A susceptibility locus for bipolar affective disorder on chromosome 4q35

A linkage and exome study implicates rare variants of KANK4 and CAP2 in bipolar disorder in a multiplex family

OBJECTIVES

Bipolar disorder (BD) is a neuropsychiatric disorder with a complex pattern of inheritance. Although many genetic studies have been conducted on BD, its genetic correlates remain uncertain. This study was aimed at  identifying the genetic underpinnings of the disorder in an Indian family, which has been under comprehensive clinical evaluation and follow-up for over 12 years.

METHODS

We analysed a four-generation family with several of its members diagnosed for BD employing a combination of genetic linkage and exome analysis.

RESULTS

We obtained suggestive LOD score for a chromosome 1 and a chromosome 6 marker (D1S410; LOD = 3.01, Ө = 0; and D6S289; LOD = 1.58, Ө = 0). Manual haplotyping of the regions encompassing these two markers helped delimit a critical genomic interval of 32.44 Mb (D1S2700-D1S435; chromosome 1p31.1-13.2) and another of 10.34 Mb (D6S470-D6S422; chromosome 6p22.3-22.2). We examined the exomic sequences corresponding to these two intervals and found rare variants, NM_181712.4: c.2461G>T (p.Asp821Tyr) in KANK4 at 1p31.1-13.2; and NM_006366:c.-93G>A, in the 5' UTR of CAP2 at 6p22.3-22.2.

CONCLUSIONS

Our studysuggests involvement of KANK4 or CAP2 or both in BD in this family. Further analysis of these two genes in BD patients and functional evaluation of the allelic variants identified are suggested.

Comprehensive cross-disorder analyses of CNTNAP2 suggest it is unlikely to be a primary risk gene for psychiatric disorders

The contactin-associated protein-like 2 (CNTNAP2) gene is a member of the neurexin superfamily. CNTNAP2 was first implicated in the cortical dysplasia-focal epilepsy (CDFE) syndrome, a recessive disease characterized by intellectual disability, epilepsy, language impairments and autistic features. Associated SNPs and heterozygous deletions in CNTNAP2 were subsequently reported in autism, schizophrenia and other psychiatric or neurological disorders. We aimed to comprehensively examine evidence for the role of CNTNAP2 in susceptibility to psychiatric disorders, by the analysis of multiple classes of genetic variation in large genomic datasets. In this study we used: i) summary statistics from the Psychiatric Genomics Consortium (PGC) GWAS for seven psychiatric disorders; ii) examined all reported CNTNAP2 structural variants in patients and controls; iii) performed cross-disorder analysis of functional or previously associated SNPs; and iv) conducted burden tests for pathogenic rare variants using sequencing data (4,483 ASD and 6,135 schizophrenia cases, and 13,042 controls). The distribution of CNVs across CNTNAP2 in psychiatric cases from previous reports was no different from controls of the database of genomic variants. Gene-based association testing did not implicate common variants in autism, schizophrenia or other psychiatric phenotypes. The association of proposed functional SNPs rs7794745 and rs2710102, reported to influence brain connectivity, was not replicated; nor did predicted functional SNPs yield significant results in meta-analysis across psychiatric disorders at either SNP-level or gene-level. Disrupting CNTNAP2 rare variant burden was not higher in autism or schizophrenia compared to controls. Finally, in a CNV mircroarray study of an extended bipolar disorder family with 5 affected relatives we previously identified a 131kb deletion in CNTNAP2 intron 1, removing a FOXP2 transcription factor binding site. Quantitative-PCR validation and segregation analysis of this CNV revealed imperfect segregation with BD.

This large comprehensive study indicates that CNTNAP2 may not be a robust risk gene for psychiatric phenotypes.

Genetic mutations that disrupt both copies of the CNTNAP2 gene lead to severe disease, characterized by profound intellectual disability, epilepsy, language difficulties and autistic traits, leading to the hypothesis that this gene may also be involved in autism given some overlapping clinical features with this disease. Indeed, several large DNA deletions affecting one of the two copies of CNTNAP2 were found in some patients with autism, and later also in patients with schizophrenia, bipolar disorder, ADHD and epilepsy, suggesting that this gene was implicated in several psychiatric or neurologic diseases. Other studies considered genetic sequence variations that are common in the general population, and suggested that two such sequence variations in CNTNAP2 predispose to psychiatric diseases by influencing the functionality and connectivity of the brain. To better understand the involvement of CNTNAP2 in risk of mental illness, we performed several genetic analyses using a series of large publicly available or in-house datasets, comprising many thousands of patients and controls. Furthermore, we report the deletion of one copy of CNTNAP2 in two patients with bipolar disorder and one unaffected relative from an extended family where five relatives were affected with this condition. Despite the previous consideration of CNTNAP2 as a strong candidate gene for autism or schizophrenia, we show little evidence across multiple classes of DNA variation, that CNTNAP2 is likely to play a major role in risk of psychiatric diseases.

nArgBP2-SAPAP-SHANK, the core postsynaptic triad associated with psychiatric disorders

Despite the complex genetic architecture, a broad spectrum of psychiatric disorders can still be caused by mutation(s) in the same gene. These disorders are interrelated with overlapping causative mechanisms including variations in the interaction among the risk-associated proteins that may give rise to the specific spectrum of each disorder. Additionally, multiple lines of evidence implicate an imbalance between excitatory and inhibitory neuronal activity (E/I imbalance) as the shared key etiology. Thus, understanding the molecular mechanisms underlying E/I imbalance provides essential insight into the etiology of these disorders. One important class of candidate risk genes is the postsynaptic scaffolding proteins, such as nArgBP2, SAPAP, and SHANK that regulate the actin cytoskeleton in dendritic spines of excitatory synapses. This review will cover and discuss recent studies that examined how these proteins, especially nArgBP2, are associated with psychiatric disorders. Next, we propose a possibility that variations in the interaction among these proteins in a specific brain region might contribute to the onset of diverse phenotypes of psychiatric disorders.

The assembly of scaffolding proteins, key regulators of many signaling pathways, found in the brain’s synapses underpin a diverse range of neuropsychiatric disorders. Sunghoe Chang and colleagues from Seoul National University, South Korea, review how these postsynaptic proteins regulate the cellular cytoskeleton in nerve cell protrusions to maintain the balance between excitatory and inhibitory inputs in the brain. They discuss how perturbations in three particular proteins can cause an imbalance in synaptic signals that leads to conditions such as bipolar disorder, schizophrenia and autism. The authors propose that these proteins form a “core scaffolding triad” and interact in different ways to cause different mental illnesses. Dysregulation of these proteins could explain how mutations in the same genes, depending on whether they boost or decrease gene expression, contribute to the onset of diverse psychiatric disorders.

Chromosome 18p11.2 harbors susceptibility marker: D18S452, for bipolar affective disorder

AIM

The aim of our study was to investigate whether the tandem repeat polymorphism in D18S452 microsatellite marker at locus 18p11.2 is a risk factor of bipolar affective disorder (BPAD) in Kashmiri population.

MATERIALS AND METHODS

The repeat polymorphism in D18S452 was evaluated by polymerase chain reaction (PCR) analysis of in 74 diagnosed BPAD patients and 74 controls subjects.

RESULTS

Tandem repeat (300 bp*) allele frequency was found to be 1.35% in controls and 8.108% in cases. The tandem repeat (250 bp*) allele frequency was found to be in 91.89% in cases and 98.65% in controls. The 252 bp/252 bp genotype was found to be present in 89.18% of cases and 98.64% of controls, the 300 bp/300 bp genotype in 5.40% of cases and 1.35% of controls and the 252 bp/300 bp variant in 5.40% of cases and none among the controls. Although the proportion of patients homozygous for tandem repeat (300 bp/300 bp) was higher in cases than in controls, the difference was not statistically significant when 252 bp/252 bp genotype was taken as reference (odds ratio [OR]=4.4242; 95% confidence interval [CI] 0.4822-40.5924); P=0.1529). However, when the frequency of heterozygous genotype (252 bp/300 bp) was compared with 252 bp/252 bp statistical significance was observed (OR=8.0603; 95% CI 1.1112-58.4646; P=0.0383).

