Scientists have discovered a new inherited form of obesity and type 2 diabetes in humans. A large number of genes are involved in regulating body weight, and there are now over 30 genes known in which people with harmful changes in DNA sequence become extremely overweight. Similarly, there are a number of genes that can, when altered, cause type 2 diabetes. These conditions are inherited through families in exactly the same way as disorders such as cystic fibrosis or Huntington's disease.

It is unclear what proportion of severe obesity and type 2 diabetes is caused by genetic disease.

Researchers at Imperial College London discovered the new defect by sequencing the DNA of an extremely obese young woman and members of her family. In addition to an increased appetite leading to severe weight problems from childhood, she had type 2 diabetes, learning difficulties, and reproductive problems. 

They found that she had inherited two copies of a harmful genetic change that meant she could not make a protein called carboxypeptidase-E (CPE). This is an enzyme that is important in the proper processing of a number of hormones and brain transmitters controlling appetite, insulin and other hormones important in the reproductive system.

Studies have previously shown that CPE deficiency causes obesity, diabetes, and impaired memory in mice, but no humans with the condition have been found before. CPE deficiency is a recessive condition, so a person would need to inherit the altered genetic sequence from both parents to be affected.

The study, published in the journal PLOS ONE, was funded by the NIHR Imperial Biomedical Research Centre and Diabetes UK.