The db/db mice have a deletion mutation in the leptin receptor (LepRdb/db) that results in abnormal splicing and a defective receptor for the adipocyte-derived hormone leptin [31], which leads to typical T2DM symptoms including abnormal hyperglycemia and IR in this mouse class [32], making it the most widely used model of T2DM. The gene discussed is LEP; the disease is type 2 diabetes mellitus.