Dr. Vaisse focuses on the identification of genetic defects implicated in multi-factorial metabolic diseases such as obesity and diabetes. His work combines human genetic approaches with molecular biology and animal studies, concentrating on the molecular mechanisms of the adipocyte secreted, weight regulating hormone, leptin. After finding that genetic alterations in the Melanocortin 4 receptor (MC4R), a mediator of the hypothalamic effects of leptin, are responsible for both rare and common forms of human obesity, he has been investigating the frequency of mutations in the MC4R gene as well as additional candidate genes in large cohorts of obese patients.