PM20D1 and obesity due to melanocortin 4 receptor deficiency: In addition, using genetic approaches to either increase or decrease the levels of Pm20d1, we show that the metabolic and thermogenic differences between BALB/c and C57BL/6 mice can be shifted by interventions to either reduce or increase the levels of Pm20d1. Finally, we show that variants in the promoter region of the PM20D1 gene in humans are associated with obesity and metabolic syndrome.