LRP4 and myasthenia gravis: On the other hand, myasthenia gravis (MG) is a rare organ-specific autoimmune disease of the neuromuscular junction characterized by autoantibodies against the nicotinic acetylcholine receptor (nACHR), the lipoprotein receptor-related protein 4 (LRP4), or the muscle-specific tyrosine kinase (MuSK) receptors [214].