Increases Effectiveness of Genetic Tests for Cancer Risk

The Johns Hopkins scientists whose research led to the first blood tests for colon cancer predisposition have now developed a technology that dramatically improves the accuracy of such tests. They can now detect -- nearly 100 percent of the time -- genetic mutations associated with certain hereditary diseases. A report of their work is in the February 17, 2000, issue of Nature.

"Of those who seek genetic testing, up to 50 percent will walk away with no clear answer, not because a gene mutation wasn't there, but because the technology was not sophisticated enough to detect it," says Bert Vogelstein, M.D., Clayton Professor of Oncology at Johns Hopkins and Investigator, Howard Hughes Medical Institute. "Now, we can tell people who seek testing, with much greater certainty, whether or not they have inherited specific genetic predispositions to colon cancer."

The team from the Johns Hopkins Oncology Center and the Howard Hughes Medical Institute overcame a major obstacle to testing for genetic mutations in inherited diseases by unmasking mutated genes. The new technology, called Conversion, takes advantage of what has long been a weakness in genetic testing.

Every person carries two copies of a gene, scientifically known as alleles (one inherited from the father, one from the mother). Normal genes can "mask" or hide defective ones. Conventional genetic tests analyze both copies of potentially mutated genes at the same time. Conversion separates the two copies of the gene, allowing them to be individually analyzed.

"With current tests, if a portion of a gene was deleted, that deletion mutation could be masked or hidden by the normal copy of the gene. By separating and looking at each copy individually, we can now detect these and other kinds of genetic alterations that were previously missed," explains Kenneth W. Kinzler, Ph.D., professor of oncol
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Contact: Vanessa Wasta
wastava@jhmi.edu
410-955-1287
Johns Hopkins Medical Institutions
16-Feb-2000