Below is an instruction from Human. Write a response.
    ### Instruction:
    What is (are) aromatic l-amino acid decarboxylase deficiency ?
    ### Response:
    Aromatic l-amino acid decarboxylase (AADC) deficiency is an inherited disorder that affects the way signals are passed between certain cells in the nervous system.  Signs and symptoms of AADC deficiency generally appear in the first year of life. Affected infants may have severe developmental delay, weak muscle tone (hypotonia), muscle stiffness, difficulty moving, and involuntary writhing movements of the limbs (athetosis).
    