A resource of induced pluripotent stem cell (iPSC) lines including clinical, genomic, and cellular data from genetically isolated families with mood and psychotic disorders

Genome-wide (GWAS) and copy number variant (CNV) association studies have reproducibly identified numerous risk alleles associated with bipolar disorder (BD), major depressive disorder (MDD), and schizophrenia (SCZ), but biological characterization of these alleles lags gene discovery, owing to the inaccessibility of live human brain cells and inadequate animal models for human psychiatric conditions. Human-derived induced pluripotent stem cells (iPSCs) provide a renewable cellular reagent that can be differentiated into living, disease-relevant cells and 3D brain organoids carrying the full complement of genetic variants present in the donor germline. Experimental studies of iPSC-derived cells allow functional characterization of risk alleles, establishment of causal relationships between genes and neurobiology, and screening for novel therapeutics. Here we report the creation and availability of an iPSC resource comprising clinical, genomic, and cellular data obtained from genetically isolated families with BD and related conditions. Results from the first 324 study participants, 61 of whom have validated pluripotent clones, show enrichment of rare single nucleotide variants and CNVs overlapping many known risk genes and pathogenic CNVs. This growing iPSC resource is available to scientists pursuing functional genomic studies of BD and related conditions.

Basic Molecular Genetics Concepts and Tools

Progress in genetics in the last decades has been spurred largely by the Human Genome Project. Successful sequencing of the human genome and genomes of organisms across the evolutionary scale has been achieved. Scientific discoveries and innovations steered the refinement and annotation of sequences, cataloging of variation including SNPs and CNVs, development of fast, precise, high throughput methods and improved bioinformatics and statistical tools. These advances boosted GWAS on large samples identifying multiple susceptibility loci in diverse complex diseases and traits. Exome, whole genome and RNA sequencing has uncovered intricate elements of coding, noncoding and regulatory regions and the richness of the transcriptome. Evolution in genome editing has heightened the ability to alter any nucleotide and discern its biological effect. Exploiting these innovations in studies involving cells derived from patients through the iPSC technology offers manifold possibilities for functional studies that could enhance disease modeling and yield new therapeutic targets.

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

OBJECTIVE

The assessment of response to lithium maintenance treatment in bipolar disorder (BD) is complicated by variable length of treatment, unpredictable clinical course, and often inconsistent compliance. Prospective and retrospective methods of assessment of lithium response have been proposed in the literature. In this study we report the key phenotypic measures of the "Retrospective Criteria of Long-Term Treatment Response in Research Subjects with Bipolar Disorder" scale currently used in the Consortium on Lithium Genetics (ConLiGen) study.

MATERIALS AND METHODS

Twenty-nine ConLiGen sites took part in a two-stage case-vignette rating procedure to examine inter-rater agreement [Kappa (κ)] and reliability [intra-class correlation coefficient (ICC)] of lithium response. Annotated first-round vignettes and rating guidelines were circulated to expert research clinicians for training purposes between the two stages. Further, we analyzed the distributional properties of the treatment response scores available for 1,308 patients using mixture modeling.

RESULTS

Substantial and moderate agreement was shown across sites in the first and second sets of vignettes (κ = 0.66 and κ = 0.54, respectively), without significant improvement from training. However, definition of response using the A score as a quantitative trait and selecting cases with B criteria of 4 or less showed an improvement between the two stages (ICC1 = 0.71 and ICC2 = 0.75, respectively). Mixture modeling of score distribution indicated three subpopulations (full responders, partial responders, non responders).

CONCLUSIONS

We identified two definitions of lithium response, one dichotomous and the other continuous, with moderate to substantial inter-rater agreement and reliability. Accurate phenotypic measurement of lithium response is crucial for the ongoing ConLiGen pharmacogenomic study.

