A dopamine transporter gene functional variant associated with cocaine abuse in a Brazilian sample

doi:10.1073/pnas.0504789103

A dopamine transporter gene functional variant associated with cocaine abuse in a Brazilian sample

^aMedical Research Council Social Genetic and Developmental Psychiatry Research Centre,
^gDivision of Psychological Medicine, and
^hNational Addiction Centre, Institute of Psychiatry, King’s College London, London SE5 8AF, United Kingdom;
^bInstitute of Psychiatry, University of São Paulo Medical School, 01422-000 São Paulo, Brazil;
^dDepartments of Physiology and
^eHuman Anatomy and Cell Biology, School of Biomedical Sciences, University of Liverpool, Liverpool L69 3BX, United Kingdom;
^fUnit of Drug and Alcohol Research, Department of Psychiatry, Federal University of São Paulo, 04023-900 São Paulo, Brazil;
ⁱDepartment of Psychiatry, University of California at San Diego, La Jolla, CA 92093; and
^jDepartment of Psychiatry, San Diego Veterans Affairs Healthcare System, La Jolla, CA 92093

Edited by Susan G. Amara, University of Pittsburgh School of Medicine, Pittsburgh, PA, and approved January 17, 2006
↵ ^cC.G. and M.H. contributed equally to this work. (received for review June 8, 2005)

Abstract

The dopamine (DA) transporter DAT1 is a major target bound by cocaine in brain. We examined the influence of functional genetic variants in DAT1 on cocaine addiction. Repeat polymorphisms, including a 30-bp variable-number tandem repeat (VNTR) in intron 8 (Int8 VNTR) with two common alleles, were genotyped in cocaine-dependent abusers (n = 699) and in controls with no past history of drug abuse (n = 866) from São Paulo, Brazil. Positive association was observed with allele 3 of the Int8 VNTR and cocaine abuse (allele odds ratio = 1.2, 95% confidence interval = 1.01–1.37, P = 0.036; 3/3 homozygote odds ratio = 1.45, 95% confidence interval = 1.18–1.78, P = 0.0008). Population stratification was assessed and did not affect the results. Haplotypic analyses using additional polymorphisms indicated that the Int8 VNTR is responsible for the observed association. Functional analyses in reporter–gene constructs, demonstrated that allele 3 mediates significant (P < 0.05) but small reduced expression compared with the “protective” allele 2. This difference increased when 1 and 10 μM cocaine was added to the cell culture (≈40% reduction of the 3 allele expression versus the 2 allele). The 3 allele also demonstrated ≈3-fold-increased expression over the 2 allele in response to KCl plus forskolin challenge. We demonstrate a robust association between cocaine dependence and a VNTR allele in SLC6A3, conferring a small but detectible effect, and we show that this VNTR may be functional. This study suggests that DAT1 gene variation may play a role in cocaine dependence etiology.

Footnotes

^kTo whom correspondence should be addressed at:
Section of Genetics, Medical Research Council Social Genetic and Developmental Psychiatry Research Centre, Institute of Psychiatry, Kings College London, Room 222, Social, Genetic, and Developmental Psychiatry Centre, P.O. Box 81, London SE5 8AF, United Kingdom.
E-mail: g.breen{at}iop.kcl.ac.uk
Author contributions: R.L., D.C., I.C., T.G., J.K., P.A., A.C., J.P.Q., H.V., and G.B. designed research; C.G., M.H., K.H., R.L., N.A., C.O., A.C., H.V., and G.B. performed research; I.C., V.J.B., P.A., and J.P.Q. contributed new reagents/analytic tools; C.G., M.H., K.H., N.A., C.O., J.P.Q., and G.B. analyzed data; and C.G., M.H., D.C., I.C., R.M.M., J.P.Q., H.V., and G.B. wrote the paper.
Conflict of interest statement: No conflicts declared.
This paper was submitted directly (Track II) to the PNAS office.
Abbreviations:

DA,

dopamine;

DAT,

DA transporter;

VNTR,

variable-number tandem repeat;

SNP,

single-nucleotide polymorphism;

LD,

linkage disequilibrium;

Int8,

intron 8;

LRT,

likelihood ratio test.