Clinical and genetic characteristics of rare pathogenic variants of the CFTR gene in Russian patients with cystic fibrosis

The variety of clinical manifestations of cystic fibrosis is driven by the diversity of the CFTR gene nucleotide sequence. Descriptions of the clinical manifestations in patients with the newly identified genetic variants are of particular interest.

The aim of this study was to describe clinical manifestations of the disease with the newly identified genetic variants.

Methods. Data from Registry of patients with cystic fibrosis in the Russian Federation (2018) were used. The data review included three steps — the search for frequent mutations, Sanger sequencing, and the search for extensive rearrangements by MLPA. 38 pathogenic variants were identified that were not previously described in the international CFTR2 database. We selected and analyzed full case histories of 15 patients with 10 of those 38 pathogenic variants: p.Tyr84*, G1047S, 3321delG, c.583delC, CFTRdele13,14del18, CFTRdele19-22, c.2619+1G>A, c.743+2T>A, p.Glu1433Gly, and CFTRdel4-8del10-11.

Results. A nonsense variant p.Tyr84* was found in 5 patients (0.08 %). Two missense variants c.3139G>A were found in 2 siblings (0.03 %). The c.4298A>G was found in 1 patient. Other variants were detected in a single patient (0.02 %) each. They included two variants of a deletion with a shift of the reading frame 3321delG and c.583delC, two splicing disorders c.2619+1G>A and c.743+2T>A, three extended rearrangements CFTRdele19-22, CFTRdele13,14del18, and CFTRdel4-8del10-11. The last two variants include 2 rearrangements on one allele, which cause the severe course in two young children. 8 of the 10 variants are accompanied by pancreatic insufficiency (PI). Among patients with p.Tyr84*, one had ABPA, one had liver transplantation, and all had Pseudomonas aeruginosa infection. Nasal polyps were diagnosed in 2 patients with p.Tyr84*, 1 with G1047S, 1 with CFTRdel4-8del10-11, and 1 patient with 3321delG, who also had osteoporosis and cystic fibrosis-related diabetes (CFRD). 2 patients with PI with 3321delG and CFTRdel4-8del10-11 genetic variants, and 1 with PI with p.Glu1433Gly genetic variant had severe protein-energy malnutrition (PEM).

Conclusion. Clinical manifestations of previously undescribed CFTR genetic variants were described. 5/10 genetic variants should be attributed to class I, 3/10 – to class 7 of the function classification of pathogenic CFTR gene variants associated with transcription and translation disruptions. Class of the identified missense variants c.3139G>A and c.4298A>G has not been established and requires further functional, cultural, and molecular genetic studies.

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