Table 1.

Key findings from molecular genetic studies of ADHD

Gene	Type of studies	Evidence	Function
DRD4 7-repeat allele	Association studies and meta-analysis47	Consistent	G protein-coupled receptor that binds dopamine
DRD5 148-bp microsatellite repeat	Association studies and meta-analysis47	Consistent	G protein-coupled receptor that binds dopamine
DAT1 480-bp VNTR	Association studies and meta-analysis47	Mixed evidence	Membrane-spanning protein that removes dopamine from the synaptic cleft
COMT Val158Met	Association studies and meta-analysis47	Not associated with ADHD but associated with CD in ADHD	Enzyme catalyzing the degradation of dopamine, adrenaline and noradrenaline
CDH13	Genome-wide association studies65,67	Overlap from GWAS studies but needs replication	Cell-cell adhesion protein and regulator of neural cell growth
GFOD1	Genome-wide association studies65,67	Overlap from GWAS studies but needs replication	Predicted to be involved in electron transport and metabolic processes
TLL	Genome-wide association studies63,65,67	Overlap from GWAS studies but needs replication	Metalloproteases that cleave collagen, expressed in brain

Abbreviations: GWAS, genome-wide association study; DRD4, dopamine D4 receptor gene; DRD5, dopamine D5 receptor gene; DAT1, dopamine transporter gene; COMT, catechol-o-methyltransferase; CDH13, cadherin 13; GFOD1, glucose-fructose oxidoreductase-domain containing 1; TLL, tolloid-like genes.