Prenatal Testing

A chromosomal test developed at Baylor College of Medicine could be a new tool to help doctors diagnose fetal disorders. Houston Public Radio's Laurie Johnson reports.

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Current prenatal genetic tests include amniocentesis which can detect some chromosomal problems. But Dr. Arthur Beaudet, chair of molecular and human genetics at Baylor College of Medicine, says a new test he has developed uses a gene chip to analyze DNA samples and identify even more disorders than conventional tests.

"We've seen technology come available that will pick up tinier and tinier defects and this test allows us to do many specific regions at once in a very efficient way because of the technology so instead of testing one region at a time, we're testing eight or nine hundred regions at a time so it gives us a much better ability to detect disorders in the genome."

The gene chip, or microarray, is similar to a map covered with tiny dots of DNA. Lab technicians compare a patient's DNA to a control sample. If the DNA for both the patient and control evens out, then everything is normal. If the patient's DNA turns red it means there are too many chromosomes and if it turns green there are too few.

"Most of the disorders we're talking about involve mental retardation and serious disabilities. Any one of them is not too common, but there are names like DeGeorge Syndrome....Angelman's Syndrome and Williams Syndrome. These would all be disorders that would not be detected by a usual amniocentesis but would be detected by the new form of the test."

The test can be used at both the prenatal stage as well as in children and even adults. Beaudet says parents could use this test in cases of mental retardation to get a firm diagnosis. And he says there is debate on regarding the issue of prenatal testing because some parents could decide to terminate a pregnancy based on the results of the test.

"I think it does allow us to diagnose more conditions in utero. The whole issue of prenatal diagnosis and abortion is obviously one in which society is divided at the present time."

Beaudet says he thinks this test is going to get cheaper and give more information over the next few years. Right now the test is somewhat expensive, at about $2,000, but still costs far less than the individual tests that would be needed to screen for these various chromosomal disorders. Laurie Johnson Houston Public Radio News.

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