Successful Therapy over 12 Months of People with Cystic Fibrosis with Rare Non-phe508del Cystic Fibrosis Transmembrane Conductance Regulator (CFTR) Mutations with Elexacaftor/Tezacaftor/Ivacaftor (ETI)

<b>Background:</b> Elexacaftor/Tezacaftor/Ivacaftor (ETI) is a CFTR modulator therapy approved for people with cystic fibrosis (pwCF) who have at least one phe508del mutation. However, its approval in the European Union (EU) for pwCF with non-phe508del mutations is lacking, because data on treatment response in this subgroup are scarce. <b>Methods:</b> This retrospective observational study evaluated six pwCF (ages 6 to 66) with responsive CFTR mutations (M1101K, R347P, 2789+5G>A, G551D) undergoing off-label ETI therapy. Evaluations were conducted at 0, 3, 6, 9, and 12 months, assessing lung function (FEV₁), sweat chloride levels, body mass index (BMI), quality of life, medication satisfaction, ear, nose and throat (ENT) symptoms, and physical activity. A control group of four pwCF with classic symptoms and no ETI treatment was included. <b>Results:</b> FEV₁ improved significantly after 3 and 6 months (<i>p</i> < 0.05) and stabilized by 12 months. Sweat chloride levels decreased significantly, with four pwCF achieving levels <60 mmol/L. Improvements in the upper and lower airway symptoms, medication satisfaction, and increased BMI were noted. <b>Conclusions:</b> ETI demonstrates high efficacy in this small group of pwCF with rare CFTR mutations, offering a treatment option that warrants further monitoring and evaluation.