The first common genetic variant that substantially increases a person’s risk of obesity has been identified, researchers claim. They hope that their discovery will open doors to new treatments for the condition.
The team identified a small genetic change in a region of DNA near a gene known as INSIG2 as being linked to obesity. DNA code is made up of four bases, or "letters". A single change in this particular region, from a G to a C, makes a person more prone to obesity, according to the study.
They believe this change somehow affects the regulation of the gene INSIG2, which has a role in fat production.
The US researchers, led by Alan Herbert at the Boston University Medical School, found that an individual with two copies of the C variant is 22% more likely to have a body mass index (BMI) greater than 30 – the point where people move from being "overweight" to "obese".
This is the first study to strongly identify a genetic component in obesity in a number of populations, comments Carol Shoulders at Imperial College London, UK.
Environmental factors
More than one-third of people in the US are obese and other countries’ populations are increasingly facing similar weight issues. Scientists predict that genes may contribute anywhere from 30% to 70% of the risk of obesity, but they stress that environmental factors, like diet, play a crucial role.
Herbert and colleagues looked at almost 87,000 points in the human genome which show variation between individuals, and related this to the BMIs of over 900 people. They studied families from a long-running coronary study in Massachusetts, called the Framingham Heart Study.
The team found that one particular genetic variation near the INSIG2 gene correlated well with obesity.
Slim nurses
In follow-up studies involving about 9000 individuals in total, they found the same association. The C variant was found to increase the risk of obesity in populations including people of Western European ancestry, African Americans and children. About 10% of populations they studied carried two copies of this mutation.
Herbert notes that the C variant did not show a strong influence on obesity risk in a population of nurses they also examined. He says that this might be because nurses concerned about maintaining a healthy weight were more likely to participate in the study.
People with two copies of the C variant were about 1 BMI unit heavier than other individuals – a relatively small difference in weight – than those with one or no copies of this variant. This underscores the idea that the genetic variant simply tips people from overweight to obese, believes Shoulders.
Journal reference: Science (DOI: 10.1126/science.1124779)
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