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C. A Pioneering Human Genetics Study

Narrator : This is Science Today. In 1998, researchers discovered the first mutation in proteins called melanocortin 4 receptors, which it turns out, are found in two to four percent of all severely obese people. Christian Vaisse, an assistant professor of medicine at the University of California, San Francisco, is leading the pioneering Genetics of Human Obesity Study.

Vaisse: And so what we've been doing now is systematically screen a lot of patients for this receptor and then try to understand what this mutation did to the receptor and how they made this receptor dysfunctional and then try to learn more about how this receptor functioned normally.

Narrator: Vaisse recently discovered a new group of mutations in these receptors that interrupt the body's baseline level of activity, which is crucial to maintain normal body weight.

Vaisse: Many of the mutations that we found, they impaired the response to the melancortins, so if they don't activate a receptor anymore, they can't inhibit food intake anymore and therefore, you eat a little more.

Narrator: For Science Today, I'm Larissa Branin.