CONCLUSION

This is the first study reporting a significant association between D18S452 maker with tandem repeat polymorphism in heterozygous condition (252 bp/300 bp) and the development of BPAD in Kashmiri population.

Genome-wide linkage analysis of 972 bipolar pedigrees using single-nucleotide polymorphisms

Because of the high costs associated with ascertainment of families, most linkage studies of Bipolar I disorder (BPI) have used relatively small samples. Moreover, the genetic information content reported in most studies has been less than 0.6. Although microsatellite markers spaced every 10 cM typically extract most of the genetic information content for larger multiplex families, they can be less informative for smaller pedigrees especially for affected sib pair kindreds. For these reasons we collaborated to pool family resources and carried out higher density genotyping. Approximately 1100 pedigrees of European ancestry were initially selected for study and were genotyped by the Center for Inherited Disease Research using the Illumina Linkage Panel 12 set of 6090 single-nucleotide polymorphisms. Of the ~1100 families, 972 were informative for further analyses, and mean information content was 0.86 after pruning for linkage disequilibrium. The 972 kindreds include 2284 cases of BPI disorder, 498 individuals with bipolar II disorder (BPII) and 702 subjects with recurrent major depression. Three affection status models (ASMs) were considered: ASM1 (BPI and schizoaffective disorder, BP cases (SABP) only), ASM2 (ASM1 cases plus BPII) and ASM3 (ASM2 cases plus recurrent major depression). Both parametric and non-parametric linkage methods were carried out. The strongest findings occurred at 6q21 (non-parametric pairs LOD 3.4 for rs1046943 at 119 cM) and 9q21 (non-parametric pairs logarithm of odds (LOD) 3.4 for rs722642 at 78 cM) using only BPI and schizoaffective (SA), BP cases. Both results met genome-wide significant criteria, although neither was significant after correction for multiple analyses. We also inspected parametric scores for the larger multiplex families to identify possible rare susceptibility loci. In this analysis, we observed 59 parametric LODs of 2 or greater, many of which are likely to be close to maximum possible scores. Although some linkage findings may be false positives, the results could help prioritize the search for rare variants using whole exome or genome sequencing.

Identification of chromosome abnormalities in screening of a family with manic depression and psoriasis: predisposition to aneuploidy

Cytogenetic analysis is an important stage in understanding the genetic background of manic depression (MD), and may provide a valuable clue to the identification of target loci and successful search for major genes. In order to identify chromosomal regions we aimed to detect the relationships between chromosomal aberrations (CAs) and immunological markers in a family with MD and psoriasis. We used the cell cultivation and conventional G-banding. We found predominantly numerical aberrations. The most common aneuploidy was chromosome 8, followed by chromosome 22, 21, 15, X and Y. However, structural aberrations consisted of duplications, deletions, translocations and breaks, with a focus on: loci on del(1)(q12-q23), del(1)(q21.1-q24), del(1)(q21.1-q23), del(10)(p11.2-pter), der(2)t(2;4)(p25;p12), t(2;22)(p14;p13), t(19;Y)? and dup(10)(q26). The susceptibility genes of MD or psoriasis may be located on these loci. Numerical sex CAs included 4(5.8%) with 45,X, 3(4.3%) with 47,XXY, and 4(5.8%) with structural chromosome X; del(X)(q13); del(X)(p11-pter) del(X)(q21.3) and inv(Y)(q11.2). We also conducted an immunological study. According results of this study, the percentage of CD2+, CD4+ and CD8+ lymphocytes of the father were significantly higher, whereas CD4+ lymphocytes were decreased in the mother, when compared the healthy persons. The percentage of CD4 level of the son was decreased, whereas CD8+ lymphocytes were higher. The CD4/CD8 ratio of the father and the son was found to be significantly high. These results may suggest that MD and psoriasis have a significant impact on both genetic and immunological parameters.

Genome-scan for bipolar disorder with sib-pair families in the Sardinian population: a new susceptibility locus on chromosome 1p22-p21?

The discovery of the genetic factors implicated in the predisposition to complex diseases may greatly profit from genetic studies in isolated populations. In this perspective, we performed a genome-wide scan using 507 microsatellite markers, with an average interval size of 7.6 cM, on a sample of 88 nuclear families with at least two affected sibs with bipolar disorder recruited in the Sardinian population. An initial analysis yielded non-parametric linkage exceeding 3.4 with P-values <0.0003 at two adjacent markers, D1S206 and D1S435 in the 1p22-p21 chromosomal region. Moreover, positive linkage ranging between 2.0 and 3.0 was obtained for other loci in several cases in regions that have already been linked to predisposition to bipolar disorder, such as 5p15.33, 8q24.13, and 11q14.3. A subsequent analysis of the 1p22-p21 region using the same set of families and a dense panel of 20 new microsatellite markers, spaced at 1.2 cM on average, reinforced the finding of suggestive linkage for this region. Interestingly, NPL values above 2.1 and P-values <0.02 were obtained for a cluster of 10 markers comprising D1S435. Thus, this study suggests that the 1p22-p21 region may contain a new locus participating to the genetic susceptibility to bipolar disorder and reproduces positive linkage for several other loci already implicated in this pathology. Since the Sardinian population presents a peculiar genetic homogeneity, these results may pave the way to further studies for replication in this population contributing to the rapid discovery of the genetic factors predisposing to bipolar disorder.

Assessing oxidative pathway genes as risk factors for bipolar disorder

OBJECTIVES

There is a growing body of evidence implicating oxidative stress and the glutathione system in the pathogenesis of major psychiatric illnesses, including schizophrenia and bipolar disorder. Here we investigate whether genes involved in oxidative stress regulation are associated with increased risk for bipolar disorder.

METHODS

Four candidate genes were selected a priori from two different steps in the oxidative stress pathway, specifically the synthesis of glutathione [catalytic subunit of glutamate cysteine ligase (GCLC) and regulatory subunit of glutamate cysteine ligase (GCLM)] and the removal of reactive oxygen species [superoxide dismutase 2 (SOD2) and glutathione peroxidase 3 (GPX3)]. Haplotype tagging and functional nucleotide polymorphisms were selected in each gene and tested for association with bipolar disorder under narrow (n = 240) and broad (n = 325) phenotypic models, compared to healthy controls (n = 392, comprising 166 psychiatrically assessed unaffected controls plus 226 healthy individuals).

RESULTS

Single marker association analysis did not reveal significant association with bipolar disorder; however, haplotypes in the SOD2 gene showed nominal association (global chi(2) = 8.94, p = 0.03; broad model). Interaction analysis revealed a significant interaction between SOD2 and GPX3 haplotypes, which further increases risk for bipolar disorder (odds ratio = 2.247, chi(2) = 9.526, p = 0.002, corrected p = 0.029).

CONCLUSIONS

Further characterization of the SOD2 and GPX3 interaction using larger cohorts is required to determine the role of these oxidative pathway genes as risk factors for bipolar disorder.

A new susceptibility locus for bipolar affective disorder in PAR1 on Xp22.3/Yp11.3

We present the findings of a linkage study of bipolar affective disorder (BPAD) that involve the pseudoautosomal region 1 of the human sex chromosomes. We analyzed a substantial subset of pedigrees (89 families of German and Spanish origin; 661 participants; 298 affected individuals) from the large collection of BPAD-affected families with which a genomewide linkage analysis was previously performed and where the pseudoautosomal regions were poorly covered. Nonparametric linkage (Z(lr)) scores were calculated. The highest Z(lr) scores were obtained on Xp22.3/Yp11.3 in the Spanish subsample (DXS1071; Z(lr) = 3.54, P(empirical) = 0.0009 for the broad definition of affection sttuts; Z(lr) = 2.63, P(empirical) = 0.0129 for the medium definition of affection status; Z(lr) = 2.12, P(empirical) = 0.0429 for the narrow definition of affection status). Empirical P-values are adjusted using the Bonferroni correction to account for the testing of three affection status definitions. This region has not drawn much attention in previous linkage studies of BPAD. On the basis of these results, Xp22.3/Yp11.3 should now be considered a candidate region for BPAD.

