Clinical Consequences and Functional Impact of the Rare S737F CFTR Variant and Its Responsiveness to CFTR Modulators.

S737F is a Cystic Fibrosis (CF) transmembrane conductance regulator (CFTR) missense variant. The aim of our study was to describe the clinical features of a cohort of individuals carrying this variant. In parallel, by exploiting ex vivo functional and molecular analyses on nasal epithelia derived from a subset of S737F carriers, we evaluated its functional impact on CFTR protein as well as its responsiveness to CFTR modulators. We retrospectively collected clinical data of all individuals bearing at least one S737F CFTR variant and followed at the CF Centre of Tuscany region (Italy). Nasal brushing was performed in cooperating individuals. At study end clinical data were available for 10 subjects (mean age: 14 years; range 1-44 years; 3 adult individuals). Five asymptomatic subjects had CF, 2 were CRMS/CFSPID and 3 had an inconclusive diagnosis. Ex vivo analysis on nasal epithelia demonstrated different levels of CF activity. In particular, epithelia derived from asymptomatic CF subjects and from one of the subjects with inconclusive diagnosis showed reduced CFTR activity that could be rescued by treatment with CFTR modulators. On the contrary, in the epithelia derived from the other two individuals with an inconclusive diagnosis, the CFTR-mediated current was similar to that observed in epithelia derived from healthy donors. In vitro functional and biochemical analysis on S737F-CFTR expressed in immortalized bronchial cells highlighted a modest impairment of the channel activity, that was improved by treatment with ivacaftor alone or in combination with tezacaftor/elexacaftor. Our study provide evidence towards the evaluation of CFTR function on ex vivo nasal epithelial cell models as a new assay to help clinicians to classify individuals, in presence of discordance between clinical picture, sweat test and genetic profile.

Modulator Therapy in Cystic Fibrosis Patients with cis Variants in F508del Complex Allele: A Short-Term Observational Case Series.

Previous studies reported the influence of cis variants in F508del cystic fibrosis (CF) patients in their responses to CFTR modulators. The current study is a prospective, observational study involving three patients with CF and pancreatic insufficiency, carrying a complex allele including F508del with A238V, I1027T, or L467F. We report clinical data before and after 4 weeks of treatment with tezacaftor (TEZ)/ivacaftor (IVA), elexacaftor (ELX)/TEZ/IVA, and lumacaftor (LUM)/IVA for patients with complex alleles A238V, I1027T, and L467F, respectively. The 50-year-old patient bearing F508del;A238V/D1152H showed a normal sweat test (13 mEq/L) and improvements in forced expiratory volume in the first second (FEV1) (+7 points), body mass index (BMI) (+0.85), and respiratory CF Questionnaire-Revised (CFQ-R) domain (+22.2 points). The 12-year-old patient bearing F508del;I1027T/R709X showed an improvement in a sweat test (-40 mEq/l), FEV1 (+9 points) and the respiratory CFQ-R domain (+16.7 points). No changes in outcomes were observed for the 6-year-old patient F508del;L467F/F508del. Our data highlight that the reported variants do not modify the phenotypic expression of F508del. Searching L467F is crucial in CF patients with F508del nonresponsive to ELX/TEZ/IVA. Further data are needed to evaluate the clinical effect of these variants after a longer follow up.

Impact of Pancreatitis-Associated Protein on Newborn Screening Outcomes and Detection of CFTR-Related Metabolic Syndrome (CRMS)/Cystic Fibrosis Screen Positive, Inconclusive Diagnosis (CFSPID): A Monocentric Prospective Pilot Experience.

