Subjects who complete both Stage 1 and Stage 2 of the study as scheduled may be offered the opportunity to participate in an open-label treatment extension phase with AT1001. The open-label treatment extension phase will last 12 months and will involve 2 visits to the clinic. A follow-up visit will be undertaken 1 month following completion or discontinuation from the open-label treatment extension. Subjects completing the 12 month open-label treatment extension and providing consent to enter a separate long term extension will not be required to complete this follow-up visit.