HLA antigens in Japanese patients with myasthenia gravis

New treatment strategies in Myasthenia gravis

Myasthenia gravis (MG) is a chronic autoimmune neuromuscular disorder characterized by muscle weakness and fatigue. The disease is primarily caused by antibodies targeting acetylcholine receptors (AChR) and muscle-specific kinase (MuSK) proteins at the neuromuscular junction. Traditional treatments for MG, such as acetylcholinesterase inhibitors, corticosteroids, and immunosuppressants, have shown efficacy but are often associated with significant long-term side effects and variable patient response rates. Notably, approximately 15% of patients exhibit inadequate responses to these standard therapies. Recent advancements in molecular therapies, including monoclonal antibodies, B cell-depleting agents, complement inhibitors, Fc receptor antagonists, and chimeric antigen receptor (CAR) T cell-based therapies, have introduced promising alternatives for MG treatment. These novel therapeutic approaches offer potential improvements in targeting specific immune pathways involved in MG pathogenesis. This review highlights the progress and challenges in developing and implementing these molecular therapies. It discusses their mechanisms, efficacy, and the potential for personalized medicine in managing MG. The integration of new molecular therapies into clinical practice could significantly transform the treatment landscape of MG, offering more effective and tailored therapeutic options for patients who do not respond adequately to traditional treatments. These innovations underscore the importance of ongoing research and clinical trials to optimize therapeutic strategies and improve the quality of life for individuals with MG.

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.

Clinical Characteristics and Prognosis of Very late-onset Myasthenia Gravis in China

Alteration in onset-age distribution in myasthenia gravis (MG) and its increasing prevalence among the elderly underscores the need for a better understanding of the clinical course of MG and the establishment of personalized treatment. In this study we reviewed the demographics, clinical profile, and treatment of MG. Based on onset age, eligible patients were classified as early-onset MG (onset age ≥18 and <50 years), late-onset MG (onset age ≥50 and <65 years), and very late-onset MG (onset age ≥65 years). Overall, 1160 eligible patients were enrolled. Patients with late- and very late-onset MG showed a male predominance (P=0.02), ocular MG subtype (P=0.001), and seropositivity for acetylcholine receptors and titin antibodies (P<0.001). In very late-onset MG, a lower proportion of patients retained minimal manifestations status or better, a higher proportion of patients had MG-related deaths (P<0.001), and a shorter maintenance time of minimal manifestation status or better was seen at the last follow-up (P=0.007) than that in patients with early- and late-onset MG. Non-immunotherapy may associated with a poor prognosis in patients in the very late-onset group. Further studies on very late-onset MG patients should be performed to evaluate the relationship between immunotherapy and prognosis.

Two-step nationwide epidemiological survey of myasthenia gravis in Japan 2018

Objective

To study the updated prevalence and clinical features of myasthenia gravis (MG) in Japan during 2017.

Methods

We sent survey sheets to the randomly selected medical departments (number = 7,545). First, we asked the number of MG patients who visited medical departments from January 1, 2017, to December 31, 2017. Then, we sent the second survey sheet to the medical departments that answered the first survey to obtain the clinical information of patients who received MG diagnosis between January 1, 2015, and December 31, 2017.

Results

The received answer to the first survey were 2,708 (recovery rate: 35.9%). After all, the prevalence of the 100,000 population was estimated as 23.1 (95%CI: 20.5–25.6). As a result of the second survey, we obtained 1,464 case records. After checking the duplications and lacking data, we utilized 1,195 data for further analysis. The median [interquartile range (IQR)] from the onset age of total patients was 59 (43–70) years old. The male-female ratio was 1: 1.15. The onset age [median (IQR)] for female patients was 58 (40–72) years old, and that for male patients was 60 (49–69) years old (Wilcoxon-Mann-Whitney test, p = 0.0299). We divided patients into four categories: 1) anti-acetylcholine receptor antibody (AChRAb) (+) thymoma (Tm) (-), 2) AChRAb(+)Tm(+), 3) anti-muscle-specific kinase antibody (MuSKAb) (+), and AChRAb(-)MuSKAb(-) (double negative; DN). The onset age [median (IQR)] of AChRAb(+)Tm(-) was 64 (48–73) years old, and AChRb(+)Tm(+) was 55 (45–66), MuSKAb(+) was 49 (36–64), DN was 47 (35–60) year old. The multivariate logistic regression analysis using sex, initial symptoms, repetitive nerve stimulation test (RNST), and edrophonium test revealed that sex, ocular symptoms, bulbar symptoms, and RNST were factors to distinguish each category. The myasthenia gravis activities of daily living profile at the severest state were significantly higher in MuSKAb(+). MuSKAb(+) frequently received prednisolone, tacrolimus plasmapheresis, and intravenous immunoglobulin; however, they received less acetylcholine esterase inhibitor. 99.2% of AChRAb(+)Tm(+) and 15.4% of AChRAb(+)Tm(-) received thymectomy. MuSKAb(+) did not receive thymectomy, and only 5.7% of DN received thymectomy. The prognosis was favorable in all categories.

Conclusion

Our result revealed that the prevalence of Japanese MG doubled from the previous study using the same survey method in 2006. We also found that the onset age shifted to the elderly, and the male-female ratio reached almost even. Classification in four categories; AChRAb(+)Tm(-), AChRAb(+)Tm(+), MuSKAb(+), and DN, well describe the specific clinical features of each category and differences in therapeutic approaches.