Pancreatitis-Associated Protein (PAP)-based Cystic Fibrosis (CF) newborn bloodspot screening (NBS) protocols detect less CFTR-Related Metabolic Syndrome (CRMS)/CF Screen Positive, Inconclusive Diagnosis (CFSPID). We prospectively evaluated the impact of PAP as the second step of the CF NBS protocol, before the CFTR genetic analysis, on NBS outcomes and CRMS/CFSPID detection in the Tuscany region, Italy. In parallel to the usual protocol (IRT/DNA, protocol 1), PAP was analyzed in IRT-positive infants (IRT/PAP/DNA, protocol 2) from 1 June 2020 until 31 May 2022. We defined an infant as NBS positive if PAP was >1.8 µg/L for IRT value 99th percentile-100 µg/L or >0.6 µg/L for IRT value >100 µg/L. To increase the positive predictive value (PPV) of protocol 2, we retrospectively lowered the upper IRT range value from 100 to 90 µg/L (modified protocol 2). We identified 8 CF and 13 CRMS/CFSPID with protocol 1, 5 CF and 5 CRMS/CFSPID with protocol 2 and 8 CF and 5 CRMS/CFSPID with modified protocol 2. With the PAP-based protocols, we observed a reduction of sweat tests, healthy carrier detection and a significant increase in PPV to 15.38%. Further data are needed in order to evaluate the outcomes of CRMS/CFSPID after a long follow-up.

Clinical outcomes of a large cohort of individuals with the F508del/5T;TG12 CFTR genotype.

BACKGROUND: In recent years, patients with cystic fibrosis (CF) conductance regulator (CFTR) variant poly(T) sequences have been increasingly reported with a wide spectrum of clinical severity. We describe the long-term clinical outcomes and progression to a CF diagnosis over time in a large Italian cohort of patients carrying the CFTR F508del/5T;TG12 genotype. METHODS: A retrospective analysis of subjects from 10 CF centres in Italy with the F508del/5T;TG12 genotype was performed. Demographic, clinical, microbiological, and biochemical data, as well as information about the follow-ups and complications of the enroled patients, were collected. RESULTS: A total of 129 subjects (54 females; median age: 15.0 years, range: 0-58 years; 59 older than 18 years) were included. In terms of initial diagnoses, 30 were CF (23.3%), 41 were CFTR-related disorder (CFTR-RD) (31.7%), and 58 were CF transmembrane conductance regulator-related metabolic syndrome/cystic fibrosis screen positive, inconclusive diagnosis (CRMS/CFSPID) (45.0%). After a median follow-up of 6.7 years (range 0.2-25 years), 15 patients progressed to CF, bringing the total number of CF diagnoses to 45/129 (34.9%). Most of these patients had mild lung diseases with pancreatic sufficiency and a low prevalence of CF-related complications. CONCLUSIONS: At the end of the study, 34.9% of subjects with the CFTR F508del/5T;TG12 genotype were diagnosed with CF. We suggest including patients with the F508del/5T;TG12 genotype in long-term follow-ups.

Cystic fibrosis in Tuscany: evolution of newborn screening strategies over time to the present.

BACKGROUND: Cystic fibrosis (CF) is a life-threatening disease affecting about 1:3000 newborns in Caucasian populations. The introduction of newborn screening for cystic fibrosis (CF NBS) has improved the clinical outcomes of individuals with CF through early diagnosis and early treatment. NBS strategies have been implemented over time. CF NBS was introduced extensively in 1984 in Tuscany, a region with 3.7 million people, characterized by a high allelic heterogeneity of CFTR gene. AIM AND METHODS: The aim of the study is to present the results from 34 years (1984-2018) of CF NBS, retrospectively evaluating the sensitivity, specificity and predictive values of the tests. In particular, we studied the impact of the introduction of DNA molecular analysis in NBS in a region with high allelic heterogeneity, such as Tuscany. RESULTS: Over these 34 years, 919,520 neonates were screened, using four different NBS strategies. From 1984 to 1991, CF NBS was performed by the determination of albumin on dried meconium (sensitivity 68.75%; specificity 99.82%). Subsequently, the analysis of immunoreactive trypsinogen on a blood spot was adopted as CF NBS protocol (sensitivity 83.33%; specificity 99.77%). From 1992 to 2010, this strategy was associated with lactase meconium dosage: IRT1/IRT2 + LACT protocol (sensitivity 87.50%; specificity 99.82%). From 2011, when the existing algorithm was integrated by analysis of CF causing variants of the CFTR gene (IRT1/IRT2 + LACT + IRT1/DNA protocol), a substantial improvement in sensitivity was seen (senisitivity 96.15%; specificity 99.75%). Other improved parameters with DNA analysis in the NBS programme, compared with the previous method, were the diagnosis time (52 days vs. 38 days) and the recall rate (0.58 to 0.38%). CONCLUSION: The inclusion of DNA analysis in the NBS was a fundamental step in improving sensitivity, even in a region with high allelic variability.

