A comprehensive study of a rare pathogenic CFTR gene variant G1047S in two siblings

   Most of the known pathogenic variants of the CFTR gene are rare. Studying these variants allows us to gain new knowledge about the pathogenesis of cystic fibrosis, assess the variability of its manifestations among patients, and optimize therapeutic approaches.

   The aim was to comprehensively study a rare variant of the CFTR gene G1047S (c.3139G>A, p.(Gly1047Ser)) in two siblings, including a description of the clinical picture, functional assessment of the CFTR channel ex vivo by determining the intestinal current measurement (ICM) and the forskolin-induced swelling (FIS) assay of the effect of CFTR modulators in vitro in the intestinal organoids.

   Methods. The case history was presented. The ICM was used to study membrane channels of the intestinal epithelium. The FIS assay in the intestinal organoids of the patients was used to assess the sensitivity of the G1047S variant to ivacaftor, lumacaftor, tezacaftor, and elexacaftor.

   Results. The missense variant G1047S is pathogenic but “mild” since the residual CFTR function is observed. The results of functional tests are consistent with the clinical picture: the siblings have pancreatic sufficiency, no nutritional deficiency, and a “mild” course of the disease. The ivacaftor + tezacaftor + elexacaftor therapy can be recommended for patients with the G1047S variant since the intestinal organoid model shows restoration of CFTR functional activity.

   Conclusion. The G1047S variant is “mild”, but with lower sensitivity to known combination targeted drugs compared to F508del/F508del.

1. Fajac I., Burgel P.R., Martin C. New drugs, new challenges in cystic fibrosis care. Eur. Respir. Rev. 2024; 33 (173): 240045. DOI: 10.1183/16000617.0045-2024.

2. Voronkova A.Yu., Amelina E.L., Kashirskaya N.Yu. et al. [Register of patients with cystic fibrosis in the Russian Federation. 2022]. Moscow: Medpraktika-M; 2024 (in Russian).

3. Vonk A., van Mourik P., Ramalho A. et al. Protocol for application, standardization and validation of the forskolin-induced swelling assay in cystic fibrosis human colon organoids. STAR Protoc. 2020; 1 (1): 100019. DOI: 10.1016/j.xpro.2020.100019.

4. Efremova A.S., Bukharova T.B., Kashirskaya N.Y., Goldshtein D.V. [Intestinal organoids and their application for personalized diagnostics and treatment of cystic fibrosis]. Meditsinskaya genetika. 2018; 17(9):3–12. Available at: https://www.medgen-journal.ru/jour/article/view/579 (in Russian).

5. Lefferts J.W., Bierlaagh M.C., Kroes S. et al. CFTR function restoration upon Elexacaftor/Tezacaftor/Ivacaftor treatment in patient-derived intestinal organoids with rare CFTR genotypes. Int. J. Mol. Sci. 2023; 24 (19):14539. DOI: 10.3390/ijms241914539.

6. Ministry of Health of the Russian Federation. [Clinical guidelines: Cystic fibrosis]. 2021. Available at: https://cr.minzdrav.gov.ru/preview-cr/372_2 (in Russian).

7. Derichs N., Sanz J., Von Kanel T. et al. Intestinal current measurement for diagnostic classification of patients with questionable cystic fibrosis: validation and reference data. Thorax. 2010; 65 (7): 594–599. DOI: 10.1136/thx.2009.125088.

8. Kondratyeva E., Efremova A., Melyanovskaya Y. et al. Clinical and genetic characterization of patients with cystic fibrosis and functional assessment of the chloride channel with the pathogenic variant c.831G>A (p.Trp277*), described for the first time. Gene. 2020; 761: 145023. DOI: 10.1016/j.gene.2020.145023.

9. Melyanovskaya Yu.L., Kondratyeva E.I., Kutsev S.I. [Determination of reference values for the method of determining the difference in intestinal potentials in the Russian Federation]. Meditsinskiy vestnik Severnogo Kavkaza. 2020; 15: 162–166. DOI: 10.14300/mnnc.2020.15039 (in Russian).

10. Dekkers J.F., Wiegerinck C.L., de Jonge H.R. et al. A functional CFTR assay using primary cystic fibrosis intestinal organoids. Nat. Med. 2013; 19 (7): 939–945. DOI: 10.1038/nm.3201.

11. Boj S.F., Vonk A.M., Statia M. et al. Forskolin-induced swelling in intestinal organoids: an in vitro assay for assessing drug response in cystic fibrosis patients. J. Vis. Exp. 2017; (120): 55159. DOI: 10.3791/55159.

12. Kondratyeva E.I., Melyanovskaya Yu.L., Efremova A.S. et al. [Experience of evaluating functionality of anionic CFTR channel methods application in patients with cystic fibrosis diagnosed and supposed]. Sibirskoe meditsinskoe obozrenie. 2019; (2): 60–69. DOI: 10.20333/2500136-2019-2-60-69 (in Russian).

13. Voronkova A.Yu., Melyanovskaya Yu.L., Petrova N.V. et al. [Clinical and genetic characteristics of rare pathogenic variants in the CFTR gene in Russian patients with cystic fibrosis]. Pul’monologiya. 2021; 31 (2): 148–158. DOI: 10.18093/0869-0189-2021-31-2-148-158 (in Russian).

14. de Poel E., Spelier S., Hagemeijer M.C. et al. FDA-approved drug screening in patient-derived organoids demonstrates potential of drug repurposing for rare cystic fibrosis genotypes. J. Cyst. Fibros. 2023; 22 (3): 548–559. DOI: 10.1016/j.jcf.2023.03.004.

15. Venkatachalam K. Regulation of aging and Longevity by Ion channels and transporters. Cells. 2022; 11 (7): 1180. DOI: 10.3390/cells11071180.

16. Fiedorczuk K., Chen J. Mechanism of CFTR correction by type I folding correctors. Cell. 2022; 185 (1): 158–168.e11. DOI: 10.1016/j.cell.2021.12.009.

17. Fiedorczuk K., Chen J. Molecular structures reveal synergistic rescue of F508del CFTR by Trikafta modulators. Science. 2022; 378 (6613): 284–290. DOI: 10.1126/science.ade2216