Up to 30 patients, recruited from the National Institutes Health, Bethesda, USA and the Institute of Child Health, London, U.K. will be randomized to OGT 918 or no treatment in a 2:1 ratio for the 12 month study period. Patients will be clinically diagnosed with neuronopathic Gaucher disease, 12 years of age or older, on a stable dose of enzyme replacement therapy (ERT) for at least 6 months and be able to swallow capsules. Randomization will be stratified based on whether or not the patient has undergone a splenectomy.