Inclusion Criteria:

• * Persistent presence of an antiphospholipid antibody, as defined by one or both of the following criteria:
• 1. Medium or high anticardiolipin antibody level in the blood on two or more occasions at least 6 weeks apart
• 2. Presence of lupus anticoagulant in the plasma on two or more occasions at least 6 weeks apart
• * Presence of clinical symptoms seen in patients with APS, including vascular thrombosis (one or more clinical episodes of arterial, venous, or small vessel thrombosis in any tissue or organ) and/or pregnancy morbidity, defined as any of the following:
• 1. One or more unexplained deaths of a morphologically normal fetus at or beyond the 10th week of gestation, with normal fetus morphology documented by ultrasound or direct examination or the fetus
• 2. One or more premature births of a morphologically normal baby at or before the 34th week of gestation because of severe pre-eclampsia, eclampsia, or severe placental insufficiency
• 3. Three or more unexplained consecutive spontaneous abortions before the 10th week of gestation, with maternal anatomic or hormonal abnormalities and paternal and maternal chromosomal causes excluded
• * People who have elevated antiphospholipid antibody levels but do not fully meet clinical criteria for APS, and do have affected family members, will be considered for enrollment

Exclusion Criteria:

• * No documented presence of antiphospholipid antibody