Researchers have found the genetic cause for extreme thinness, finding that people with extra copies of certain genes are more likely to be really skinny.
Part of chromosome 16 is duplicated in one in 2000 people, making men 23 times more likely to be underweight and women five times as likely. Most people usually have one copy of each chromosome from each parent but parts of some chromosomes can be duplicated or deleted, leading to abnormality.
Researchers at Imperial College London and the University of Lausanne linked duplication of a part of chromosome 16 with being underweight, which is defined as a a body mass index below 18.5, after examining the DNA of around 95,000 people.
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