Further pathological examination revealed a significant increase in apoptosis and a notable decrease in the proliferation of pancreatic β cells (Fig. 3l–o), which led to a substantial decrease in the number and volume of pancreatic islets (Fig. 3h, p), along with a reduction in insulin expression in the β cells of the RegIIIγ cKO mice with T1DM (Fig. 3i–k). The gene discussed is INS; the disease is type 1 diabetes mellitus.