Although approximately 5% of people with cystic fibrosis (CF) have residual function (RF) CFTR mutations, published data on disease trajectory in this population is limited

This retrospective study characterized lung function decline in CFTR modulator-untreated patients who were heterozygous for F508del-CFTR and an RF mutation (F/RF genotypes) compared with patients who were homozygous for F508del-CFTR (F/F genotype)

Lung function decline was observed in all age groups of patients with F/RF genotypes

Findings reinforce the importance of early intervention to preserve lung function in all people with CF, including those with F/RF genotypes