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Antiphospholipid syndrome

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Antiphospholipid syndrome (APS), sometimes known as Hughes syndrome, is a disorder of the immune system that causes an increased risk of blood clots.

  • Occurs when the immune system mistakenly creates antibodies that make the blood much more likely to clot.
  • This means people with APS are at greater risk of developing conditions such as:
    • Kidney failure can result from decreased blood flow to the kidneys
    • Deep vein thrombosis (DVT), a blood clot that usually develops in the leg.
    • Arterial thrombosis (a clot in an artery), which can cause a stroke, heart attack or a pulmonary embolism.
    • Blood clots in the brain, leading to problems with balance, mobility, vision, speech and memory
    • Pregnant women with APS also have an increased risk of having a miscarriage or stillbirth although the exact reasons for this are uncertain.
      • Other complications of pregnancy include dangerously high blood pressure (preeclampsia) and premature delivery.
  • APS doesn't always cause noticeable problems, but some people have general symptoms that can be similar to those of multiple sclerosis a common condition affecting the central nervous system).
  • There's no cure for antiphospholipid syndrome, but medications can reduce your risk of blood clots.

What causes antiphospholipid syndrome?

  • APS is an autoimmune condition. This means the immune system, which usually protects the body from infection and illness, attacks healthy tissue by mistake.
  • In APS, the immune system produces abnormal antibodies called antiphospholipid antibodies.
  • These target proteins attached to fat molecules (phospholipids), which makes the blood more likely to clot.
  • It's not known what causes the immune system to produce abnormal antibodies.
  • As with other autoimmune conditions, genetic, hormonal and environmental factors are thought to play a part.

Who's affected

  • APS can affect people of all ages, including children and babies.
  • But most people are diagnosed with APS between 20 and 50 years of age, and it affects 3 to 5 times as many women as men.

Catastrophic antiphospholipid syndrome

  • In very rare cases, blood clots can suddenly form throughout the body, resulting in multiple organ failure. This is known as catastrophic antiphospholipid syndrome (CAPS).
  • CAPS requires immediate emergency treatment in hospital with high-dose anticoagulants.

Risk factors

  • 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.

Epidemiology Frequency

APS affects males and females, but a large percentage of primary APS patients are women with recurrent pregnancy loss. Some estimates suggest that 1 in 5 cases of recurrent miscarriages or deep vein thromboses are due to APS. As many as one-third of cases of stroke in people under 50 years of age may be due to APS. Secondary APS occurs mainly in lupus, and about 90% of lupus patients are female.

United States

  • The actual frequency of APS in the general population is unknown. One to 5% of healthy individuals have aPL antibodies. It is estimated that the incidence of APS is approximately 5 cases per 100,000 persons per year, and the prevalence is approximately 40-50 cases per 100, 000 persons. aCL antibodies tend to be found more frequently in elderly persons; thus, positive titer results should be interpreted with caution in this population. aPL antibodies are found in approximately 30-40% of patients with SLE, but only about 10% have APS. Approximately half of APS cases are not associated with another rheumatic disease. In a study of 100 patients with confirmed venous thrombosis and no history of SLE, aCL antibodies were found in 24% and LA in 4%.
  • aPL are positive in approximately 13% of patients with stroke, 11% with myocardial infarction, 9.5% of patients with deep vein thrombosis, and 6% of patients with pregnancy morbidity.


  • International frequency is probably similar to US frequency.


  • APS may contribute to an increased frequency of stroke or MI, especially in younger individuals. Strokes may develop secondary to in situ thrombosis or embolization that originates from the valvular lesions of Libman-Sacks (sterile) endocarditis, which may be seen in patients with APS. Cardiac valvular disease may be severe enough to require valve replacement. Recurrent pulmonary emboli or thrombosis can lead to life-threatening pulmonary hypertension.
  • Catastrophic APS (CAPS) is a rare, serious, and often fatal manifestation (mortality rate of approximately 50%) characterized by multiorgan infarctions over a period of days to weeks.
  • Late spontaneous fetal loss (second or third trimester) is common; however, it can occur at any time during pregnancy. Recurrent early fetal loss (< 10 weeks’ gestation) is also possible.

Resources for People Diagnosed with APS

  • APS Foundation of America, Inc. – Founded in 2005, The APS Foundation of America, Inc. (APSFA) is the leading United States nonprofit health agency dedicated to bringing national awareness to Antiphospholipid Antibody Syndrome (APS).
  • Antiphospholipid Syndrome Facebook Support Group – Antiphospholipid syndrome (or antiphospholipid antibody syndrome) (APS) is a disorder of coagulation, which causes blood clots (thrombosis) in both arteries and veins, as well as pregnancy-related complications such as miscarriage, preterm delivery, or severe preeclampsia. The syndrome occurs due to the autoimmune production of antiphospholipid antibodies (aPL). The name Antiphospholipid Syndrome is a misnomer because the target antigen of aPL is not phospholipids but actually plasma proteins that bind to phopholipids (eg: β2-glycoprotein 1 or prothrombin). This is an open support group where we come together to talk about it.

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