Association study between the PIK4CA gene and methamphetamine use disorder in a Japanese population.

Accumulating evidence suggests that phosphatidylinositol (PI) pathways have been involved in the secretion of dopamine (DA) and the regulation of DA transporter, which is a target of methamphetamine (METH). A recent large-scale gene-association study in a Dutch population demonstrated that the PIK4CA gene was closely linked to schizophrenia [Jungerius et al. (2007); Mol Psychiatry]. Here, we conducted a case (N = 232)-control (N = 233) study of the PIK4CA gene on Japanese METH abusers, which can manifest severe psychosis similar to schizophrenia. The genotype and allelic distributions of all four single nucleotide polymorphisms (SNPs) did not differ significantly between the METH abusers and the controls. The comparisons based on the classification of the psychosis as transient or prolonged and on the presence or absence of spontaneous relapse revealed no significant distribution of the four SNPs compared to the controls. Furthermore, haplotype analyses showed almost the same frequencies between the METH abusers and the controls. The present study suggests that the PIK4CA gene does not play a significant role in the vulnerability to METH use disorder in the Japanese population.

Reduced CYP2D6 activity is a negative risk factor for methamphetamine dependence.

Because methamphetamine (METH) is metabolized by CYP2D6 at the first step of hydroxylation and demethylation, it is possible that functional variants of CYP2D6 alter susceptibility to methamphetamine-induced dependence. We genotyped CYP2D6*1, *4, *5, *10, and *14 for 202 patients with METH dependence and 337 controls in a Japanese population and found a significant association of the CYP2D6 gene with METH dependence (p=0.0299). The patients had fewer *10 and *14 alleles, which are hypofunction alleles, than the controls. CYP2D6 genotypes were divided into three phenotypes: extensive metabolizers, intermediate metabolizers, and poor metabolizers. There was no poor metabolizer among our Japanese subjects, and intermediate metabolizers of CYP2D6 were significantly fewer in methamphetamine-dependent subjects than in controls (p=0.0212), with an odds ratio of 0.62 (95% confidence interval: 0.51-0.76). The present study demonstrated that reduced CYP2D6 activity was a negative risk factor for methamphetamine dependence.

Association study between polymorphisms in glutathione-related genes and methamphetamine use disorder in a Japanese population.

Accumulating evidence suggests that oxidative stress plays a role in the mechanisms of action of methamphetamine (METH) in the brain. In the present study, we investigated the association between the genetic polymorphisms among glutathione (GSH)-related enzymes; glutathione S-transferases (GSTs) such as GSTT1 (Non-deletion/Null), GSTT2 (Met139Ile), GSTA1 (-69C/T), and GSTO1 (Ala140Asp); glutathione peroxidase 1 (GPX1) (Pro198Leu); and glutamate-cysteine ligase modifier (GCLM) subunit and METH use disorder in a Japanese population. Two hundred eighteen METH abusers and 233 healthy controls were enrolled in the study. There was a significant difference in GSTT1 genotype frequency between patients with METH psychosis and controls (P = 0.039, odds ratio: 1.52, 95% CI 1.03-2.24). Furthermore, the frequency (66.0%) of the GSTT1 null genotype among prolonged-type METH psychotic patients with spontaneous relapse was significantly higher (P = 0.025, odds ratio: 2.43, 95% CI 1.13-5.23) than that (44.4%) of transient-type METH psychotic patients without spontaneous relapse. However, there were no associations between the polymorphisms of other genes and METH abuse. The present study suggests that the polymorphism of the GSTT1 gene might be a genetic risk factor of the development of METH psychosis in a Japanese population.

The glycine transporter 1 gene (GLYT1) is associated with methamphetamine-use disorder.

