Guidelines for the clinical management and follow-up of infants with inconclusive cystic fibrosis diagnosis through newborn screening

Literary evidence of the impact of nonbiological risk factors on CRMS/CFSPID: A scoping review

Newborn screening for cystic fibrosis (CF) occasionally results in an inconclusive diagnosis of this disease, and these individuals are designated as CFTR-related metabolic syndrome (CRMS) in the United States, and CF Screen Positive Inconclusive Diagnosis (CFSPID) in other countries. Some of these asymptomatic individuals will progress to symptomatic disease, but risk factors associated with disease progression are not well understood. This scoping review was conducted to comprehensively map nonbiological risk factors in the CRMS/CFSPID literature and to identify understudied topics. Six electronic databases were systematically searched, resulting in 2951 studies. Forty nine eligible works were identified as including information on nonbiological risk factors related to CRMS/CFPSID. Eligible studies were published from 2002 to 2024, most prevalently in the United States (36.7%), and as quantitative data (81.6%). Of the 49 eligible works, 23 articles contributed only intellectual conjecture, while 26 articles contained original data, which underwent full-text qualitative content analysis. Key themes identified in descending order of content coverage included Psychological Impact, Management Care, Newborn Screening and Diagnostics, Communicating Diagnosis, and Lifestyle and External Exposures. This scoping review identified that while nonbiological risk factors are being studied in the CRMS/CFSPID literature, there was nearly equal distribution of works gathering original data to those citing previously published information. These findings indicate a critical need for original data collection on these risk factors, particularly on understudied topics identified herein.

Biochemical and genetic tools to predict the progression to Cystic Fibrosis in CRMS/CFSPID subjects: A systematic review

OBJECTIVES

Aim of this study was to identify risk factors for a progression to cystic fibrosis (CF) in individuals detected as CF Screening Positive, Inconclusive Diagnosis (CFSPID).

METHODS

This is a systematic review through literature databases (2015-2023). Blood immunoreactive trypsinogen (b-IRT) values, CFTR genotype, sweat chloride (SC) values, isolation of Pseudomonas aeruginosa (Pa) from respiratory samples, Lung Clearance Index (LCI) values in CFSPIDs who converted to CF (CFSPID > CF) and age at CF transition were assessed.

RESULTS

Percentage of CFSPID > CF varies from 5.3 % to 44 %. Presence of one CF-causing CFTR variant in trans with a variant with variable clinical consequences (VVCC), an initial SC ≥ 40 mmol/L, an increase of SC > 2.5 mmol/L/year and recurrent isolation of pseudomonas aeruginosa (Pa) from airway samples could allow identification of subjects at risk of progression to CF.

CONCLUSIONS

CFSPIDs with CF causing variant/VVCC genotype and first SC in the higher borderline range may require more frequent and prolonged clinical follow-up.

Feasibility of performing the 3-minute step test with remote supervision in children and adolescents with cystic fibrosis: A comparative study

Importance

The 3-min step test is a simple option to monitor submaximal exercise capacity, although its use via remote video monitoring has not been investigated in children with cystic fibrosis (CF).

Objective

This study aimed to assess the feasibility and reproducibility of performing the 3-min step test with remote supervision.

Methods

A cross-sectional study including CF patients (6-18 years) from two CF services were performed. Demographic, anthropometric, clinical, and lung function data were collected and two 3-min step tests were performed: (i) in-person supervision, and (ii) remotely supervised by video monitoring. Before and after the tests, heart rate (HR), oxygen saturation (SpO2), and the Borg score for dyspnea and lower limb fatigue were monitored.

