Patients are randomized to receive either placebo or one of two oral doses of CPI-1189 daily. Patients are assessed for safety and tolerability during Weeks 2, 6, and 10. At Week 10, efficacy assessments are also made. For those who volunteer, a sample of cerebrospinal fluid is obtained at baseline and at Week 10. Blood samples for CPI-1189 pharmacokinetic trough measurements are taken at Weeks 2 and 10. The open-label phase starts at Week 11. At Weeks 13 and 16, a safety evaluation is performed. At the end of the open-label phase, Week 22, a final set of safety and efficacy assessments and a blood sample for CPI-1189 pharmacokinetic trough measurement are obtained.