The alleles at HLA-DPB1 associated with the poorest outcomes are also common (risk allele frequency of 86% for rs2856830-T), such that 1432 (69%) of 2085 patients with pulmonary arterial hypertension had the T/T genotype associated with the poorest outcomes and 1975 (95%) of 2085 patients had at least one T allele. Here, HLA-DPB1 is linked to pulmonary arterial hypertension.