CFTR and cystic fibrosis: Polymorphisms in the Cystic Fibrosis Transmembrane Conductance Regulator (CFTR) gene, which regulates the flow of sodium and chloride ions across cell membranes, affect the viscosity of mucous and increase the risk of ABPA.38 CF patients are known to have an increased risk of ABPA, and evidence has been found that mutations in the CFTR gene (insufficient for a diagnosis of CF) are associated with ABPA in asthmatic patients.