A genetic analysis of weight and overweight in 4-year-old twin pairs.
OBJECTIVE
Although many twin and adoption studies document genetic influence on individual differences in weight, much less is known about genetic influences on overweight, about the genetic links between weight and overweight, or about the origins of weight and overweight in childhood, an age that might provide a good target for prevention of obesity. We tested the hypothesis that, in early childhood, overweight is as heritable as weight and that weight and overweight are linked genetically.


METHODS
Model-fitting analyses were used to compare monozygotic (MZ) and dizygotic (DZ) twins (same-sex and opposite-sex) for weight and overweight.


METHODS
The sample included 3636 4-y-old twins born in the UK in 1994.


METHODS
Heights and weights reported by parents were used to assess weight corrected for height, which yields results similar to body mass index (BMI) but corrects more completely for genetic effects on height.


RESULTS
At 4 y of age, genetic factors contributed substantially both to individual differences in weight throughout the distribution and to the mean weight difference between overweight children and the rest of the population. Unlike results later in life, weight and overweight in 4-y-olds also suggest substantial shared family environmental influence. Results are similar for boys and girls.


CONCLUSIONS
Overweight is the quantitative extreme of genetic and environmental factors responsible for normal variation in weight in childhood. Genes associated with overweight are likely to be associated with variation in weight throughout the distribution, as assumed by quantitative trait locus (QTL) theory. These findings linking weight and overweight in childhood have far-reaching implications for molecular genetic attempts to identify specific genes responsible for genetic influence, for investigating pathways between genes and behaviour, and for intervention and prevention.
Koeppen-Schomerus
G
G
Social, Genetic and Developmental Psychiatry Research Centre, Institute of Psychiatry, King's College London, 113 Denmark Hill, London SE5 8AF, UK. G.Koeppen-Schomerus@iop.kcl.ac.uk
Wardle
J
J
Plomin
R
R
D001827:Body Height / Q000235:genetics; D015992:Body Mass Index; D001835:Body Weight / Q000235:genetics*; D002675:Child, Preschool; D004777:Environment; D005260:Female; D006801:Humans; D008297:Male; D009765:Obesity / Q000209:etiology* / Q000235:genetics*; D019655:Quantitative Trait, Heritable; D014427:Twins / Q000235:genetics*; D014429:Twins, Dizygotic / Q000235:genetics; D014430:Twins, Monozygotic / Q000235:genetics; D006113:United Kingdom