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.

Association of genetic polymorphisms in the type II deiodinase gene with bipolar disorder in a subset of Chinese population

OBJECTIVE

Genetic factors play a critical role in the etiology of bipolar disorder (BPAD). Previous studies suggested an association between thyroid dysfunction and BPAD. We hypothesize that genetic variations in the type II deiodinase (DIO2) gene that possibly alter the bioactivity of thyroid hormones are associated with BPAD.

METHOD

A case-control association study was conducted in a subset of Chinese Han population. Two single nucleotide polymorphisms (SNP), open reading frame a (ORFa)-Gly3Asp (rs12885300) and Thr92Ala (rs225014) with potential functions on the activity of DIO2, were selected. The frequencies of allele, genotype and haplotype of the two SNPs were compared between the BPAD patients and the control group.

RESULTS

Statistical significance between the BPAD patients and the control group was observed for the allele (chi(2)=7.746, P=0.005, df=1) and genotype frequencies (chi(2)=8.158, P=0.017, df=2) at the locus of ORFa-Gly3Asp, and for the allele (chi(2)=15.838, P=7.00e-005, df=1) and genotype frequencies (chi(2)=17.236, P=0.0002, df=2) at Thr92Ala. Distribution of allele 3Gly and 92Ala were significantly higher in the BPAD patients, with odds ratios of 1.489 [95% confidence interval (CI)=1.124-1.973] and 1.616 [95% CI=1.275-2.048], respectively. Individuals with two copies of the variant 3Gly or 92Ala were at greater risk of BPAD than individuals with one copy (dose-response manner). Haplotypes ORFa-3Asp-92Ala and ORFa-3Gly-92Ala indicated higher susceptibility for BPAD with odds ratios of 3.759 (95% CI=2.013-7.020) and 1.292 (95% CI=1.017-1.642), respectively, while ORFa-3Asp-92Thr probably played a protective role with an odds ratio of 0.395 (95% CI=0.284-0.549).

CONCLUSION

Data generated from this study supported our hypothesis that genetic variations of the DIO2 gene were associated with BPAD and suggested further consideration on the possible involvement of these functionally active variants in the pathophysiology of BPAD.

A genome screen of 35 bipolar affective disorder pedigrees provides significant evidence for a susceptibility locus on chromosome 15q25-26

Bipolar affective disorder is a heritable, relatively common, severe mood disorder with lifetime prevalence up to 4%. We report the results of a genome-wide linkage analysis conducted on a cohort of 35 Australian bipolar disorder families which identified evidence of significant linkage on chromosome 15q25-26 and suggestive evidence of linkage on chromosomes 4q, 6q and 13q. Subsequent fine-mapping of the chromosome 15q markers, using allele frequencies calculated from our cohort, gave significant results with a maximum two-point LOD score of 3.38 and multipoint LOD score of 4.58 for marker D15S130. Haplotype analysis based on pedigree-specific, identical-by-descent allele sharing, supported the location of a bipolar susceptibility gene within the Z(max-1) linkage confidence interval of 17 cM, or 6.2 Mb, between markers D15S979 and D15S816. Non-parametric and affecteds-only linkage analysis further verified the linkage signal in this region. A maximum NPL score of 3.38 (P=0.0008) obtained at 107.16 cM (near D15S130), and a maximum two-point LOD score of 2.97 obtained at marker D15S1004 (affecteds only), support the original genome-wide findings on chromosome 15q. These results are consistent with four independent positive linkage studies of mood and psychotic disorders, and raise the possibility that a common gene for susceptibility to bipolar disorder, and other psychiatric disorders may lie in this chromosome 15q25-26 region.

The expression of folate sensitive fragile sites in patients with bipolar disorder

PURPOSE

Genetic factors are known to be important in the etiology of bipolar disorder (BD). The fragile sites (FSs) are a very interesting subject for the study of clinical disorders. The aim of this study was to evaluate fragile sites seen in patients with bipolar disorder and find a correlation between some fragile sites and bipolar disorder.

PATIENTS AND METHODS

The frequencies of folate sensitive FSs were compared in short-term whole blood cultures from bipolar patients and from normal individuals.

RESULTS

The rate of FS expression in the patients was considerably higher than in the controls (p < 0.001). Several chromosome regions including 1p36, 1q21, 1q32, 3p25, 7q22, 7q32, 11q23, 12q24, 13q32, 14q24, Xp22 and Xq26 were represented considerably more often in the patients than in the controls (p value between 0.001 to 0.036). Among these FSs, the sites 1p36, 1q21, 3p25, 7q22, 7q32, and 14q24 were not observed in other studies.

CONCLUSION

These regions can be the most active of hot spots in the genomes of bipolar patients, and may harbor important genes associated with BD.

Characteristics of bipolar disorder in an Australian specialist outpatient clinic: comparison across large datasets

OBJECTIVES

There have been relatively few detailed reports on the sociodemographic and clinical characteristics of bipolar disorder in large outpatient clinical samples. This paper reports on findings from the Black Dog Institute Bipolar Disorders Clinic (BDI-BDC) and compares this dataset with the predominantly outpatient Stanley Foundation Bipolar Disorders Network (SFBN) and Systematic Treatment Enhancement Program for Bipolar Disorder (STEP-BD) samples.

METHODS

A total of 217 patients with DSM-IV bipolar disorder were assessed in detail in the BDI-BDC using a series of standardized and non-standardized structured interviews. Ninety per cent had bipolar I disorder, and 10% bipolar II disorder. This sample was compared with the SFBN and STEP-BD datasets.

RESULTS

The sociodemographic characteristics of the three samples were remarkably similar. Female gender and younger age were overrepresented compared to the general population. Functional impairment, indicated by marital status and labour force participation, was clearly more common among the study subjects than in the general population. In all three samples, prior educational attainment was higher than the general population. With respect to clinical features, approximately half of each sample was euthymic and approximately one-third was in a DSM-IV episode of depression at study entry. One-half reported depression as their first episode of mood disturbance. Similar proportions identified positive family histories of bipolar disorder (40%) and unipolar depression (55%). Other clinical characteristics demonstrated more variation between the samples. The STEP-BD population reported an earlier age of onset. The SFBN subjects reported higher numbers of overall episodes, but psychotic features and suicide attempts were less common than in the BDI-BDC sample.

CONCLUSIONS

This report highlights the marked commonalities of the sociodemographic and clinical characteristics of patients with bipolar disorder recruited predominantly in the outpatient setting in three different continents, that is, Australia, North America and Europe. It also demonstrates some critical distinctions between such samples, emphasizing the need to be aware of these differences when interpreting findings, such as treatment outcome, from different bipolar disorder datasets.

Genome-wide parametric linkage analyses of 644 bipolar pedigrees suggest susceptibility loci at chromosomes 16 and 20

OBJECTIVE

Our aim is to map chromosomal regions that harbor loci that increase susceptibility to bipolar disorder.

METHODS

We analyzed 644 bipolar families ascertained by the National Institute of Mental Health Human Genetics Initiative for bipolar disorder. The families have been genotyped with microsatellite loci spaced every approximately 10 cM or less across the genome. Earlier analyses of these pedigrees have been limited to nonparametric (model-free) methods and thus, information from unaffected subjects with genotypes was not considered. In this study, we used parametric analyses assuming dominant and recessive transmission and specifying a maximum penetrance of 70%, so that information from unaffecteds could be weighed in the linkage analyses. As in previous linkage analyses of these pedigrees, we analyzed three diagnostic categories: model 1 included only bipolar I and schizoaffective, bipolar cases (1565 patients of whom approximately 4% were schizoaffective, bipolar); model 2 included all individuals in model 1 plus bipolar II patients (1764 total individuals); and model 3 included all individuals in model 2 with the addition of patients with recurrent major depressive disorder (2046 total persons).

RESULTS

Assuming dominant inheritance the highest genome-wide pair-wise logarithm of the odds (LOD) score was 3.2 with D16S749 using model 2 patients. Multipoint analyses of this region yielded a maximum LOD score of 4.91. Under recessive transmission a number of chromosome 20 markers were positive and multipoint analyses of the area gave a maximum LOD of 3.0 with model 2 cases.