Ablation of Mrds1/Ofcc1 induces hyper-γ-glutamyl transpeptidasemia without abnormal head development and schizophrenia-relevant behaviors in mice

Mutations in the Opo gene result in eye malformation in medaka fish. The human ortholog of this gene, MRDS1/OFCC1, is a potentially causal gene for orofacial cleft, as well as a susceptibility gene for schizophrenia, a devastating mental illness. Based on this evidence, we hypothesized that this gene could perform crucial functions in the development of head and brain structures in vertebrates. To test this hypothesis, we created Mrds1/Ofcc1-null mice. Mice were examined thoroughly using an abnormality screening system referred to as "the Japan Mouse Clinic". No malformations of the head structure, eye or other parts of the body were apparent in these knockout mice. However, the mutant mice showed a marked increase in serum γ-glutamyl transpeptidase (GGT), a marker for liver damage, but no abnormalities in other liver-related measurements. We also performed a family-based association study on the gene in schizophrenia samples of Japanese origin. We found five single nucleotide polymorphisms (SNPs) located across the gene that showed significant transmission distortion, supporting a prior report of association in a Caucasian cohort. However, the knockout mice showed no behavioral phenotypes relevant to schizophrenia. In conclusion, disruption of the Mrds1/Ofcc1 gene elicits asymptomatic hyper-γ-glutamyl-transpeptidasemia in mice. However, there were no phenotypes to support a role for the gene in the development of eye and craniofacial structures in vertebrates. These results prompt further examination of the gene, including its putative contribution to hyper-γ-glutamyl transpeptidasemia and schizophrenia.

A systems approach to the biology of mood disorders through network analysis of candidate genes

Meta analysis of association data of mood disorders has shown evidence for the role of particular genes in genetic risk. Integration of association data from meta analysis with differential expression data in brains of mood disorder patients could heighten the level of support for specific genes. To identify molecular mechanisms that may be disrupted in disease, a systems approach that involves analysis of biological networks created by these selected genes was employed.Interaction networks of hierarchical groupings of selected genes were generated using the Michigan Molecular Interactions (MiMI) software. Large networks were deconvoluted into subclusters of core complexes by using a community clustering program, GLay. Network nodes were functionally annotated in DAVID Bioinformatics Resource to identify enriched pathways and functional clusters. MAPK and beta adrenergic receptor signaling pathways were significantly enriched in the ANK3 and CACNA1C network. The PBRM1 network bolstered the enrichment of chromatin remodeling and transcription regulation functional clusters. Lowering the stringency for inclusion of other genes in network seeds increased network complexity and expanded the recruitment of enriched pathways to include signaling by neurotransmitter and hormone receptors, neurotrophin, ErbB and the cell cycle. We present a strategy to interrogate mechanisms in the cellular system that might be perturbed in disease. Network analysis of meta analysis- generated candidate genes that exhibited differential expression in mood disorder brains identified signaling pathways and functional clusters that may be involved in genetic risk for mood disorders.

Interaction networks of lithium and valproate molecular targets reveal a striking enrichment of apoptosis functional clusters and neurotrophin signaling

The overall neurobiological mechanisms by which lithium and valproate stabilize mood in bipolar disorder patients have yet to be fully defined. The therapeutic efficacy and dissimilar chemical structures of these medications suggest that they perturb both shared and disparate cellular processes. To investigate key pathways and functional clusters involved in the global action of lithium and valproate, we generated interaction networks formed by well-supported drug targets. Striking functional similarities emerged. Intersecting nodes in lithium and valproate networks highlighted a strong enrichment of apoptosis clusters and neurotrophin signaling. Other enriched pathways included MAPK, ErbB, insulin, VEGF, Wnt and long-term potentiation indicating a widespread effect of both drugs on diverse signaling systems. MAPK1/3 and AKT1/2 were the most preponderant nodes across pathways suggesting a central role in mediating pathway interactions. The convergence of biological responses unveils a functional signature for lithium and valproate that could be key modulators of their therapeutic efficacy.

The International Consortium on Lithium Genetics (ConLiGen): an initiative by the NIMH and IGSLI to study the genetic basis of response to lithium treatment

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

Meta-analysis of genome-wide association data identifies a risk locus for major mood disorders on 3p21.1

The major mood disorders, which include bipolar disorder (BD) and major depressive disorder (MDD), are substantially heritable, but few risk loci have been identified. We performed a meta-analysis of 5 major mood disorder case-control samples, including over 13,600 unique individuals genotyped with approximately 500,000 to 1 million single nucleotide polymorphism (SNP) markers on high-density arrays. Allele-wise association results were meta-analyzed with a method that weights results by sample size. We found genome-wide significant evidence that SNPs in a region of chromosome 3p21.1were associated with major mood disorders. The SNP rs2251219 returned the smallest meta-analysis p-value, 3.63 × 10⁻⁸, with a pooled odds ratio of 0.87. Supportive results were observed in 2 out of 3 independent samples tested in a replication study. These results implicate one or more genes in this region in the etiology of major mood disorders and suggest that BD and MDD share genetic risk factors.

