Trial participants will be randomly assigned to receive ALK-001 (30 subjects) or placebo (20 subjects) for one year. After one year of treatment, half of the participants (10 subjects) receiving placebo will be randomly crossed over to receive ALK-001 for the following 12 months, while the remaining 10 subjects will continue on the placebo. All subjects initially receiving ALK-001 will remain on the same treatment for 12 months.