ABCMdb

PMID: 21507732

de Nooijer RA, Nobel JM, Arets HG, Bot AG, van Berkhout FT, de Rijke YB, de Jonge HR, Bronsveld I
Assessment of CFTR function in homozygous R117H-7T subjects.
J Cyst Fibros. 2011 Sep;10(5):326-32. Epub 2011 Apr 19., [PubMed]

Sentences

No. Mutations Sentence Comment

0 ABCC7 p.Arg117His ABCC7 p.Arg117His ABCC7 p.Arg117His Original Article Assessment of CFTR function in homozygous R117H-7T subjects R.A. de Nooijer a,⁎, J.M. Nobel a , H.G.M. Arets b , A.G. Bot a , F. Teding van Berkhout a , Y.B. de Rijke c , H.R. de Jonge a,d , I. Bronsveld a a Department of Pulmonology, University Medical Centre Utrecht, P.O. Box 85500, 3508 GA Utrecht, The Netherlands b Department of Paediatric Pulmonology, Wilhelmina Children's Hospital, University Medical Centre Utrecht, P.O. Box 85090, 3508 AB Utrecht, The Netherlands c Department of Clinical Chemistry, Erasmus MC Sophia, P.O. Box 2040, 3000 CA Rotterdam, The Netherlands d Department of Biochemistry, Erasmus Medical Center, P.O. Box 2040, 3000 CA Rotterdam, The Netherlands Received 2 January 2011; received in revised form 4 March 2011; accepted 22 March 2011 Abstract Background: R117H is a frequent missense mutation included in most CFTR mutation panels. Login to comment 1 ABCC7 p.Arg117His However knowledge about the residual function of R117H-CFTR channels in cystic fibrosis-affected organs, e.g. airways, intestines and sweat glands is presently lacking. Login to comment 2 ABCC7 p.Arg117His Methods: We evaluated clinical CF symptoms and assessed CFTR function by sweat tests, nasal potential difference and intestinal current measurements in 2 homozygous R117H individuals (7T variant). Login to comment 5 ABCC7 p.Arg117His Conclusions: The lack of impact of the R117H mutation on chloride secretion in intestine and nose contrasts with the ~80% loss of CFTR activity reported in patch clamp studies. Login to comment 8 ABCC7 p.Arg117His Keywords: Cystic fibrosis; R117H; NPD; ICM; CFTR 1. Login to comment 13 ABCC7 p.Arg117His However, some atypical mutations, such as R117H, are less suitable for this classification because their phenotypical manifestations are more sensitive to variations in other genetic and epigenetic factors or environmental factors such as a certain lifestyle [3]. Login to comment 14 ABCC7 p.Arg117His The R117H mutation is a relatively frequent mutation in cystic fibrosis (CF) patients worldwide [4]. Login to comment 17 ABCC7 p.Arg117His R117H can occur in cis with either the polypyrimidine stretch T5 or T7 [6]. Login to comment 19 ABCC7 p.Arg117His Therefore only 10% of the CFTR protein produced by an allele with the 5T variant may be functional, and the combined effect of R117H and T5 on the same chromosome, with e.g. a F508del mutation on the other allele, results in classic CF. Login to comment 21 ABCC7 p.Arg117His Whereas much is known about the phenotypic variation among compound heterozygotes for F508del and R117H, www.elsevier. Login to comment 25 ABCC7 p.Arg117His doi:10.1016/j.jcf.2011.03.009 Journal of Cystic Fibrosis 10 (2011) 326-332 www.elsevier.com/locate/jcf present information about the phenotype of the individual R117H mutation is restricted to expression studies in heterologous host cells [5,8]. Login to comment 26 ABCC7 p.Arg117His doi:10.1016/j.jcf.2011.03.009 Please cite this article as: de Nooijer RA, et al, Assessment of CFTR function in homozygous R117H-7T subjects, J Cyst Fibros (2011), doi:10.1016/j. Login to comment 27 ABCC7 p.Arg117His ABCC7 p.Arg117His jcf.2011.03.009 Journal of Cystic Fibrosis xx (2011) xxx-xxx JCF-00675; No of Pages www.elsevier.com/locate/jcf present information about the phenotype of the individual R117H mutation is restricted to expression studies in heterologous host cells [5,8]. Login to comment 28 ABCC7 p.Arg117His In vivo and ex vivo assays to measure residual CFTR function in both patients, i.e. the sweat test, the nasal potential difference (NPD), and intestinal current measurements (ICM) in freshly excised rectal suction biopsies were applied to gain insight into the phenotype of the R117H mutation. Login to comment 29 ABCC7 p.Arg117His This report describes 2 rare index cases of individuals who are homozygous for the R117H-7T CFTR mutation. Login to comment 30 ABCC7 p.Arg117His In vivo and ex vivo assays to measure residual CFTR function in both patients, i.e. the sweat test, the nasal potential difference (NPD), and intestinal current measurements (ICM) in freshly excised rectal suction biopsies were applied to gain insight into the phenotype of the R117H mutation. Login to comment 32 ABCC7 p.Arg117His A 33-year old female had no clinical symptoms but was recognized by mutation analysis after her son was identified with F508del/R117H by newborn screening. Login to comment 33 ABCC7 p.Arg117His Both individuals were homozygous for the R117H-7T CFTR mutation, diagnosed on the basis of mutation analysis at the CFTR