Fast Five Quiz: Aromatic L-Amino Acid Decarboxylase Deficiency Diagnosis and Management

Stephen L. Nelson, Jr, MD, PhD; Germaine L. Defendi, MD, MS, FAAP


February 07, 2022

The enzyme aromatic L-amino acid decarboxylase (AADC) is involved in the biosynthesis of the monoamine neurotransmitters serotonin and dopamine. Because dopamine is the precursor for norepinephrine and epinephrine, AADC deficiency (or dopa decarboxylase (DDC) deficiency) results in severe combined deficiency of all of these four neurotransmitters: serotonin, dopamine, norepinephrine, and epinephrine. AADC deficiency is an extremely rare neurometabolic disorder with an estimated global prevalence of less than 1 per 1 million persons. Inheritance of AADC deficiency is autosomal recessive and is due to mutations in the DDC gene, mapped to the short arm of chromosome 7 (7p12.2-7p12.1).

Patients born with AADC deficiency may be asymptomatic at birth, but then typically show clinical clues within the first year of life (average onset is 3 months of age). Affected infants present with muscular hypotonia; severe developmental delay; movement disorders, such as oculogyric crisis, dystonia, hypertonia, and hypokinesia; and autonomic symptoms, namely hyperhidrosis, hypersalivation, and ptosis. Most patients with severe forms of AADC deficiency die before the age of 7 years.

Currently, there is no cure for AADC deficiency; however, treatment approaches incorporating several medications, such as monoamine oxidase inhibitors, dopamine agonists, and pyridoxine (vitamin B6), have shown clinical improvement for patients in both tone and movement. Gene therapy is also being investigated.

How much do you know about the diagnosis and management of AADC deficiency? Test your knowledge with this quick quiz.


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