In ob/ob mice, a model of obesity-diabetes with markedly elevated levels of circulating GIP, functional K-cell hyperplasia and intact β-cell GIP responsiveness [316,327,328], a range of essential and nonessential neutral and basic amino acids, including arginine, cysteine, histidine, alanine, hydroxyproline and lysine increased plasma levels of GIP [329]. The gene discussed is GIP; the disease is obesity due to melanocortin 4 receptor deficiency.