C) in mood disorders

Psychiatry Research 87 Ž1999. 233]237

Serotonin-2A receptor polymorphism ž 102TrC/ in mood disorders Shih-Jen Tsai a,b, Chen-Jee Hong a,b,U , Ching-Chi Hsu c , Chih-Ya Cheng a , Wen-Yu Liao a , Hsiu-Li Song a , Hao-Che Lai a a

Department of Psychiatry, Veterans General Hospital-Taipei, No. 201, Shih-Pai Road, Sec. 2, Taipei 11217, Taiwan, ROC b Di¨ ision of Psychiatry, School of Medicine, National Yang-Ming Uni¨ ersity, Taipei, Taiwan, ROC c Tao-Yuan Veterans Hospital, Taipei, Taiwan, ROC Received 11 December 1998; received in revised form 4 June 1999; accepted 15 June 1999

Abstract Serotonergic dysfunction has been implicated in mood disorders and suicidal behaviors. This study examined the association between a serotonin-2A Ž5HT2A . receptor gene polymorphism Ž102TrC. and mood disorders. The genotype and allele frequencies did not differ between patients with mood disorders and control subjects. Furthermore, the 102TrC polymorphism was not found to be associated with suicidal history in mood disorder patients. Our results suggest that this polymorphism is unlikely to play a role in the genetic susceptibility to mood disorders. Q 1999 Elsevier Science Ireland Ltd. All rights reserved. Keywords: Genetics; Association study; Polymorphism; 5HT2A receptor; Mood disorders; Suicide

1. Introduction Abnormalities of the serotonergic system have been implicated in the pathogenesis of mood dis-

U

Corresponding author. Tel.: q886-2-2875-7027, ext. 304; fax: q886-2-2872-5643. E-mail address: [email protected] ŽC. Hong.

orders. Among the various serotonin receptors, the serotonin-2A receptor Ž5HT2A . is of particular importance in mood disorders. For instance, 5HT2A receptor down-regulation is a common mechanism of antidepressant action, and increased densities of 5HT2A receptors have been reported in the brains of depressed patients ŽMann et al., 1986; McKeith et al., 1987.. Biegon et al. Ž1990. reported that 5HT2A receptors bind-

0165-1781r99r$ - see front matter Q 1999 Elsevier Science Ireland Ltd. All rights reserved. PII: S 0 1 6 5 - 1 7 8 1 Ž 9 9 . 0 0 0 5 9 - 1

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S.-J. Tsai et al. r Psychiatry Research 87 (1999) 233]237

ing on platelet membranes from patients with major depression changed in correlation with changes in their clinical state. In addition, there are several lines of evidence for an association between 5HT activity and suicidal behaviors not related to mood disorders ŽStanley and Mann, 1983; Mann et al., 1986; Arora and Meltzer, 1989.. Parallel to these findings, the implication of genetic factors in the pathogenesis of mood disorders has been confirmed by traditional methods such as twin, adoption and family studies ŽMendlewicz, 1994.. Case-control association study provides a powerful strategy in studying complex diseases because this non-parametric method does not require knowledge of genetic parameters such as mode of transmission or penetrance. Previously, three studies have examined a silent variant of the 5HT2A gene Ž102TrC. in bipolar disorders and found no evidence for an etiological involvement ŽGutierrez et al., 1995; Arranz et al., 1997; Mahieu et al., 1997.. One Japanese study examined both depressive disorders and bipolar disorders for such an association, and it also had negative findings ŽZhang et al., 1997.. Considering the 5HT2A receptor gene as a candidate gene for an association with mood disorders, we investigated the potential implications of the 5HT2A receptor gene in Chinese patients with mood disorders in a case-control association study design. Furthermore, we analyzed the TrC polymorphism for any relation to suicidal history in these patients.

2. Methods

The study group included 144 patients who met the criteria for mood disorders. In addition, 96 normal comparison subjects ŽMrFs 46:50. who had agreed to be interviewed by a staff member and who were confirmed by a semi-structured interview with a psychiatric staff member to be free of psychiatric problems were included to test the association of the 102TrC 5HT2A polymorphism with mood disorders. The controls were older than 60 years Žmean s 71.6 years, S.D.s 0.7.. We added the selection criterion of age over 60 for the normal controls to reduce the risk of including control subjects who might have a mood disorder with late onset. 2.2. Laboratory methods DNA was isolated from lymphocytes using routine procedures. Genotyping of the 102TrC polymorphism of the 5HT2A receptor gene was done according to the polymerase chain reaction ŽPCR. method described by Warren et al. Ž1993. with some modifications. Briefly, a standard PCR was carried out in a 25-ml volume containing 100 ng of genomic DNA, 200 mM of each dNTP, 1.5 mM MgCl 2 , 250 nM of the sense Ž59TCTGCTACAAGTTCTGGCTT-39. and antisense Ž59-CTGCAGCTTTTTCTCTAGGG-39. primers, and 0.6 U DNA Taq polymerase. The PCR products were digested with HpaII ŽBM.. The digestion products were separated by electrophoresis and visualized under UV light. The 102T allele PCR products remained uncut, with a single DNA band of 342 bp, whereas the 102C allele showed two bands of 216 bp and 126 bp.

2.1. Subjects 2.3. Statistical analysis Mood disorder patients were inpatients from the acute wards of Veterans General HospitalTaipei. The diagnosis was based on interview, clinical observation, medical record, past history and DSM-IV criteria ŽAmerican Psychiatric Association, 1994., and was reassessed by a boardcertified psychiatrist. The medical record of each patient was retrospectively reviewed in detail for demographic data and suicidal history.

