A recent article in the Journal of American Medicine reports that conventional genetic testing may not be identifying genetic mutations that contribute to hereditary form of colon cancer.
Colorectal cancer is the second leading cause of cancer related deaths in the United States. Colorectal cancer is a malignancy that involves both the large intestines (colon) and a distal portion of the colon known as the rectum. Hereditary nonpolyposis colorectal cancer (HNPCC) is a genetic mutation that is characterized by an increased risk of colon cancer, as well as other cancers, such as ovarian, stomach, liver, brain and skin cancer. Genetic abnormalities among 4 genes (MLH1, MSH2, MSH6, and PMS2) can be detected by genetic testing and those found to have mutations among these genes have an 80% lifetime risk for developing colon cancer. The average age for colorectal cancer diagnosis among this group is 44. MLH1 and MSH 2 mutations account for approximately 90% of all patients diagnosed with HNPCC. Mutation of the MSH6 gene occurs in 7-10% of families with HNPCC and PMS2 accounts for less than 5% of families diagnosed with HNPCC.
In this recent multi-center study, researchers sought to compare the findings of two types of genetic examinations: conversion analysis versus DNA sequencing. These tests were performed and evaluated to detect mutations in the MLH, MSH2 and MSH6 genes of patients with colorectal cancer. Study participants included 64 patients with HNPCC colon cancer, 8 cases similar to HNPCC, as well as 17 cases of HNPCC that were diagnosed prior to 50 years of age.
Results of the study revealed that DNA sequencing identified 70 likely or definite genetic mutations. Conversion analysis detected the same 70 alterations, plus 13 additional mutations, and other genetic changes as well, which increased the overall findings by 56%.
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Researchers concluded that conventional DNA sequence testing might miss many of the genetic mutations associated with HNPCC. Conversion analysis substantially increases the diagnostic findings for patients diagnosed with colorectal cancer. Patients are encouraged to speak to their physician regarding their risk of colorectal cancer and genetic testing.
Reference: Casey G, Lindor N, Papadopoulos N, et al. Conversion Analysis for Mutation Detection in MLH-1 and MSH-2 in Patients With Colorectal Cancer. Journal of American Medical Association. 2005; 293: 799-809.
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