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gene-enviroment interaction

Past studies of birth defects have been hampered by limited perspective. Epidemiologic researchlooking at occurrence patterns in a populationassumes that all individuals are equally susceptible to environmental exposures. Genetic studieslooking at biologic variation between individuals tend to ignore environmental influences. In either case, misclassification of conditions (for example, lumping together defects with different origins) can mask links between birth defects and their causes.

The California Birth Defects Monitoring Program is at the forefront of a new era of birth defects research, combining both genetic and environmental information. Recent studies take advantage of genetic discoveries accompanying the Human Genome Project as well as technologic advances in measuring exposures. When combined with in-depth interview data, biologic testing often clarifies associations. Some of the techniques we use include:

bullet DNA testing. Study subjects are often asked to swab the inside of their mouths to painlessly collect cells for genetic analysis. These results help supplement exposure information gained from interviews.
bullet Biomarkers. Saved blood samples from prenatal or newborn screening tests can be analyzed for substances that indicate the presence of infection or other environmental exposures at the time of fetal development
bullet Refined classification. Genetic tests can help distinguish different types of birth defects, guiding the search for clues. For example, determining whether the extra chromosome seen in Down syndrome came from the egg or sperm can focus attention to exposures in either the mother or father.


smoking and oral clefts

picture of cigaretteOne example of gene-environment interactions was uncovered in a study of smoking and oral clefts. Past research had been confusing some investigators found an association between clefts and tobacco use, but others did not. Our study combined interview data detailing mothers' smoking habits with DNA testing to determine the infants' status for a particular gene, transforming growth factor alpha (TGFA). We found:

bullet Mothers who smoked in early pregnancy were more likely to have babies with oral clefts. Risk increased with the amount smokedheavy smokers had double the risk of nonsmokers.
bullet Babies with a rare form of the TGFA gene were slightly more likely to have isolated cleft palate but not cleft lip.
bullet The combination of both factorsgene status and smokingcreated a huge jump in risk. Babies with the uncommon gene form whose mothers smoked had a 6-10 times higher risk of oral clefts

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