Glycine transporter (GlyT)-1 plays a pivotal role in maintaining the glycine level at the glutamatergic synapse. Glycine is an allosteric agonist of N-methyl-D-aspartate (NMDA) receptors. Because activation of NMDA receptors is an essential step for induction of methamphetamine dependence and psychosis, differences in the functioning of GlyT-1 due to genetic variants of the GlyT-1 gene (GLYT1) may influence susceptibility. A case-control genetic association study of the GLYT1 gene examined 204 patients with methamphetamine-use disorder and 210 healthy controls. We examined three single nucleotide polymorphisms (SNPs), SNP1, IVS3 + 411C > T, rs2486001; SNP2, 1056G > A, rs2248829; and SNP3, IVS11 + 22G > A, rs2248632, of the GLYT1 gene and found that SNP1 showed a significant association in both genotype (P = 0.0086) and allele (P = 0.0019) with methamphetamine-use disorder. The T-G haplotype at SNP1 and SNP2 was a significant risk factor for the disorder (P = 0.000039, odds ratio: 2.04). The present findings indicate that genetic variation of the GLYT1 gene may contribute to individual vulnerability to methamphetamine dependence and psychosis.

GABRB2 association with schizophrenia: commonalities and differences between ethnic groups and clinical subtypes.

BACKGROUND: Single nucleotide polymorphisms (SNPs) and haplotypes in intron 8 of type A gamma-aminobutyric acid (GABA(A)) receptor beta2 subunit gene (GABRB2) were initially found to be associated with schizophrenia in Chinese. This finding was subjected to cross-validation in this study with Japanese (JP) and German Caucasian (GE) subjects. METHODS: Single nucleotide polymorphisms discovery and genotyping were carried out through resequencing of a 1839 base pair (bp) region in GABRB2. Tagging SNPs (tSNPs) were selected based on linkage disequilibrium (LD), combinations of which were analyzed with Bonferroni correction and permutation for disease association. Random resampling was applied to generate size- and gender-balanced cases and control subjects. RESULTS: Out of the 17 SNPs (9.2/kilobase [kb]) revealed, 6 were population-specific. Population variations in LD were observable, and at least two low LD points were identified in both populations. Although disease association at single SNP level was only shown in GE, strong association was demonstrated in both JP (p = .0002 - .0191) and GE (p = .0033 - .0410) subjects, centering on haplotypes containing rs1816072 and rs1816071. Among different clinical subtypes, the most significant association was exhibited by systematic schizophrenia. CONCLUSIONS: Cross-population validation of GABRB2 association with schizophrenia has been obtained with JP and GE subjects, with the genotype-disease correlations being strongest in systematic schizophrenia, the most severe subtype of the disease.

Identification of functional polymorphisms in the promoter region of the human PICK1 gene and their association with methamphetamine psychosis.

OBJECTIVE: Protein interacting with C-kinase-1 (PICK1) plays a role in the targeting and clustering of dopamine transporter, which is the primary target site for the abused drug methamphetamine. Based on the interaction of PICK1 with dopamine transporter, it is of particular interest to investigate the association between the PICK1 gene and methamphetamine abusers. METHOD: The authors studied the association between PICK1 gene polymorphisms and methamphetamine abusers in a Japanese group. Two hundred and eight methamphetamine abusers and 218 healthy comparison subjects were enrolled in the study. Furthermore, the authors also examined the effects of single nucleotide polymorphisms (SNPs) in the promoter and 5'-untranslated region on transcription levels of PICK1. RESULTS: The authors identified four highly frequent SNPs, rs737622 (-332 C/G) and rs3026682 (-205 G/A) in the promoter region and rs713729 (T/A) in intron3 and rs2076369 (T/G) in intron4. Of these SNPs, rs713729 was significantly associated with methamphetamine abusers in general, and rs713729 and rs2076369 were significantly associated with those with spontaneous relapse of psychosis. Furthermore, haplotype analysis revealed that specific haplotypes of these SNPs were associated with methamphetamine abusers. A gene reporter assay revealed that the two SNPs in the promoter region significantly altered transcriptional activity. CONCLUSIONS: Our findings suggest that the PICK1 gene may be implicated in the susceptibility to spontaneous relapse of methamphetamine psychosis and that, as an intracellular adapter protein, PICK1 may play a role in the pathophysiology of methamphetamine psychosis.

An association study between catechol-O-methyl transferase gene polymorphism and methamphetamine psychotic disorder.