Clinical and Genotypical Features of False-Negative Patients in 26 Years of Cystic Fibrosis Neonatal Screening in Tuscany, Italy.

Cystic fibrosis (CF) is a life-threatening and common genetic disorder. Cystic fibrosis newborn screening (CF NBS) has been implemented in many countries over the last 30 years, becoming a widely accepted public health strategy in economically developed countries. False-negative (FN) cases can occur after CF NBS, with the number depending on the method. We evaluated the delayed diagnosis of CF, identifying the patients who had false-negative CF NBS results over 26 years (1992-2018) in Tuscany, Italy. The introduction of DNA analysis to the newborn screening protocol improved the sensitivity of the test and reduced the FNs. Our experience showed that, overall, at least 8.7% of cases of CF received FNs (18 cases) and were diagnosed later, with an average age of 6.6 years (range: 4 months to 22 years). Respiratory symptoms and salt-loss syndrome (metabolic hypochloremic alkalosis) are suggestive symptoms of CF and were commons events in FN patients. In Tuscany, a region with a high CFTR allelic heterogeneity, the salt-loss syndrome was a common event in FNs. Therefore, we provided evidence to support the claim that the FN patients had CFTR mutations rarer compared with the true-positive cases. We underline the importance of vigilance toward clinical manifestations suggestive of CF on the part of the primary care providers and hospital physicians in a region with an efficient newborn screening program.

Cystic fibrosis screen positive inconclusive diagnosis (CFSPID): Experience in Tuscany, Italy.

OBJECTIVE: The implementation of cystic fibrosis (CF) newborn screening (NBS) has led to identification of infants with a positive NBS test but inconclusive diagnosis classified as "CF screen positive, inconclusive diagnosis" (CFSPID). We retrospectively evaluated the prevalence and clinical outcome of CFSPID infants diagnosed by 2 NBS algorithms in the period from 2011 to 2016 in the Tuscany region of Italy. METHODS: In 2011-2016, we assessed the diagnostic impact of DNA analysis on the NBS 4-tier algorithm [immunoreactive trypsin (IRT) - meconium lactase - IRT2 - sweat chloride (SC)]. All CFSPID patients repeated SC testing every 6 months, and CFTR gene analysis was performed (detection rate 98%). We reclassified children as: CF diagnosis in presence of at least 2 pathological SC results; healthy carrier or healthy in presence of at least 2 normal SC results for age and either 1 or 0 CF-causing mutations, respectively. RESULTS: We identified 32 CF and 50 CFSPID cases: 20/50 (40%) were diagnosed only by the IRT-DNA-SC algorithm and 16/50 (32%) only by IRT-meconium lactase-IRT2-SC. Both protocols identified the remaining 14 cases (28%). Thirty-seven of 50 (74%) CFSPID patients had a conclusive diagnosis on December 31, 2017:5 (10%) CF, 17 (34%) healthy and 15 (30%) healthy carriers; 13/50 (26%) cases were asymptomatic with persistent intermediate SC and followed as CFSPID (CF:CFSPID ratio 2.85:1). CONCLUSIONS: In 6 years, the CF:CFSPID ratio modified from 0.64:1 to 2.85:1, and 10% of CFSPID cases progressed to CF. Genetic analysis improved positive predictive value and identified a higher number of CFSPID infants progressing to CF.

S737F is a new CFTR mutation typical of patients originally from the Tuscany region in Italy.

