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Atypical-HUS is a complex, rare disease with various risk factors, including genetic and environmental components.
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The complement system is a part of the immune system that helps to rid the body of damaged cells
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.
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
Most people with atypical-HUS will not have any overt signs or symptoms of the disease until
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.
This list is not exhaustive of all potential triggers
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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