Obesity Mutation MC4R Reveals more about the 'Pleasures' of Overeating

People who have a common genetic mutation connected to obesity may also respond to pictures of appetizing foods differently than overweight, obese or regular-weight individuals who do not carry the same mutation. 

A recent study published in the Endocrine Society's Journal of Clinical Endocrinology & Metabolism (JCEM), found that a mutation that occurs in about 1 percent of obese people can significantly contribute to weight gain at an early age.

Statistics show that more than one-third of adults are obese--a health issue that typically results from a combination of eating too much, getting too little physical activity and certain genetic components.

A reward signal is triggered in specific areas of the brain that release dopamine and feelings of pleasure when a highly appetizing food is consumed. For many individuals, the chemical release can increase the risk of overeating. However, just how the reward centers of the brain work in overweight or obese individuals is still uncertain.

The most common genetic cause of obesity is from the mutation in the melanocortin 4 receptor (MC4R), which occurs in about 1 percent of obese people and can contribute to weight gain at an early age.

For the study, researchers compared three groups of people: eight people who were obese due to a problem in the MC4R gene, 10 people who were overweight or obese without the gene mutation and eight people who were normal weight.They used functional Magnetic Resonance Imaging (fMRI) scans to examine which reward center areas of the brain were activated when pictures of certain foods were viewed.

"In our study, we found that people with the MC4R mutation responded in the same way as normal weight people, while the overweight people without the gene problem had a lower response," said lead researcher Agatha van der Klaauw, MD, PhD, of the Wellcome Trust-MRC Institute of Metabolic Science at Addenbrooke's Hospital in Cambridge, U.K., in a news release. "In fact, the brain's reward centers light up when people with the mutation and normal weight people viewed pictures of appetizing foods. But overweight people without the mutation did not have the same level of response."

Findings revealed that obese individuals with the MC4R mutation had similar activity in the reward centers of their brains when shown a picture of a decedent dessert as normal weight people. However, researchers found that the reward centers were underactive in overweight people and obese volunteers who did not carry the mutation.

"For the first time, we are seeing that the MC4R pathway is involved in the brain's response to food cues and its underactivity in some overweight people," van der Klaauw added. "Understanding this pathway may help in developing interventions to limit the over-consumption of highly palatable foods that can lead to weight gain."