A Phase 1b Study to Investigate Safety and Tolerability of ARGX-119 in Adult Participants With DOK7-Congenital Myasthenic Syndromes (CMS)

Inclusion Criteria:

• At least 18 years of age.

• Has genetically confirmed congenital myasthenic syndromes due to mutation ofdownstream of kinase 7 (DOK7-CMS).

• Participants taking oral beta agonists (eg, albuterol, salbutamol, ephedrine) musthave been receiving the medication for more than 3 months and agree to remain on asame stable dosing regimen of the same medication until the end of the study.

Exclusion Criteria:

• Diagnosis of CMS due to mutation of any gene other than DOK7.

• Known medical condition that would interfere with an accurate assessment of CMS,confound the results of the study, or put the patient at undue risk, as assessed bythe investigator.

• History of malignancy, cancer, unless considered cured by adequate treatment with noevidence of recurrence for more than 5 years. Adequately treated participants withthe following 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.

• Pregnant or lactating state or intention to become pregnant during the study.