Scientists have traced a rare genetic defect that greatly increases the risk of colon cancer to perhaps a single married couple who immigrated to the US some time around 1630. Two populations, one in Utah and one in New York, have been discovered to possess this defect, but it's possible others have yet to be discovered. While the defect seems quite rare, it increases the risk of cancer from 1 in 25 to a whopping 2 out of 3. If a test can be developed, it would at least eliminate that indication (or provide an early warning sign for extra vigilance.)