Amiloride mitigates respiratory distress caused by WFDC2 deficiency via inhibiting the epithelial sodium channel.

Chronic airway diseases such as cystic fibrosis (CF) and primary ciliary dyskinesia (PCD) pose substantial clinical challenges. Here, we explore the p.C97W variant in WAP four-disulfide core domain protein 2 (WFDC2), proposed as a new genetic origin of respiratory distress, especially among Koreans. Whole-exome and whole-genome sequencing (WES/WGS) are performed on 64 patients from 62 families presenting with severe bronchiectasis and chronic rhinosinusitis. Pathogenic variants are found in 19.4% of families, including a novel homozygous WFDC2 missense variant (c.291 C > G, p.Cys97Trp) in five unrelated families. WFDC2 is expressed in lung epithelial cells, and the p.C97W variant impairs WFDC2 protein folding, secretion, and function. Wfdc2 p.C147W knock-in mice exhibit respiratory failure due to the hyperactive epithelial sodium channel (ENaC) linked to increased PRSS8 activity and recapitulate human disease. Treatment with amiloride, an ENaC inhibitor, improves survival and respiratory function in these mice. In conclusion, the p.C97W variant in WFDC2 is a critical genetic factor in severe chronic airway disease that shares clinical features with CF and PCD. Given its implications for diagnosis and treatment, genetic testing for WFDC2 mutations in individuals with CF- or PCD-like symptoms is recommended.