The MuSK Ab-positive subgroup of “seronegative patients,” anti-MuSK MG, does have clinical similarities to AChR-MG but tends to differ significantly in exhibiting more focal involvement than AChR-MG, frequently with severe involvement of neck, shoulder, facial and bulbar-innervated muscles, although there is considerable variability from patient to patient (78–82). The gene discussed is MUSK; the disease is myasthenia gravis.