Shinichiro Nanko

SEROTONIN TRANSPORTER GENE POLYMORPHISMS : ETHNIC DIFFERENCE AND POSSIBLE ASSOCIATION WITH BIPOLAR AFFECTIVE DISORDER

There is some evidence suggesting that a polymorphism of variable number of tandem repeats (VNTR) in the second intron of the serotonin transporter (5-HTT) gene and another variation which lies 1.2 kb upstream of the promoter of the gene (5-HTTLPR) are associated with affective disorders. However, conflicting results have also been reported. We examined an allelic association of these two polymorphisms in a Japanese sample of 191 patients with affective disorders (142 bipolar and 49 unipolar) and 212 controls. Substantial differences in the number and frequency of alleles between Caucasians and Japanese were observed for both polymorphisms. A significant association between the VNTR polymorphism and bipolar disorder (genotypic association: odds ratio 2.2, 95% CI 1.2–4.0; allelic association: odds ratio 1.7, 95% CI 1.0–3.0) was found, but not between the 5-HTTLPR polymorphism and bipolar disorder. No significant association with unipolar depression was detected using either genetic marker, although this may be attributable to the relatively small number of subjects with unipolar depression. Our results suggest that the VNTR itself or another unknown functional polymorphism which would be in linkage disequilibrium to the VNTR has an effect on susceptibility to bipolar disorder.

Impaired feedback regulation of XBP1 as a genetic risk factor for bipolar disorder.

The pathophysiology of bipolar disorder is still unclear, although family, twin and linkage studies implicate genetic factors. Here we identified XBP1, a pivotal gene in the endoplasmic reticulum (ER) stress response, as contributing to the genetic risk factor for bipolar disorder. Using DNA microarray analysis of lymphoblastoid cells derived from two pairs of twins discordant with respect to the illness, we found downregulated expression of genes related to ER stress response in both affected twins. A polymorphism (−116C→G) in the promoter region of XBP1, affecting the putative binding site of XBP1, was significantly more common in Japanese patients (odds ratio = 4.6) and overtransmitted to affected offspring in trio samples of the NIMH Bipolar Disorder Genetics Initiative. XBP1-dependent transcription activity of the −116G allele was lower than that of the −116C allele, and in the cells with the G allele, induction of XBP1 expression after ER stress was markedly reduced. Valproate, one of three mood stabilizers, rescued the impaired response by inducing ATF6, the gene upstream of XBP1. These results indicate that the −116C→G polymorphism in XBP1 causes an impairment of its positive feedback system and increases the risk of bipolar disorder.

A combined analysis of D22S278 marker alleles in affected sib-pairs: Support for a susceptibility locus for schizophrenia at chromosome 22q12

Several groups have reported weak evidence for linkage between schizophrenia and genetic markers located on chromosome 22q using the lod score method of analysis. However these findings involved different genetic markers and methods of analysis, and so were not directly comparable. To resolve this issue we have performed a combined analysis of genotypic data from the marker D22S278 in multiply affected schizophrenic families derived from 11 independent research groups worldwide. This marker was chosen because it showed maximum evidence for linkage in three independent datasets (Vallada et al., Am J Med Genet 60:139-146, 1995; Polymeropoulos et al., Neuropsychiatr Genet 54:93-99, 1994; Lasseter et al., Am J Med Genet, 60:172-173, 1995. Using the affected sib-pair method as implemented by the program ESPA, the combined dataset showed 252 alleles shared compared with 188 alleles not share (chi-square 9.31, 1df, P = 0.001) where parental genotype data was completely known. When sib-pairs for whom parental data was assigned according to probability were included the number of alleles shared was 514.1 compared with 437.8 not shared (chi-square 6.12, 1df, P = 0.006). Similar results were obtained when a likelihood ratio method for sib-pair analysis was used. These results indicate that may be a susceptibility locus for schizophrenia at 22q12.

