A Rare ISL1 Promoter Variant in a Case-Control Cohort of Patent Ductus Arteriosus: In Vitro Functional Characterization

Patent ductus arteriosus (PDA) is a common congenital heart disease. ISL LIM Homeobox 1 (ISL1), a master transcription factor for cardiac progenitor cells, has been linked to CHD, but its promoter variants in PDA have not been explored. We sequenced the ISL1 promoter in 320 PDA patients and 302 healthy controls. Ten variants were found across the ISL1 promoter. Six were identified in patients; five were also present in controls, and one novel heterozygous variant, g.5238 C>T, was found exclusively in a single PDA patient and absent in all controls (two-sided Fisher exact test, p = 1.00). Functional assays using dual‑luciferase reporter in HEK293 and A7r5 cells and electrophoretic mobility shift assay (EMSA) demonstrated that this variant significantly increased reporter activity and altered nuclear protein binding patterns. In addition, bioinformatic analysis predicted disruption of an E2F1 site and creation of novel MYC, MAX, NFE2L2, USF1, and MYCN binding sites. This variant may be associated with PDA susceptibility, although its clinical significance remains uncertain. Our findings highlight the importance of promoter region variants in PDA and provide preliminary information for future studies.