IRS1 and obesity due to melanocortin 4 receptor deficiency: Since phosphorylation of IRS-1 Ser612 is a physiological characteristic of cardiovascular pathology [25, 32], type 2 diabetes [26], obesity and hypertension [26, 27], our data suggest that the high levels of phosphorylation of Ser612 in young WT mice may promote cardiovascular pathology and also serve as a marker of this disease as well as of aging.