Idursulfase (Elaprase®, Shire, Lexington, MA, USA), a recombinant human iduronate-2-sulfatase, has been approved as an intravenous (IV) medicinal product for the treatment of MPS II since 2006 in the United States and 2007 in Europe [8]. The gene discussed is IDS; the disease is mucopolysaccharidosis type 2.