A Study to Test the Possibility of Cross Reaction Induced by the Idursulfase Drug to GSK2788723

Study IDS116406 will be a non-interventional, phlebotomy study in Hunter Syndrome patients who are currently being treated with idursulfase, an enzyme replacement therapy, and in at least a single patient who is naïve to treatment, if possible to recruit. All patients enrolled into the study will have a single blood draw for the analysis of antibodies induced by this enzyme replacement therapy (idursulfase). Patient samples with positive responses to antibodies induced by idursulfase will be used to further evaluate whether the antibodies induced by idursulfase bind to GSK2788723 molecules in vitro and if these antibodies neutralize the bioactivity of GSK2788723 in vitro. Each subject will have a screening visit, which may occur at their regularly scheduled out-patient visit. If the patient consents to participate in the study, a blood sample (total volume of approximately 3mL) for immunogenicity analysis will be drawn before their current treatment infusion