CFTR and cystic fibrosis: The US Cystic Fibrosis Foundation (Bethesda) listed diagnostic criteria for CF: one or more of the phenotypic features of the disease with positive immunoreactive trypsin (IRT, a neonatal screening test), positive sweat test, a CF‐causing mutation in each CFTR gene, or an abnormal nasal potential difference (NPD).9 Most atypical CF patients can be confidently diagnosed with the help of reliable sweat tests and/or genetic analysis.