aHUS is a disease of complement disregulation. The complement system is a group of proteins in the blood, which help the immune system in fighting infections. Often due to a genetic mutation the production of complement proteins is disrupted, resulting in aHUS.
It is estimated that there are about 2 cases of aHUS in the U.S. per 1,000,000 of population, and about 60% of aHUS patients are diagnosed as children. The condition is potentially life threatening, and either can be chronic or can recur at intervals.
Treatment for aHUS is supportive, there is no cure and no standard treatment protocol. Some patients respond well to plasma infusion ( liquid portion of the blood, added to the patient's body via IV treatment). Others respond better to plasmapheresis, also called plasma exchange. In plasmapheresis the blood plasma (the portion that does not contain cells, but does contain antibodies) is centifuged out with this removed liquid replaced by donor plasma then added back into the patient's blood stream.
Lab values for aHUS patients often show low platelets counts (due to the clumping), low red blood cell counts (vessel linings rise up to shear red blood cells into pieces-hemolysis), high levels of creatinine (a gauge of kidney function), and a high LDH ( a marker for the level of aHUS disease activity).
You may recall news stories reporting HUS outbreaks due to contaminated spinach or raw hamburger, but atypical HUS is not caused by exposure to a bacteria or virus. It is unclear how an internal sequence of events triggers the disease into activity. Many cases of aHUS have an underlying inherited genetic mutation, but it is unclear why the disease activates in so few people within family groups. Idiopathic cases, seeming to appear out of the blue, have also been reported as have such aHUS cases with triggering factors such as pancreatitis or pregnancy.
CFH (Serum Complement Factor H) is a regulatory protein. The secreted protein product of CFH consists of 20 repetitive units named "short consensus repeats" or SCRs (each approximately 60 amino acids). In patients with aHUS the last 5 "pearls" in the twenty pearl strand protein, SCR16 - SCR20, should bind to protect cells but do not- they are defective in one or more of the last 5 SCR locations. If they cannot bind or stick to the kidney to protect that tissue, the platelets clump into clots that affect the glomeruli of the kidney -potentially causing acute renal failure