The experiments described here indicate that ARGX-119 has the potential to provide benefit to 70 to 80% of MuSK-MG patients, who carry antibodies only to the first Ig-like domain in MuSK but do provide insight into whether ARGX-119 may provide benefit to the minority of MuSK-MG patients who also carry antibodies to additional domains in MuSK. This evidence concerns the gene MUSK and myasthenia gravis.