The underlying cause of a very slim constitution of individuals who fail to gain weight would be an excess of genes, according to a study by researchers from several countries on 100,000 people.
The results of the study focused on the cause of this pathological condition that is associated with a higher mortality risk, were published in the British journal Nature. The research was conducted by a team of French, British and Swiss specialists, coordinated by Philippe Froguel, from Imperial College London and Institut Pasteur in Lille, and Jacques Beckmann from the University of Lausanne.
Researchers have shown that obesity and slenderness is based on the number of copies of a gene of the chromosome 16 fragment. Most people have two copies of each gene in this fragment of chromosome, one from each parent. However, approximately one in 2,500 has only one copy, and one in 2,000 has three copies.
The same team of researchers found in 2010 that the presence of a single copy in this fragment of chromosome 16 could be the cause of 1% of cases of severe obesity.
In this study, they demonstrated that the persons with an excess of genetic material – three copies of genes – are extremely thin. These people have a risk 20 times higher than the general population to have a weight below the one considered normal.
Genes with three copies, 28 in number, are probably “genes of appetite”, said Froguel.
Thus, half of children with this anomaly have a weight below normal and are very difficult to feed. They may suffer from disturbances in development and can get to weigh at four years old as a child of one and a half, Froguel said.
The researchers identified 138 carriers of these abnormalities among the 100,000 people studied. In one third of cases, this mutation was not found in the parents and for the other two thirds was inherited, said Froguel.
For adults of both sexes, weighing 40 kg is a mortality rate as high as for those of 100 kg, he said. “There are no elders among identified carriers”, said Froguel.