Perhaps the most interesting SNPs are those where the birthweight-increasing allele identified in Horikoshi et al.6 has opposite effects on birthweight through the fetal and maternal genotype, half of which are known type 2 diabetes loci (HHEX-IDE, CDKAL1, ADCY5 and ANK1-NXK6-3). Here, CDKAL1 is linked to type 2 diabetes mellitus.