Genetic Clue Found To Diabetes

by Rebecca Kolberg

Copyright © 1995 by the National Federation of the Blind.

From the Associate Editor: On February 15, 1991, newspapers across the country carried a story written by UPI Science Writer, Rebecca Kolberg. It reported on a breakthrough in the ongoing struggle to conquer diabetes. Researchers have now identified the gene that seems to cause one form of adult-onset diabetes. This is only the beginning of a long battle to correct the gene in question, but it is a beginning. Here is the story as it appeared on February 15:

After more than three years of searching, scientists reported that for the first time they have closed in on a genetic defect that appears to cause a common form of diabetes.

Researchers said Thursday that they have traced a gene responsible for non-insulin-dependent diabetes to chromosome twenty, although they have not yet pinpointed the genetic culprit's precise location. Every human has twenty-three pairs of chromosomes, which carry the genetic blueprints for traits ranging from hair color to risk of cancer.

About thirteen million Americans suffer from non-insulin- dependent diabetes and another one million have insulin-dependent diabetes, the American Diabetes Association said.

It has long been known that inheritance plays a major role in diabetes, but until the latest work scientists have not been able to find a specific genetic clue to the most common type of diabetes.

"This finding confirms, first of all, that genetics play a role in the development of diabetes," said Graeme Bell of the University of Chicago, who led the study published in the Proceedings of the National Academy of Sciences.

Diabetes refers to disorders related to abnormal levels of sugar in the blood. In healthy individuals chemical messengers such as insulin help control blood sugar levels to prevent damage to organs and other tissues.

The two major forms are called Type 1, or insulin-dependent, and Type 2, adult-onset or non-insulin-dependent diabetes. Type 1 diabetics do not have enough insulin; Type 2 diabetics often have insulin, but their bodies do not respond properly to this messenger.

Diabetics are two to six times as likely to have strokes. One in five develops cataracts or glaucoma. About five percent go blind.

In the study University of Chicago, University of Michigan, and University of Pennsylvania researchers examined the genetic makeup of members of a large white family from Michigan with a high rate of non-insulin-dependent diabetes. About forty of the two-hundred-seventy-five family members, who spanned five generations, had a subtype of diabetes usually detectable before the patient reaches the age of twenty-five.

Family members with diabetes shared a pattern in the genetic material on the long arm of chromosome 20 that was different from the pattern seen in their healthy relatives, the researchers said.

Bell's team now is trying to find the exact site of the gene and determine its function in the hope of gaining insights into the underlying cause of the disease and perhaps better ways to treat the illness.

"A lot depends on how lucky we get. A couple years (until the gene is found) would not be unreasonable," said Bell, who is a professor of biochemistry and molecular biology.

Richard Kahn, chief scientific officer for the American Diabetes Association, called the latest finding "a major advance." "For the first time, this begins to address the issue of what gene or genes are responsible for Type 2 diabetes, Kahn said. "This opens the way towards better understanding of the disease and how to prevent or cure it."

However, Kahn cautioned that it is uncertain what proportion of people with non-insulin-dependent diabetes would be affected by the new discovery. It is not known exactly how many of the people with non-insulin-dependent diabetes suffer from the subtype of the disease that troubled the Michigan family. Estimates of the frequency of the subtype, which is called mature-onset diabetes of the young, range from one percent to eighteen percent in various ethnic groups.

Researchers are now testing other families with a high rate of non-insulin-dependent diabetes to see if they have a genetic pattern similar to that found in the Michigan family.

Bell said it is unlikely the gene will be the only one responsible for insulin-dependent diabetes, and other genes also probably will be found to play a role in the disease.

"If we can identify these genes, it might be possible for doctors to develop more specific therapies to treat the disorder," Bell said.

In the meantime Bell said the new genetic patterns can be used in the Michigan family to tell which individuals are likely to develop diabetes and which do not have to worry about getting the disease.

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