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What is aHUS?

courtesy of Bill Biermann

Atypical Hemolytic-uremic syndrome (HUS) is a syndrome characterized by three major problems areas: 1) progressive renal failure 2) problems associated with red blood cell and platelet counts and 3) problems that occur in the vascular system. Atypical HUS should be differentiated from “regular or typical” HUS because the diseases have quite a few differences. Regular HUS is typically caused by the E-Coli virus, and while it is quite a severe disease, if the patient can recover from the disease, they may live the rest of their lives without another episode. Atypical HUS patients, however, frequently have recurring bouts with the disease.

Atypical HUS is not caused by an external agent (such as a bacteria, virus etc). Instead, some sort of internal chain of events sets the disease off, and the syndrome becomes active. The syndrome is not well understood. In many cases, it has been identified as a genetic problem due to an irregularity in several suspect genes. In these cases, there appears to be strong inherited tendencies. In other cases, the disease appears out of nowhere. This is called an “idiopathic” cause. Idiopathic causes are believed to originate from a mutated gene. There are a variety of other Atypical causes, such as HIV and Pregnancy induced HUS. In either case, Atypical HUS patients have many of the same symptoms as “Typical HUS Patients, but there are significant differences as well, as we see below:

As we can see, the Atypical form is subject to longer lingering effects, and is much more likely to become a chronic problem. Recurring episodes are much more common with the Atypical form of the disease. Atypical Cases frequently start out with flu-like symptoms that do not go away. Eventually, the lethargic behavior results in loss of appetite. A simple blood test will show shattered red blood cells, and low platelet counts, a definite sign of Atypical HUS.

Typical or regular HUS is rare, but Atypical HUS is even more rare. The number of cases in the US are believed to be around 300, and it occurs worldwide, but the frequency is unknown. Since Atypical HUS is not a communicable disease, reporting on it is not mandatory, but optional.

The Adult Version
Atypical HUS is most common with young children. The reason for that is unknown, but some believe that the genetic problem is present, but does not become activated until a virus such as the flu, or a bacterial infection occurs. Adults can get a disease with many of the same symptoms. Sometimes, the adults are diagnosed with Atypical HUS. But more often, the adult version involves different symptoms. So quite often, the adult version is called TTP, or thrombotic thrombocytopenic purpura. TTP has a lot of similarities to Atypical HUS, but the symptoms do not show up as kidney failure. Instead, the disease exhibits a lot of Neurological signs. See the links page for some additional sites related to TTP.

Typical HUS
The most common type of HUS (Hemolytic Uremic Syndrome) is called “Typical HUS”, or simply HUS

• Rare condition occurring mostly in children
• Also called infectious HUS
• Often accompanied by severe vomiting and diarrhea
• Most common source is E-Coli bacteria (from improperly cooked meat)
• Other Gastronomical bacteria and viruses could also be a cause

If the child survives the initial stages of the disease, the long term prognosis is good.
• Disease causes destruction of red blood cells, damage to the lining of blood vessel walls, and in severe cases, kidney failure
• Recovery time varies from several days to months
• Damaged red blood cells may clog the tiny blood vessels in the kidneys, making kidneys work hard, and dialysis may be necessary

Atypical HUS

• Recurrence
• Kidney failure
• Seizures/Neurological problems
• No response to supportive treatments
• Return of HUS even after kidney transplant occurs
• Severe Hypertension (high blood pressure)

The Details
While kidney failure may be the most obvious characteristic of this disease, the disease does not originate in the kidney. Instead, the root of the problem originates in either the blood or the vascular system. Microangiopathic hemolytic anemia occurs. This long word simply means that red blood cells are shattered and destroyed, because the small blood vessels are obstructed. Obstructed by what? Good question. The blood vessels are obstructed by very small clots. Clots, as you know, are usually good things. Clots occur when platelets rush to a site to stop bleeding. However, in Atypical HUS patients, the platelets begin aggregating in areas where they are not needed. These tiny clots usually are not the same type of clots that can go to the heart or the brain, because they are too small to do any damage there. But they are just the right size to get caught in the renal system, thereby damaging the kidneys.

 What are the symptoms of atypical HUS?
In most cases, Atypical HUS does not begin with a violent illness. Instead, the patient starts off ill, fatigue, irritable, and lethargic to a point where hospitalization is needed. Urine may be dark, due to an elevated BUN (Blood Urine Nitrogen) count. The diagnosis of the disease is actually quite easy to make if a simple blood test is given. The blood test show damaged or shattered red blood cells, a low red blood cell count, and a drastically reduced platelet count.

What causes atypical HUS?
There are 3 major causation categories of Atypical HUS. Some cases of Atypical HUS seem to originate from an external source. Pregnancy induced Atypical HUS is the most common external source, but some forms of cancer, HIV and other rare pneumonia diseases are a trigger for the disease.

A second major causal category are familial or genetic cases. It has been demonstrated that a sizable potion of the genetic cases (30%) are the result of a factor H deficiency. Factor H is a protein that protects the tissues of the kidneys from damage when clots form. Some of the other cases appear to originate from a problem with the gene known as the ADAMTS13 gene.
The third major causal category are the idiopathic, or unknown cases. In idiopathic cases, the disease seems to come out of nowhere. Genetic testing does not reveal any factor H or an ADAMTS13 gene problem, and yet the patient has recurrent bouts with the disease for no apparent reason. It is believed that the unknown cases are probably traceable to a gene problem, but that has not yet been proven.

What treatment is available?
There is no standard treatment, as each case is different. Children with Atypical HUS often develop various complications, so therapy is tailored for each case, and tends to be supportive. The symptoms are analyzed and a treatment plan is developed. Nephrologists have tried drugs that interfere with clotting, drugs that interfere with platelet function, blood transfusions, plasma infusions (plasma is the liquid part of the blood), and plasmapheresis (a blood filtering process). The best therapy is to closely monitor the disease, provide supportive techniques to control blood pressure and minimized the damage to kidneys though plasma and blood transfusions. Early dialysis may be life saving until the kidney function is able to return to normal. Recurring cases must be watched very closely, and immediate treatment should begin to prevent another full blown HUS episode.

There is one important thing that you can do once you have been diagnosed. Be Proactive. Or more importantly, have your doctor be proactive. Do not sit and wait passively for the next attack to occur, and then rush to the hospital in a panic effort to save the kidneys. INSTEAD a) Find the initial treatment that works b) Gradually, back off that treatment, but only when the key numbers support backing off….for example, it has taken us a full year to back our plasma infusion down to once a week c) Keep testing ….get on a periodic plan to test your key numbers (red blood cell count, platelet count, H & H, Hemoglobin and Hematocrit, BUN etc) d) The first several times you notice an illness coming on, get tested at the hospital for your key numbers before your body has a total “crash”

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