Comparisons of the genotypic or allele frequencies between the mood disorder patients and the controls were performed using the chi-square test or Fisher’s exact test Ž2 = 2.. Bonferroni corrections were applied by dividing 0.05 by the number of comparisons to determine the P-value necessary to achieve significance. Data are presented as the mean ŽS.E.M...

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3. Results Table 1 represents demographic data for the patients, and Table 2 shows the genotype and allele distributions of the 102TrC polymorphism of the 5HT2A receptor gene in the mood disorder patients and the controls. The distributions of the 102TrC genotype in mood disorder cases and controls were in Hardy]Weinberg equilibrium. Neither the genotype Žpower of performed test with a s 0.050: 0.070. nor the allelic frequencies Žpower of performed test with a s 0.050: 0.070. were statistically different between the two groups ŽTable 2.. Also, no statistical association was found in the genotype and allele frequency between patients with subtypes of mood disorders Ži.e. depressive disorders and bipolar disorders. and healthy controls. The frequencies of genotypes did not differ if the patients were divided according to whether or not they had a suicidal history Ž x 2 s 3.991, d.f.s 2, Ps 0.136..

4. Discussion The results of this study suggest that the 102TrC polymorphism of the 5HT2A receptor gene was not directly involved in the pathogenesis of mood disorders, depressive disorders or bipolar disorders in our sample. This finding confirms the results of previous reports that the 102TrC polymorphism was not associated with bipolar disorders ŽGutierrez et al., 1995; Arranz et al., 1997; Mahieu et al., 1997; Zhang et al., 1997.. However, Zhang et al. Ž1997. reported a positive association between the 102TrC polymorphism and depressive disorders among Japanese patients, which

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differs from our finding. There are several explanations for the negative association in this study. First, our results must be qualified based on the low statistical power of the comparisons, owing to the limited sample size. If 5HT2A is an uncommon disease locus or one of small effect, our power to detect a gene would be reduced. Second, the 5HT2A receptor gene may have no involvement in the pathogenesis of mood disorders. This is in agreement with the findings of a previous study which, based on analysis of the 5HT2 receptor using single photon emission tomography, suggested that this receptor may not be altered significantly in the depressed brain ŽD’haenen et al., 1992.. Third, the relevant segment of the 5HT2A receptor gene locus may not be in linkage disequilibrium with the 102TrC polymorphism. Recently, Arranz et al. Ž1997. demonstrated that no strong association exists between any of four 5HT2A polymorphisms and bipolar disorders. A fourth possible explanation for the lack of association between this 5HT2A receptor gene polymorphism and mood disorders is the phenotypic heterogeneity of patients in the sample. Since the diagnosis of mood disorders is based on symptom-oriented criteria, selecting cases according to standard diagnostic criteria does not assure an etiologically homogeneous sample. It would be of great interest to test for an association between the 5HT2A receptor gene and subgroups of mood disorder patients. An alternative interpretation of the results may be that modulation of the 5HT2A receptor is not the primary etiologic mechanism in mood disorders but is secondary to the disease process. To test this hypothesis, we further analyzed the relation between the presence of the TrC polymor-

Table 1 Demographic data of the mood disorder patients n Depressive disorders Bipolar disorders Total

Sex ŽMrF.

Age

Age of onset

79 65

36r43 28r37

45.2 Ž2.1. 36.0 Ž1.5.

39.7 Ž2.0. 27.6 Ž1.4.

144

64r80

41.0 Ž1.4.

34.2 Ž1.4.

S.-J. Tsai et al. r Psychiatry Research 87 (1999) 233]237

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Table 2 Genotype distribution and allele frequencies of the 102CrT polymorphism of the 5HT2A receptor gene among mood disorder patients and normal controls Group

Mood disorders Depressive disorders Bipolar disorders Suicidal patients Non-suicidal patients Controls a

n

144 79 65 61 83 96

Genotypes

Allele frequency

102Tr102T

102Tr102C

102Cr102C

Pa

102T

102C

Pa

51 Ž0.35. 26 Ž0.33. 25 Ž0.39. 23 Ž0.38. 28 Ž0.34. 36 Ž0.38.

75 Ž0.52. 44 Ž0.56. 31 Ž0.48. 27 Ž0.44. 48 Ž0.58. 50 Ž0.52.

18 Ž0.13. 9 Ž0.11. 9 Ž0.14. 11 Ž0.18. 7 Ž0.08. 10 Ž0.10.

0.868 0.818 0.762 ] ] ]

0.61 0.61 0.62 0.60 0.63 0.59

0.39 0.39 0.38 0.40 0.37 0.41

0.645 0.658 0.906 ] ] ]

Compared with the control group.

phism and suicidal history. The frequencies of genotypes were not found to be associated with suicidal history. This finding is in contrast with that of a Japanese report which demonstrated a slight association between the 5HT2A genotype and suicide attempts ŽZhang et al., 1997.. It should be noted that multiple genes are likely to contribute to complex traits such as suicide, and the association of specific genes with a trait may be quite modest and vary between samples. Another finding in this study is that the allele frequency of 102T is higher than that of 102C in both the patient and control groups ŽTable 2.. This allele frequency of 102T is similar to that found in another Chinese sample ŽChen et al., 1997.. However, in Western and Japanese reports, the study samples had a lower allele frequency of 102T than of 102C. These results suggest that the allele frequencies of the 102TrC polymorphism of the 5HT2A receptor gene are ethnic-dependent, a factor that should be taken into account when carrying out genetic studies.

Acknowledgements

This work was supported by Grant NSC-872314-B-075-025 from the National Science Council, Taiwan, ROC, and Grant VGH-87-287 from the Veterans General Hospital-Taipei.

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