In addition, for HSPG alterations in T2D, Simeonovic et al. proposed the “ER stress” model: β-cell endoplasmic reticulum (ER) homeostasis is disrupted during the pathological process of T2D, resulting in ER luminal misfolded protein accumulation and ER stress [168,169]. The gene discussed is SDC2; the disease is type 2 diabetes mellitus.