Exploring necrotizing autoimmune myopathies with a novel immunoassay for anti-3-hydroxy-3-methyl-glutaryl-CoA reductase autoantibodies

Abstract

IntroductionNecrotizing 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).MethodsRecombinant 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.ResultsNo 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.ConclusionsBoth 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.

The IgG2 Isotype of Anti–Transcription Intermediary Factor 1γ Autoantibodies Is a Biomarker of Cancer and Mortality in Adult Dermatomyositis

“…The results of the present study were obtained using a newly developed immunoassay to quantify and characterize anti TIF1γ autoantibodies in accordance with our previous expertise (23,33). Immunoprecipitation is valuable for autoantibody discovery but less adapted to routine clinical biology, due to technical complex ity and interpretation difficulties (7,14,27).…”

The Clinical Features of Myositis-Associated Autoantibodies: a Review

“…There is now considerable focus to develop commercially available tests and ELISAs, immunoblotting and line or bead immunoassays that can test for the majority of anti-synthetase group, anti-PM-Scl, anti-SRP and anti-Mi2 [6][7][8][9]. A number of research groups are now producing ELISA and line-blot testing for some of the novel autoAb including the rarer non-Jo1 anti-synthetases, anti-MDA5, anti-TIF1g, anti-NXP2 and anti-HMGCR [6,8,[10][11][12][13][14][15][16][17][18]. Cross collaboration is required to ensure methods are reproducible and validated in large patient cohorts, so that in the near future, we can routinely test for all CTD-myositis overlap antibodies in a clinical setting.…”

“…In addition, the highest risk for anti-HMGCR statin-induced AINM has been shown in HLA-DR11 carriers (HLA DRB1*11:01 allele) [95,96], in comparison to the single nucleotide polymorphism in SLCO1B1, a genetic risk factor seen in 'standard' statin toxic myositis [97]. It is notable that anti-HMGCR AINM is also seen in patients with no prior history of statin exposure [18,95]. Therefore, the finding of anti-HMGCR autoAb-associated myositis should signify to the clinician that patients require treatment with steroids and at least one other immunomodulatory agent with most showing either partial or full response [94,98,99].…”

“…Commercially available ELISA kits are available for a number of autoAb including most anti-ARS, nucleolar SSc-myositis ANAs, anti-Mi2 and anti-SRP. In addition, a number of research groups have developed ELISAs using highly purified recombinant proteins to detect the more novel MAAs, namely the rarer anti-ARS, anti-MDA5, anti-TIF1, anti-NXP2 and anti-HMGCR [9][10][11][12][13][14][15][16][17][18]. The advantage of ELISA detection is higher sensitivity and efficiency with rapid turnover and results.…”

Statins and myositis: the role of anti-HMGCR antibodies

“…[6,7] Laboratory technicians should be aware that when anti-HMCGR is determined by ELISA, the test may yield false-positive results in patients with anti-cortactin antibody, another recently described myositisassociated antibody. [8] Therefore, confirmation of positive ELISA results by immunoblotting is mandatory.…”