CONCLUSION

The chromosome 16p and 20 regions have been implicated by some studies and the data reported herein provide additional suggestive evidence of bipolar susceptibility genes in these regions.

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.

Genetic variation of the FAT gene at 4q35 is associated with bipolar affective disorder

A recent study suggested that the cadherin gene FAT exerts an influence on susceptibility to bipolar affective disorder (BPAD). We aimed to replicate this finding in a German sample (425 BPAD I and 419 controls). In addition, we performed a comprehensive linkage disequilibrium mapping of the whole genomic region of FAT and the neighboring circadian gene MTNR1A (48 single nucleotide polymorphisms (SNPs) covering 191 kb). No significant association was observed for SNPs located in the MTNR1A gene. In FAT, however, nine SNPs showed association, eight of them being located in the same haplotype block found to be associated with BPAD by Blair et al. The smallest P-value of 0.00028 (OR 1.71) was seen for non-synonymous SNP rs2637777. A combination of five markers including this marker showed a haplotype distribution with a nominal P-value of 1.8 x 10(-5) that withstands correction for multiple testing. While the control allele frequencies between our sample and the samples of the original study are comparable, tendencies of risk allele frequencies are opposite. Possible explanations for this include potential differences in linkage disequilibrium structure between the German, Australian, UK, and Bulgarian populations sampling variation, multilocus effects and/or the occurrence of independent mutational events. We conclude that our results support an involvement of variation at the FAT gene in the etiology of BPAD, but that further work is needed both to clarify possible reasons for the observed risk allele differences and to ultimately identify the functionally relevant variant(s).

Attitudes towards childbearing, causal attributions for bipolar disorder and psychological distress: a study of families with multiple cases of bipolar disorder

BACKGROUND

For families with multiple cases of bipolar disorder this study explored: attitudes towards childbearing; causal attributions for bipolar disorder, in particular the degree to which a genetic model is endorsed and its impact on the perceived stigma of bipolar disorder; and predictors of psychological distress.

METHOD

Two hundred individuals (95 unaffected and 105 affected with either bipolar disorder, schizo-affective disorder - manic type, or recurrent major disorder) were surveyed, using mailed, self-administered questionnaires.

RESULTS

Thirty-five (35%) participants reported being 'not at all willing to have children' or 'less willing to have children' as a result of having a strong family history of bipolar disorder. Being not at all or less willing to have children was associated with perceived stigma of bipolar disorder [odds ratio (OR) 2.42, p = 0.002], endorsement of a genetic model (OR 1.76, p = 0.046), and being affected (OR 2.16, p = 0.01). Among unaffected participants only, endorsement of a genetic model was strongly correlated with perceived stigma (rs = 0.30, p = 0.004). Perceiving the family environment as an important factor in causing bipolar disorder was significantly associated with psychological distress (OR 1.58, p = 0.043) among unaffected participants. Among affected participants, perceived stigma was significantly correlated with psychological distress (OR 2.44, p = 0.02), controlling for severity of symptoms (p < 0.001).

CONCLUSIONS

Having a genetic explanation for bipolar disorder may exacerbate associative stigma among unaffected members from families with multiple cases of bipolar disorder, while it does not impact on perceived stigma among affected family members. Affected family members may benefit from interventions to ameliorate the adverse effects of perceived stigma.

Genome-wide scan of bipolar II disorder

OBJECTIVE

Bipolar disorder (BD) II is characterized by recurrent hypomanic and depressive episodes and has been somewhat of a controversial diagnosis since its description in the 1970s. Clinical opinions notwithstanding, the biological validity of BD II was supported in a genetic study of 58 multiplex bipolar families wherein the statistical evidence for linkage derived from BD II sibling-pairs sharing marker alleles on chromosome 18q. The BD II phenotype alone has never been studied in a genome-wide scan analysis in the current or other bipolar family samples. We have performed genome-wide non-parametric analysis on 74 bipolar pedigrees using only the BD II phenotype as affection model.

METHODS

This sample consists of the 65 pedigrees previously reported and 9 additional novel pedigrees that had BD II exclusively, as the affected phenotype. In the entire sample, there were 146 all possible relative-pairs. Analysis was performed using the non-parametric method in GENEHUNTER, with the 'ALL' option that computes linkage scores in all individuals in a pedigree simultaneously.

RESULTS

The current analyses supported the previous finding on chromosome 18q21. In addition a peak with a non-parametric LOD (NPL) of 2.07 occurred between D9S915 and D9S2157, located on 9q34. Analysis of the nine BD II families alone identified peaks on 9p13 and 9q33, with NPL scores of 3.20 and 2.09, respectively. There was no evidence at 18q21 in these nine families.

CONCLUSIONS

This suggests that there may be substantial differences in the etiology of BD in families that have BD II exclusively as the diagnosis.

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.

Molecular genetics of bipolar disorder

Bipolar disorder (BPD) is an often devastating illness characterized by extreme mood dysregulation. Although family, twin and adoption studies consistently indicate a strong genetic component, specific genes that contribute to the illness remain unclear. This study gives an overview of linkage studies of BPD, concluding that the regions with the best evidence for linkage include areas on chromosomes 2p, 4p, 4q, 6q, 8q, 11p, 12q, 13q, 16p, 16q, 18p, 18q, 21q, 22q and Xq. Association studies are summarized, which support a possible role for numerous candidate genes in BPD including COMT, DAT, HTR4, DRD4, DRD2, HTR2A, 5-HTT, the G72/G30 complex, DISC1, P2RX7, MAOA and BDNF. Animal models related to bipolar illness are also reviewed, with special attention paid to those with clear genetic implications. We conclude with suggestions for strategies that may help clarify the genetic bases of this complex illness.

Positional cloning, association analysis and expression studies provide convergent evidence that the cadherin gene FAT contains a bipolar disorder susceptibility allele

A susceptibility locus for bipolar disorder was previously localized to chromosome 4q35 by genetic linkage analysis. We have applied a positional cloning strategy, combined with association analysis and provide evidence that a cadherin gene, FAT, confers susceptibility to bipolar disorder in four independent cohorts (allelic P-values range from 0.003 to 0.024). In two case-control cohorts, association was identified among bipolar cases with a family history of psychiatric illness, whereas in two cohorts of parent-proband trios, association was identified among bipolar cases who had exhibited psychosis. Pooled analysis of the case-control cohort data further supported association (P=0.0002, summary odds ratio=2.31, 95% CI: 1.49-3.59). We localized the bipolar-associated region of the FAT gene to an interval that encodes an intracellular EVH1 domain, a domain that interacts with Ena/VASP proteins, as well as putative beta-catenin binding sites. Expression of Fat, Catnb (beta-catenin), and the three genes (Enah, Evl and Vasp) encoding the Ena/VASP proteins, were investigated in mice following administration of the mood-stabilizing drugs, lithium and valproate. Fat was shown to be significantly downregulated (P=0.027), and Catnb and Enah were significantly upregulated (P=0.0003 and 0.005, respectively), in response to therapeutic doses of lithium. Using a protein interaction map, the expression of genes encoding murine homologs of the FAT (ft)-interacting proteins was investigated. Of 14 interacting molecules that showed expression following microarray analysis (including several members of the Wnt signaling pathway), eight showed significantly altered expression in response to therapeutic doses of lithium (binomial P=0.004). Together, these data provide convergent evidence that FAT and its protein partners may be components of a molecular pathway involved in susceptibility to bipolar disorder.

