MUSK and myasthenia gravis: The Abs classically found in MG are the anti-nicotinic AChR, followed in considerably smaller proportions by Abs against muscle-specific tyrosine kinase (MuSK; 1%–10% of cases) and lipoprotein receptor-related protein 4 (LRP4; 1%–3% of patients) (Guptill et al., 2011; Gilhus 2016; Farrugia and Goodfellow 2020).