Neuropathological and clinical correlations in hurler disease

We report studies on two patients (1 and 2) with Hurler disease. They both had all of the non‐neurological features of Hurler disease to a similar and extreme degree and similar signs of brain damage on computed tomography. However, intellectual function was unusually well‐preserved in patient 1, but seriously and typically impaired in patient 2. The reason for this discrepancy has been investigated by reference to the neuropathological findings, the results of α‐ l ‐iduronidase assays using different substrates and comparisons to other cases (patients 3 and 4). We suggest that patient 1 is an unusual variant of the disease who may have had a very low residual α‐ l ‐iduronidase activity in neuronal cells only, and that this could not be demonstrated by either enzyme assays on whole brain using the 4‐methylumbelliferyliduronide substrate (Crow et al. , 1983) or in studies on fibroblast lysates using a radioactive disaccharide substrate.