What Causes Thrombotic Thrombocytopenic Purpura?

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

Not having enough enzyme activity causes platelets to clump together and form blood clots. In TTP, when blood clots form, the result is fewer platelets in the blood.

This can cause bleeding into the skin (purpura), prolonged bleeding from cuts, and internal bleeding. It also can cause 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, the ADAMTS13 gene is faulty, which affects 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 through the genes. A person who has inherited TTP 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 faulty. Instead, the body makes antibodies (proteins) 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 may include:

• Some diseases and conditions, such as pregnancy, cancer, HIV, infections, and lupus
• Some medical procedures, such as surgery and blood and marrow stem cell transplant
• Some medicines, such as chemotherapy, ticlopidine, clopidogrel, cyclosporine A, and hormone replacement therapy and estrogens
• Quinine, which is a substance often found in tonic water and nutritional health products