Ever wondered how some women can eat whatever they want and still appear underweight? They might have an "overdose" of a certain gene, new research has found.
Scientists at Britain's Imperial College London and the University of Lausanne in Switzerland discovered that a duplication of a part of chromosome 16 is associated with being underweight, Reuters reported.
Previously, researchers found that people with a missing copy of this gene are 43 times more likely to be morbidly obese but this study was the first to identify a cause of extreme thinness.
"This is the first genetic cause of extreme thinness that has been identified," said Professor Philippe Froguel from Imperial's school of public health, who led the study. "It's also the first example of a deletion and a duplication of one part of the genome having opposite effects."
DNA of more than 95,000 children were analysed and half of those with the duplication of the chromosome had previously been diagnosed with a "failure to thrive", which means their rate of weight gain is significantly slower.
Researchers said that a duplication of chromosome makes men 23 times and women five times more likely to be underweight.
Professor Froguel said that while more research is needed, this may lead to new treatments of obesity and eating disorders.
"We now plan to sequence these genes and find out what they do, so we can get an idea of which ones are involved in regulating appetite," he said.
The study was published in the journal Nature.