locus. Login to comment 34 ABCC7 p.Arg117His A 33-year old female had no clinical symptoms but was recognized by mutation analysis after her son was identified with F508del/R117H by newborn screening. Login to comment 35 ABCC7 p.Arg117His Both individuals were homozygous for the R117H-7T CFTR mutation, diagnosed on the basis of mutation analysis at the CFTR locus. Login to comment 57 ABCC7 p.Arg117His 2 R.A. de Nooijer et al. / Journal of Cystic Fibrosis xx (2011) xxx-xxx Please cite this article as: de Nooijer RA, et al, Assessment of CFTR function in homozygous R117H-7T subjects, J Cyst Fibros (2011), doi:10.1016/j. Login to comment 61 ABCC7 p.Arg117His Four rectal biopsies were obtained in both R117H-7T homozygous individuals. Login to comment 64 ABCC7 p.Arg117His Four rectal biopsies were obtained in both R117H-7T homozygous individuals. Login to comment 76 ABCC7 p.Arg117His CFTR mutation analysis Both subjects were tested homozygous for the R117H-7T CFTR mutation by INNO-LiPA which was subsequently confirmed by direct sequence analysis. Login to comment 79 ABCC7 p.Arg117His CFTR mutation analysis Both subjects were tested homozygous for the R117H-7T CFTR mutation by INNO-LiPA which was subsequently confirmed by direct sequence analysis. Login to comment 89 ABCC7 p.Arg117His NPD tracings of the R117H-7T homozygotes. Login to comment 92 ABCC7 p.Arg117His NPD tracings of the R117H-7T homozygotes. Login to comment 98 ABCC7 p.Arg117His ABCC7 p.Arg117His 4 R.A. de Nooijer et al. / Journal of Cystic Fibrosis xx (2011) xxx-xxx Please cite this article as: de Nooijer RA, et al, Assessment of CFTR function in homozygous R117H-7T subjects, J Cyst Fibros (2011), doi:.1016/j. Login to comment 102 ABCC7 p.Arg117His Therefore, both R117H-7T homozygotes showed a normal electrophysiological phenotype in their upper airways, not indicative of CF disease. Login to comment 103 ABCC7 p.Arg117His In both R117H-7T individuals the Isc responses to secretagogues (Fig. 4), and the cumulative value of the Clse- cretory responses (=ΔIsccarbachol +ΔIscforskolin/cAMP +ΔIschistamine ) were normal and far above the CF range (Fig. 4, legend; Table 1). Login to comment 104 ABCC7 p.Arg117His According to the new criterium [21], both R117H homozygotes would therefore belong to the "CF unlikely" group. Login to comment 107 ABCC7 p.Arg117His In both R117H-7T individuals the Isc responses to secretagogues (Fig. 4), and the cumulative value of the Clse- cretory responses (=ΔIsccarbachol +ΔIscforskolin/cAMP +ΔIschistamine ) were normal and far above the CF range (Fig. 4, legend; Table 1). Login to comment 108 ABCC7 p.Arg117His According to the new criterium [21], both R117H homozygotes would therefore belong to the "CF unlikely" group. Login to comment 109 ABCC7 p.Arg117His This indicates that CFTR activity is reduced but not absent in at least one tissue, the sweat duct, in line with the substantial loss of CFTR conductance of the R117H mutant (70-85%) reported in heterologous expression systems in vitro [5,8]. Login to comment 111 ABCC7 p.Arg117His Discussion In this study we describe both clinical and electrophysiological findings in two R117H-7T homozygous subjects. Login to comment 113 ABCC7 p.Arg117His ABCC7 p.Arg117His This indicates that CFTR activity is reduced but not absent in at least one tissue, the sweat duct, in line with the substantial loss of CFTR conductance of the R117H mutant (70-85%) reported in heterologous expression systems in vitro [5,8]. Login to comment 114 ABCC7 p.Arg117His This loss of function results for a minor part from a small reduction in pore conductance for Cl- (14%) but is mainly due to a strong reduction in channel open probability (~72%), indicating that the R117H mutation affects both the pore properties and the gating of the CFTR channel, i.e. it has mixed class III and class IV properties [5]. Login to comment 115 ABCC7 p.Arg117His ABCC7 p.Arg117His Discussion In this study we describe both clinical and electrophysiological findings in two R117H-7T homozygous subjects. Login to comment 116 ABCC7 p.Arg117His ABCC7 p.Ala455Glu In addition, the normal bioelectrical phenotype in the nasal epithelium of the R117H homozygous subjects contrasts with the elevated sodium absorption and minimal Cl- conductance reported in NPD measurements for CF patients carrying the A455E mutation [22]. Login to comment 117 ABCC7 p.Arg117His Because these assays measure the basic defect in CF, i.e. abnormalities in CFTR-mediated chloride transport in epithelial tissues, there is a clear discrepancy between the apparently normal CFTR chloride channel function in airways and intestine reported here and the findings in patch clamp studies of the R117H CFTR channel in heterologous host cells in vitro, showing a loss of Cl-conductance of ~70-85% [5,8]. Login to comment 118 ABCC7 p.Arg117His This loss of function results for a minor part from a small reduction in