In an observational study, the change in Mucopolysaccharidosis Health Assessment Questionnaire scores was assessed after 5–9 years of IV idursulfase in 15 patients with MPS II; improvements were reported in 23 of 52 questionnaire items in patients with non-neuronopathic MPS II (worsening in 3 of the 52 items), whereas improvements in only 9 of the 52 items were shown in patients with neuronopathic MPS II (worsening in 32 of the 52 items) [33]. This evidence concerns the gene IDS and mucopolysaccharidosis type 2.