Determining prognosis and response to treatment for MPS I conditions is currently inadequate, even mutation analysis being imprecise. We hypothesize that neurochemical profiles will differ between MPS I Hurler (post-HCT), Hurler-Scheie (ERT) and age-matched controls and that inflammation and oxidative stress will be more pronounced in ERT patients than post-HCT patients. We hypothesize that within the Hurler-Scheie group, which is more clinically diverse; there will be higher degree of neuroinflammation and oxidative stress in severe patients as defined by genotype and clinical status.