NPY and obesity due to melanocortin 4 receptor deficiency: DNA methylation can alter the expression of obesity-associated genes, such as neuropeptide Y (NPY) [15], peroxisome proliferator-activated receptor gamma (PPARγ) [16], fatty acid binding protein 4 (FABP4) [17], and sterol regulatory element-binding protein-1 (SREBP-1) [18].