Connexin 30 (GJB6) deletion as a cause of a false positive sweat test result

The sweat test (ST) is the gold standard for the diagnosis of cystic fibrosis. There are several reports in the literature regarding conditions that are known to be associated with a false positive result. The aim of this article is to describe a previously unreported cause of a false positive ST. An observational, cross-sectional single-center study was performed. We recruited three patients with a neurosensory deafness caused by a deletion in both alleles of connexin 30. The first-degree relatives of these three patients with hearing impairment due to other mutations were also included. A ST was performed in all the selected cases. Among the three patients with a deletion in both connexin 30 alleles, two had a positive ST, whereas the third patient had a close-to-positivity borderline result (57 mmol/L). Moreover, there were no positive sweat tests in individuals with other mutation patterns.

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

• The sweat test is the gold standard for the diagnosis of cystic fibrosis. However, the causes of false positives in the test are increasingly recognized.

• This study describes a previously unreported cause of a false positive sweat test. Three patients with homozygous mutations in the connexin 30 gene are described. All of them had an abnormal sweat test, and two of them presented with severe hyponatremic dehydration.