Below is an instruction from Human. Write a response.
    ### Instruction:
    What causes Citrullinemia type I ?
    ### Response:
    What causes citrullinemia type I? Citrullinemia type I is caused by mutations in the ASS1 gene. This gene provides instructions for making an enzyme, argininosuccinate synthetase 1, that is responsible for the third step in the urea cycle. Mutations in the ASS1 gene reduce the activity of the enzyme, which disrupts the urea cycle and prevents the body from processing nitrogen effectively.
    