Below is an instruction from Human. Write a response.
    ### Instruction:
    What is (are) pyruvate kinase deficiency ?
    ### Response:
    Pyruvate kinase deficiency is an inherited disorder that affects red blood cells, which carry oxygen to the body's tissues. People with this disorder have a condition known as chronic hemolytic anemia, in which red blood cells are broken down (undergo hemolysis) prematurely, resulting in a shortage of red blood cells (anemia).
    