Mucopolysaccharidosis II, also known as Hunter syndrome, is a rare, X-linked disease caused by a deficiency of the lysosomal enzyme iduronate-2-sulfatase, which catalyses a step in the catabolism of glycosaminoglycans. The glycosaminoglycans accumulate within tissues affecting multiple organs and physiologic systems. The clinical manifestations include neurologic involvement, severe airways obstruction, skeletal deformities and cardiomyopathy. The disease has a variable age of onset and variable rate of progression. In those with severe disease, death usually occurs in the second decade of life, whereas those patients with less severe disease may survive into adulthood. Enzyme replacement therapy with intravenous infusions of Idursulfase ( Elaprase ) has emerged as a new treatment for mucopolysaccharidosis type II.

Researchers have evaluated the effectiveness and safety of enzyme replacement therapy with Idursulfase compared to other interventions, placebo or no intervention, for treating mucopolysaccharidosis type II.

One study ( 96 patients ) met the inclusion criteria, although the primary outcome of this review - z score for height and weight, was not assessed in the study. Following 53 weeks of treatment, patients in the weekly Idursulfase 0.5 mg/kg group demonstrated a significant improvement rate compared with placebo for the primary outcome: distance walked in six minutes on the basis of the sum of ranks of change from baseline, mean difference 37.00.
The every-other-week Idursulfase 0.5 mg/kg group also showed an improvement, which was not significant compared with placebo, mean difference 23.00.
After 53 weeks, there was no statistical significance difference in per cent predicted forced vital capacity between the three groups and absolute forced vital capacity was significantly increased from baseline in the weekly dosing group compared to placebo, mean difference 0.16.
No difference was observed between the every-other-week Idursulfase 0.5 mg/kg group and placebo.
In addition, liver and spleen volumes and urine glycosaminoglycan excretion were significantly reduced from baseline by both Idursulfase dosing regimens.
Idursulfase was generally well tolerated, but infusion reactions did occur. Idursulfase antibodies were detected in 31.7% of patients at the end of the study and they were related to a smaller reduction in urine glycosaminoglycan levels.

The current evidence is limited. While the randomised clinical trial identified was considered to be of good quality, it failed to describe important outcomes. It has been demonstrated that enzyme replacement therapy with Idursulfase is effective in relation to functional capacity ( distance walked in six minutes and forced vital capacity ), liver and spleen volumes and urine glycosaminoglycan excretion in patients with mucopolysaccharidosis type II compared with placebo.
There is no available evidence in the included study and in the literature on outcomes such as improvement in growth, sleep apnoea, cardiac function, quality of life and mortality.
More studies are needed to obtain more information on the long-term effectiveness and safety of enzyme replacement therapy.

Source: Cochrane Database of Systematic Reviews, 2011

XagenaMedicine2011