Researchers report they have narrowed the location of a gene they say causes a common form of diabetes, a breakthrough that could lead to early identification and treatment of people who develop the disease.

The gene is believed to cause adult-onset diabetes, also called non-insulin dependent or Type 2 diabetes. Of the estimated 14 million diabetics in the United States, 90 percent suffer from the non-insulin type, usually developing it after age 40.The tracking of the gene was reported in this week's issue of the Proceedings of the National Academy of Sciences.

One of the researchers, Graeme Bell of the University of Chicago, said the gene was tracked to the long arm of chromosome 20.

The nucleus of every cell in the body has 23 pairs of chromosomes. The chromosomes carry the genes that determine a person's hereditary characteristics.

"We have the neighborhood for the gene, but we don't have the address," Bell said. "We started out with 3 billion possible genes. We've narrowed it down to 10 million."

The researchers - from the University of Chicago, University of Pennsylvania and University of Michigan - located the gene by studying the work of Dr. Stefan Fajans. The University of Michigan endocrinologist has spent 32 years tracking one family - with more than 275 members spanning five generations - in which more than 40 people suffered from non-insulin dependent diabetes.