Cystic fibrosis (CF) is a severe multisystemic genetic disease. The sweat test (ST) is the gold standard for its diagnosis. It is based on the measurement of chloride concentration in a sweat sample, which is typically abnormally high in patients with CF. However, several reports in the literature describe conditions known to be associated with false positive results. We have recently described a previously unreported cause of a false positive ST.

An observational, cross-sectional, single-center study was conducted. We recruited three patients with neurosensory deafness caused by a deletion in both alleles of the connexin 30 gene. First-degree relatives of these three patients, who also had hearing impairment due to other mutations, were also included. An ST was performed in all selected cases. Among the three patients with a deletion in both connexin 30 alleles, two had a positive ST, while the third had a borderline result close to the positivity threshold (57 mmol/L). Moreover, no positive sweat tests were found in individuals with other mutation patterns.

Patients with alterations in both alleles of the connexin 30 gene were the only ones to show a positive ST, which may indicate a higher risk of hyponatremic dehydration. The reason for this ST positivity remains unclear and may be related to the role of connexin 30 in modulating other molecules in both the inner ear and sweat glands.

This study highlights the importance of evaluating pediatric patients in a holistic and multidisciplinary manner, which allows not only for the proper management of their conditions and complications, but also for a deeper understanding of their underlying causes.