Intracisternal ERT with species-matched recombinant enzyme was safe with no signs of reactive meningitis, and there were significant improvements in deep cerebrocortical vacuolation, superficial cortex ‘vacuole per neuron’, cortical astrocytosis, and cortical LAMP-1 gene expression in the fucosidosis CNS as a result of treatment. The gene discussed is LAMP1; the disease is fucosidosis.