Atypical hemolytic uremic syndrome is a rare disorder that can cause abnormal blood clotting in small blood vessels and may affect the kidneys and other organs. It is often associated with abnormal regulation of the complement system, which is part of the immune system. Genetic changes can increase susceptibility, although not everyone with a genetic variant develops the condition.
Atypical hemolytic uremic syndrome, commonly called aHUS, is a rare condition involving uncontrolled activation of the complement system. This can damage the lining of small blood vessels and contribute to the formation of tiny blood clots. These clots can reduce blood flow to organs, particularly the kidneys. aHUS may develop because of genetic susceptibility, acquired factors, or a combination of both. Certain infections, pregnancy, medications, autoimmune conditions, or other physical stresses may act as triggers in susceptible individuals.
The causes of aHUS are complex because the condition can involve several biological and environmental factors. Genetic variants affecting proteins that regulate the complement system can increase the likelihood of excessive complement activity. However, having a genetic variant does not necessarily mean that a person will develop aHUS.
Commonly discussed contributing factors include:
Because genetic and acquired factors can overlap, identifying the underlying mechanism may require specialized testing. Family history can also be relevant when clinicians evaluate possible inherited susceptibility.
Diagnosing aHUS generally requires several laboratory investigations because its symptoms can resemble other conditions, including thrombotic thrombocytopenic purpura and other forms of hemolytic uremic syndrome. Doctors may assess platelet levels, red blood cell destruction, kidney function, urine findings, and markers associated with hemolysis. Additional testing may help determine whether another condition better explains the findings.
Diagnostic and follow-up assessments may include:
Genetic counseling can help patients understand what genetic findings may mean for themselves and potentially affected family members. Genetic results must be interpreted alongside clinical findings because not every detected variant proves that aHUS is responsible for a person's symptoms. Treatment decisions are individualized and may involve specialist care focused on controlling complement activity, managing kidney complications, and addressing potential triggers.
Overall, aHUS requires careful evaluation because the condition can affect kidney function and other organs. Recognizing possible symptoms and obtaining appropriate medical assessment can support timely diagnosis and management. Long-term follow-up may be necessary to monitor kidney function, blood counts, and recurrence risk. Medical care should be guided by specialists familiar with complement-mediated disorders.