Practical Management for Use of Eculizumab in the Treatment of Severe, Refractory, Non-Thymomatous, AChR + Generalized Myasthenia Gravis: A Systematic Review

Myasthenia gravis (MG) is a rare autoimmune disorder caused by specific autoantibodies at the neuromuscular junction. MG is classified by the antigen specificity of these antibodies. Acetylcholine receptor (AChR) antibodies are the most common type (74–88%), followed by anti-muscle specific kinase (MuSK) and other antibodies. While all these antibodies lead to neuromuscular transmission failure, the immuno-pathogenic mechanisms are distinct. Complement activation is a primary driver of AChR antibody-positive MG (AChR+ MG) pathogenesis. This leads to the formation of the membrane attack complex and destruction of AChR receptors and the postsynaptic membrane resulting in impaired neurotransmission and muscle weakness characteristic of MG. Broad-based immune-suppressants like corticosteroids are effective in controlling MG; however, their long-term use can be associated with significant adverse effects. Advances in translational research have led to the development of more directed therapeutic agents that are likely to alter the future of MG treatment. Eculizumab is a humanized monoclonal antibody that inhibits the cleavage of complement protein C5 and is approved for use in generalized MG. In this review, we discuss the pathophysiology of MG; the therapeutic efficacy and tolerability of eculizumab, as well as the practical guidelines for its use in MG; future studies exploring the role of eculizumab in different stages and subtypes of MG subtypes; the optimal duration of therapy and its discontinuation; the characterization of non-responder patients; and the use of biomarkers for monitoring therapy are highlighted. Based on the pathophysiologic mechanisms, emerging therapies and new therapeutic targets are also reviewed.

The Epidemiology and Phenotypes of Ocular Manifestations in Childhood and Juvenile Myasthenia Gravis: A Review

Myasthenia gravis (MG) appears to have a similar incidence among adult populations worldwide. However, epidemiological and phenotypic differences have been noted among children and juveniles with MG. We reviewed the literature on childhood- and juvenile-onset MG among different populations, with the focus on ocular involvement, antibody profiles, the genetic susceptibility to juvenile MG phenotypes, the use of immune treatments, and the reported responses of extraocular muscles to therapies. Although epidemiological studies used different methodologies, reports from Asia, compared to Europe, showed more than two-fold higher proportions of prepubertal onset (before 12 years) vs. postpubertal-onset juveniles with MG. Compared to European children, ocular MG was 4-fold more frequent among Asian children, and 2–3-fold more frequent among children with African ancestry both in prepubertal and postpubertal ages at onset. These results suggest genetic influences. In Asia, HLA-B^*46 and DRB1^*09 appeared overrepresented in children with ocular MG. In Europe, children with MG had a significantly higher rate of transforming from ocular to generalized disease and with an overrepresentation of HLADRB1^*04. Although treatment regimens vary widely and the responses to immune therapies of the ocular muscles involved in MG were generally poorly described, there were indications that earlier use of steroid therapy may have better outcomes. Reports of treatment-resistant ophthalmoplegia may be more frequent in African and Asian juvenile MG cohorts compared to Europeans. Genetic and muscle gene expression studies point to dysregulated muscle atrophy signaling and mitochondrial metabolism pathways as pathogenetic mechanisms underpinning treatment-resistant ophthalmoplegia in susceptible individuals. In conclusion, phenotypic differences in juveniles with ocular manifestations of MG were evident in different populations suggesting pathogenetic influences. Treatment responses in MG-associated ocular disease should attract more careful descriptive reports. In MG, extraocular muscles may be vulnerable to critical periods of poor force generation and certain individuals may be particularly susceptible to developing treatment-resistant ophthalmoplegia. The development of prognostic biomarkers to identify these susceptible individuals is an unmet need.

Sex difference in anti-sperm antibodies

Background

Some diseases have sex differences. There have been no reports on the relationship between anti-sperm antibodies (ASA) and sex differences.

Methods

ASA are detected by sperm-immobilization test using patients' sera in women. In men, the ASA testing is generally performed by direct-immunobead test.

Main findings

Sperm-immobilizing antibodies in women inhibit sperm migration in their genital tract and exert inhibitory effects on fertilization. ASA bound to sperm surface in men also show inhibitory effect on sperm passage through cervical mucus. The fertilization rate of IVF significantly decreased when sperm were coated with higher numbers of ASA. For women with the antibodies, it is important to assess individual patients' SI50 titers. In patients with continuously high SI50 titers, pregnancy can be obtained only by IVF. For men with abnormal fertilizing ability by ASA, it is necessary to select intracytoplasmic sperm injection. Production of sperm-immobilizing antibodies is likely to occur in women with particular HLA after exposure to sperm. The risk factors for ASA production in men are still controversial.

Conclusion

Attention to sex differences in specimens, test methods and the diagnosis of ASA should be paid. For patients with ASA, treatment strategies have been established by considering sex difference for each.

Effect of Buzhong Yiqi decoction on anti-acetylcholine receptor antibody and clinical status in juvenile ocular myasthenia gravis

Ocular myasthenia gravis (MG) is the mainly widespread type of MG among juveniles. Buzhong Yiqi decoction (BZ) is a well-known traditional Chinese medicine prescription for treating MG. It has rarely been discussed whether the concentration of anti-acetylcholine receptor (AChR) antibodies is related to the clinical status of juvenile ocular myasthenia gravis (JOMG) treated with BZ.The patients with JOMG who had more than once AChR-antibody (ab) test and treated with BZ were retrospectively identified from June 2013 to January 2020 in the first hospital in Shijiazhuang. The presence or absence of ocular symptoms was used to grade the effectiveness of treatment. Generalized estimating equations logistic regression analysis was used to evaluate the effect of AChR ab concentration on the clinical status of MG.A total of 549 AChR-ab tests were performed in 135 patients, and the corresponding clinical status was recorded. One hundred two patients received treatment with BZ only and 33 combined with immunosuppressive drugs. In the group receiving only BZ treatment, the anti-acetylcholine receptor ab concentration was positively correlated with the clinical score after treatment.The results suggest that BZ could affect the AChR-ab. Repeated AChR-ab assays can provide information about the clinical status. For JOMG patients who only receive Buzhong Yiqi Decoction treatment, this can support treatment decisions.

