Ichiro Kusumi

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.

DNA Methylation Profiles of the Brain-Derived Neurotrophic Factor (BDNF) Gene as a Potent Diagnostic Biomarker in Major Depression

Major depression, because of its recurring and life-threatening nature, is one of the top 10 diseases for global disease burden. Major depression is still diagnosed on the basis of clinical symptoms in patients. The search for specific biological markers is of great importance to advance the method of diagnosis for depression. We examined the methylation profile of 2 CpG islands (I and IV) at the promoters of the brain-derived neurotrophic factor (BDNF) gene, which is well known to be involved in the pathophysiology of depression. We analyzed genomic DNA from peripheral blood of 20 Japanese patients with major depression and 18 healthy controls to identify an appropriate epigenetic biomarker to aid in the establishment of an objective system for the diagnosis of depression. Methylation rates at each CpG unit was measured using a MassArray® system (SEQUENOM), and 2-dimensional hierarchical clustering analyses were undertaken to determine the validity of these methylation profiles as a diagnostic biomarker. Analyses of the dendrogram from methylation profiles of CpG I, but not IV, demonstrated that classification of healthy controls and patients at the first branch completely matched the clinical diagnosis. Despite the small number of subjects, our results indicate that classification based on the DNA methylation profiles of CpG I of the BDNF gene may be a valuable diagnostic biomarker for major depression.

Aberrant DNA methylation associated with bipolar disorder identified from discordant monozygotic twins

To search DNA methylation difference between monozygotic twins discordant for bipolar disorder, we applied a comprehensive genome scan method, methylation-sensitive representational difference analysis (MS-RDA) to lymphoblastoid cells derived from the twins. MS-RDA isolated 10 DNA fragments derived from 5′ region of known genes/ESTs. Among these 10 regions, four regions showed DNA methylation differences between bipolar twin and control co-twin confirmed by bisulfite sequencing. We performed a case–control study of DNA methylation status of these four regions by pyrosequencing. Two regions, upstream regions of spermine synthase (SMS) and peptidylprolyl isomerase E-like (PPIEL) (CN265253), showed aberrant DNA methylation status in bipolar disorder. SMS, a gene on X chromosome, showed significantly higher DNA methylation level in female patients with bipolar disorder compared with control females. However, there was no difference of mRNA expression. In PPIEL, DNA methylation level was significantly lower in patients with bipolar II disorder than in controls. The expression level of PPIEL was significantly higher in bipolar II disorder than in controls. We found strong inverse correlation between gene expression and DNA methylation levels of PPIEL. These results suggest that altered DNA methylation statuses of PPIEL might have some significance in pathophysiology of bipolar disorder.

Olanzapine increases plasma ghrelin level in patients with schizophrenia

OBJECTIVE Increased appetite and weight gain are frequently reported in treatment with olanzapine. However, the mechanism behind this appetite gain remains unclear. Ghrelin is a newly discovered appetite-stimulating peptide that has a role in the regulation of feeding behavior. Ghrelin is synthesized principally in the stomach, and the concentration of circulating ghrelin is negatively correlated with leptin and body fat mass. To elucidate the mechanism of appetite and weight gain during olanzapine treatment, we investigated the circulating ghrelin levels. METHODS Seven patients with schizophrenia were examined before and after 6-month administration of olanzapine. The concentrations of circulating ghrelin, leptin, glucose and lipid metabolic parameters were measured. RESULTS Body fat percentage (P=0.0121) and serum leptin (P=0.0284) were significantly increased after 6-month administration of olanzapine. Both plasma total ghrelin (P=0.0188) and active ghrelin levels (P=0.0057) were significantly increased. Six of the seven patients reported increased appetite during olanzapine treatment. Other glucose and lipid parameters were not altered significantly. CONCLUSIONS Although, the leptin level and body fat percentage were significantly increased, the concentration of circulating ghrelin was also significantly increased. Olanzapine may directly act on the secretion of ghrelin and induce appetite, resulting in weight gain.

