Below is an instruction from Human. Write a response.
    ### Instruction:
    What is (are) hypermethioninemia ?
    ### Response:
    Hypermethioninemia is an excess of a particular protein building block (amino acid), called methionine, in the blood. This condition can occur when methionine is not broken down (metabolized) properly in the body.  People with hypermethioninemia often do not show any symptoms.
    