WS13.01Characterization of two novel F508del-CFTR complex alleles and their impact on drug responsiveness

Abstract

Objectives

In cystic fibrosis (CF), a complete and correct genetic diagnosis is essential for appropriate therapeutic intervention with CFTR modulating drugs. The triple combination of modulators Elexacaftor, Tezacaftor, and Ivacaftor (ETI) successfully overcome molecular defects of the most frequent variant F508del-CFTR. In this scenario, complex alleles of F508del-CFTR can modify both clinical manifestations and the response to treatment. Indeed, each variant may impact on the structure, folding and activity of the CFTR channel [doi: 10.3390/ijms23063175]. In the frame of a large theratyping project of the Italian CF population, we recruited two unrelated CF patients, compound heterozygous for F508del and a minimal function variant, who were referred as having limited or negligible beneficial effects following treatment with ETI.

Methods

We performed molecular, functional and biochemical studies on primary cultures of nasal epithelial cells isolated from patients with CF (pwCF) and on immortalized bronchial cells.

Results

Ex vivo functional studies on patient-derived nasal epithelia confirmed the lack of response to ETI. In-depth molecular characterization highlighted the presence of additional amino acid substitutions in cis with the F508del variant. The first patient carried a rare poorly characterized variant, while the second patient carried a variant not listed in any database. The double mutant CFTR proteins produced by the complex alleles display reduced activity with negligible rescue by CFTR modulators.

Conclusion

This study suggests that in pwCF carrying F508del variant and not responding to modulators, the genotype should be re-evaluated in search of possible complex alleles; it also provides new information regarding poorly or not yet described CFTR variants.

Supported by The Italian Ministry of Health (PNRR-MR1-2023-12378412), CFF (PEDEMO20G0), FFC Ricerca (FFC#10/2021, “Kaftrio nella vita reale – substudy 1”).