pore conductance for Cl- (14%) but is mainly due to a strong reduction in channel open probability (~72%), indicating that the R117H mutation affects both the pore properties and the gating of the CFTR channel, i.e. it has mixed class III and class IV properties [5]. Login to comment 119 ABCC7 p.Arg117His ABCC7 p.Arg117His The intracellular processing of the R117H channel, and its trafficking to the cell surface are not affected by the mutation, ensuring normal levels of mature CFTR protein in the apical membrane of the epithelial tissues. Login to comment 120 ABCC7 p.Arg117His ABCC7 p.Ala455Glu In addition, the normal bioelectrical phenotype in the nasal epithelium of the R117H homozygous subjects contrasts with the elevated sodium absorption and minimal Cl-conductance reported in NPD measurements for CF patients carrying the A455E mutation [22]. Login to comment 123 ABCC7 p.Arg117His ICM tracing of the R117H-7T homozygotes. Login to comment 124 ABCC7 p.Arg117His ABCC7 p.Ala455Glu CBAVD in males [24], have distinct effects on the bioelectrical phenotype of the airways, ranging from normal (R117H) to severe (A455E). Login to comment 127 ABCC7 p.Arg117His For example, functional rescue of a class III regulatory mutant including R117H may depend on the expression of stimulating co-factors such as the IRBIT (Inositol 1,4,5-triphosphate receptor-binding protein released with Inositol 1,4,5-triphosphate) that reduces channel mean close time or the NHERF1 (Na+ /H+ exchange regulatory factor 1) scaffolding protein that drives CFTR dimerization and is known to increase the open probability of the CFTR channel [26,27]. Login to comment 128 ABCC7 p.Arg117His ABCC7 p.Ala455Glu 5R.A. CBAVD in males [24], have distinct effects on the bioelectrical phenotype of the airways, ranging from normal (R117H) to severe (A455E). Login to comment 130 ABCC7 p.Arg117His ABCC7 p.Arg117His Why the in vitro and in vivo phenotypes do not match is not clear but several mechanisms could be involved: first, rescue mechanisms may operate in native epithelium which are completely or partially lacking in the heterologous host cells in vitro.For example, functional rescue of a class III regulatory mutant including R117H may depend on the expression of stimulating co-factors such as the IRBIT (Inositol 1,4,5-triphosphate receptor-binding protein released with Inositol 1,4,5-triphosphate) that reduces channel mean close time or the NHERF1 (Na+ /H+ exchange regulatory factor 1) scaffolding protein that drives CFTR dimerization and is known to increase the open probability of the CFTR channel [26,27]. Login to comment 133 ABCC7 p.Arg117His ABCC7 p.Arg117His ABCC7 p.Ala455Glu The lack of an intestinal bioelectrical phenotype in both R117H homozygous individuals may likewise result from intestine-specific rescue mechanisms but is also readily explained by the known insensitivity of the intestinal current measurements to a partial loss of CFTR function [30-32]. Login to comment 134 ABCC7 p.Arg117His Still another explanation can be given for the lack of pancreatic insufficiency noted in both R117H homozygotes and compound heterozygotes for this mutation. Login to comment 135 ABCC7 p.Arg117His Despite the severe loss of Cl- channel function of the R117H mutant CFTR, its bicarbonate transport function is not impaired [8] or even enhanced [34], in clear contrast to all known mutations associated with pancreatic insufficiency [8]. Login to comment 136 ABCC7 p.Arg117His ABCC7 p.Arg117His ABCC7 p.Ala455Glu The R117H (and the A455E) CFTR mutants may therefore behave as borderline cases in which the homozygous expression is associated with a normal ICM pattern (≥20% residual CFTR conductance) whereas compound heterozygotes carrying a second more severe mutation (e.g. F508del) show a more variable residual CFTR Cl- current in the intestine ranging from normal to severely reduced, but not absent [24,33]. Login to comment 137 ABCC7 p.Arg117His ABCC7 p.Arg117His Still another explanation can be given for the lack of pancreatic insufficiency noted in both R117H homozygotes and compound heterozygotes for this mutation. Login to comment 138 ABCC7 p.Arg117His Despite the severe loss of Cl-channel function of the R117H mutant CFTR, its bicarbonate transport function is not impaired [8] or even enhanced [34], in clear contrast to all known mutations associated with pancreatic insufficiency [8]. Login to comment 139 ABCC7 p.Arg117His The finding of pancreatic sufficiency in both R117H homozygous subjects therefore confirms the notion that the loss of HCO3 - transport function is of more importance for the pathogenesis of CF in the pancreas than the loss of Cl-transport function. Login to comment 140 ABCC7 p.Arg117His In conclusion, the only CFTR-associated abnormalities found in the R117H-7T homozygous subjects in this study were a slightly elevated sweat Cl- and CBAVD in the male individual. Login to comment