Association Between Novelty Seeking andDopamine Receptor D4 (DRD4) Exon IIIPolymorphism in Japanese Subjects

Midori Tomitaka,* Shin-ichiro Tomitaka, Yoshiko Otuka, Keiko Kim, Hideyuki Matuki,Kaoru Sakamoto, and Akemi TanakaDepartment of Psychiatry, Tokyo Women’s Medical College, Japan

In this study, we investigated the associa-tion between dopamine receptor D4 (DRD4)exon III polymorphism and novelty seekingin 69 Japanese women. The group of sub-jects with long allele (≥≥≥5 repeats) exhibitedsignificantly elevated novelty seekingscores in comparison with subjects lackingthe long allele. By contrast, the scores forharm avoidance, reward dependence, andpersistence were statistically indistinguish-able in the two group of subjects. With re-gard to the subscales of novelty seeking, thescores for exploratory excitability and ex-travagance were significantly higher in sub-jects with the long allele than in subjectslacking the long allele. However, no signifi-cant associations with impulsiveness or dis-orderliness were recognized. Our resultssuggest that although long alleles of thepolymorphic exon III repeats are low in theJapanese population, there is an associationbetween long alleles of DRD4 exon III poly-morphism and novelty seeking. Am. J. Med.Genet. (Neuropsychiatr. Genet.) 88:469–471,1999. © 1999 Wiley-Liss, Inc.

KEY WORDS: dopamine receptor D4; tem-perament and character in-ventory; novelty seeking;Japanese

INTRODUCTION

Human personality traits are partially determinedby genetic factors. A decade ago, Cloninger [1987] pos-tulated the existence of the heritable behavioral trait of

novelty seeking, which is hypothesized to be a heritabletendency toward intense exhilaration and reflectsvariation in the dopaminergic system. Ebstein et al.[1996] and Benjamin et al. [1996] reported significantassociations between the long repeat polymorphism ofthe dopamine receptor D4 (DRD4) and the personalitytrait of novelty seeking. A number of genetic associa-tion studies have been conducted to obtain further con-firmation of the association. Some of the subsequentstudies did not replicate these initial findings [Mal-horta et al., 1996; Jonsson et al., 1997; Vandenbergh etal., 1997; Sullivan et al., 1998;], whereas other re-searchers reported additional evidence for the associa-tion between this polymorphism and novelty seeking[Ebstein et al., 1997; Ono et al., 1997]. It remains to beelucidated whether this polymorphism participates inthe determination of this personality dimension.

Recently, Ebstein et al. [1997] reported that the fail-ure to confirm this association is possibly explained bydifferences in demographic and ethnic structure of sub-sequent studies. They suggested that, since the esti-mated effect size of the DRD4 on novelty seeking issmall and explains only 3–4% of the total variance, thenoise generated by demographic or methodological dif-ferences may be sufficient to obscure the weak effect ofthis gene on novelty seeking. With regard to ethnicstructure, there is a diversity of allele frequency of thispolymorphism among different ethnic populations[Chang et al., 1996]. To clarify these problems, furtherstudies are needed. In the present study, we investi-gated the association between novelty seeking andDRD4 gene polymorphism among a sample from theJapanese population, which has relatively minimizeddemographic, cultural, and ethnic differences amongsubjects.

MATERIALS AND METHODSSubjects

Normal volunteers were recruited from medical stu-dents and hospital residents from the Tokyo Women’sMedical College Hospital. Volunteers gave informedconsent and the protocol was approved by the EthicsCommittee of Tokyo Women’s Medical Hospital. Theywere all unrelated Japanese (69 females) and theirmean age was 25.0 ± 2.4 (mean ± SD) years.

Contract grant sponsor: Ministry of Education, Science, andCulture of Japan.

*Correspondence to: Midori Tomitaka, Neurology Service 127,Veterans Affairs Medical Center, 4150 Clement Street, San Fran-cisco, CA 94121. E-mail: mtomita@itsa.ucsf.edu

Received 28 July 1998; Accepted 9 November 1998

American Journal of Medical Genetics (Neuropsychiatric Genetics) 88:469–471 (1999)

© 1999 Wiley-Liss, Inc.

Genotyping

Venous blood was drawn and genomic DNA was iso-lated from lymphocytes. Genomic DNA was analyzedby the method of Nanko et al. [1993]. Polymerase chainreaction (PCR) amplification was done in 20mL reac-tion buffer containing 50 mmol/L KCl, 10 mmol/L Tris-HCl (pH 8.3),1.5 mmol/L MgCl2, 0.001% gelatin, and10% dymethyl-sulphoxide. The reaction contained 20ng genomic DNA; 25 mmol/L of each primer (58 AG-GTGGCACGTCGCGCCAAGCTGCA38 sense, 58 TCT-GCGGTGGAGTCTGGGGTGGGAG38 antisense); 1unit Taq polymerase; 200 mmol/L each of dATP, dTTP,and dCTP; and 200 mmol/L 5-deazaguanosine was usedin place of dGTP. PCR conditions were initial denatur-ing at 95°C for 5 min, followed by 40 cycles (annealing65°C, 1 min; extension 72°C, 1 min; denaturing 95°C,30 s), and final elongation at 72°C for 5 min. WholePCR reactions were loaded on a 2% agarose gel, elec-trophoresed, and stained with ethidium bromide.