The genetics of schizophrenia and bipolar disorder: dissecting psychosis

Much work has been done to identify susceptibility genes in schizophrenia and bipolar disorder. Several well established linkages have emerged in schizophrenia. Strongly supported regions are 6p24-22, 1q21-22, and 13q32-34, while other promising regions include 8p21-22, 6q16-25, 22q11-12, 5q21-q33, 10p15-p11, and 1q42. Genomic regions of interest in bipolar disorder include 6q16-q22, 12q23-q24, and regions of 9p22-p21, 10q21-q22, 14q24-q32, 13q32-q34, 22q11-q22, and chromosome 18. Recently, specific genes or loci have been implicated in both disorders and, crucially, replicated. Current evidence supports NRG1, DTNBP1, DISC1, DAOA(G72), DAO, and RGS4 as schizophrenia susceptibility loci. For bipolar disorder the strongest evidence supports DAOA(G72) and BDNF. Increasing evidence suggests an overlap in genetic susceptibility across the traditional classification systems that dichotomised psychotic disorders into schizophrenia or bipolar disorder, most notably with association findings at DAOA(G72), DISC1, and NRG1. Future identification of psychosis susceptibility genes will have a major impact on our understanding of disease pathophysiology and will lead to changes in classification and the clinical practice of psychiatry.

The phenotypes of bipolar disorder: relevance for genetic investigations

The search for susceptibility genes for bipolar disorder (BD) depends on appropriate definitions of the phenotype. In this paper, we review data on diagnosis and clinical features of BD that could be used in genetic studies to better characterize patients or to define homogeneous subgroups. Clinical symptoms, long-term course, comorbid conditions, and response to prophylactic treatment may define groups associated with more or less specific loci. One such group is characterized by symptoms of psychosis and linkage to 13q and 22q. A second group includes mainly bipolar II patients with comorbid panic disorder, rapid mood switching, and evidence of chromosome 18 linkage. A third group comprises typical BD with an episodic course and favourable response to lithium prophylaxis. Reproducibility of cognitive deficits across studies raises the possibility of using cognitive profiles as endophenotypes of BD, with deficits in verbal explicit memory and executive function commonly reported. Brain imaging provides a more ambiguous data set consistent with heterogeneity of the illness.

Identification, characterization, and association analysis of novel genes from the bipolar disorder susceptibility locus on chromosome 4q35

The cause of bipolar disorder remains unknown, with little knowledge of the underlying biological, anatomical, biochemical, or genetic defect. The disorder is genetically complex, with an increasing number of loci being implicated through genetic linkage studies. We previously identified a bipolar disorder susceptibility locus on chromosome 4q35 and refined the interval harboring this susceptibility gene to approximately 5 Mb, a size that is amenable to positional cloning. Several independent studies have reported the presence of a susceptibility gene at this locus. To identify candidate genes for testing for association with bipolar disorder, we previously established a transcript map that encompasses the candidate interval. We have continued to seek novel genes from this region in order to expand this transcript map. Here, we describe the further identification and characterization of eight novel genes from the chromosome 4q35 bipolar candidate interval. Expression analysis determined that six of these novel genes are expressed in the brain, and these genes were therefore analyzed for association with bipolar disorder. Single nucleotide polymorphisms were identified from the candidate genes and tested for association in our case-control cohort. Our data suggest that the six candidate genes analyzed can be excluded from involvement in the disorder.

Linkage and candidate gene analysis of 14q22-24 in bipolar disorder: support for GCHI as a novel susceptibility gene

Using a collection of Irish sib-pair nuclear families, we previously obtained modest evidence of linkage implicating 14q22-24 in bipolar disorder (BPD). To follow-up on this preliminary finding, an extended linkage analysis was performed which employed thirteen microsatellite markers, spanning a total distance of 85 cM on 14q. Effectively, P-values <0.05 were observed for a region extending over 41.88 cM, with the marker D14S281 displaying a peak multipoint non-parametric lod (NPL) score of 2.72 and an associated P-value of 0.003. Support for this finding was also obtained from flanking markers indicating excess allele sharing at 14q22-24 in Irish bipolar sib-pairs. A web-based candidate gene search of 14q22-24 resulted in the selection of GTP cyclohydrolase I (GCHI), located 200 kb 3' of D14S281, as the best plausible candidate gene for involvement in BPD. GCHI is the rate-limiting enzyme in the biosynthesis of tetrahydrobiopterin (BH(4)), a natural cofactor for tyrosine and tryptophan hydroxylases. These enzymes play an essential role in the biosynthesis of various hormones and neurotransmitters such as dopamine, noradrenaline, adrenaline, and serotonin. Numerous studies have also suggested that the clinical symptoms of depression might be related to a deficiency of BH(4). An association study between BPD and a novel single nucleotide polymorphism (SNP) in GCHI (G to A at position -959 bp, upstream of the ATG codon), is also presented here. This study revealed that the variant A allele is preferentially transmitted to BPI probands (chi(2) = 4.54, P = 0.033) suggesting that variants within GCHI may contribute to BPD in the Irish population.

Techniques for the identification of genes involved in psychiatric disorders

OBJECTIVE

Most psychiatric disorders are complex genetic traits involving both genetic and environmental risk factors. This paper aims to review the gene identification strategies being applied by molecular geneticists in their efforts to elucidate the genetic and molecular basis of psychiatric disorders. Future strategies will also be canvassed.

METHOD

The psychiatric genetic literature was reviewed to identify current strategies applied to gene identification, with examples provided where available. The future strategies and applications that will arise from genome projects, including the International Haplotype Mapping Project, are also discussed.

RESULTS

Many advances in the techniques of gene discovery, and the increasing resources available, are rapidly being adopted by researchers and applied to the complex problem of identifying susceptibility genes for mental illnesses. Perhaps the single most important advance to date is the Human Genome Project and all that has stemmed from the vast quantity of information that this endeavour has provided. With these technological advances and the massive increase of publicly available genetic resources, several genes have recently been implicated in the susceptibility to psychiatric illnesses including schizophrenia and depression. After many years of fruitless endeavours, these recent reports indicate that the labours of researchers in psychiatric genetics are beginning to show exciting results.

CONCLUSIONS

Identification of these susceptibility genes holds great promise, with the unravelling of the molecular and biochemical basis of some conditions now being a more realistic and tangible goal. The increasing number of genes being identified augers well for the future treatment of psychiatric disorders. The genes identified, and the pathways of genes and proteins that they implicate, will provide potential novel targets for new therapeutic drugs. Psychiatric genetics appears to be poised for significant advances in our knowledge and understanding of the molecular genetic basis of mental illness.

Recent findings on the genetic basis of bipolar disorder

What began as a search for a specific gene for bipolar disorder has now become a search for multiple susceptibility genes as it has be-come clear that the genetic basis of bipolar disorder probably involves multiple genes interacting with each other and with environmental components in as-yet mysterious ways. This article reviews the most recent findings and the emerging picture in the genetics of bipolar disorder.

Association analysis of transcripts from the bipolar susceptibility locus on chromosome 4q35, exclusion of a pathogenic role for eight positional candidate genes

Bipolar affective disorder is a major psychiatric illness with a population prevalence of up to 1.6%. The disorder is genetically complex. To date, no specific gene or DNA sequence variation that predisposes to the disorder has been described, however several susceptibility loci have been proposed through genetic linkage analysis. We previously identified one such susceptibility locus on chromosome 4q35, and refined the interval harboring this susceptibility gene to a size that is amenable to positional cloning. Several independent studies have now been described that support the presence of a susceptibility gene at this locus. In order to identify candidate genes for testing association with bipolar disorder, we previously established a comprehensive transcript map that encompasses the chromosome 4q35 susceptibility locus implicated in our linkage analysis. In this study, we have selected full-length genes from the transcript map and determined the genomic structure of each gene. We identified informative, intragenic single nucleotide polymorphisms (SNPs) by screening all exons and flanking intron sequences in affected individuals from seven bipolar pedigrees that we previously reported as showing evidence for linkage to chromosome 4q35. Analysis of these SNPs was then extended to our unrelated bipolar case-control cohort to test for association with the disorder. Our data suggests that all genes analyzed can be excluded from direct involvement in the disorder. We have therefore, excluded approximately half the genes within the chromosome 4q35 candidate interval from playing a direct pathogenic role in bipolar disorder.

