- Email: [email protected]
No association between the TPH A218C polymorphism and personality traits in Japanese healthy subjects
Progress in Neuro-Psychopharmacology & Biological Psychiatry 31 (2007) 395 – 398 www.elsevier.com/locate/pnpbp
No association between the TPH A218C polymorphism and personality traits in Japanese healthy subjects Akihito Suzuki ⁎, Takashi Fukasawa, Hiroaki Shiraishi, Genki Ishii, Shingo Oshino, Toshiaki Aoshima, Koichi Otani Department of Psychiatry, Yamagata University School of Medicine, 2-2-2 Iidanishi, Yamagata-city, Yamagata 990-9585, Japan Received 22 March 2006; received in revised form 11 October 2006; accepted 16 October 2006 Available online 20 November 2006
Abstract It has been suggested that the central serotonergic activity is implicated in personality traits. Tryptophan hydroxylase (TPH) is the rate-limiting enzyme in serotonin synthesis. In the present study, the association between the TPH A218C polymorphism and personality traits assessed by the Temperament and Character Inventory (TCI) was examined in 345 Japanese healthy subjects. The TPH A218C polymorphism was determined by a PCR-RFLP method. There were no significant differences in the seven dimension scores of TCI among the A/A, A/C, and C/C genotype groups by the one-way ANOVA. There was a significant negative correlation between age and the NS scores. Females showed significantly higher scores of HA, RD, and ST, and significantly lower scores of SD than males. The multiple regression analysis using age, gender, and the TPH genotype as independent variables also showed no significant association between any dimension score and the genotype. The present study thus suggests that the TPH A218C polymorphism does not affect personality traits in Japanese healthy subjects. © 2006 Elsevier Inc. All rights reserved. Keywords: Healthy subjects; Personality; TCI; TPH A218C polymorphism
1. Introduction From biological perspectives, Cloninger et al. (1993) developed the Temperament and Character Inventory (TCI) to evaluate personality traits. The TCI has four temperament dimensions, i.e., novelty seeking (NS), harm avoidance (HA), reward dependence (RD), and persistence, and three character dimensions, i.e., self-directedness (SD), cooperativeness (C), and self-transcendence (ST). NS is the activation of behavior in response to novelty and signals of reward or relief of punishment, HA is the inhibition of behavior in response to signals of punishment or non-reward, RD is the maintenance of
Abbreviations: C, cooperativeness; CSF, cerebrospinal fluid; HA, harm avoidance; 5-HIAA, 5-hydroxyindolacetic acid; 5-HT, 5-hydroxytryptamine; NS, novelty seeking; P, persistence; RD, reward dependence; SD, selfdirectedness; ST, self-transcendence; TCI, Temperament and Character Inventory; TPH, tryptophan hydroxylase. ⁎ Corresponding author. Tel.: +81 23 628 5322; fax: +81 23 628 5325. E-mail address: [email protected] (A. Suzuki). 0278-5846/$ - see front matter © 2006 Elsevier Inc. All rights reserved. doi:10.1016/j.pnpbp.2006.10.003
behavior which was previously rewarded, and P is the perseveration with behavior despite frustration and fatigue. SD is the concept of the self as an autonomous individual, C is the concept of the self as an integral part of humanity or society, and ST is the concept of the self as an integral part of the universe and its source. Cloninger et al. (1993) hypothesized that NS, HA, and RD were related to dopamine, serotonin (5-hydroxytryptamine: 5-HT), and norepinephrine, respectively. There are many studies suggesting disturbances of the 5-HT system in psychiatric disorders (Asberg, 2004). One of the most consistent findings in these studies is low concentrations of the 5-HT metabolite, 5-hydroxyindolacetic acid (5-HIAA), in cerebrospinal fluid (CSF) of suicide attempters (Asberg, 2004). 5-HT is synthesized from tryptophan in two steps, i.e., tryptophan is firstly hydroxylated to 5-hydroxytryptophan by tryptophan hydroxylase (TPH), and then 5-hydroxytryptophan is decarboxylated to 5-HT by aromatic amino acid decarboxylase (Cooper et al., 2003). Therefore, TPH is the rate-limiting enzyme in 5-HT synthesis. The TPH gene is mapped on chromosome 11p15.3–p14, and contains an A to C transversion
396
A. Suzuki et al. / Progress in Neuro-Psychopharmacology & Biological Psychiatry 31 (2007) 395–398