Two variants in Ankyrin 3 (ANK3) are independent genetic risk factors for bipolar disorder

Two recent reports have highlighted ANK3 as a susceptibility gene for bipolar disorder (BD). We first reported association between BD and the ANK3 marker rs9804190 in a genome-wide association study (GWAS) of two independent samples (Baum et al., 2008). Subsequently, a meta-analysis of GWAS data based on samples from the US and the UK reported association with a different ANK3 marker, rs10994336 (Ferreira et al., 2008). The markers lie about 340 kb apart in the gene. Here, we test both markers in additional samples and characterize the contribution of each marker to BD risk. Our previously reported findings at rs9804190, which had been based on DNA pooling, were confirmed by individual genotyping in the National Institute of Mental Health (NIMH) waves 1-4 (P=0.05; odds ratio (OR)=1.24) and German (P=0.0006; OR=1.34) samples. This association was replicated in an independent US sample known as NIMH wave 5 (466 cases, 212 controls; P=0.017; OR=1.38). A random-effects meta-analysis of all three samples was significant (P=3 x 10(-6); OR=1.32), with no heterogeneity. Individual genotyping of rs10994336 revealed a significant association in the German sample (P=0.0001; OR=1.70), and similar ORs in the NIMH 1-4 and NIMH 5 samples that were not significant at the P<0.05 level. Meta-analysis of all three samples supported an association with rs10994336 (P=1.7 x 10(-5); OR=1.54), again with no heterogeneity. There was little linkage disequilibrium between the two markers. Further analysis suggested that each marker contributed independently to BD, with no significant marker x marker interaction. Our findings strongly support ANK3 as a BD susceptibility gene and suggest true allelic heterogeneity.

A genome-wide association study implicates diacylglycerol kinase eta (DGKH) and several other genes in the etiology of bipolar disorder

The genetic basis of bipolar disorder has long been thought to be complex, with the potential involvement of multiple genes, but methods to analyze populations with respect to this complexity have only recently become available. We have carried out a genome-wide association study of bipolar disorder by genotyping over 550,000 single-nucleotide polymorphisms (SNPs) in two independent case-control samples of European origin. The initial association screen was performed using pooled DNA, and selected SNPs were confirmed by individual genotyping. While DNA pooling reduces power to detect genetic associations, there is a substantial cost saving and gain in efficiency. A total of 88 SNPs, representing 80 different genes, met the prior criteria for replication in both samples. Effect sizes were modest: no single SNP of large effect was detected. Of 37 SNPs selected for individual genotyping, the strongest association signal was detected at a marker within the first intron of diacylglycerol kinase eta (DGKH; P=1.5 x 10(-8), experiment-wide P<0.01, OR=1.59). This gene encodes DGKH, a key protein in the lithium-sensitive phosphatidyl inositol pathway. This first genome-wide association study of bipolar disorder shows that several genes, each of modest effect, reproducibly influence disease risk. Bipolar disorder may be a polygenic disease.

Gene-based SNP mapping of a psychotic bipolar affective disorder linkage region on 22q12.3: association with HMG2L1 and TOM1

Genetic linkage studies in both bipolar affective disorder (BPAD) and schizophrenia have implicated overlapping regions of chromosome 22q. We previously reported that BPAD pedigrees containing multiple members with psychotic symptoms showed suggestive linkage to chromosome 22q12.3. Now we have tested 189 single nucleotide polymorphisms (SNPs) spanning a 3 Mb region around the linkage peak for association with BPAD in 305 families, unrelated cases, and controls. SNPs were selected in or near genes, resulting in coverage at a density of 1 SNP per 6.7 kb across the 22 annotated genes in the region. The strongest signal emerged from family-based association analysis of an 11-SNP, 54 kb haplotype straddling the gene HMG2L1 and part of TOM1. A 3-marker haplotype of SNPs within TOM1 was associated with BPAD (allele-wise P = 0.0011) and with psychotic BPAD (allele-wise P = 0.00049). As hypothesized, the mean odds ratio for the risk alleles across the region was 1.39 in the psychotic but only 0.96 in the non-psychotic subset. Genotype-wise analyses yielded similar results, but the psychotic/non-psychotic distinction was more pronounced with mean odds ratios of 1.91 versus 0.8. Permutation of genotype-wise results for rs2413338 in HMG2L1 showed an empirical P = 0.037 for the difference between subsets. HMG2L1 is a negative regulator of Wnt signaling, a pathway of interest in psychotic BPAD as it is activated by both mood stabilizer and anti-psychotic medications. Further work is needed to confirm these results and uncover the functional variation underlying the association signal.

