Description of the clinical picture and assessment of functional activity of the CFTR channel in a patient with a complex allele [S466X; R1070Q]

Abstract

The presence of pathogenic variants in the CFTR gene causes cystic fibrosis (CF) through various molecular mechanisms that affect the formation and functional activity of the CFTR chloride channel. An important factor affecting the phenotypic manifestations of CF and the effectiveness of targeted therapy is the presence of complex alleles with > 2 consecutive mutations per 1 allele, or in the cis position. The influence of complex alleles on the manifestations of CF has not been sufficiently studied globally due to the small number of studies.The aim of the study was to investigate the influence of the complex allele [S466X; R1070Q] on the phenotypic manifestations of CF and the effectiveness of targeted therapy in a model of intestinal organoids from a patient with [S466X; R1070Q]/CFTRdele2,3 genotype.Methods. We used medical history data, intestinal current measurement, intestinal organoid method, and forskolin test.Results. The progressive nature of the disease with a clear degradation of lung function was established. The ICM method showed absent chloride channel function. The tests on the culture of organoids obtained from the intestinal tissue indicated a complete loss of the chloride channel function. In addition, the complex allele [S466X; R1070Q] was insensitive to all targeted drugs tested.Conclusion. The complex allele [S466X; R1070Q] causes a complete loss of the functional CFTR protein and is not sensitive to any of the approved targeted drugs.

Advances in the Study of Common and Rare CFTR Complex Alleles Using Intestinal Organoids

“…Table 1. Alterations of organoid size with CAs after 60 min treatment of 5 µM forskolin and CFTR modulators (each at a concentration of 3.5 µM) (results of our previous studies [6,38,39]). The initial organoid area before forskolin stimulation (0 min) was taken as 100%; data are presented as means ± SD (%); F508del/F508del-control.…”

“…Calculations were based on the results of three independent experiments obtained from a single culture. The CA [S466X;R1070Q] was previously studied in an individual with the [S466X;R1070Q]/ CFTRdele2,3 genotype [38]. [S466X;R1070Q] was show to be pathogenic, and according to the RF Register 2021, occurs in Russia at a frequency rate of 0.46% among CF individuals, ranking 17th among 233 CFTR pathogenic variants described in the Russian Federation [5].…”

The Effect of Complex Alleles of the CFTR Gene on the Clinical Manifestations of Cystic Fibrosis and the Effectiveness of Targeted Therapy

“…Additional studies to assess the functional activity of the CFTR channel conducted on intestinal organoids confirmed the absence of an organoid swelling to forskolin and targeted drugs for [S466X;R1070Q] [23]. Thus, this complex allele can be attributed to a Class 1 mutation with a high degree of probability [22][23][24].…”

“…The first examples of the study of the effect of CFTR modulators on the restoration of the function of the chloride channel in patients with CF in the presence of complex alleles in the genotype are given in the works of Russian researchers on the model of intestinal organoids [ 20 , 21 , 22 , 23 , 24 , 66 ]. The effectiveness of this approach has been proven in real clinical practice.…”

“…The study of the phenotypic manifestations of the complex allele allowed to conclude that this mutation belongs to Class 1 and has a severe phenotype [22]. Additional studies to assess the functional activity of the CFTR channel conducted on intestinal organoids confirmed the absence of an organoid swelling to forskolin and targeted drugs for [S466X;R1070Q] [23]. Thus, this complex allele can be attributed to a Class 1 mutation with a high degree of probability [22][23][24].…”