polymorphism at nucleotide 218 in intron 7 (A218C) (Nielsen et al., 1994). The A allele of this polymorphism was reported to be associated with low CSF concentrations of 5-HIAA in healthy subjects (Jonsson et al., 1997) and violent alcoholic offenders (Nielsen et al., 1994), and high TPH immunoreactivity in postmortem brain of suicide victims and control samples (Ono et al., 2002). Therefore, the TPH polymorphism may be implicated in psychiatric disorders such as suicidal behavior. The TPH A218C polymorphism was originally suggested to be associated with aggressive–impulsive behaviors such as violence and suicide attempt (Nielsen et al., 1994). The meta-analysis confirmed the association between the A allele and suicidal behavior (Bellivier et al., 2004; Rujescu et al., 2003). Meanwhile, risk of suicide attempt in community-based sample has been related to personality traits of HA and SD (Grucza et al., 2005). These discussions suggest the possibility that the TPH A218C polymorphism affects suicidality via some personality traits, especially HA and SD. However, Ham et al. (2004) have shown that this polymorphism is not related to the TCI dimensions in healthy subjects. This negative result is rather surprising in light of the associations between TPH and suicidality and between suicidality and personality traits. Therefore, the present study re-examined the association between the TPH A218C polymorphism and personality traits assessed by the TCI in Japanese healthy subjects. 2. Methods 2.1. Subjects The subjects were 345 unrelated Japanese who were medical students or the staff of three hospitals. Well-trained psychiatrists confirmed that they did not have any Axis I or II disorders of DSM-IV (American Psychiatric Association, 1994) by interviews. The personality traits of the subjects were assessed by the Japanese version of the TCI, which has been shown to have high reliability (Kijima et al., 1996). The mean (± S.D.) of age was 29.7 (± 9.0) years. One hundred eighty-five subjects were females, and 160 were males. The study protocol was approved by the Ethics Committee of Yamagata University School of Medicine, and all subjects provided written informed consent to participate. 2.2. Genotyping analysis DNA was extracted from peripheral leucocytes using a QIAamp DNA Blood Kit (Qiagen, Tokyo, Japan). The TPH
A218C genotype was determined by the PCR-RFLP method of Bellivier et al. (1998). The PCR was performed using primers (5′-TTC AGA TCC CTT CTA TAC CCC AGA-3′ and 5′-GGA CAT GAC CTA AGA GTT CAT GGC A-3′) in 25 ul volume containing 100 ng of genomic DNA, 0.5 uM of each primer, 200 uM of each dNTP, 1.5 mM of MgCl2, and 1.25 U of HotStar Taq DNA polymerase (Qiagen, Tokyo, Japan). After an initial denaturation step at 95 °C for 15 min, 30 cycles were performed at 95 °C for 0.5 min, 53 °C for 0.5 min, and 72 °C for 0.5 min. Finally, an elongation step was performed at 72 °C for 10 min. Five microliters of the PCR product was digested overnight with 7.5 U of Xsp I (Takara Bio Inc., Otsu, Japan). The fragments were electrophoresed on a 2% of agarose gel with ethidium bromide staining and visualized using ultraviolet light. After digestion, the A allele gives 860- and 58-bp fragments, and the C allele gives 615-, 245-, and 58-bp fragments. Genotyping accuracy was checked by random replicate analyses of 10% of the subjects, with complete concordance. 2.3. Statistical analysis The difference in each dimension score among the subjects with A/A, A/C, and C/C genotypes was tested by the one-way ANOVA followed by Tukey test. The correlation between age and each dimension score was tested by the linear regression analysis. The Student t-test was used for the comparison of each dimension score between males and females. The multiple regression analysis was performed with each dimension score as a dependent variable, and age, gender, and the TPH genotype as independent variables. A dummy variable was used for gender (female = 0, male = 1). For the TPH genotype, two dummy variables, X1 and X2, were used; if the genotype was the A/A, both X1 and X2 were coded as 0, if the genotype was the A/C, X1 and X2 were coded as 1 and 0, respectively, and if the genotype was the C/C, X1 and X2 were coded as 0 and 1, respectively. All statistical analyses were performed by SPSS 13.0 J for Windows (SPSS Japan, Inc.), and a p value of less than .05 was regarded as significant. 3. Results In the present sample, 93 subjects had the A/A genotype, 177 had the A/C genotype, and 75 had the C/C genotype. The TPH genotype distribution in the total subjects was in the Hardy– Weinberg equilibrium. In the one-way ANOVA, there were no significant differences in seven dimension scores among the three genotype groups (Table 1).
Table 1 Seven TCI dimension scores in the three TPH A218C genotype groups
A/A A/C C/C p
N
NS
HA
RD
P
SD
C
ST
93 177 75
21.2 ± 5.4 21.9 ± 4.8 20.9 ± 5.3 .259
18.4 ± 6.4 19.9 ± 5.7 19.5 ± 5.9 .123
16.5 ± 4.0 16.5 ± 3.4 16.0 ± 3.3 .598
4.2 ± 1.8 4.1 ± 1.8 4.1 ± 1.7 .900
28.7 ± 6.5 27.6 ± 6.6 27.5 ± 6.7 .357
28.9 ± 6.0 28.5 ± 4.6 28.1 ± 4.2 .528
10.2 ± 5.1 9.3 ± 4.6 8.9 ± 4.8 .215
TCI, Temperament and Character Inventory; TPH, tryptophan hydroxylase; NS, novelty seeking; HA, harm avoidance; RD, reward dependence; P, persistence; SD, self-directedness; C, cooperativeness; ST, self-transcendence. The data on the table indicate mean ± S.D.
