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

People with APS are at risk of developing conditions such as deep vein thrombosis (a blood clot that usually develops in the leg) and arterial thrombosis (a clot in an artery), which can cause a stroke or heart attack.

Pregnant women with APS also have an increased risk of having a miscarriage, although the exact reasons for this are uncertain.

It is estimated that APS is responsible for one in every six cases of deep vein thrombosis (DVT), strokes and heart attacks in people under 50 and one in every six cases of recurrent (three or more) miscarriages.

There is currently no cure for APS. However, if it is correctly diagnosed, the risk of developing blood clots can be greatly reduced.

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 that target proteins attached to fat molecules called phospholipids, which makes the blood more likely to clot.

It is not known what causes the immune system to produce abnormal antibodies, but like other autoimmune conditions, genetic, hormonal and environmental factors are thought to play a part.

Read more about the causes of APS.

Who is affected

APS can affect people of all ages, including children and babies. However, it usually affects adults aged 20–50, and affects three to five times as many women as men.

It's not clear how many people in the UK have the condition.

Signs and symptoms

As well having a history of conditions caused by blood clots, such as stokes and deep vein thrombosis, people with APS may have:

Diagnosing APS can sometimes be tricky, as some of the symptoms are similar to multiple sclerosis (a common condition affecting the central nervous system). Therefore, blood tests designed to help identify the antibodies responsible for APS are essential in diagnosing the condition.

Read more about the symptoms of APS and diagnosing APS.

How antiphospholipid syndrome is treated

As there is no cure for APS, treatment aims to reduce the risk of developing further blood clots.

Anticoagulant medicines such as warfarin or an antiplatelet such as low-dose aspirin are usually prescribed. These reduce the likelihood of blood clots forming when they are not needed but still allow clots to form when you cut yourself.

Treatment with these medications can also help pregnant women improve their chances of having a successful pregnancy. With treatment, it's estimated there is about an 80% chance of having a successful pregnancy.

Most people respond well to treatment and can lead normal, healthy lives. However, a small number of people with APS continue to experience blood clots despite extensive treatment.

Read more about treating APS and the complications of APS.

APS is an immune system disorder that causes an increased risk of blood clots 

Page last reviewed: 06/11/2013

Next review due: 06/11/2015