Below is an instruction from Human. Write a response.
    ### Instruction:
    What is (are) antiphospholipid syndrome ?
    ### Response:
    Antiphospholipid syndrome is a disorder characterized by an increased tendency to form abnormal blood clots (thromboses) that can block blood vessels. This clotting tendency is known as thrombophilia. In antiphospholipid syndrome, the thromboses can develop in nearly any blood vessel in the body, but most frequently occur in the vessels of the lower limbs.
    