A. Suzuki et al. / Progress in Neuro-Psychopharmacology & Biological Psychiatry 31 (2007) 395–398 Table 2 Multiple regression analyses of seven TCI dimension scores by age, gender, and the TPH A218C genotype NS
HA
Age − .178 Gender .020 TPH A218C .076 genotype X1 X2 − .025 Multiple correlation .203 coefficient p .006
b
RD
P
SD
C
ST
.080 −.028 − .084 −.022 .032 − .051 − .122a −.151 − .039 .178b − .048 − .126 .124 .002 .026 −.077 − .050 − .092 .068 .190 .014
−.062 − .018 −.062 .160 .100 .197 .066
.486
.009
− .075 − .116 .086 .160 .636
.065
TCI, Temperament and Character Inventory; TPH, tryptophan hydroxylase; NS, novelty seeking; HA, harm avoidance; RD, reward dependence; P, persistence; SD, self-directedness; C, cooperativeness; ST, self-transcendecne, X1 and X2; dummy variables for TPH genotype. The figures on the table indicate β. a : p b .05, b: p b .01.
There was a significant negative correlation between age and the NS scores (r = − .179, p = .001). Females showed significantly higher scores of HA (female vs. male: 20.2 ± 5.9 vs. 18.5 ± 6.0, p = .011), RD (16.9 ± 3.3 vs. 15.8 ± 3.7, p = .007), and ST (10.0 ± 4.7 vs. 8.9 ± 4.8, p = .036), and significantly lower scores of SD (26.7 ± 6.5 vs. 29.1 ± 6.5, p = .001) than males. Similarly, the multiple regression analysis also showed that each dimension score was not related to the TPH genotype (Table 2). The statistical power for one-way ANOVA in the present sample size (n = 345) was 0.98 to detect a medium effect size (0.25) at an alpha value of 5% two-tailed (Cohen, 1988). 4. Discussion Originally, Cloninger et al. (1993) proposed that the temperament dimensions are highly heritable and stable throughout life, while the character dimensions are influenced by social learning. However, subsequent reports have demonstrated significant effects of age and gender not only on the character dimensions but also on the temperament dimensions (Cloninger et al., 1994; Duijsens et al., 2000; Pelissolo and Lepine, 2000). For example, Pelissolo and Lepine (2000) reported that NS decreased with aging, while HA, RD, and ST were higher and SD was lower in females. Therefore, age and gender effects should be taken into account in genetic studies on personality. However, these effects were not taken into account in the study by Ham et al. (2004), and this together with the small number of subjects (n = 146) might be the causes of their negative result. In the present study, there was no significant association between seven dimension scores of the TCI and the TPH genotype by the univariate analysis like in the study by Ham et al. (2004). Contrary to our expectation, even by taking age and gender effects into account in the multiple regression analysis, no significant association appeared between any dimension score and the genotype. The TPH A218C polymorphism is a silent mutation, and is suggested to be in linkage disequilibrium with other polymorphism(s) in the regulatory region of TPH gene (Jonsson et al.,
397
1997; Nielsen et al., 1994; Ono et al., 2002). Rotondo et al. (1999) identified four polymorphisms in the promoter region of TPH gene, which may affect the TPH expression. They reported that one of them, the −6526ANG polymorphism, was in strong linkage disequilibrium with the A218C polymorphism in Finns but not in Italians or American Indians. Therefore, the TPH A218C polymorphism may be associated with psychiatric disorders in some ethnic groups but not in others. In fact, two meta-analyses (Bellivier et al., 2004; Rujescu et al., 2003) have shown that there is an association between the A allele and suicidal attempts in Caucasians, while this association is unclear in Asians. To date, the relationship between the TPH A218C polymorphism and personality has been examined in Asians only, i.e., Koreans (Ham et al., 2004) and Japanese (this study). Therefore, a significant association may be observed in other ethnic groups. There is also the possibility that other genetic polymorphisms conceal the effect of the TPH A218C polymorphism on the TCI dimensions. For example, a recent meta-analysis (Munafo et al., 2005) showed a significant association between the polymorphism of the serotonin transporter linked polymorphic region and HA. To confirm this point, the effect of combinations of the TPH A218C polymorphism with other polymorphisms on the TCI dimensions should be examined in further studies. In the present study, age influenced NS, while gender influenced HA, RD, ST, and SD. The higher NS in younger subjects and higher HA and RD in females observed in the present study have been reported in other studies (Cloninger et al., 1994; Duijsens et al., 2000; Pelissolo and Lepine, 2000) as well. According to Cloninger et al. (1994), high scores of NS are exploratory, curious, impulsive, extravagant, enthusiastic, and disorderly, those of HA are worrying, pessimistic, fearful, doubtful, shy, and fatigable, and those of RD are sentimental, warm, dedicated, attached, and dependent. As suggested by McCrae et al. (2000), adults may become less extraverted as a natural consequence of aging, just as children develop mentally in a fixed order and time course. The higher HA and RD in females may be related to the general tendency that females are more likely to ruminate unhelpfully over psychosocial difficulties, and less likely to have a sense of controlling the world as argued by Rutter et al. (2003). As a limitation of the present study, the subjects were young and the age range was narrow. The present results would have been different if subjects from a wide age range had been included, in the light of the age effects on personality traits (Cloninger et al., 1994; Duijsens et al., 2000; Pelissolo and Lepine, 2000). 5. Conclusion In conclusion, the present study suggests that the TPH A218C polymorphism does not affect personality traits in Japanese healthy subjects. References American Psychiatric Association. Diagnostic and statistical manual of mental disorders. 4th ed. Washington, DC: American Psychiatric Association; 1994.
