MuSK Ab described in seropositive MG sera found to be Ab to alkaline phosphatase

Abstract

We previously reported finding autoantibodies to muscle-specific receptor tyrosine kinase (MuSK) in 41% of patients with acetylcholine receptor antibody (AChR Ab)–seronegative MG (SNMG),1 as in other reports.2-4 In addition, and in contrast with previous data,2-4 we found a 10.5% positivity rate of MuSK Abs in AChR Ab–seropositive MG (SPMG) patients in the RIA using a recombinant MuSK fusion protein with placental alkaline phosphatase (AP). In this study, we tested MG sera for MuSK Ab in an RIA that uses His-Tag human recombinant MuSK (rMuSK) and for AP Ab using placental AP. The data presented in our earlier article on MuSK Abs in SPMG sera proved to be incorrect, and what we initially believed were MuSK Abs are Abs to AP. Serum samples were obtained from 41 SNMG patients with severe generalized MG and from 229 SPMG patients (50 with, 179 without thymoma). The control populations comprised 70 healthy subjects and 91 patients with other neurologic or immunologic diseases. His-Tag MuSK protein was constructed …