A case of Sjögren's syndrome with selective anion exchanger 1 defect causing distal renal tubular acidosis.

Distal renal tubular acidosis (dRTA) is a significant clinical expression of Sjögren's syndrome (SS). While SS-related dRTA is traditionally linked to impaired H-ATPase, we report a unique case demonstrating selectively decreased anion exchanger 1 (AE1) expression with preserved H-ATPase expression. A 16-year-old girl with SS presented with muscle weakness, difficulty in ambulation, and severe hypokalemia. Laboratory studies revealed non-anion gap metabolic acidosis, elevated urinary potassium excretion, and overt proteinuria. Renal histology identified a notably reduced expression of AE1 but normal H-ATPase in intercalated cells, a previously undescribed finding. Despite high-dose potassium and bicarbonate supplementation, her hypokalemia and metabolic acidosis showed inadequate response; however, the clinical condition improved dramatically following corticosteroid therapy. This case sheds light on an atypical SS-associated dRTA mechanism characterized by selective AE1 impairment, presumed to be mediated by autoantibodies. The discovery accentuates AE1's critical role in SS-induced renal pathology and underscores the efficacy of steroids in the management of SS-related dRTA.