Definition of Thrombotic thrombocytopenic purpura:

Thrombotic thrombocytopenic purpura (TTP) is a blood disorder that causes blood clots to form in small blood vessels around the body, and leads to a low platelet count (thrombocytopenia).

See also: Hemolytic-uremic syndrome

Causes, incidence, and risk factors:

This disease may be 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 to occur. As the platelets clump together in these clots, fewer platelets are available in the blood in other parts of the body to help with clotting. This can lead to bleeding under the skin and purple-colored spots called purpura.

In many cases, the disorder is passed down through families (inherited). The condition also may be related to:

• Bone marrow transplantation
• Cancer
• Chemotherapy
• HIV infection
• Hormone replacement therapy and estrogens
• Many commonly used medications (including ticlopidine, clopidogrel, and cyclosporine A)