This is an international (North America, Europe, Africa, Asia and Australia), multi-center, one-year, randomized, prospective, double-blind, placebo controlled, phase III study, designed to assess the effect of two non-overlapping dose ranges of EDS-EP, administered by IV infusion once per month, on neurological symptoms of patients with AT. All patients who complete the assessments as designed over the initial 6 months of the trial will be eligible to continue in an additional 6-month, double-blind, placebo-controlled extension designed to collect information on the long-term safety and efficacy of the trial treatments. 

 Upon completion of all screening assessments for eligibility patients meeting all selection criteria at baseline will be randomized in a 1:1:1 fashion to one of the two EDS-EP dose levels or placebo. A minimization procedure will be employed to ensure that the proportions of male and female, and younger (6 to <10 years) and older (≥10 years), patients are comparable across the three treatment groups. Every attempt will be made to ensure the same balance is achieved across different regions. 

 A minimum of 180 patients will be enrolled, hence, each group will consist of 60 patients randomly assigned to receive one of the two doses of EDS-EP or placebo, as follows:

• Group 1: EDS-EP dose range of ~5-10 mg DSP/infusion,
• Group 2: EDS-EP dose range of ~14-22 mg DSP/infusion,
• Group 3: Placebo EDS infusion. 

The initial 6-month treatment period will be considered complete when the endpoint assessment (at Visit 9/Month 6 or at early discontinuation) has been performed for all patients.  Patients who are not experiencing severe side effects, or have deteriorated significantly while on the treatment and provide informed consent will be eligible to continue treatment for an additional 6 months in a double-blind, placebo-controlled extension treatment period. Patients meeting all entry criteria will be treated as follows:

• Patients originally randomized to EDS-EP treatment groups (Group 1 or Group 2) will continue on the same treatment;
• Patients originally randomized to the Placebo group (Group 3) will be rerandomized in equal proportions (1:1) to receive either the EDS-EP ~5-10 mg DSP/infusion or ~14-22 mg DSP/infusion, as follows:
• Following 6 months of treatment, one third of the originally randomized placebo patients will be re-randomized to treatment with EDS-EP, as described above;
• After 9 months of treatment, one third of the originally randomized placebo patients will be re-randomized to treatment with EDS-EP, as described above;
• At 12 months, all remaining placebo patients who continue open label treatment will receive treatment with EDS-EP, as described above. 

The ICARS will be administered by a site rater and scoring verified by a central remote qualified rater, based on a video recording of the assessment at the site.  The scores provided by the central remote raters will be used for the primary analysis of the ‘Modified’ ICARS (primary efficacy endpoint).  The site ICARS rater will not be involved in the rating of the CGI-S and CGI-C, VABS, or QoL scale. The CGI rater will not have access to the ICARS ratings, but may refer to other scales in scoring the CGI.