• Male or female patients of any age, including minors, who have been diagnosed with aHUS

• Patients with or without an identified complement pathogenic variant or anti-complement factor antibody

• Able to give written informed consent. Patient or patient's parent/legal guardian must be willing and able to given written informed consent and the patient (if minor) must be willing to give written informed assent \[if applicable as determined by the central Institutional Review Boards/Independent Ethics Committees (IRB/IEC)\].

• ADAMTS13 \> 5%, if performed.