Genome-wide scan in Portuguese Island families implicates multiple loci in bipolar disorder: fine mapping adds support on chromosomes 6 and 11

The neurocognitive and functional profile of schizophrenia in a genetically homogenous European sample

Schizophrenia is a complex heritable brain disorder that entails significant social, neurocognitive, and functional deficits, and significant psychosocial challenges to affected and unaffected family members. In this cross-sectional study, we explore impairments in specific neurocognitive and social cognition processes in patients affected with schizophrenia, unaffected relatives, and in controls to provide a characterization of a genetically homogenous European sample from an endophenotypic and functional standpoint. A sample of 38 affected patients, 28 first-degree relatives, and 97 controls performed a series of computerized and skills-based assessments. Samples were compared across several neurocognitive, social, and functional domains. Significant impairments in episodic memory, executive function, social cognition, complex cognition, sensorimotor domains were found in patients and first-degree relatives. Findings also showed increased processing speed in memory and other complex cognitive processes relevant to autonomous living. A discriminant function analysis yielded 2 functions allowing 79% of correct group classifications based on social cognition and functional skills, neurocognition, and age. The study highlights the importance of resourcing to wide-ranging assessment methodologies, of developing research efforts to further understand the decline of social and neurocognitive processes, and the need for designing more targeted intervention strategies to be implemented both with affected patients and families.

Genomic variants in an inbred mouse model predict mania-like behaviors

Contemporary rodent models for bipolar disorders split the bipolar spectrum into complimentary behavioral endophenotypes representing mania and depression. Widely accepted mania models typically utilize single gene transgenics or pharmacological manipulations, but inbred rodent strains show great potential as mania models. Their acceptance is often limited by the lack of genotypic data needed to establish construct validity. In this study, we used a unique strategy to inexpensively explore and confirm population allele differences in naturally occurring candidate variants in a manic rodent strain, the Madison (MSN) mouse strain. Variants were identified using whole exome resequencing on a small population of animals. Interesting candidate variants were confirmed in a larger population with genotyping. We enriched these results with observations of locomotor behavior from a previous study. Resequencing identified 447 structural variants that are mostly fixed in the MSN strain relative to control strains. After filtering and annotation, we found 11 non-synonymous MSN variants that we believe alter protein function. The allele frequencies for 6 of these variants were consistent with explanatory variants for the Madison strain's phenotype. The variants are in the Npas2, Cp, Polr3c, Smarca4, Trpv1, and Slc5a7 genes, and many of these genes' products are in pathways implicated in human bipolar disorders. Variants in Smarca4 and Polr3c together explained over 40% of the variance in locomotor behavior in the Hsd:ICR founder strain. These results enhance the MSN strain's construct validity and implicate altered nucleosome structure and transcriptional regulation as a chief molecular system underpinning behavior.

Genome-wide haplotype-based association analysis of major depressive disorder in Generation Scotland and UK Biobank

Genome-wide association studies using genotype data have had limited success in the identification of variants associated with major depressive disorder (MDD). Haplotype data provide an alternative method for detecting associations between variants in weak linkage disequilibrium with genotyped variants and a given trait of interest. A genome-wide haplotype association study for MDD was undertaken utilising a family-based population cohort, Generation Scotland: Scottish Family Health Study (n = 18,773), as a discovery cohort with UK Biobank used as a population-based replication cohort (n = 25,035). Fine mapping of haplotype boundaries was used to account for overlapping haplotypes potentially tagging the same causal variant. Within the discovery cohort, two haplotypes exceeded genome-wide significance (P < 5 × 10^-8) for an association with MDD. One of these haplotypes was nominally significant in the replication cohort (P < 0.05) and was located in 6q21, a region which has been previously associated with bipolar disorder, a psychiatric disorder that is phenotypically and genetically correlated with MDD. Several haplotypes with P < 10^-7 in the discovery cohort were located within gene coding regions associated with diseases that are comorbid with MDD. Using such haplotypes to highlight regions for sequencing may lead to the identification of the underlying causal variants.

TLX: A master regulator for neural stem cell maintenance and neurogenesis

The orphan nuclear receptor TLX, also known as NR2E1, is an essential regulator of neural stem cell (NSC) self-renewal, maintenance, and neurogenesis. In vertebrates, TLX is specifically localized to the neurogenic regions of the forebrain and retina throughout development and adulthood. TLX regulates the expression of genes involved in multiple pathways, such as the cell cycle, DNA replication, and cell adhesion. These roles are primarily performed through the transcriptional repression or activation of downstream target genes. Emerging evidence suggests that the misregulation of TLX might play a role in the onset and progression of human neurological disorders making this factor an ideal therapeutic target. Here, we review the current understanding of TLX function, expression, regulation, and activity significant to NSC maintenance, adult neurogenesis, and brain plasticity. This article is part of a Special Issue entitled: Nuclear receptors in animal development.

The genomic psychiatry cohort: partners in discovery

The Genomic Psychiatry Cohort (GPC) is a longitudinal resource designed to provide the necessary population-based sample for large-scale genomic studies, studies focusing on Research Domain Criteria (RDoC) and/or other alternate phenotype constructs, clinical and interventional studies, nested case-control studies, long-term disease course studies, and genomic variant-to-phenotype studies. We provide and will continue to encourage access to the GPC as an international resource. DNA and other biological samples and diagnostic data are available through the National Institute of Mental Health (NIMH) Repository. After appropriate review and approval by an advisory board, investigators are able to collaborate in, propose, and co-lead studies involving cohort participants.

