NOS3 (endothelial nitric oxide synthase) is the primary isoform responsible for nitric oxide (NO) production in the cardiovascular system 1. NOS3 synthesizes NO from L-arginine in endothelial cells through a calcium-calmodulin-dependent mechanism 2, producing a critical vasodilator essential for cardiovascular homeostasis 1. The enzyme functions as a dimer whose expression and activity are regulated at transcriptional, posttranscriptional, and posttranslational levels 1. Mechanistically, NOS3 mediates endothelium-dependent vasodilation and regulates systemic arterial blood pressure, with its activity influenced by multiple genetic polymorphisms including SNPs, VNTRs, and insertions/deletions 1. The NOS3 gene contains 26 exons and is located on chromosome 7-36 2. Several NOS3 polymorphisms (rs2070744, rs1799983, 4a/4b variant) show functional effects on NO formation 1. Clinically, NOS3 polymorphisms associate with diabetic nephropathy risk in type 2 diabetes, with rs2070744 and rs1799983 minor alleles increasing susceptibility 3. The 4a/4b intron variant correlates with oligoasthenozoospermia in male infertility 4. However, meta-analyses found no significant associations between NOS3 polymorphisms and prostate cancer, Alzheimer's disease, general cancer risk, or unstable angina [PMID:24577889; 5; 6; 74]. NOS3 gene mutations have been identified in lung adenocarcinoma patients with potential therapeutic implications 8.