Application of Mass Spectrometry in Newborn Screening: About Both Small Molecular Diseases and Lysosomal Storage Diseases

Abstract

OBJECTIVES To determine the prevalence of anti-myeloperoxidase (MPO) antibodies of IgA (IgA anti-MPO) isotype in patients with eosinophilic granulomatosis with polyangiitis (EGPA), and the association of the IgA antibodies with IgG anti-MPO and with disease activity. METHODS Serum samples from patients with EGPA followed in a multi-center longitudinal cohort were tested by ELISA for the presence of IgA anti-MPO and IgG anti-MPO antibodies. Sera from 87 healthy controls were used to define a positive test. Sera from 168 patients with EGPA (298 samples) were tested. Frequencies of positive testing for IgA anti-MPO were compared between patients with active EGPA, patients in remission, and controls. RESULTS IgA anti-MPO was detected in 10 of 168 (6%) patients with EGPA (11 of 298 serum samples) compared to 1 of 87 (1%) healthy controls (p=0.10). All 11 samples testing positive for IgA anti-MPO also tested positive for IgG anti-MPO. Ninety samples tested positive for IgG anti-MPO but negative for IgA. Samples taken during active EGPA were positive for IgA anti-MPO in 6/72 cases (8%), compared to 5/226 (2%) during remission (p=0.03). Among samples taken during moderate or high disease activity, 5/41 were positive (12%, p=0.01 compared to remission). CONCLUSIONS Although IgA anti-MPO antibodies are detectable in some patients with EGPA and may be detectable more frequently during active disease, their presence seems unlikely to provide information beyond what is obtained from conventional IgG anti-MPO.