Contribution of HLA-DRB1 * 09: 01 allele to development of minocycline induced antineutrophil cytoplasmic antibody (ANCA)-associated cutaneous vasculitis: report of two cases

We report two cases of antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV) that developed after long-term oral administration of minocycline and consider the contribution of human leukocyte antigen (HLA)-DRB 1 * 09: 01 allele to its development. Case 1; A 47-year-old man receiving minocycline for palmoplantar pustulosis for 24 months developed fever, arthralgia, and irregular livedo on the bilateral lower legs. Skin biopsy demonstrated vasculitis, while a blood test showed positivity of myeloperoxidase (MPO)-ANCA. Discontinuation of minocycline and oral administration of prednisolone relieved the symptoms promptly. Case 2; A 53-year-old woman developed reddish-brown livedo reticularis with tenderness on the bilateral lower legs after administration of minocycline to treat palmoplantar pustulosis for 24 months. Although skin biopsy did not demonstrate vasculitis, a blood test showed MPO-ANCA positivity. Cessation of minocycline resulted in rapid improvement of the cutaneous lesions and constitutional symptoms. We diagnosed both cases as having Drug-associated ANCA-associated Vasculitis (DAV) caused by minocycline according to the diagnostic criteria proposed by Cluver et al. Further examination revealed the presence of HLA-DRB1 * 09:01 allele in both cases. This allele has been implicated in the genetic background of idiopathic microscopic polyangiitis (MPA) in the Japanese population. Our finding suggests a relationship between the development of MPO-ANCA or DAV caused by minocycline and HLA-DRB1 * 09:01 allele, but will have to confirmed by further studies with larger numbers of patients.

A Patient with Fulminant Myasthenia Gravis Is Seropositive for Both AChR and LRP4 Antibodies, Complicated by Autoimmune Polyglandular Syndrome Type 3

This article describes the first reported case of myasthenia gravis (MG) seropositive for both acetylcholine receptor antibody and low-density lipoprotein receptor-related protein 4 antibody, complicated by autoimmune polyglandular syndrome (APS) type 3. The patient exhibited myasthenic weakness restricted to the ocular muscles and ptosis. Severe clinical deterioration ensued with predominant bulbar symptoms. MG rapidly worsened, the patient was intubated, and agranulocytosis due to thiamazole was also present, so it was necessary to perform thyroidectomy with tracheostomy and thymectomy in two phases. Both the double-seropositive MG and the APS were involved in the patient's rapid deterioration.

Molecular and clinical relationship between live-attenuated Japanese encephalitis vaccination and childhood onset myasthenia gravis

Objective

The incidence of childhood onset myasthenia gravis (CMG) in China is higher than that in other countries; however, the reasons for this are unclear.

Methods

We investigated the clinical and immunological profiles of CMG, and assessed the potential precipitating factors. For the mouse studies, the possible implication of vaccination in the pathogenesis was explored.

Results

In our retrospective study, 51.22% of the 4,219 cases of myasthenia gravis (MG) were of the childhood onset type. The cohort study uncovered that the pathophysiology of CMG was mediated by immune deviation, rather than through gene mutations or virus infections. The administration of the live‐attenuated Japanese encephalitis vaccine (LA‐JEV), but not the inactivated vaccine or other vaccines, in mice induced serum acetylcholine receptor (AChR) antibody production, reduced the AChR density at the endplates, and decreased both muscle strength and response to repetitive nerve stimulation. We found a peptide (containing 7 amino acids) of LA‐JEV similar to the AChR‐α subunit, and immunization with a synthesized protein containing this peptide reproduced the MG‐like phenotype in mice.

Interpretation

Our results describe the immunological profile of CMG. Immunization with LA‐JEV induced an autoimmune reaction against the AChR through molecular mimicry. These findings might explain the higher occurrence rate of CMG in China, where children are routinely vaccinated with LA‐JEV, compared with that in countries, where this vaccination is not as common. Efforts should be made to optimize immunization strategies and reduce the risk for developing autoimmune disorders among children. Ann Neurol 2018;84:386–400

Long-term efficacy and safety of eculizumab in Japanese patients with generalized myasthenia gravis: A subgroup analysis of the REGAIN open-label extension study

The terminal complement inhibitor eculizumab was shown to improve myasthenia gravis-related symptoms in the 26-week, phase 3, randomized, double-blind, placebo-controlled REGAIN study (NCT01997229). In this 52-week sub-analysis of the open-label extension of REGAIN (NCT02301624), eculizumab's efficacy and safety were assessed in 11 Japanese and 88 Caucasian patients with anti-acetylcholine receptor antibody-positive refractory generalized myasthenia gravis. For patients who had received placebo during REGAIN, treatment with open-label eculizumab resulted in generally similar outcomes in the Japanese and Caucasian populations. Rapid improvements were maintained for 52 weeks, assessed by change in score from open-label extension baseline to week 52 (mean [standard error]) using the following scales (in Japanese and Caucasian patients, respectively): Myasthenia Gravis Activities of Daily Living (-2.4 [1.34] and - 3.3 [0.65]); Quantitative Myasthenia Gravis (-2.9 [1.98] and - 4.3 [0.79]); Myasthenia Gravis Composite (-4.5 [2.63] and - 4.9 [1.19]); and Myasthenia Gravis Quality of Life 15-item questionnaire (-8.6 [5.68] and - 6.5 [1.93]). Overall, the safety of eculizumab was consistent with its known safety profile. In this interim sub-analysis, the efficacy and safety of eculizumab in Japanese and Caucasian patients were generally similar, and consistent with the overall REGAIN population.

