Congenital malformations affecting multiple organ systems are at least three times more common in infants of mothers with IDDM than in infants born to nondiabetic mothers. Numerous studies have confirmed the teratogenic effect of hyperglycemia on the developing embryo, although no direct mechanism has been determined. In this study, we aimed to correlate the frequency of lacI mutations with degree of hyperglycemic exposure and severity of malformations in mouse embryos from in vitro cultures. Day 8 transgenic mouse embryos cultured in 30 or 50 mmol/l glucose for 48 h exhibited a higher incidence of morphological abnormalities, as well as an increase in lacI mutation frequency, compared with embryos cultured in 10 mmol/l glucose with no abnormalities and a lower frequency of lacI mutations. We also used a transgenic lacI rat system to evaluate the relationship between abnormal embryonic development and DNA mutation frequency in day 11 embryos of severely diabetic rats (serum glucose >20 mmol/l). Compared with control embryos, the embryos from diabetic rats displayed significantly more malformations, shorter crown-rump lengths, fewer somites, and more than six times greater genomic DNA mutation frequency. Genetic analysis of the mutated lacI gene from both in vitro cultured mouse embryos and in vivo developed rat embryos revealed that the majority of mutations were due to base substitutions (transitions and transversions), but that the rate of large DNA mutations tended to increase in embryos exposed to a diabetic environment. Our results support the interrelationship between increased rates of congenital malformations and DNA mutations in the offspring of diabetic pregnancy.

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