Below is an instruction from Human. Write a response.
    ### Instruction:
    What is (are) Porphyria ?
    ### Response:
    Each of the eight types of porphyria corresponds to low levels of a specific enzyme in the heme biosynthetic pathway. Experts often classify porphyrias as acute or cutaneous based on the symptoms a person experiences:
                
- Acute porphyrias affect the nervous system.
    