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Uncontrolled complement system

The complement system is a part of the immune system that helps to rid the body of damaged cells and foreign substances, such as bacteria and viruses.

In atypical-HUS, the body's ability to control the complement system is compromised. In people with atypical-HUS, the complement system kicks into overdrive and doesn't shut off. It starts attacking healthy cells, such as those in small blood vessels, in a condition called thrombotic microangiopathy (TMA). TMA can result in damage to vital organs—a lifelong risk for people with unmanaged atypical-HUS.

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Up to 70% of people with atypical-HUS first experience symptoms as the result of an unrelated health event that triggers complement activity*

*N/n = 191/273

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Most people with atypical-HUS will not have any overt signs or symptoms of the disease until they experience a triggering event.

The trigger can be an autoimmune disease, such as lupus, or an infection, a medication, pregnancy, or another condition, such as severe/malignant hypertension, that rapidly increases complement activity.

The triggering event reveals the complement system control issues that cause symptoms of TMA. The risk of triggering TMA is ongoing, and lifelong, in people with atypical-HUS.






Severe/Malignant Hypertension





Autoimmune Desease

Autoimmune Desease

This list is not exhaustive of all potential triggers

aHUS Genetics


Atypical-HUS is considered a genetic disorder: more than 120 gene mutations have been linked to increased susceptibility to uncontrolled complement activation.

Knowing if you have one or more of these mutations can be helpful in determining your risk of certain complications of atypical-HUS—for example, how likely you might be to develop kidney disease or experience a relapse of TMA.

However, identifying a genetic mutation isn't necessary for diagnosis. Approximately one-third of people with atypical-HUS have none of the known mutations identified as playing a role in the disease.

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