A new mouse model for mania shares genetic correlates with human bipolar disorder

Bipolar disorder (BPD) is a debilitating heritable psychiatric disorder. Contemporary rodent models for the manic pole of BPD have primarily utilized either single locus transgenics or treatment with psychostimulants. Our lab recently characterized a mouse strain termed Madison (MSN) that naturally displays a manic phenotype, exhibiting elevated locomotor activity, increased sexual behavior, and higher forced swimming relative to control strains. Lithium chloride and olanzapine treatments attenuate this phenotype. In this study, we replicated our locomotor activity experiment, showing that MSN mice display generationally-stable mania relative to their outbred ancestral strain, hsd:ICR (ICR). We then performed a gene expression microarray experiment to compare hippocampus of MSN and ICR mice. We found dysregulation of multiple transcripts whose human orthologs are associated with BPD and other psychiatric disorders including schizophrenia and ADHD, including: Epor, Smarca4, Cmklr1, Cat, Tac1, Npsr1, Fhit, and P2rx7. RT-qPCR confirmed dysregulation for all of seven transcripts tested. Using a novel genome enrichment algorithm, we found enrichment in genome regions homologous to human loci implicated in BPD in replicated linkage studies including homologs of human cytobands 1p36, 3p14, 3q29, 6p21–22, 12q24, 16q24, and 17q25. Using a functional network analysis, we found dysregulation of a gene system related to chromatin packaging, a result convergent with recent human findings on BPD. Our findings suggest that MSN mice represent a polygenic model for the manic pole of BPD showing much of the genetic systems complexity of the corresponding human disorder. Further, the high degree of convergence between our findings and the human literature on BPD brings up novel questions about evolution by analogy in mammalian genomes.

Genome-wide association study of antidepressant treatment-emergent suicidal ideation

Emergence of suicidal ideation (TESI) during treatment with antidepressants in major depression led to a black box warning. We performed a genome-wide association study to identify genetic markers, which increase the risk for this serious side effect. TESI was evaluated in depressed in-patients (N=397) and defined by an emergence of suicidal thoughts during hospitalization without suicidal thoughts at admission using the suicide item (3) of the Hamilton Depression Rating Scale. Genotype distribution of 405.383 single-nucleotide polymorphisms (SNPs) in patients with TESI (N=32/8.1%) was compared to patients without increase in suicidal ideation (N=329/82.9%) and to a subgroup never reported suicidal ideation (N=79/19.9%). Top results were analyzed in an independent sample (N=501). None variant reached genome-wide significance, the best associated SNP was rs1630535 (p-value=1.3 × 10(-7)). The top 79 SNPs could be analyzed in an independent sample, and 14 variants showed nominal significant association with the same risk allele in the replication sample. A discriminant analysis classifying patients using these 79 SNPs revealed a 91% probability to classify TESI vs non-TESI cases correctly in the replication sample. Although our data need to be interpreted carefully owing to the small numbers in both cohorts, they suggest that a combination of genetic markers might indeed be used to identify patients at risk for TESI.

Convergent functional genomic studies of ω-3 fatty acids in stress reactivity, bipolar disorder and alcoholism

Omega-3 fatty acids have been proposed as an adjuvant treatment option in psychiatric disorders. Given their other health benefits and their relative lack of toxicity, teratogenicity and side effects, they may be particularly useful in children and in females of child-bearing age, especially during pregnancy and postpartum. A comprehensive mechanistic understanding of their effects is needed. Here we report translational studies demonstrating the phenotypic normalization and gene expression effects of dietary omega-3 fatty acids, specifically docosahexaenoic acid (DHA), in a stress-reactive knockout mouse model of bipolar disorder and co-morbid alcoholism, using a bioinformatic convergent functional genomics approach integrating animal model and human data to prioritize disease-relevant genes. Additionally, to validate at a behavioral level the novel observed effects on decreasing alcohol consumption, we also tested the effects of DHA in an independent animal model, alcohol-preferring (P) rats, a well-established animal model of alcoholism. Our studies uncover sex differences, brain region-specific effects and blood biomarkers that may underpin the effects of DHA. Of note, DHA modulates some of the same genes targeted by current psychotropic medications, as well as increases myelin-related gene expression. Myelin-related gene expression decrease is a common, if nonspecific, denominator of neuropsychiatric disorders. In conclusion, our work supports the potential utility of omega-3 fatty acids, specifically DHA, for a spectrum of psychiatric disorders such as stress disorders, bipolar disorder, alcoholism and beyond.

European collaborative study of early-onset bipolar disorder: Evidence for genetic heterogeneity on 2q14 according to age at onset

Bipolar disorder has a genetic component, but the mode of inheritance remains unclear. A previous genome scan conducted in 70 European families led to detect eight regions linked to bipolar disease. Here, we present an investigation of whether the phenotypic heterogeneity of the disorder corresponds to genetic heterogeneity in these regions using additional markers and an extended sample of families. The MLS statistic was used for linkage analyses. The predivided sample test and the maximum likelihood binomial methods were used to test genetic homogeneity between early-onset bipolar type I (cut-off of 22 years) and other types of the disorder (later onset of bipolar type I and early-onset bipolar type II), using a total of 138 independent bipolar-affected sib-pairs. Analysis of the extended sample of families supports linkage in four regions (2q14, 3p14, 16p23, and 20p12) of the eight regions of linkage suggested by our previous genome scan. Heterogeneity testing revealed genetic heterogeneity between early and late-onset bipolar type I in the 2q14 region (P = 0.0001). Only the early form of the bipolar disorder but not the late form appeared to be linked to this region. This region may therefore include a genetic factor either specifically involved in the early-onset bipolar type I or only influencing the age at onset (AAO). Our findings illustrate that stratification according to AAO may be valuable for the identification of genetic vulnerability polymorphisms. © 2010 Wiley-Liss, Inc.

Genome-wide linkage scan of bipolar disorder in a Colombian population isolate replicates Loci on chromosomes 7p21-22, 1p31, 16p12 and 21q21-22 and identifies a novel locus on chromosome 12q

BACKGROUND/AIMS

Bipolar disorder (BP) is a severe psychiatric illness, characterised by alternating episodes of depression and mania, which ranks among the top ten causes of morbidity and life-long disability world-wide. We have previously performed a whole-genome linkage scan on 6 pedigrees segregating severe BP from the well-characterised population isolate of Antioquia, Colombia. We recently collected genotypes for the same set of 382 autosomal microsatellite markers in 9 additional Antioquian BP pedigrees. Here, we report the analysis of the combined pedigree set.

