Below is an instruction from Human. Write a response.
    ### Instruction:
    What is (are) Genetic Brain Disorders ?
    ### Response:
    A genetic brain disorder is caused by a variation or a mutation in a gene. A variation is a different form of a gene. A mutation is a change in a gene. Genetic brain disorders affect the development and function of the brain.    Some genetic brain disorders are due to random gene mutations or mutations caused by environmental exposure, such as cigarette smoke.
    