Internal Medicine

Aromatic L-amino acid decarboxylase (AADC) deficiency


Aromatic L-amino acid decarboxylase (AADC), a vitamin B6-requiring enzyme that converts L-dopa to dopamine and 5-hydroxytryptophan to serotonin.

Deficiency of this enzyme results in developmental delay, muscular hypotonia, dystonia, involuntary movements, autonomic dysfunction, and oculogyric crises.
  • Autosomal recessive inheritance

Clinical features

Characteristic movement disorders:

  • Hypotonia trunk
  • Oculogyric crisis
    • Abnormal rotation of eyeballs with elevation of gaze
    • Uncontrolled movement of head & neck
    • Agitation/irritability

Less common movement disorders:

  • Hypokinesia
  • Hypertonia
  • Tremors (involuntary movements)
  • Dystonia (twisting movements)
  • Athetosis (writhing movements)
  • Chorea (dance-like movements)

ANS manifestations:

Due to catecholamine deficiency
  • ↑ Sweating/salivation
  • Ptosis
  • Nasal congestion
  • Unstable body temperature
  • Low blood pressure
  • Hypoglycemia

Other CNS symptoms:

Seizures, abnormal sleep & reflexes

Developmental symptoms:

Learning disabilities, development delays, failure to reach milestones

GI symptoms:

Reflux, diarrhoea, constipation


Blood tests:

↓ AADC enzyme activity

CSF examination:

↓ Neurotransmitters

Genetic testing:

Mutated DDC gene


No definitive treatment.

Dopamine agonist

↑ Dopamine

MAO inhibitors

↓ MAO activity → ↑ Neurotransmitters

Vitamin B6 (Pyridoxine)

↑ AADC enzyme activity


Sleeping difficulties

Benzodiazepines/anticholinergic medications

Improve movement disorders

Multidisciplinary management:

Physical, speech & psychotherapy

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