Scientists have developed a technique that can
detect a genetic risk for colon cancer with nearly 100% accuracy.
new method is able to detect defective genes otherwise masked when one copy of
the gene in question is normal.
The technique may also be used to
enhance the accuracy of diagnostic tests for a wide range of inherited diseases,
including other forms of cancer and neurological disorders.
two copies of each gene, one of which is inherited from the mother and one from
One of the weaknesses of genetic testing is that a normal
gene can mask the presence of the defective or missing gene.
diagnostic tests will either not detect the genetic defect or will prove far
less sensitive to it.
A team from Johns Hopkins University in Baltimore
has developed a technique to separate the individual genes and analyse them
They have done this by fusing
human cells with a special strain of mouse cells developed by the researchers.
This enables the scientists to create cells that carry only the defective
version of a gene, rather than both normal and defective gene copies.
Using this technique, the researchers were able to confirm the presence
of mutant genes in 22 patients with hereditary non-polyposis colorectal cancer.
In contrast, conventional genetic testing detected the mutant gene in
only 10 of the 22 patients.
Researcher Professor Bert Vogelstein said
until now up to 50% of those tested do not get a clear answer from genetic tests
whether they are at risk of certain types of inherited colon cancer.
said: "Now we can tell people who seek testing, with much greater certainty,
whether or not they have inherited specific genetic predispositions to colon
"The sensitivity of the test for other diseases will depend on
the nature of the mutations.
"But certainly for many of them, the
sensitivity should be similarly increased substantially.
The two types
of colon cancer for which the test has been shown to work are hereditary
non-polyposis colorectal cancer (HNPCC) and familial adenomatous polyposis