OBJECTIVE: A series of methamphetamine psychosis reveals two kinds of clinical courses of methamphetamine psychosis: transient type and prolonged type. Furthermore, paranoid psychosis sometimes recurs without methamphetamine reuse, referred to as spontaneous relapse. Dysfunction of central dopaminergic neurotransmission has been implicated in the pathogenesis of these psychiatric states. Catechol-O-methyl transferase appears to play a unique role in regulating synaptic dopaminergic activity. This study aimed to investigate whether a functional polymorphism of the catechol-O-methyl transferase gene would be involved in the development of these psychiatric states. BASIC METHODS: We examined the functional polymorphism of val 158 met (catechol-O-methyl transferase) in 143 patients with methamphetamine psychosis and 200 healthy controls in Japan. The patients were divided into subgroups by several characteristic clinical features. MAIN RESULTS: We found a significant difference in the catechol-O-methyl transferase allele frequency between patients with spontaneous relapse and the controls (P=0.018, odds ratio=1.67). Odds ratio implied that the patients with spontaneous relapse had a nearly 1.7-fold higher rate of the low activity alleles (met) than the controls. CONCLUSIONS: Our results indicate that the met allele frequency of the catechol-O-methyl transferase is associated with patients who experienced methamphetamine psychosis and spontaneous relapse, suggesting that patients with a met allele appear to be at increased risk of an adverse response to methamphetamine.

Genetic variant of prodynorphin gene is risk factor for methamphetamine dependence.

Previous studies have indicated that genetic factors substantially affect development of substance use disorders, including methamphetamine dependence. Prodynorphin (PDYN) is an opioid peptide precursor that yields dynorphins, endogenous kappa opioid-receptor agonists that play important roles in substance abuse. A physiologically active polymorphism of 1-4 repeats of a 68-bp element in the promoter region of the PDYN gene has been identified. We analyzed this polymorphism of the PDYN gene by a case-control association study in 143 patients with methamphetamine dependence and 209 healthy controls in the Japanese population. A 3- or 4-repeat allele in the PDYN gene promoter was found significantly more frequently in patients with methamphetamine dependence than in controls (chi(2)=9.45, p=0.0021). A 3- or 4-repeat allele in the PDYN gene promoter, which was shown to produce significantly higher transcription activity of the PDYN gene than a 1- or 2-repeat allele, is a genetic risk factor for development of methamphetamine dependence (odds ratio: 1.83, 95% CI=1.24-2.68).

The X-box binding protein 1 (XBP1) gene is not associated with methamphetamine dependence.

Bipolar disorder has known as a high risk factor for substance abuse and dependence such as alcohol and illegal drugs. Recently, Kakiuchi et al. reported that the -116C/G polymorphism in the promoter region of the X-box binding protein 1 (XBP-1) gene, which translates a transcription factor specific for endoplasmic reticulum stress caused by misfolded proteins, was associated with bipolar disorders and schizophrenia in a Japanese population. Abuse of methamphetamine often produces affective disorders such as manic state, depressive state, and psychosis resembling paranoid-type schizophrenia. To clarify a possible involvement of XBP-1 in the etiology of methamphetamine dependence, we examined the genetic association of the -116C/G polymorphism of the XBP-1 gene by a case-control study. We found no significant association in allele and genotype frequencies of the polymorphism either with methamphetamine dependence or any clinical phenotype of dependence. Because the polymorphism is located in the promoter region of the XBP-1 gene and affects transcription activity of the gene, it is unlikely that dysfunction of XBP-1 may induces susceptibility to methamphetamine dependence.

A nonsynonymous polymorphism in the human fatty acid amide hydrolase gene did not associate with either methamphetamine dependence or schizophrenia.

Genetic contributions to the etiology of substance abuse and dependence are topics of major interest. Acute and chronic cannabis use can produce drug-induced psychosis resembling schizophrenia and worsen positive symptoms of schizophrenia. The endocannabinoid system is one of the most important neural signaling pathways implicated in substance abuse and dependence. The fatty acid amide hydrolase (FAAH) is a primary catabolic enzyme of endocannabinoids. To clarify a possible involvement of FAAH in the etiology of methamphetamine dependence/psychosis or schizophrenia, we examined the genetic association of a nonsynonymous polymorphism of the FAAH gene (Pro129Thr) by a case-control study. We found no significant association in allele and genotype frequencies of the polymorphism with either disorder. Because the Pro129Thr polymorphism reduces enzyme instability, it is unlikely that dysfunction of FAAH and enhanced endocannabinoid system induce susceptibility to either methamphetamine dependence/psychosis or schizophrenia.

