PECAM1 and hereditary hemorrhagic telangiectasia: At this time, we are not able to quantify the EB images; however, when comparing iPSC-ACVRL1wt/wt- and iPSC-ACVRL1wt/mut-derived EBs, the CD31+ structures in mutant EBs resemble dilated vessels in a reduced capillary bed—as is typical for HHT patients.