A proliferation-inducing ligand (APRIL), which is highly secreted by myeloid precursor cells (e.g., megakaryocytes, eosinophils, monocytes) and osteoclasts within the MM BM microenvironment [49], canonically binds B-cell maturation antigen (BCMA) on the MM-cell surface to drive survival and proliferation, has also been shown to bind a transmembrane activator, calcium modulator, and cyclophilin ligand interactor (TACI) on Tregs to drive MM-mediated Treg differentiation, proliferation, and survival [50,51]. Here, TNFRSF13B is linked to Miyoshi myopathy.