SAA2 and obesity due to melanocortin 4 receptor deficiency: To investigate whether SAA plays a role in the development of diet-induced obesity and insulin resistance, male and female wild type (WT) and SAA-deficient (TKO) mice were fed either normal rodent diet or a high fat, high sucrose diet with added cholesterol (HFHSC) ad libitum for 16 weeks (study design in Fig 1).