The most significant group (direct biomarkers) contained genes with direct evidence of association to H-I disease: PIEZO2 and HPGD (shared), TSIX and SAA1 (PAH - specific), GSTM1, DNTT, and IGKC (HAPC - specific), LEP, SERPINA3, and ARHGEF4 (PE - specific), CD3D, ITK, and RPL18A (IS - specific). This evidence concerns the gene ARHGEF4 and pulmonary arterial hypertension.