2026 American Academy of Neurology Abstract Website

James Howard¹, Tuan Vu², Chongbo Zhao³, Sushan Luo³, Sarah Hoffmann⁴, Kristl Claeys⁵, Rosa Jimenez⁶, Ineke Seghers⁶, Delphine Masschaele⁶, Wan-Yi Huang⁶, Łukasz Rzepiński⁷, Elisabeth Chroni⁸, Ali Mohammed Alshehri⁹, Ari Breiner¹⁰
¹The University of North Carolina, ²University of South Florida Morsani College of Medicine, ³Huashan Hospital, Fudan University, ⁴Charité – Universitätsmedizin Berlin, ⁵University Hospitals Leuven; and KU Leuven, ⁶argenx, ⁷10th Military Research Hospital and Polyclinic; and University of Science and Technology, ⁸University Hospital of Patras, ⁹King Faisal Specialist Hospital and Research Centre, ¹⁰The Ottawa Hospital/The University of Ottawa

Objective:

To evaluate the efficacy and safety of efgartigimod IV in adults with anti-acetylcholine receptor antibody (AChR-Ab) seronegative generalized myasthenia gravis (gMG) in a Phase 3 trial (ADAPT SERON).

Background:

Approximately 15%-20% of patients with gMG are classified as AChR-Ab seronegative. There is an unmet need for approved treatments for the AChR-Ab seronegative gMG population. Efgartigimod is a human immunoglobulin G1 (IgG1) antibody Fc fragment that reduces IgG levels (including pathogenic autoantibodies) via neonatal Fc receptor blockade.

Design/Methods:

Diagnosis of gMG was confirmed by an MG diagnostic adjudication committee. In the double-blinded, placebo-controlled Part A, adult participants were randomized 1:1 to receive 4 once-weekly infusions of 10 mg/kg efgartigimod IV or placebo followed by a 5-week follow-up period. Part B included an open-label extension (≤2 years).

Results:

Topline results included 119 participants (n=40, MuSK-Ab+; n=6, LRP4-Ab+; n=73, triple seronegative), 58 received efgartigimod IV, and 61 received placebo. The change in Myasthenia Gravis Activities of Daily Living (MG-ADL) total score from baseline to week 4 (primary endpoint) was significantly (P=0.0068) different between efgartigimod IV and placebo groups (overall population), with least squares mean difference (90% CI) of −3.35 (−3.98 to −2.72) and −1.90 (−2.51 to −1.28) in each group, respectively. Incremental improvements in MG-ADL total scores were observed during Part B over subsequent treatment cycles across all three subgroups. Efgartigimod IV was well tolerated, with no new safety signals observed.

Conclusions:

Efgartigimod IV demonstrated statistically significant improvement in MG-ADL total score compared with placebo (primary endpoint), with a clinically meaningful change from baseline, and was well tolerated in participants with AChR-Ab seronegative gMG.