METHODS

Linkage analysis using both parametric and nonparametric approaches was conducted for 3 different diagnostic models: severe BP only (BPI); mood disorders (BPI, BPII and major depression); and psychosis (operationally defined by the occurrence of at least 1 episode of hallucinations and/or delusions).

RESULTS AND CONCLUSION

For BPI only, the most interesting result was obtained for chromosome 7p21.1-p22.2 under a recessive model of inheritance (heterogeneity LOD score = 2.80), a region that had previously been linked to BP in a study on Portuguese Island families. For both BPI and mood disorders, nonparametric analyses identified a locus on chromosome 12ct-q14 (nonparametric linkage = 2.55 and 2.35, respectively). This locus has not previously been reported as a candidate region for BP. Additional candidate regions were found on chromosomes 1p22-31 (mood disorders) and 21q21-22 (BPI), 2 loci that have repeatedly been implicated in BP susceptibility. Linkage analysis of psychosis as a phenotype identified candidate regions on chromosomes 2q24-31 and 16p12-q12. The finding on chromosome 16p is noteworthy because the same locus has been implicated by genome-wide association analyses of BP.

An investigation of candidate regions for association with bipolar disorder

We performed a case-control study of 1,000 cases and 1,028 controls on 1,509 markers, 1,139 of which were located in a 8 Mb region on chromosome 6 (105-113 Mb). This region has shown evidence of involvement in bipolar disorder (BP) in a number of other studies. We find association between BP and two SNPs in the gene LACE1. SNP rs9486880 and rs11153113 (both have P-values of 2 × 10(-5)). Both P-values are in the top 5% of the distribution derived from null simulations (P = 0.02 and 0.01, respectively). LACE is a good candidate for BP; it is an ATPase. We genotyped 173 other markers in 17 other positional and/or functional loci but found no further evidence of association with BP.

Early life stressors and genetic influences on the development of bipolar disorder: the roles of childhood abuse and brain-derived neurotrophic factor

OBJECTIVES

Although there is increasing research exploring the psychosocial influences and biological underpinnings of bipolar disorder, relatively few studies have specifically examined the interplay between these factors in the development of this illness. Social-biological models within a developmental psychopathology perspective are necessary to advance our understanding of the processes involved in the onset and course of bipolar disorder. This article presents a review of the empirical literature linking childhood abuse to bipolar disorder, the research to date on the possible role of brain-derived neurotrophic factor (BDNF) in the development of this disorder, followed by a discussion of how childhood abuse may interact with BDNF.

METHODS

A literature search was conducted using Psycinfo to identify relevant articles on childhood abuse, BDNF, and bipolar disorder.

RESULTS

The extant research implicates both childhood abuse and BDNF in the etiology of bipolar disorder. Specifically, there is growing evidence associating early abuse to the development of bipolar disorder. Similarly, the BDNF Val66 allele has been linked with increased susceptibility to bipolar disorder. Based on existing research, a genetic diathesis-transactional stress model is proposed incorporating childhood abuse and the BDNF gene in the pathogenesis of bipolar disorder.

CONCLUSIONS

Although there is some support for this model, the relatively modest amount of relevant literature highlights the need for further research. An integrative theoretical framework including both social and biological processes in bipolar disorder is important for the development of effective prevention and treatment strategies for this disorder.

Hyperactivity, startle reactivity and cell-proliferation deficits are resistant to chronic lithium treatment in adult Nr2e1(frc/frc) mice

The NR2E1 region on Chromosome 6q21-22 has been repeatedly linked to bipolar disorder (BP) and NR2E1 has been associated with BP, and more specifically bipolar I disorder (BPI). In addition, patient sequencing has shown an enrichment of rare candidate-regulatory variants. Interestingly, mice carrying either spontaneous (Nr2e1(frc) ) or targeted (Tlx(-) ) deletions of Nr2e1 (here collectively known as Nr2e1-null) show similar neurological and behavioral anomalies, including hypoplasia of the cerebrum, reduced neural stem cell proliferation, extreme aggression and deficits in fear conditioning; these are the traits that have been observed in some patients with BP. Thus, NR2E1 is a positional and functional candidate for a role in BP. However, no Nr2e1-null mice have been fully evaluated for behaviors used to model BP in rodents or pharmacological responses to drugs effective in treating BP symptoms. In this study we examine Nr2e1(frc/frc) mice, homozygous for the spontaneous deletion, for abnormalities in activity, learning and information processing, and cell proliferation; these are the phenotypes that are either affected in patients with BP or commonly assessed in rodent models of BP. The effect of lithium, a drug used to treat BP, was also evaluated for its ability to attenuate Nr2e1(frc/frc) behavioral and neural stem cell-proliferation phenotypes. We show for the first time that Nr2e1-null mice exhibit extreme hyperactivity in the open field as early as postnatal day 18 and in the home cage, deficits in open-field habituation and passive avoidance, and surprisingly, an absence of acoustic startle. We observed a reduction in neural stem/progenitor cell proliferation in Nr2e1(frc/frc) mice, similar to that seen in other Nr2e1-null strains. These behavioral and cell-proliferation phenotypes were resistant to chronic-adult-lithium treatment. Thus, Nr2e1(frc/frc) mice exhibit behavioral traits used to model BP in rodents, but our results do not support Nr2e1(frc/frc) mice as pharmacological models for BP.

