Scientists Identify DNA Flanking Region As Trigger For Genetic Instability

Trinucleotide repeat disorders are neuromuscular, neurological or neurodegenerative in nature and include myotonic dystrophy (a form of muscular dystrophy), Huntington disease, and Fragile X syndrome (the most common form of inherited mental retardation). In these disorders, a disease state is caused when too many of the triplet DNA sequences within the gene are repeated. This mutation affects either gene expression or produces irregular proteins. The age of onset and severity of the disease are also associated with the number of triplet repeats. This type of genetic problem, known as an expansion mutation, was identified only a decade ago and is now known to be the cause of at least 15 diseases.

The genetic information gathered from affected families over the years had led researchers to believe that there was something in the flanking region (in the DNA sequence surrounding the triplet) that was causing the DNA triplets to repeat too many times.

"We have proven for the first time that there is something in the flanking DNA sequence that is triggering the genetic instability. These flanking regions effectively drive the mutation. Such flanking regions are a possible new therapeutic target for treating, or preventing, the trinucleotide repeat disorders," said Dr. Christopher Pearson, the study's principal investigator, a scientist in Genetics and Genomic Biology in the HSC Research Institute and an assistant professor of Molecular and Medical Genetics at the University of Toronto.

This research group has also developed a technique (an assay) that allows the DNA expansion to be reconstituted in a test tube (published in the April 19 issue of the Journal of Biological Chemistry). This is the first assay that will allow researchers to study this type of genetic mutation using human cells, and at a much quicker rate than previously possible.

###This research was supported by Canadian Institutes for Health Research, Muscular Dystrophy Association USA, Premier's Research Excellence Awards, Canadian Genetic Diseases Network, Natural Sciences and Engineering Council of Canada, National Institutes of Health, March of Dimes and The Hospital for Sick Children Foundation.

The Hospital for Sick Children Research Institute is a world-class scientific research centre performing fundamental and clinical research leading to the improved understanding, prevention, treatment and care of children's diseases. The Hospital for Sick Children, affiliated with the University of Toronto, is the largest paediatric academic health sciences centre in Canada and one of the largest in the world. For more information, please visit http://www.sickkids.ca.