Myasthenia gravis or certain specified neuromuscular junction disorders

**Definition:** Neuromuscular junction disorders result from damage, malfunction or absence of one or more key proteins involved in neuromuscular transmission. The most common pathology is antibody-mediated lesion or down regulation of ion channels or receptors, resulting in myasthenia gravis, Lambert-Eaton myasthenic syndrome, and acquired neuromyotonia (or Isaac’s syndrome). A second important group of disorders are the congenital myasthenic syndromes caused by mutations in neuromuscular junction proteins.

Myasthenia gravis is the most common autoimmune disease affecting the neuromuscular junction and is characterised by painless fatigable muscle weakness. It is caused by autoantibodies against neuromuscular junction proteins, either the nicotinic acetylcholine receptor (AChR) or the muscle specific tyrosine kinase (MuSK). Mutations in neuromuscular junction proteins cause congenital myasthenic syndromes. Other antibodies mediated conditions affecting the neuromuscular junction, including Lambert Eaton myasthenic syndrome and neuromyotonia.