Consistent with this we found an increase in the phosphorylated Drp1 at Serine 616 (Figures 4A–D) and a strong trend to decreased MFN2 expression (Supplementary Figures S3, S4) in RVfib in MCT-PAH, without significant changes in the other two fusion mediators (MFN1 and OPA1) (Supplementary Figure S3). The gene discussed is MFN1; the disease is pulmonary arterial hypertension.