Results

Twenty-three patients (10.7 ± 3.7 years) with a mean FEV1 of 89.5% ± 23.2% were included. There were no significant differences between tests, with mean differences (95% confidence intervals) in final HR of -3.3 (-8.9, 2.4), change in HR of -1.9 (-6.1, 2.1), final SpO2 of 0.3 (-0.4, 1.0), and final dyspnea of 0.1 (-0.8, 0.9). The intraclass correlation coefficient was 0.852 (final HR), 0.762 (final SpO2), and 0.775 (final lower limb fatigue). Significant and moderate correlations were found between tests for final HR (r = 0.75), change in HR (r = 0.61), and final SpO2 (r = 0.61). The Bland-Altman analysis showed a mean difference in final SpO2 between tests of 0.3% (limit of agreement -3.0%, 3.5%).

Interpretation

Physiological responses between tests were similar, indicating it was feasible to perform the 3-min step test with remote supervision in CF children.

Pseudo-Bartter syndrome in infant with cystic fibrosis screen positive, inconclusive diagnosis: A case report

The introduction of newborn screening for cystic fibrosis (CF) increased diagnosis of cystic fibrosis screen positive inconclusive diagnosis (CFSPID). We described the case of a 12-month-old boy with CFSPID who, during summer, presented Pseudo-Bartter syndrome with no diagnostic criteria for CF.

Recent advances in proteomic-based diagnostics of cystic fibrosis

INTRODUCTION

Cystic fibrosis (CF) is a genetic disease characterized by thick and sticky mucus accumulation, which may harm numerous internal organs. Various variables such as gene modifiers, environmental factors, age of diagnosis, and CF transmembrane conductance regulator (CFTR) gene mutations influence phenotypic disease diversity. Biomarkers that are based on genomic information may not accurately represent the underlying mechanism of the disease as well as its lethal complications. Therefore, recent advancements in mass spectrometry (MS)-based proteomics may provide deep insights into CF mechanisms and cellular functions by examining alterations in the protein expression patterns from various samples of individuals with CF.

AREAS COVERED

We present current developments in MS-based proteomics, its application, and findings in CF. In addition, the future roles of proteomics in finding diagnostic and prognostic novel biomarkers.

EXPERT OPINION

Despite significant advances in MS-based proteomics, extensive research in a large cohort for identifying and validating diagnostic, prognostic, predictive, and therapeutic biomarkers for CF disease is highly needed.

Cystic Fibrosis Screen Positive, Inconclusive Diagnosis Genotypes in People with Cystic Fibrosis from the U.S. Patient Registry

Rationale: Variants within the cystic fibrosis (CF) transmembrane conductance regulator gene, CFTR, that are of unknown significance or are categorized as non-CF causing may be observed in persons with CF. These variants are frequently detected in children with inconclusive newborn screen results and, in some cases, may be associated with a benign presentation in early childhood that progresses to a CF phenotype later in life. Objectives: To analyze data from individuals enrolled in the U.S. Cystic Fibrosis Foundation Patient Registry who have received a diagnosis of CF and who have variants found in a population of children with a CF screen positive, inconclusive diagnosis (CFSPID). Methods: This retrospective review analyzed registry data from individuals with a diagnosis of CF who also harbor one or more variants of interest because of their frequency within a CFSPID population and/or their interpretation as non-CF causing. Three groups were defined by the number of CF-causing variants identified (CF-Cx2, CF-Cx1, and CF-Cx0), which were reported in addition to the variant(s) of interest. Multivariate quantile regression modeling of the outcome for forced expiratory volume in 1 second (FEV1) generated a disease severity score for each person determined by six selected variables. Median scores were calculated for the three groups. Results: Patients carrying one CF-causing variant and at least one variant of interest (CF-Cx1) had higher median disease severity scores compared with those carrying CF-Cx2, suggesting a milder phenotype (P < 0.05). However, there was no statistically significant difference in scores between CF-Cx2 and the two other groups combined (CF-Cx1 and CF-Cx0; P = 0.33). Analysis revealed that the CF-Cx1 and CF-Cx0 groups, when compared with the CF-Cx2 group, had later median diagnoses (8 years vs. newborn; P < 0.0001), lower median sweat chloride (48 mmol/L vs. 94.5 mmol/L; P < 0.0001), lower prevalence of pancreatic insufficiency (29% vs. 78%; P < 0.0001), and higher median FEV1% predicted (95% vs. 87%; P = 0.0002). Conclusions: Individuals with CF who have specific variants frequently identified in children with CFSPID have a similar range of disease severity scores compared with those who have two CF-causing variants, but a milder phenotype overall. Variants that should be given careful scrutiny because of their high prevalence are G576A+R668C, T854T, R75Q, F1052V, R1070W, R31C, and L967S.