BACKGROUND: An increasing number of patients have been described as having a number of Cystic Fibrosis Transmembrane conductance Regulator (CFTR) variants for which it lacks a clear genotype-phenotype correlation. We assesses the clinical features of patients bearing the S737F (p.Ser737Phe) CFTR missense variant and evaluated the residual function of CFTR protein on nasal epithelial cells (NEC). METHODS: A retrospective database was performed from individuals homozygous or compound heterozygous for the S737F variant followed in the Cystic Fibrosis (CF) Centre of Florence. We performed a nasal brushing in cooperating patients and compared the results with those of patients followed in the pediatric CF Centre of Naples. RESULTS: 9/295 (3%) subjects carrying at least S737F CFTR variant on one allele were identified. Patients were diagnosed in 7/9 cases by newborn screening and in two cases for dehydration with hypochloremic metabolic alkalosis; at diagnosis sweat chloride levels (SCL) were in the pathological range in only one case. After a mean follow up of 8,6 years (range 0,5-15,8), SCL were in the pathological range in 8/9 cases (mean age at CF diagnosis: 1,5 years), all patients were pancreatic sufficiency and respiratory function was normal. The gating activity on NEC was 15.6% and 12.7% in two patients compound heterozygous for W1282X and DelE22_24, while it was ranged between 6,2% and 9,8% in CF patients. CONCLUSIONS: S737F is a CFTR mutation associated to hypochloremic alkalosis in childhood, mild CF phenotype in teenage years and a residual function of CFTR protein.

Characterization of a novel isolated deletion of the exon 3 within the CFTR gene: Relevance for phenotypic expression and genetic counseling.

OBJECTIVES: To characterize a novel deletion of exon 3 of CFTR gene and to evaluate the implications in Cystic Fibrosis (CF) care and genetic counseling. DESIGN AND METHODS: We performed a wide mutational analysis of CFTR gene, using reverse dot blot, Multiplex Ligation-dependent Probe Amplification (MLPA) assay and Real Time Quantitative PCR, in a carrier male and two CF patients with the F508del mutation. RESULTS: We found a novel isolate 538bp deletion of exon 3, described as 328del538, giving rise to a nonsense codon 60bp at the 3' end of the new coding sequence or, alternatively, a novel splice site at the breakpoints. CONCLUSIONS: The 328del538 is a rare lesion with the characteristics of a complete, but moderate, phenotypic expression. Its finding underlines the importance of improving the detection of mutations using different methods.

Cytogenetic and molecular evaluation of 241 small supernumerary marker chromosomes: cooperative study of 19 Italian laboratories.

PURPOSE: We evaluated the experiences of 19 Italian laboratories concerning 241 small supernumerary marker chromosomes (sSMCs) with the aim of answering questions arising from their origin from any chromosome, their variable size and genetic content, and their impact on the carrier's phenotype. METHODS: Conventional protocols were used to set up the cultures and chromosome preparations. Both commercial and homemade probes were used for the fluorescent in situ hybridization analyses. RESULTS: A total of 113 of the 241 sSMCs were detected antenatally, and 128 were detected postnatally. There were 52 inherited and 172 de novo cases. Abnormal phenotype was present in 137 cases (57%), 38 of which were antenatally diagnosed. A mosaic condition was observed in 87 cases (36%). In terms of morphology, monocentric and dicentric bisatellited marker chromosomes were the most common, followed by monocentric rings and short-arm isochromosomes. The chromosomes generating the sSMCs were acrocentric in 132 cases (69%) and non-acrocentric chromosomes in 60 cases (31%); a neocentromere was hypothesized in three cases involving chromosomes 6, 8, and 15. CONCLUSION: The presented and published data still do not allow any definite conclusions to be drawn concerning karyotype-phenotype correlations. Only concerted efforts to characterize molecularly the sSMCs associated or not with a clinical phenotype can yield results suitable for addressing karyotype-phenotype correlations in support of genetic counseling.