Safety and Efficacy Study of OMS721 in Patients With Atypical Hemolytic Uremic Syndrome

Inclusion Criteria:

• Competent to provide informed consent, or if a minor, have at least one parent orlegal guardian to provide informed consent with written assent from the subject.

• Are at least 12 years old at screening (Visit 1).

• Have a clinically diagnosis of primary atypical hemolytic uremic syndrome (aHUS), withADAMTS13 activity greater than 5% in plasma.

• Plasma therapy-resistant aHUS patients must have a screening platelet count less than 150,000/uL, evidence of microangiopathic hemolysis, and serum creatinine greater thanupper limit of normal.

• Plasma therapy-responsive aHUS patients must have documented history of requiringplasma therapy to prevent aHUS exacerbation and received plasma therapy at least onceevery 2 weeks at an unchanged frequency for at least 8 weeks before first dose ofOMS721.

Exclusion Criteria:

• Have STEC-HUS, a direct positive Coombs test, history of hematopoietic stem celltransplant, and/or HUS from an identified drug.

• History of vitamin B12 deficiency-related HUS, systemic lupus erythematosus, and/orantiphospholipid syndrome.

• Active cancer or history of cancer (except non-melanoma skin cancers) within 5 yearsof screening.

• Have been on hemodialysis or peritoneal dialysis for greater than or equal to 12weeks.

• Have an active systemic bacterial or fungal infection requiring systemic antimicrobialtherapy (prophylactic antimicrobial therapy administered as standard of care isallowed).

• Baseline resting heart rate less than 45 beats per minute or greater than 115 beatsper minute.

• Baseline QTcF greater than 470 milliseconds.

• Have malignant hypertension (diastolic blood pressure [BP] greater than 120 mm Hg withbilateral hemorrhages or "cotton-wool" exudates on funduscopic examination).

• Have a poor prognosis with a life expectancy of less than three months in the opinionof the Investigator.

• Are pregnant or lactating.

• Have received treatment with an investigational drug or device within four weeks priorto screening.

• Have abnormal liver function tests defined as ALT or AST > five times ULN.

• Have HIV infection.

• History of cirrhosis of the liver.

• Have previously completed treatment in an OMS721study.