LEP and obesity due to melanocortin 4 receptor deficiency: In contrast, the obese non-diabetic Zucker model (OZR), characterized by a mutation in the leptin receptor yielding high circulating leptin levels, obesity and insulin resistance but normal fasting blood glucose, does not present any of the characteristic features of pulmonary vascular disease but rather a hyporresponsiveness to several pulmonary vasoconstrictors [16].