Implications of genetic risk information in families with a high density of bipolar disorder: an exploratory study

While major susceptibility genes for bipolar disorder are yet to be identified, the opportunity exists to systematically ascertain the important issues and societal implications of genetic risk determination for bipolar disorder prior to these technological advances becoming widely available. This study explores, in a sample of families with a high density of bipolar disorder: (i) attitudes to predictive genetic and prenatal testing, using different risk frames; (ii) attributions for bipolar disorder, in particular the degree to which a genetic model is endorsed; and (iii) the impact of these attributions on the perceived stigma of bipolar disorder. A qualitative methodology was selected as most appropriate as no previous research has examined this issue. Participants were ascertained through a molecular genetics study of bipolar disorder. In-depth interviews were conducted with 21 members of families with a high density of bipolar disorder. Most participants reported being interested in genetic testing if it gave a definitive answer, while expressed interest in testing was lower if it gave a probable answer only. Almost all stressed that a genetic susceptibility and environmental factors interacted. Most participants felt that a genetic explanation was likely to decrease the stigma associated with bipolar disorder as it shifted the locus of control and responsibility away from the individual towards the role of heredity. Findings indicate that expressed interest in genetic testing depends on the certainty imparted by the test. Results suggest that families with bipolar disorder are likely to benefit psychologically from information about the genetic basis of bipolar disorder.

Genetics of major mood disorders

The results presented in recent research suggest that nosology must be changed to reflect the genetic origins of the multiple disorders that are collectively described by the term bipolar disorder.

A 4q35.2 subtelomeric deletion identified in a screen of patients with co-morbid psychiatric illness and mental retardation

Background

Cryptic structural abnormalities within the subtelomeric regions of chromosomes have been the focus of much recent research because of their discovery in a percentage of people with mental retardation (UK terminology: learning disability). These studies focused on subjects (largely children) with various severities of intellectual impairment with or without additional physical clinical features such as dysmorphisms. However it is well established that prevalence of schizophrenia is around three times greater in those with mild mental retardation. The rates of bipolar disorder and major depressive disorder have also been reported as increased in people with mental retardation. We describe here a screen for telomeric abnormalities in a cohort of 69 patients in which mental retardation co-exists with severe psychiatric illness.

Methods

We have applied two techniques, subtelomeric fluorescence in situ hybridisation (FISH) and multiplex amplifiable probe hybridisation (MAPH) to detect abnormalities in the patient group.

Results

A subtelomeric deletion was discovered involving loss of 4q in a patient with co-morbid schizoaffective disorder and mental retardation.

Conclusion

The precise region of loss has been defined allowing us to identify genes that may contribute to the clinical phenotype through hemizygosity. Interestingly, the region of 4q loss exactly matches that linked to bipolar affective disorder in a large multiply affected Australian kindred.

Possible evidence for a common risk locus for bipolar affective disorder and schizophrenia on chromosome 4p16 in patients from the Faroe Islands

Patients with schizophrenia (n=11) and bipolar affective disorder (n=17) from the relatively isolated population of the Faroe Islands were genotyped for 34 polymorphic markers on chromosome 4 in a search for allelic association and haplotype sharing among distantly related patients. When considering bipolar patients only, there was no clearcut support for any region on chromosome 4. The two-marker segment D4S394-D4S2983 at 4p16.1 was, however, supported by a P-value of 0.0162. For patients with schizophrenia, there was reasonable support for 4p16.1 as marker D4S2281 (P=0.0019), a two-marker segment (D4S2281-D4S1605, P=0.0009) and a three-marker segment (D4S2923-D4S2928-D4S1582, P-0.0005) appeared to be associated with schizophrenia, with some alleles/haplotypes occurring with different frequencies in patients compared to controls. When combining both psychiatric disorders, chromosome 4p16.1 received further support from five partially overlapping two- and three-marker segments (D4S394-D4S2983, P=0.0039; D4S2281-D4S1605, P=0.0027 and D4S394-D4S2983-D4S2923, P=0.006; D4S2923-D4S2928-D4S1582, P=0.00007; D4S1582-D4S1599-D4S2281, P=0.005). Increased haplotype sharing in patients with schizophrenia and in the combined data set was partly supported by Fisher's exact test and tests based on the genealogy. Our study yields support for a common risk gene for schizophrenia and bipolar affective disorder on the short arm of chromosome 4, as suggested by previous findings in the neighbouring Scottish population.

Genetic linkage in bipolar disorder

Bipolar disorder is an etiologically complex syndrome that is clearly heritable. Multiple genes, working singly or in concert, are likely to cause susceptibility to bipolar disorder. Bipolar disorder genetics has progressed rapidly in the last few decades. However, specific causal genetic mutations for bipolar disorder have not been identified. Both candidate gene studies and complete genome screens have been conducted. They have provided compelling evidence for several potential bipolar disorder susceptibility loci in several regions of the genome. The strongest evidence suggests that bipolar disorder susceptibility loci may lie in one or more genomic regions on chromosomes 18, 4, and 21. Other regions of interest, including those on chromosomes 5 and 8, are also under investigation. New approaches, such as the use of genetically isolated populations and the use of endophenotypes for bipolar disorder, hold promise for continued advancement in the search to identify specific bipolar disorder genes.

Genome-wide scan and conditional analysis in bipolar disorder: evidence for genomic interaction in the National Institute of Mental Health genetics initiative bipolar pedigrees

BACKGROUND

In 1989 the National Institute of Mental Health began a collaborative effort to identify genes for bipolar disorder. The first 97 pedigrees showed evidence of linkage to chromosomes 1, 6, 7, 10, 16, and 22 (Nurnberger et al 1997). An additional 56 bipolar families have been genotyped, and the combined sample of 153 pedigrees studied.

METHODS

Three hierarchical affection status models were analyzed with 513 simple sequence repeat markers; 298 were common across all pedigrees. The primary analysis was a nonparametric genome-wide scan. We performed conditional analyses based on epistasis or heterogeneity for five regions.

RESULTS

One region, on 16p13, was significant at the genome-wide p <.05 level. Four additional chromosomal regions (20p12, 11p15, 6q24, and 10p12) showed nominally significant linkage findings (p </=.01). Conditional analysis assuming epistasis identified a significant increase in linkage at four regions. Families linked to 6q24 showed a significant increase in nonparametric logarithms of the odds (NPL) scores at 5q11 and 7q21. Epistasis also was observed between 20p12 and 13q21, and 16p13 and 9q21.

CONCLUSIONS

The findings are presented in rank order of nominal significance. Several of these regions have been previously implicated in independent studies of either bipolar disorder or schizophrenia. The strongest finding is at 16p13 at D16S748 with an NPL of 3.3, there is evidence of epistasis between this locus and 9q21. Application of conditional analyses is potentially useful in larger sample collections to identify susceptibility genes of modest influence that may not be identified in a genome-wide scan aimed to identify single gene effects.

Psychiatric genetics in Australia

Australian research in psychiatric genetics covers molecular genetic studies of depression, anxiety, alcohol dependence, Alzheimer's disease, bipolar disorder, schizophrenia, autism, and attention deficit hyperactivity disorder. For each disorder, a variety of clinical cohorts have been recruited including affected sib pair families, trios, case/controls, and twins from a large population-based twin registry. These studies are taking place both independently and in collaboration with international groups. Microarray studies now complement DNA investigations, while animal models are in development. An Australian government genome facility provides a high throughput genotyping and mutation detection service to the Australian scientific community, enhancing the contribution of Australian psychiatric genetics groups to gene discovery.

Genome scan of the fifty-six bipolar pedigrees from the NIMH genetics initiative replication sample: chromosomes 4, 7, 9, 18, 19, 20, and 21

The NIMH genetics initiative on bipolar disorder was established to collect uniformly ascertained bipolar pedigrees for genetic studies. In 1997, the four participating sites published a genome scan on the initial set of 97 bipolar pedigrees. Fifty-six additional bipolar pedigrees have now been ascertained and evaluated. This replication pedigree set contains 354 genotyped subjects, including 139 bipolar I (BPI) subjects, five schizoaffective bipolar type SA/BP subjects, 41 bipolar II (BPII) subjects, and 43 recurrent unipolar (RUP) depression subjects. Our site has recently genotyped the replication study bipolar pedigrees using 107 microsatellite markers from chromosomes 4, 7, 9, 18, 19, 20, and 21. We are now reporting parametric and nonparametric linkage results from this effort. Multipoint nonparametric linkage analysis produced three candidate regions with allele sharing LOD scores >/= 1.0. The linkage signal on 4q35 peaked between markers D4S3335 and D4S2390 with an allele sharing LOD score of 2.49. This finding exceeds standard criteria for suggestive linkage. Two additional loci approach suggestive linkage levels: the 4q32 finding had its maximum near marker D4S1629 with an allele sharing LOD score of 2.16, and the 20p12 finding peaked at D20S162 with an allele sharing LOD score of 1.82. Multipoint parametric linkage analysis produced similar findings. When we combined the genotype data from the original and the replication pedigree sets, 20p12 yielded a nonparametric LOD score of 2.38, which exceeds standard criteria for suggestive linkage, and a corresponding parametric HLOD score of 2.98. The combined analysis did not provide further support for linkage to 4q32 and 4q35.

