title: Muscle-specific receptor tyrosine kinase autoantibodies--a new immunoprecipitation assay.
abstract: BACKGROUND
  It has been reported that measurement of autoantibodies to a muscle-specific receptor tyrosine kinase (MuSK) may be useful in the assessment and management of patients with acetylcholine receptor antibody (AChRAb)-negative myasthenia gravis (MG).
  
  
  METHODS
  A new and convenient assay for MuSKAb measurement based on 125I-labeled purified recombinant MuSK is described. In the assay, serum samples (5 microl) were incubated with 50 microl of 125I-MuSK and any immune complexes formed precipitated with antihuman IgG (50 microl).
  
  
  RESULTS
  With this assay, MuSKAbs were detected in 8/33 (24%) sera from AChRAb-negative MG patients studied. In contrast, no MuSKAb was detected in 53 AChRAb-positive MG patient sera; furthermore, 0/18 Lambert-Eaton myasthenic syndrome sera, 0/5 non-MG neuromuscular disease sera, 0/95 control autoimmune disease sera, and 0/50 healthy blood donor sera contained detectable MuSKAb. In this assay, inter-assay coefficients of variation (n = 5) were 6.8%, 5.9%, and 3.6% for samples with MuSKAbs at 0.73, 0.32, and 0.11 nmol/l, respectively. Similar results were obtained with 125I-labeled rat and human MuSK.
  
  
  CONCLUSIONS
  The 125I-MuSK immunoprecipitation assay we have described provides a simple, specific, and precise procedure for detecting MuSKAbs.
authors.affiliation: FIRS Laboratories, RSR Ltd., Parc Ty Glas, Llanishen, Cardiff CF14 5DU, UK.
authors.forename: Ian
authors.initials: I
authors.lastname: Matthews
authors.forename: Shu
authors.initials: S
authors.lastname: Chen
authors.forename: Rachel
authors.initials: R
authors.lastname: Hewer
authors.forename: Vivienne
authors.initials: V
authors.lastname: McGrath
authors.forename: Jadwiga
authors.initials: J
authors.lastname: Furmaniak
authors.forename: Bernard
authors.initials: B
authors.lastname: Rees Smith
mesh_terms: D000818:Animals; D001323:Autoantibodies / Q000097:blood*; D006801:Humans; D047468:Immunoprecipitation / Q000379:methods; D007457:Iodine Radioisotopes; D009157:Myasthenia Gravis / Q000175:diagnosis; D051381:Rats; D020794:Receptor Protein-Tyrosine Kinases / Q000276:immunology*; D011950:Receptors, Cholinergic / Q000276:immunology*; D012680:Sensitivity and Specificity
chemical_list: D001323:Autoantibodies; D007457:Iodine Radioisotopes; D011950:Receptors, Cholinergic; C095714:MUSK protein, human; C475048:MuSK protein, rat; D020794:Receptor Protein-Tyrosine Kinases