Myasthenia gravis

Myasthenia gravis (MG) is an autoimmune disease caused by antibodies against the acetylcholine receptor (AChR), muscle-specific kinase (MuSK) or other AChR-related proteins in the postsynaptic muscle membrane. Localized or general muscle weakness is the predominant symptom and is induced by the antibodies. Patients are grouped according to the presence of antibodies, symptoms, age at onset and thymus pathology. Diagnosis is straightforward in most patients with typical symptoms and a positive antibody test, although a detailed clinical and neurophysiological examination is important in antibody-negative patients. MG therapy should be ambitious and aim for clinical remission or only mild symptoms with near-normal function and quality of life. Treatment should be based on MG subgroup and includes symptomatic treatment using acetylcholinesterase inhibitors, thymectomy and immunotherapy. Intravenous immunoglobulin and plasma exchange are fast-acting treatments used for disease exacerbations, and intensive care is necessary during exacerbations with respiratory failure. Comorbidity is frequent, particularly in elderly patients. Active physical training should be encouraged.

Low conversion rate of ocular to generalized myasthenia gravis in Singapore

INTRODUCTION

Ocular myasthenia gravis (OMG) is a common condition of the neuromuscular junction that may convert to generalized myasthenia gravis (GMG). Our aim in this study was to determine the conversion rate and predictive factors for generalization in OMG, in an Asian population.

METHODS

The investigation consisted of a retrospective study of OMG patients with a minimum 2 years of follow-up.

RESULTS

Among 191 patients with OMG, 155 had the minimum 2-year follow-up. The conversion rate at median follow-up (40.8 months) was 10.6% (95% confidence interval 7.9%-13.3%), and at the 2-year follow-up it was 7.7% (95% confidence interval 5.6%-9.8%). At baseline, the predictive factors for generalization were positive acetylcholine receptor antibodies (hazard ratio 3.71, P = 0.024), positive repetitive nerve stimulation (RNS) studies (hazard ratio 4.42, P = 0.003), and presence of radiologically presumed or pathologically confirmed thymoma (hazard ratio 3.10, P = 0.013).

DISCUSSION

The conversion rate of OMG to GMG in Asian patients is low, as predicted by presence of acetylcholine receptor antibodies, presence of thymoma, and positive RNS studies. Muscle Nerve 57: 756-760, 2018.

Juvenile myasthenia gravis in Norway: HLA-DRB1*04:04 is positively associated with prepubertal onset

Background

Juvenile myasthenia gravis (MG) is a rare autoantibody mediated autoimmune disorder targeting the neuromuscular endplate. The clinical hallmark is muscle weakness and fatigability. Disease aetiology is complex, including both genetic and environmental factors. The involvement of genes in the human leukocyte antigen (HLA) is well established in adult MG. However, HLA associations in European juvenile MG have not been studied. This case-control study aimed to investigate and characterize genetic risk factors in prepubertal and postpubertal onset juvenile MG.

Methodology/Principal findings

A population based Norwegian cohort of 43 juvenile MG patients (17 with prepubertal onset, 26 with postpubertal onset) and 368 controls were included. Next generation sequencing of five HLA loci (HLA-A, -B, -C, -DRB1 and -DQB1) was performed, and a positive association was seen with HLA-B*08 (OR (95% CI) = 3.27 (2.00–5.36), P_c = 0.00003) and HLA-DRB1*04:04 (OR (95% CI) = 2.65 (1.57–4.24), P_c = 0.03). Stratified in postpubertal and prepubertal onset, HLA-DRB1*04:04 was only positively associated with the latter (P = 0.01). The HLA-B*08 allele (12.9% in the controls), previously described associated with early onset adult MG, was most frequently observed in postpubertal onset MG (40.4%, P = 0.0002) but also increased among prepubertal onset MG (23.5%, P = 0.05).

Conclusion

This study provides novel information about HLA susceptibility alleles in Norwegian juvenile MG where HLA-DRB1*04:04 was associated with prepubertal onset.

Protective Role of HLA-DRB1*13:02 against Microscopic Polyangiitis and MPO-ANCA-Positive Vasculitides in a Japanese Population: A Case-Control Study

Among antineutrophil cytoplasmic antibody (ANCA)-associated vasculitides (AAV), granulomatosis with polyangiitis (GPA) and proteinase 3-ANCA-positive AAV (PR3-AAV) are prevalent in European populations, while microscopic polyangiitis (MPA) and myeloperoxidase-ANCA-positive AAV (MPO-AAV) are predominant in the Japanese. We previously demonstrated association of DRB1*09:01-DQB1*03:03 haplotype, a haplotype common in East Asians but rare in the European populations, with MPA/MPO-AAV, suggesting that a population difference in HLA-class II plays a role in the epidemiology of this disease. To gain further insights, we increased the sample size and performed an extended association study of DRB1 and DPB1 with AAV subsets in 468 Japanese patients with AAV classified according to the European Medicines Agency algorithm (MPA: 285, GPA: 92, eosinophilic GPA [EGPA]: 56, unclassifiable: 35) and 596 healthy controls. Among these patients, 377 were positive for MPO-ANCA and 62 for PR3-ANCA. The significance level was set at α = 3.3x10-4 by applying Bonferroni correction. The association of DRB1*09:01 with MPO-AAV was confirmed (allele model, P = 2.1x10-4, odds ratio [OR] = 1.57). Protective association of DRB1*13:02 was detected against MPO-AAV (allele model, P = 2.3x10-5, OR = 0.42) and MPA (dominant model, P = 2.7x10-4, OR = 0.43). A trend toward increased frequency of DPB1*04:01, the risk allele for GPA in European populations, was observed among Japanese patients with PR3-AAV when conditioned on DRB1*13:02 (Padjusted = 0.0021, ORadjusted = 3.48). In contrast, the frequency of DPB1*04:01 was decreased among Japanese patients with MPO-AAV, and this effect lost significance when conditioned on DRB1*13:02 (Padjusted = 0.16), suggesting that DRB1*13:02 or other allele(s) in linkage disequilibrium may be responsible for the protection. The differential association of DPB1*04:01 with PR3-AAV and MPO-AAV and difference in DPB1*04:01 allele frequencies between populations supported the hypothesis that the HLA-class II population difference may account in part for these epidemiologic characteristics. Furthermore, taken together with our previous observations, the haplotype carrying DRB1*13:02 was suggested to be a shared protective factor against multiple autoimmune diseases.

