Icelandic researchers say they've identified a variant gene that increases the risk of Type 2 diabetes (T2D).

The TCF7L2 gene is carried by about 38 per cent of the US population, according to the researchers.

"This is a milestone in human genetics," said Kari Stefansson, chief executive of biopharmaceutical company deCODE and senior author on the study.

"A common gene variant conferring elevated risk of T2D has been earnestly sought by the genetics community for many years. We have found such a variant, which we estimate accounts for about 20 per cent of T2D cases.

"This discovery sheds new light on the biological causes of the disease. Importantly, virtually all of this risk can be captured by looking at a single-letter change in DNA - ideal for the development of a genetic test for assessing individual risk and developing more personalized and effective prevention strategies.

"This is also an exciting starting point for the discovery of new drugs, and we are actively pursuing the development of both diagnostic and therapeutic products to better prevent and treat T2D."

deCODE isolated the gene by following up on the results of a population-based, genome-wide linkage scan in Iceland that identified a promising region on chromosome 10.

The deCODE team genotyped 228 microsatellite markers - polymorphic signposts along the genome - in this region in a total of more than 2000 patients and controls.

Analysis of the frequency of different alleles, or versions, of these markers pinpointed a version of one marker within the gene encoding TCF7L2 that is approximately 1.5 times more common in patients than in controls.

This corresponds to a 50 per cent increase in risk of T2D per copy carried (there are two copies of each chromosome in every cell).

Diabetes affects nearly 200 million people worldwide and an estimated 21 million in the US.

The vast majority of diabetes patients have T2D, a condition where the body does not produce enough insulin and/or the cells in the body do not properly use insulin.

The study findings are published in the online edition of Nature Genetics.