What is Atypical HUS?

What is Atypical HUS | Information for Parents

So you have received the news from your Doctor/ Hospital: “Your Child has Atypical HUS.” What does that mean? Who do you turn to for more information?

Not too long ago, you would have very limited choices for information and help. Finding answers to your questions would be extremely difficult to answer. Then, it was not very encouraging when your Doctor admitted that he or she has only seen a small number of cases in their entire career. However, thanks to a dedicated group of parents, that has not changed. We now have access to a lot more medical and parental advice that can be shared. We hope you will find this website and our other associated websites helpful.

This website is meant to be an easy source of knowledge for both parents and medical professionals. We also have an affiliate website that is interactive in nature, and we encourage you to become a member of that website: www.atypicalhus.org. If you join that website as a member, you will immediately belong to a caring community that is eager to help you.

Atypical HUS (Hemolytic Uremic Syndrome) historically has fallen under the category of “kidney disease”, as the kidney was the main organ system involved. Recent advances in understanding now demonstrate it is a “complement mediated disease” and can affect more than one organ. The kidney is the “innocent bystander” that is impacted the most, or at least is the most obvious organ impacted, but there may be others as well. We will explain a little bit more on Complement disease later.

Atypical HUS is a rare disease that has a wide range of severity: some patients may experience one episode or “attack”, while others have regular episodes that can become quite severe. The disease is genetic in origin, and the major internal symptom is TMA, or Thrombotic Microangiapathy.

A Simple way to view Atypical HUS

Information Atypical HUS | The Atypical HUS Foundation

Any real simply answer is risky, because the real issue is much more complex, but let’s try to do so without losing accuracy.

Your body circulates blood continuously. Your blood contains many proteins, red blood cells, platelets and other things as well. When your blood passes thru your kidneys, small vessels (called nephrons) filter out waste. In aHUS, the walls of your blood vessels can become clogged with platelets. So now your body is filtering blood, and the platelets are clotting up the kidney function. (TMA). So when your red blood cells pass thru, they are shattered (shistocytes). Therefore, your platelet counts start to decrease, and your red blood cell count decreases.

As a result, your kidney struggles to do its job. As a result,wastes such as creatinine are not filtered out properly, and the creatinine level rises. Also, your BUN (blood Urea Nitrogen) levels may increase.

What is the root cause of this clotting? One of the proteins in your blood is out of whack. There are a number of different proteins that could be the cause. Your Genes are responsible for directing the proteins, so ultimately, one of your genes is not “ doing its job right when it comes to the assembly line job” that your body has. So one little gene, seemingly unimportant, become might important when it does not function properly. As an analogy, lets say an assembly line worker fails to put on the lug nuts on your wheels. So your beautiful new car, which looks perfect in every way, unexpectedly crashes.

Atypical HUS Information & Research

So the root cause of aHUS lies in the genetics in most cases. Some cases have not been linked to any specific gene, but it is believed that ultimately, more genes will be uncovered. The suspect genes that have been identified all play a role in “complement activation”. So the root cause of the “micro clots” is uncontrolled complement activation. Complement is part of our innate immune system (alternative pathway): do not confuse it with the acquired immune system. The complement system is always ready to attack foreign invaders. However, the complement system has “referees” who control the game, so to speak. These referees mediate on behalf of the body, and tell the immune system ‘when the play is over”. However, when one of the genes makes a protein that is defective, the protein refuses to “play by the rules”, and continues to attach the body when the attack is not really justified. As a result, the cell walls become injured, micro clotting occurs, and organs can become damaged. Historically, the kidney was believed to the only organ damaged, but that view has changed, and it is now believed that other organs, even the brain, can become affected.

Read a more detailed explanation of the complement system and look at the relationship between complement and atypical HUS.