CTLA4 variants and haplotype contribute genetic susceptibility to myasthenia gravis in northern Chinese population

BACKGROUND

Cytotoxic T lymphocyte-associated antigen-4 (CTLA4), a critical negative regulator of the T-cell response, has been considered a candidate for many autoimmune diseases. Evidence from Caucasians supported a genetic predisposition of CTLA4 to myasthenia gravis (MG), but the contribution in East Asians has not been established.

OBJECTIVES

To investigate the role of CTLA4 variants in the susceptibility to MG and the contribution to subtypes of MG.

METHODS

Six autoimmune disease-related risk alleles of CTLA4 (rs1863800, rs733618, rs4553808, rs5742909, rs231775, and rs3087243) were investigated for MG in northern Chinese. 168 patients with MG (mean age 37.1±20.5 years, 64 men and 104 women) and 233 healthy controls (mean age 53.3±8.7 years, 96 men and 137 women) were screened, and the contribution of CTLA4 to the general risk of MG and each subgroup was explored.

RESULTS

rs1863800*C, rs733618*C, and rs231775*G were significantly associated with the whole cohort of patients with MG after permutation correction for multiple-testing adjustment (P = 0.027, 0.001, and 0.032, respectively). A risk haplotype (CCACG) [odds ratio (OR) = 1.535, range = 1.150-2.059, P = 0.004)] was also identified. The stratified subtype analysis indicated that the positive contribution was possibly derived from early onset MG (EOMG), seropositive MG (SPMG), female patients, and MG without thymoma. No association was observed in juvenile MG/LOMG, and MG coupled with thymoma.

CONCLUSION

A predisposing effect of rs1863800*C, rs733618*C, and rs231775*G of CTLA4 gene to general risk of MG in Chinese was demonstrated for the first time, which was likely derived from EOMG, SPMG, MG without thymoma and the female patients.

Characterization of CD4 and CD8 T cell responses in MuSK myasthenia gravis

Muscle specific tyrosine kinase myasthenia gravis (MuSK MG) is a form of autoimmune MG that predominantly affects women and has unique clinical features, including prominent bulbar weakness, muscle atrophy, and excellent response to therapeutic plasma exchange. Patients with MuSK MG have predominantly IgG4 autoantibodies directed against MuSK on the postsynaptic muscle membrane. Lymphocyte functionality has not been reported in this condition. The goal of this study was to characterize T cell responses in patients with MuSK MG. Intracellular production of IFN-gamma, TNF-alpha, IL-2, IL-17, and IL-21 by CD4+ and CD8+ T cells was measured by polychromatic flow cytometry in peripheral blood samples from 11 Musk MG patients and 10 healthy controls. Only one MuSK MG patient was not receiving immunosuppressive therapy. Regulatory T cells (Treg) were also included in our analysis to determine if changes in T cell function were due to altered Treg frequencies. CD8+ T cells from MuSK MG patients had higher frequencies of polyfunctional responses than controls, and CD4+ T cells had higher IL-2, TNF-alpha, and IL-17. MuSK MG patients had a higher percentage of CD4+ T cells producing combinations of IFN-gamma/IL-2/TNF-gamma, TNF-alpha/IL-2, and IFN-gamma/TNF-alpha. Interestingly, Treg numbers and CD39 expression were not different from control values. MuSK MG patients had increased frequencies of Th1 and Th17 cytokines and were primed for polyfunctional proinflammatory responses that cannot be explained by a defect in CD39 expression or Treg number.

Genetics of microscopic polyangiitis in the Japanese population

The epidemiology of ANCA-associated vasculitis is substantially different between Caucasians and Japanese, which may be related to differences in genetic backgrounds. In this review, I discussed our findings on the genetics of microscopic polyangiitis (MPA) in Japanese. Analysis of HLA genes revealed a significant increase in the HLA-DRB1*09:01-DQB1*03:03 haplotype MPA. This is one of the most frequent haplotypes in Japanese, but is nearly absent in Caucasians, and has been shown to be associated with multiple autoimmune diseases. Analysis of KIR genes revealed significant decreases in the carrier frequency of an activating receptor KIR2DS3 in MPA. When KIRs were analyzed in combination with HLA ligands, the proportion of individuals carrying KIR3DL1 and HLA-Bw4 but not KIR3DS1, the most inhibitory of all KIR3DS1/3DL1/HLA-B combinations, was significantly increased in MPA. These results suggested that decreased activation of NK and/or T cells may cause a predisposition to MPA. LILRA2 is an activating receptor involved in granulocyte and macrophage activation. LILRA2 SNP rs2241524 G >A, which disrupts the intron 6 splice acceptor site, was significantly associated with MPA. The risk allele produces an LILRA2 isoform lacking three amino acids in the linker region. These findings, when confirmed by larger-scale studies, will shed light on the molecular mechanisms of MPA. (*English Translation of J Jpn Coll Angiol 2009; 49: 31-37.).

Genetics of ANCA-associated vasculitis in Japan: a role for HLA-DRB1*09:01 haplotype

The epidemiology of antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV) is considerably different between European and Asian populations. Whereas granulomatosis with polyangiitis is the most common form of AAV in northern European populations, microscopic polyangiitis (MPA) accounts for the majority of AAV in Japan. This difference may at least in part derive from the difference in genetic background. In this review, I focus on our observation on HLA, an obvious candidate gene for immune disorders, and discuss its potential implication. In Japanese AAV, significant association was detected with HLA-DRB1*09:01, the carrier frequency of which was increased in MPA [P=0.0087, odds ratio (OR) 1.90, 95% confidence interval (CI) 1.17-3.08] and in myeloperoxidase (MPO)-ANCA-positive AAV (P=0.0016, OR 2.05, 95% CI 1.31-3.23) when compared with healthy Japanese controls. HLA-DRB1*09:01 is one of the most common HLA-DRB1 alleles in Asians but is rare in Caucasian populations. Interestingly, HLA-DRB1*09:01 has been shown to be associated with multiple autoimmune diseases, including type 1 diabetes, rheumatoid arthritis, and systemic lupus erythematosus, suggesting that either HLA-DRB1*09:01 itself or other genes in tight linkage disequilibrium may play a role in a molecular pathway shared by various autoimmune diseases in Japanese and possibly in other Asian populations.

