Key Findings from Recent Birth Defects and Pediatric Genetics Branch Projects

CDC scientists analyzed right vs. left side distribution of external birth defects and found that some types of defects occur more often on one side of the body than the other.

The records of 6,390 metropolitan Atlanta children with external unilateral birth defects were examined to determine whether defects occur more often on one side of the body than on the other.

• Fifty-seven (56%) of the 102 defect types studied had a right-sided excess, 39 (38%) had a left-sided excess, and 6 (6%) were equally distributed.

• Among the 102 defect types, the percentage of children who had right-sided defects was correlated with the percentage of children who were male.

• Some genes are differentially expressed on the right and left sides of the developing embryo. Differential left-right expression of genes during development may cause right vs. left sided differences in cell proliferation, morphogenetic movement, cell-to-cell communication, or other morphogenetic processes that could influence the susceptibility of specific bilateral structures to birth defects.

• Some evidence suggests that genes related to right vs. left side of the body may be located on the sex chromosomes. This may explain the correlation observed between sex and right vs. left side defects.

• Differences in the right vs. left side distribution of birth defects and the association with sex of the infant may provide important clues about the origins of specific birth defects.

Results published in: Teratology 1999;60:265-271. (Abstract)