Sequence variation in DOCK9 and heterogeneity in bipolar disorder

BACKGROUND

Linkage of bipolar disorder to a broad region on chromosome 13q has been supported in several studies including a meta-analysis on genome scans. Subsequent reports have shown that variations in the DAOA (G72) locus on 13q33 display association with bipolar disorder but these may not account for all of the linkage evidence in the region.

OBJECTIVE

To identify additional susceptibility loci on 13q32-q33 by linkage disequilibrium mapping and explore the impact of phenotypic heterogeneity on association.

METHODS

In the initial phase, 98 single nucleotide polymorphism (SNPs) located on 13q32-q33 were genotyped on 285 probands with bipolar disorder and their parents were drawn from families in the NIMH Genetics Initiative consortium for bipolar disorder (NIMH1-4) and two other series. Fine scale mapping using one family series (NIMH1-2) as the test sample was targeted on a gene that displayed the highest evidence of association. A secondary analysis of familial component phenotypes of bipolar disorder was conducted.

RESULTS

Three of seven SNPs in DOCK9, a gene that encodes an activator of the Rho-GTPase Cdc42, showed significant excess allelic transmission (P=0.0477-0.00067). Fine scale mapping on DOCK9 yielded evidence of association at nine SNPs in the gene (P=0.02-0.006). Follow-up tests detected excess transmission of the same allele of rs1340 in two out of three other sets of families. The association signals were largely attributable to maternally transmitted alleles (rs1927568: P=0.000083; odds ratio=3.778). A secondary analysis of familial component phenotypes of bipolar disorder detected significant association across multiple DOCK9 markers for racing thoughts, psychosis, delusion during mania and course of illness indicators.

CONCLUSION

These results suggest that DOCK9 contributes to both risk and increased illness severity in bipolar disorder. We found evidence for the effect of phenotypic heterogeneity on association. To our knowledge this is the first report to implicate DOCK9 or the Rho-GTPase pathway in the etiology of bipolar disorder.

A promoter haplotype of the inositol monophosphatase 2 gene (IMPA2) at 18p11.2 confers a possible risk for bipolar disorder by enhancing transcription

Lithium is an effective mood stabilizer for bipolar disorder patients and its therapeutic effect may involve inhibition of inositol monophosphatase activity. In humans, the enzyme is encoded by two genes, IMPA1 and IMPA2. IMPA2 maps to 18p11.2, a genomic interval for which evidence of linkage to bipolar disorder has been supported by several reports. We performed a genetic association study in Japanese cohorts (496 patients with bipolar disorder and 543 control subjects). Interestingly, we observed association of IMPA2 promoter single nucleotide polymorphisms (SNPs) (-461C and -207T) with bipolar disorder, the identical SNPs reported previously in a different population. In vitro promoter assay and genetic haplotype analysis showed that the combination of (-461C)-(-207T)-(-185A) drove enhanced transcription and the haplotypes containing (-461C)-(-207T)-(-185A) contributed to risk for bipolar disorder. Expression study on post-mortem brains revealed increased transcription from the IMPA2 allele that harbored (-461C)-(-207T)-(-185A) in the frontal cortex of bipolar disorder patients. The examination of allele-specific expressions in post-mortem brains did not support genomic imprinting of IMPA2, which was suggested nearby genomic locus. Contrasting to a prior report, therapeutic concentrations of lithium could not suppress the transcription of IMPA2 mRNA, and the mood-stabilizing effect of lithium is, if IMPA2 was one of the targets of lithium, deemed to be generated via inhibition of enzymatic reaction rather than transcriptional suppression. In conclusion, the present study suggests that a promoter haplotype of IMPA2 possibly contributes to risk for bipolar disorder by elevating IMPA2 levels in the brain, albeit the genetic effect varies among populations.

