Should isolated Pseudo‐Bartter syndrome be considered a CFTR‐related disorder of infancy?

Abstract Background Infants that are negative to cystic fibrosis (CF) newborn screening (NBS) programs, or in countries without NBS, may present with metabolic alkalosis and severe salt depletion, a well‐known clinical manifestation of CF termed Pseudo‐Bartter syndrome (PBS). Here, we report the cases of three CF‐negative children, who carry rare mutations in the CF transmembrane conductance regulator (CFTR) gene, and, for whom, PBS was the only manifestation of CFTR protein dysfunction. There is no diagnostic label for these cases. Methods Medical records of patients followed at our Cystic Fibrosis Centre were revised and data were collected for all patients who presented with an isolated PBS. The syndrome was defined as an episode of dehydration with low levels of serum sodium ( < 134mmol/L), potassium ( < 3.4mmol/L), and chloride ( < 100mmol/L), with metabolic alkalosis (bicarbonatemia >27mmol/L) in the absence of renal tubulopathy. Results Three out of 73 (4%) CF infants presented with a severe metabolic alkalosis with salt depletion; two of these required admission to the intensive care unit. Two infants had a negative NBS, and one was identified as a CF carrier. Sweat test was repeatedly in the negative/borderline ranges for all patients. Less than two CF causing mutations were identified (F508del/R1070W, F508del; L467F/P5L, R1066H/P5L). During a mean follow‐up of 9 years, the children had no other CF manifestations. Conclusion We suggest that PBS as the sole manifestation of CFTR dysfunction might be considered a CFTR‐related disorder of infancy.