Cystic fibrosis transmembrane conductance regulator-related metabolic syndrome/cystic fibrosis screen positive, inconclusive diagnosis (CRMS/CFSPID)

Newborn bloodspot screening (NBS) for cystic fibrosis (CF) is an effective strategy for the early recognition of infants with a CF diagnosis. Some infants with a positive NBS result for CF have an inconclusive diagnosis and evidence suggests the number of these infants is increasing, as more extensive gene analysis is integrated into screening protocols. There is an internationally agreed, but complex, designation for infants with an unclear diagnosis after a positive screening result: cystic fibrosis transmembrane conductance regulator (CFTR)-related metabolic syndrome/cystic fibrosis screen positive, inconclusive diagnosis (CRMS/CFSPID). Infants with a CRMS/CFSPID designation have no clinical evidence of disease and do not meet the criteria for a CF diagnosis, but the NBS result indicates some risk of developing CF or a CFTR-related disorder. In this review, we describe the accurate designation of these and reflect on emerging management pathways, with particular attention given to clear and consistent communication.

Educational aims

To clarify the definition of the global harmonised designation: cystic fibrosis transmembrane conductance regulator-related metabolic syndrome (CRMS)/cystic fibrosis screen positive, inconclusive diagnosis (CFSPID).To understand what impact a CRMS/CFSPID result has for the patient and their family.

Reclassifying inconclusive diagnosis after newborn screening for cystic fibrosis. Moving forward

BACKGROUND

Newborn screening for Cystic Fibrosis (CF) is associated with situations where the diagnosis of CF or CFTR related disorders (CFTR-RD) cannot be clearly ruled out.

MATERIALS/PATIENTS AND METHODS

We report a case series of 23 children with unconclusive diagnosis after newborn screening for CF and a mean follow-up of 7.7 years (4-13). Comprehensive investigations including whole CFTR gene sequencing, in vivo intestinal current measurement (ICM), nasal potential difference (NPD), and in vitro functional studies of variants of unknown significance, helped to reclassify the patients.

RESULTS

Extensive genetic testing identified, in trans with a CF causing mutation, variants with varying clinical consequences and 3 variants of unknown significance (VUS). Eighteen deep intronic variants were identified by deep resequencing of the whole CFTR gene in 13 patients and were finally considered as non-pathogenic. All patients had normal CFTR dependent chloride transport in ICM. NPD differentiated 3 different profiles: CF-like tracings qualifying the patients as CF, such as F508del/D1152H patients; normal responses, suggesting an extremely low likelihood of developing a CFTR-RD such as F508del/TG11T5 patients; partial CFTR dysfunction above 20% of the normal, highlighting a remaining risk of developing CFTR-RD such as F508del/F1052V patients. The 3 VUS were reclassified as variant with defective maturation (D537N), defective expression (T582I) or with no clinical consequence (M952T).

CONCLUSION

This study demonstrates the usefulness of combining genetic and functional investigations to assess the possibility of evolving to CF or CFTR-RD in babies with inconclusive diagnosis at neonatal screening.

