1. From the Center for Congenital Heart Diseases, Dutch National Referral Center for Children with Pulmonary Hypertension, Beatrix Children’s Hospital (M.-J.P., M.T.R.R., J.M.D., B.B., N.J.E., D.v.d.W., R.M.F.B) and Department of Epidemiology (H.L.H), University Medical Center Groningen, University of Groningen, Groningen, The Netherlands.