RAPSN and myasthenia gravis: The active form of vitamin D (1.25D) upregulates the agrin-induced AChR clustering in association with the upregulated expression of rapsyn in C2C12 myotubes (Arakawa and Wagatsuma, 2020); this pharmacologic effect could apply to a group of MG, the antibodies of which are maleficient more to rapsyn-clustered AChR than non-clustered AChR (Cetin et al., 2020).