NPY and obesity due to melanocortin 4 receptor deficiency: Secondly, in a research study conducted by Corgosinho et al., adolescents carrying the C allele of rs2767485 in LEPR presented increased leptin concentrations and increased expression of orexigenic peptides NPY, AgRP, and MCH, a metabolic state constituting an obstacle to weight loss, with a concomitant increase of AgRP concentration after a one-year obesity lifestyle intervention [49].