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Atypical Hemolytic Syndrome !full! Jun 2026
Atypical hemolytic uremic syndrome (aHUS) is a rare and complex blood disorder characterized by the formation of blood clots in small blood vessels throughout the body. It is a type of thrombotic microangiopathy (TMA) that can cause multi-organ dysfunction, including kidney failure. aHUS is distinct from typical hemolytic uremic syndrome (HUS), which is often caused by Shiga toxin-producing E. coli (STEC).
Not required for diagnosis but helpful when presentation is atypical. Histology shows glomerular thrombotic microangiopathy with double-contoured capillary walls, mesangiolysis, and arteriolar thrombi. Immunofluorescence shows C3 deposition without immunoglobulins.
Unlike STEC-HUS, aHUS is often preceded by non-diarrheal triggers: upper respiratory infection (Streptococcus pneumoniae, influenza), pregnancy (post-partum aHUS), malignancy, solid organ or stem cell transplant, and certain medications (calcineurin inhibitors, chemotherapy). atypical hemolytic syndrome
Complications of aHUS can include:
Historically, the only treatment for aHUS was plasma exchange or plasma infusion. While this helped manage some symptoms, it did not address the underlying genetic cause, and many patients eventually progressed to end-stage renal disease (ESRD). Atypical hemolytic uremic syndrome (aHUS) is a rare
Without complement inhibition, aHUS recurs in the allograft in 50-80% of patients with CFH, CFI, C3 mutations. Isolated MCP mutation carriers have low recurrence risk (15-20%) with kidney alone. Combined liver-kidney transplantation (to replace mutant FH produced in liver) has been performed but carries high morbidity.
Atypical Hemolytic Uremic Syndrome (aHUS) is a rare, life-threatening genetic disease that causes abnormal blood clots to form in small blood vessels throughout the body. These clots can lead to serious medical issues, including kidney failure, stroke, and heart attack. Unlike the more common form of HUS, which is typically triggered by E. coli bacteria from contaminated food, aHUS is driven by a chronic, uncontrolled activation of the complement system—a vital part of the body’s immune response. The Underlying Causes of aHUS coli (STEC)
The treatment of aHUS involves:
| Condition | Key distinguishing features | |-----------|----------------------------| | | Diarrhea (often bloody), positive stool Shiga toxin/PCR, normal complement levels, self-limited. | | Thrombotic thrombocytopenic purpura (TTP) | Severe ADAMTS13 deficiency (<10%), more neurological symptoms, fewer renal symptoms. | | Secondary TMA | Malignant hypertension, scleroderma renal crisis, post-transplant (calcineurin inhibitor toxicity), HIV, catastrophic antiphospholipid syndrome. | | Cobalamin C deficiency (Pediatric) | Methylmalonic aciduria, homocystinuria, typically presents <1 year. |
Loss of regulation leads to unchecked C3bBb activity, generating C3a (anaphylatoxin) and C3b, which deposits on glomerular endothelial cells. This triggers: