Interplay between genetic and environmental factors determine birth weight


By Karla Gale

NEW YORK (Reuters Health) – Maternal genetic susceptibility can modify the effects of cigarette smoking on infant birthweight and gestational age, according to a report in the January 9th issue of the Journal of the American Medical Association.

Dr. Xiaobin Wang, of Boston University School of Medicine, and colleagues assessed genotype frequencies for two genes involved in the metabolism of tobacco smoke toxins among 741 mothers. The group included 124 women who had smoked continuously during pregnancy. A total of 207 infants were preterm or low birth weight or both.

Continuous maternal smoking during pregnancy was associated with mean reduction in birth weight of 377 g. In women who were homozygous wild type for the CYP1a1 genotype, the reduction was smaller at 252 g, but increased to 520 g among mothers with one or two of the variant alleles.

Similarly, the presence of the GSTT1 genotype was associated with a mean reduction of 285 g, while absence of the genotype was associated with a reduction of 642 g. The combination of the presence of the variant allele of CYP1a1 and the absence of GSTT1 resulted in the greatest mean reduction in birth weight, 1285 g.

The effects of the genotypes were similar regarding gestational age and the ratio of observed birth weight to mean birth weight for gestational age. However, the genotypes had no significant effect on the offspring of nonsmoking mothers.

"Our study represents one of the first to show how maternal genes interact with environmental exposures to affect infant birth weight," Dr. Wang said in an interview with Reuters Health. "However, much work remains to be done before there are any practical applications."

Dr. Wang and her associates plan to "systematically investigate other environmental and genetic determinants of low birth weight," including maternal stress, nutrition, alcohol and illicit drug use.

While agreeing with Dr. Wang that clinical applications of these findings remain in the future, editorialists Dr. George P. Vogler and Dr. Lynn T. Kozlowski, of Pennsylvania State University in University Park, suggest that understanding "gene-environment interactions provides the opportunity to develop individual-based interventions that use variability…to improve public health outcomes."

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