Linkage of the dopamine D4 receptor gene and attention-deficit/hyperactivity disorder.
OBJECTIVE
There is considerable evidence supporting a genetic component in the etiology of attention-deficit/hyperactivity disorder (ADHD). Because stimulant medications act primarily on the dopaminergic system, dopamine system genes are prime candidates for genetic susceptibility factors for ADHD. Previous studies by several groups have observed a significant association of ADHD and an allele with 7 copies of the 48 base pair repeat in the third exon of the dopamine D4 receptor.


METHODS
The authors sought to replicate these previous findings by collecting an independent sample of families from Toronto, Ontario, Canada, and confirming this finding in an expanded sample of ADHD families collected from Irvine, California. Using the transmission disequilibrium test (TDT), the authors tested for biased transmission of the 7-repeat allele at the exon III polymorphism of the dopamine D4 receptor locus in these samples of ADHD subjects.


RESULTS
Biased transmission of the 7-repeat allele from parents to ADHD probands and their affected siblings was observed in the 2 new samples of families collected in Toronto and Irvine (TDT chi2 = 2.711, 1 df, one-sided p value = .050) and for these samples combined with the 52 families previously reported from Irvine (TDT chi2 = 6.426, 1 df, one-sided p value = .006).


CONCLUSIONS
The results of this study further support the possibility of a role of the dopamine D4 receptor locus in ADHD.
Sunohara
G A
GA
Neurogenetics Section, The Centre for Addiction and Mental Health, Toronto, Ontario, Canada.
Roberts
W
W
Malone
M
M
Schachar
R J
RJ
Tannock
R
R
Basile
V S
VS
Wigal
T
T
Wigal
S B
SB
Schuck
S
S
Moriarty
J
J
Swanson
J M
JM
Kennedy
J L
JL
Barr
C L
CL
D000293:Adolescent; D001289:Attention Deficit Disorder with Hyperactivity / Q000453:epidemiology / Q000235:genetics*; D002140:California / Q000453:epidemiology; D002648:Child; D008040:Genetic Linkage; D020022:Genetic Predisposition to Disease; D006801:Humans; D009864:Ontario / Q000453:epidemiology; D011110:Polymorphism, Genetic; D017448:Receptors, Dopamine D2 / Q000235:genetics*; D050638:Receptors, Dopamine D4; D012306:Risk
C493599:DRD4 protein, human; D017448:Receptors, Dopamine D2; D050638:Receptors, Dopamine D4