Clinical implementation of anti-acetylcholine receptor antibodies

Myasthenia gravis in childhood

Clinical features, serum acetylcholine receptor antibody (AChRAb) titres and course were reviewed in a series of 25 congenital (CMG) and 30 juvenile (JMG) myasthenia gravis cases to recognize characteristics of childhood-onset myasthenia and its subgroups. The initial symptom for CMG is ptosis accompanied or followed by generalized weakness; myasthenic crises do not occur and spontaneous remissions are rare. In JMG, the distribution of weakness remains the same, but the severity fluctuates: spontaneous remissions (6 patients) and myasthenic crises (10 patients) are observed. Good response to anticholinesterase drugs is slightly more frequent in JMG (62 versus 41%). AChRAbs were present in 9/26 JMG tested, girls with onset after 11 years being more likely to be Ab-positive. Since patients with autoimmune myasthenia and a young age of onset are often seronegative, clinical features such as changing distribution of weakness, fluctuating severity, or response to treatment might be considered as supportive criteria for differentiating JMG from CMG.

Exacerbation of myasthenia gravis after removal of thymomas

It appeared from this prospective and non-randomized study, that the removal of thymomas in myasthenia gravis (MG) patients resulted in rapid exacerbation of the clinical severity of the disease and of anti-acetylcholine receptor antibodies titres, which peaked after about 300 days and continued for up to 2 years. Long-term follow-up after thymomectomy (mean duration +/- SEM after surgery 5.5 +/- 0.8 years) showed that the immunological and clinical state observed prior to surgery was eventually restored, but long-term benefit attributable to surgery could not be demonstrated. Non-thymoma MG cases, however, exhibited post-operative amelioration in clinical course and decreasing antibodies titres, both of which were already significant one year after surgery, and additional improvement was observed at the time of long-term follow-up (mean 4.3 +/- 0.5 years). Furthermore, the prognosis for MG patients not operated on was also favourable. It is suggested that the occurrence of thymomas is linked to genetic factors and that neoplasia of the thymus may be part of immunoregulatory mechanisms with predominance of inhibition.

Anti-acetylcholine receptor (AChR) antibodies measurement in myasthenia gravis: the use of cell line TE671 as a source of AChR antigen

Acetylcholine receptor (AChR) from the human rhabdomyosarcoma cell line TE671 was compared with that of human ischaemic muscle AChR as a source of the antigen for the diagnosis of myasthenia gravis (MG). The sera, which were anti-TE671 cell AChR antibody-negative, all came from patients with low anti-human muscle AChR antibody titers. None of the sera that were seronegative as a result of the human muscle AChR RIA became positive with TE671 cell AChR. The overall sensitivity was 7% less using TE671 cell AChR. The lower sensitivity was observed irrespective of the clinical form of MG. It also appeared from this study that epitopes specific to the junctional isoform of human AChR are essential for the detection of low antibody titers, which accounts for this feature, since TE671 cells only express the extrajunctional isoform of AChR in the surface membrane. Accordingly, AChR from cell line TE671 cannot replace human muscle AChR in the conventional diagnostic immunoprecipitation RIA. There are, however, many other useful implications of AChR from cell line TE671.