Nucleotide Variant in the SLC26A9 Gene in Two Siblings with Cystic Fibrosis

Background: Currently, increasing attention is being paid to the role of genes other than CFTR and their variants as factors modifying the course of cystic fibrosis (CF). One such gene is SLC26A9, which encodes a protein involved in chloride and bicarbonate transport across the epithelial cell membrane. Variants of SLC26A9, such as c.229G>A (p.Gly77Ser) and c.1885C>T (p.Pro629Ser), have been described in patients with severe and rapidly progressive CF. The aim of this study was to identify SLC26A9 variants in a group of 20 patients with CF. Methods: DNA was isolated from blood samples and collected from all patients. Fragments of exons 3 and 17 of the SLC26A9 gene were amplified by PCR and sequenced using the Sanger method. Results: An SLC26A9 variant was identified in two siblings. These patients were diagnosed with CF in adulthood and presented with moderate pulmonary symptoms without exocrine pancreatic insufficiency. In both siblings carrying the CFTR variants p.Phe508del and c.3140-26A>G, the SLC26A9 variant c.1847C>T (p.Pro616Leu) was detected. This variant has not been widely described in the literature and has not previously been associated with CF. Conclusions: The c.1847C>T (p.Pro616Leu) variant is located near a domain that may affect the transport function of the SLC26A9 protein. However, patients in whom the variant was identified did not present a severe disease phenotype. Further studies on larger patient cohorts are required, and at present this variant should be considered of uncertain significance in CF.