A systematic association mapping on chromosome 6q in bipolar affective disorder--evidence for the melanin-concentrating-hormone-receptor-2 gene as a risk factor for bipolar affective disorder

Strong evidence of linkage between chromosomal region 6q16-q22 and bipolar affective disorder (BPAD) has previously been reported. We conducted a systematic association mapping of the 6q-linkage interval using 617 SNP markers in a BPAD case-control sample of German descent (cases = 330, controls = 325). In this screening step, 46 SNPs showed nominally significant BPAD-association (P-values between 0.0007 and 0.0484). Although none of the 46 SNPs survived correction for multiple testing, they were genotyped in a second and ethnically matched BPAD sample (cases = 328, controls = 397). At the melanin-concentrating-hormone-receptor-2 (MCHR2) gene, we found nominal association in both the initial and second BPAD samples (combined P = 0.008). This finding was followed up by the genotyping of 17 additional MCHR2-SNPs in the combined sample in order to define our findings more precisely. We found that the MCHR2-locus can be divided into three different haplotype-blocks, and observed that the MCHR2-association was most pronounced in BPAD male patients with psychotic symptoms. In two neighboring blocks, putative risk-haplotypes were found to be 7% more frequent in patients (block II: 23.3% vs. 16.2%, P = 0.005, block III: 39.2% vs. 32.0%, P = 0.024), whereas the putative protective haplotypes were found to be 5-8% less frequent in patients (block II: 11.6% vs. 16.4%, P = 0.041, block III: 30.0% vs. 38.8%, P = 0.007). The corresponding odds ratios (single-marker analysis) ranged between 1.25 and 1.46. Our findings may indicate that MCHR2 is a putative risk factor for BPAD. These findings should be interpreted with caution and replicated in independent BPAD samples.

A novel analytical framework for dissecting the genetic architecture of behavioral symptoms in neuropsychiatric disorders

BACKGROUND

For diagnosis of neuropsychiatric disorders, a categorical classification system is often utilized as a simple way for conceptualizing an often complex clinical picture. This approach provides an unsatisfactory model of mental illness, since in practice patients do not conform to these prototypical diagnostic categories. Family studies show notable familial co-aggregation between schizophrenia and bipolar illness and between schizoaffective disorders and both bipolar disorder and schizophrenia, revealing that mental illness does not conform to such categorical models and is likely to follow a continuum encompassing a spectrum of behavioral symptoms.

RESULTS AND METHODOLOGY

We introduce an analytic framework to dissect the phenotypic heterogeneity present in complex psychiatric disorders based on the conceptual paradigm of a continuum of psychosis. The approach identifies subgroups of behavioral symptoms that are likely to be phenotypically and genetically homogenous. We have evaluated this approach through analysis of simulated data with simulated behavioral traits and predisposing genetic factors. We also apply this approach to a psychiatric dataset of a genome scan for schizophrenia for which extensive behavioral information was collected for each individual patient and their families. With this approach, we identified significant evidence for linkage among depressed individuals with two distinct symptom profiles, that is individuals with sleep disturbance symptoms with linkage on chromosome 2q13 and also a mutually exclusive group of individuals with symptoms of concentration problems with linkage on chromosome 2q35. In addition we identified a subset of individuals with schizophrenia defined by language disturbances with linkage to chromosome 2p25.1 and a group of patients with a phenotype intermediate between those of schizophrenia and schizoaffective disorder with linkage to chromosome 2p21.

CONCLUSIONS

The findings presented are novel and demonstrate the efficacy of this approach in detection of genes underlying such complex human disorders as schizophrenia and depression.

Two-dimensional genome scan identifies multiple genetic interactions in bipolar affective disorder

BACKGROUND

Bipolar disorder is a highly heritable psychiatric condition, the etiology of which remains largely unknown despite extensive efforts to identify susceptibility genes. Interactions between genes of small individual effect could partially explain the difficulties of traditional one-dimensional approaches to identify genetic risk factors.

METHODS

A nonparametric linkage (NPL) analysis of 65 Australian extended pedigrees containing 643 genotyped individuals (of whom 40% were diagnosed with affective disorder) was conducted. Chromosome-by-chromosome correlation analysis of family-specific NPL scores was conducted to detect evidence of genetic interaction. Interaction-specific multipoint NPL and permutation analysis was used to assess linkage interdependence, using family weights derived from the alternative interacting chromosome. Finally, a single nucleotide analysis of each interaction region was conducted using the publicly available genome-wide association, datasets (2933 cases, 2534 controls).

RESULTS

Significant NPL peaks were detected on chromosomes 2q24-33, 7q21-31, and 17q11-25 (Z = 3.12, 3.01, and 2.95 respectively), with four additional suggestive peaks identified. Four robust interchromosomal interaction clusters exceeding Bonferroni correction at alpha = .05 (uncorrected p < 5.38e-07) were detected on 11q23-25-2p15-12, 4q32-35-1p36, 12q23-24-4p16-15, and 20q13-9q21-22. This linkage interdependence was determined significant after permutation analysis (p = .002-.0002). A suggestive interaction was observed in the combined data on 2p14-11q23 (uncorrected p = 5.76E-10, Bonferroni corrected p = .068).

CONCLUSIONS

This study indicates a complex interplay between multiple loci underlying bipolar disorder susceptibility, and highlights the continuing usefulness of extended pedigrees in complex genetics. The challenge lies in the identification of specific gene interactions and their biological validation.

Long tandem repeats as a form of genomic copy number variation: structure and length polymorphism of a chromosome 5p repeat in control and schizophrenia populations

OBJECTIVES

Genomic copy number variations (CNVs) are a major form of variation in the human genome and play an etiologic role in several neuropsychiatric diseases. Tandem repeats, particularly with long (>50 bp) repeat units, are a relatively common yet underexplored type of CNV that may significantly contribute to human genomic variation and disease risk. We therefore carried out a pilot experiment to explore the potential role of long tandem repeats as risk factors in psychiatric disorders.

METHODS

A bacterial artificial chromosome-based array comparative genomic hybridization (aCGH) platform was used to examine CNVs in genomic DNA from 34 probands with schizophrenia or schizoaffective disorder.

RESULTS

The aCGH screen detected an apparent deletion on 5p15.1 in two probands, caused by the presence in each proband of two low copy number (short) alleles of a tandem repeat that ranges in length from fewer than 10 to greater than 50 3.4 kb units in the population examined. Short alleles partially segregate with schizophrenia in a small number of families, though linkage was not significant. An association study showed no significant difference in repeat length between 406 schizophrenia cases and 392 controls.

