How is AADC deficiency diagnosed?

dignosis doctor

Early identification can help improve the care and management of individuals with AADC deficiency.1-4 Despite the onset of symptoms during infancy, diagnosis is typically delayed, primarily because many of the symptoms of AADC deficiency are commonly shared with other diseases.1,2,5-7 The average age of diagnosis is 3.5 years; however, the range of diagnosis is 2.7 months to 23 years.7

If your child has weak muscle tone and delayed development, the doctor may perform a range of tests such as a magnetic resonance imaging (MRI), a computed tomography (CT) scan, or an electroencephalogram (EEG) to look for problems in the brain. Each of these tools can produce images from inside the body to help doctors with their diagnosis.5,7,8

How to test for AADC deficiency

There are 4 core tests that can be used to confirm a diagnosis of AADC deficiency7,8:

  • Plasma enzyme activity assay7
  • A plasma enzyme activity assay blood test measures the activity level of the AADC enzyme, which is reduced in individuals with AADC deficiency.

  • 3-OMD testing9
  • 3-OMD or 3-O-methyldopa is a metabolic product of L-dopa that accumulates in individuals with AADC deficiency and can be detected in blood.

  • Genetic testing7
  • Your child's doctor may recommend genetic testing to look for a mutation, or change, in the dopa decarboxylase (DDC) gene. Consensus guidelines recommend confirming an AADC deficiency diagnosis with a genetic test.

  • Cerebrospinal fluid neurotransmitter metabolite panel7
  • This panel measures the levels of some of the metabolites, or precursors and by-products, of neurotransmitters. A lumbar puncture or spinal tap is performed to collect some of the fluid in the spine to measure these levels.

The doctor may also order other tests that will be helpful in diagnosing your child, including blood and urine tests. No-cost diagnostic testing is available for eligible individuals and include plasma 3-OMD measurement, AADC enzyme activity analysis, and DDC gene sequencing.

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Resources

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

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

3. 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.

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

5. 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.

6. 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.

7. 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.

8. 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.

9. Chen PW, Lee NC, Chien YH, Wu JY, Wang PC, Hwu WL. Diagnosis of aromatic L-amino acid decarboxylase deficiency by measuring 3-O-methyldopa concentrations in dried blood spots. Clin Chim Acta. 2014;431:19-22.

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