Results of enzyme replacement therapy in Bulgarian patients with a severe form of hunter syndrome: A 42-month follow-up

Hunter syndrome (Mucopolysaccharidosis type II, MPS II) is a rare X-linked disease caused by a deficiency of the enzyme iduronate-2-sulphatase (IDS), which results in the lysosomal accumulation of the undegraded glycosaminoglycans (GAGs) dermatan and heparan sulfate in various tissues and organs. Enzyme replacement therapy (ERT) with recombinant iduronate-2-sulphatase is the first disease-specific treatment for Hunter syndrome. Clinical trial data for the use of idursulfase to treat severe Hunter patients are limited and controversial. Our study analyzes therapeutic responses after ERT over 42 months of five Hunter patients and further expanding the knowledge of benefits and disadvantages of such therapy. Five boys with the severe form of MPS II (age range, 5−17 years) were treated with idursulfase for a minimum period of 8 months to a maximum period of 42 months. ERT with idursulfase in patients with the severe form of MPS II was associated with improvements in urinary GAG excretion and spleen size, stabilization of cardiac disease, and not effective on joint contractures, and on liver volume. MPS II is a progressive disease and response to ERT is influenced by the severity of the phenotype at treatment initiation