In relapsed/refractory MM (RRMM), treatment is line-dependent, with bispecific antibodies (BsAbs) (e.g., teclistamab [BCMA × CD3], talquetamab [GPRC5D × CD3], elranatamab [BCMA × CD3]) and CAR-T (idecabtagene vicleucel [ide-cel], ciltacabtagene autoleucel [cilta-cel]) therapies have reshaped options for triple-class refractory disease [40,44]. This evidence concerns the gene GPRC5D and Miyoshi myopathy.