Autistic-like phenotypes in Cadps2-knockout mice and aberrant CADPS2 splicing in autistic patients

Autism, characterized by profound impairment in social interactions and communicative skills, is the most common neurodevelopmental disorder, and its underlying molecular mechanisms remain unknown. Ca(2+)-dependent activator protein for secretion 2 (CADPS2; also known as CAPS2) mediates the exocytosis of dense-core vesicles, and the human CADPS2 is located within the autism susceptibility locus 1 on chromosome 7q. Here we show that Cadps2-knockout mice not only have impaired brain-derived neurotrophic factor release but also show autistic-like cellular and behavioral phenotypes. Moreover, we found an aberrant alternatively spliced CADPS2 mRNA that lacks exon 3 in some autistic patients. Exon 3 was shown to encode the dynactin 1-binding domain and affect axonal CADPS2 protein distribution. Our results suggest that a disturbance in CADPS2-mediated neurotrophin release contributes to autism susceptibility.

Distinguishable haplotype blocks in the HTR3A and HTR3B region in the Japanese reveal evidence of association of HTR3B with female major depression

BACKGROUND

Genetic variations in the serotonin receptor 3A (HTR3A) and 3B (HTR3B) genes, positioned in tandem on chromosome 11q23.2, have been shown to be associated with psychiatric disorders in samples of European ancestry. But the polymorphisms highlighted in these reports map to different locations in the two genes, therefore it is unclear which gene exerts a stronger effect on susceptibility.

METHODS

To determine the haplotype block structure in the genomic regions of HTR3A and HTR3B, and to examine whether genetic variations in the region show evidence of association with schizophrenia and affective disorder in the Japanese, we performed haplotype-based case-control analysis using 29 polymorphisms.

RESULTS

Two haplotype blocks each were revealed for HTR3A and HTR3B in Japanese samples. In HTR3B, haplotype block 2 that included a nonsynonymous single nucleotide polymorphism (SNP), yielded evidence of association with major depression in females (global p = .0023). Analysis employing genome-wide SNPs using the STRUCTURE program did not detect population stratification in the samples.

CONCLUSIONS

Our results suggest an important role for HTR3B in major depression in women and also raise the possibility that previously proposed disease-associated SNPs in the HTR3A/B region in Caucasians are in linkage disequilibrium with haplotype block 2 of HTR3B in the Japanese.

G72/G30 in schizophrenia and bipolar disorder: review and meta-analysis

Association of the G72/G30 locus with schizophrenia and bipolar disorder has now been reported in several studies. The G72/G30 locus may be one of several that account for the evidence of linkage that spans a broad region of chromosome 13q. However, the story of G72/G30 is complex. Our meta-analysis of published association studies shows highly significant evidence of association between nucleotide variations in the G72/G30 region and schizophrenia, along with compelling evidence of association with bipolar disorder. But the associated alleles and haplotypes are not identical across studies, and some strongly associated variants are located approximately 50 kb telomeric of G72. Interestingly, G72 and G30 are transcribed in opposite directions; hence, their transcripts could cross-regulate translation. A functional native protein and functional motifs for G72 or G30 remain to be demonstrated. The interaction of G72 with d-amino acid oxidase, itself of interest as a modulator of N-methyl-d-aspartate receptors through regulation of d-serine levels, has been reported in one study and could be a key functional link that deserves further investigation. The association findings in the G72/G30 region, among the most compelling in psychiatry, may expose an important molecular pathway involved in susceptibility to schizophrenia and bipolar disorder.

Fine mapping of a susceptibility locus for bipolar and genetically related unipolar affective disorders, to a region containing the C21ORF29 and TRPM2 genes on chromosome 21q22.3

Linkage analyses of bipolar families have confirmed that there is a susceptibility locus near the telomere on chromosome 21q. To fine map this locus we carried out tests of allelic association using 30 genetic markers near the telomere at 21q22.3 in 600 bipolar research subjects and 450 ancestrally matched supernormal control subjects. We found significant allelic association with the microsatellite markers D21S171 (P=0.016) and two closely linked single-nucleotide polymorphisms, rs1556314 (P=0.008) and rs1785467 (P=0.025). A test of association with a three locus haplotype across the susceptibility region was significant with a permutation test of P=0.011. A two SNP haplotype was also significantly associated with bipolar disorder (P=0.01). Only two brain expressed genes, TRPM2 and C21ORF29 (TSPEAR), are present in the associated region. TRPM2 encodes a calcium channel receptor and TSPEAR encodes a peptide with repeats associated with epilepsy in the mouse. DNA from subjects who had inherited the associated marker alleles was sequenced. A base pair change (rs1556314) in exon 11 of TRPM2, which caused a change from an aspartic acid to a glutamic acid at peptide position 543 was found. This SNP showed the strongest association with bipolar disorder (P=0.008). Deletion of exon 11 of TRPM2 is known to cause dysregulation of cellular calcium homeostasis in response to oxidative stress. A second nonconservative change from arginine to cysteine at position 755 in TRPM2 (ss48297761) was also detected. A third nonconservative change from histidine to glutamic acid was found in exon 8 of TSPEAR. These changes need further investigation to establish any aetiological role in bipolar disorder.