398
A. Suzuki et al. / Progress in Neuro-Psychopharmacology & Biological Psychiatry 31 (2007) 395–398
Asberg M. Neurotransmitters and suicidal behavior. Ann NY Acad Sci 2004;836:158–81. Bellivier F, Leboyer M, Courtet P, Buresi C, Beaufils B, Samolyk D, et al. Association between the tryptophan hydroxylase gene and manic– depressive illness. Am J Psychiatry 1998;55:33–7. Bellivier F, Chaste P, Malafosse A. Association between the TPH gene A218C polymorphism and suicidal behavior: a meta-analysis. Am J Med Genet 2004;124:87–91. Cloninger CR, Svrakic DM, Przybeck TR. A psychobiological model of temperament and character. Arch Gen Psychiatry 1993;50:975–90. Cloninger CR, Przybeck TR, Svrakic DM, Wetzel RD. The Temperament and Character Inventory (TCI): a guide to its development and use. St Louis, Missouri, USA: Center for Psychobiology of personality; 1994. Cohen J. Statistical power analysis for the behavioral sciences. Hillsdale, New Jersey: Lawrence Erlbaum Associates, Publishers; 1988. Cooper JR, Bloom FE, Roth RH. The biochemical basis of neurophamacology. 8th ed. Oxford: Oxford University Press; 2003. Duijsens IJ, Spinhoven P, Goekoop JG, Spermon T, Eurelings-Bontekoe EHM. The Dutch Temperament and Character Inventory (TCI): dimensional structure, reliability and validity in a normal and psychiatric outpatient sample. Pers Individ Differ 2000;28:487–99. Grucza RA, Przybeck TR, Cloninger CR. Personality as a mediator of demographic risk factors for suicide attempts in a community sample. Compr Psychiatry 2005;46:214–22. Ham BJ, Kim YH, Choi MJ, Cha JH, Choi YK, Lee MS. Serotonergic genes and personality traits in the Korean population. Neurosci Lett 2004;354:2–5. Jonsson EG, Goldman D, Spurlock G, Gustavsson JP, Nielsen DA, Linnoila M, et al. Tryptophan hydroxylase and catechol-O-methyltransferase gene polymorphisms: relationship to monoamine metabolite concentrations in CSF of healthy volunteers. Eur Arch Psychiatry Clin Neurosci 1997;247:297–302.
Kijima N, Saito R, Suzuki M, Yoshino A, Ono Y, Kato M, et al. Cloninger's seven factor model of temperament and character and Japanese version of Temperament and Character Inventory (TCI). Jpn J Psychiatry Diagn 1996;7:379–99 (Japanese). McCrae RR, Costa Jr PT, Ostendorf F, Angleitner A, Hrebickova M, Avia MD, et al. Nature over nurture: temperament, personality, and life span development. J Pers Soc Psychol 2000;78:173–86. Munafo MR, Clark T, Flint J. Does measurement instrument moderate the association between the serotonin transporter gene and anxiety-related personality traits? A meta-analysis. Mol Psychiatry 2005;10:415–9. Nielsen DA, Goldman D, Virkkunen M, Tokola R, Rawlings R, Linnoila M. Suicidality and 5-hydroxyindoleacetic acid concentration associated with a tryptophan hydroxylase polymorphism. Arch Gen Psychiatry 1994;51:34–8. Ono H, Shirakawa O, Kitamura N, Hashimoto T, Nishiguchi N, Nishimura A, et al. Tryptophan hydroxylase immunoreactivity is altered by the genetic variation in postmortem brain samples of both suicide victims and controls. Mol Psychiatry 2002;7:1127–32. Pelissolo A, Lepine JP. Normative data and factor structure of the Temperament and Character Inventory (TCI) in the French version. Psychiatry Res 2000;94:67–76. Rotondo A, Schebel K, Bergen A, Aragon R, Virkkunen M, Linnoila M, et al. Identification of four variants in the tryptophan hydroxylase promoter and association to behavior. Mol Psychiatry 1999;4:360–8. Rujescu D, Giegling I, Sato T, Hartmenn AM, Moller HJ. Genetic variations in tryptophan hydroxylase in suicidal behavior: analysis and meta-analysis. Biol Psychiatry 2003;54:465–73. Rutter M, Caspi A, Moffitt TE. Using sex differences in psychopathology to study causal mechanisms: unifying issues and research strategies. J Child Psychol Psychiatry 2003;44:1092–115.
