Below is an instruction from Human. Write a response.
    ### Instruction:
    What are the genetic changes related to hypermethioninemia ?
    ### Response:
    Mutations in the AHCY, GNMT, and MAT1A genes cause hypermethioninemia.  Inherited hypermethioninemia that is not associated with other metabolic disorders can be caused by shortages (deficiencies) in the enzymes that break down methionine. These enzymes are produced from the MAT1A, GNMT and AHCY genes.
    