Hunter disease (mucopolysaccharidosis type II) is a lysosomal storage disease caused by deficiency of the enzyme iduronate-2-sulphatase. Deficiency of iduronate sulphatase enzyme causes accumulation of the products dermatan sulphate and heparan sulphate in lysosomes leading to cell death. Hunter disease can vary from mild to severe, depending on the level of enzyme deficiency. Features of the disease include dwarfism, enlarged liver and spleen, cardiovascular disorders and deafness.