Study of ALXN1210 in Children and Adolescents With Atypical Hemolytic Uremic Syndrome (aHUS)

Inclusion Criteria:

Cohort 1:

1. Patients from birth up to < 18 years of age and weighing ≥ 5 kg at the time of
consent.

2. Evidence of thrombotic microangiopathy (TMA), including low platelet count, hemolysis
(breaking of red blood cells inside of blood vessels), and decreased kidney function.

3. Documented meningococcal vaccination not more than 3 years prior to dosing, and
vaccination against Streptococcus pneumoniae and Haemophilus influenzae

4. Female patients of childbearing potential must use highly effective contraception
starting at screening and continuing until at least 8 months after the last dose of
ALXN1210

Cohort 2:

1. Patients between 12 and <18 years of age who have been treated with eculizumab for
aHUS for at least 90 days prior to Screening

2. Patients with documented diagnosis of aHUS

3. Patients with clinical evidence of response to eculizumab indicated by stable TMA
parameters at Screening

4. Documented meningococcal vaccination not more than 3 years prior to dosing, and
vaccination against Streptococcus pneumoniae and Haemophilus influenzae

5. Females of childbearing potential must use highly effective contraception starting at
screening and continuing until at least 8 months after the last dose of ALXN1210

Exclusion Criteria:

1. ADAMTS13 deficiency (Activity < 5%)

2. Shiga toxin-related hemolytic uremic syndrome (STEC-HUS)

3. Positive direct Coombs test

4. Females who plan to become pregnant during the study or are currently pregnancy or
breastfeeding

5. Identified drug exposure-related hemolytic uremic syndrome (HUS)

6. Bone marrow transplant (BMT)/hematopoietic stem cell transplant (HSCT) within last 6
months prior to start of Screening

7. Known genetic defects of cobalamin C metabolism

8. Systemic sclerosis (scleroderma), systemic lupus erythematosus (SLE), or
antiphospholipid antibody positivity or syndrome

9. Chronic dialysis (defined as dialysis on a regular basis as renal replacement therapy
for end-stage kidney disease (ESKD)

10. For Cohort 2 patients, prior use of complement inhibitors other than eculizumab

11. For Cohort 2 patients, any known abnormal TMA parameters within 90 days prior to
Screening