WHAT CAUSES TTP-HUS?
In most patients there is no explanation for the occurrence of TTP-HUS. However we do know many things about this illness:
1) TTP-HUS is not contagious.
2) TTP-HUS is not inherited (except for very rare families).
3) TTP-HUS can occur at all ages.
4) TTP-HUS occurs more often in women.
5) Many patients with TTP-HUS are overweight.
6) TTP-HUS can occur during or immediately following pregnancy. In pregnant women the diagnosis of TTP-HUS is difficult because all of its features can also be present in preeclampsia (sometimes also called “toxemia of pregnancy”). Preeclampsia is typically only a problem of high blood pressure that resolves after delivery.
7) TTP-HUS can be caused by an allergic reaction to a medicine. The most common drug that can cause TTP-HUS is quinine, the remedy many people use for leg cramps.
8) TTP-HUS can be caused by infection with the bacteria, E. coli 0157:H7, which can be in undercooked beef or hamburger. In this form of TTP-HUS, patients initially have bloody diarrhea; this occurs most commonly in young children.
9) Some types of TTP-HUS have an autoimmune cause, in which the patient makes an antibody that blocks the function of one of their own enzymes, named ADAMTS13. Antibodies are described in the section on Platelets. Enzymes are proteins that digest other materials. The most common enzymes are in our mouth, stomach, and intestines that digest our food. ADAMTS13 is an enzyme in the blood that digests the protein that makes platelets stick together, called von Willebrand factor or VWF. When VWF is made in the cells that line the blood vessel, it is too big. ADAMTS13 is required to cut the VWF into smaller pieces, cutting it down to its normal size. When there is a deficiency of ADAMTS13 enzyme, the VWF is too large and too sticky for platelets. It can cause the platelet clumps that block blood vessels and cause TTP. Therefore, ADAMTS13 helps to prevent the formation of platelet thrombi. Immunity describes the normal development of antibodies against foreign substances, such as bacteria, viruses, or a transplanted organ. These diseases are called “autoimmune” because the patients make antibodies against their own tissues. Some patients with TTP-HUS may have symptoms similar to other illnesses that are described as “autoimmune”, such as lupus.
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