EIF2AK3 and Miyoshi myopathy: L363, H929, U266, JJN3, RPMI-8226, OPM-2, KMS11, and JIM3 MM cell lines and CD138+ patient-derived cells pinpointed PERK protein overexpression, especially in L363, and H929 cells, which also exhibited the lowest IC50 values upon GSK2606414 treatment, a PERK kinase activity inhibitor.