Missing genes may be linked to obesity, says study

As a result they are missing around 30 genes. The impact on weight could be dramatic, say scientists, suggesting that obesity can run in families.

The abnormality is thought to affect around seven in every 1,000 obese people whose weight is great enough to pose a risk to health.

In England there are around 700,000 such "morbidly" obese individuals.

The research is the first to show that obesity in otherwise physically normal men and women can be caused by the rare loss of a section of DNA.

Scientists do not know the functions of the missing genes. However, previous research suggests that some of them may be associated with delayed development, autism and schizophrenia.

Study leader Prof Philippe Froguel, from Imperial College London, said: "Although the recent rise in obesity in the developed world is down to an unhealthy environment...the difference in the way people respond to this environment is often genetic. It is becoming increasingly clear that for some morbidly obese people, their weight gain has an underlying genetic cause.

"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."

The scientists first identified the missing genes in teenagers and adults who had learning difficulties or delayed development. They found 31 people who had nearly identical "deletions" in one of the two copies of their DNA inherited from parents.

All of the adults with this genetic change had Body Mass Index (BMI) scores of over 30, signifying obesity.

The researchers then went on to study the DNA of 16,053 European people who were either obese or normal weight.

They found 19 more people with the same genetic deletion, all of whom were severely obese. However, the abnormality was not seen in any healthy normal weight people.