A step forward for an intermediate cystic fibrosis population

Extract

Cystic fibrosis (CF) is a life-long and life-shortening disease, best treated with early interventions to prevent complications across multiple organs and to extend the lifespan of this population. In the USA and Europe, the diagnosis of CF occurs primarily through newborn screening [1]. Newborns with two defective copies of the cystic fibrosis transmembrane conductance regulator (Cftr) gene have elevated levels of immuno-reactive trypsinogen (IRT) in their serum. A high IRT result at birth triggers a confirmatory test for diagnosis that involves a functional assay, such as sweat chloride concentration measured by evaporimetry. Normal sweat chloride concentration by this method falls in a range of 29 mmol·L⁻¹ or lower while a CF diagnosis is made when sweat chloride reaches values of 60 mmol·L⁻¹ or higher [2]. However, some patients fall into an intermediate range with sweat chloride results ranging between 30 and 59 mmol·L⁻¹. For these patients, it is not known if they are carriers of a mutation to the gene or if they have two mutated copies of the Cftr [3]. Because the rare mutations can be difficult to identify [4], this distinction is important.