What is AADC deficiency?

aadc deficiency image

Aromatic L-amino acid decarboxylase (AADC) deficiency is a rare genetic disorder of the central nervous system that commonly results in developmental delays in children.1-4 AADC is an enzyme important in the brain and nervous system.1-4 AADC deficiency interferes with the way the cells in the nervous system talk to each other through substances called neurotransmitters.1-3 Patients with AADC deficiency lack the functioning AADC enzyme, which is responsible for the final step in the synthesis of key neurotransmitters dopamine and serotonin.3 This deficiency results in delays or failure to reach developmental milestones such as walking, talking, sitting unassisted, or having head control, hypotonia, oculogyric crises, autonomic abnormalities, and the need for lifelong care.1-3

What are the symptoms of AADC?

The most common symptoms of AADC deficiency are the following1-3,5:

  • Developmental delays
  • Hypotonia (low muscle tone)
  • Unusual movements and movement disorders, especially involuntary eye movements

Developmental delays can vary from child to child.1-3,5 Children with AADC deficiency may be unable to perform the following tasks3,4,6:

  • Lifting and controlling their heads
  • Crawling
  • Sitting
  • Walking
  • Standing
  • Speaking clearly (delayed speech development)

The involuntary eye movements commonly observed in children with AADC deficiency are called oculogyric crises.7 These moments occur when a child's eyes suddenly and involuntarily roll upward.3,6-8 An episode can last from a few seconds to hours and can occur several times a day or several times a week.6,7,9 When this happens, it often looks like the child is having a seizure.2,3 Other involuntary movements, such as sudden jerking, flailing, or twisting may be present.3

Additional common symptoms you might notice include the following1,3,8:

  • Excessive sweating
  • Drooling
  • Drooping eyelids
  • Stuffy or runny nose

Common misdiagnosis of AADC deficiency

Early diagnosis of AADC deficiency is critical, and patients with AADC deficiency syndrome can remain undiagnosed or can be easily misdiagnosed as having epilepsy, cerebral palsy, or autism.2,3,5,9-11 A misdiagnosis can occur due to overlapping symptoms between AADC deficiency and other neurotransmitter disorders.5,9,10 A delayed or misdiagnosis of any kind can lead to improper or delayed treatment.3,5,9

Children with AADC deficiency might experience seizures, difficulty sleeping, behavioral problems like irritability or excessive crying, problems with digestion (diarrhea, constipation, and/or reflux), and problems with feeding, including trouble swallowing without choking or coughing.3

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1. Brun L, Ngu LH, Keng WT, et al. Clinical and biochemical features of aromatic L-amino acid decarboxylase deficiency. Neurology. 2010;75(1):64-71.

2. Manegold C, Hoffmann GF, Degen I, et al. Aromatic L-amino acid decarboxylase deficiency: clinical features, drug therapy and follow-up. J Inherit Metab Dis. 2009;32(3):371-380.

3. Wassenberg T, Molero-Luis M, Jeltsch K, et al. Consensus guideline for the diagnosis and treatment of aromatic L-amino acid decarboxylase (AADC) deficiency. Orphanet J Rare Dis. 2017;12(1):12.

4. Hwu WL, Chien YH, Lee NC, Li MH. Natural history of aromatic L-amino acid decarboxylase deficiency in Taiwan. JIMD Rep. 2018;40:1-6.

5. Ng J, Papandreou A, Heales SJ, Kurian MA. Monoamine neurotransmitter disorders—clinical advances and future perspectives. Nat Rev Neurol. 2015;11(10):567-584.

6. Swoboda KJ, Hyland K, Goldstein DS, et al. Clinical and therapeutic observations in aromatic L-amino acid decarboxylase deficiency. Neurology. 1999;53(6):1205-1211.

7. Solberg M, Koht J. Oculogyric crises. Tremor Other Hyperkinet Mov (N Y). 2017;7:491.

8. Pons R, Ford B, Chiriboga CA, et al. Aromatic L-amino acid decarboxylase deficiency: clinical features, treatment, and prognosis. Neurology. 2004;62(7):1058-1065.

9. Lee, WT. Disorders of monoamine metabolism: inherited disorders frequently misdiagnosed as epilepsy. Epilepsy Seizure. 2010;3:147-153.

10. Pearson TS, Pons R, Ghaoui R, Sue CM. Genetic mimics of cerebral palsy. Mov Disord. 2019;34(5):625-636.

11. Himmelreich N, Montioli R, Bertoldi M, et al. Aromatic amino acid decarboxylase deficiency: Molecular and metabolic basis and therapeutic outlook. Mol Genet Metab. 2019;127(1):12-22.

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