'Obesity' Gene at Work in Some People

But Gene Accounts for Obesity in Very Few People

From the WebMD Archives

Sept. 29, 2004 - An obesity gene does appear to pack on excess pounds in some people. But most of us can't point to our genetics as a reason for our tight jeans, researchers say.

Previous research has shown that people with abnormalities, or mutations, in certain genes are more likely to be obese. But these abnormal genes are rare and are found in only 2%-5% of obese people, according to new research.

In the study, German researchers focused on one of several genes that are linked to weight and metabolism -- the melanocortin-4 receptor gene, also called "MC4R." Mutations of the gene have been linked to obesity in mice and humans.

At least 34 mutations of this gene have been identified in various studies. Previous research has shown that some people with a mutated gene are overweight while others are not.

Johannes Hebebrand of Philipps University Marburg's child and adolescent psychiatry department, and colleagues studied 25 extremely obese people. They also looked at 181 of their relatives who were of normal weight or overweight, but not obese.

After screening for MC4R gene mutations, the researchers considered the participants' body mass index, or BMI, an indicator of body fat. You can calculate your BMI with WebMD's BMI calculator.

Hebebrand found that people with the gene mutations had a "significantly higher" current BMI than their relatives without the mutations.

The link was twice as strong in women as men.

Middle-aged women with the gene mutation weighed on average nearly 21 pounds more than those without the mutation. Among middle-aged men, the difference was smaller, almost a 9 pound difference between those with the mutation and those without.

The results are consistent with animal studies.

However, some normal-weight relatives also had one of these gene mutations. The researchers say that MCR4 is major gene for the development of obesity. However, given that not everyone with the gene was obese, they note that there are many factors at play in causing obesity.

The report appears in the October issue of the Journal of Medical Genetics.

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SOURCES: Hebebrand, J. Journal of Medical Genetics, October 2004; vol 41: pp 795-800. News release, BMJ Specialist Journals.
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