CONCLUSION

Although we did not demonstrate a relationship between the 5p15.1 repeat and schizophrenia, our results illustrate that long tandem repeats represent an intriguing type of genetic variation that have not been studied in earlier connection with psychiatric illness. aCGH can detect a small subset of these repeats, but systematic investigation will require the development of specific arrays and improved analytical methods.

Genomic imprinting in the development and evolution of psychotic spectrum conditions

I review and evaluate genetic and genomic evidence salient to the hypothesis that the development and evolution of psychotic spectrum conditions have been mediated in part by alterations of imprinted genes expressed in the brain. Evidence from the genetics and genomics of schizophrenia, bipolar disorder, major depression, Prader-Willi syndrome, Klinefelter syndrome, and other neurogenetic conditions support the hypothesis that the etiologies of psychotic spectrum conditions commonly involve genetic and epigenetic imbalances in the effects of imprinted genes, with a bias towards increased relative effects from imprinted genes with maternal expression or other genes favouring maternal interests. By contrast, autistic spectrum conditions, including Kanner autism, Asperger syndrome, Rett syndrome, Turner syndrome, Angelman syndrome, and Beckwith-Wiedemann syndrome, commonly engender increased relative effects from paternally expressed imprinted genes, or reduced effects from genes favouring maternal interests. Imprinted-gene effects on the etiologies of autistic and psychotic spectrum conditions parallel the diametric effects of imprinted genes in placental and foetal development, in that psychotic spectrum conditions tend to be associated with undergrowth and relatively-slow brain development, whereas some autistic spectrum conditions involve brain and body overgrowth, especially in foetal development and early childhood. An important role for imprinted genes in the etiologies of psychotic and autistic spectrum conditions is consistent with neurodevelopmental models of these disorders, and with predictions from the conflict theory of genomic imprinting.

The genetics of bipolar disorder: genome 'hot regions,' genes, new potential candidates and future directions

Bipolar disorder (BP) is a complex disorder caused by a number of liability genes interacting with the environment. In recent years, a large number of linkage and association studies have been conducted producing an extremely large number of findings often not replicated or partially replicated. Further, results from linkage and association studies are not always easily comparable. Unfortunately, at present a comprehensive coverage of available evidence is still lacking. In the present paper, we summarized results obtained from both linkage and association studies in BP. Further, we indicated new potential interesting genes, located in genome 'hot regions' for BP and being expressed in the brain. We reviewed published studies on the subject till December 2007. We precisely localized regions where positive linkage has been found, by the NCBI Map viewer (http://www.ncbi.nlm.nih.gov/mapview/); further, we identified genes located in interesting areas and expressed in the brain, by the Entrez gene, Unigene databases (http://www.ncbi.nlm.nih.gov/entrez/) and Human Protein Reference Database (http://www.hprd.org); these genes could be of interest in future investigations. The review of association studies gave interesting results, as a number of genes seem to be definitively involved in BP, such as SLC6A4, TPH2, DRD4, SLC6A3, DAOA, DTNBP1, NRG1, DISC1 and BDNF. A number of promising genes, which received independent confirmations, and genes that have to be further investigated in BP, have been also systematically listed. In conclusion, the combination of linkage and association approaches provided a number of liability genes. Nevertheless, other approaches are required to disentangle conflicting findings, such as gene interaction analyses, interaction with psychosocial and environmental factors and, finally, endophenotype investigations.

Beacon-like/ubiquitin-5-like immunoreactivity is highly expressed in human hypothalamus and increased in haloperidol-treated schizophrenics and a rat model of schizophrenia

The beacon gene is involved in the regulation of energy metabolism, food intake, and obesity. We localized its gene product, beacon-/ubiquitin 5-like immunoreactivity in brains of normal-weight, non-psychotic individuals, adipose (BMI over 32), non-psychotic individuals, and haloperidol-treated schizophrenics. The protein was found to be highly expressed in many neurons of the paraventricular and supraoptic hypothalamic nuclei. Besides, it was detected in neurons of other hypothalamic areas (suprachiasmatic, arcuate, and ventromedial nuclei) as well as outside the hypothalamus (Nuc. basalis Meynert, thalamus, hippocampus, and some neocortical areas). A morphometric analysis of beacon-immunoreactive hypothalamic and neocortical neurons revealed that compared to normal-weight controls in haloperidol-treated schizophrenics, there was a significant increase of protein-expressing supraoptic, paraventricular, and orbitofrontal neurons. However, a significant increase in beacon-expressing supraoptic neurons was also seen in adipose, non-psychotic individuals in comparison with normal-weight controls. Haloperidol at different doses has no effect on beacon expression in SHSY5Y neuroblastoma cells, which makes the assumption unlikely that haloperidol per se is responsible for the increased neuronal expression of the peptide in schizophrenics. In rats with a neonatal lesion of the ventral hippocampus (a widely used animal model of schizophrenia), we found an increased neuronal expression of beacon in the paraventricular and supraoptic nuclei. We suppose that elevated hypothalamic expression of beacon-like protein in non-obese schizophrenics is not primarily related to metabolic alterations, but to a certain role in schizophrenia, which is possibly unrelated to aspects of weight gain and obesity. The latter assumption finds some support by data obtained in rats with ventral hippocampus lesion.

Susceptibility of schizophrenia and affective disorder not associated with loci on chromosome 6q in Han Chinese population

Background

Several linkage studies across multiple population groups provide convergent support for susceptibility loci for schizophrenia – and, more recently, for affective disorder – on chromosome 6q. We explore whether schizophrenia and affective disorder have common susceptibility gene on 6q in Han Chinese population.

Methods

In the present study, we genotyped 45 family trios from Han Chinese population with mixed family history of schizophrenia and affective disorder. Twelve short tandem repeat (STRs) markers were selected, which covered 102.19 cM on chromosome 6q with average spacing 9.29 cM and heterozygosity 0.78. The transmission disequilibrium test (TDT) was performed to search for susceptibility loci to schizophrenia and affective disorder.

