Polymorphisms in the glutamate decarboxylase 1 gene associated with heroin dependence

W. Wu; Y.S. Zhu; S.B. Li

doi:10.1016/j.bbrc.2012.04.112

Polymorphisms in the glutamate decarboxylase 1 gene associated

with heroin dependence

W. Wu

a,b,1

, Y.S. Zhu

a,b,c,

⇑

,1

, S.B. Li

a,b,

⇑

a

Department of Forensic Science, School of Medicine, Xi’an Jiaotong University, Xi’an, Shannxi, PR China

b

Key Laboratory of Ministry of Public Health for Forensic Science, Xi’an, Shannxi, PR China

c

Key Laboratory of Fertility Preservation and Maintenance, Ningxia Medical University, Ministry of Education, Ningxia, Yinchuan, PR China

article info

Article history:

Received 7 April 2012

Available online 30 April 2012

Keywords:

Glutamic acid decarboxylase gene 1

Single nucleotide polymorphisms

Heroin dependence

abstract

The GAD1 gene encodes the 67-kDa glutamic acid decarboxylase isoform (GAD67), the rate-limiting

enzyme responsible for

c

-aminobutyric acid (GABA) biosynthesis from glutamic acid, and may be

involved in the development of drug dependence. To identify markers contributing to the genetic suscep-

tibility to heroin dependence, this study examined the potential association between heroin dependence

and 15 single nucleotide polymorphisms (SNPs, rs1978340, rs3762556, rs3791878, rs3749034,

rs11542313, rs2241165, rs2241164, rs769407, rs3749033, rs16858977, rs701492, rs16858988,

rs4668331, rs7578661, rs769395) of GAD1 gene using the MassARRAY system. Participants included

370 heroin-dependent subjects and 389 healthy controls. The allelic or genotypic frequencies of the

rs1978340 (promoter region), rs3791878 (promoter region), and rs11542313 (exon 3) polymorphisms

in heroin addicts were signiﬁcantly different from those in healthy controls. Strong linkage disequilib-

rium was observed in two blocks (D

0

> 0.9). Signiﬁcantly more C-C-C-C-A haplotypes (p = 0.0053 after

Bonferroni correction) and signiﬁcantly fewer T-C-A-C-A haplotypes (p = 0.0003 after Bonferroni correc-

tion) were found in heroin dependent subjects. These ﬁndings point to a role for GAD1 polymorphism in

heroin dependence among Han Chinese, and may be informative for future genetic or neurobiological

studies on heroin dependence.

1. Introduction

Heroin addiction is a chronic, relapsing brain disease that is

characterized by drug dependence, tolerance, compulsive seeking,

and use despite harmful consequences. As with other types of sub-

stance abuse, genetic predisposition has been shown as a potential

risk factor in heroin dependence [1]. Family, adoption, and twin

studies have consistently demonstrated a substantial genetic inﬂu-

ence on the development of drug addiction, with inherited risk esti-

mates in the range of 40–60% [2,3]. Other studies have suggested

that polymorphisms in the glutamic acid decarboxylase gene 1

(GAD1) may relate to addiction to drugs including heroin [4,5].

Glutamic acid decarboxylase (GAD) is the rate-limiting enzyme

in the conversion of glutamate to GABA (11). Two isoforms of GAD

have been identiﬁed, GAD1 and GAD2, which previously were

called GAD67 and GAD65, respectively. GAD1 is involved in cyto-

solic GABA synthesis and is responsible for maintaining basal GABA

levels, whereas GAD2 is predominately involved in synaptosomal

GABA release, and can be rapidly activated when there is high de-

mand for GABA [6]. Rodent studies suggest that knockout of GAD1

(which is important in maintaining GABA levels in the brain) is

usually lethal, while knockout of GAD2 has no effect on brain GABA

levels [4,7,8], suggesting that GAD1 is the primary rate-limiting en-

zyme regulating GABA levels under normal conditions. Thus, regu-

lation of GAD1 expression may exert a more profound effect on

GABA homeostasis and, possibly, be more sensitive to exogenous

agents. Several studies have shown that chronic administration

of drugs of abuse, such as alcohol [9], methamphetamine [10],

cocaine [11], nicotine [12], and amphetamine [13] alters the

activity of GAD1 in the brain, suggesting that the GAD1 gene is

an excellent candidate for addiction disorders.

Alcohol dependence and heroin dependence have been

associated with polymorphisms in GAD1. Loh et al. examined the

association of nine single nucleotide polymorphisms (SNPs) for

GAD1 and three SNPs for GAD2 with alcoholism in 140 alcoholic

cases and 146 controls in Han Taiwanese [14]. They found evidence

of an association of alcohol dependence (AD) with GAD1 but not

GAD2. We are aware of only one published report examining the

association of GAD1 with heroin dependence in humans. Levran

et al. have performed a case–control association analysis of 1350

variants of 130 genes and found experiment-wise signiﬁcant asso-

http://dx.doi.org/10.1016/j.bbrc.2012.04.112

⇑

Corresponding authors. Address: Department of Forensic Science, School of

Medicine, Xi’an Jiaotong University, Xi’an 710061, PR China. Fax: +86 029

82655113.

E-mail addresses: zhuyongsheng3000@yahoo.com.cn (Y.S. Zhu), shbinlee@

mail.xjtu.edu.cn (S.B. Li).

1

The ﬁrst two authors contribute equally to this study/work.

Biochemical and Biophysical Research Communications 422 (2012) 91–96

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Biochemical and Biophysical Research Communications

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Polymorphisms in the glutamate decarboxylase 1 gene associated with heroin dependence

Wu, W.; Zhu, Y.S.; Li, S.B.

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