Hunter Disease

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.

Mutations in the IDS gene located at Xq28 causes loss of the iduronidate sulfatase enzyme. A pseudogene IDS2 also exists 20 kb from the active IDS gene. The pseudogene IDS2 shares homology to exon 2, intron 2, exon 3, intron 3 and intron 7 of the IDS gene.

Mutations that have been reported in the IDS gene in Hunter patients include gene rearrangements caused by recombination with the IDS2 gene (10 per cent patients), deletions of certain exons or the entire IDS gene (10 per cent patients) or small mutations including insertions, deletions and point mutations (80 per cent patients). To detect all possible types of mutations in the IDS gene causing Hunter disease, three procedures are necessary. These include Southern blot to look for gene rearrangements, multiplex dosage analysis to detect large deletions and DHPLC and sequencing to detect small mutations.

An accurate biochemical test is available for the diagnosis of Hunter disease consisting of the analysis of iduronate-2-sulfatase activity in plasma, leucocytes or cultured cells. This test should be considered before molecular analysis is undertaken. Molecular identification of the mutation in individuals with a confirmed diagnosis can be used for carrier testing and prenatal diagnosis in the family. The biochemical test is not reliable for identifying carriers.

See related information sheet: Hunter Disease