetics* / Q000706:statistics & numerical data*; D014481:United States / Q000453:epidemiology; D055815:Young Adult