Scientists overcome genetic testing failure rate

Scientists have found how to overcome the technical limitations of genetic tests, which frequently fail to detect inherited disorders, even though they are carried by a patient.

Scientists have found how to overcome the technical limitations of genetic tests, which frequently fail to detect inherited disorders, even though they are carried by a patient.

Doctors believe the technique is cheap and reliable enough to be introduced in a couple of years, benefiting people at risk of illnesses from colon cancer to Alzheimer's.

Existing tests do not distinguish between the two sets of chromosomes inherited from a person's mother and father, so many mutations and other defects are often "masked" by the second, healthy chromosome.

The test, described in the journal Nature, is based on a method of teasing apart two identical sets of maternal and paternal chromosomes and testing each separately. "Of those who seek genetic testing, up to 50 per cent 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," said Bert Vogelstein, professor of oncology at Johns Hopkins University, Baltimore. "Now we can tell people ... with much greater certainty whether or not they have inherited specific genetic predispositions to colon cancer." In a group of 22 patients with inherited colon cancer, the new test identified every case, whereas the conventional test correctly identified only 10.

The researchers fused human cells with cells from a strain of mouse which lacked the normal machinery for chromosome rejection, enabling them to separate similar maternal and paternal human chromosomes.

"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," said Kenneth Kinzler, the co-director of the study. "By separating and looking at each copy individually, we can now detect these and other kinds of genetic alterations that were previously missed."