Below is an instruction from Human. Write a response.
    ### Instruction:
    What is (are) Mitochondrial DNA-associated Leigh syndrome ?
    ### Response:
    Mitochondrial DNA-associated Leigh syndrome is a progressive brain disorder that usually appears in infancy or early childhood. Affected children may experience vomiting, seizures, delayed development, muscle weakness, and problems with movement. Heart disease, kidney problems, and difficulty breathing can also occur in people with this disorder.
    