GAST and Helicobacter pylori infectious disease: INS‐GAS mice express human gastrin under the control of the insulin promoter yielding a twofold increase of amidated gastrin in the serum of these mice.106 In the absence of Helicobacter infection, INS‐GAS mice show an increase in gastric acid secretion and parietal cell mass at 1–3 months of age and eventually develop atrophy as a result of hypergastrinemia.