P021 Change in sweat chloride concentration following elexacaftor/tezacaftor/ivacaftor in siblings with cystic fibrosis heterozygous for R334W/N1088D/R75Q mutations

Abstract

Objectives: The introduction of elexacaftor-tezacaftor-ivacaftor (ETI) has been life-changing for many people with cystic fibrosis (CF). Clinical improvement is associated with significant but variable reduction in sweat chloride concentration. We describe the sweat chloride concentration levels and clinical response following ETI therapy in two siblings with CF and a CFTR R75Q mutation. Although R75Q is categorised as non-CF causing (as per CFTR2 database) with in vitro studies suggesting normal chloride conductance, this variant is associated with disrupted bicarbonate conductance and is ETI-responsive.