Below is an instruction from Human. Write a response.
    ### Instruction:
    What is (are) familial erythrocytosis ?
    ### Response:
    Familial erythrocytosis is an inherited condition characterized by an increased number of red blood cells (erythrocytes). The primary function of these cells is to carry oxygen from the lungs to tissues and organs throughout the body. Signs and symptoms of familial erythrocytosis can include headaches, dizziness, nosebleeds, and shortness of breath.
    