Rationale: Pulmonary arterial hypertension (PAH) is a serious lung condition characterized by vascular remodeling in the precapillary pulmonary arterioles. We and others have demonstrated chromosomal abnormalities and increased DNA damage in PAH lung vascular cells, but their timing and role in disease pathogenesis is unknown.

Objectives: We hypothesized that if DNA damage predates PAH, it might be an intrinsic cell property that is present outside the diseased lung.

Methods: We measured DNA damage, mutagen sensitivity, and reactive oxygen species (ROS) in lung and blood cells from patients with Group 1 PAH, their relatives, and unrelated control subjects.

Measurements and Main Results: Baseline DNA damage was significantly elevated in PAH, both in pulmonary artery endothelial cells (P < 0.05) and peripheral blood mononuclear cells (PBMC) (P < 0.001). Remarkably, PBMC from unaffected relatives showed similar increases, indicating this is not related to PAH treatments. ROS levels were also higher (P < 0.01). DNA damage correlated with ROS production and was suppressed by antioxidants (P < 0.001). PBMC from patients and relatives also showed markedly increased sensitivity to two chemotherapeutic drugs, bleomycin and etoposide (P < 0.001). Results were consistent across idiopathic, heritable, and associated PAH groups.

Conclusions: Levels of baseline and mutagen-induced DNA damage are intrinsically higher in PAH cells. Similar results in PBMC from unaffected relatives suggest this may be a genetically determined trait that predates disease onset and may act as a risk factor contributing to lung vascular remodeling following endothelial cell injury. Further studies are required to fully characterize mutagen sensitivity, which could have important implications for clinical management.