[Newborn screening for cystic fibrosis in France]

Neonatal screening for cystic fibrosis has optimised the prognosis for patients allowing very early multidisciplinary care. Over the past 20 years, screening programmes have undergone major international expansion. The performances of the French neonatal cystic fibrosis screening programme, established in 2002, has met European guideline standards, with positive predictive value of 0.31 (against a minimum of 0.30) and sensitivity value of 0.95 (against a minimum of 0.95). It is also important to highlight the very high percentage of sweat tests performed (95.5%), of mutations identified (96.6%), the 9:1 ratio of cystic fibrosis cases to cases of inconclusive diagnosis achieved and the effectiveness of the strategy implemented for the detection of false negative cases. A new organisation for cystic fibrosis neonatal screening has now been established in France. It is vital that effectiveness is maintained throughout the process, from newborn maternity care to diagnosis in cystic fibrosis care centres, and that further knowledge is gained through exhaustive data collection and validation.

Potential of Intestinal Current Measurement for Personalized Treatment of Patients with Cystic Fibrosis

Refinement of personalized treatment of cystic fibrosis (CF) with emerging medicines targeting the CF basic defect will likely benefit from biomarkers sensitive to detect improvement of cystic fibrosis transmembrane conductance regulator (CFTR) function in individual patients. Intestinal current measurement (ICM) is a technique that enables quantitative assessment of CFTR chloride channel function in rectal tissues or other intestinal epithelia. ICM was originally developed to study the CF ion transport defect in the intestine and has been established as a sensitive biomarker of CFTR function and diagnostic test for CF. With the emergence of CFTR-directed therapeutics, ICM has become an important tool to estimate the level of rescue of CFTR function achieved by approved CFTR modulators, both at the level of CFTR genotype groups, as well as individual patients with CF. In combination with preclinical patient-derived cell culture models, ICM may aid the development of targeted therapies for patients with rare CFTR mutations. Here, we review the principles of ICM and examine how this CFTR biomarker may be used to support diagnostic testing and enhance personalized medicine for individual patients with common as well as rare CFTR mutations in the new era of medicines targeting the underlying cause of CF.

Genetic diagnosis in practice: From cystic fibrosis to CFTR-related disorders

Cystic fibrosis (CF) is a channelopathy caused by mutations in the gene encoding the CF transmembrane conductance regulator (CFTR) protein. Diagnosis of CF has long relied on a combination of clinical (including gastrointestinal and/or respiratory) symptoms and elevated sweat chloride concentration. After cloning of the CFTR gene in 1989, genetic analysis progressively became an important aspect of diagnosis. Although combination of sweat test and genetic analysis have simplified the diagnosis of CF in most cases, difficult situations remain, especially in cases that do not fulfill all diagnostic criteria. Such situations are most frequently encountered in patients presenting with a single-organ disease (e.g., congenital absence of the vas deferens, pancreatitis, bronchiectasis) leading to a diagnosis of CFTR-related disorder, or when the presence/ absence of CF is not resolved after newborn screening. This article reviews the diagnostic criteria of CF, with special emphasis on genetic testing. © 2020 French Society of Pediatrics. Published by Elsevier Masson SAS. All rights reserved.

Current and future diagnosis of cystic fibrosis: Performance and limitations

Cystic fibrosis (CF) is the most frequent genetic disorder in the Caucasian population benefiting from systematic newborn screening tests. It is also the most frequent indication of prenatal and preimplantation genetic diagnosis for a single gene disorder. During the past thirty years, thanks in part to the evolution of diagnostic techniques, our knowledge on CFTR genetics and pathophysiological mechanisms involved in CF have significantly improved. With the implementation of newborn screening in France and in several countries, the diagnosis now often occurs in clinically asymptomatic infants and this has modified the criteria for CF diagnosis. Recently, guidelines for CF diagnosis have been reformulated in Europe and the US, in regard to sweat chloride usual values and disease terminology. This review describes the methods and molecular approaches that are used in routine practice or are being developed to detect CFTR protein dysfunction and to identify disease-causing CFTR variants. Ultimately, an optimal use of all these functional and genetic resources may improve patient care and therapeutic decision-making. © 2020 French Society of Pediatrics. Published by Elsevier Masson SAS. All rights reserved.