Linkage disequilibrium analysis in the LOC93081-KDELC1-BIVM region on 13q in bipolar disorder

Genome-wide scans in bipolar disorder and a meta analysis on published data have provided evidence for linkage to chromosome 13q, although the reported peaks from various studies have not converged in a narrow region. Recently, single nucleotide polymorphisms (SNPs) at the G72/G30 locus have been shown to be associated with bipolar disorder suggesting its potential role in increasing disease risk. The proposed linkage region on 13q extends over a wide span, and could provide a clue to the existence of other susceptibility variants. In the present study, SNPs in the LOC93081-KDELC1-BIVM, a region proximal to G72, were interrogated in two bipolar family series. KDELC1 has a predicted filamin domain and BIVM contains an immunoglobulin-like motif. The small pedigree series yielded a nominally significant global P-value due to under-transmission of a rare haplotype but this finding was not supported by results from the larger series and in the case-control study that compared 278 cases and 277 controls.

Genetic association studies in mood disorders: issues and promise

Genetic association is a powerful method for identifying genetic variants that contribute to the molecular basis of complex diseases. There is now a wealth of informative, validated and densely-spaced single nucleotide polymorphism (SNP) markers for use in association studies, and the delineation of the genome-wide haplotype architecture will greatly enhance our ability to conduct whole genome association screens, fine mapping of linkage regions, and systematic screening of functional candidate genes. Single nucleotide polymorphism-based genotyping technology has progressed dramatically to the point of high-throughput methods that can assay up to thousands of SNPs on many samples in one experiment. Genotyping cost remains a limiting factor in complex disease studies, where numerous SNPs and large sample sets are needed to maximize statistical power. Strategies designed to reduce cost include DNA pooling and analysis with tagSNPs. As larger clinical samples become available, it will be increasingly important to test for hidden stratification in case-control studies, as well as transmission distortion in family-based studies, either of which can lead to spurious association findings. As yet, there is no widely-accepted genetic association finding in mood disorders, but functional candidate genes, such as the serotonin transporter, and positional candidates, such as G72/G30 on chromosome 13q, are beginning to be identified in several studies. Relating associated variants to the phenotype represents the next critical step toward establishing the pathogenic role of gene variants in mood disorders.

Loci on chromosomes 6q and 6p interact to increase susceptibility to bipolar affective disorder in the national institute of mental health genetics initiative pedigrees

BACKGROUND

We have reported genetic linkage between bipolar disorder and markers on chromosome 6q16.3-22.1 in the National Institute of Mental Health Genetics Initiative wave 3 pedigrees. Here we test for: 1) robustness of the linkage to differing analysis methods, genotyping error, and gender-specific maps; 2) parent-of-origin effects; and 3) interaction with markers within the schizophrenia linkage region on chromosome 6p.

METHODS

Members of 245 families ascertained through a sibling pair affected with bipolar I or schizoaffective-bipolar disorder were genotyped with 18 markers spanning chromosome 6. Nonparametric linkage analysis was performed.

RESULTS

Linkage to 6q is robust to analysis method, gender-specific map differences, and genotyping error. The locus confers a 1.4-fold increased risk. Affected siblings share the maternal more often than the paternal chromosome (p =.006), which could reflect a maternal parent-of-origin effect. There is a positive correlation between family-specific linkage scores on 6q and those on 6p22.2 (r =.26; p <.0001). Linkage analysis for each locus conditioned on evidence of linkage to the other increases the evidence for linkage at both loci (p <.0005). Logarithm of the odds (LOD) scores increased from 2.26 to 5.42 on 6q and from.35 to 2.26 on 6p22.2.

CONCLUSIONS

These results support linkage of bipolar disorder to 6q, uncover a maternal parent-of-origin effect, and demonstrate an interaction of this locus with one on chromosome 6p22.2, previously linked only to schizophrenia.

