NOS3 and chronic obstructive pulmonary disease: Meanwhile, another NOS3 polymorphism—the 27-bp VNTR (4b/a)—showed a trend toward association in younger patients (≤50 years) without COPD, with the 4b allele and 4b/4b genotype more frequent in severe cases (p values around 0.06–0.07), though these findings did not reach conventional statistical significance.