What Causes Thrombotic Thrombocytopenic Purpura?

A lack of activity in the ADAMTS13 enzyme (a type of protein in the blood) causes thrombotic thrombocytopenic purpura (TPP). The ADAMTS13 gene controls the enzyme, which is involved in blood clotting.

Not having enough enzyme activity causes platelets to clump together, forming blood clots. In TTP, when blood clots form, there are fewer platelets in the blood. This can cause bleeding into the skin (purpura), drawn-out bleeding from cuts, and internal bleeding. It also causes small blood clots to form suddenly throughout the body, including in the brain and kidneys.

TTP also can cause red blood cells to break apart faster than the body can replace them. This leads to hemolytic anemia.

Inherited Thrombotic Thrombocytopenic Purpura

In the inherited form of TTP, changes in the ADAMTS13 gene affect the enzyme’s function. The gene doesn’t prompt the body to make a normal ADAMTS13 enzyme. As a result, enzyme activity is lacking or is altered.

“Inherited” means that the condition is passed from parents to children. In inherited TTP, a person is born with two copies of the altered gene—one from each parent. Most often, the parents each have one copy of the altered gene, but have no signs or symptoms of the disorder.

Acquired Thrombotic Thrombocytopenic Purpura

In the acquired type of TTP, the ADAMTS13 gene isn’t changed. Instead, the body makes proteins called antibodies that block the ADAMTS13 enzyme’s activity.

“Acquired” means you aren’t born with the condition, but you develop it.

Triggers for Thrombotic Thrombocytopenic Purpura

What triggers TTP isn’t known, but some factors may play a role. These include:

• Diseases and conditions such as pregnancy, cancer, HIV, infection, and lupus
• Medical procedures such as surgery and bone marrow transplant
• Medicines such as chemotherapy, ticlopidine, clopidogrel, cyclosporine A, and hormone replacement therapy and estrogens