Genetic Defect Linked to Childhood Obesity

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British researchers have found that some children may become severely obese because they lack particular portions of DNA which causes excessive hunger.

Dr. Sadaf Farooqui, of Cambridge University, and colleagues studied the DNA of 300 morbidly obese children, looking for mutations called copy number variants (CNVs) which are large chunks of DNA either duplicated or deleted from the genes. The researchers found that several deletions in the DNA chain promoted obesity. The condition is rare, affecting less than 1 percent of severely obese children.

The defect was found on chromosome 16. The missing gene, called SH2B1, has been previously linked to weight regulation and blood sugar control. The mutation affects the body’s response to the hormone Leptin, which signals the brain that the body has had enough to eat. Children with the chromosome deletion have a very strong desire to eat. Follow-up studies found the same gene mutation in some of the children’s parents, who were also obese.

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Prader-Willi syndrome (PWS) is a similar genetic condition that causes a chronic sensation of hunger, leading to overeating and obesity. This abnormality is also related to missing segments of DNA, but on the 15th chromosome, and affects about 1 in 15,000 children, according to the Prader-Willi Syndrome Association.

The study has already had some positive results. Farooqi found four children with the chromosomal defect in Britain who had come to the attention of the British Child Welfare authorities who blamed the parents for abuse. Two of the children were returned to their parents after discovery of the genetic anomaly. The cases of the other two children are in discussions.

"We were able to intervene," said Dr. Farooqui. "It's a slightly unusual outcome of our research, but one we think is very important. (This) has been an emotional rollercoaster for them (the families) and a very stigmatizing experience.”

The study is published online in the current issue of the journal Nature, and adds to the body of knowledge that genetic factors play a major role in obesity today.

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