Missing DNA tied to obesity

Last Updated: Wednesday, February 3, 2010 | 6:02 PM ET
CBC News

Some severely obese people are missing a set of genes, a new study has found.

Researchers have found a small proportion of obese people are born without 30 or so of the estimated 30,000 genes in the human genome.

This deletion of genes was not found in any subjects of normal weight, the team from Imperial College London and their colleagues in Europe, the United States and Montreal reported in Wednesday’s issue of the journal Nature.

The missing genes may account for seven out of 1,000 cases of morbid obesity — people with a body mass index, or BMI, over 40, the study found. The body mass index is a tool used to determine the healthy weight range for a particular height. A BMI over 30 is considered obese and 25 to 29.9 is overweight.

The recent rise in obesity in the developed world has been attributed to an abundance of unhealthy food and too little exercise, but the way people respond to these environmental factors is often genetic, said Prof. Phillipe Froguel, lead author of the study at the School of Public Health at Imperial College London.

“It is becoming increasingly clear that for some morbidly obese people, their weight gain has an underlying genetic cause,” Froguel said in a news release.

“If we can identify these individuals through genetic testing, we can then offer them appropriate support and medical interventions, such as the option of weight-loss surgery, to improve their long-term health.”

Searched general population
In the first part of the study, researchers looked for the genes in obese teenagers and adults with learning difficulties or delayed development. They found 31 severely obese people with nearly identical deletions in one copy of their DNA.

The second part of the study looked at the genomes of 16,053 European people in the general population, reflecting a range of weights. Nineteen people in this group were missing the same set of genes, and all were morbidly obese.

Those lacking the genes tended to be normal weight as toddlers, overweight during childhood and severely obese as adults, the researchers said.

The study is the first to confirm that severe obesity in otherwise physically healthy individuals can be caused by a rare deletion of DNA, the authors said.

Until now, individual genes linked to weight gain have had a relatively modest effect of about two pounds.

“The genetic change identified in this study is much less common but leads to much more substantial changes in the body weight of the individuals that it affects,” study co-author Dr. Robert Sladek of McGill University in Montreal said in a release Wednesday.

Researchers have found a similar modest effect with genes influencing Type 2 diabetes. The approach the obesity researchers used — identifying the deletion in very obese people and then looking for the variant in a much broader population — could help to identify genetic influences on Type 2 diabetes and other diseases, the researchers said.

They now plan to study the function of the missing genes. Previous studies have suggested that deletions of these genes may be linked with delayed development, autism and schizophrenia.

DNAWellnessinfo.com Resource: http://www.cbc.ca/health/story/2010/02/03/obesity-dna-deletion.html

Missing DNA Can Promote Childhood Obesity

By MALCOLM RITTER AP Science Writer
NEW YORK December 6, 2009 (AP)

Some children get severely obese because they lack particular chunks of DNA, which kicks their hunger into overdrive, researchers report.

The British researchers checked the DNA of 300 children who’d become very fat, on the order of 220 pounds by age 10. They looked for deletions or extra copies of DNA segments.

They found evidence that several rare deletions may promote obesity, including one kind they studied further and found in less than 1 percent of about 1,200 severely obese children.

That deletion, on chromosome 16, apparently causes trouble because it removes a gene that the brain needs to respond to the appetite-controlling hormone leptin, said Dr. Sadaf Farooqi of Cambridge University.

In her study, children with a chromosome 16 DNA deletion “have a very strong drive to eat,” said Farooqi, who co-led the research. “They’re very, very hungry, they always want to eat.”

The work, reported online Sunday by the journal Nature, has already produced a real-world payoff. Farooqi said four children with the chromosome 16 deletion had drawn the attention of British child welfare authorities, who blamed the parents for overfeeding them.

“We were able to intervene” and get the parents of two children off the hook, and the other two cases are under discussion, she said.

That’s happened before when the scientists uncovered genetic causes for severe childhood obesity, she said.

“It’s a slightly unusual outcome of our research, but one we think is very important,” she said.

While scientists had previously discovered particular genes that promote obesity when damaged, the new work looked at larger chunks of DNA that can span several genes. The chromosome 16 deletion includes nine genes.

Eric Ravussin, an obesity expert at the Pennington Biomedical Research Center in Baton Rouge, La., who wasn’t involved in the study, said the work provides “a gold mine of information.” That’s because it identifies specific chromosome areas that scientists can explore to discover obesity-related genes, he said.

Nature: http://www.nature.com/nature

DNAWellnessinfo.com Resource:  http://abcnews.go.com/Technology/wirestory?id=9263514&page=1