Muscle-specific kinase antibody-positive (MuSK Ab+) generalized myasthenia gravis (gMG) is often more severe and harder to treat than acetylcholine receptor antibody-positive (AChR Ab+) gMG
This study was conducted to analyze the efficacy of rozanolixizumab, a neonatal Fc receptor inhibitor, in a subgroup of patients with MuSK Ab+ gMG.
The Phase 3, double-blind MycarinG study (MG0003/NCT03971422) randomized 200 patients (≥18 years with MGFA Class II–IVa gMG, AChR Ab+ or MuSK Ab+) to weekly rozanolixizumab 7mg/kg, 10mg/kg or placebo for 6 weeks. The primary endpoint was change from baseline (CFB) at Day 43 in Myasthenia Gravis Activities of Daily Living (MG-ADL) score; other efficacy endpoints were Myasthenia Gravis Composite (MGC) and Quantitative Myasthenia Gravis (QMG) scores. Efficacy was tested statistically in the overall population and described in prespecified antibody subgroups.
Patients (N=200 [21 historical MuSK Ab+]) were randomized to rozanolixizumab 7mg/kg (n=66 ), 10mg/kg (n=67 ), or placebo (n=67 ). Day 43 least squares mean CFBs in MG-ADL for the overall population were −3.37 for 7mg/kg and −3.40 for 10mg/kg vs −0.78 for placebo (both dose groups statistically significant vs placebo, p<0.001); MGC and QMG CFBs for both rozanolixizumab groups were also statistically significantly different vs placebo CFB (p<0.001). Autoantibody subgroup Day 43 CFBs for 7mg/kg, 10mg/kg and placebo were as follows: MG-ADL: −7.28, −4.16, 2.28 (MuSK) vs −3.03, −3.36, −1.10 (AChR); MGC: −14.14, −8.56, 1.40 (MuSK) vs −4.45, −6.70, −1.83 (AChR); and QMG: −10.79, −7.01, −3.87 (MuSK) vs −6.14, −7.77, −3.09 (AChR). Conclusion Rozanolixizumab improved myasthenia gravis-specific outcomes in MuSK Ab+ gMG, consistent with results in AChR Ab+ gMG and the overall population. Funding: UCB Pharma. These data were previously presented at the MGFA Scientific Session at AANEM, 21–24 September 2022.