People with extra copies of certain genes are much more likely to be very skinny, scientists said in the first finding of a genetic cause for extreme thinness.
In a study in the journal Nature, researchers from Britain's Imperial College London and the University of Lausanne in Switzerland found that a duplication of a part of chromosome 16 is associated with being underweight.
Previous research has found that people with a missing copy of these genes are 43 times more likely to be morbidly obese.
"This is the first genetic cause of extreme thinness that has been identified," said 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."
Men more likely to be underweight
He said one reason this latest finding was important is that it shows that failure to thrive in childhood can be genetically driven. "If a child is not eating, it's not necessarily the parents' fault," he said.
According to the researchers, in around one in 2,000 people, part of chromosome 16 is duplicated, making men 23 times and women five times more likely to be underweight i.e., body mass index below 18.5 kg/m2.
Froguel's team examined the DNA of more than 95,000 people for their study. They found that half of all children with the duplication in the study had previously been diagnosed with failure to thrive..
Potential treatment for obesity
A quarter of people with the duplication had microcephaly, which is linked to neurological defects and shorter life expectancy.
Froguel said scientists still have much work to do to find out more about the genes in this region, but their discovery could eventually lead to new potential treatments for obesity and appetite 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.
(Reuters Health, September 2011)