Case report: positive sweat tests, cystic fibrosis (CF) symptoms, no CFTR mutation – CF or not CF?

An 8-year-old male was referred to our CF clinic due to recurrent pulmonary infections and bronchiectasis. Despite the repeated elevated sweat chloride concentrations, genetic testing via whole exome sequencing could not identify any mutations linked to CF or ciliopathy. Our case report depicts a rare cause of generalized type I pseudohypoaldosteronism (PHA1), which, according to previous case reports, is able to mimic CF. The boy presented with hyperkalaemia and metabolic acidosis right after birth without any abnormalities in the Austrian newborn screening. In the light of the patient’s sister’s known genetic condition, pseudohypoaldosteronism was suspected and was confirmed by the identification of a homozygous mutation in the SCNN1A gene. Throughout the preceding years he was admitted several times due to electrolyte imbalance, but he also received antibiotic courses for pulmonary infections with increasing frequency and developed a chronic productive cough prior to referral. A CT scan and bronchoscopy revealed bronchiectasis and viscous mucus in the airways. After the sweat and genetic testing, inhalation therapy with nebulized hypertonic saline and chest physiotherapy were established and the patient is now evaluated every three months in our CF clinic. PHA1 is a genetic disorder characterized by aldosterone unresponsiveness characteristically resulting in hyponatraemia, hyperkalaemia, metabolic acidosis and elevated levels of aldosterone. Symptoms include vomiting, weight loss, dehydration and failure to thrive. The generalized autosomal recessive form has an estimated prevalence of 1:166.000 and is caused by a mutation in the genes SCNN1A, SCNN1B and SCNN1G which encode subunits of the epithelial sodium channel (ENaC). ENaCs are not only located in the collecting ducts of the nephrons, but also in the lungs, sweat glands, colon, pancreas and saliva glands. The role of the channels in the lungs is not yet fully understood, but dysfunction results in an altered airway surface liquid, and therefore, may affect mucociliary clearance. This report suggests that positive sweat tests without any genetic findings on the CFTR gene might require a thorough review for CF-like syndromes. Patients with (generalized type I) PH may profit from being monitored at a CF centre and a similar treatment as CF patients. Publication History Article published online: 26 February 2026 © 2026. Thieme. All rights reserved. Georg Thieme Verlag KG Oswald-Hesse-Straße 50, 70469 Stuttgart, Germany