Evidence of susceptibility loci on 4q32 and 16p12 for bipolar disorder

We performed a genome-wide scan for susceptibility loci in bipolar disorder in a study sample colleted from the isolated Finnish population, consisting of 41 families with at least two affected siblings. We identified one distinct locus on 16p12 providing significant evidence for linkage in two-point analysis (Z(max)=3.4). Furthermore, three loci with a two-point LOD score >2.0 were observed with markers on 4q32, 12q23 and Xq25, the latter locus having been earlier identified in one extended Finnish pedigree. In the second stage we fine mapped these chromosomal regions and also genotyped additional family members. In the fine mapping stage, 4q32 provided significant evidence of linkage for the three-point analyses (Z(max)=3.6) and 16p12 produced a three-point LOD score of 2.7. Since the identified chromosomal regions replicate earlier linkage findings in either bipolar disorder or other mental disorders, they should be considered good targets for further genetic analyses.

JI, Craddock N, DePaulo JR, Baron M, Gershon ES, Ekholm J, Cichon S, Turecki G, Claes S, Kelsoe JR, Schofield PR, Badenhop RF, Morissette J, Coon H, Blackwood D, McInnes LA, Foroud T, Edenberg HJ, Reich T, Rice JP, Goate A, McInnis MG, McMahon FJ, Badner JA, Goldin LR, Bennett P, Willour VL, Zandi PP, Liu J, Gilliam C, Juo SH, Berrettini WH, Yoshikawa T, Peltonen L, Lönnqvist J, Nöthen MM, Schumacher J, Windemuth C, Rietschel M, Propping P, Maier W, Alda M, Grof P, Rouleau GA, Del-Favero J, Van Broeckhoven C, Mendlewicz J, Adolfsson R, Spence MA, Luebbert H, Adams LJ, Donald JA, Mitchell PB, Barden N, Shink E, Byerley W, Muir W, Visscher PM, Macgregor S, Gurling H, Kalsi G, McQuillin A, Escamilla MA, Reus VI, Leon P, Freimer NB, Ewald H, Kruse TA, Mors O, Radhakrishna U, Blouin JL, Antonarakis SE, Akarsu N. Genome scan meta-analysis of schizophrenia and bipolar disorder, part III: Bipolar disorder

Genome scans of bipolar disorder (BPD) have not produced consistent evidence for linkage. The rank-based genome scan meta-analysis (GSMA) method was applied to 18 BPD genome scan data sets in an effort to identify regions with significant support for linkage in the combined data. The two primary analyses considered available linkage data for "very narrow" (i.e., BP-I and schizoaffective disorder-BP) and "narrow" (i.e., adding BP-II disorder) disease models, with the ranks weighted for sample size. A "broad" model (i.e., adding recurrent major depression) and unweighted analyses were also performed. No region achieved genomewide statistical significance by several simulation-based criteria. The most significant P values (<.01) were observed on chromosomes 9p22.3-21.1 (very narrow), 10q11.21-22.1 (very narrow), and 14q24.1-32.12 (narrow). Nominally significant P values were observed in adjacent bins on chromosomes 9p and 18p-q, across all three disease models on chromosomes 14q and 18p-q, and across two models on chromosome 8q. Relatively few BPD pedigrees have been studied under narrow disease models relative to the schizophrenia GSMA data set, which produced more significant results. There was no overlap of the highest-ranked regions for the two disorders. The present results for the very narrow model are promising but suggest that more and larger data sets are needed. Alternatively, linkage might be detected in certain populations or subsets of pedigrees. The narrow and broad data sets had considerable power, according to simulation studies, but did not produce more highly significant evidence for linkage. We note that meta-analysis can sometimes provide support for linkage but cannot disprove linkage in any candidate region.

Evidence for a putative bipolar disorder locus on 2p13-16 and other potential loci on 4q31, 7q34, 8q13, 9q31, 10q21-24, 13q32, 14q21 and 17q11-12

Bipolar disorder (BP) is a severe and common psychiatric disorder characterized by extreme mood swings. Family, twin and adoption studies strongly support a genetic component. The mode of inheritance is complex and likely involves multiple, as yet unidentified genes. To identify susceptibility loci, we conducted a genome-wide scan with 343 microsatellite markers in one of the largest, well-characterized pedigree samples assembled to date (373 individuals in 40 pedigrees). To increase power to detect linkage, scan statistics were used to examine the logarithm of odds (lod) scores based on evidence at adjacent chromosomal loci. This analysis yielded significant evidence of linkage (genome-wide P&<0.05) for markers on 2p13-16. Standard linkage analysis was also supportive of linkage to 2p13-16 (lod=3.20), and identified several other interesting regions: 4q31 (lod=3.16), 7q34 (lod=2.78), 8q13 (lod=2.06), 9q31 (lod=2.07), 10q24 (lod=2.79), 13q32 (lod=2.2), 14q21 (lod=2.36) and 17q11-12 (lod=2.75). In this systematic, large-scale study, we identified novel putative loci for BP (on 2p13-16, 8q13 and 14q21) and found support for previously proposed loci (on 4q31, 7q34, 9q31, 10q21-24, 13q32 and 17q11-12). Two of the regions implicated in our study, 2p13-14 and 13q32, have also been linked to schizophrenia, suggesting that the two disorders may have susceptibility genes in common.

Genome-wide scan of bipolar disorder in 65 pedigrees: supportive evidence for linkage at 8q24, 18q22, 4q32, 2p12, and 13q12

The purpose of this study was to assess 65 pedigrees ascertained through a Bipolar I (BPI) proband for evidence of linkage, using nonparametric methods in a genome-wide scan and for possible parent of origin effect using several analytical methods. We identified 15 loci with nominally significant evidence for increased allele sharing among affected relative pairs. Eight of these regions, at 8q24, 18q22, 4q32, 13q12, 4q35, 10q26, 2p12, and 12q24, directly overlap with previously reported evidence of linkage to bipolar disorder. Five regions at 20p13, 2p22, 14q23, 9p13, and 1q41 are within several Mb of previously reported regions. We report our findings in rank order and the top five markers had an NPL>2.5. The peak finding in these regions were D8S256 at 8q24, NPL 3.13; D18S878 at 18q22, NPL 2.90; D4S1629 at 4q32, NPL 2.80; D2S99 at 2p12, NPL 2.54; and D13S1493 at 13q12, NPL 2.53. No locus produced statistically significant evidence for linkage at the genome-wide level. The parent of origin effect was studied and consistent with our previous findings, evidence for a locus on 18q22 was predominantly from families wherein the father or paternal lineage was affected. There was evidence consistent with paternal imprinting at the loci on 13q12 and 1q41.

