Below is an instruction from Human. Write a response.
    ### Instruction:
    What causes Chiari malformation type 1 ?
    ### Response:
    What causes Chiari malformation type 1? Primary or congenital Chiari malformations are caused by structural defects in the brain and spinal cord that occur during fetal development. The underlying cause of the structural defects are not completely understood, but may involve genetic mutations or lack of proper vitamins or nutrients in the maternal diet.
    