MUSK and myasthenia gravis: The major described MG subgroups include: age of onset [early-onset MG (EOMG; onset ≤ 50 years) versus late-onset MG (LOMG; onset > 50 years]; the presence of a thymoma (thymoma-associated MG, TAMG); and antibody subtype [acetylcholine receptor antibody-seropositive (AChR+) versus muscle-specific tyrosine kinase antibody seropositive (MuSK+)] (1).