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 overactive blood clotting. In TTP, blood clots form in small blood vessels throughout the body. These clots can limit or block the flow of oxygen-rich blood to the body's organs, such as the brain, kidneys, and heart. As a result, serious health problems can develop.
The increased clotting that occurs in TTP also uses up many of the blood's platelets. With fewer platelets available in the blood, bleeding problems can occur.
People who have TTP may bleed inside their bodies, underneath the skin, or from the surface of the skin. When cut or injured, they also may bleed longer than normal.
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 inherited TTP, the ADAMTS13 gene is faulty. It doesn't prompt the body to make a normal ADAMTS13 enzyme. As a result, enzyme activity is lacking or changed.
"Inherited" means that the condition is passed from parents to children through genes. A person who inherits TTP is born with two copies of the faulty gene—one from each parent.
Most often, the parents each have one copy of the faulty gene, but have no signs or symptoms TTP.
Acquired Thrombotic Thrombocytopenic Purpura
In acquired TTP, the ADAMTS13 gene isn't faulty. Instead, the body makes antibodies (proteins) that block the activity of the ADAMTS13 enzyme.
"Acquired" means you aren't born with the condition, but you develop it sometime after birth.
Triggers for Thrombotic Thrombocytopenic Purpura
It's unclear what triggers inherited and acquired TTP, but some factors may play a role. These factors may include:
- Some diseases and conditions, such as pregnancy, cancer, HIV, lupus, and infections
- Some medical procedures, such as surgery and blood and marrow stem cell transplant
- Some medicines, such as chemotherapy, ticlopidine, clopidogrel, cyclosporine A, and hormone therapy and estrogens
- Quinine, which is a substance often found in tonic water and nutritional health products