Results

The results showed STRs D6S257, D6S460, D6S1021, D6S292 and D6S1581 were associated with susceptibility to psychotic disorders. When families were grouped into schizophrenia and affective disorder group, D6S257, D6S460 and D6S1021, which map closely to the centromere of chromosome 6q, were associated with susceptibility to schizophrenia. Meanwhile, D6S1581, which maps closely to the telomere, was associated with susceptibility to affective disorder. But after correction of multiple test, all above association were changed into no significance (P > 0.05).

Conclusion

These results suggest that susceptibility of schizophrenia and affective disorder not associated with loci on chromosome 6q in Han Chinese population.

Increased familial risk and genomewide significant linkage for Alzheimer's disease with psychosis

Psychotic symptoms are common in Alzheimer's disease (AD) and are associated with increased cognitive impairment and earlier institutionalization. One study has suggested that they are genetically modified and two genome screens have been performed to search for susceptibility loci for AD with psychosis (AD + P). The aim of this study was to further investigate the familial aggregation of AD + P and perform a genome screen for AD, conditioning on the presence or absence of psychotic symptoms. Samples from the UK and US were combined, providing data from 374 families in which at least two members met criteria for AD and had complete data regarding psychotic symptoms. Generalized estimating equations (GEE) were used to assess the relationship of psychotic symptoms between siblings. A total of 321 affected relative pairs (ARPs) were genotyped for linkage. There was a significant association between proband psychosis status and the occurrence of AD + P in siblings in the UK (OR = 4.17, P = 0.002) and US (OR = 3.2, P < 0.001) samples. Chromosomewide and genomewide significant linkage peaks were observed on chromosomes 7 (LOD = 2.84) and 15 (LOD = 3.16), respectively, with the strongest evidence coming from pairs concordant for AD without psychosis. A LOD score of 2.98 was observed close to a previously reported AD + P linkage region on chromosome 6, however the increase in LOD attributable to psychosis was not significant. These findings support the hypothesis that psychotic symptoms in AD are genetically modified and that a gene/s implicated in their aetiology may be located on chromosome 7 and 15.

Linked gene ontology categories are novel and differ from associated gene ontology categories for the bipolar disorders

Family, and twin genetic studies strongly indicate gene variants as predisposing to the bipolar disorders. Now, about 3000 genes are genetically linked and about 44 genes are genetically associated. Rank differences, however, exist between the linked gene Genetic ontology categories and the associated gene Genetic ontology categories. For the linked gene Genetic ontology categories, the activation of NF-kappaB-inducing kinase category is over-represented; in contrast, the associated genes show the Synaptic transmission category as over-represented. Association studies report selecting positional candidate genes from previous linkage studies, or, selecting genes on the basis of pathophysiologic hypotheses. Only a few of the pathophysiologic hypotheses genes, however, had been previously linked to the bipolar disorders. In particular, only a couple of the Synaptic transmission genes had been previously linked to bipolar disorders.

No association between the PREP gene and lithium responsive bipolar disorder

BACKGROUND

Bipolar disorder (BD) is a major psychiatric condition that commonly requires prophylactic and episodic treatment. Lithium (Li) has been used for over 40 years now as an effective prophylactic agent. Response to Li treatment seems to be, at least in part, genetically determined. Although we ignore how Li specifically prevents mood episodes, it has previously been suggested that Li exerts an effect on the phosphoinositide pathway, and more recently, it has been proposed that Li may modulate prolyl endopeptidase (PREP).

METHODS

In this study we carried out an association study looking at the PREP gene, located on ch 6q22. Five intronic single nucleotide polymorphisms (SNP), three coding SNPs and one SNP in the 5' UTR were investigated for their frequency in a BD sample of 180 excellent Li responders, 69 Li nonresponders and 126 controls. Genotyping was carried out using the SNaPshot reaction from Applied Biosystems, which is a modified fluorescent single base pair extension procedure.

RESULTS

Following correction for multiple testing, no significant genotypic, allelic or estimated haplotypic differences were found between responders and nonresponders or between BD patients and controls.

CONCLUSION

PREP is an interesting candidate gene to investigate in genetic studies of BD, but our findings do not support the hypothesis that genetic variation in this gene plays a major role in the etiology of BD or Li response.

Chasing genes for mood disorders and schizophrenia in genetically isolated populations

Major affective disorders and schizophrenia are among the most common brain diseases worldwide and their predisposition is influenced by a complex interaction of genetic and environmental factors. So far, traditional linkage mapping studies for these complex disorders have not achieved the same success as the positional cloning of genes for Mendelian diseases. The struggle to identify susceptibility genes for complex disorders has stimulated the development of alternative approaches, including studies in genetically isolated populations. Since isolated populations are likely to have both a reduced number of genetic vulnerability factors and environmental background and are therefore considered to be more homogeneous compared to outbred populations, the use of isolated populations in genetic studies is expected to improve the chance of finding susceptibility loci and genes. Here we review the role of isolated populations, based on linkage and association studies, in the identification of susceptibility genes for bipolar disorder and schizophrenia.

Complete maternal uniparental isodisomy of chromosome 4 in a subject with major depressive disorder detected by high density SNP genotyping arrays

Uniparental isodisomy (iUPD) is a rare genetic condition caused by non-disjunction during meiosis that ultimately leads to a duplication of either the maternal or paternal chromosome in the affected individual. Two types of disorders can result, those due to imprinted genes and those due to homozygosity of recessive disease-causing mutations. Here, we describe the third known case of complete chromosome 4 iUPD of maternal origin. This condition became apparent during whole genome linkage studies of psychiatric disorders in the Portuguese population. The proband is an adult female with normal fertility and no major medical complaints, but a history of major depressive disorder and multiple suicide attempts. The proband's siblings and parents had normal chromosome 4 genotypes and no history of mood disturbance. A brief review of other studies lends support for the possibility that genes on chromosome 4 might confer risk for mood disorders. We conclude that chromosome 4 maternal uniparental disomy (UPD) is a rare disorder that may present with a major depressive phenotype. The lack of a common disease phenotype between this and two other cases of chromosome 4 iUPD [Lindenbaum et al. [1991] Am J Med Genet 49(Suppl 285):1582; Spena et al. [2004] Eur J Hum Genet 12:891-898) would suggest that there is no vital maternal gene imprinting on chromosome 4. However, since there is no reported case of paternal chromosome 4 UPD, paternal gene imprinting on chromosome 4 cannot be excluded.

