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High cholesterol in young black males
Genetic effect appears, then seems to disappear
  
By
Edward R. Winstead



Last week, scientists announced that high cholesterol levels in a population of young African-American men were due to genetic differences. But the more interesting finding was that the high levels returned to the normal range toward the end of the study, causing the researchers to hypothesize that the genetic effect they observed had weakened as the men aged.



Why the levels dropped is a mystery


The study examined three common forms of a gene called MTP in hundreds of black males under age 40 whose cholesterol levels were tested five times during the course of a decade. In the first four tests, men with two copies of the "T" version had significantly higher levels of cholesterol than men with other combinations of MTP variants. Why the blood cholesterol levels of men in the "TT" group eventually dropped is a mystery.

"The real surprise of this study was that in the fifth exam the genetic effect disappeared," says Suh-Hang Hank Juo, of Columbia Genome Center, Columbia University. "We are following this population and may be able to explain this result in five years."

The researchers focused on African-American men because their cholesterol and other blood fat levels are different from Caucasians and they have a higher incidence of cardiovascular diseases than the white population, says Juo. The study included 586 individuals.

Total cholesterol levels for the TT group were between 6 percent and 11 percent higher and the LDL, or "bad," cholesterol was 8 percent to 15 percent higher than the other two groups. To isolate differences due to genetic variation, the researchers controlled for risk factors such as smoking and exercise habits, age, body weight, and alcohol consumption.

The medical information and surveys were collected from participants in a long-term study called CARDIA (Coronary Artery Risk Development in Young Adults), which is sponsored by the National Heart, Lung and Blood Institute. The study has tracked blood cholesterol in several thousand black and white men and women in four US cities since the 1980s.



The first study of its kind


Blood samples were used to determine the MPT variant for each participant. MPT plays a role in the production of a particle that contains cholesterol, and Juo says that a genetic test could be developed if further studies confirm this result. But he is not overstating the findings. Only 39 men in the study (7 percent) had the TT variant, and it remains to be seen whether the effect goes away with age.

Still, this was the first study of its kind, and the researchers produced a significant result even when controlling for a variety of factors. The findings are published this month in Arteriosclerosis, Thrombosis, and Vascular Biology.

"One of the next steps is to look at this gene and cholesterol levels in whites and African-American women," says Juo. He hopes to have those results by the end of next year.

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Juo, S.-H.H. et al. Common polymorphism in promoter of microsomal triglyceride transfer protein gene influences cholesterol, apoB, and triglyceride levels in young African American men: Results from the Coronary Artery Risk Development in Young Adults (CARDIA) study. Arterioscler Thromb Vasc Biol 20, 1316-1322 (May 2000).
 

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