Autoantibodies to low‐density lipoprotein receptor‐related protein 4 that is essential for the neuromuscular junction formation

Myasthenia gravis ( MG ) is an autoimmune disorder characterized by skeletal muscle fatigability and muscle weakness resulting from inhibition of neuromuscular transmission by autoantibodies against synaptic apparatus in the neuromuscular junction ( NMJ ). MG is probably classified into three groups: anti‐acetylcholine receptor ( AC hR) antibody‐positive MG ; antimuscle‐specific kinase (Mu SK ) antibody‐positive MG ; and seronegative MG , which is negative for both antibodies. In patients with seronegative MG , pathogenic factors remain elusive. Recently, a new autoantibody against low‐density lipoprotein receptor‐related protein 4 (Lrp4), which is one of the postsynaptic apparatus and indispensable for the formation of the NMJ , has been identified and has attracted attention as a third MG ‐related autoantibody. In the present review, we discuss the role of Lrp4 in the formation of NMJ , and the molecular mechanism(s) of pathogenesis for anti‐Lrp4 antibody‐positive MG .