Reddy, A.

Abstract Introduction: Cystic fibrosis (CF) is a genetic disorder characterized by defective chloride ion transport, leading to thick mucus production, chronic respiratory infections, and other multisystem involvement. Although CF is often diagnosed in childhood, the condition can be missed or misdiagnosed in adults. Description of Case: We present the case of a 60-year-old male from India who was diagnosed with CF after a prolonged period of sinopulmonary symptoms. He initially presented in 2014. His medical history was pertinent for asthma, and multiple episodes of clinically and radiographically confirmed pneumonia and polypoid sinusitis requiring IV antibiotics and sinus surgery. He carried a prior diagnosis of allergic bronchopulmonary aspergillosis treated with itraconazole and steroids, as well as elevated IgE levels. His CT chest was notable for extensive bronchiectasis, bronchial wall thickening, and mucus plugging of both lungs. He had no known family history of CF. Sweat chloride testing was in the intermediate range (44, 47 mmol/L; normal <30 mmol/L, intermediate 30 to 59 mmol/L, abnormal >59 mmol/L). Given high suspicion for CF, cystic fibrosis transmembrane conductance regulator (CFTR) full gene analysis was pursued. Sequence analysis and multiplex ligation-dependent probe amplification of the CFTR gene detected heterozygous sequence changes c.1717-2A>T, classified as likely deleterious, and c.1367T>C (p.V456A), variant of uncertain significance. He was thus initially diagnosed as a CF carrier. He re-presented in 2024 with decline in pulmonary function testing and continued sinopulmonary infections. Genetic testing results from 2014 were re-analyzed. Between initial presentation and present, his V456A variant was upgraded to pathogenic. He met diagnostic criteria for CF with two pathogenic CFTR variants, a repeated intermediate sweat chloride (47 mmol/L) suggestive of CFTR protein dysfunction, and disease that could be attributed to CFTR dysfunction. He subsequently started TRIKAFTA® (elexacaftor/tezacaftor/ivacaftor and ivacaftor) and airway clearance therapy. Discussion: The diagnosis of CF in adults can be challenging, particularly in individuals without a known family history, intermediate sweat chloride testing, and with inconclusive genetic testing. Our understanding of CF in Asian populations is limited. CF is suspected to be underreported in patients with Southeast Asian ancestry in part due to genetic heterogeneity. The interpretation of certain genetic variants can evolve over time. A variant of unknown significance may later be reclassified as pathogenic, revealing its true role in disease development. This highlights the critical importance of regularly re-evaluating genetic test results.