Personality Test

We used the Japanese version of the Temperamentand Character Inventory (TCI), which is a 226-itemquestionnaire measuring seven dimensions of person-ality. The reliability and validity of the Japanese ver-sion of the TCI have already been verified in Japan[Kijima et al., 1996; Ono et al., 1997]. Differences be-tween genotype group for each TCI score were deter-mined by t-test.

RESULTS

As shown in Table I, allele frequencies were similarto those observed in other samples from the Japanesepopulation [Nanko et al., 1993; Chang et al., 1996; Onoet al., 1997]. The most abundant allele was the 4 repeatallele followed by the 2 repeat allele, whereas the 6repeat and 7 repeat alleles were extremely low. Weclassified genotypes into two groups: those containingonly the short (S) DRD4 alleles with 2 to 4 exon IIIrepeats (n 4 56) and those containing one or two copiesof the long (L) DRD4 alleles with 5 to 7 exon III repeats(n 4 13) [Ono et al.,1997]. The t-test revealed that thegroup of subjects with the long allele exhibited signifi-

cantly elevated novelty seeking scores in comparisonwith subjects lacking the long allele (Table II). In con-trast, the scores for harm avoidance, reward depen-dence, and persistence were statistically indistinguish-able in the two groups of subjects. In addition, weevaluated the novelty seeking subscale between thetwo groups. Table II shows that the scores for explor-atory excitability (NS1) and extravagance (NS3) weresignificantly higher in subjects with the long allelethan in subjects with the short allele. However, no sig-nificant associations with impulsiveness (NS2) or dis-orderliness (NS4) were recognized.

DISCUSSION

There is a controversy over the association betweenthe long alleles of the polymorphic exon III repeat se-quence of DRD4 and novelty seeking. Although somereports [Ebstein et al., 1997; Ono et al.,1997] replicatedinitial findings, several studies [Malhorta et al., 1996;Jonsson et al., 1997; Vandenbergh et al., 1997; Sullivanet al., 1998] did not. In our study, we confirmed theassociation between the long alleles of the polymorphicexon III repeat sequence of DRD4 and the overall di-mension of novelty seeking at least in a sample fromthe Japanese population. The demographic and ethnicstructure of our study may account for the replicationof initial findings. As Ebstein et al. [1997] reported, thenoise generated by demographic or methodological dif-ferences may be sufficient to obscure the weak effect ofthis gene on personality. Therefore, we examined lim-ited demographic, ethnic, and cultural subjects. First,our study was limited to women of similar age (25.0 ±2.4). It is possible that women show a greater tendencyfor this association than men. In fact, the associationreported by Ono et al. [1997] was in women, and fur-ther study by Ebstein et al. [1997] shows significantassociation in women not in men. In addition, we usedmedical school students and hospital residents as sub-jects. It is possible that the choice of the subjects withalmost the same vocation may contribute to minimizethe effect of sociocultural factors that effect personal-ity. With regard to ethnic factors, it is intriguing thatalthough the 7 repeat alleles are rare in Japanesepopulations, two Japanese studies including oursfound significant association between novelty seekingand the long allele of this polymorphism.

The discovery of the dopamine receptor D4 polymor-phism led many researchers to investigate the associa-tions between these alleles and mental disorders [VanTol et al., 1992]. Although some findings are controver-sial, there have been reports of associations between

TABLE I. Allele Frequencies for Exon III Polymorphismof DRD4

Allele repeats 2 3 4 5 6 7

N (total 4 138) 19 1 105 9 1 3Percentage 13.8% 0.7% 76.1% 6.5% 0.7% 2.2%

TABLE II. TCI Personality Score in Subjects Group Sorted by DRD4 Allele*

Noveltyseeking

Harmavoidance

Rewarddependence Persistence NS1 NS2 NS3 NS4

S (56)a 21.82 17.98 16.20 3.93 5.73 5.04 6.11 4.95L (13)b 25.85 17.69 16.39 3.39 7.23 6.08 7.15 5.39P value 0.014 ns ns ns 0.025 ns 0.011 ns

*TCI scores are reported as mean scores ± SD; NS1, exploratory vs. rigidity; NS2, impulsiveness vs.reflection; NS3, extravagance vs. reserve; NS4, disorderliness vs. regimentation.aS, genotypes with only the short DRD4 alleles.bL, genotypes with one copy of the long alleles.

470 Tomitaka et al.

this polymorphism and alcoholism [George et al., 1993;Muramatsu et al., 1996; Geijer et al., 1997], opiateabuse [Li et al., 1996; Kotler et al., 1997], and attentiondeficit hyperactivity syndrome [LaHoste et al., 1996]. Itis interesting that patients with these mental disordershave been shown to exhibit higher novelty seekingscores than normal controls [Bardo et al., 1996; Galenet al., 1996; Downey et al., 1997].

In summary, we replicated an association betweenthe long alleles of the polymorphism of exon III of theDRD4 and the personality traits of novelty seeking in aJapanese sample. Considering the reports that haveconfirmed the initial findings by Ebstein et al. and Ben-jamin et al., it is suggested that demographic andmethodological structure is important to replicate thisassociation.

ACKNOWLEDGMENTS

We thank Nobuhiro Kijima for his advice for theJapanese version of TCI and Bryan K. Tolliver for help-ful comments on this manuscript.

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