Noting the absence of differential gene expression for the BMP9 gene (GDF2) in PoPH clusters, we then sought to validate and confirm low circulating BMP9 levels as characteristic of PoPH in subjects with underlying liver cirrhosis, and to assess a possible discrepancy between BMP9 liver transcriptomic signature and circulating protein levels, which may have implications for PoPH disease pathogenesis9–11. The gene discussed is GDF2; the disease is cirrhosis of liver.