Gene mutations behind obesity identified

London: Researchers have discovered mutationsin a gene related to obesity, offering new treatment possibilities in the fight against the global epidemic. Research into the genetic causes of obesity, and related conditions, could be incredibly valuable in finding ways to treat them, researchers said.

There are some drugs available or being tested, but knowing what specific mutations cause obesity allows scientists to create drugs that target them specifically. The study, led by researchers at Imperial College London in the UK, focused on children suffering from obesity in Pakistan, where genetic links to obesity had been previously identified by the team in about 30 per cent of cases.

This link of genes to obesity is due to recessive mutations that are more likely to be inherited and passed on to children in a region like Pakistan because of the high level of consanguinity (inter-family relationships) in its population, researchers said.

This is because parents who are closely related are more likely to be carrying the same mutation, so a child may inherit from both sides, causing the mutation to take effect. The new study, published in the journal Nature Genetics, used genome sequencing and found mutations in one specific gene related to obesity: adenylate cyclase 3 (ADCY3).

When mutations occur in ADCY3, the protein it codes for forms abnormally and does not function properly. This leads to abnormalities relating to appetite control, diabetes, and even sense of smell. "Early studies into ADCY3 tested mice that were bred to lack that gene, found that these animals were obese and also lacked the ability to smell, known as anosmia," said Professor

Philippe Froguel, chair of Genomic Medicine at Imperial. "When we tested our patients, we found that they also had anosmia, again showing a link to mutations in ADCY3," said Froguel. ADCY3 is thought to impact a system that links the hypothalamus (part of the brain) to the production of hormones that regulate a wide variety of biological functions, including appetite.

After identifying the mutations in the Pakistani patients, the researchers entered their results into GeneMatcher, described by Froguel as a "dating agency for genetics". This led to another group of scientists in the Netherlands contacting the team with their own ADCY3 findings in one of their patients with obesity.

This new European patient inherited different mutations on the same ADCY3 gene from both parents (as they were not closely related, as in Pakistan) so the ADCY3 gene of the offspring was not functioning properly, leading to obesity. Further connections were made with a group of Danish scientists, studying the Inuit population of Greenland.

Whilst not traditionally consanguineous (as in close family marriages), this population is small, so inbreeding is likely to have occurred, researchers said. This research also found a link between ADCY3 mutations and obesity, and is published alongside the Imperial research in Nature Genetics.