Some obese people have a genetic mutation that causes their condition, according to researchers based at the Philipps-University in Marburg, Germany. They found that around 2-3 per cent of very obese people inherit an altered version of a gene involved in weight regulation. The researchers, who published their results in the Journal of Medical Genetics, say that it may be harder for people carrying the mutation to lose weight through diet and exercise. Their findings confirm earlier studies published last year.
A person's weight is influenced by many different genetic and non-genetic factors, but it seems as though mutations in a gene called MC4R can have a 'major' impact on body mass index (BMI: your body weight in kilograms divided by the square of your height in metres). The gene, which has previously been linked to obesity in mice and humans, makes a protein called melanocortin-4 receptor. In the latest study, scientists looked at DNA from 25 very obese people, as well as 181 of their relatives. They found that people with MC4R gene mutations had a 'significantly higher' BMI than those that did not, and that the effect was twice as strong in women as it was in men.
The effects of the gene mutation seems to run in families, with first and second degree relatives of obese people with MC4R mutations also likely to be obese. However, some non-obese relatives had also inherited mutations, confirming that many different factors cause obesity. The MC4R gene is only one gene of many likely to be involved in obesity, since it is only altered in 2-3 per cent of very obese people. Last year, an international team of researchers reported that people who inherit an altered version of a gene called GAD are more likely to overeat and become obese. Other research has implicated mutations in the gene that makes the appetite-control hormone leptin.