Obesity Due to Melanocortin 4 Receptor Deficiency, also known as mc4r deficiency, is related to body mass index quantitative trait locus 20 and leptin deficiency or dysfunction. An important gene associated with Obesity Due to Melanocortin 4 Receptor Deficiency is MC4R (Melanocortin 4 Receptor). Affiliated tissues include bone and brain, and related phenotypes are obesity and increased adipose tissue