Dopa decarboxylase gene polymorphisms and attention deficit hyperactivity disorder (ADHD): No evidence for association in the Irish population

Z. Hawi, D. Foley, A. Kirley, M. McCarron, M. Fitzgerald, M. Gill

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Dopa decarboxylase (DDC) is an enzyme which catalyses the decarboxylation of both dopa to dopamine and L-5 hydroxytryptophan to serotonin. Both catecholamines are major neurotransmitters of the mammalian nervous system. It has been suggested that genes involved in the dopaminergic system play a primary role in predisposing to attention deficit hyperactivity disorder (ADHD). In this study, the 4-bp insertion/deletion variant mapped to the first neuronally expressed exon 1 at the dopa decarboxylase gene and two microsatellite markers flanking the gene were investigated for possible association with ADHD. Using HHRR, we observed an increased transmission (though not significant) of the 4-bp insertion (allele 1) to ADHD cases (X2 = 2.72, P = 0.1, RR = 1.25). However marginally significant excess transmission of allele 10 (213 bp) of the 3′ microsatellite D7S2422 (∼0.75 cM distal to dopa decarboxylase gene) was found (X2 = 4.2, P = 0.04, RR=1.48). Interestingly, a haplotype containing both alleles is transmitted more frequently (X2 = 5, P = 0.025). Analysing data by the sex of transmitting parent showed a greater relative risk for paternal transmission of the 4-bp insertion allele and allele 10 of the D7S2422 (RR = 1.48 and 1.63 respectively). This provides preliminary evidence that this locus or a closely mapped DNA variant may be involved in the genetic susceptibility to ADHD. However, further studies are required to either confirm or refute these observations.

Original languageEnglish
Pages (from-to)420-424
Number of pages5
JournalMolecular Psychiatry
Issue number4
Publication statusPublished - 2001
Externally publishedYes


  • Association
  • Attention deficit hyperactivity disorder (ADHD)
  • Dopa decarboxylase
  • Dopamine
  • Haplotype based haplotype relative risk (HHRR)

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