Possible association between a haplotype of the GABA-A receptor alpha 1 subunit gene (GABRA1) and mood disorders

BACKGROUND

The gamma-aminobutyric acid (GABA) neurotransmitter system has been implicated in the pathogenesis of mood disorders. The GABRA1 gene encodes one of the subunits of GABA-A receptor and is located on human chromosome 5q34-q35, which is a region reportedly linked to mood disorders. We examined the GABRA1 gene as a candidate for mood disorders.

METHODS

We performed mutation screening of GABRA1 in 24 Japanese bipolar patients and evaluated associations in Japanese case-control subjects consisting of 125 patients with bipolar disorder, 147 patients with depressive disorders, and 191 healthy control subjects. Associations were confirmed in the National Institute of Mental Health (NIMH) Initiative Bipolar Pedigrees, which consists of 88 multiplex pedigrees with 480 informative persons.

RESULTS

We identified 13 polymorphisms in the GABRA1 gene. Nonsynonymous mutations were not found. Association of a specific haplotype with affective disorders was suggested in the Japanese case-control population (corrected p=.0008). This haplotype association was confirmed in the NIMH pedigrees (p=.007).

CONCLUSIONS

These results indicate that the GABRA1 gene may play a role in the etiology of bipolar disorders.

Findings in an independent sample support an association between bipolar affective disorder and the G72/G30 locus on chromosome 13q33

Markers near the nested genes G72 and G30 on chromosome 13q33 have been implicated in the etiology of schizophrenia and, recently, bipolar affective disorder (BPAD). Hattori et al (2003) reported that single-nucleotide polymorphisms (SNPs) near the G72/G30 locus were associated with BPAD in a sample of 22 pedigrees, and that SNP haplotypes were associated in a second, larger sample of triads. The present study attempts to replicate this finding in an independent case-control sample. Six SNPs near the G72/G30 locus, including the most strongly associated markers in the previous study, were tested in 139 cases and 113 ethnically matched controls. Significant association was detected between BPAD and two adjacent SNPs (smallest P=0.007; global P=0.024). Haplotype analysis produced additional support for association (smallest P=0.004; global P=0.004). Analysis of 31 unlinked microsatellite markers detected no population stratification in the cases or controls studied. Although the associated alleles and haplotypes differ from those previously reported, these new results provide further evidence, in an independent sample, for an association between BPAD and genetic variation in the vicinity of the genes G72 and G30.

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.

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.

Association between serotonin 4 receptor gene polymorphisms and bipolar disorder in Japanese case-control samples and the NIMH Genetics Initiative Bipolar Pedigrees

Possible irregularities in serotonergic neurotransmission have been suggested as causes of a variety of neuropsychiatric diseases. We performed mutation and association analyses of the HTR4 gene, on 5q32, encoding the serotonin 4 receptor in mood disorders and schizophrenia. Mutation analysis was performed on the HTR4 exons and exon/intron boundaries in 48 Japanese patients with mood disorders and 48 patients with schizophrenia. Eight polymorphisms and four rare variants were identified. Of these, four polymorphisms at or in close proximity to exon d, g.83097C/T (HTR4-SVR (splice variant region) SNP1), g.83159G/A (HTR4-SVRSNP2), g.83164 (T)9-10 (HTR4-SVRSNP3), and g.83198A/G (HTR4-SVRSNP4), showed significant association with bipolar disorder with odds ratios of 1.5 to 2. These polymorphisms were in linkage disequilibrium, and only three common haplotypes were observed. One of the haplotypes showed significant association with bipolar disorder (P = 0.002). The genotypic and haplotypic associations with bipolar disorder were confirmed by transmission disequilibrium test in the NIMH Genetics Initiative Bipolar Pedigrees with ratios of transmitted to not transmitted alleles of 1.5 to 2.0 (P = 0.01). The same haplotype that showed association with bipolar disorder was suggested to be associated with schizophrenia in the case-control analysis (P = 0.003) but was not confirmed when Japanese schizophrenia families were tested. The polymorphisms associated with mood disorder were located within the region that encodes the divergent C-terminal tails of the 5-HT(4) receptor. These findings suggest that genomic variations in the HTR4 gene may confer susceptibility to mood disorder.

