DDAH1 and pulmonary hypertension: Therefore, we selected 16 single nucleotide polymorphisms in NOS3, DDAH1, DDAH2, AGXT2, ARG1, ARG2, and PRMT1 genes and studied their associations with dimethylarginine concentrations and the incidence of high-altitude pulmonary hypertension as well as acclimatization to high altitude.