EDS in Ataxia Telangiectasia Patients

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 D SP/infusion, Group 2: EDS-EP dose range of ~14-22 mg
D SP/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 re-randomized 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.

All patients who complete 12 months of treatment in the trial, complete the study
assessments, and provide informed consent will be eligible to continue treatment with EDS-EP
in an open-label, extension study (IEDAT-03-2016). Retrieved drop-outs (RDO), i.e. patients
who discontinued treatment prematurely but completed the final (Visit 15/Month 12) efficacy
assessments will also be eligible to enter the open-label extension study. Patients will
continue on the dose of EDS-EP they were receiving at the end of Study IEDAT-02, or if on
placebo, the patient will be randomly switched (1:1) to one of the two doses of EDS-EP.

Main Inclusion Criteria:

- Patient meets clinical criteria for diagnosis of AT. The neurological signs of AT
(incoordination of the head and eyes in lateral gaze deflection, gait ataxia
associated with an inappropriately narrow base) must be documented.

- Patient is in autonomous gait or is helped by periodic use of a support.

- Patient will be investigated for the proven genetic diagnosis of AT (prior
documentation or by central laboratory test report).

- Patient is at least 6 years of age, of either sex

- Body weight > 15 kg.

- The patient and his/her parent/caregiver (if below the age of consent), or a legal
representative, has provided written informed consent to participate. If consent is
provided solely by the caregiver in accordance with local regulations, the patient
must provide assent to participate in the study.

Main Exclusion Criteria:

General

- Females that are

1. pregnant, or are breast-feeding (for EU countries only);

2. of childbearing potential, pregnant, or are breast-feeding (for US and Rest of
World countries).

Females of childbearing potential using adequate birth control, as determined by
their Health Care Provider, will be eligible.

- A disability that may prevent the patient from completing all study requirements.

- Current participation in another clinical study. Medical History and Current Status

- CD4+ lymphocytes count <400/mm3 (for patients 6 years of age) or <200/mm3 (for
patients >6 years).

- Loss/removal of 250 mL or more of blood within the past 4 weeks prior to screening.

- Current neoplastic disease or previous neoplastic disease not in remission for at
least 2 years.

- History of severe impairment of the immunological system.

- Severe or unstable pulmonary disease.

- Uncontrolled diabetes. Patients with diabetes that has been stabilized (i.e. no
hypoglycemic or hyperglycemic episodes in the past 3 months) will be eligible.

- Any other severe, unstable, or serious disease or condition that in the Investigator's
opinion would put the patient at risk for imminent life-threatening morbidity, need
for hospitalization, or mortality.

- Any clinically significant abnormality on standard laboratory examinations
(hematology, biochemistry, urinalysis) at screening that remains abnormal on repeat
testing. Eligibility of patients with abnormal laboratory test values will be
determined by the Investigator in consultation with the Medical Monitor.

- Confirmed hemoglobinopathies, e.g. hemoglobin C disease, sickle cell anemia, or
thalassemia.

- Moderate or severe renal and/or hepatic impairment. Prior/Concomitant Medication

- Any previous oral or parenteral steroid use within 4 weeks before Baseline. Treatment
with inhaled or intranasal steroids for asthma or allergies, as well as use of topical
steroids will be permitted

- Chronic condition or prior allergic reaction representing a contraindication to the
use of dexamethasone or other steroid drugs.

- Has participated in any other trial with an investigational drug and received a dose
within 30 days or 10 half-lives (whichever is greater) from the start of the 30-day
Screening Period.

- Has participated in a previous trial with EDS.

- Requires any concomitant medication prohibited by the protocol.

- Has taken a drug or treatment known to cause major organ system toxicity during the
past year.

- Use of any drug that is a strong inducer/inhibitor of CYP3A4 within 4 weeks before
baseline.