Brain natriuretic peptide (BNP) levels remained normal, suggesting right-ventricular metabolic adaptation rather than decompensation.<h4>Discussion</h4>This case supports a model of <i>slowly progressive PAH</i> driven by chronic immune imbalance from asplenia, toxin-induced oxidative stress, and nitric-oxide scavenging by free hemoglobin. The gene discussed is NPPB; the disease is familial isolated congenital asplenia.