Updated guidance on the management of children with cystic fibrosis transmembrane conductance regulator-related metabolic syndrome/cystic fibrosis screen positive, inconclusive diagnosis (CRMS/CFSPID)

Over the past two decades there has been considerable progress with the evaluation and management of infants with an inconclusive diagnosis following Newborn Screening (NBS) for cystic Fibrosis (CF). In addition, we have an increasing amount of evidence on which to base guidance on the management of these infants and, importantly, we have a consistent designation being used across the globe of CRMS/CFSPID. There is still work to be undertaken and research questions to answer, but these infants now receive more consistent and appropriate care pathways than previously. It is clear that the majority of these infants remain healthy, do not convert to a diagnosis of CF in childhood, and advice on management should reflect this. However, it is also clear that some will convert to a CF diagnosis and monitoring of these infants should facilitate their early recognition. Those infants that do not convert to a CF diagnosis have some potential of developing a CFTR-RD later in life. At present, it is not possible to quantify this risk, but families need to be provided with clear information of what to look out for. This paper contains a number of changes from previous guidance in light of developing evidence, but the major change is the recommendation of a detailed assessment of the child with CRMS/CFSPID in the sixth year of age, including respiratory function assessment and imaging. With these data, the CF team can discuss future care arrangements with the family and come to a shared decision on the best way forward, which may include discharge to primary care with appropriate information. Information is key for these families, and we recommend consideration of a further appointment when the individual is a young adult to directly communicate the implications of the CRMS/CFSPID designation.

Dehydrated patient without clinically evident cause: A case report

BACKGROUND

Patients affected by cystic fibrosis can present with metabolic alkalosis such as Bartter’s syndrome. In this case report we want to underline this differential diagnosis and we aimed focusing on the suspect of cystic fibrosis, also in case of a negative newborn screening.

CASE SUMMARY

In a hot August –with a mean environmental temperature of 36 °C– an 8-mo-old female patient presented with severe dehydration complicated by hypokalemic metabolic alkalosis, in absence of fever, diarrhea and vomiting. Differential diagnosis between cystic fibrosis and tubulopathies causing metabolic alkalosis (Bartter’s Syndrome) was considered. We started intravenous rehydration with subsequent improvement of clinical conditions and serum electrolytes normalization. We diagnosed a mild form of cystic fibrosis (heterozygous mutations: G126D and F508del in the cystic fibrosis transmembrane conductance regulator gene). The trigger factor of this condition had been heat exposure.

CONCLUSION

When facing a patient with hypokalemic metabolic alkalosis, cystic fibrosis presenting with Pseudo-Bartter’s syndrome should be considered in the differential diagnosis, even if the newborn screening was negative.

Penetrance is a critical parameter for assessing the disease liability of CFTR variants

BACKGROUND

Major issues of newborn screening (NBS) for CF are the assessment of disease liability of variants and of the penetrance of clinical CF, notably in inconclusive diagnosis. The penetrance of CF is defined as the risk of a particular genotype to lead to a CF phenotype.

METHODS

We aimed to get insight into the penetrance of CF for fifteen CFTR variants: 5 frequent CF-causing and 10 classified as of varying clinical consequence (VCC) or associated with a CFTR-related disorder (CFTR-RD) in CFTR2 or CFTR-France databases. The penetrance was approached by: (1) comparison of variant allelic frequencies in CF patients (CFTR2) and in the general population; (2) estimation of the likelihood of a positive NBS test for the 14 compound heterozygous with F508del and the F508del homozygous genotypes, defined as the ratio of detected/expected number of neonates with a given genotype in the 2002-2017 period.

RESULTS

A full penetrance was observed for severe CF-causing variants. Five variants were more frequently found in the general population than in CF patients: TG11T5, TG12T5, TG13T5, L997F and R117H;T7. The likelihood of a positive NBS test was 0.03% for TG11T5, 0.3% for TG12T5, 1.9% for TG13T5, 0.6% for L997F, 11.7% for D1152H, and 17.8% for R117H;T7. Penetrance varied greatly for variants with discrepant classification between CFTR2 and CFTR-France: 5.1% for R117C, 12.3% for T338I, 43.5% for D110H and 52.6% for L206W.

