To evaluate utility of caveolae-associated protein 4 (cavin-4) peptide enzyme-linked immunosorbent assay (ELISA) for detection of cavin-4 IgG among patients with immune-mediated rippling muscle disease (iRMD).
iRMD is an autoimmune muscle disease associated with wave-like muscle rippling and percussion-/stretch-induced muscle mounding. Cavin-4-IgG is a novel autoantibody biomarker of iRMD discovered utilizing phage immunoprecipitation sequencing (PhIP-Seq). Peptide-based ELISA offers a high-throughput method to detect patient IgG targeting varying epitopes of cavin-4 in iRMD patients.
Sera from iRMD patients evaluated at Mayo Clinic were tested on whole-human proteome PhIP-Seq to identify cavin-4 epitopes. Peptide-based ELISA and cavin-4-transfected HEK293 cell-based assay (CBA) were utilized for autoantigen confirmation.
Nine patients (5 males) with archived sera within 1 year of iRMD diagnosis were identified (median age 53 [range 19-77] years). PhIP-Seq data revealed cavin-4 as the candidate autoantigen in all patients. Cavin-4 peptide 288-337 amino acid had one of the highest enrichment scores on whole human proteome PhIP-Seq in the majority of patients evaluated (56%). All nine patients were positive by cavin-4 288-337 amino acid peptide ELISA, while only seven of the nine patients were positive on cavin-4 CBA. Archived sera from healthy (CBA n=66, ELISA n=76) and disease controls (ELISA: hyper-gamma globulinemia [HGG], n=9; systemic lupus erythematosus, n=10; multiple sclerosis [MS], n=8; anti-mitochondrial antibody [AMA], n=12 and CBA: HGG, n=7; MS, n=8; AMA, n=12) tested uniformly negative. Clinical presentation of cavin-4 IgG seropositive patients included rippling of lower limb muscles (n=9), proximal weakness (n=4), and myalgia (n=9). All patients had percussion-induced muscle rippling and half had percussion- or stretch-induced muscle mounding. Only one of nine patients had underlying malignancy.
Cavin-4-IgG is a novel biomarker associated with immune-mediated rippling muscle disease. Our study highlights that cavin-4 epitope-based ELISA improves sensitivity without sacrificing specificity for cavin-4 IgG detection in iRMD.