Below is an instruction from Human. Write a response.
    ### Instruction:
    What is (are) Pyruvate kinase deficiency ?
    ### Response:
    Pyruvate kinase deficiency is a genetic blood disorder characterized by low levels of an enzyme called pyruvate kinase, which is used by red blood cells. Without pyruvate kinase, red blood cells break down too easily, resulting in low levels of these cells (hemolytic anemia).
    