The two IPAH patients with pathogenic variants in the genes GDF2 or SMAD9 had lower BMPR2 mRNA expression levels (0.394 and 0.433, respectively) than average in the BMPR2 non-carrier group (0.445), albeit having higher values than the average of the BMPR2 variant carrier group (0.353). This evidence concerns the gene SMAD9 and idiopathic pulmonary arterial hypertension.