No association between the TPH A218C polymorphism and personality traits in Japanese healthy subjects Akihito Suzuki ⁎, Takashi Fukasawa, Hiroaki Shiraishi, Genki Ishii, Shingo Oshino, Toshiaki Aoshima, Koichi Otani Department of Psychiatry, Yamagata University School of Medicine, 2-2-2 Iidanishi, Yamagata-city, Yamagata 990-9585, Japan Received 22 March 2006; received in revised form 11 October 2006; accepted 16 October 2006 Available online 20 November 2006
Abstract It has been suggested that the central serotonergic activity is implicated in personality traits. Tryptophan hydroxylase (TPH) is the rate-limiting enzyme in serotonin synthesis. In the present study, the association between the TPH A218C polymorphism and personality traits assessed by the Temperament and Character Inventory (TCI) was examined in 345 Japanese healthy subjects. The TPH A218C polymorphism was determined by a PCR-RFLP method. There were no significant differences in the seven dimension scores of TCI among the A/A, A/C, and C/C genotype groups by the one-way ANOVA. There was a significant negative correlation between age and the NS scores. Females showed significantly higher scores of HA, RD, and ST, and significantly lower scores of SD than males. The multiple regression analysis using age, gender, and the TPH genotype as independent variables also showed no significant association between any dimension score and the genotype. The present study thus suggests that the TPH A218C polymorphism does not affect personality traits in Japanese healthy subjects. © 2006 Elsevier Inc. All rights reserved. Keywords: Healthy subjects; Personality; TCI; TPH A218C polymorphism
1. Introduction From biological perspectives, Cloninger et al. (1993) developed the Temperament and Character Inventory (TCI) to evaluate personality traits. The TCI has four temperament dimensions, i.e., novelty seeking (NS), harm avoidance (HA), reward dependence (RD), and persistence, and three character dimensions, i.e., self-directedness (SD), cooperativeness (C), and self-transcendence (ST). NS is the activation of behavior in response to novelty and signals of reward or relief of punishment, HA is the inhibition of behavior in response to signals of punishment or non-reward, RD is the maintenance of
Abbreviations: C, cooperativeness; CSF, cerebrospinal fluid; HA, harm avoidance; 5-HIAA, 5-hydroxyindolacetic acid; 5-HT, 5-hydroxytryptamine; NS, novelty seeking; P, persistence; RD, reward dependence; SD, selfdirectedness; ST, self-transcendence; TCI, Temperament and Character Inventory; TPH, tryptophan hydroxylase. ⁎ Corresponding author. Tel.: +81 23 628 5322; fax: +81 23 628 5325. E-mail address: [email protected] (A. Suzuki). 0278-5846/$ - see front matter © 2006 Elsevier Inc. All rights reserved. doi:10.1016/j.pnpbp.2006.10.003
behavior which was previously rewarded, and P is the perseveration with behavior despite frustration and fatigue. SD is the concept of the self as an autonomous individual, C is the concept of the self as an integral part of humanity or society, and ST is the concept of the self as an integral part of the universe and its source. Cloninger et al. (1993) hypothesized that NS, HA, and RD were related to dopamine, serotonin (5-hydroxytryptamine: 5-HT), and norepinephrine, respectively. There are many studies suggesting disturbances of the 5-HT system in psychiatric disorders (Asberg, 2004). One of the most consistent findings in these studies is low concentrations of the 5-HT metabolite, 5-hydroxyindolacetic acid (5-HIAA), in cerebrospinal fluid (CSF) of suicide attempters (Asberg, 2004). 5-HT is synthesized from tryptophan in two steps, i.e., tryptophan is firstly hydroxylated to 5-hydroxytryptophan by tryptophan hydroxylase (TPH), and then 5-hydroxytryptophan is decarboxylated to 5-HT by aromatic amino acid decarboxylase (Cooper et al., 2003). Therefore, TPH is the rate-limiting enzyme in 5-HT synthesis. The TPH gene is mapped on chromosome 11p15.3–p14, and contains an A to C transversion
396
A. Suzuki et al. / Progress in Neuro-Psychopharmacology & Biological Psychiatry 31 (2007) 395–398