HLA and SNP haplotype mapping in the Japanese population

The genes that encode the human leukocyte antigen (HLA) class I and II molecules are highly polymorphic and located in the major histocompatibility complex (MHC) region, where there is a high density of immune-related genes. Numerous studies have identified disease susceptibility in this region; however, interpretation of the results is complicated because of the strong linkage disequilibrium (LD) among HLA alleles and single-nucleotide polymorphisms (SNPs). In this study, we evaluated the correlation between the HLA alleles of 6 loci (HLA-A, C, B, DRB1, DQB1 and DPB1) and 6502 SNPs within 8 Mb of the extended MHC region using 92 Japanese subjects to identify SNP single loci or haplotypes that tag HLA alleles. We found a total of 39 HLA alleles that showed strong LD (r(2)≥0.8) with SNPs, including 11 non-synonymous SNPs in non-HLA genes. In addition, we identified several SNP haplotypes in strong LD (r(2)≥0.8) with eight HLA alleles, which do not possess tag SNPs. Our detailed list of tag SNPs and haplotypes could be utilized for a better understanding of the results obtained by association studies in the Japanese population and for the characterization of the differences in LD structures between races.

ANCA-associated vasculitis with dual ANCA positivity in coexistence with mixed connective tissue disease

We here report a rare case of dual antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV) in a 38-year-old Japanese woman previously diagnosed with mixed connective tissue disease. The patient was found to be positive for myeloperoxidase- and proteinase 3-ANCA, and was diagnosed with AAV following admission to hospital with fervescence, polyarthralgia, purpura, and asymmetric numbness of the extremities. Examination of her genetic background revealed that she carried HLA-DR9, which confers risk of both diseases in Japanese populations.

Subtle differences in HLA DQ haplotype-associated presentation of AChR α-chain peptides may suffice to mediate myasthenia gravis

The HLA DQA1 and DQB1 alleles were determined on a set of 24 myasthenia gravis patients that had previously been examined for their T-cell proliferative responses to the 18 overlapping peptides representing the extracellular domain of hAChR alpha-chain. Patient responses according to assumed cis or trans haplotypes were significantly higher in most cases relative to normal controls. Comparisons of in vitro peptide-stimulated T-cell responses of patient pairs which had DQA1:DQB1 in common displayed responses in tighter distribution relative to comparisons in which patient pairs did not share the same DQA1:DQB1 haplotype. Similar haplotypes, such as DQA1*0102:DQB1*0602 and DQA1*0102:DQB1*0604, tended to exhibit similar responses and were grouped according to this similarity. Modified F-test and Student's T-test analyses on DQ isoform bearing groups revealed that high responses to peptide alpha34-49 were associated with A1*0102:B1*0602/0604, A1*0301:B1*0302 and A1*0401/0303:B1*0301. Peptide alpha146-162 showed higher responses in A1*0301:B1*0302 group and moderate responses in A1*0401/0303:B1*0301 groups. Differences in the age of disease onset relative to DQ haplotypes were also observed. Groups of A1*0301:B1*0302, A1*0501:B1*0201 and A1*0102:B1*0604 showed earlier ages of disease onset relative to those of A1*0102:B1*0602 or A1*0505:B1*0301.

Suppression by mAbs against DQB1 peptides ofin vitroproliferation of AChR-specific T cells from myasthenia gravis patients

It has been indicated that multiple genes, including HLA genes, are collectively involved in the susceptibility to myasthenia gravis (MG). DQB1 alleles represent one of those associated with MG. We have prepared B-cell hybridomas that produce mAbs against peptides corresponding to the tip of the MHC antigen-binding cavity (region 70-90) of alleles DQB1*02, *03, *05 and *06. The mAbs bound to DQ molecules isolated from cells. In the assays using peripheral blood lymphocytes (PBL) from patients with MG, the mAbs against peptides of the correlate HLA DQ sequences inhibited the in vitro proliferation of acetylcholine receptor (AChR)-specific T cells. The results indicate that the function of disease-related MHC alleles may be blocked by directly and selectively targeting the antigen-presenting region on these MHC molecules. The results also suggest that DQ molecules are one of those involved in the restriction of autoimmune anti-AChR responses in MG. The strategy could provide an effective means for immunointervention in MG. It may also potentially be adapted for down-regulation of undesirable immune responses such as in other autoimmune diseases, allergic reactions, or clinical conditions where immune responses to a therapeutic protein develop.

Autoimmune myasthenia gravis: emerging clinical and biological heterogeneity

Acquired myasthenia gravis (MG) is an autoimmune disorder of the neuromuscular junction in which patients experience fluctuating skeletal muscle weakness that often affects selected muscle groups preferentially. The target of the autoimmune attack in most cases is the skeletal muscle acetylcholine receptor (AChR), but in others, non-AChR components of the neuromuscular junction, such as the muscle-specific receptor tyrosine kinase, are targeted. The pathophysiological result is muscle endplate dysfunction and consequent fatigable muscle weakness. Clinical presentations vary substantially, both for anti-AChR positive and negative MG, and accurate diagnosis and selection of effective treatment depends on recognition of less typical as well as classic disease phenotypes. Accumulating evidence suggests that clinical MG subgroups might respond differently to treatment. In this Review, we provide current information about the epidemiology, immunopathogenesis, clinical presentations, diagnosis, and treatment of MG, including emerging therapeutic strategies.

