Below is an instruction from Human. Write a response.
    ### Instruction:
    What are the symptoms of Tetrahydrobiopterin deficiency ?
    ### Response:
    What are the signs and symptoms of Tetrahydrobiopterin deficiency? Infants with tetrahydrobiopterin (BH4) deficiency typically appear normal and healthy at birth. Neurological signs and symptoms usually become apparent over time, and can range from mild to severe.
    