Finally, variation at one locus, ANK1, shows association with both higher birth weight and higher risk of type 2 diabetes [20], but unlike MTNR1B, this association does not appear to be driven by the maternal genotype, raising the possibility of a genetic mechanism contributing to the observational association between higher birth weight and type 2 diabetes that operate independently of maternal hyperglycemia. Here, MTNR1B is linked to type 2 diabetes mellitus.