No Association Between GRM3 and Japanese Methamphetamine-Induced Psychosis

Several investigations have suggested that abnormalities in glutamate neural transmission play a role in the pathophysiology of psychiatric disorders, including schizophrenia. The metabotropic glutamate 3 receptor (mGluR3) gene was reported to be associated with schizophrenia, and paranoid type schizophrenia has symptoms that are similar to those of methamphetamine-induced psychosis. This suggests that mGluR3 gene (GRM3) is a good candidate gene for the pathogenesis of methamphetamine-induced psychosis. To evaluate the association between GRM3 and methamphetamine-induced psychosis, we conducted a case-control study of Japanese samples (181 methamphetamine-induced psychosis and 232 controls). Methods: We selected one functional SNP (rs6465084), reported to be associated with prefrontal brain functioning, for an association analysis. Written informed consent was obtained from each subject. This study was approved by the ethics committees at Fujita Health University, Nagoya University Graduate School of Medicine and each participating member of the Institute of the Japanese Genetics Initiative for Drug Abuse (JGIDA). Results: We did not detect an association between rs6465084 in GRM3 and Japanese methamphetamine-induced psychosis. Conclusion: Our findings suggest that rs6465084 in GRM3 does not play a major role in the pathophysiology of methamphetamine-induced psychosis in the Japanese population. However, because we did not perform an association analysis based on linkage disequilibrium (LD) or a mutation scan of GRM3, a replication study using a larger sample and based on LD may be required for conclusive results.


1.INTRODUCTION
The glutamate hypothesis is one of the prevailing hypotheses for the pathophysiology of schizophrenia [1]. Also, a recent clinical study showed that LY379268, an agonist of metabotropic glutamate 2/3 receptor (mGluR2/3) that is involved in group II mGluR regulate glutamate neurotransmission through a presynaptic negative regulatory mechanism, has an effect on psychotic symptoms in schizophrenia almost equivalent to that of olanzapine [1].
*Address correspondence to this author at the Department of Psychiatry, Fujita Health University School of Medicine, Toyoake, Aichi 470-1192, Japan; Tel: +81-562-93-9250; Fax: +81-562-93-1831; E-mail: tarok@fujita-hu.ac.jp # These authors contributed equally to this work Several investigations have suggested that metabotropic glutamate 3 receptor (mGluR3) gene has an association with schizophrenia [2][3][4]. Since the symptoms of methamphetamine-induced psychosis are similar to those of paranoid type schizophrenia [5], it would seem that the mGluR3 gene (GRM3) is a good candidate gene for the pathogenesis of methamphetamine-induced psychosis. To evaluate the association between GRM3 and methamphetamine-induced psychosis, we conducted a case-control study of Japanese samples (181 methamphetamine-induced psychosis patients and 232 controls). The mGluR3 gene (GRM3 OMIM *601115, 6 exons in a genomic region spanning 221.763Kb) is at 7q21. We selected rs6465084 in GRM3, which is reported to be associated with prefrontal brain functioning. Rs6465084 has been found to be associated with decreased verbal list learn- ing and verbal fluency [3]. In addition, Egan and colleagues reported that the rs6465084 A allele predicted decreased levels of N-acetylaspartate in the prefrontal cortex in an in vivo study, and suggested that the rs6465084 A allele reduced tissue glutamate levels and synaptic abundance [3].

Subjects
The subjects in the association analysis were 181 methamphetamine-induced psychosis patients(155 males and 26females; mean age33.3 ± 11.4) and 232 controls (187males and 45females; mean age36.4 ± 11.3). All subjects were unrelated to each other, ethnically Japanese, and lived in the central area of Japan. The patients were diagnosed according to DSM-IV criteria with consensus of at least two experienced psychiatrists on the basis of unstructured interviews and a review of medical records. One hundred thirty-seven subjects with METH-induced psychosis also had dependence on drugs other than METH. Subjects with METHinduced psychosis were excluded if they had a clinical diagnosis of psychotic disorder, mood disorder, anxiety disorder or eating disorder. More detailed characterizations of these subjects have been published elsewhere [6][7][8]. All healthy controls were also psychiatrically screened based on unstructured interviews including current and past psychiatric history. None had severe medical complications such as cirrhosis, renal failure, heart failure or other Axis-I disorders according to DSM-IV. No structured methods were used to assess psychiatric symptoms in the controls, which included hospital staff, their families and medical students.
The study was described to subjects and written informed consent was obtained from each. This study was approved by the Ethics Committee at Fujita Health University, Nagoya University School of Medicine and and each participating member of the Institute of the Japanese Genetics Initiative for Drug Abuse (JGIDA).

SNP Selection
We selected rs6465084 in GRM3, which is reported to be associated with prefrontal brain functioning, for the following association analysis.

Statistical Analysis
Genotype deviation from the Hardy-Weinberg equilibrium (HWE) was evaluated with the chi-square test (SAS/ Genetics, release 8.2, SAS Japan Inc, Tokyo, Japan).
Marker-trait association analysis was used to evaluate allele-and genotype-wise association with the chi-square test (SAS/Genetics, release 8.2, SAS Japan Inc, Tokyo, Japan). To control inflation of the type I error rate, we used Bonferroni's correction. Power calculation was performed using a statistical program prepared by Purcell et al.
The significant level for all statistical tests was 0.05.

RESULTS
Rs6465084 is in HWE. We detected no association between rs6465084 in GRM3 and METH-induced psychosis in the allele/genotype-wise analysis ( Table 1).

DISCUSSION
We performed an association study of rs6465084 in GRM3 and METH-induced psychosis in the Japanese population. Although, we recently found an association between GRM2 and METH-induced psychosis in the Japanese population [10], in the present study we detected no association between GRM3 with METH-induced psychosis.
Egan and colleagues reported that the rs6465084 A allele predicted decreased levels of N-acetylaspartate in the prefrontal cortex in an in vivo study, and suggested that the rs6465084 A allele reduced tissue glutamate levels and synaptic abundance [3]. This influence of GRM3 on prefrontal cortex and cognitive function suggests that abnormalities in glutamate neurotransmission may be involved in the pathophysiology of METH-induced psychosis. However, we did not detect an association between GRM3 and METH-induced psychosis. We designed the present study based on common disease-common variants hypothesis (CD-CV hypothesis) [11]. In addition, we selected only one SNP in GRM3. A recent study has showed an association between common diseases such as schizophrenia and rare variants. If the genetic background of METH-induced psychosis is accurately described by the common disease-rare variants hypothesis, further investigation such as medical resequencing using larger samples will be required [8,[12][13][14][15][16][17].
There are a few limitations in this study. First, the lack of association may be due to biased samples, such as small sample sizes. Second, we selected only one SNP in GRM3. To overcome these limitations, it will be necessary conduct a replication study using gene based association analysis and larger samples.

CONCLUSION
Our results suggest that rs6465084 in GRM3 does might not play a role in the pathophysiology of METH-induced psychosis in the Japanese population. However, our results have limitations and replication study using gene-based association analysis and larger samples will be required.