Below is an instruction from Human. Write a response.
    ### Instruction:
    What causes Ornithine transcarbamylase deficiency ?
    ### Response:
    What causes ornithine transcarbamylase (OTC) deficiency? Ornithine transcarbamylase (OTC) deficiency is caused by mutations in the OTC gene. OTC deficiency belongs to a class of genetic diseases called urea cycle disorders. The urea cycle is a sequence of reactions that occurs in liver cells.
    