Gene polymorphisms of the mu opioid receptor in methamphetamine abusers.

In drug addiction, the opioid system is thought to mediate motivational effects through dopamine-independent mechanisms. We have investigated associations of the mu-opioid receptor gene (OPRM) variations with methamphetamine (MAP) dependence/psychosis. The allelic frequency of A118G (Asn40Asp) in exon 1 of ORPM was 45.3% in our control subjects, but only 7.5-25.8% in the Caucasian or African-American population of previous studies. We have identified several novel polymorphisms in intron 1 and the 5' untranslated region (5'UTR) of OPRM. Polymorphisms in the functionally relevant 5' regulatory region of OPRM were different in our Japanese population from Caucasian or African-American populations. No significant differences between controls and MAP abusers were found in either genotype or allele frequency at any single nucleotide polymorphism (SNP) or (AC)n dinucleotide repeat in intron 1. A subdivision of our MAP group revealed that A118G of OPRM shows a significant association with MAP psychosis having latency less than three years. Further analysis should be capable of identifying associations between the OPRM variations and MAP dependence/psychosis.

Study of association between alpha-synuclein gene polymorphism and methamphetamine psychosis/dependence.

Methamphetamine (MAP) dissipates proton gradients across the membranes of synaptic vesicles, enhances cytoplasmic dopamine (DA) concentrations, and causes calcium-independent, nonvesicular DA release into synapses. MAP is taken into the cytosol by the dopamine transporter (DAT) on the synaptic terminals of DA neurons, and endogenous DA is concurrently released through the transporter by carrier exchange mechanisms, resulting in a robust increase in DA concentration in the synaptic clefts. The enhanced DA release through DAT by MAP is the main mechanism for the reinforcing effects of MAP. The complexes of alpha-synuclein and DAT facilitate membrane clustering of the DAT, thereby accelerating DA uptake in vitro. alpha-Synuclein has been shown to be overexpressed in the midbrain DA neurons of chronic cocaine abusers. The present study was performed to study the association between the alpha-synuclein gene polymorphisms and MAP psychosis/dependence in Japanese population. Since the T10A7 polymorphic site at the 5' end of the noncoding exon 1' in the alpha-synuclein gene is highly polymorphic, we analyzed the noncoding exon 1' and intron 1, including this polymorphic site by sequencing. We confirmed four single nucleotide polymorphisms (SNPs) within 1.38 kbp of the T10A7 polymorphic site. No significant difference was found in genotype or allele frequencies in the T10A7 polymorphic site between MAP psychotic/dependent and control subjects. We found significant association between three SNPs in the vicinity of this polymorphic site in intron 1 and MAP psychosis/dependence in female subjects, but not in males. These results suggest an association of the alpha-synuclein gene polymorphisms with MAP psychosis/dependence in our female subjects. Further analyses are necessary to clarify the gender difference, by using a larger sample size and/or different ethnic groups, as well as functional variations in the alpha-synuclein gene.

A recombination hotspot in a schizophrenia-associated region of GABRB2.

BACKGROUND: Schizophrenia is a major disorder with complex genetic mechanisms. Earlier, population genetic studies revealed the occurrence of strong positive selection in the GABRB2 gene encoding the beta(2) subunit of GABA(A) receptors, within a segment of 3,551 bp harboring twenty-nine single nucleotide polymorphisms (SNPs) and containing schizophrenia-associated SNPs and haplotypes. METHODOLOGY/PRINCIPAL FINDINGS: In the present study, the possible occurrence of recombination in this 'S1-S29' segment was assessed. The occurrence of hotspot recombination was indicated by high resolution recombination rate estimation, haplotype diversity, abundance of rare haplotypes, recurrent mutations and torsos in haplotype networks, and experimental haplotyping of somatic and sperm DNA. The sub-segment distribution of relative recombination strength, measured by the ratio of haplotype diversity (H(d)) over mutation rate (theta), was indicative of a human specific Alu-Yi6 insertion serving as a central recombining sequence facilitating homologous recombination. Local anomalous DNA conformation attributable to the Alu-Yi6 element, as suggested by enhanced DNase I sensitivity and obstruction to DNA sequencing, could be a contributing factor of the increased sequence diversity. Linkage disequilibrium (LD) analysis yielded prominent low LD points that supported ongoing recombination. LD contrast revealed significant dissimilarity between control and schizophrenic cohorts. Among the large array of inferred haplotypes, H26 and H73 were identified to be protective, and H19 and H81 risk-conferring, toward the development of schizophrenia. CONCLUSIONS/SIGNIFICANCE: The co-occurrence of hotspot recombination and positive selection in the S1-S29 segment of GABRB2 has provided a plausible contribution to the molecular genetics mechanisms for schizophrenia. The present findings therefore suggest that genome regions characterized by the co-occurrence of positive selection and hotspot recombination, two interacting factors both affecting genetic diversity, merit close scrutiny with respect to the etiology of common complex disorders.

