Prevalence and Clinical Associations of Calcium-Sensing Receptor and NALP5 Autoantibodies in Finnish APECED Patients

Context: Previous studies have identified the calcium-sensing receptor (CaSR) and NALP5 as parathyroid autoantibody targets in patients with autoimmune polyendocrinopathy-candidiasis-ectodermal dystrophy (APECED). However, although NALP5 antibodies have been associated with the occurrence of hypoparathyroidism (HP) in APECED, it is unclear whether CaSR antibodies are a specific or sensitive marker for APECED-associated HP. Objective: The objective of the study was to identify associations between the presence of CaSR and NALP5 antibodies and the disease manifestations and demographic characteristics of Finnish APECED patients. Design, Subjects, and Methods: This was a case-control study including 44 APECED patients and 38 age-and sex-matched healthy controls. Antibodies against the CaSR and NALP5 were detected using immunoprecipitation assays and radioligand binding assays, respectively. Results: CaSR and NALP5 antibodies were detected in 16 of 44 (36%) and 13 of 44 (30%) patients, respectively. No statistically significant associations were found between the presence of CaSR or NALP5 antibodies and the disease manifestations of APECED including HP (P > .05). For the diagnosis of HP, CaSR and NALP5 antibodies had specificities of 83% and 50%, respectively, and sensitivities of 39% and 26%, respectively. A significant association between both a shorter APECED and HP duration (<10 y) and positivity for CaSR antibodies was noted (P = .019 and P = .0061, respectively). Conclusion: Neither CaSR nor NALP5 antibodies were found to be specific or sensitive markers for HP in APECED. Further investigations are required to determine the exact role of the autoimmune response against the CaSR and NALP5 in the pathogenesis of this autoimmune syndrome.