To validate the live cell-based assay (CBA) for testing of clustered acetylcholine receptor antibodies (AchR Ab) in serum for the diagnosis of myasthenia gravis (MG). To show increased sensitivity of this assay in double seronegative children with MG.

A significant proportion of MG patients do not have detectable AchR Ab or muscle-specific tyrosine kinase antibodies by radioimmunoprecipitation (RIPA). This is particularly true for children. The antibody negative status poses an increased problem as more effective therapies present. A live CBA that involves expressing clustered AchR on the cell surface through the co-expression of intracellular anchoring protein rapsyn has demonstrated the ability to detect AchR Ab in 16% to 60% of seronegative MG patients.

100 serum samples, 50 positive for AchR Ab by RIPA and 50 healthy controls, were blinded and assayed three times on different days. Once validated, a cohort of 45 samples from children 16 years old and younger previously tested negative for AchR Ab by RIPA were assayed.

One sample that was previously RIPA positive was omitted due to a processing error before blinding. 100% concurrence was observed with CBA results between the three blinded assays of 100 samples. Of the 49 RIPA positive, 48 tested CBA positive or low positive, and one was negative. All 50 healthy controls tested CBA negative. Of the 45 double seronegative children samples that were tested, 7 were positive by CBA. Follow-up of these 7 patients showed that 3 have ocular MG and 4 have generalized MG.

The AchR Ab test by CBA is a highly sensitive, specific and reproducible assay. It has shown to improve diagnostic sensitivity of AchR Ab in children with MG.