Definition of Thrombotic thrombocytopenic purpura:

Thrombotic thrombocytopenic purpura (TTP) is a blood disorder that causes blood clots to form in blood vessels around the body.

See also: Hemolytic-uremic syndrome

Causes, incidence, and risk factors:

In some cases, this disease is caused by the lack of an enzyme (a type of protein) that is involved in blood clotting. Not having enough of this enzyme causes clotting substances (platelets) in the blood to clump. As the platelets clump together, there are fewer platelets available in the bloodstream. This can lead to bleeding under the skin and purple-colored spots called purpura. It also can cause red blood cells to break apart and be destroyed prematurely.

TTP can lead to low platelets, low red blood cell count (caused by premature breakdown of red blood cells), abnormal kidney function, and problems with the nervous system.

Most cases of this disorder have no known cause, but some cases may be caused by a lack of the ADAMTS13 gene at birth. This gene gives the instructions for making the enzyme involved in blood clotting. The condition also may be related to cancer, chemotherapy, HIV infection, hormone replacement therapy and estrogens, and a number of commonly used medications (including ticlopidine, clopidogrel, and cyclosporine A).