Autoimmune polyendocrine syndrome type 1: Utility of KCNRG autoantibodies as a marker of active pulmonary disease and successful treatment with rituximab.

Autoimmune polyendocrine syndrome type 1 (APS-1), also known as Autoimmune Polyendocrinopathy Candidiasis and Ectodermal Dysplasia (APECD) is a disorder caused by mutations in the autoimmune regulator (AIRE) gene. In some APS-1 patients, significant pulmonary disease is observed. Autoantibodies directed against the potassium channel regulatory protein (KCNRG), found in epithelial cells of terminal bronchioles, have been suggested as a marker for pulmonary disease in APS-1 patients. We report two patients with APS-1; one with and one without lung disease. Patient 1 had multiple admissions for pneumonia and respiratory insufficiency, required non-invasive ventilation, and had findings of bronchiectasis on thoracic imaging and significant lymphocytic infiltrates of the airways on lung biopsy. To verify the autoimmune cause of pulmonary symptoms APS-1 patients, both were tested in a blinded manner for the presence of autoantibodies to KCNRG in serum. We found that only Patient 1 had autoantibodies present. Additionally, Patient 1 had progressive disease despite treatment with several immunomodulating agents, including corticosteroids, azathioprine, and mycophenolate. Patient 1 had a lung biopsy performed which was consistent with B cell lymphocytic aggregates. Rituximab treatment was initiated with apparent good response. This report illustrates the practical use of KCNRG autoantibodies to identify APS-1 patients with pulmonary risk and the successful use of the monoclonal antibody, Rituximab, to treat pulmonary disease in APS-1 patients.