Hyperplasia of α-cells has also been reported in humans [17, 18] and a patient harboring a homozygous GCGR mutation (P86S) has been identified, who showed hyperglucagonemia without the glucagonoma symptoms, diffuse α-cell hyperplasia, and pancreatic neuroendocrine tumors [19]. The gene discussed is GCGR; the disease is pancreatic neuroendocrine tumor.