Muscle-specific receptor tyrosine kinase autoantibodies--a new immunoprecipitation assay.
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.
Matthews
Ian
I
FIRS Laboratories, RSR Ltd., Parc Ty Glas, Llanishen, Cardiff CF14 5DU, UK.
Chen
Shu
S
Hewer
Rachel
R
McGrath
Vivienne
V
Furmaniak
Jadwiga
J
Rees Smith
Bernard
B
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
D001323:Autoantibodies; D007457:Iodine Radioisotopes; D011950:Receptors, Cholinergic; C095714:MUSK protein, human; C475048:MuSK protein, rat; D020794:Receptor Protein-Tyrosine Kinases