Excitement and confusion on chromosome 6q: the challenges of neuropsychiatric genetics in microcosm

The search for genes that are implicated in the pathogenesis of schizophrenia (SCZ), bipolar disorder (BPD) and other complex neuropsychiatric phenotypes has yielded a plethora of positive findings, but has also engendered a substantial degree of confusion. Exciting findings include positive linkage results in a number of chromosomal regions and the identification of several genes that have been associated with SCZ and to a lesser extent with BPD. Confusing aspects include the difference between studies in localization of linkage peaks in the same chromosomal regions, raising the possibility that these regions may harbor more than one gene, the fact that positive linkage findings as well as associated genes appear in several cases to be shared by more than one disorder, and the failure to identify thus far the precise pathogenic variants in associated genes. Recent findings of linkage and association studies on chromosome 6q illustrate the current status of neuropsychiatric genetics in intriguing microcosm. Positive findings from linkage and association studies are reviewed in order to identify approaches that may help to settle apparent contradictions and allow an interpretation of the results that may prove useful in application to findings from other chromosomal regions. Not only SCZ and BPD but also other psychiatric and neurological phenotypes are considered. Taking a topographic approach, we identify five foci of positive findings on chromosome 6q and suggest that each may harbor gene(s) that confer susceptibility to SCZ or BPD or may modify their onset or clinical course. We further suggest that in searching for these genes the possibility that they may be implicated in more than one disorder should be taken into account. We also discuss the potential contribution of rare genetic variants identified in homogeneous, isolated populations to the subsequent identification of common variants in the same gene that contribute to disease susceptibility in outbred populations.

Genomewide scan and fine-mapping linkage studies in four European samples with bipolar affective disorder suggest a new susceptibility locus on chromosome 1p35-p36 and provides further evidence of loci on chromosome 4q31 and 6q24

We present the findings of a large linkage study of bipolar affective disorder (BPAD) that involved genomewide analysis of 52 families (448 genotyped individuals) of Spanish, Romany, and Bulgarian descent and further fine mapping of the 1p34-p36, 4q28-q31, and 6q15-q24 regions. An additional sample of 56 German families (280 individuals) was included for this fine-mapping step. The highest nonparametric linkage scores obtained in the fine mapping were 5.49 for 4q31 and 4.87 for 6q24 in the Romany families and 3.97 for 1p35-p36 in the Spanish sample. MOD-score (LOD scores maximized over genetic model parameters) analysis provided significant evidence of linkage to 4q31 and at least borderline significance for the 1p and 6q regions. On the basis of these results and previous positive research findings, 4q31 and 6q24 should now be considered confirmed BPAD susceptibility loci, and 1p35-p36 is proposed as a new putative locus that requires confirmation in replication studies.

Family, twin, adoption, and molecular genetic studies of juvenile bipolar disorder

Juvenile bipolar disorder (JBD) has been a subject of significant research and debate. Phenotypic differences between JBD and adult-onset bipolar disorder have led researchers to question whether or not similar neuropathologic mechanisms will be found. While much is known about the genetic and environmental contributions to the adult-onset phenotype, less is known about their contributions to JBD. Here, we review family, twin, adoption, and molecular genetic studies of JBD. Behavioral genetic data suggest both genetic and environmental contributions to JBD, while molecular genetic studies find linkage to age of onset of bipolar disorder to chromosomes 12p, 14q, and 15q. Additionally, changes associated with symptom age of onset have been recently reported in the brain-derived neurotrophic factor (BDNF) and glycogen synthase kinase 3-beta (GSK3-beta) genes. We contend that further progress in discovering the precise genetic and environmental contributions to JBD may depend on advances in phenotypic refinement, an increased appreciation of comorbid conditions, and more investigation of the longitudinal course of the disorder.

Combined analysis from eleven linkage studies of bipolar disorder provides strong evidence of susceptibility loci on chromosomes 6q and 8q

Several independent studies and meta-analyses aimed at identifying genomic regions linked to bipolar disorder (BP) have failed to find clear and consistent evidence of linkage regions. Our hypothesis is that combining the original genotype data provides benefits of increased power and control over sources of heterogeneity that outweigh the difficulty and potential pitfalls of the implementation. We conducted a combined analysis using the original genotype data from 11 BP genomewide linkage scans comprising 5,179 individuals from 1,067 families. Heterogeneity among studies was minimized in our analyses by using uniform methods of analysis and a common, standardized marker map and was assessed using novel methods developed for meta-analysis of genome scans. To date, this collaboration is the largest and most comprehensive analysis of linkage samples involving a psychiatric disorder. We demonstrate that combining original genome-scan data is a powerful approach for the elucidation of linkage regions underlying complex disease. Our results establish genomewide significant linkage to BP on chromosomes 6q and 8q, which provides solid information to guide future gene-finding efforts that rely on fine-mapping and association approaches.

Stage 2 of the Wellcome Trust UK-Irish bipolar affective disorder sibling-pair genome screen: evidence for linkage on chromosomes 6q16-q21, 4q12-q21, 9p21, 10p14-p12 and 18q22

Bipolar affective disorder (BPAD) is a common psychiatric disorder with complex genetic aetiology. We have undertaken a genome-wide scan in one of the largest samples of bipolar affected sibling pairs (ASPs) using a two-stage approach combining sample splitting and marker grid tightening. In this second stage analysis, we have examined 17 regions that achieved a nominally significant maximum likelihood LOD score (MLS) threshold of 0.74 (or 1.18 for the X-chromosome) in stage one. The second stage has added 135 ASP families to bring the total stage 2 sample to 395 ASPs. In total, 494 microsatellite markers have been used to screen the human genome at a density of 10 cM in the first stage sample (260 ASPs) and 5 cM in the second stage. Under the broad diagnostic model, two markers gave LOD scores exceeding 3 with two-point analysis: D4S392 (LOD=3.30) and D10S197 (LOD=3.18). Multipoint analysis demonstrated suggestive evidence of linkage between BPAD and chromosomal regions 6q16-q21 (MLS=2.61) and 4q12-q21 (MLS=2.38). 6q16-q21 is of particular interest because our data, together with those from two recent genome scans, make this the best supported linkage region in BPAD. Further, our data show evidence of a gender effect at this locus with increased sharing predominantly within the male-male pairs. Our scan also provides support for linkage (MLS> or =1.5) at several other regions that have been implicated in meta-analyses of bipolar disorder and/or schizophrenia including 9p21, 10p14-p12 and 18q22.

