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February 18, 2010

SickKids scientists discover a genetic clue for Type 1 diabetes

New genetic loci may provide insights into blood glucose control in people with diabetes

A new discovery is providing important insight into how genes may influence a patient’s ability to regulate blood glucose. Researchers at The Hospital for Sick Children (SickKids) have identified four regions in the human genome that correlate with glucose control in patients with Type 1 diabetes. This discovery is published in the February 2010 issue of Diabetes.

Type 1 diabetes affects over 50,000 people in Canada and is usually diagnosed before age 30, often in childhood or early adolescence. High blood sugar is a risk factor for long-term complications of Type 1 diabetes such as eye and kidney complications. Controlling blood sugar is therefore one of the most important things that can be done to reduce both the rate and severity of diabetes-related complications.

"The results of this study challenge the assumption that blood glucose levels are solely under the control of the patient,” says Dr. Andrew Paterson, Senior Scientist in Genetics & Genome Biology at SickKids Research Institute. “Although how well the patient controls their blood glucose is an important factor, the new study indicates that some individuals may be predetermined to have an easier or harder time controlling blood glucose levels based upon their genetic makeup. In the future, this information may help us to target specific treatments or strategies to individuals who are known to have a genetic background that will make controlling their diabetes more difficult.”

Dr. Paterson and his team studied the DNA of over a thousand patients with Type 1 diabetes. “We looked for DNA changes, called Single Nucleotide Polymorphisms, or SNPs,” says Dr. Paterson, “and took a sequential approach to identifying the SNPs that were most strongly correlated with high blood glucose and multiple diabetic complications.”

The study identified 13 SNPs, concentrated into four loci, or regions of the genome. The major locus identified was SORCS1, which is strongly associated with hypoglycemia (low blood glucose). The other three loci include BNC2, which is correlated with eye and kidney complications. Results were verified by comparison to other patient cohorts, both with and without Type 1 diabetes.

Genetics are also a major cause of Type 1 diabetes. Progression of the disease is thought to be influenced by a complex mixture of environmental, genetic and therapeutic factors. This is the first time, however, that a potential genetic contributor to the control of blood glucose in individuals with Type 1 diabetes has been identified.

While the discovery of the SORSC1 locus may not immediately influence clinical practice, in the future it may allow doctors to determine which treatments will be the most effective to help individual patients manage their diabetes.

Further research in this area will involve fine-mapping of the four loci to determine if these genes are associated with blood glucose levels in people with Type 1 diabetes in all ethnic groups, and with other common complications of the disease.

This research was supported by grants from the National Institute of Health, the Canadian Network of Centres of Excellence in Mathematics (MITACS), Genome Canada (through the Ontario Genomics Institute), and SickKids Foundation. Dr. Paterson is an Associate Professor of Public Health Sciences at the Dalla Lana School of Public Health at the University of Toronto and a member of the Diabetes Control and Complications Trial/Epidemiology of Diabetes Interventions and Complications (DCCT/EDIC) research group. He holds a Canadian Research Chair in the Genetics of Complex Diseases.