Why is type 2 diabetes an increasing problem?

PUBLIC RELEASE DATE:

9-Jan-2014

Contact: Aileen Sheehy press.office@sanger.ac.uk 44-012-234-92368 Wellcome Trust Sanger Institute

Contrary to a common belief, researchers have shown that genetic regions associated with increased risk of type 2 diabetes were unlikely to have been beneficial to people at stages through human evolution.

Type 2 diabetes is responsible for more than three million deaths each year and this number is increasing steadily. The harmful genetic variants associated with this common disease have not yet been eliminated by natural selection.

To try to explain why this is, geneticists have previously hypothesised that during times of 'feast or famine' throughout human evolution, people who had advantageous or 'thrifty' genes processed food more efficiently. But in the modern developed world with too much food, these same people would be more susceptible to type 2 diabetes.

"This thrifty gene theory is an attractive hypothesis to explain why natural selection hasn't protected us against these harmful variants," says Dr. Yali Xue, lead author of the study from the Wellcome Trust Sanger Institute. "But we find little or no evidence to corroborate this theory."

The team tested this theory by examining 65 genetic regions that were known to increase type 2 diabetes risk, the most detailed study of its kind.

If these harmful variants were beneficial in the past, the team would expect to see a genetic imprint of this in the DNA around the affected regions. Despite major developments in tests for positive selection and a four-fold increase in the number of genetic variants associated with diabetes to work with, they found no such imprint.

"We found evidence for positive selection in only few of the 65 variants and selection favoured the protective and risk alleles for type 2 diabetes in similar proportions," notes Dr. Qasim Ayub, first author from The Wellcome Trust Sanger Institute, "This is no more than what we would expect to find for a random set of genomic variants."

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Why is type 2 diabetes an increasing problem?