Genetic and environmental influences on body size in early childhood: a twin birth-cohort study.
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.
Dubois
Lise
L
Department of Epidemiology and Community Medicine, Faculty of Medicine, University of Ottawa, and Institute of Population Health, Ottawa, Canada. lise.dubois@uottawa.ca
Girard
Manon
M
Girard
Alain
A
Tremblay
Richard
R
Boivin
Michel
M
Pérusse
Daniel
D
D001724:Birth Weight / Q000235:genetics; D001827:Body Height / Q000235:genetics; D049628:Body Size / Q000235:genetics*; D001835:Body Weight / Q000235:genetics; D002675:Child, Preschool; D015331:Cohort Studies; D004777:Environment; D005260:Female; D006801:Humans; D007223:Infant; D008137:Longitudinal Studies; D008297:Male; D011792:Quebec; D014429:Twins, Dizygotic / Q000235:genetics; D014430:Twins, Monozygotic / Q000235:genetics