An association study of monoamine oxidase A (MAOA) gene polymorphism in methamphetamine psychosis.

Methamphetamine continues to be the most widely abused drug in Japan. Chronic methamphetamine users show psychiatric signs, including methamphetamine psychosis. Monoamine oxidase A (MAOA) is one of the major enzymes responsible for the degradation of neurotransmitters. Abnormalities in MAO levels have been related to a wide range of psychiatric disorders. We examined whether or not the MAOA-u variable-number tandem repeat (VNTR) has a functional polymorphism in methamphetamine psychosis and whether or not such a polymorphism is related to the prolongation of psychosis. As expected, there was a significant difference in the MAOA-u VNTR between males with persistent versus transient methamphetamine psychosis (p=0.018, odds ratio (OR)=2.76, 95% CI: 1.18-6.46). Our results suggest that the high-activity allele class of MAOA-u VNTR in males may be involved in susceptibility to a persistent course of methamphetamine psychosis. We found no differences among females. The sample size of females with methamphetamine psychosis was too small to have significant analysis.

Short allele of 5-HTTLPR as a risk factor for the development of psychosis in Japanese methamphetamine abusers.

Accumulating evidence suggests that genetic factors contribute to the vulnerability to methamphetamine (MAP) abuse and associated psychiatric symptoms. Chronic MAP abuse leads to psychosis, which may be of a transient or a prolonged type. Serotonergic dysfunction has been proposed as one of the contributory factors in the development of MAP psychosis. Our PET studies revealed that the serotonin transporter (5-HTT) density in global brain regions is significantly lower in MAP abusers. In this study, we examined the role of a functional polymorphism in the 5' flanking region of the 5-HTT gene (5-HTTLPR) in the development of MAP psychosis in a Japanese population. We analyzed DNA samples from 166 MAP patients (95 with transient and 71 with prolonged psychosis) and 197 age-, sex-, and geographic-origin-matched healthy controls. Patients were also subdivided according to the presence (n= 119) or absence (n= 148) of spontaneous relapse. We observed significant genotypic association of the 5-HTTLPR polymorphism with MAP psychosis (P= 0.022), particularly in patients who show prolonged psychosis. The frequency of the S allele in patients with prolonged psychosis was significantly higher than that of the controls (P= 0.045); it was further higher in patients with prolonged psychosis with spontaneous relapse (P= 0.004). 5-HTTLPR has been suggested to regulate the transcriptional activity of 5-HTT, with S alleles showing lesser transcriptional efficiency and also lower 5-HT(1A) receptor-binding potential. Prolonged MAP use, combined with the high frequency of 5-HTTLPR S-alleles, may lead to reduced 5-HTT levels and 5-HT(1A) receptor-binding potential in the brain, resulting in the dysfunction of the serotonergic system. Thus, we suggest a possible role for the 5-HTTLPR polymorphism in MAP psychosis.

Glutamate cysteine ligase modifier (GCLM) subunit gene is not associated with methamphetamine-use disorder or schizophrenia in the Japanese population.

