Note: Funding Information: J.W.W.H., O.V., H.L.S and J.N. have nothing to declare. F.W.G.L. has received unrestricted research grants from CSL Behring, Takeda and uniQure, and is consultant for Takeda, uniQure and BioMarin. He is DSMB member for a study sponsored by Roche. S.C.G. has received unrestricted research grants from Sobi. K.F. has received speaker's fees from Bayer, Baxter/Shire, Biotest, CSL Behring, Octapharma, Pfizer, Novo Nordisk; performed consultancy for Baxter/Shire, Biogen, CSL Behring, Freeline, Novo Nordisk, Pfizer, Roche and Sobi; and has received research support from Bayer, Pfizer, Baxter/Shire and Novo Nordisk.