A novel polymorphism of the brain-derived neurotrophic factor (BDNF) gene associated with late-onset Alzheimer's disease

Several lines of evidence have suggested altered functions of the brain-derived neurotrophic factor (BDNF) in the pathogenesis of neurodegenerative diseases including Alzheimers disease (AD). In the search for polymorphisms in the 5′-flanking and 5′-noncoding regions of the BDNF gene, we found a novel nucleotide substitution (C270T) in the noncoding region. We performed an association study between this polymorphism and AD in a Japanese sample of 170 patients with sporadic AD (51 early-onset and 119 late-onset) and 498 controls. The frequency of individuals who carried the mutated type (T270) was significantly more common in patients with late-onset AD than in controls (P = 0.00004, odds ratio: 3.8, 95% CI 1.9–7.4). However, there was no significant difference in the genotype distribution between the patients with early-onset AD and the controls, although this might be due to the small sample size of the early-onset group. Our results suggest that the C270T polymorphism of the BDNF gene or other unknown polymorphisms, which are in linkage disequilibrium, give susceptibility to late-onset AD. We obtained no evidence for the possible interactions between the BDNF and apolipoprotein E (APOE) genes, suggesting that the possible effect of the BDNF gene on the development of late-onset AD might be independent of the APOE genotype.

Association between serotonin transporter gene polymorphism and anxiety-related traits

BACKGROUND Polymorphism in the serotonin transporter promoter gene has been recently reported to be associated with the personality trait known as anxiety-related traits. We have attempted to replicate these findings in 101 healthy Japanese subjects. METHODS The personality traits of the subjects were assessed with the tridimensional personality questionnaire. RESULTS An association was observed in the present study between individuals grouped according to the transporter gene and harm avoidance scores. CONCLUSIONS These data supported that there was an association between the serotonin transporter gene and anxiety.

Assessment of the Dexamethasone/CRH Test as a State-Dependent Marker for Hypothalamic-Pituitary-Adrenal (HPA) Axis Abnormalities in Major Depressive Episode: A Multicenter Study

There is compelling evidence for the involvement of hypothalamic-pituitary-adrenal (HPA) axis abnormalities in depression. Growing evidence has suggested that the combined dexamethasone (DEX)/corticotropin-releasing hormone (CRH) test is highly sensitive to detect HPA axis abnormalities. We organized a multicenter study to assess the DEX/CRH test as a state-dependent marker for major depressive episode in the Japanese population. We conducted the DEX/CRH test in 61 inpatients with major depressive episode (Diagnostic and Statistical Manual of Mental Disorders 4th edition (DSM-IV)) and 57 healthy subjects. In all, 35 patients were repeatedly assessed with the DEX/CRH test on admission and before discharge. The possible relationships between clinical variables and the DEX/CRH test were also examined. Significantly enhanced pituitary–adrenocortical responses to the DEX/CRH test were observed in patients on admission compared with controls. Such abnormalities in patients were significantly reduced after treatment, particularly in those who underwent electroconvulsive therapy (ECT) in addition to pharmacotherapy. Age and female gender were associated with enhanced hormonal responses to the DEX/CRH test. Severity of depression correlated with DEX/CRH test results, although this was explained, at least in part, by a positive correlation between age and severity in our patients. Medication per se was unrelated to DEX/CRH test results. These results suggest that the DEX/CRH test is a sensitive state-dependent marker to monitor HPA axis abnormalities in major depressive episode during treatment. Restoration from HPA axis abnormalities occurred with clinical responses to treatment, particularly in depressed patients who underwent ECT.

High and low activity alleles of catechol-O-methyltransferase gene: ethnic difference and possible association with Parkinson's disease

Catechol-O-methyltransferase (COMT) is an enzyme that inactivates catecholamines such as adrenaline, noradrenaline, dopamine, and levodopa. Recently an amino acid change (Val-108-Met) of the COMT protein was found to determine high and low activity alleles of the COMT gene. We genotyped 109 Japanese patients with Parkinsons disease (PD) and 153 controls by using polymerase chain reaction (PCR) amplification and digestion by the restriction enzyme NlaIII. The frequency of low activity allele in the controls was 0.29, which was significantly different from that reported in Caucasians (0.50). When comparison was made between patients with PD and controls, homozygosity for the low activity allele was significantly more common among the patients than among the controls (P = 0.017; odds ratio, 2.8, 95% CI 1.2-6.5), suggesting that homozygosity for the low activity allele may increase susceptibility to PD.

