Genetic studies have now identified more than 30 genes involved in extreme overweight and type 2 diabetes. Both are genetic conditions that run through families.
However, the proportion of type 2 diabetes and severe obesity caused by genetic alterations remains poorly understood by scientists. Using DNA sequencing, the team of researchers was able to identify a new genetic defect in a young obese woman and her family members. She had increased appetite that led to weight problems from childhood. The woman also had reproductive problems, learning difficulties and type 2 diabetes.
The researchers identified that the women had inherited two copies of a harmful genetic change that meant she could not produce a protein called carboxypeptidase-E (CPE), an enzyme that processes hormones and brain transmitters responsible for the control of appetite and the reproductive system.
CPE deficiency has been found in previous studies to cause obesity, diabetes, and impaired memory in mice, however, there is a lack of research in humans. Since CPE deficiency is a recessive disorder, for the patient in to study to have been affected, she had to inherit the genetic mutation sequence from both parents.
Professor Alex Blakemore from the Department of Medicine at Imperial College London, who led the study, said in a recent news release: “There are now an increasing number of single-gene causes of obesity and diabetes known. We don’t know how many more have yet to be discovered, or what proportion of the severely obese people in our population have these diseases — it is not possible to tell just by looking.”
He went on to explain that, “these are serious disorders that affect the body’s ability to regulate hunger and fullness signals. They are inherited in the just same way as other genetic diseases and the sufferers should not be stigmatised for their condition. They should be offered genetic counseling and specialised lifelong support to allow them as healthy a life as possible.”
The parents of the patients involved in the study are cousins, which increased her likelihood of inheriting the same genetic change. Her brother, who had the same symptoms, died when he was 21 years old.
The first author of the study, Dr. Sanne Alsters, also in the Department of Medicine, said: “Finding a genetic cause for the patient’s problems has helped her and her family to understand and manage her condition better. We can also look at members of her family with one abnormal copy of the gene, to see they are affected in more subtle ways that could increase their risk of obesity.”
Professor Blakemore said that patients with severe obesity should have genetic tests available. “If people are diagnosed with a genetic condition like this one, we can look for other possible symptoms, and offer genetic advice to other family members if they want this. Diagnosis is very valuable to the patient. It helps to set realistic expectations, and can help them get the best possible treatment,” she said.