Calcium-sensing receptor autoantibodies in primary hyperparathyroidism.

BACKGROUND: Mutations in the extracellular calcium-sensing receptor (CaSR) gene are known to be implicated in some cases of primary hyperparathyroidism. However, not all patients display such mutations and so the mechanisms of primary hyperparathyroidism are still largely unknown. An autoimmune origin has been suggested, as autoantibodies against the CaSR have been detected in some patients. The aim of our study was to investigate the presence of CaSR autoantibodies in a large cohort of patients with primary hyperparathyroidism. METHODS: Seventy-five patients were tested for the presence of anti-parathyroid antibodies using an immunoblotting assay with the recombinant extracellular domain of the human CaSR and an immunofluorescence technique with parathyroid adenoma. RESULTS: Five of 75 (6.7%) patients had CaSR autoantibodies. There was no statistically significant difference in the decrease of parathyroid hormone (PTH) level after surgery between patients with or without autoantibodies. Histological examination of parathyroid tissue did not show greater lymphocytic infiltration in patients with autoantibodies than in those without. CONCLUSIONS: This study confirmed that some patients with primary hyperparathyroidism displayed CaSR autoantibodies. The pathophysiological role of these autoantibodies in hyperparathyroidism needs to be further elucidated.

Improvement in diagnosis of rheumatoid arthritis using dual indirect immunofluorescence and immunoblotting assays for antifilaggrin autoantibodies: a retrospective 3 year study.

OBJECTIVE: To determine the clinical usefulness of measuring antistratum corneum (ASC) and antifilaggrin autoantibodies (AFA) to discriminate between rheumatoid arthritis (RA) and other rheumatic or autoimmune diseases, using an indirect immunofluorescence (IIF) assay, along with a complementary immunoblotting technique (IB) when IIF detection of ASC was negative. METHODS: Sera from 346 patients were studied: 189 sera from patients with RA seen in the same clinic, 92 from patients with non-RA rheumatic diseases, 24 from nonrheumatic autoimmune diseases, and 41 from healthy blood donors. ASC and AFA were detected using IIF and IB, respectively. RESULTS: ASC detection using IIF showed a specificity of 97.5% for RA with 44.4% sensitivity. When both IIF and IB techniques were used, sensitivity for RA increased significantly (up to 53.4%; p < 0.01) with no decrease in specificity (p < 0.01). CONCLUSION: These data confirm the usefulness of 2 different techniques performed simultaneously for detecting ASC/AFA, and the usefulness of these biological markers for discriminating between RA and other rheumatic diseases in clinical practice.