Cystic Fibrosis With No Known Cystic Fibrosis Transmembrane Conductance Regulator (CFTR) Mutation and a Negative Newborn Screening Test: A Case Report.

Cystic fibrosis (CF) is a progressive, autosomal recessive disease primarily affecting the pulmonary and gastrointestinal systems of afflicted individuals. Cystic fibrosis transmembrane receptor (CFTR) genes encode the CFTR protein, which allows chloride ions to pass from inside the cell to the outside of the cell. CF symptoms, such as thick, sticky mucous, result from CFTR gene dysfunction. Although many mutations in the CFTR gene have been identified, there remains an absence of a comprehensive database encompassing all known and potential mutations contributing to the pathogenesis of CF. We present a 12-year-old male with recurrent sino-pulmonary infections, asthma exacerbations, and failure to thrive. Despite a negative newborn screening test, CF was suspected. The sweat chloride test is considered the gold standard for confirming CF. This patient's sweat chloride test showed elevated levels of 63 and 66 mmol/L, respectively. Levels >60 mmol/L are considered consistent with CF. CF genotyping, however, did not uncover a known CFTR mutation. The purpose of this case report is to highlight the importance of the sweat chloride test in diagnosing CF in the setting of a negative newborn screen and the absence of a known CFTR mutation, to enhance the diagnosis and recognition of CF in pediatric patients, and to ultimately improve patient outcomes.