Yes. Though Mysathenia Gravis is treated in S. Korea it is very expensive.

 begin partial quote from previous article

• Insurance & Costs: While major hospitals deliver excellent care, the full cost of MG treatment for complex cases can be very high. Many of the newest, most expensive targeted drugs can pose a significant financial burden if they have not yet obtained full national health insurance reimbursement for every patient. 
• end quote.
•  
• So, likely the medical tourism for this disease isn't likely going to work for my son or likely for others from around the world. So, even though people living in S. Korea might get this help at a reasonable price this isn't true for Medical Tourists.