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MED NEWS |
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Gene for Diabetes Found
From bio.com 10/25/04 -- A gene involved
in the action of insulin is associated with type 2 diabetes and the body's response to insulin, report scientists at Donald W. Bowden, Ph.D., the principal investigator, and his colleagues described the gene in two
articles in the November issue of Diabetes, a journal of the American Diabetes Association. Bowden said the gene is called
PTPN1 (Protein Tyrosine Phosphatase N1) and is found on the human chromosome 20, which has long been targeted by investigators
as a likely site for diabetes genes. "The protein that this gene makes represses
the insulin response, so if you are making a lot of this protein, your ability to respond to insulin would be blunted, which
would lead to higher glucose (sugar) in your bloodstream. If it is too high, that's diabetes," said Bowden, professor of biochemistry
and internal medicine - endocrinology. The researchers found several variants of the PTPN1 gene, he said. "One common form is associated
with diabetes, and there's another common form that appears to be protective." The
risky variant of PTPN1 gene is found in about 35 percent of the Caucasian population and the protective form of PTPN1 is found
in about 45 percent. The other variants are apparently neutral, neither enhancing nor reducing the risk of diabetes. "There
are certainly other genes that contribute to diabetes," Bowden said. "This is good evidence for one." The researchers found a "remarkably similar pattern" in Hispanics. "In Hispanic families, people who had
the risky form of the gene did not respond to insulin well and had higher levels of glucose in their blood - both risk factors
for diabetes." Bowden said the newly discovered gene could be a significant contributor
to diabetes in Americans. With Josyf C. Mychaleckyj, "we've carried out calculations to try to assess how much of an impact
the different forms of this gene have on diabetes in the population. The best guess right now is it contributes to about 20
percent of diabetes in Caucasian Americans." But the picture becomes more complex in other racial groups. "The effect doesn't seem to be there
in African-Americans," Bowden said. Other genes may be responsible for diabetes in African-Americans, and the research team
is pursuing those genes. Bowden said the research was conducted in three population
studies. The first group involved 300 Caucasian patients with type 2 diabetes and end-stage kidney disease, matched with 310
unrelated Caucasian subjects who do not have diabetes. The results were confirmed in a second completely independent group
of 275 Caucasians with diabetes who are participating in the Diabetes Heart Study and a 200-person control group. The third group was from the IRAS Family Study (Insulin Resistance Atherosclerosis Family Study), a national
study in which He said fifth-year graduate student Jennifer Bento used the latest genetic technologies to work
through the entire region of chromosome 20, "genotyped hundreds of markers," and found the different forms of PTPN1. Besides Bowden, Bento and Mychaleckyj, the team also included Nicholette D. Palmer,
Leslie A. Lange, Carl D. Langefeld , Ph.D., and Stephen Rich. Ph.D. of Public Health Sciences and Barry I. Freedman, M.D.,
a nephrologist. Source: MJA 1995; 163: 372-375 (Medical Journal of Hypertension is twice as prevalent in diabetic as in
non-diabetic individuals.1 Furthermore, it has been clearly shown that hypertension in diabetic patients is associated
with accelerated progression of both microvascular (retinopathy and nephropathy)5 and macrovascular (atherosclerotic) complications.3 Macrovascular disease accounts for the majority of deaths in patients with non-insulin-dependent
diabetes mellitus (NIDDM). The presence of hypertension in this type of diabetes is associated with a 4-5-fold increase in
mortality, predominantly from coronary artery disease and stroke MJA 1995; 163: 372-375 (Medical Journal of |
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