The DDC gene provides instructions for making the aromatic l-amino acid decarboxylase (AADC) enzyme, which plays an important role in the brain and nervous system. This enzyme is involved in the final step of the chemical pathways that produce dopamine and serotonin, which are two types of neurotransmitters. Neurotransmitters are chemical messengers that transmit signals between nerve cells (neurons) and other cells in the body. Dopamine is involved in the creation of two additional neurotransmitters called norepinephrine and epinephrine.

The AADC enzyme plays a role in the two-step process that is used to create dopamine. First, the protein building block (amino acid) tyrosine is converted into a molecule called L-dopa. The AADC enzyme then removes a molecular structure called a carboxyl group (which consists of a carbon atom, two oxygen atoms, and a hydrogen atom) from L-dopa, creating dopamine. A similar process is used to make serotonin. The amino acid tryptophan is converted to 5-hydroxytryptophan before the AADC enzyme removes a carboxyl group, producing serotonin. 

Tests Listed in the Genetic Testing Registry

• Tests of DDC

Scientific Articles on PubMed

• PubMed

Catalog of Genes and Diseases from OMIM

• DOPA DECARBOXYLASE; DDC

Gene and Variant Databases

• NCBI Gene
• ClinVar

• Bertoldi M. Mammalian Dopa decarboxylase: structure, catalytic activity and inhibition. Arch Biochem Biophys. 2014 Mar 15;546:1-7. doi: 10.1016/j.abb.2013.12.020. Epub 2014 Jan 6. Citation on PubMed
• Blau N, Pearson TS, Kurian MA, Elsea SH. Aromatic L-Amino Acid Decarboxylase Deficiency. 2023 Oct 12 [updated 2025 Jan 23]. In: Adam MP, Feldman J, Mirzaa GM, Pagon RA, Wallace SE, Amemiya A, editors. GeneReviews(R) [Internet]. Seattle (WA): University of Washington, Seattle; 1993-2025. Available from http://www.ncbi.nlm.nih.gov/books/NBK595821/ Citation on PubMed
• Brun L, Ngu LH, Keng WT, Ch'ng GS, Choy YS, Hwu WL, Lee WT, Willemsen MA, Verbeek MM, Wassenberg T, Regal L, Orcesi S, Tonduti D, Accorsi P, Testard H, Abdenur JE, Tay S, Allen GF, Heales S, Kern I, Kato M, Burlina A, Manegold C, Hoffmann GF, Blau N. Clinical and biochemical features of aromatic L-amino acid decarboxylase deficiency. Neurology. 2010 Jul 6;75(1):64-71. doi: 10.1212/WNL.0b013e3181e620ae. Epub 2010 May 26. Citation on PubMed
• Hyland K. Inherited disorders affecting dopamine and serotonin: critical neurotransmitters derived from aromatic amino acids. J Nutr. 2007 Jun;137(6 Suppl 1):1568S-1572S; discussion 1573S-1575S. doi: 10.1093/jn/137.6.1568S. Citation on PubMed
• Pearl PL, Capp PK, Novotny EJ, Gibson KM. Inherited disorders of neurotransmitters in children and adults. Clin Biochem. 2005 Dec;38(12):1051-8. doi: 10.1016/j.clinbiochem.2005.09.012. Epub 2005 Nov 18. Citation on PubMed
• Pearl PL, Taylor JL, Trzcinski S, Sokohl A. The pediatric neurotransmitter disorders. J Child Neurol. 2007 May;22(5):606-16. doi: 10.1177/0883073807302619. Citation on PubMed
• Verbeek MM, Geurtz PB, Willemsen MA, Wevers RA. Aromatic L-amino acid decarboxylase enzyme activity in deficient patients and heterozygotes. Mol Genet Metab. 2007 Apr;90(4):363-9. doi: 10.1016/j.ymgme.2006.12.001. Epub 2007 Jan 19. Citation on PubMed
• Yu Y, Panhuysen C, Kranzler HR, Hesselbrock V, Rounsaville B, Weiss R, Brady K, Farrer LA, Gelernter J. Intronic variants in the dopa decarboxylase (DDC) gene are associated with smoking behavior in European-Americans and African-Americans. Hum Mol Genet. 2006 Jul 15;15(14):2192-9. doi: 10.1093/hmg/ddl144. Epub 2006 Jun 1. Citation on PubMed
• Zhang H, Ye Y, Wang X, Gelernter J, Ma JZ, Li MD. DOPA decarboxylase gene is associated with nicotine dependence. Pharmacogenomics. 2006 Dec;7(8):1159-66. doi: 10.2217/14622416.7.8.1159. Citation on PubMed