<prompt> Myasthenia gravis is an autoimmune disorder and antibodies against which of the following can cause the disease?Acetylcholine receptors AchRMuscle specific kinase protein MUSKLowdensity lipoprotein receptor related protein 4 LRP4All of the above  <response>: MG is an autoimmune disorder most commonly caused by anti- AChR antibodies. The anti-AChR antibodies reduce the number of available AChRs. An immune response to muscle-specific kinase MuSK, a protein involved in AChR clustering at the NMJ, can also result in MG, with reduction of AChRs demonstrated experimentally. Anti-MuSK antibody occurs in about 10 of patients about 40 of AChR antibody negative patients, while 1-3 have antibodies to another protein at the NMJ--low-density lipoprotein receptor-related protein 4 LRP4--that is also impoant for clustering of AChRs. The pathogenic antibodies are IgG and are T cell dependent. Ref harrison 20th edition page 3232 