Seronegative Myasthenia Gravis - Efgartigimod IV

Inclusion Criteria:

• Evidence of signed and dated informed consent document(s) indicating that thesubject has been informed of all pertinent aspects of the trial. Subjects must bewilling and able to comply with the protocol, complete study assessments, and returnfor follow-up visits.

• Male or female subjects ≥ 18 years old.

• Diagnosis of SN MG defined as: (a) clinical syndrome consistent with a diagnosis ofMG, and not otherwise explained by another condition, (b) abnormal neuromusculartransmission test results demonstrated by single-fiber electromyography orrepetitive nerve stimulation; and (c) negative serologic test for anti-AChR andanti- MuSK antibodies as confirmed at screening, (d) limited, if any, response totherapy with immunotherapy and/or antiacetylcholinesterase (AChE) treatment. Furthertesting for low affinity antibodies to rapsyn-clustered AChR by cell-based assayswill be done at baseline and the results included as part of subgroup analysis. Allpatients will have a negative genetic test for congenital myasthenic syndromes byhistory or at baseline to exclude the possibility of congenital myasthenic syndromemimicking SN MG.

• MGFA Clinical Classification Class II, III, or IV at the time of screening andbaseline.

• Moderate to severe myasthenia gravis as defined by a generalized myasthenia gravisimpairment index score > 11 or MG-ADL score of at least 5 (with >50% of the scoredue to non-ocular symptoms) and a PASS response of "No" and a SSQ of < 70% with atleast 6 months of historical data as the baseline.

• Stable or worsening MG as defined by MGII remaining stable or increasing in the 4week run-in interval.

• Patients are required to be on a stable dose of their MG treatment (Standard ofcare-SoC) for at least one month prior to screening. The SoC is limited to AChEinhibitors, steroids and NSISTs (e.g., azathioprine, methotrexate, cyclosporine,tacrolimus, and mycophenolate mofetil. There is no requirement for specificgeneralised myasthenia gravis therapies.

• Patients who discontinued early from previous trials of efgartigimod for reasonsother than pregnancy, rescue therapy or a SAE can be included.

• Females of childbearing potential who are sexually active with a non-sterilized malepartner must be willing to use at least one highly effective contraception methodfrom the time of screening and for 3 months after the final dose of efgartigimod.

• Non-sterilized males who are sexually active with a female partner of childbearingpotential must be willing to use a condom for the duration of the study and for 3months after the last dose of efgartigimod. Because male condom is not a highlyeffective contraception method, it is strongly recommended that female partners of amale study subject also use a highly effective method of contraception throughoutthis period.

• Vital signs, electrocardiogram (ECG), and laboratory parameters within the normalranges at screening, or, if outside normal ranges, deemed not clinically significantby the Investigator.

• Patient has documented IgG >6 g/L within one month of screening

• Vaccinated for COVID-19 at least 2 weeks prior to screening visit.

Exclusion Criteria:

• Patients who discontinued early from trials of efgartigimod for pregnancy or rescuereasons or an SAE that was likely to result in a life-threatening situation or posea serious safety risk.

• Pregnant and lactating women, and those intending to become pregnant during thetrial or within 3 months after the last dosing. Women of childbearing potentialshould have a negative urine pregnancy test at screening and baseline.

• Male patients who are sexually active and do not intend to use effective methods ofcontraception (as mentioned above) during the trial or within 3 months after thelast dosing or male patients who plan to donate sperm during the trial or within 3months after the last dosing.

• Patients with known hepatitis B virus (HBV), hepatitis C virus (HCV) or humanimmunodeficiency virus (HIV) seropositivity.

• Patients with known autoimmune disease other than MG (e.g., rheumatoid arthritis)which in the investigator opinion would interfere with an accurate assessment ofclinical symptoms.

• Patients with clinical evidence of other significant disease or patients whounderwent a recent major surgery, which could confound the results of the trial orput the patient at undue risk.

• Patients with renal/hepatic function impairment as defined by (Cr>1.5 x elevated)and/or (transaminases > 2.5 x elevation) at screening.

• Patients with known medical history of hypersensitivity to any of the ingredients ofefgartigimod.

• Patients who have received rituximab or eculizumab in the 6 months before screening.

• Patients who have undergone thymectomy within 3 months of screening.

• Patients who had intravenous immunoglobulin or plasma exchange within 4 weeks ofscreening.

• Patient who has clinically significant uncontrolled active or chronic bacterial,viral, or fungal infection at screening

• Patient has received a live or a live-attenuated vaccination during the month beforescreening