D106-15 Clonal Hematopoiesis in Pulmonary Arterial Hypertension

Rationale The molecular basis of pulmonary arterial hypertension (PAH) remains incompletely understood, except in heritable cases with known germline risk variants. Although most of these variants are autosomal dominant, their low penetrance suggests additional contributing factors. We previously demonstrated that hematopoietic stem cells (HSCs) contribute mechanistically to PAH pathogenesis. HSCs can acquire mutations that confer a proliferative advantage, leading to clonal hematopoiesis (CH). We hypothesized that somatic mutations in HSCs act as a second hit, increasing susceptibility to PAH. Methods Targeted next generation sequencing (NGS) of a 63 gene panel was performed on peripheral blood from 71 PAH patients and 31 controls to identify somatic variants. The assay has a variant allele frequency (VAF) detection threshold of 2%. Raw sequence data were aligned to the human genome (GRCh38) using a published CH workflow incorporating bwa mem, Picard, and GATK for duplicate marking, base recalibration, and somatic variant calling with Mutect2, followed by annotation with VEP. Variants were filtered based on read depth, allele frequency, predicted functional consequence, and recurrence in known myeloid driver genes, with additional gene-specific criteria applied. Clinical data were obtained from electronic medical records. Results PAH patients and controls were matched for age, race and sex (all p > 0.1). The mean age of PAH participants was 50 ±15 years; 85% were white and 75% female. The PAH cohort included 27 (38%) idiopathic, 16 (22.5%) heritable, 27 (38%) associated-PAH and one patient had pulmonary veno-occlusive disease. CH variants were identified in 36 (50.7%) PAH patients compared to 7 (22.6%) controls (age adjusted p = 0.02). Among PAH patients with CH, 50% had one somatic variant, 33% two and 17% three, compared to 71%, 14% and 14%, respectively, in controls (age adjusted p = 0.02). A total of 60 somatic variants were identified in the PAH patients, most commonly in DNMT3A (22%) and TET2 (15%). Time from PAH diagnosis to sampling did not affect CH status or number of variants detected. The largest clones in PAH were DNMT3A variants with VAF of 26.8 and 47.8%. Conclusion Somatic mutations associated with clonal hematopoiesis are enriched in PAH supporting a hematopoietic contribution to pulmonary vascular remodeling and highlighting clonal hematopoiesis as a modifier of genetic susceptibility in disease pathogenesis.