Genotype–phenotype correlation and functional studies in patients with cystic fibrosis bearing CFTR complex alleles

• Published in: Journal of medical genetics Vol. 54; no. 4; pp. 224 - 235
• Main Authors: Terlizzi, Vito, Castaldo, Giuseppe, Salvatore, Donatello, Lucarelli, Marco, Raia, Valeria, Angioni, Adriano, Carnovale, Vincenzo, Cirilli, Natalia, Casciaro, Rosaria, Colombo, Carla, Di Lullo, Antonella Miriam, Elce, Ausilia, Iacotucci, Paola, Comegna, Marika, Scorza, Manuela, Lucidi, Vincenzina, Perfetti, Anna, Cimino, Roberta, Quattrucci, Serena, Seia, Manuela, Sofia, Valentina Maria, Zarrilli, Federica, Amato, Felice
• Format: Journal Article
• Language: English
• Published: England BMJ Publishing Group LTD 01.04.2017
• Subjects: Adolescent; Adult; Alleles; Child; Child, Preschool; Cystic fibrosis; Cystic Fibrosis - genetics; Cystic Fibrosis - pathology; Cystic Fibrosis Transmembrane Conductance Regulator - genetics; Diabetes; Female; Genetic Association Studies; Genetic Predisposition to Disease; Genotype; Genotype & phenotype; Heterozygote; Homozygote; Humans; Laboratories; Liver diseases; Male; Medical screening; Middle Aged; Mutation; Nasal Mucosa - metabolism; Nasal Mucosa - pathology; Pancreatitis; Patients; Phenotype; Young Adult; nasal brushing; R74W;V201M;D1270N; I148T;3199del6bp; L997F;R117L; gating activity
• ISSN: 0022-2593; 1468-6244
• DOI: 10.1136/jmedgenet-2016-103985

BackgroundThe effect of complex alleles in cystic fibrosis (CF) is poorly defined for the lack of functional studies.ObjectivesTo describe the genotype–phenotype correlation and the results of either in vitro and ex vivo studies performed on nasal epithelial cells (NEC) in a cohort of patients with CF carrying cystic fibrosis transmembrane conductance regulator (CFTR) complex alleles.MethodsWe studied 70 homozygous, compound heterozygous or heterozygous for CFTR mutations: p.[Arg74Trp;Val201Met;Asp1270Asn], n=8; p.[Ile148Thr;Ile1023_Val1024del], n=5; p.[Arg117Leu;Leu997Phe], n=6; c.[1210-34TG[12];1210-12T[5];2930C>T], n=3; p.[Arg74Trp;Asp1270Asn], n=4; p.Asp1270Asn, n=2; p.Ile148Thr, n=6; p.Leu997Phe, n=36. In 39 patients, we analysed the CFTR gating activity on NEC in comparison with patients with CF (n=8) and carriers (n=4). Finally, we analysed in vitro the p.[Arg74Trp;Val201Met;Asp1270Asn] complex allele.ResultsThe p.[Ile148Thr;Ile1023_Val1024del] caused severe CF in five compound heterozygous with a class I–II mutation. Their CFTR activity on NEC was comparable with patients with two class I–II mutations (mean 7.3% vs 6.9%). The p.[Arg74Trp;Asp1270Asn] and the p.Asp1270Asn have scarce functional effects, while p.[Arg74Trp;Val201Met;Asp1270Asn] caused mild CF in four of five subjects carrying a class I–II mutation in trans, or CFTR-related disorders (CFTR-RD) in three having in trans a class IV–V mutation. The p.[Arg74Trp;Val201Met;Asp1270Asn] causes significantly (p<0.001) higher CFTR activity compared with compound heterozygous for class I–II mutations. Furthermore, five of six compounds heterozygous with the p.[Arg117Leu;Leu997Phe] had mild CF, whereas the p.Leu997Phe, in trans with a class I–II CFTR mutation, caused CFTR-RD or a healthy status (CFTR activity: 21.3–36.9%). Finally, compounds heterozygous for the c.[1210-34TG[12];1210-12T[5];2930C>T] and a class I–II mutation had mild CF or CFTR-RD (gating activity: 18.5–19.0%).ConclusionsThe effect of complex alleles partially depends on the mutation in trans. Although larger studies are necessary, the CFTR activity on NEC is a rapid contributory tool to classify patients with CFTR dysfunction.