Adult glucose metabolism in extremely birthweight-discordant monozygotic twins

Low birthweight (BW) is associated with increased risk of type 2 diabetes. We compared glucose metabolism in adult BW-discordant monozygotic (MZ) twins, thereby controlling for genetic factors and rearing environment. Among 77,885 twins in the Danish Twin Registry, 155 of the most BW-discordant MZ twin pairs (median BW difference 0.5 kg) were assessed using a 2 h oral glucose tolerance test with sampling of plasma (p-)glucose, insulin, C-peptide, glucose-dependent insulinotropic polypeptide and glucagon-like peptide-1. HOMA for beta cell function (HOMA-beta) and insulin resistance (HOMA-IR), and also insulin sensitivity index (BIGTT-SI) and acute insulin response (BIGTT-AIR), were calculated. Subgroup analyses were performed in those with: (1) double verification of BW difference; (2) difference in BW > 0.5 kg; and (3) no overt metabolic disease (type 2 diabetes, hyperlipidaemia or thyroid disease). No intra-pair differences in p-glucose, insulin, C-peptide, incretin hormones, HOMA-beta, HOMA-IR or BIGTT-SI were identified. p-Glucose at 120 min was higher in the twins with the highest BW without metabolic disease, and BIGTT-AIR was higher in those with the highest BW although not in pairs with a BW difference of > 0.5 kg. BW-discordant MZ twins provide no evidence for a detrimental effect of low BW on glucose metabolism in adulthood once genetic factors and rearing environment are controlled for.