What is Hemolytic-uremic Syndrome

Hemolytic-uremic syndrome (HUS) is a serious condition characterized by the destruction of red blood cells, low platelet counts, and acute kidney injury. It most commonly occurs following an infection with specific bacteria, such as Shiga toxin-producing E. coli, though it can also be caused by genetic factors or underlying health conditions.

What exactly happens in the body during Hemolytic-uremic syndrome?

When a patient develops Hemolytic-uremic syndrome, the body’s small blood vessels become damaged and inflamed. This damage leads to the formation of tiny blood clots throughout the circulatory system. As red blood cells try to pass through these narrowed, obstructed vessels, they are physically shredded (hemolysis). Simultaneously, platelets—the cells responsible for clotting—are consumed to form these micro-clots, leading to a dangerously low platelet count (thrombocytopenia). The combination of these factors significantly restricts blood flow to vital organs, most notably the kidneys, leading to sudden renal failure.

What are the different types of Hemolytic-uremic syndrome?

Medical experts generally classify Hemolytic-uremic syndrome into two primary categories based on the underlying cause:

• Typical HUS (STEC-HUS): This is the most common form, usually triggered by an infection with bacteria that produce Shiga toxins, such as E. coli O157:H7. It is often preceded by a bout of bloody diarrhea.


• Atypical HUS (aHUS): This is a rarer, non-infectious form primarily caused by genetic mutations that lead to the uncontrolled activation of the complement system, a part of the immune system. It can also be associated with other conditions like cancer, pregnancy, or autoimmune diseases.

How common is Hemolytic-uremic syndrome and who is at risk?

The incidence of Hemolytic-uremic syndrome varies based on the subtype. Typical HUS is most frequently diagnosed in children under the age of 5, often following a gastrointestinal infection. In contrast, atypical HUS is extremely rare, with an estimated annual incidence of approximately 1 to 2 cases per million people. While it can occur at any age, atypical cases often manifest in individuals with a genetic predisposition. Currently, 93 people with Hemolytic-uremic syndrome have joined the DiseaseMaps community to share their experiences, highlighting the diverse backgrounds of those affected by this complex condition.

What differentiates Hemolytic-uremic syndrome from similar conditions?

It is common to confuse Hemolytic-uremic syndrome with Thrombotic Thrombocytopenic Purpura (TTP). While both involve microangiopathic hemolytic anemia and low platelets, they are distinct clinical entities:

1. Organ Involvement: HUS primarily affects the kidneys, leading to severe renal failure.


2. Neurological Symptoms: TTP is more likely to present with significant neurological changes (confusion, seizures) compared to HUS.


3. Underlying Mechanism: TTP is typically caused by a deficiency in the ADAMTS13 enzyme, whereas HUS is driven by toxins or complement system dysregulation.

Next steps

• Consult a nephrologist or a hematologist immediately if you or a loved one experience unexplained bruising, decreased urination, or extreme fatigue.


• Request genetic testing if your physician suspects atypical Hemolytic-uremic syndrome to identify potential complement system mutations.


• Join the DiseaseMaps community to connect with other patients and caregivers navigating the challenges of this diagnosis.


• Keep a detailed log of all symptoms and recent illnesses to assist your medical team in determining the most likely subtype of your condition.

Medical disclaimer: This content is for informational purposes only and does not constitute professional medical advice, diagnosis, or treatment; always seek the advice of your physician or other qualified health provider with any questions regarding a medical condition.

References

• NIH Genetic and Rare Diseases Information Center (GARD): Hemolytic-uremic syndrome overview.


• Orphanet: Atypical Hemolytic-uremic syndrome (aHUS) portal.


• OMIM (Online Mendelian Inheritance in Man): Genetic basis of complement-mediated HUS.


• National Kidney Foundation: Information on hemolytic-uremic syndrome and acute kidney injury.