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Exploring necrotizing autoimmune myopathies with a novel immunoassay for anti-3-hydroxy-3-methyl-glutaryl-CoA
Introduction:
Necrotizing autoimmune myopathies (NAM) have recently been defined as a distinct group of severe acquired myopathies, characterized by prominent myofiber necrosis without significant muscle inflammation. Because of the lack of appropriate biomarkers, these diseases have been long misdiagnosed as atypical forms of myositis. NAM may be associated to autoantibodies directed against signal recognition particle (SRP) or 3-hydroxy-3-methyl-glutaryl-CoA reductase (HMGCR). The objective of this work was to quantify anti-HMGCR autoantibodies in patients with suspicion of NAM through the development of a new addressable laser bead immunoassay (ALBIA).
Methods:
Recombinant HMGCR C-domain was bound to fluorescent beads. After incubation with serum, autoantibodies were revealed using class- or subclass-specific anti-human immunoglobulin G (IgG) antibodies. Anti-HMGCR levels were assayed in 150 patients with suspicion of NAM, 142 controls with different inflammatory/autoimmune diseases and 100 healthy donors. Inhibition with free recombinant HMGCR and immunoprecipitation experiments confirmed test specificity. Reproducibility and repeatability were determined from sera with various levels of anti-HMGCR autoantibodies. A multiplex assay (ALBIA-NAM) was also developed to permit the simultaneous quantification of anti-HMGCR and anti-signal recognition particle autoantibodies.
Results:
No controls scored positive. Of 150 patients with suspicion of NAM, 24% were positive for anti-HMGCR autoantibodies with levels ranging from 24 to 2,656 AU/mL. Anti-HMGCR positivity could be associated to a cytoplasmic pattern in immunofluorescence assay on HEp-2 cells. Anti-HMGCR-positive patients had high creatine kinase (CK) levels (mean 6,630 IU/L) and only 40% of them had been exposed to statins. Multiplex ALBIA-NAM was equally as effective as monoplex anti-HMGCR and anti-SRP ALBIA.
Conclusions:
Both monoplex ALBIA-HMGCR and multiplex ALBIA-NAM reliably detect and quantify anti-HMGCR autoantibodies. A positive result allows ascribing patients with a necrotizing myopathy to an autoimmune form. Anti-HMGCR autoantibodies may be found in patients who have not taken statins.
Insights
Necrotizing autoimmune myopathies (NAM) can now be accurately diagnosed using a new assay for anti-3-hydroxy-3-methyl-glutaryl-CoA reductase (HMGCR) autoantibodies. This test reliably detects these antibodies, aiding in the identification of autoimmune causes of myopathy, even in patients not taking statins.
Area of Science:
- Immunology
- Neurology
- Autoimmunity
Background:
- Necrotizing autoimmune myopathies (NAM) are severe acquired muscle disorders characterized by myofiber necrosis.
- Misdiagnosis is common due to a lack of specific biomarkers, often leading to confusion with other forms of myositis.
- NAM can be associated with autoantibodies against signal recognition particle (SRP) or 3-hydroxy-3-methyl-glutaryl-CoA reductase (HMGCR).
Purpose of the Study:
- To develop and validate a novel addressable laser bead immunoassay (ALBIA) for quantifying anti-HMGCR autoantibodies.
- To improve the diagnostic accuracy of necrotizing autoimmune myopathies.
Main Methods:
- Recombinant HMGCR C-domain was immobilized on fluorescent beads for antibody detection.
- Serum samples from patients with suspected NAM, controls, and healthy donors were tested.
- Specificity was confirmed through inhibition assays and immunoprecipitation; reproducibility and repeatability were assessed.
Main Results:
- The assay reliably detected anti-HMGCR autoantibodies in 24% of patients with suspected NAM.
- Anti-HMGCR positivity was linked to high creatine kinase levels and a cytoplasmic immunofluorescence pattern.
- No controls tested positive, confirming assay specificity.
Conclusions:
- The developed monoplex (ALBIA-HMGCR) and multiplex (ALBIA-NAM) assays accurately detect and quantify anti-HMGCR autoantibodies.
- Positive results aid in classifying necrotizing myopathies as autoimmune in origin.
- Anti-HMGCR autoantibodies can be present in patients without statin exposure.
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