Below is an instruction from Human. Write a response.
    ### Instruction:
    What is (are) MTHFR gene mutation ?
    ### Response:
    MTHFR gene mutation is a genetic change that disrupts the production of an enzyme that plays an important role in breaking down the amino acid homocysteine (a building block of protein). These mutations may cause a mild to severe loss of activity of this enzyme that can lead to elevated levels of homocysteine in the blood and/or urine.
    