A Study of Efgartigimod PH20 SC in Children Between 2 and Less Than 18 Years of Age with Generalized Myasthenia Gravis

Inclusion Criteria:

• The participant (and/or their legally authorized representative) understands therequirements of the study and is capable of providing written informedconsent/assent and complying with protocol requirements

• The participant is aged 2 to <18 years at the time of informed consent/assent

• The participant has been diagnosed with generalised Myasthenia Gravis that issupported by a physical examination and confirmed seropositivity foranti-acetylcholine receptor antibodies

• The participant has had an unsatisfactory response to immunosuppressants,corticosteroids, or acetylcholinesterase inhibitors but is on stable concomitant MGtherapy. If receiving corticosteroids and/or immunosuppressants, must be on a stabledose for ≥1 month before screening

• The participant agrees to use birth control consistent with local regulations andpeople of child-bearing potential must have a negative blood pregnancy test atscreening and a negative urine pregnancy test before receiving the study drug

Exclusion Criteria:

• Is a female adolescent of child-bearing potential who is pregnant and/or lactatingor intends to become pregnant during their participation in the study

• Has worsening muscle weakness secondary to a concurrent infection or as a result ofa medication

• Has a documented lack of clinical response to plasma exchange (PLEX)

• Received a live or live-attenuated vaccine within <4 weeks before screening

• Received a thymectomy within 3 months before screening or is planning to get athymectomy during their participation in the study

• Has a known autoimmune disease or any medical condition that would interfere with anaccurate assessment of clinical symptoms of generalised Myasthenia Gravis or putsthe participant at undue risk

• History of malignancy, cancer, unless considered cured by adequate treatment with noevidence of recurrence for ≥3 years. Adequately treated participants with thefollowing cancers can be included at any time: Basal cell or squamous cell skincancer, Carcinoma in situ of the cervix, Carcinoma in situ of the breast, Incidentalhistological findings of prostate cancer

• Clinically significant active infection that is not sufficiently resolved in theinvestigator's opinion or positive serum test at screening for active infection withany of the following: Hepatitis B virus (HBV), Hepatitis C virus (HCV), HIV

• Has a positive PCR test for SARS-CoV-2 at screening

• Has/had a clinically significant disease, had recent major surgery (within 3 monthsof screening) or intends to have major surgery during the study, or has/had anyother medical condition that, in the investigator's opinion, would confound theresults of the study or put the participant at undue risk

• Has received a different study drug in another clinical study within <12 beforescreening

• Is currently participating in another interventional clinical study

• Has previously participated in an efgartigimod clinical study and received at leastone dose of study drug

• Has a known hypersensitivity to study drug or any of its excipients

• Has a history of or current episode of alcohol, drug, or medication abuse asassessed by the investigator

• Use of some medications before screening (more information is found in the protocol)

The complete list of exclusion criteria can be found in the protocol.