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Mutant gene offers cholesterol resistance.

Some people can eat whatever they want and never seem to suffer ill effects. A prime example of that maxim was the 1991 report of an 88-year-old man who ate about 25 soft-boiled egges each day.

Despite his voracious appetite for cholesterol-rich eggs, this man did not appear to suffer from atherosclerosis, the deposition of cholesterol and fatty debris on artery walls (SN: 4/13/91, p.236). Researcher Fred Kern Jr. at the University of Colorado School of Medicine in Denver attributes this man's avoidance of heart trouble to unusually efficient methods of cholesterol metabolism.

Indeed, the man has a mutant gene that allows him to eat high-cholesterol foods with no corresponding rise in low-density lipoprotein (LDL), the carrier molecule that deposits fat-like cholesterol on artery walls, which can cause a heart attack, says Richard B. Weinberg. Weinberg was studying the normal form of the gene and suspected a genetic explanation for the man's apparent cholesterol immunity. He found the mutant form in a frozen sample of the man's blood, which he had obtained from Kern.

Now, Weinberg is reporting findings from a pilot study that confirms previous evidence that the gene plays a role in the way the body manages dietary cholesterol. Weinberg, who is at the Bowman Gray School of Medicine at Wake Forest University in Winston-Salem, N.C., and his colleagues presented their data last week at the American Heart Association's 66th scientific sessions in Atlanta.

The mutant gene produces a protein that differs by a single amino acid from the protein coded for by the normal gene, he says.

Weinberg and his colleagues began their study by recruiting 23 medical students. With a simple blood test, the team looked for the mutation, determining that 11 students produced the flawed version of the protein. The remainder made the normal protein.

For the first two weeks of the study, the investigators told the students to eat a diet that limited cholesterol intake to 200 milligrams (mg) per day. The researchers then told the recruits to eat four eggs per day, a diet that provided the students with 1,000 mg of cholesterol daily. In both phases of the study, students consumed the same amount of fat.

The team discovered that in students who had the normal gene, the concentration of LDL cholesterol in the blood-stream increased from 92.2 mg per deciliter (mg/dl) at the end of the first two weeks to 11.4 mg/dl at the end of the egg-rich dietary phase.

For the 11 students with the mutant gene, that high-cholesterol diet seemed to do little to their LDL amounts. Their LDL rose from 93.8 mg/dl to 95.3 mg/dl during the same period, Weinberg reports.

The students with the mutant gene appeared to escape the deletrious effects of eating lots fo dietary cholesterol, at least in this pilot study, Weinberg says.

"If the results are confirmed, it would be a very important finding," comments Kern.

There may be an evolutionary advantage to inheriting the mutant gene, which is relatively common in some parts of the world. The altered gene may help protect people from clogged arteries, Weinberg speculates. Previous studies have shown the mutation occurs in about 15 percent of people living in societies (such as the United States) that favor high-fat, high-cholesterol diets. By contrast, the mutation appears uncommon in Asia and Africa, where low-fat, low-cholesterol diets are the rule.

If this gene does play a role in a person's response to dietary cholesterol, it may lead to a more individualized approach to preventing hear disease, Weinberg says. It may be that people with the mutant gene can tolerate a high-cholesterol diet and should focus on other risk factors for heart disease, such as smoking, he suggests.

Much about this gene remains mysterious. Researchers have yet to find the mechanism by which the flawed gene shields the body from dietary cholesterol. It may be that the protein produced by the mutant gene inhibits absorption of cholesterol passing through the intestine, Weinberg says. Indeed, Kern, who is retired now, points out that his former patient absorbed just a fraction of the cholesterol in those daily servings of 25 eggs.

And nobody really knows whether the mutant gene alters the body's response to saturated fat in the diet, which can also lead to high cincentrations of cholesterol in the bloodstream (SN: 3/13/92, p.390). If it does, the positive effect on arterial health may be even more significant.
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Author:Fackelmann, Kathy A.
Publication:Science News
Date:Nov 20, 1993
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