The Detection Of Antibodies Against Postsynaptic Membrane At Neuromuscular Junction And The Study Of Clinical Characteristics In Myasthenia Gravis

Objective:Mysthenia gravis(MG) is a kind of autoimmue disease induced by antibodies,80% of MG patients have detectable acetylcholine receptor abtibodies(AChR-Ab). At present, it was found a variable proportion of AChR-Ab negative patients have antibodies to the muscle specific tyrosine kinase (MuSK-Ab), which inhibited the clusting of AChRs at the postsynaptic membrane of neuromusclar junction during development, related with the pathogenesis MG closely. We detected the levels of AChR-Ab and MuSK-Ab with fluoroimmunoprecipitation assay, collected the clinical information of patients, compared the clinical feature of AChR antibody -positive MG,MuSK antibody-positive MG and seronegative MG(SNMG).Methods:1. build the fluoroimmunoprecipitation assay MuSK/AChR plasmid was transfected into the human embryonic kidney cells₂93 with polyethylenimine(PEI), optimized PEI/DNA ratio to achieve the best transfecrion efficiency. The antigen extracts were precipitated with serum of MG patients,and the fluorescence unit was read on a fluorescence plate reader. If it is higher than the standard curve which is the mean value of health control group add 3SD, it was considered the patients to be positive for the detected Abs.2. Collected the serum specimen and clinical informations of the 103 patients, detected the antibodies levels of AChR-Ab and MuSK-Ab. Summaried and compared the clinical feature of AChR antibody-positive MG, MuSK antibody-positive MG and seronegative MG(SNMG).Results:Age of the disease onset ranged from 13 to 78 years. There was no significant difference between the three groups regarding sex and age at onset. The mean age of onset was 44.9(18.1) years in woman, and was 45.8(16.2) years in man. The age at onset ranged from 40-59 years in 50% patients. The primary symptom of onset was ocular palsy(86.2%), and it also was the most common feature(96.1%)during the disease process. The percent of patients whose stymptoms at onset involved limb muscles or bulbar muscles was 7.4%(8/103) and 6.4%(6/103).42.7%(44/103) of patients only involved ocular palsy and 57.3%(59/103)patients involved generalized muscles. 71.8% of 103 patients were AChR-Ab positive(64/103), which the 50%of MG patients(20/40) who only involved ocular muscles were AChR-Ab positive and about 85.7% of patients(54/63) who involved generalized muscles were AChR-Ab positive. Among the 29 AChR-Ab negative patients,5 patients were MuSK-Ab positive (17%,5/29). There was no difference regarding sex, age at onset and symptom at onset among AChR-Ab positive group, MuSK-Ab positive group and SNMG group. The striking feature of these patients were the bulbar symptoms that were significantly more common in MuSK-Ab positive patients(60%) compared with SNMG patients(8.3%,P=0.02). The patients involved in bulbar muscles were more common in AChR-Ab positive patients than SNMG patients(P=0.001). There was significant difference regarding the patients involved in limb muscles in AChR-Ab poitive patients compared with SNMG patients(P=0.008). The more common symptom was ocular palsy in SNMG patients.The disease severity was evaluated using the Myasthenia Gravis Foundation of American(MGFA) scales and quantitive MG score. The proportion of SNMG patients(75%,18/24) in MFGA I was higher than AChR-Ab positive patients and MuSK-Ab positive patients(P=0.001). The proportion of AChR-Ab positive patients in MGFAII was higer than other two groups(60.8%, P=0.013). The proportion of MuSK-Ab positive patients (MGFA≥Ⅲ) was the higest(40%,P=0.023). The levels of MuSK antibodies correlated with quantitive MG score(r=0.949, P=0.014), but the levels of AChR antibodies had no coreelation with disease severity.The proportion of thymus disorder(thymic hyperplasia/thymoma)in all MG patients was 41.7%(43/103), including 22.3%(23/103) of patients with thymoma and 19.4%(20/103) of patients with thymic hyperplasia. It was found that there was no patients with thymic hyperplasia or thymoma in MuSK-Ab positive groups, but the frequency of patients with thymic hyperplasia or thymoma changes in AChR-Ab positive patients and SNMG patients was 23%,27%and 12.5%,12.5%respectively. In contrast with the 61.7%of patients without thymus changes were AChR-Ab positive, the higher frequency of patients with thymic hyperplasia(85%) or thymoma(87%) were AChR-Ab positive(P=0.025). Conclusions:The age at onset of MG patients was predominantly between 40 and 59 years, and there was no difference in gender. Ocular palsy was the primary symptom at onset, and it also was the most common feature with or without involved generalized muscles.71.8% of 103 patients were AChR-Ab positive, which the 50% of MG patients who only involved ocular muscles were AChR-Ab positive and about 85.7% of patients who involved generalized muscles were AChR-Ab positive. MuSK antibodies,which can be detected in 17% of patients without AChR antibodies, were never found in patients with AChR antidodies. The levels of MuSK antibodies correlated with disease severity. The thymic hyperplasia and thymoma were not found in the patients with MuSK antibodies. The patients involved in limb muscles were more common in AChR-Ab positive patients,which mainly be in MGFAⅡ, most in MGFA II b. The higher frequency of patients with thymus disease were AChR antibody positive. Mild symptom of patients in SNMG groups,who involved in ocular palsy were more common,mainly belonged in MGFA I...