Conversion Analysis Improves Genetic Testing

Researchers have found that a technique that separates chromosomes into separate alleles before mutational analysis is able to detect a substantial number of mutations or deleted DNA sequences that were missed when pairs of alleles were analyzed together.

Investigators at the Cleveland Clinic (OH, USA) and the Mayo Clinic (Rochester, MN, USA) used this technique, called "conversion technology” and "conversion analysis,” to separate and analyze chromosomes in a study of inherited colon cancer. They studied samples from a total of 64 hereditary nonpolyposis colorectal cancer cases, eight hereditary nonpolyposis colorectal cancer-like cases, and 17 cases diagnosed prior to age 50.

Results published in the February 16, 2005, issue of the Journal of the American Medical Association revealed that traditional DNA sequencing identified 28 likely deleterious exon mutations, four in-frame deletion mutations, 16 mis-sense changes, and 22 putative splice site mutations. In addition to identifying all mutations detected by genomic DNA sequencing, conversion analysis found an additional exon mutation, 12 large genomic deletions, and one exon duplication mutation--an increase of 33% (14/42) in diagnostic yield of deleterious mutations.

"Conversion technology has the potential to improve the accuracy of gene-based tests. For many genetic disorders, a variety of different types of mutations can be found to cause disease. Additionally, these mutations can often occur anywhere within the gene being analyzed,” said contributing author Dr. Stephen Thibodeau, co-director of the molecular genetics laboratory at the Mayo Clinic. "In some cases, the identification of gene mutations can be difficult to detect with conventional methods. This study highlights the potential to identify disease-causing mutations in a higher proportion of patients being studied.”




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