Below is an instruction from Human. Write a response.
    ### Instruction:
    What is (are) essential thrombocythemia ?
    ### Response:
    Essential thrombocythemia is a condition characterized by an increased number of platelets (thrombocythemia). Platelets (thrombocytes) are blood cell fragments involved in blood clotting. While some people with this condition have no symptoms, others develop problems associated with the excess platelets.
    