Low birthweight and metabolic abnormalities in twins with increased susceptibility to Type 2 diabetes mellitus.

AIMS: To evaluate the role of environmental intra-uterine factors in determining the birthweights of twins with increased susceptibility to diabetes and discordant for abnormal responses to the oral glucose tolerance test (OGTT) and verify the possible association of within-pair birthweight differences and metabolic abnormalities in adult life. METHODS: Forty-six monozygotic (MZ) and 32 dizygotic (DZ) twins were enrolled; 13 MZ twins were discordant for impaired glucose tolerance (IGT) and/or hyperinsulinaemia compared to their co-twins. RESULTS: The 13 MZ discordant twins showed significantly lower birthweights than their normal co-twins (P < 0.001). When dividing all twins in those with the highest birthweights within the couple and those with the lowest, all subjects with abnormal OGTT were found in the latter group (P < 0.0001). Within-pair birthweight difference was significantly higher in MZ twins with abnormal OGTT and the metabolic syndrome compared to normal MZ twins. The relative risk of developing the metabolic syndrome was 8.7 (1.6-46.9) when comparing the higher tertile of within-pair birthweight differences (> or = 0.450 kg) to the two lower tertiles (< 0.450 kg). Logistic regression analysis confirmed within-pair birthweight difference as a significant predictor of abnormal responses to the OGTT and the metabolic syndrome. CONCLUSIONS: These data suggest a causative role for environmental intrauterine factors on the determination of birthweight and support the hypothesis that within-pair birthweight difference, rather than an absolute low birthweight, is responsible for the metabolic abnormalities in the adult life.