Low serum cholesterol in suicide attempters

Previous studies have shown an association between low serum cholesterol concentration and suicide; however, conflicting results have also been reported. To examine this potential association, cholesterol levels in 99 patients admitted to an emergency ward following an attempted suicide were compared with those in 74 nonsuicidal psychiatric inpatients, and those in 39 psychiatrically normal individuals with accidental injuries. Cholesterol concentrations in suicide attempters were found to be significantly lower compared with both psychiatric and normal controls, when sex, age, psychiatric diagnosis, and physical conditions (serum total protein and red blood cell count) were adjusted for. This significant relationship was observed in mood disorders and personality or neurotic disorders, but not in schizophrenia spectrum disorders. These results support the previous claim that lower cholesterol level is associated with an increased risk of suicidal behavior.

Mitochondrial DNA polymorphisms in bipolar disorder

BACKGROUND Previous studies suggested mitochondrial abnormality in bipolar disorder: (1) possible contribution of parent-of-origin effect in transmission of bipolar disorder; (2) abnormal brain phosphorus metabolism detected by phosphorus-31 magnetic resonance spectroscopy; (3) comorbidity of affective disorders in patients with mitochondrial encephalopathy; (4) increased levels of the 4977bp deletion of mitochondrial DNA (mtDNA) in the postmortem brains. We investigated mtDNA polymorphisms in association with bipolar disorder. METHODS Twelve PCR fragments including all tRNA genes were examined by the single-strand conformation polymorphism method in 43 bipolar patients. All observed polymorphisms were sequenced. Association of these polymorphisms with bipolar disorder was examined by restriction fragment length polymorphism method in 135 bipolar patients and 187 controls. RESULTS In total, we found 28 polymorphisms including 14 polymorphisms that have not been reported previously. The A10398G polymorphism was significantly associated with bipolar disorder (10398A genotype: 33.1% in bipolar, 22.2% in the control, P<0.05). Although this difference was not significant after Bonferroni correction, the CA haplotype of the 5178 and 10398 polymorphisms was still significantly associated with bipolar disorder (CA haplotype: 33.6% in bipolar, 16.8% in control, P<0.001). Three rare mutations substituting evolutionary conserved bases; A5539G in tRNA(Trp) gene, A5747G in the origin of L-strand replication, and A8537G in ATPase subunit-6 and -8 genes, were found in patients with family history in which maternal transmission was suspected. DISCUSSION The 5178C/10398A haplotype in mtDNA may be a risk factor of bipolar disorder (odds ratio, 2.4). Pathophysiological significance of rare mtDNA mutations needs to be verified in the future. This finding may imply the pathophysiological significance of mtDNA in bipolar disorder.

Catechol-O-methyltransferase polymorphisms and schizophrenia: a transmission disequilibrium study in multiply affected families

Catechol-O-methyltransferase (COMT) metabolizes catecholamines such as dopamine, noradrenaline and adrenaline. It exists as common high and low activity alleles in the population (determined by a valine 158 methionine polymorphism), and high red blood cell activity of COMT has previously been associated with schizophrenia. To examine the relationship between COMT and schizophrenia genetically, the transmission disequilibrium test was performed on 22 multiply affected Caucasian and Japanese families genotyped for val158met and a second, silent, polymorphism (C256G), using PCR based assays. The high activity val158 allele was transmitted from parents to the affected individuals more frequently than the low activity met158 allele, although this was not statistically significant. Combining this data with a previous study using Chinese family trios with schizophrenia (Li et al., 1996) gave a highly significant result (p = 0.0015). The G256 allele was also transmitted preferentially to the affected offspring, and this was statistically significant when schizophrenia, schizoaffective disorder and unspecified functional psychosis were included in the definition of the affected phenotype (p = 0.03). Overall, these findings may indicate an effect of COMT alleles on susceptibility to schizophrenia, or reflect linkage disequilibrium with a different causative polymorphism in the vicinity. Other reported associations of COMT with obsessive compulsive and rapid cycling bipolar disorder indicate that the COMT gene may have complex and pleiotropic effects on susceptibility and symptomatology of neuropsychiatric disorders.