Clinical and molecular characterization of the R751L-CFTR mutation

Abstract

Cystic fibrosis (CF) arises from mutations in the CF transmembrane conductance regulator (CFTR) gene, resulting in progressive and life-limiting respiratory disease. R751L is a rare CFTR mutation that is poorly characterised. Our aims were to describe the clinical and molecular phenotypes associated with R751L. Relevant clinical data were collected from three heterozygote individuals harbouring R751L (2 patients with G551D/R751L and 1 with F508del/R751L). Assessment of R751L-CFTR function was made in primary human bronchial epithelial cultures (HBEs) and Xenopus oocytes. Molecular properties of R751L-CFTR were investigated in the presence of known CFTR modulators. Although sweat chloride was elevated in all three patients, the clinical phenotype associated with R751L was mild. Chloride secretion in F508del/R751L HBEs was reduced compared to non-CF HBEs and associated with a reduction in sodium absorption by the epithelial sodium channel (ENaC). However, R751L-CFTR function in Xenopus oocytes together with folding and cell surface transport of R751L-CFTR were not different to wild-type CFTR. Overall, R751L-CFTR was associated with reduced sodium chloride absorption but had similar functional properties to wild-type CFTR. This is the first report of R751L-CFTR that combines clinical phenotype with characterisation of functional and biological properties of the mutant channel. Our work will build upon existing knowledge of mutations within this region of CFTR and importantly inform approaches for clinical management. Elevated sweat chloride and reduced chloride secretion in HBEs may be due to alternative non-CFTR factors, which require further investigation.

CFTR bearing variant p.Phe312del exhibits function inconsistent with phenotype and negligible response to ivacaftor

“…Of note, the missense variant c.2252G>T (p.Arg751Leu; legacy: R751L), located in the R domain of CFTR and associated with elevated sweat chloride and mild CF features in 3 related individuals was shown to have minimal effect on CFTR function. Interestingly, function of the epithelial sodium channel (ENaC) was reduced, suggesting that R751L may affect the interaction between CFTR and ENaC in the sweat gland ( 49 ). The 3 individuals with genotype F312del/F508del have different responses to amiloride, ranging 20–120 μA/cm 2 .…”

ABC-transporter CFTR folds with high fidelity through a modular, stepwise pathway

“…VX-809 stabilizes TMD1 and thereby enhances expression of almost all CFTR mutants [ 34 – 38 ]. VX-770 destabilizes T1f at the gain of T1d, improving detection of T1d [ 25 , 39 ]. The T1d fragment was immunoprecipitated with TMD1C (epitope aa S364–K381) lacking 35 (∆N35), but not 45 residues (∆N45) from the N-terminus, (Fig.…”

Precision Medicine Based on CFTR Genotype for People with Cystic Fibrosis

“…92 Primary human nasal epithelial cells (HNEs) can be obtained from nasal mucosal brushings. 93 Conditionally reprogrammed expansion of HNEs can increase the number of cultures available for ex vivo investigation of ion transport and response to modulators. Organoid cultures have also been developed from intestinal biopsies and nasal and bronchial cells isolated from individuals with CF, which provide a 3D model where forskolininduced swelling (FIS) provides a higher throughput assessment of response to modulators.…”