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.