The C/C genotype was present in 49.4% of patients with PAH, and in the PAH genome-wide association study (8), each copy of the A allele (associated with higher SMAD5 levels) was associated with an 8.5% reduction in the risk of developing PAH (odds ratio, 0.915; 95% confidence interval, 0.846–0.990; P = 0.0266). This evidence concerns the gene SMAD5 and pulmonary arterial hypertension.