GPRC5D and Miyoshi myopathy: Chimeric antigen receptor T (CAR-T) cells (Figure 5B), engineered to target specific antigens on MM cells, such as B-cell maturation antigen (BCMA), CD38, or G-protein-coupled receptor family C group 5 member D (GPRC5D), have demonstrated significant efficacy in patients with relapsed or refractory MM [121,122].