Genetic factors in autoimmune myasthenia gravis

Autoimmune myasthenia gravis (MG) is a multifactorial disease, markedly influenced by genetic factors, even though it shows limited heritability. The clinically typical form of autoimmune MG with thymus hyperplasia shows the most reproducible genetic associations, especially with the A1-B8-DR3 (8.1) haplotype of the major histocompatibility complex (MHC). However, because of strong linkage disequilibrium, the causative polymorphism in this region is not known yet. Increasing the density of genetic markers has nevertheless recently revealed the complex, but highly significant contribution of this essential genetic region in controlling the disease phenotype and the quantitative expression of serum autoantibodies. The advances of the human genome program, the development of genotyping and sequencing tools with increasing throughput, and the availability of powerful statistical methods now make feasible the dissection of a complex genetic region, such as the MHC and beyond, the systematic search throughout the genome for variants influencing disease predisposition. The identification of such functional variants should provide new clues to the pathogenesis of MG, as recently illustrated by the study of a promoter polymorphism of the CHRNA1 locus, influencing its thymic expression and central tolerance, or of a coding variant of the PTPN22 intracellular phosphatase.

A study of the factors inducing the development of childhood-onset myasthenia gravis using CDR3 spectratyping analysis of the TCR repertoire

Myasthenia gravis (MG) is an autoimmune disease. AChR-specific autologous helper T (Th) cells are essential to the pathogenesis of MG. Factors correlated with the development of childhood-onset MG are unknown. In longitudinal studies, we found TCR Vbeta 2/5.1/6/7 usage in the development or relapse phases, but not in the remission phase. We also found that TCR Vbeta 8/9/13.1/15/18/20 usage persisted. The polyclonally expanded TCR Vbeta 2/5.1/6/7 by CDR3 spectratyping was found to be associated with the development of disease. These data suggest that in patients with childhood-onset MG, stimuli such as superantigens induced by a preceding infection, which cause development of the polyclonal pattern in TCR Vbeta families, play an important role in the development of the disease.

Clinical and serological study of myasthenia gravis in HuBei Province, China

BACKGROUND

Ocular and childhood myasthenia gravis (MG) cases seem relatively more common in Oriental than in Caucasian populations, but there have been no comprehensive serological studies on patients from mainland China.

METHODS

391 unselected patients with MG attending Tongji Hospital in WuHan (the largest hospital in the province of HuBei, China) were studied during a 15-month period; most had already received treatment for their condition.

RESULTS

The male to female ratio was 0.8. 50% of the patients were children (<15 years), and age at onset showed a single peak at between 5 and 10 years of age. 64% of the children and 66% of the adults were positive for acetylcholine receptor (AChR) antibodies but the antibody titres were lower than in similar Caucasian studies, although this was partly due to the high incidence of ocular MG. Of the 43 patients with generalised MG without AChR antibodies, only 1 had muscle-specific kinase antibodies (2.5%) and 2 had voltage-gated calcium channel antibodies indicating probable Lambert-Eaton myasthenic syndrome. 75% of the children, compared with only 28% of the adults, had ocular MG. Thymoma was evident by MRI in 1.5% of children and in 20% of adults. Despite most patients having received prednisone, very few had obtained full clinical remission.

CONCLUSION

This study emphasises the frequency of early childhood onset with ocular symptoms and shows that many of these patients have AChR antibodies. By contrast, patients presenting in later age seem to be very uncommon in comparison with recent studies in Caucasian populations.

Myasthenia gravis: clinical, immunological, and therapeutic advances

We give an update on clinical, immunological, and therapeutic advances in the field of myasthenia gravis, including a summary of suggested therapeutic recommendations.

A variant of childhood-onset myasthenia gravis: HLA typing and clinical characteristics in Japan

To investigate the correlation between clinical features and HLA DR/DQ genetic variability in myasthenia gravis (MG), we evaluated HLA DR/DQ allele frequencies in 87 Japanese patients with childhood-onset disease. HLA genotypes DRB1*1302/DQA1*0102/DQB1*0604 and DRB1*0901/DQA1*0301/DQB1*0303 were significantly higher in patients than in healthy controls (P(c) < 0.0001, RR = 5.5; P(c) < 0.0001, RR = 8.5, for two genotypes, respectively). Patients who had a significantly higher likelihood of the HLA types DRB1*1302/DQA1*0102/DQB1*0604 or DRB1*0901/DQA1*0301/DQB1*0303 belonged to the latent general type (LG) of MG; this is clinically ocular type, but shows myasthenic electromyographic findings in extremity muscles. The LG type of MG was observed in 78% of patients exhibiting the clinically ocular type; this group comprised approximately 75% of patients with childhood-onset MG. These date suggest that LG type of MG may present a particular subset of childhood-onset MG, which is associated with the specific HLA subtypes DRB1*1302/DQA1*0102/DQB1*0604 and DRB1*0901/DQA1*0301/DQB1*0303.

HLA Class II and class I polymorphism in venezuelan patients with myasthenia gravis

Oligotyping performed among ethnically mixed Venezuelan patients with myasthenia gravis (MG) and controls has revealed positive associations of HLA class I A*31, B*08, B*39, B*40, C*15, C*17, and class II DRB1*09 and negative associations of DQB1*06 and DQA1*02 with the disease. Sequential removal of human leukocyte antigen B (HLA-B) alleles when relative predispositional effects (RPEs) were looked for demonstrated that B*08 is the allele group with the largest contribution in the overall MG patients followed by B*39 and B*40. Several specificities (A*31, B*08, C*17, DRB1*03, DQA1*05, and DQB1*02) indicated increased frequencies among patients with thymic hyperplasia versus patients without hyperplasia or controls. Tests to identify alleles with the strongest association to MG in our patients detected DRB1*13 and B*38 as possible predisposing secondarily associated alleles in patients with hyperplasia. The associations observed disappear after Bonferoni correction of probability values and have been described in patients of Caucasian and/or Oriental ethnic background. Thus, our results reflect the heterogeneity of our population and of the patients tested and suggest a limited influence of several HLA genes in this heterogeneous disease or that these might be only markers of nearby non-HLA genes responsible for the susceptibility or resistance effect.

