This Phase 2 proof-of-concept, dose range finding study aims to evaluate the safety and efficacy of 3 dose levels of NMD670 vs placebo in adult patients with MG with antibodies against AChR or MuSK, administered twice a day (BID) for 21 days.

Inclusion Criteria:

• Participant must be a male or female being 18 or more, at the time of signing the informed consent
• Diagnosis of MG, MGFA class II, III or IV
• Documented positive AChR or MuSK antibody test.
• Participant must be able to swallow tablets
• Body mass index between 18 and 35 kg/m2, inclusive, at screening, and with a minimum weight of 40 kg
• Contraceptive use by men and women must be consistent with local regulations regarding the methods of contraception for those participating in clinical studies
• Participant is capable of and has given signed informed consent

Exclusion Criteria:

• Known medical or psychological condition(s) or risk factor that, in the opinion of the Investigator, might interfere with the patient's full participation in the study, pose any additional risk for the patient, or confound the assessment of the patient or outcome of the study
• Participants with other significant clinical and/or laboratory safety findings that may interfere with the conduction or interpretation of the study
• Participants that received treatment with an investigational medical product within 30 days or 5 half-lives of the medication, whichever is longer prior to Day 1
• Participants with history of poor compliance with relevant MG therapy
• Female patients who plan to become pregnant during the study or are currently pregnant or breastfeeding