Clinical presentation of exclusive cystic fibrosis lung disease

The diagnosis of cystic fibrosis (CF) is based on the occurrence of two mut ations in the cystic fibrosis transmembrane conductance regulator (CFTR) ge ne and on assays that measure the basic defect of abnormal chloride transpo rt in the affected organs. However, in cases of atypical CF not all diagnos tic tests may be positive. We present a patient with an atypical CF phenoty pe in whom the only presenting symptom was severe CF-like lung disease subs tantiated by an abnormal nasal potential difference. Genetic analysis showe d that the patient was a symptomatic heterozygote, which suggests that one lesion in the CFTR gene may be sufficient to cause CF-like lung disease.