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Genetic mutation identified for insulin sensitivity

17 September 2012
Appeared in BioNews 673

The first single gene responsible for insulin sensitivity in humans has been identified by researchers at the University of Oxford. The discovery has implications for understanding type II diabetes.

A mutation was identified in a gene which was previously known to put people at risk of developing type II diabetes - the tumor suppressor phosphatase and tensin homologue (PTEN) gene. Mutations in this gene were also already associated with an increased risk of cancer.

Study leader Dr Anna Gloyn, of the Oxford Centre for Diabetes Endocrinology and Metabolism, UK, told Fox News that the research demonstrated 'a link between the cell cycle and a risk for type II diabetes, which has started to suggest there might be a genetic overlap in terms of your predisposition for getting diabetes and cancer'.

Insulin, the hormone which controls the levels of glucose in blood, is produced, stored and released by cells of the pancreas called beta cells. In type II diabetes either the body does not produce enough insulin or the cells do not respond to it, and this results in high levels of glucose in the blood.

To understand the role of the PTEN gene, the team examined patients with a rare condition called Cowden syndrome, also caused by a mutation of PTEN. A central feature of Cowden syndrome is the development of non-cancerous, tumor-like growths.

The researchers measured insulin sensitivity and beta cell function in 15 patients and 15 healthy volunteers, and observed how they metabolised glucose. The participants affected by Cowden syndrome showed increased insulin sensitivity.

The paper, published in the New England Journal of Medicine, concludes that these results 'support the hypothesis that the epidemiologic and genetic associations between cancer and type II diabetes may be based on common signaling pathways linking tumor-suppressor genes to metabolic pathways that mediate insulin action'.

The researchers also noted that patients with Cowden Syndrome were better at clearing glucose, but had a higher level of obesity. This was a counterintuitive finding as the Cowden Syndrome patients, with their greater sensitivity to insulin, should be able to clear glucose faster.

'You would think if we have insulin sensitive people they’d be thin', Dr Gloyn told Fox News, 'but that wasn't the case'.

In an editorial accompanying the paper, Dr Ulf Smith writes that scientists 'need to know more about the role and complex regulation of PTEN activity in insulin-resistant states in humans' and notes that the findings 'further underscore concerns that [anti-cancer] therapeutic approaches aimed at increasing PTEN activity will effect a decrease in insulin sensitivity and will increase the risk for type 2 diabetes'.
SOURCES & REFERENCES
Gene responsible for insulin sensitivity discovered
Diabetes.co.uk |  13 September 2012
'Obesity' gene may lower diabetes risk
MedPage Today |  12 September 2012
PTEN Mutations as a Cause of Constitutive Insulin Sensitivity and Obesity
New England Journal of Medicine |  13 September 2012
Single gene mutation found to cause insulin sensitivity
Fox News |  13 September 2012
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