Genomewide High-Density SNP Linkage Analysis of 236 Japanese Families Supports the Existence of Schizophrenia Susceptibility Loci on Chromosomes 1p, 14q, and 20p

The Japanese Schizophrenia Sib-Pair Linkage Group (JSSLG) is a multisite collaborative study group that was organized to create a national resource for affected sib pair (ASP) studies of schizophrenia in Japan. We used a high-density single-nucleotide-polymorphism (SNP) genotyping assay, the Illumina BeadArray linkage mapping panel (version 4) comprising 5,861 SNPs, to perform a genomewide linkage analysis of JSSLG samples comprising 236 Japanese families with 268 nonindependent ASPs with schizophrenia. All subjects were Japanese. Among these families, 122 families comprised the same subjects analyzed with short tandem repeat markers. All the probands and their siblings, with the exception of seven siblings with schizoaffective disorder, had schizophrenia. After excluding SNPs with high linkage disequilibrium, we found significant evidence of linkage of schizophrenia to chromosome 1p21.2-1p13.2 (LOD=3.39) and suggestive evidence of linkage to 14q11.2 (LOD=2.87), 14q11.2-q13.2 (LOD=2.33), and 20p12.1-p11.2 (LOD=2.33). Although linkage to these regions has received little attention, these regions are included in or partially overlap the 10 regions reported by Lewis et al. that passed the two aggregate criteria of a meta-analysis. Results of the present study--which, to our knowledge, is the first genomewide analysis of schizophrenia in ASPs of a single Asian ethnicity that is comparable to the analyses done of ASPs of European descent--indicate the existence of schizophrenia susceptibility loci that are common to different ethnic groups but that likely have different ethnicity-specific effects.

The International Consortium on Lithium Genetics (ConLiGen): An Initiative by the NIMH and IGSLI to Study the Genetic Basis of Response to Lithium Treatment

For more than half a decade, lithium has been successfully used to treat bipolar disorder. Worldwide, it is considered the first-line mood stabilizer. Apart from its proven antimanic and prophylactic effects, considerable evidence also suggests an antisuicidal effect in affective disorders. Lithium is also effectively used to augment antidepressant drugs in the treatment of refractory major depressive episodes and prevent relapses in recurrent unipolar depression. In contrast to many psychiatric drugs, lithium has outlasted various pharmacotherapeutic ‘fashions’, and remains an indispensable element in contemporary psychopharmacology. Nevertheless, data from pharmacogenetic studies of lithium are comparatively sparse, and these studies are generally characterized by small sample sizes and varying definitions of response. Here, we present an international effort to elucidate the genetic underpinnings of lithium response in bipolar disorder. Following an initiative by the International Group for the Study of Lithium-Treated Patients (www.IGSLI.org) and the Unit on the Genetic Basis of Mood and Anxiety Disorders at the National Institute of Mental Health,lithium researchers from around the world have formed the Consortium on Lithium Genetics (www.ConLiGen.org) to establish the largest sample to date for genome-wide studies of lithium response in bipolar disorder, currently comprising more than 1,200 patients characterized for response to lithium treatment. A stringent phenotype definition of response is one of the hallmarks of this collaboration. ConLiGen invites all lithium researchers to join its efforts.

Involvement of a polymorphism in the 5-HT2A receptor gene in impulsive behavior.

Rationale and objectiveImpulsive behavior has been suggested to occur due to a dysfunction of serotonergic 5-HT neurotransmission. After evaluation by a self-reporting measure, a polymorphism in the promoter of the 5-HT2A receptor gene has been proposed to underlie the impulsive behavior; however, this hypothesis is not convincing. In this study, we examined whether this 5-HT2A receptor gene polymorphism is involved in impulsive aggression by evaluating a behavioral task (go/no-go task) in normal volunteers.Materials and methodsThe polymorphism of the 5-HT2A receptor gene promoter was analyzed by polymerase chain reaction using lymphocytes from 71 volunteers. Impulsivity was defined as the number of commission errors (responding when one should not) made during a go/no-go task (a larger number of commission errors indicates greater difficulty in inhibiting the behavior).ResultsThe subjects in the group with the A-1438A allele of the 5-HT2A receptor gene (A-1438A group) made more commission errors under the punishment–reward condition in a go/no-go task than those in the G-1438G group.ConclusionsThese results suggest the possible involvement of the A-1438A polymorphism of the 5-HT2A receptor gene in impulsive behavior; this was evaluated using a behavioral task measure that can directly reveal the traits of human impulsive behavior.

