Apart from rare cases of genetically determined myasthenic syndromes, the majority (up to 85%) of patients have auto-antibodies (auto-abs) directed against the nicotinic acetylcholine receptor (AChR) [1,2]; low affinity abs against AChR have been found in 5% of the remaining MG patients [3,4]; up to 50% of patients without anti-AChR abs display immunoreactivity to muscle-specific tyrosine kinase (MuSK) [5–7]. Here, MUSK is linked to myasthenia gravis.