A recent study showed a significant association between schizophrenia in European samples and the glutamate cysteine ligase modifier (GCLM) subunit gene, which is the key glutathione (GSH)-synthesizing enzyme. Since the symptoms of methamphetamine (METH)-induced psychosis are similar to those of schizophrenia, the GCLM gene is thought to be a good candidate gene for METH-use disorder or related disorders. To evaluate the association between the GCLM gene and METH-use disorder and schizophrenia, we conducted a case-control study of Japanese subjects (METH-use disorder, 185 cases; schizophrenia, 742 cases; and controls, 819). Four SNPs (2 SNPs from an original report and JSNP database, and 2 "tagging SNPs" from HapMap database) in the GCLM gene were examined in this association analysis; one SNP showed an association with both METH-use disorder and METH-induced psychosis. After Bonferroni's correction for multiple testing, however, this significance disappeared. No significant association was found with schizophrenia. Our findings suggest that a common genetic variation in the GCLM gene might not contribute to the risk of METH-use disorder and schizophrenia in the Japanese population.

Alpha4 and beta2 subunits of neuronal nicotinic acetylcholine receptor genes are not associated with methamphetamine-use disorder in the Japanese population.

The mesolimbic system is thought to be involved in the reinforcing action of many addictive drugs and the release of dopamine modulated by neuronal nicotine cholinergic receptors (nAChRs). Several investigations suggested that nAChRs on dopaminergic terminals play an important role in the development of some long-lasting adaptations associated with drug abuse. A majority of high-affinity nicotine binding sites in the brain have been showed in heteropentameric alpha4 (alpha4) and beta2 subunit (beta2) of nAChRs. Therefore, we conducted a genetic association analysis of the alpha4 gene (CHRNA4) and beta2 gene (CHRNB2) with methamphetamine (METH)-use disorder (191 cases and 753 controls). We first evaluated the linkage disequilibrium (LD) structure of these genes and selected 7 and 5 tagging SNPs (tag SNPs) on CHRNA4 and CHRNB2, respectively. Some tag SNPs were significantly associated with total METH-use disorder and METH-induced psychosis; however, these associations were no longer statistically significant after Bonferroni's correction for multiple testing. In conclusion, our results suggest that neither CHRNA4 nor CHRNB2 plays a major role in Japanese METH-use disorder.

Prostate apoptosis response 4 gene is not associated with methamphetamine-use disorder in the Japanese population.

Abnormal intracellular signaling molecules in dopamine signal transduction are thought to be associated with the pathophysiology of methamphetamine (METH)-use disorder. A recent study reported that a new intracellular protein, prostate apoptosis response 4 (Par-4), plays a critical role in dopamine 2 receptor signaling. We therefore analyzed the association between the Par-4 gene (PAWR) and METH-use disorder in a Japanese population (191 patients with METH-use disorder and 466 healthy controls). Using the recommended "gene-based" association analysis, we selected five tagging SNPs in PAWR from the HapMap database. No significant allele/genotype-wise or haplotype-wise association was found between PAWR and METH-use disorder. These results suggest that PAWR does not play a major role in METH-use disorders in the Japanese population.

The dysbindin gene (DTNBP1) is associated with methamphetamine psychosis.

BACKGROUND: The dysbindin (DTNBP1 [dystrobrevin-binding protein 1]) gene has repeatedly been shown to be associated with schizophrenia across diverse populations. One study also showed that risk haplotypes were shared with a bipolar disorder subgroup with psychotic episodes, but not with all cases. DTNBP1 may confer susceptibility to psychotic symptoms in various psychiatric disorders besides schizophrenia. METHODS: Methamphetamine psychosis, the psychotic symptoms of which are close to those observed in schizophrenia, was investigated through a case (n = 197)-control (n = 243) association analyses of DTNBP1. RESULTS: DTNBP1 showed significant associations with methamphetamine psychosis at polymorphisms of P1635 (rs3213207, p = .00003) and SNPA (rs2619538, p = .049) and the three-locus haplotype of P1655 (rs2619539)-P1635-SNPA (permutation p = .0005). The C-A-A haplotype, which was identical to the protective haplotype previously reported for schizophrenia and psychotic bipolar disorders, was a protective factor (p = .0013, odds ratio [OR] = .62, 95% confidence interval [CI] .51-.77) for methamphetamine psychosis. The C-G-T haplotype was a risk for methamphetamine psychosis (p = .0012, OR = 14.9, 95% CI 3.5-64.2). CONCLUSIONS: Our genetic evidence suggests that DTNBP1 is involved in psychotic liability not only for schizophrenia but also for other psychotic disorders, including substance-induced psychosis.