Feasibility and normal values of an integrated conductivity (Nanoduct™) sweat test system in healthy newborns

Clinical characteristics of rare CFTR mutations causing cystic fibrosis in Polish population

INTRODUCTION

More than 2000 mutations have been identified since the discovery of the CFTR gene in 1989. However, only 346 mutations have been classified as cystic fibrosis (CF)-causing mutations. Due to the increasing number of mutations and poor correlation between the genotype and phenotype, there is an urgent need to determine the mutations that are pathogenic, nonpathogenic, or lead to variable symptoms.

AIM

The aim of the study was to present the clinical characteristics of Polish patients with rare and novel CFTR mutations, with an attempt to determine the pathogenicity status of those variants.

MATERIALS AND METHODS

The group included 13 patients born between September 2006 and May 2019, who underwent CF newborn screening and in whom two CFTR mutations, including at least one rare or a novel mutation, were identified.

RESULTS

We identified 13 patients with mutations in both alleles of the CFTR gene, one of which was at least rare in Polish population (R289NfsX17, I618RfsX2, T682KfsX40, S1347PfsX13, W356X, E33X, dup.16,17A) or was a mutation of unknown clinical consequences (H199R, L468P, A1217E, Q359R, T1036I, W1282R). None of them were described in the CFTR2 database. In all examined patients, sweat tests were elevated. The diagnosed patients presented with a wide spectrum of clinical symptoms. Broad clinical characteristics and test results are presented.

CONCLUSION

Pathogenic mutations are H199R, L468P, A1217E, Q359R, T1036I, W1282R, R289NfsX17, I618RfsX2, T682KfsX40, S1347PfsX13, W356X, E33X, dup.16,17A. Every patient with a mutation of unknown clinical consequences in one CFTR allele requires attentive follow-up.

Comparison of two sweat test systems for the diagnosis of cystic fibrosis in newborns

OBJECTIVES

In the national newborn screening programme for CF in Switzerland, we compared the performance of two sweat test methods, by investigating the feasibility and diagnostic performance of the Macroduct^® collection method (with chloride mesurement) and Nanoduct^® test (measuring conductivity) for diagnosing CF.

STUDY-DESIGN

We included all newborns with a positive screening result between 2011 and 2015 who were referred to a CF-centre for sweat testing. In the CF-centre, a Macroduct and Nanoduct sweat test were performed simultaneously. If sweat test results were positive or borderline, a DNA analysis was performed. Final diagnosis was based on genetic mutations.

RESULTS

Over 5 years, 445 children were screened positive and in 413 (114 with CF) at least one sweat test was performed (median age at first test, 22 days); both tests were performed in 371 children. A sweat test result was more often available with the Nanoduct compared to the Macroduct (79 vs 60%, P < 0.001). The Nanoduct was equally sensitive as the Macroduct in identifying newborns with CF (sensitivity 98 vs 99%) but less specific (specificity 79 vs 93%; P-value comparing ROC curves = 0.033).

CONCLUSIONS

This national multicentre study revealed high failure rates for Macroduct and Nanoduct in newborns in real life practice. While this needs to be addressed, our results suggested that performing the Nanoduct in addition to the Macroduct might speed up the diagnostic process because it more often yields valid results with comparable diagnostic performance. The addition of the Nanoduct sweat test can therefore help to reduce the stressful time of uncertainty for parents and to start appropriate treatment earlier.