SAA3-/- mice demonstrated increased gene expression for CD36, a fatty acid transporter linked to obesity and metabolic disease, and decreased expression of the insulin-sensitive genes Glut4 and Irs1, with no change in the expression of peroxisome proliferator-activated receptor γ coactivator-1 alpha (Pgc1a). The gene discussed is IRS1; the disease is obesity due to melanocortin 4 receptor deficiency.