The mechanisms involved in associations between birth weight within the normal range and adult-onset diseases remain unclear. Horikoshi et al. carried out a genome-wide association meta-analysis and follow-up study of birth weight in up to 69,308 individuals. They identified seven loci associated with birth weight, which accounted for a proportion of variance in birth weight similar to that reported for maternal smoking. Two of these loci are associated with type 2 diabetes mellitus (ADCY5 and CDKAL1), one with adult blood pressure (ADRB1) and two with adult height (HMGA2 and LCORL).