MUSK and myasthenia gravis: In fact, as reported by Gasperi and coworkers, anti-agrin abs were not found in any double sero-negative-MG sera but only in 5/54 MG-patients, who were also single positive for anti-AChR or anti-MuSK auto-abs or double-seropositive for anti-MuSK/LRP4 abs [33].