“Cystic Fibrosis and Sweat Test – Clinic and Genetic Characterization of a Portuguese Sample Non-Screened not included in the Neonatal Screening”- preliminary results

Abstract

Cystic fibrosis (CF) is the most common and lethal autosomal recessive disorder among the Caucasian population. Advances in medical care have extended the life expectancy of affected individuals to beyond 40-50 years, transitioning CF from a predominantly pediatric disease to a chronic, multi-system condition. In Portugal, neonatal screening for CF was introduced in 2013, becoming the primary diagnostic method. However, for cases not detected through neonatal screening, clinical presentation becomes vital for diagnosis and the sweat test (ST) remains the gold standard for CF diagnosis, particularly when sweat chloride levels are ≥60 mmol/L and two CFTR mutations are identified. Diagnosis becomes complex with chloride levels of 30-59 mmol/L. In 2015, intermediate chloride levels (30-59 mmol/L) were recognized for all ages, reclassifying previously 'unlikely CF' cases (30-40 mmol/L) to 'possible CF'. Despite advances, late diagnoses with significant lung impairment are still reported globally, affecting patient outcomes. Moreover, CFTR variants can lead to atypical CF manifestations. The phenotypic variability, particularly in the Portuguese population, suggests many undiagnosed cases and uncertain CFTR mutation impacts.

This study focuses on a sample of Portuguese individuals selected through three methods: analysis of all STs performed at Centro Hospitalar do Porto over seven years, identifying those with intermediate ST levels; identification of individuals followed at northern Portugal hospitals over five years with clinical suspicion of CF but without diagnosis; and analysis of bronchiectasis databases, selecting cases without iontophoretic ST determination or with intermediate ST levels. Inclusion required at least two STs performed by iontophoresis, with two intermediate and/or positive results necessary for final inclusion. Exclusion criteria included prior CF diagnosis, normal ST results by iontophoresis, other etiologic diagnoses of non-CF bronchiectasis, or neonatal diagnosis (post-October 2013 births). Participants completed a questionnaire to gather clinical and demographic data, fecal elastase quantification, spirometry, and CF serum genetic data (most common mutations, followed by sequencing if fewer than two mutations were detected). Data were encoded, stored in a database, and analyzed descriptively and correlatively, with statistical significance set at p<0.05.

This ongoing study faced limitations primarily due to the SARS/COV2 pandemic. Adjustments to the initial schedule were necessary due to increased clinical care demands and efforts to minimize exposure risk for eligible individuals. Initially, the study focused on the CHP Sweat Test Database. From 2010 to 2016, 1817 sweat tests were conducted at CHP, with 303 showing intermediate values; 150 of these were included in the final sample. The sample consisted of 150 individuals, with a median age of 13 years at the initial data collection (November 2020). Among these, 69.3% (n=103) were under 18 years, with a slight male predominance (n=81, 54%). The primary symptoms prompting sweat tests were difficult-to-control asthma (n=60, 40%), poor weight gain (n=27, 18%), bronchiectasis/pulmonary CT alterations (n=20, 13.3%), and recurrent pneumonia (n=11, 7.3%).

The genetic characterization of CFTR mutations/variants in a sample of Portuguese individuals will provide valuable insights into the frequency of specific mutations/variants and their correlation with phenotypic manifestations. It is important to note that this study is ongoing, and we eagerly await the final results.