polymorphism at nucleotide 218 in intron 7 (A218C) (Nielsen et al., 1994). The A allele of this polymorphism was reported to be associated with low CSF concentrations of 5-HIAA in healthy subjects (Jonsson et al., 1997) and violent alcoholic offenders (Nielsen et al., 1994), and high TPH immunoreactivity in postmortem brain of suicide victims and control samples (Ono et al., 2002). Therefore, the TPH polymorphism may be implicated in psychiatric disorders such as suicidal behavior. The TPH A218C polymorphism was originally suggested to be associated with aggressive–impulsive behaviors such as violence and suicide attempt (Nielsen et al., 1994). The meta-analysis confirmed the association between the A allele and suicidal behavior (Bellivier et al., 2004; Rujescu et al., 2003). Meanwhile, risk of suicide attempt in community-based sample has been related to personality traits of HA and SD (Grucza et al., 2005). These discussions suggest the possibility that the TPH A218C polymorphism affects suicidality via some personality traits, especially HA and SD. However, Ham et al. (2004) have shown that this polymorphism is not related to the TCI dimensions in healthy subjects. This negative result is rather surprising in light of the associations between TPH and suicidality and between suicidality and personality traits. Therefore, the present study re-examined the association between the TPH A218C polymorphism and personality traits assessed by the TCI in Japanese healthy subjects. 2. Methods 2.1. Subjects The subjects were 345 unrelated Japanese who were medical students or the staff of three hospitals. Well-trained psychiatrists confirmed that they did not have any Axis I or II disorders of DSM-IV (American Psychiatric Association, 1994) by interviews. The personality traits of the subjects were assessed by the Japanese version of the TCI, which has been shown to have high reliability (Kijima et al., 1996). The mean (± S.D.) of age was 29.7 (± 9.0) years. One hundred eighty-five subjects were females, and 160 were males. The study protocol was approved by the Ethics Committee of Yamagata University School of Medicine, and all subjects provided written informed consent to participate. 2.2. Genotyping analysis DNA was extracted from peripheral leucocytes using a QIAamp DNA Blood Kit (Qiagen, Tokyo, Japan). The TPH
A218C genotype was determined by the PCR-RFLP method of Bellivier et al. (1998). The PCR was performed using primers (5′-TTC AGA TCC CTT CTA TAC CCC AGA-3′ and 5′-GGA CAT GAC CTA AGA GTT CAT GGC A-3′) in 25 ul volume containing 100 ng of genomic DNA, 0.5 uM of each primer, 200 uM of each dNTP, 1.5 mM of MgCl2, and 1.25 U of HotStar Taq DNA polymerase (Qiagen, Tokyo, Japan). After an initial denaturation step at 95 °C for 15 min, 30 cycles were performed at 95 °C for 0.5 min, 53 °C for 0.5 min, and 72 °C for 0.5 min. Finally, an elongation step was performed at 72 °C for 10 min. Five microliters of the PCR product was digested overnight with 7.5 U of Xsp I (Takara Bio Inc., Otsu, Japan). The fragments were electrophoresed on a 2% of agarose gel with ethidium bromide staining and visualized using ultraviolet light. After digestion, the A allele gives 860- and 58-bp fragments, and the C allele gives 615-, 245-, and 58-bp fragments. Genotyping accuracy was checked by random replicate analyses of 10% of the subjects, with complete concordance. 2.3. Statistical analysis The difference in each dimension score among the subjects with A/A, A/C, and C/C genotypes was tested by the one-way ANOVA followed by Tukey test. The correlation between age and each dimension score was tested by the linear regression analysis. The Student t-test was used for the comparison of each dimension score between males and females. The multiple regression analysis was performed with each dimension score as a dependent variable, and age, gender, and the TPH genotype as independent variables. A dummy variable was used for gender (female = 0, male = 1). For the TPH genotype, two dummy variables, X1 and X2, were used; if the genotype was the A/A, both X1 and X2 were coded as 0, if the genotype was the A/C, X1 and X2 were coded as 1 and 0, respectively, and if the genotype was the C/C, X1 and X2 were coded as 0 and 1, respectively. All statistical analyses were performed by SPSS 13.0 J for Windows (SPSS Japan, Inc.), and a p value of less than .05 was regarded as significant. 3. Results In the present sample, 93 subjects had the A/A genotype, 177 had the A/C genotype, and 75 had the C/C genotype. The TPH genotype distribution in the total subjects was in the Hardy– Weinberg equilibrium. In the one-way ANOVA, there were no significant differences in seven dimension scores among the three genotype groups (Table 1).
Table 1 Seven TCI dimension scores in the three TPH A218C genotype groups
A/A A/C C/C p
N
NS
HA
RD
P
SD
C
ST
93 177 75
21.2 ± 5.4 21.9 ± 4.8 20.9 ± 5.3 .259
18.4 ± 6.4 19.9 ± 5.7 19.5 ± 5.9 .123
16.5 ± 4.0 16.5 ± 3.4 16.0 ± 3.3 .598
4.2 ± 1.8 4.1 ± 1.8 4.1 ± 1.7 .900
28.7 ± 6.5 27.6 ± 6.6 27.5 ± 6.7 .357
28.9 ± 6.0 28.5 ± 4.6 28.1 ± 4.2 .528
10.2 ± 5.1 9.3 ± 4.6 8.9 ± 4.8 .215
TCI, Temperament and Character Inventory; TPH, tryptophan hydroxylase; NS, novelty seeking; HA, harm avoidance; RD, reward dependence; P, persistence; SD, self-directedness; C, cooperativeness; ST, self-transcendence. The data on the table indicate mean ± S.D.
