Antiphospholipid syndrome occurs when your immune system mistakenly attacks some of the normal proteins in your blood. Antiphospholipid syndrome can cause blood clots to form within your arteries or veins. It can also cause pregnancy complications, such as miscarriage and stillbirth.
Antiphospholipid syndrome may cause blood clots to form in your leg veins, a condition known as deep vein thrombosis (DVT). Antiphospholipid syndrome may also cause blood clots to form in organs such as your kidneys or lungs. Damage depends on the extent and location of the clot. For instance, a clot in your brain can cause stroke. There's no cure for antiphospholipid syndrome, but medications can be effective in reducing your risk of blood clots.