Hard-to-Detect Balanced Chromosomal Abnormalities (BCAs) May Cause Large Percentage of Neurodevelopmental Birth Defects; Findings from New MGH/Broad Institute Study Reported at ASHG 2015 Annual Meeting

Balanced chromosomal abnormalities (BCAs), a category of structural changes to the human genome, may account for a large portion of birth defects related to brain development and function, according to research presented on Saturday, October 10, at the American Society of Human Genetics (ASHG) 2015 Annual Meeting in Baltimore, Maryland. BCAs are changes to the structure of an individual’s chromosomes, in which one or more fragments of DNA breaks apart from the regions around it and is reattached elsewhere in the genome, either on the same chromosome or on a different one. In their simplest form, a single fragment is moved to another region of the genome, but more complex BCAs may involve more than one fragment from more than one chromosome. Unlike chromosomal deletions or duplications, BCAs do not result in the gain or loss of any genetic material. However, they do disrupt the function of DNA at the breakpoints of the fragments involved, in both their original locations and their new ones, and BCAs have been implicated in neurodevelopmental birth defects. “We studied BCAs in 111 patients with congenital neurodevelopmental conditions and 36 with other conditions and mapped where the breakpoints were,” explained Claire Redin (photo), Ph.D., a postdoctoral researcher at Massachusetts General Hospital (MGH) and the Broad Institute, and first author on the new study. “By mapping the breakpoints, we were able to identify genes that were disrupted in patients with birth defects, which suggests that these genes play a key role in normal brain development,” she said. Because no genetic material is gained or lost, conventional tools for genome analysis cannot generally detect BCAs. Thus, they have not received much attention as a significant cause of disease. To overcome this challenge, Dr.
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