Under physiological conditions, most of the proteins transiting through the ER are properly folded, whereas in pathological situations there is an accumulation of misfolded proteins that can originate in the ER or cytoplasm. Misfolded proteins can accumulate within the ER owing to direct mutations in disease-related genes or perturbations in the function of the secretory pathway at different levels (FIG. 3). The load of misfolded protein in the ER is reduced by ER-associated protein degradation (ERAD), a process in which these proteins are targeted to the cytoplasm for proteasome-mediated degradation.