Assessment of Response to Lithium Maintenance Treatment in Bipolar Disorder: A Consortium on Lithium Genetics (ConLiGen) Report

Objective The assessment of response to lithium maintenance treatment in bipolar disorder (BD) is complicated by variable length of treatment, unpredictable clinical course, and often inconsistent compliance. Prospective and retrospective methods of assessment of lithium response have been proposed in the literature. In this study we report the key phenotypic measures of the “Retrospective Criteria of Long-Term Treatment Response in Research Subjects with Bipolar Disorder” scale currently used in the Consortium on Lithium Genetics (ConLiGen) study. Materials and Methods Twenty-nine ConLiGen sites took part in a two-stage case-vignette rating procedure to examine inter-rater agreement [Kappa (κ)] and reliability [intra-class correlation coefficient (ICC)] of lithium response. Annotated first-round vignettes and rating guidelines were circulated to expert research clinicians for training purposes between the two stages. Further, we analyzed the distributional properties of the treatment response scores available for 1,308 patients using mixture modeling. Results Substantial and moderate agreement was shown across sites in the first and second sets of vignettes (κ = 0.66 and κ = 0.54, respectively), without significant improvement from training. However, definition of response using the A score as a quantitative trait and selecting cases with B criteria of 4 or less showed an improvement between the two stages (ICC1 = 0.71 and ICC2 = 0.75, respectively). Mixture modeling of score distribution indicated three subpopulations (full responders, partial responders, non responders). Conclusions We identified two definitions of lithium response, one dichotomous and the other continuous, with moderate to substantial inter-rater agreement and reliability. Accurate phenotypic measurement of lithium response is crucial for the ongoing ConLiGen pharmacogenomic study.

Serotonin-induced platelet intracellular calcium mobilization in depressed patients

Serotonin(5-HT)-stimulated intracellular calcium(Ca) mobilization was measured in the platelets of depressed patients to assess 5-HT2 receptor function. The 5-HT-induced Ca response was significantly higher in unmedicated patients with bipolar depression and melancholic major depression than in those with non-melancholic major depression and normal controls. The enhanced Ca response to 5-HT failed to correlate with severity of depressive symptoms. In patients with bipolar disorder and melancholic major depression, there was no significant difference in 5-HT-stimulated Ca response between the unmedicated group and those in remission. These results suggest that 5-HT2 receptor function is increased in some types of depression, and raise the possibility that the enhanced Ca response to 5-HT may be trait dependent rather than state dependent.

Hypermethylation of serotonin transporter gene in bipolar disorder detected by epigenome analysis of discordant monozygotic twins

Bipolar disorder (BD) is a severe mental disorder characterized by recurrent episodes of mania and depression. Serotonin transporter (HTT) is a target of antidepressants and is one of the strongest candidate molecules of mood disorder, however, genetic study showed equivocal results. Here, we performed promoter-wide DNA methylation analysis of lymphoblastoid cell lines (LCLs) derived from two pairs of monozygotic twins discordant for BD. To rule out the possible discordance of copy number variation (CNV) between twins, we performed CNV analysis and found the copy number profiles were nearly identical between the twin pairs except for immunoglobulin-related regions. Among the three genes we obtained as candidate regions showing distinct difference of DNA methylation between one of the two pairs, hypermethylation of SLC6A4, encoding HTT, in the bipolar twin was only confirmed by bisulfite sequencing. Then, promoter hypermethylation of SLC6A4 in LCLs of BD patients was confirmed in a case–control analysis. DNA methylation of SLC6A4 was significantly correlated with its mRNA expression level in individuals with the S/S genotype of HTTLPR, and mRNA expression level was lower in BD patients carrying the S/S genotype. Finally, DNA methylation of the same site was also higher in the postmortem brains of BD patients. This is the first study to report the role of epigenetic modification of SLC6A4 in BD using an unbiased approach, which provides an insight for its pathophysiology.