Querying the Tandem Splice Site DataBase (TassDB), a comprehensive online database dedicated to recognizing tandem acceptor sites, identified two NAGNAG motifs in CFTR. Mutations in the CFTR gene, which encodes a cAMP-regulated Cl− channel located at the apical membrane of epithelial cells, cause cystic fibrosis (CF). The gene discussed is CFTR; the disease is cystic fibrosis.