Pharmacological and genetic studies suggest the importance of the dopaminergic, serotonergic, and noradrenergic systems in the pathogenesis of
attention deficit hyperactivity disorder (
ADHD). Monoamine
oxidases A and B (
MAO-A and
MAO-B) degrade
biogenic amines such as
dopamine and
serotonin and thereby control the levels of these
neurotransmitters in the central nervous system. We examined four polymorphisms in the
MAO-A gene (30 bp promoter VNTR, CA microsatellite in intron 2, 941G/T SNP in exon 8, and A/G SNP in intron 12) as well as two markers in the
MAO-B gene (CA microsatellite in intron 2 and T/C SNP in intron 13) for association with
ADHD in an Irish sample of 179 nuclear families. TDT analysis of the examined
MAO-A markers revealed a significant association of the more active
MAO-A 941G allele with the disorder (chi2 = 5.1, P = 0.03, OR = 1.7). In addition, haplotype analysis revealed a significantly increased transmission of a haplotype consisting of the shorter allele of the promoter VNTR (allele 1), the 6-repeat allele of the CA microsatellite and the G-allele of the 941G/T SNP (famhap global statistic 34.54, P = 0.01) to
ADHD cases. No significant distortion in the number of transmitted alleles was observed between the two examined
MAO-B polymorphisms and
ADHD. These findings suggest the importance of the 941G/T
MAO-A polymorphism in the development of
ADHD at least in the Irish population.