HSPD1 and pulmonary arterial hypertension: While residual activity of p.Asp229Gly PAH variant remained null when co-expressed with GroEL/ES, the activities of p.Gly239Ala, p.Phe263Ser, and p.Ala342Pro PAH variants increased to 0.9% ± 1.5%, 0.9% ± 2.2%, and 9.9% ± 0.7% compared to WT PAH, respectively.