A. Suzuki et al. / Progress in Neuro-Psychopharmacology & Biological Psychiatry 31 (2007) 395–398 Table 2 Multiple regression analyses of seven TCI dimension scores by age, gender, and the TPH A218C genotype NS
HA
Age − .178 Gender .020 TPH A218C .076 genotype X1 X2 − .025 Multiple correlation .203 coefficient p .006
b
RD
P
SD
C
ST
.080 −.028 − .084 −.022 .032 − .051 − .122a −.151 − .039 .178b − .048 − .126 .124 .002 .026 −.077 − .050 − .092 .068 .190 .014
−.062 − .018 −.062 .160 .100 .197 .066
.486
.009
− .075 − .116 .086 .160 .636
.065
TCI, Temperament and Character Inventory; TPH, tryptophan hydroxylase; NS, novelty seeking; HA, harm avoidance; RD, reward dependence; P, persistence; SD, self-directedness; C, cooperativeness; ST, self-transcendecne, X1 and X2; dummy variables for TPH genotype. The figures on the table indicate β. a : p b .05, b: p b .01.
There was a significant negative correlation between age and the NS scores (r = − .179, p = .001). Females showed significantly higher scores of HA (female vs. male: 20.2 ± 5.9 vs. 18.5 ± 6.0, p = .011), RD (16.9 ± 3.3 vs. 15.8 ± 3.7, p = .007), and ST (10.0 ± 4.7 vs. 8.9 ± 4.8, p = .036), and significantly lower scores of SD (26.7 ± 6.5 vs. 29.1 ± 6.5, p = .001) than males. Similarly, the multiple regression analysis also showed that each dimension score was not related to the TPH genotype (Table 2). The statistical power for one-way ANOVA in the present sample size (n = 345) was 0.98 to detect a medium effect size (0.25) at an alpha value of 5% two-tailed (Cohen, 1988). 4. Discussion Originally, Cloninger et al. (1993) proposed that the temperament dimensions are highly heritable and stable throughout life, while the character dimensions are influenced by social learning. However, subsequent reports have demonstrated significant effects of age and gender not only on the character dimensions but also on the temperament dimensions (Cloninger et al., 1994; Duijsens et al., 2000; Pelissolo and Lepine, 2000). For example, Pelissolo and Lepine (2000) reported that NS decreased with aging, while HA, RD, and ST were higher and SD was lower in females. Therefore, age and gender effects should be taken into account in genetic studies on personality. However, these effects were not taken into account in the study by Ham et al. (2004), and this together with the small number of subjects (n = 146) might be the causes of their negative result. In the present study, there was no significant association between seven dimension scores of the TCI and the TPH genotype by the univariate analysis like in the study by Ham et al. (2004). Contrary to our expectation, even by taking age and gender effects into account in the multiple regression analysis, no significant association appeared between any dimension score and the genotype. The TPH A218C polymorphism is a silent mutation, and is suggested to be in linkage disequilibrium with other polymorphism(s) in the regulatory region of TPH gene (Jonsson et al.,
397
1997; Nielsen et al., 1994; Ono et al., 2002). Rotondo et al. (1999) identified four polymorphisms in the promoter region of TPH gene, which may affect the TPH expression. They reported that one of them, the −6526ANG polymorphism, was in strong linkage disequilibrium with the A218C polymorphism in Finns but not in Italians or American Indians. Therefore, the TPH A218C polymorphism may be associated with psychiatric disorders in some ethnic groups but not in others. In fact, two meta-analyses (Bellivier et al., 2004; Rujescu et al., 2003) have shown that there is an association between the A allele and suicidal attempts in Caucasians, while this association is unclear in Asians. To date, the relationship between the TPH A218C polymorphism and personality has been examined in Asians only, i.e., Koreans (Ham et al., 2004) and Japanese (this study). Therefore, a significant association may be observed in other ethnic groups. There is also the possibility that other genetic polymorphisms conceal the effect of the TPH A218C polymorphism on the TCI dimensions. For example, a recent meta-analysis (Munafo et al., 2005) showed a significant association between the polymorphism of the serotonin transporter linked polymorphic region and HA. To confirm this point, the effect of combinations of the TPH A218C polymorphism with other polymorphisms on the TCI dimensions should be examined in further studies. In the present study, age influenced NS, while gender influenced HA, RD, ST, and SD. The higher NS in younger subjects and higher HA and RD in females observed in the present study have been reported in other studies (Cloninger et al., 1994; Duijsens et al., 2000; Pelissolo and Lepine, 2000) as well. According to Cloninger et al. (1994), high scores of NS are exploratory, curious, impulsive, extravagant, enthusiastic, and disorderly, those of HA are worrying, pessimistic, fearful, doubtful, shy, and fatigable, and those of RD are sentimental, warm, dedicated, attached, and dependent. As suggested by McCrae et al. (2000), adults may become less extraverted as a natural consequence of aging, just as children develop mentally in a fixed order and time course. The higher HA and RD in females may be related to the general tendency that females are more likely to ruminate unhelpfully over psychosocial difficulties, and less likely to have a sense of controlling the world as argued by Rutter et al. (2003). As a limitation of the present study, the subjects were young and the age range was narrow. The present results would have been different if subjects from a wide age range had been included, in the light of the age effects on personality traits (Cloninger et al., 1994; Duijsens et al., 2000; Pelissolo and Lepine, 2000). 5. Conclusion In conclusion, the present study suggests that the TPH A218C polymorphism does not affect personality traits in Japanese healthy subjects. References American Psychiatric Association. Diagnostic and statistical manual of mental disorders. 4th ed. Washington, DC: American Psychiatric Association; 1994.