Gene expression analysis of peripheral blood leukocytes from discordant sib-pairs with schizophrenia and bipolar disorder reveals points of convergence between genetic and functional genomic approaches

We performed global RNA transcript analysis and comprehensive gene group analysis of peripheral blood leukocyte (PBL) RNA from two groups of matched sib-pairs that were discordant for either schizophrenia (n = 33 sib-pairs) or bipolar disorder (n = 5 sib-pairs). The pairs chosen for these analyses were selected from families with known patterns of genetic linkage (5q for schizophrenia and 6q for bipolar disorder). At the single gene level, we obtained lists of the transcripts with the most significant changes in expression and from these lists determined those with the highest degree of predictive power for classifying subjects according to diagnosis in these samples. At the gene group level, we comprehensively analyzed pairwise expression changes of more than 4,000 functional groups and cytogenetic locations, and present a novel method of displaying these data that we term "cytogenomic" mapping. Verification of selected changes in expression was performed using quantitative real-time RT-PCR. Our results provide compelling evidence for the utility of analyzing PBL RNA for changes in expression in neuropsychiatric disorders.

Genetic linkage of bipolar disorder to chromosome 6q22 is a consistent finding in Portuguese subpopulations and may generalize to broader populations

We recently reported genome-wide significant linkage to chromosome 6q for bipolar disorder, in a study of 25 Portuguese families, using the Human Mapping Assay Xba 131 (HMA10K). To explore the generalizability of this finding, we reanalyzed our SNP linkage data according to the families' geographic origin. Specifically, the 25 families included 20 families from the Portuguese island collection (PIC; 15 families from the Azores Islands and 5 from the Madeira Islands) and 5 families from continental Portugal. Non-parametric linkage analysis (NPL) was performed as previously described and indicated that each of these subpopulations showed evidence of linkage for the same region. To further address the potential generalizability of these findings to other populations, we have also examined allelic heterozygosity in our subpopulations and in three reference populations (Caucasian, East Asian, and African-American). This analysis indicated that the PIC population is highly correlated to the Caucasian reference population (R = 0.86) for all of chromosome 6. In contrast allelic heterozygosity was more weakly correlated between PIC and both East Asian (R = 0.37) and African-American (R = 0.32) reference populations. Taken together these observations suggest a shared genetic liability among Portuguese populations for bipolar disorder on chromosome 6q, and that the PIC population is likely representative of Caucasians in general.

Complexities in psychiatric genetics

A substantial contribution of genetic factors to the risk of psychiatric disorders such as schizophrenia, bipolar disorder, autism, and drug and alcohol dependence has already been established. However, the familial transmission of these disorders cannot be explained by simple Mendelian models of inheritance, and non-genetic factors must also play a substantial role in their etiologies. Furthermore, the prevalence of any major psychiatric disorder is a great deal higher than that of Mendelian disorders. It has been suggested that evolutionary forces would rapidly eliminate large gene effects, which would suggest that mental disorders, which are highly prevalent, are associated with minor gene effects (Risch, 1994). The current paradigm is that genes with small interacting genetic effects, in conjunction with environmental factors, affect the risk for psychiatric disease. New laboratory and statistical methodology and database tools, and the availability of large clinical samples for the study of linkage and association sustain optimism that genes involved with these diseases will be characterized in the near future. This accomplishment should in turn lead not only to a better understanding of the primary molecular pathophysiology and to more specific and effective therapies, but also to a better understanding of non-genetic risk factors that could be targets for preventive strategies.

Genomewide linkage analysis of bipolar disorder by use of a high-density single-nucleotide-polymorphism (SNP) genotyping assay: a comparison with microsatellite marker assays and finding of significant linkage to chromosome 6q22

We performed a linkage analysis on 25 extended multiplex Portuguese families segregating for bipolar disorder, by use of a high-density single-nucleotide-polymorphism (SNP) genotyping assay, the GeneChip Human Mapping 10K Array (HMA10K). Of these families, 12 were used for a direct comparison of the HMA10K with the traditional 10-cM microsatellite marker set and the more dense 4-cM marker set. This comparative analysis indicated the presence of significant linkage peaks in the SNP assay in chromosomal regions characterized by poor coverage and low information content on the microsatellite assays. The HMA10K provided consistently high information and enhanced coverage throughout these regions. Across the entire genome, the HMA10K had an average information content of 0.842 with 0.21-Mb intermarker spacing. In the 12-family set, the HMA10K-based analysis detected two chromosomal regions with genomewide significant linkage on chromosomes 6q22 and 11p11; both regions had failed to meet this strict threshold with the microsatellite assays. The full 25-family collection further strengthened the findings on chromosome 6q22, achieving genomewide significance with a maximum nonparametric linkage (NPL) score of 4.20 and a maximum LOD score of 3.56 at position 125.8 Mb. In addition to this highly significant finding, several other regions of suggestive linkage have also been identified in the 25-family data set, including two regions on chromosome 2 (57 Mb, NPL = 2.98; 145 Mb, NPL = 3.09), as well as regions on chromosomes 4 (91 Mb, NPL = 2.97), 16 (20 Mb, NPL = 2.89), and 20 (60 Mb, NPL = 2.99). We conclude that at least some of the linkage peaks we have identified may have been largely undetected in previous whole-genome scans for bipolar disorder because of insufficient coverage or information content, particularly on chromosomes 6q22 and 11p11.