Below is an instruction from Human. Write a response.
    ### Instruction:
    What causes Acute intermittent porphyria ?
    ### Response:
    What causes acute intermittent porphyria (AIP)? AIP is caused by the deficiency of an enzyme called porphobilinogen deaminase (PBGD), also known as hydroxymethylbilane synthase (HMBS) and formerly known as uroporphyrinogen I-synthase. The deficiency of PBGD is caused by a mutation in the HMBS gene.
    