Quantifying Cystic Fibrosis Lung Phenotype

Measurements of FEV₁ were collected on a quarterly basis according to international CF care recommendations (Castellani et al., 2018 (link)) and expressed as percent-predicted values (ppFEV₁) using Global Lung Function Initiative (GLI) equations (Quanjer et al., 2012 (link)). To assess the lung disease severity, FEV₁ were transformed to the Survival Adjusted Kulich Normalized (SaKnorm Z-value) CF-specific lung phenotype. SaKnorm is a quantitative phenotype that allows direct comparison of lung phenotypes between pwCF and accounts for differential survival (Kulich et al., 2005 (link)). Lung function and lung disease severity were analyzed over the last 3 years, except for post–lung transplant patients and patients under CFTR modulator therapy (ivacaftor and lumacaftor-ivacaftor) for whom FEV₁ measurements were analyzed over the 3 years prior to the event. SLC6A14 rs3788766 SNP was genotyped using Kompetitive Allele Specific PCR (KASP) chemistry (LGC, Teddington, United Kingdom).