Just half a year after announcing the detection of an entirely novel way that 
cancer can begin, scientists have isolated the gene responsible for the misdeed.    
     The discovery opens a-new phase In the genetics revolution, with all
 its wild promise and ethical quandaries. In its defective form, the gene 
predisposes people to an extremely common type of colon cancer, called 
hereditary nonpolyposis colorectal cancer. The familial disorder is thought 
to account 10 to 15 % of all colon tumors, or as many as 22,000 cases 
of the cancer each year.
    What is more, as many as  1 in 200 people , or more than a million 
Americans, are thought to carry the mutation, most without any knowledge
 of  their inherent risk.
    The finding thus holds  significance for a far greater number of people
 than any other genes isolated to date, including those for other rarer 
forms of cancer. Colon cancer is the second most frequently fatal malignancy 
in America after, lung cancer, killing about 64,000 people each year.
     "For those who carry the gene, the risk of getting colon cancer or
 one of a handful of other malignancies is  70 to 90 % , and many will develop 
tumors before the age of 50.
     Scientists predicted that a genetic test for people in families, known to be
at  risk for colon tumors could be ready within 6 months....