Clinical and molecular characterization of S1118F-CFTR

Frequency of allele variations in the CFTR gene in a Mexican population

Background

Cystic fibrosis (CF) is an autosomal recessive disorder caused by pathogenic variants in the cystic fibrosis transmembrane conductance regulator (CFTR) gene. The CF variants incidence is highly variable and even undetermined in some countries like Mexico.

Methods

In this study, the allele frequencies of 361 variants in the CFTR gene were investigated in 1455 Mexicans without a CF or CFTR-related disorders (CFTR-RD) diagnosis. We also performed a statistical comparative analysis against allele frequencies of different populations to measure genetic differences in the prevalence of CFTR variants.

Results

In the vast majority of cases, the allele frequencies of this cohort were comparable to those found in other populations. However, some variants displayed significant differences in their allele frequencies when compared with European and African populations.

Conclusions

This study provides information about CFTR variants to predict the prevalence of CF in Mexico and uncover other unknown but frequent pathogenic variants in the country. Additionally, other CFTR-RD variants have also been studied using population data of the same CFTR variants. Studies like this could help develop a regional molecular diagnostic screen to optimize the medical care of CF patients.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12920-021-01111-w.

Personalized medicine in CF: from modulator development to therapy for cystic fibrosis patients with rare CFTR mutations

Cystic fibrosis (CF) is the most common life-shortening genetic disease affecting ~1 in 3,500 of the Caucasian population. CF is caused by mutations in the CF transmembrane conductance regulator (CFTR) gene. To date, more than 2,000 CFTR mutations have been identified, which produce a wide range of phenotypes. The CFTR protein, a chloride channel, is normally expressed on epithelial cells lining the lung, gut, and exocrine glands. Mutations in CFTR have led to pleiotropic effects in CF patients and have resulted in early morbidity and mortality. Research has focused on identifying small molecules, or modulators, that can restore CFTR function. In recent years, two modulators, ivacaftor (Kalydeco) and lumacaftor/ivacaftor (Orkambi), have been approved by the U.S. Food and Drug Administration to treat CF patients with certain CFTR mutations. The development of these modulators has served as proof-of-concept that targeting CFTR by modulators is a viable therapeutic option. Efforts to discover new modulators that could deliver a wider and greater clinical benefit are still ongoing. However, traditional randomized controlled trials (RCTs) require large numbers of patients and become impracticable to test the modulators' efficacy in CF patients with CFTR mutations at frequencies much lower than 1%, suggesting the need for personalized medicine in these CF patients.

Murine and human CFTR exhibit different sensitivities to CFTR potentiators

Development of therapeutic molecules with clinical efficacy as modulators of defective CFTR includes efforts to identify potentiators that can overcome or repair the gating defect in mutant CFTR channels. This has taken a great leap forward with the identification of the potentiator VX-770, now available to patients as "Kalydeco." Other small molecules with different chemical structure also are capable of potentiating the activity of either wild-type or mutant CFTR, suggesting that there are features of the protein that may be targeted to achieve stimulation of channel activity by structurally diverse compounds. However, neither the mechanisms by which these compounds potentiate mutant CFTR nor the site(s) where these compounds bind have been identified. This knowledge gap partly reflects the lack of appropriate experimental models to provide clues toward the identification of binding sites. Here, we have compared the channel behavior and response to novel and known potentiators of human CFTR (hCFTR) and murine (mCFTR) expressed in Xenopus oocytes. Both hCFTR and mCFTR were blocked by GlyH-101 from the extracellular side, but mCFTR activity was increased with GlyH-101 applied directly to the cytoplasmic side. Similarly, glibenclamide only exhibited a blocking effect on hCFTR but both blocked and potentiated mCFTR in excised membrane patches and in intact oocytes. The clinically used CFTR potentiator VX-770 transiently increased hCFTR by ∼13% but potentiated mCFTR significantly more strongly. Our results suggest that mCFTR pharmacological sensitivities differ from hCFTR, which will provide a useful tool for identifying the binding sites and mechanism for these potentiators.

Recent advances and new perspectives in targeting CFTR for therapy of cystic fibrosis and enterotoxin-induced secretory diarrheas

The cystic fibrosis transmembrane conductance regulator (CFTR) is a cAMP-regulated chloride channel localized primarily at the apical surfaces of epithelial cells lining airway, gut and exocrine glands, where it is responsible for transepithelial salt and water transport. Several human diseases are associated with an altered channel function of CFTR. Cystic fibrosis (CF) is caused by the loss or dysfunction of CFTR-channel activity resulting from the mutations on the gene; whereas enterotoxin-induced secretory diarrheas are caused by the hyperactivation of CFTR channel function. CFTR is a validated target for drug development to treat these diseases. Significant progress has been made in developing CFTR modulator therapy by means of high-throughput screening followed by hit-to-lead optimization. Several oral administrated investigational drugs are currently being evaluated in clinical trials for CF. Also importantly, new ideas and methodologies are emerging. Targeting CFTR-containing macromolecular complexes is one such novel approach.

Detecting Common CFTR Mutations by Reverse Dot Blot Hybridization Method in Cystic Fibrosis First Report from Northern Iran

OBJECTIVE

Cystic fibrosis and its distribution vary widely in different countries and/or ethnic groups. Common cystic fibrosis transmembrane conductance regulator (CFTR) mutations were reported from Iran, but the northern population was not or underrepresented in those studies. The aim of this study was to determine the frequency of common CFTR mutations in children from northern Iran.

METHODS

Thirty unrelated Iranian cystic fibrosis patients aged less than 11 years and living in Mazandaran province (in Iran) were screened for 5 common CFTR gene mutations. deltaF508, N1303K, G542X, R347H and W1282X using Reverse Dot Blot method.

FINDINGS

Only one mutation, DeltaF508, was found in 7 patients accounting for 21.7% (13/60) of alleles.

CONCLUSION

These findings can be used for planning future screening and appropriate genetic counseling programs in Iranian CF families.