Signs and symptoms of antiphospholipid syndrome can include:

• Blood clots in your legs (DVT). Signs of a DVT include pain, swelling and redness. These clots can travel to your lungs (pulmonary embolism).

• Repeated miscarriages or stillbirths. Other complications of pregnancy include dangerously high blood pressure (preeclampsia) and premature delivery.

• Stroke. A stroke can occur in a young person who has antiphospholipid syndrome but no known risk factors for cardiovascular diseases.

• Transient ischemic attack (TIA). Similar to a stroke, a TIA usually lasts only a few minutes and causes no permanent damage.

• Rash. Some people develop a red rash with a lacy, net-like pattern.

Less common signs and symptoms include:

• Neurological symptoms. Chronic headaches, including migraines; dementia and seizures are possible when a blood clot blocks blood flow to parts of your brain.

• Cardiovascular disease. Antiphospholipid syndrome can damage heart valves.

• Bleeding. Some people have a decrease in blood cells needed for clotting. This can cause episodes of bleeding, particularly from your nose and gums. You can also bleed into your skin, which will appear as patches of small red spots.

Antiphospholipid syndrome occurs when your immune system mistakenly produces antibodies that make your blood much more likely to clot. Antibodies normally protect the body against invaders, such as viruses and bacteria.

Antiphospholipid syndrome can be caused by an underlying condition, such as an autoimmune disorder, infection or certain medications. You also can develop the syndrome without an underlying cause.

Risk factors for antiphospholipid syndrome include:

• Your sex. This condition is much more common in women than in men.

• Immune system disorders. Having another autoimmune condition, such as lupus or Sjogren's syndrome, increases your risk of antiphospholipid syndrome.

• Infections. This condition is more common in people who have certain infections, such as syphilis, HIV/AIDS, hepatitis C or Lyme disease.

• Medications. Certain medications have been linked to antiphospholipid syndrome. They include hydralazine for high blood pressure, the heart rhythm-regulating medication quinidine, the anti-seizure medication phenytoin (Dilantin) and the antibiotic amoxicillin.

• Family history. This condition sometimes runs in families.

It's possible to have the antibodies associated with antiphospholipid syndrome without developing signs or symptoms. However, having these antibodies increases your risk of developing blood clots, particularly if you:

• Become pregnant

• Are immobile for a time, such as being on bed rest or sitting during a long flight

• Have surgery

• Smoke cigarettes

• Take oral contraceptives or estrogen therapy for menopause

• Have high cholesterol and triglycerides levels

Depending on which organ is affected by a blood clot and how severe the obstruction of blood flow to that organ is, untreated antiphospholipid syndrome can lead to permanent organ damage or death. Complications include:

• Kidney failure. This can result from decreased blood flow to your kidneys.

• Stroke. Decreased blood flow to a part of your brain can cause a stroke, which can result in permanent neurological damage, such as partial paralysis and loss of speech.

• Cardiovascular problems. A blood clot in your leg can damage the valves in the veins, which keep blood flowing to your heart. This can result in chronic swelling and discoloration in your lower legs. Another possible complication is heart damage.

• Lung problems. These can include high blood pressure in your lungs and pulmonary embolism.

• Pregnancy complications. These can include miscarriages, stillbirths, premature delivery, slow fetal growth and dangerously high blood pressure during pregnancy (preeclampsia).