CONCLUSION

These results illustrate the contribution of genetics population data to assess the disease liability of variants for diagnosis and genetic counselling purposes.

Mucoviscidosis: fisiopatología, genética, aspectos clínicos y terapéuticos

La mucoviscidosis es la enfermedad autosómica recesiva grave más frecuente que afecta a la población caucásica. En Francia, por ejemplo, la incidencia es de un caso por cada 4.500 nacimientos. Esta enfermedad se debe a mutaciones en el gen CFTR (cystic fibrosis transmembrane conductance regulator, regulador de conductancia transmembrana de la fibrosis quística), situado en el brazo largo del cromosoma 7, que codifica una proteína transmembrana implicada en la regulación del transporte transepitelial de iones cloruro (Cl–). En Francia, la mutación más frecuente (alrededor del 80% de los casos) es la deleción del aminoácido 508 (fenilalanina), denominada F508del. La ausencia o la disfunción de la proteína CFTR provoca un defecto en el transporte de Cl– y un aumento de la reabsorción de sal y agua, en particular en el epitelio bronquial, lo que conlleva una reducción del líquido de la superficie bronquial. Esta exocrinopatía generalizada conduce a la producción de «moco viscoso» (de ahí el nombre de mucoviscidosis), que obstruye varios sitios en el cuerpo, en particular el sistema respiratorio, el tracto digestivo y sus anexos (páncreas, vías biliares e hígado). La detección neonatal se ha generalizado desde 2002. La prueba del sudor es la prueba complementaria de referencia, validada por la identificación de dos mutaciones patógenas, para la confirmación del diagnóstico. El tratamiento es multidisciplinario. Se basa ante todo en la kinesiterapia respiratoria diaria y el tratamiento de las sobreinfecciones broncopulmonares, así como en las recomendaciones nutricionales con el uso de extractos pancreáticos. Es probable que el pronóstico, todavía muy desfavorable, se modifique con la llegada de terapias proteínicas o de edición de ácido ribonucleico o de gen.

Insights into the variability of nasal potential difference, a biomarker of CFTR activity

BACKGROUND

Nasal potential difference (NPD) is used to evaluate CFTR function in vivo. We aimed to evaluate the intrasubject and intersubject variability of NPD measurements.

METHODS

We reviewed NPD tracings of 116 patients with CF enrolled in the placebo arm of a multicenter study. Patients carried at least one nonsense mutation and underwent repeated NPD tests every 16 weeks. NPD parameters included basal potential difference (basal PD), inhibition of sodium absorption by amiloride (Δ Amiloride), chloride (Cl^-) transport in response to a Cl^--free solution (Δ Low Cl^-), isoproterenol (Δ Isoproterenol), the sum of Δ Low Cl^- and Δ Isoproterenol (Δ Low Cl^--Isoproterenol) and ATP (Δ ATP).

RESULTS

Basal PD and Δ Amiloride displayed the highest variabilities, mainly stemming from intercenter and intrasubject effect. Δ Low Cl^-, Δ Isoproterenol and Δ Low Cl^--Isoproterenol demonstrated a large intrasubject variability but a smaller intersubject variability. The intrasubject measurement variability for Δ Low Cl^--Isoproterenol, was within ± 7.2 mV with 95% probability. It was greater in patients reporting ongoing pulmonary exacerbations.

CONCLUSIONS

The large intercenter variability of basal PD and Δ Amiloride highlights the operator-dependent aspect of these measurements. A difference greater than 7.2 mV in Δ Low Cl^--Isoproterenol in a given patient on CFTR modulator can be attributed, with 95% probability, to a treatment effect rather than to the variability inherent in the measurement.

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.