LRP4 and Fatigable weakness: AChR antibodies, which are of the IgG1 and IgG3 subtypes, are the main antibodies found in patients with seropositive myasthenia, while a smaller proportion would have antibodies directed against tyrosine kinase muscle-specific kinase (MuSK) and low-density lipoprotein receptor-related protein 4 (LRP-4) [5].