398
A. Suzuki et al. / Progress in Neuro-Psychopharmacology & Biological Psychiatry 31 (2007) 395–398
Asberg M. Neurotransmitters and suicidal behavior. Ann NY Acad Sci 2004;836:158–81. Bellivier F, Leboyer M, Courtet P, Buresi C, Beaufils B, Samolyk D, et al. Association between the tryptophan hydroxylase gene and manic– depressive illness. Am J Psychiatry 1998;55:33–7. Bellivier F, Chaste P, Malafosse A. Association between the TPH gene A218C polymorphism and suicidal behavior: a meta-analysis. Am J Med Genet 2004;124:87–91. Cloninger CR, Svrakic DM, Przybeck TR. A psychobiological model of temperament and character. Arch Gen Psychiatry 1993;50:975–90. Cloninger CR, Przybeck TR, Svrakic DM, Wetzel RD. The Temperament and Character Inventory (TCI): a guide to its development and use. St Louis, Missouri, USA: Center for Psychobiology of personality; 1994. Cohen J. Statistical power analysis for the behavioral sciences. Hillsdale, New Jersey: Lawrence Erlbaum Associates, Publishers; 1988. Cooper JR, Bloom FE, Roth RH. The biochemical basis of neurophamacology. 8th ed. Oxford: Oxford University Press; 2003. Duijsens IJ, Spinhoven P, Goekoop JG, Spermon T, Eurelings-Bontekoe EHM. The Dutch Temperament and Character Inventory (TCI): dimensional structure, reliability and validity in a normal and psychiatric outpatient sample. Pers Individ Differ 2000;28:487–99. Grucza RA, Przybeck TR, Cloninger CR. Personality as a mediator of demographic risk factors for suicide attempts in a community sample. Compr Psychiatry 2005;46:214–22. Ham BJ, Kim YH, Choi MJ, Cha JH, Choi YK, Lee MS. Serotonergic genes and personality traits in the Korean population. Neurosci Lett 2004;354:2–5. Jonsson EG, Goldman D, Spurlock G, Gustavsson JP, Nielsen DA, Linnoila M, et al. Tryptophan hydroxylase and catechol-O-methyltransferase gene polymorphisms: relationship to monoamine metabolite concentrations in CSF of healthy volunteers. Eur Arch Psychiatry Clin Neurosci 1997;247:297–302.
Kijima N, Saito R, Suzuki M, Yoshino A, Ono Y, Kato M, et al. Cloninger's seven factor model of temperament and character and Japanese version of Temperament and Character Inventory (TCI). Jpn J Psychiatry Diagn 1996;7:379–99 (Japanese). McCrae RR, Costa Jr PT, Ostendorf F, Angleitner A, Hrebickova M, Avia MD, et al. Nature over nurture: temperament, personality, and life span development. J Pers Soc Psychol 2000;78:173–86. Munafo MR, Clark T, Flint J. Does measurement instrument moderate the association between the serotonin transporter gene and anxiety-related personality traits? A meta-analysis. Mol Psychiatry 2005;10:415–9. Nielsen DA, Goldman D, Virkkunen M, Tokola R, Rawlings R, Linnoila M. Suicidality and 5-hydroxyindoleacetic acid concentration associated with a tryptophan hydroxylase polymorphism. Arch Gen Psychiatry 1994;51:34–8. Ono H, Shirakawa O, Kitamura N, Hashimoto T, Nishiguchi N, Nishimura A, et al. Tryptophan hydroxylase immunoreactivity is altered by the genetic variation in postmortem brain samples of both suicide victims and controls. Mol Psychiatry 2002;7:1127–32. Pelissolo A, Lepine JP. Normative data and factor structure of the Temperament and Character Inventory (TCI) in the French version. Psychiatry Res 2000;94:67–76. Rotondo A, Schebel K, Bergen A, Aragon R, Virkkunen M, Linnoila M, et al. Identification of four variants in the tryptophan hydroxylase promoter and association to behavior. Mol Psychiatry 1999;4:360–8. Rujescu D, Giegling I, Sato T, Hartmenn AM, Moller HJ. Genetic variations in tryptophan hydroxylase in suicidal behavior: analysis and meta-analysis. Biol Psychiatry 2003;54:465–73. Rutter M, Caspi A, Moffitt TE. Using sex differences in psychopathology to study causal mechanisms: unifying issues and research strategies. J Child Psychol Psychiatry 2003;44:1092–115.