Involvement of HLA in clinical courses of myasthenia gravis

Pathophysiology of Childhood-Onset Myasthenia: Abnormalities of Neuromuscular Junction and Autoimmunity and Its Background

The pathophysiology of myasthenia gravis (MG) has been largely elucidated over the past half century, and treatment methods have advanced. However, the number of cases of childhood-onset MG is smaller than that of adult MG, and the treatment of childhood-onset MG has continued to be based on research in the adult field. Research on pathophysiology and treatment methods that account for the unique growth and development of children is now desired. According to an epidemiological survey conducted by the Ministry of Health, Labour and Welfare of Japan, the number of patients with MG by age of onset in Japan is high in early childhood. In recent years, MG has been reported from many countries around the world, but the pattern of the number of patients by age of onset differs between East Asia and Western Europe, confirming that the Japanese pattern is common in East Asia. Furthermore, there are racial differences in autoimmune MG and congenital myasthenic syndromes according to immunogenetic background, and their pathophysiology and relationships are gradually becoming clear. In addition, treatment options are also recognized in different regions of the world. In this review article, I will present recent findings focusing on the differences in pathophysiology.

Heterogeneous immunogenetic background in Japanese adults with myasthenia gravis

The aim of this study was to elucidate the roles of human leukocyte antigen (HLA) class II genes in disease susceptibility in Japanese adult patients with myasthenia gravis (MG). A number of studies have shown that MG is correlated with DR3 in Caucasians. In Japanese, infantile MG is associated with DR9, but the HLA class II alleles associated with adult MG remains unclear. HLA-DRB1 and DQB1 alleles were determined by genotyping in 75 Japanese adult patients with MG and in 115 race-matched healthy adults. No statistically significant difference was observed in the overall prevalences of DRB1 and DQB1 alleles between MG patients and healthy controls, even when the patients and controls were stratified on the basis of their gender. MG patients with DQB1*0604 were younger and those with DQB1*0402 were older at disease onset than those without (P=0.03 and 0.008, respectively). Concomitant autoimmune thyroid disease was associated with DRB1*0803 (P=0.0009, corrected P=0.04). In addition, anti-acetylcholine receptor antibody levels were significantly higher in patients with DQB1*0604 than in those without (P=0.045). These findings indicate that immunogenetic backgrounds in Japanese adult MG patients are heterogeneous and are apparently different from those in Caucasian patients.

Change of immunological parameters in the clinical course of a myasthenia gravis patient with chronic graft-versus-host disease

The change in immunological parameters was studied during the clinical course of a myasthenia gravis (MG) patient with chronic graft-versus-host disease (GVHD), which developed after bone marrow transplantation from an HLA-identical donor. Anti-acetylcholine receptor antibody gradually decreased in the patient treated with immunosuppressive agents, but was not detected in the donor. Lymphocyte numbers were low just before the onset of MG, increased abruptly within several days and then gradually decreased with treatment. The percentage of CD3+ and CD19+ lymphocytes was higher at onset than before, the percentage of CD4+ cells was higher at onset and gradually decreased with treatment, while CD8+ cells showed the lowest level just before onset and gradually increased during the clinical course. CD4+/CD45RA- cells also showed the highest levels at onset and a gradual decrease with treatment. Cellular, as well as humoral immune responses, might be associated with the pathogenesis of MG with chronic GVHD.

Long-term change of anti-acetylcholine receptor antibody in patients with myasthenia gravis after thymectomy

Anti-acetylcholine receptor antibody (AChR Ab) plays an important role in the pathogenesis of myasthenia gravis (MG). We investigated the change of anti-AChR Ab titer after thymectomy of 10 MG patients including five patients whose age at onset was younger than 16 years. Anti-AChR Ab titer was increased in four of six patients with remission and three of four patients without remission. Change of anti-AChR Ab titer in individual patients showed an increase occurred 1-4 years after thymectomy. It is likely that thymectomy influences immune response and induces autoreactive lymphocytes and autoantibodies.

Factors influencing the clinical type and course of myasthenia gravis

Myasthenia gravis is considered to be an autoimmune disease in which several factors reciprocally influence the clinical type and course. We investigated the relative importance of the following factors: anti-acetylcholine receptor antibody (AChR Ab), HLA, age at onset, autoimmunity, thymic abnormality, duration of treatment, change in AChR Ab titer and immunosuppressive therapy. The pretreatment-AChR Ab titer and HLA were shown to significantly influence the clinical type. On the other hand, the age at onset significantly influenced the clinical course. The finding that with an onset at less than 5-year-old there was a tendency for a good prognosis suggests an association between the immaturity of the muscle and immune systems, and the clinical course.