Genetics mediate relation of birth weight to childhood IQ

EDITOR—Matte et al reported an association between birth weight and childhood IQ.1 To control for confounding by maternal and family factors they examined this relation in sibships of the same sex and found an association between birth weight and IQ within male sibships. This association may be mediated by genetic factors. The impact of genetic factors on this association can be determined through the investigation of birth weight and IQ in twin pairs. Differences within dizygotic twin pairs are a function of both genetic and non-genetic factors, whereas differences within …