A genome screen of 13 bipolar affective disorder pedigrees provides evidence for susceptibility loci on chromosome 3 as well as chromosomes 9, 13 and 19

Bipolar affective disorder is a severe mood disorder that afflicts approximately 1% of the population worldwide. Twin and adoption studies have indicated that genetic factors contribute to the disorder and while many chromosomal regions have been implicated, no susceptibility genes have been identified. We undertook a combined analysis of 10 cM genome screen data from a single large bipolar affective disorder pedigree, for which we have previously reported linkage to chromosome 13q14 (Badenhop et al, 2001) and 12 pedigrees independently screened using the same 400 microsatellite markers. This 13 pedigree cohort consisted of 231 individuals, including 69 affected members. Two-point LOD score analysis was carried out under heterogeneity for three diagnostic and four genetic models. Non-parametric multipoint analysis was carried out on regions of interest. Two-point heterogeneity LOD scores (HLODs) greater than 1.5 were obtained for 11 markers across the genome, with HLODs greater than 2.0 obtained for four of these markers. The strongest evidence for linkage was at 3q25-26 with a genome-wide maximum score of 2.49 at D3S1279. Six markers across a 50 cM region at 3q25-26 gave HLODs greater than 1.5, with three of these markers producing scores greater than 2.0. Multipoint analysis indicated a 20 cM peak between markers D3S1569 and D3S1614 with a maximum NPL of 2.8 (P = 0.004). Three other chromosomal regions yielded evidence for linkage: 9q31-q33, 13q14 and 19q12-q13. The regions on chromosomes 3q and 13q have previously been implicated in other bipolar and schizophrenia studies. In addition, several individual pedigrees gave LOD scores greater than 1.5 for previously reported bipolar susceptibility loci on chromosomes 18p11, 18q12, 22q11 and 8p22-23.

A transcript map encompassing a susceptibility locus for bipolar affective disorder on chromosome 4q35

Bipolar affective disorder is one of the most common mental illnesses with a population prevalence of approximately 1%. The disorder is genetically complex, with an increasing number of loci being implicated through genetic linkage studies. However, the specific genetic variations and molecules involved in bipolar susceptibility and pathogenesis are yet to be identified. Genetic linkage analysis has identified a bipolar disorder susceptibility locus on chromosome 4q35, and the interval harbouring this susceptibility gene has been narrowed to a size that is amenable to positional cloning. We have used the resources of the Human Genome Project (HGP) and Celera Genomics to identify overlapping sequenced BAC clones and sequence contigs that represent the region implicated by linkage analysis. A combination of bioinformatic tools and laboratory techniques have been applied to annotate this DNA sequence data and establish a comprehensive transcript map that spans approximately 5.5 Mb. This map encompasses the chromosome 4q35 bipolar susceptibility locus, which localises to a "most probable" candidate interval of approximately 2.3 Mb, within a more conservative candidate interval of approximately 5 Mb. Localised within this map are 11 characterised genes and eight novel genes of unknown function, which together provide a collection of candidate transcripts that may be investigated for association with bipolar disorder. Overall, this region was shown to be very gene-poor, with a high incidence of pseudogenes, and redundant and novel repetitive elements. Our analysis of the interval has demonstrated a significant difference in the extent to which the current HGP and Celera sequence data sets represent this region.

A genome-wide scan shows significant linkage between bipolar disorder and chromosome 12q24.3 and suggestive linkage to chromosomes 1p22-21, 4p16, 6q14-22, 10q26 and 16p13.3

The present study reports a genomewide scan using linkage analysis for risk genes involved in bipolar disorder with 613 microsatellite markers including additional testing of promising regions. As previously published significant linkage was obtained at chromosome 12q24.3 with a two-point parametric lod score of 3.42 at D12S1639 including all members in both families (empirical P-value 0.00004, genome-wide P-value 0.0417). The multipoint parametric lod score at D12S1639 was 3.63 (genome-wide P-value 0.0265). At chromosome 1p22-p21 a parametric, affecteds-only two-point lod score of 2.75 at marker D1S216 was found (empirical P-value 0.0002, genome-wide P-value 0.1622). A three-point lod score of 2.98 (genome-wide P-value 0.1022) at D1S216, and a multipoint non-parametric analysis with a maximum NPL-all score of 17.60 (P-value 0.00079) at D1S216 further supported this finding. A number of additional loci on chromosomes 4p16, 6q14-q22, 10q26 and 16p13.3 yielded parametric lod scores around or above 2.

A genome screen of 13 bipolar affective disorder pedigrees provides evidence for susceptibility loci on chromosome 3 as well as chromosomes 9, 13 and 19

Bipolar affective disorder is a severe mood disorder that afflicts approximately 1% of the population worldwide. Twin and adoption studies have indicated that genetic factors contribute to the disorder and while many chromosomal regions have been implicated, no susceptibility genes have been identified. We undertook a combined analysis of 10 cM genome screen data from a single large bipolar affective disorder pedigree, for which we have previously reported linkage to chromosome 13q14 (Badenhop et al, 2001) and 12 pedigrees independently screened using the same 400 microsatellite markers. This 13-pedigree cohort consisted of 231 individuals, including 69 affected members. Two-point LOD score analysis was carried out under heterogeneity for three diagnostic and four genetic models. Non-parametric multipoint analysis was carried out on regions of interest. Two-point heterogeneity LOD scores (HLODs) greater than 1.5 were obtained for 11 markers across the genome, with HLODs greater than 2.0 obtained for four of these markers. The strongest evidence for linkage was at 3q25-26 with a genome-wide maximum score of 2.49 at D3S1279. Six markers across a 50 cM region at 3q25-26 gave HLODs greater than 1.5, with three of these markers producing scores greater than 2.0. Multipoint analysis indicated a 20 cM peak between markers D3S1569 and D3S1614 with a maximum NPL of 2.8 (P= 0.004). Three other chromosomal regions yielded evidence for linkage: 9q31-q33, 13q14 and 19q12-q13. The regions on chromosomes 3q and 13q have previously been implicated in other bipolar and schizophrenia studies. In addition, several individual pedigrees gave LOD scores greater than 1.5 for previously reported bipolar susceptibility loci on chromosomes 18p11, 18q12, 22q11 and 8p22-23.

Genetic refinement and physical mapping of a 2.3 Mb probable disease region associated with a bipolar affective disorder susceptibility locus on chromosome 4q35

A susceptibility locus for bipolar affective disorder has been mapped to chromosome 4q35 in a large multigenerational pedigree. We have expanded this analysis to include 55 pedigrees (674 individuals, 214 affecteds). The evidence for linkage to 4q35 was strengthened in this larger cohort, with a maximum two-point LOD score of 3.2 for marker D4S1652. Several other markers in the region gave LOD scores greater than 1.5. Non-parametric analysis provided additional support for linkage to the 4q35 region. To further refine this region, haplotype analysis was carried out in 16 of the 55 pedigrees that showed evidence of linkage. As there is no evidence for an ancestral haplotype, nor a one-to-one correspondence between the disease and putative disease haplotype, we undertook an analysis based on pedigree-specific, identical-by-descent allele-sharing in order to define a probable disease region. This analysis indicated that the percentage sharing of alleles, identical-by-descent, in affecteds of all linked pedigrees increases from 60% at the centromeric markers to 75% for markers at the telomere. Maximal allele sharing occurred between markers D4S3051 and 4qTEL13 with this 24 cM region defining a probable disease region. We have constructed a physical map of the 4q35 interval consisting of a YAC contig and BAC clones. Based on this map the probable disease region between D4S3051 and 4qTEL13 corresponds to only 2.3 Mb. This region is very gene poor with only three known genes indicated from the YAC/BAC map. The small number of genes will facilitate systematic screening for variations associated with bipolar disorder.

Genomewide linkage analysis identifies polymorphism in the human interferon-gamma receptor affecting Helicobacter pylori infection

Helicobacter pylori is considered the most prevalent infectious agent among humans, and it causes gastric inflammation, gastroduodenal ulcers, and a risk of gastric cancer. We performed a genomewide linkage analysis among Senegalese siblings phenotyped for H. pylori-reactive serum immunoglobulin G. A multipoint LOD score of 3.1 was obtained at IFNGR1, the gene that encodes chain 1 of the interferon-gamma (IFN-gamma) receptor. Sequencing of IFNGR1 revealed -56C-->T, H318P, and L450P variants, which were found to be associated with high antibody concentrations. The inclusion of these in the linkage analysis raised the LOD score to 4.2. The variants were more prevalent in Africans than in whites. Our findings indicate that IFN-gamma signaling plays an essential role in human H. pylori infection, and they contribute to an explanation of the observations of high prevalences and relatively low pathogenicity of H. pylori in Africa. Moreover, they provide further support for the value of genomewide linkage studies in the analysis of susceptibility to infection and other complex genetic traits.