What causes AADC deficiency?

cause of aadc

Children with AADC deficiency have a genetic mutation (a change within the DDC gene) that leads to a decrease in neurotransmitters.1,2 The DDC gene produces an enzyme that is important for the brain and nervous system.1,2 Specifically, this enzyme functions in the biosynthetic pathway that produces dopamine and serotonin, which are chemical messengers that transmit signals between nerve cells.1-3 Mutations in the DDC gene result in reduced synthesis of dopamine and serotonin and their downstream metabolites, such as epinephrine and norepinephrine.1-4 Functioning neurotransmitters are important for the development of and communication between the brain and other organs. People with AADC deficiency have insufficient levels of the AADC enzyme, which results in disrupted communication between the brain and the nervous system, leading to developmental delays, uncontrolled movements, and other symptoms related to malfunctioning of the autonomic nervous system.1-3

AADC deficiency is inherited as an autosomal recessive disease.1-3 This means the condition does not occur unless the child inherits a mutated gene from both parents.5 If both copies of the gene are mutated, the child has severe depletion of functional DDC protein.5,6 A child who receives one normal gene and one mutated gene will be a carrier for AADC deficiency but usually will not show clinical symptoms.2,5

If both parents are carriers of the mutated gene, the risk for transmitting the disease to their children is 25%.5 Although AADC deficiency is not associated with a specific sex, there is an increased incidence among Asian populations.2,4

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1. 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.

2. 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.

3. 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.

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. Genetic Alliance. Understanding genetics. Washington DC: District of Columbia Department of Health; 2010.

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.

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