Atypical hemolytic uremic syndrome (aHUS) is an extremely rare, life-threatening, progressive disease that frequently has a genetic component. In most cases it can be effectively controlled by interruption of the complement cascade. Particular monoclonal antibodies, discussed later in the article, have proven efficacy in many cases. AHUS is usually caused by chronic, uncontrolled activation of the complement system, a branch of the bodys immune system that destroys and removes foreign particles. The disease affects both children and adults and is characterized by systemic thrombotic microangiopathy (TMA), the formation of blood clots in small blood vessels throughout the body, which can lead to stroke, heart attack, kidney failure, and death. The complement system activation may be due to mutations in the complement regulatory proteins (factor H, factor I, or membrane cofactor protein), or is occasionally due to acquired neutralizing autoantibody inhibitors of these complement system components, for example anti–factor H antibodies. : 1933    Prior to availability of eculizumab (Soliris)and ravulizumab(Ultomiris), an estimated 33–40% of patients died or developed end-stage renal disease (ESRD) (despite the use of supportive care, e.g. plasmapheresis) with the first clinical bout of aHUS. Including subsequent relapses, a total of approximately two-thirds (65%) of patients died, required dialysis, or had permanent renal damage within the first year after diagnosis despite plasma exchange or plasma infusion (PE/PI). Signs and symptoms
Clinical signs and symptoms of complement-mediated TMA can include abdominal pain, confusion, fatigue, edema (swelling), nausea/vomiting and diarrhea. aHUS often presents with malaise and fatigue, as well as microangiopathic anemia.
: 1931  However, severe abdominal pain and bloody diarrhea are unusual. : 1931   Laboratory tests may also reveal low levels of platelets (cells in the blood that aid in clotting), elevated lactate dehydrogenase (LDH, a chemical released from damaged cells, and which is therefore a marker of cellular damage), decreased haptoglobin (indicative of the breakdown of red blood cells), anemia (low red blood cell count)/schistocytes (damaged red blood cells), elevated creatinine (indicative of kidney dysfunction), and proteinuria (indicative of kidney injury). Patients with aHUS often present with an abrupt onset of systemic signs and symptoms such as acute kidney failure, hypertension (high blood pressure), myocardial infarction (heart attack), stroke, lung complications, pancreatitis (inflammation of the pancreas), liver necrosis (death of liver cells or tissue), encephalopathy (brain dysfunction), seizure, or coma. Failure of neurologic, cardiac, kidney, and gastrointestinal (GI) organs, as well as death, can occur unpredictably at any time, either very quickly or following prolonged symptomatic or asymptomatic disease progression. For example, approximately 1 in 6 patients with aHUS initially will present with proteinuria or hematuria without acute kidney failure. Patients who survive the presenting signs and symptoms endure a chronic thrombotic and inflammatory state, which puts many of them at lifelong elevated risk of sudden blood clotting, kidney failure, other severe complications and premature death. Comorbidities
Although many patients experience aHUS as a single disease, comorbidities are common. In one study, 25% (47/191) of patients with no known family history of aHUS were found to have a coexisting disease or condition.