a1 Department of Epidemiology and Community Medicine, Faculty of Medicine, University of Ottawa, and Institute of Population Health, Ottawa, Canada. email@example.com
a2 Institute of Population Health, Ottawa, Canada.
a3 Research Unit on Children's Psychosocial Maladjustment (GRIP), University of Montreal, Canada.
a4 Canada Research Chair for Child Development, University of Montreal, Canada.
a5 School of Psychology, Laval University, Québec, Canada.
a6 Departments of Anthropology and Psychiatry, University of Montreal, Canada.
Genetic and environmental contributions to body size from birth to 5 years in a population-based twin cohort were studied. Sex differences in gene–environment etiology were also explored. Analyses used data from the Quebec Newborn Twin Study (QNTS), a population-based birth cohort of 672 twin pairs. The final sample consisted of 177 complete twin pairs. Heritability of weight was moderate at birth while common environmental factors accounted for almost half of the variance. Influence of family environment disappeared by 5 months and genetic effects were high (approximately 90%) for both sexes at 5 months and 5 years. Adjustment of weight for height yielded similar results as for weight alone. Slight but significant sex-limitation of genetic effects was observed at 5 months. Overall, genetic factors accounted for 40% of birthweight variance, with intrauterine environment influences explaining almost half. However, genetic factors accounted for most of the variance in weight. These results do not imply a lack of environmental effects on body weight, but rather a lack of: (1) environmental effects that are independent from genetic liability, and/or (2) a lack of significant environmental variation in the population (e.g., uniform nutritional habits) that leaves genetic differences between children to generate most of the variance in weight.
(Received September 27 2006)
(Accepted February 09 2007)
c1 Address for correspondence: Lise Dubois, Canada Research Chair in Nutrition and Population Health, Department of Epidemiology and Community Medicine, Faculty of Medicine, University of Ottawa, Institute of Population Health, 1 Stewart Street, Office 303, Ottawa, ON Canada K1N 6N5.