About aHUS

Thrombotic microangiopathy (TMA) is a group of diseases that causes damage to the inner walls of the blood vessels (called endothelium) and results in the formation of blood clots (called thrombosis) in blood vessels.

Signs of TMA include decreased:

  • Platelets (called thrombocytopenia).  Platelets circulate in the blood and are responsible for helping our blood clot
  • Red blood cells and/or hemoglobin (called anemia).  Red blood cells contain hemoglobin which help carry oxygen
  • Kidney function (called renal failure)

Hemolytic Uremic Syndrome (HUS) is a type of TMA.  Classical or Typical HUS occurs after ingesting toxic strains of bacteria, usually types of E. coli (called shiga toxin) contained in contaminated food or water. With treatment, most people recover from this type of HUS. In some cases, and more rarely HUS can be more severe and be caused by a variety of other triggers including other types of bacterial or viral infections, medication, and radiation.

In addition to these examples, about 5-10 percent of HUS cases are due to one or several genetic mutations that cause lasting and uncontrolled activity of complement, a part of the body’s immune system.  This type of HUS is called complement-mediated atypical HUS (aHUS).

About aHUS

Atypical Hemolytic Uremic Syndrome (or aHUS) is an ultra-rare (about 1 in one million births), life-threatening, chronic, genetic disease that can damage the body’s vital organs. The disease can occur at any age and can lead to potentially devastating consequences. The condition can present with a wide range of severity and symptoms: some patients may experience one episode or “attack,” while others have regular episodes that can become quite severe.  Some experience kidney failure, while others have neurological, gastric, or cardiac symptoms. Although aHUS does affect children, almost one-half of people affected are adults.

aHUS is caused by changes or mutations to the genes that produce proteins that control part of the body’s complement system called the alternative pathway. As part of the body’s immune system, this pathway is always turned ‘on’, ready to attack foreign invaders.  During a time of “attack,” a healthy complement system has proteins (called regulators) that are able to protect the body’s own healthy cells.  If one or more of these regulators are defective, the complement attack is also directed against healthy body cells, such as the inner lining of blood vessels.

When blood vessels are damaged by this “self-attack,” a clotting system is activated in the blood and blood/platelet clots (called thrombi) form.  This clotting condition affects the function of various vital organs in the body including the brain, lung, heart, and stomach, as well as muscles and bones.

Despite the potential for damage to many of the body’s organs, aHUS often targets the kidneys. As the body filters blood through the kidneys, the platelet clots prevent the kidneys from functioning properly. When red blood cells pass through the kidney, they are shattered, becoming schistocytes. As a result, the platelet and red blood cell counts start to decrease, and the kidneys struggle to do their job.  Wastes such as creatinine are not filtered out of the blood properly, causing the creatinine level to rise. Elevated creatinine levels warn of damage to, possible malfunction, or even failure of the kidneys.