Genetics of autoimmune myasthenia gravis, a model for antibody-mediated autoimmunity in man

Autoimmune myasthenia gravis is an antibody-mediated autoimmune disease of the neuromuscular junction aimed at the muscle acetylcholine receptor. Recent genetic analyses focusing on a nonclass II HLA-linked locus, MYAS1, and on one of the genes encoding the AChR self-antigen, CHRNA1, are discussed.

HLA-DQ6 transgenic mice resistance to experimental autoimmune myasthenia gravis is linked to reduced acetylcholine receptor-specific IFN-gamma, IL-2 and IL-10 production

To comprehend the reduced susceptibility of HLA-DQ6 transgenic mice in comparison with HLA-DQ8 mice, to experimental autoimmune myasthenia gravis (EAMG), we immunized them with acetylcholine receptor (AChR) and examined in vitro, the proliferative and cytokine responses to AChR. When immunized with AChR and examined for AChR-specific lymphocyte responses to AChR, EAMG-resistant DQ6 mice exhibited significantly reduced in vitro lymphoproliferative and cytokine responses to AChR, compared to DQ8 mice. The differences in susceptibility were not linked to a difference in peptide recognition by AChR-specific lymphocytes. AChR T cell epitope mapping showed that both DQ6 and DQ8 responded to the same epitopes, although to varying degrees. Resistance of DQ6 transgenic mice to EAMG was linked to a dramatic suppression of AChR-specific IFN-gamma, IL-2 and IL-10 productions by AChR-primed lymph node cells.

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.

HLA-DR and HLA-DQ gene typing of infertile women possessing sperm-immobilizing antibody

Thirty-eight infertile women, possessing sperm-immobilizing antibody (SIA), were examined for their HLA-DR and -DQ types using DNA obtained from peripheral blood cells. The typing of HLA-DR and DQ was performed by polymerase chain reaction sequence specific oligonucleotide probes (PCR-SSOP) and PCR-restriction fragment length polymorphism (RFLP), respectively. In comparison to the normal Japanese population, the SIA positive patient population had higher genes frequencies in HLA-DRB1*0901 (26.3 vs. 13.6%, P<0.005), DQB1*0602 (13.2 vs. 6.2%, P<0.05) and -DQB1*0303 (26.3 vs. 14.8%, P<0.01), but not in any HLA-DQA1 gene types by chi2 test. After Bonferroni correction, the high frequency of HLA-DRB1*0901 remained significant (P<0.05) and HLA-DQB1*303 was slightly significant (P<0.07) but no other genes had a gene frequency significantly higher than that of the normal Japanese population. HLA-DRB1*0901 and HLA-DQB1*0303 are very rare among Caucasians but characteristically high among Japanese. The high frequency of HLA-DRB1*0901 and DQB1*0303 genes in the Japanese population may account for higher frequency of sperm-immobilizing antibody in Japanese compared to other ethnic groups.

A susceptibility region for myasthenia gravis extending into the HLA-class I sector telomeric to HLA-C

We have analyzed a series of HLA region markers in 207 UK Caucasoids with early-onset myasthenia gravis (EOMG, onset before age 40), where there is a strong female bias. The well known associations with HLA-DR3 and -B8 have now proved to be significantly stronger in the 165 females than in the 42 males. In patients (of either sex) lacking -DR3, there was also a significant increase in HLA-DR2. Although the muscle weakness in EOMG is clearly mediated by autoantibodies, the associations are consistently stronger with HLA-B8 (in class I) than with HLADR3 (in class II), as confirmed here. We therefore typed 87-137 cases for polymorphisms at four loci in the intervening class III region, and also at three in the adjacent stretch of class I. At each locus, one allele tended to co-occur with HLA-B8 and showed strong and highly significant associations in the patients. There appeared to be a region of maximal susceptibility extending from HSP70 (in class III) past HLA-B and HLA-C at least 600 kb telomerically into the class I region, which is now being mapped in detail. Any candidate genes here that act shortly after puberty may allow more precise localization of susceptibility.

Peptide-based molecular analyses of HLA class II-associated susceptibility to autoimmune diseases

Recent advances in knowledge of crystal structures of MHC class II molecules has advanced understanding of the molecular basis for interactions between peptides and HLA class II molecules. Polymorphism of HLA class II molecules influences structures of peptides bound to HLA class II molecules. To better understand mechanisms related to particular HLA class II alleles and autoimmune diseases, it is important to identify self-peptides presented by disease-susceptible HLA class II molecules and triggering disease-causative autoreactive T cells. Autoimmune diseases occur in Caucasians, Blacks and Asians, albeit with a different incidence. In some autoimmune diseases, disease-susceptible HLA class II alleles are closely related but different, and clinical manifestations of diseases differ among ethnic groups. These phenomena strongly suggest that difference in autoimmune self-peptide(s) in the context of disease-susceptible HLA class II molecules may explain the different clinical manifestations of diseases. Therefore, a comparison among disease-susceptible HLA class II alleles, autoimmune self-peptides and clinical manifestations of autoimmune diseases in different ethnic groups would be instructive. We directed efforts to determining: (1) HLA-class II alleles specific to Asian populations and which are associated with susceptibility to autoimmune diseases, (2) binding-peptide motifs for these HLA class II molecules, and (3) self-peptides presented by susceptible HLA class II molecules to stimulate autoreactive T cells related to the development of autoimmune diseases in Asians. In this review, our related recent investigations are described and the uniqueness of HLA class II-associated autoimmune diseases in Asians is given emphasis.