Vaisse: In 1998, we actually described the first mutation in the melanocortin 4 receptor in humans and it turns out about 2.5 percent of all severely obese humans have mutations in the melanocortin-4 receptors.
Narrator: Recently, Vaisse discovered a new group of mutations in this receptor that affects the body's baseline level of activity.
Vaisse: This is a protein that is implicated in the long-term regulation of energy balance. So basically, what it helps do is adapt your energy intake, which is your food intake, to your energy expenditure.
Narrator: For Science Today, I'm Larissa Branin.