It has been known for a long time that obesity tends to run in families, but it was not until about 20 years ago that scientists started to discover that changes in specific genes can have very large impacts on our weight even from early childhood.

One of these genes MC4R makes a protein that is produced in the brain where it sends signals to our appetite centers, telling them how much fat we have stored- When the MC4R gene does not work properly, our brains think we have lower fat stores than we do, signaling that we are starving and need to eat.

A new study, led by scientists from the University of Cambridge and the University of Bristol, has found that around one in every 340 people may carry a disruptive mutation (变异) at MC4R. People who carry these mutations were more likely to have a greater weight from early childhood and, by 18 years of age? they were on average 17 kg heavier, with the majority of this excess weight likely to be fat.

These results were found by studying the MC4R gene in a random sample of around 6,000 participants born in Bristol. Whenever a mutation was found, the researchers went on to study its frequency and effects in the laboratory. Based on the frequency of mutations in this study, it was estimated that around 200,000 people in the UK carry a substantial amount of unexpected fat because of mutations in MC4R.

Professor Stephen O'Rahilly, one of the researchers, said, "Parents of obese children are often blamed for poor parenting and not all children obtain appropriate professional help. Our findings should encourage a more sympathetic and reasonable approach to overweight children and their families- including genetic analysis in all seriously obese children.'

Though the MC4R gene is a striking example, this is only one gene of many that affect our weight. "In the longer term, knowledge of the brain pathways controlled by MC4R should help in the design of ding that help restore people to a healthy weight," Stephen added.