Polymorphisms at the G72/G30 gene locus, on 13q33, are associated with bipolar disorder in two independent pedigree series

Linkage evidence suggests that chromosome 13 (13q32-33) contains susceptibility genes for both bipolar disorder and schizophrenia. Recently, genes called "G72" and "G30" were identified, and polymorphisms of these overlapping genes were reported to be associated with schizophrenia. We studied two series of pedigrees with bipolar disorder: the Clinical Neurogenetics (CNG) pedigrees (in which linkage to illness had been previously reported at 13q32-33), with 83 samples from 22 multiplex families, and the National Institute of Mental Health (NIMH) Genetics Initiative pedigrees, with 474 samples from 152 families. Sixteen single-nucleotide polymorphisms (SNPs) were genotyped at and around the G72/G30 locus, which covered a 157-kb region encompassing the entire complementary DNA sequences of G72 and G30. We performed transmission/disequilibrium testing (TDT) and haplotype analysis, since a linkage-disequilibrium block was present at this gene locus. In the CNG and NIMH data sets, the results of global TDT of the entire haplotype set were significant and consistent (P=.0004 and P=.008, respectively). In the CNG series, the associated genotypes divided the families into those with linkage and those without linkage (partitioned by the linkage evidence). Analysis of the decay of haplotype sharing gave a location estimate that included G72/G30 in its 95% confidence interval. Although statistically significant association was not detected for individual SNPs in the NIMH data set, the same haplotype was consistently overtransmitted in both series. These data suggest that a susceptibility variant for bipolar illness exists in the vicinity of the G72/G30 genes. Taken together with the earlier report, this is the first demonstration of a novel gene(s), discovered through a positional approach, independently associated with both bipolar illness and schizophrenia.

Analysis of a cluster of polymorphisms in AKT1 gene in bipolar pedigrees: a family-based association study

We have previously performed a genome scan in 22 multiplex pedigrees with bipolar disorder and detected a moderate linkage signal on distal portion of chromosome 14q22-32. One of the large pedigrees displayed a parametric lod score >3 at a marker on 14q23-32. Upon inspection of genes located in this region revealed AKT1, a kinase that activates a lithium-responsive cell-survival pathway. Because lithium is an effective mood stabilizer for bipolar disorder patients, AKT1 is an interesting candidate for further investigation. We screened the gene for possible mutations and detected 14 polymorphisms. Seven polymorphic sites were clustered in a small segment spanning exon 14 and downstream intron. Transmission of haplotypes constructed from this cluster showed a weak evidence of association between the AKT1 and bipolar disorder.

Expression of the smoothelin gene is mediated by alternative promoters

OBJECTIVE

Two major isoforms of smoothelin have been reported, a 59-kDa smoothelin-A in visceral smooth muscle cells and a 110-kDa smoothelin-B in vascular smooth muscle cells. The present study was undertaken to investigate the expression of these smoothelin isoforms in different smooth muscle tissues and to determine how they are generated.

METHODS

Western blotting with a new, well-defined, smoothelin antibody was used to confirm the existence of two major smoothelin isoforms. Northern blotting, RT-PCR, primer extension and 5'RACE were applied to analyse the expression of these isoforms in human and mouse. Promoter reporter assays were carried out to establish the existence of a dual promoter system governing the expression pattern of the gene.

RESULTS

Antibody C6G confirmed the existence of two smoothelin proteins. Northern blotting showed that in vascular tissues a larger smoothelin transcript is generated than in visceral tissue. The cDNA of this larger smoothelin-B was cloned. Computer analysis of the open reading frame suggests an alpha-helical structure of 130 amino acids at the amino terminus of smoothelin-B. The smoothelin gene was cloned and sequenced. It comprises about 25 kb and contains 21 exons. The translational start of smoothelin-B is located in exon 2, whereas transcription and translation of the previously described smoothelin-A starts inside exon 10. Smoothelin-A and -B were demonstrated to be generated by two physically separated promoters. Splice variants within the calponin homology domain at the 3' end of the gene were found for both isoforms.

CONCLUSIONS

Two major smoothelin isoforms are generated from a single gene by a dual promoter system in a tissue specific manner. Further variation in the smoothelin proteins is achieved by alternative splicing in the calponin homology domain.

A mannosyltransferase gene at 11q23 is disrupted by a translocation breakpoint that co-segregates with bipolar affective disorder in a small family

Bipolar affective disorder (BPAD) is a complex neuropsychiatric disease characterized by extreme mood swings. Genetic influences affect the disease susceptibility substantially, yet the underlying mechanisms are unknown. We previously described a pedigree in which all five individuals with BPAD and one individual with recurrent major depression were carriers of a reciprocal chromosomal translocation t(9;11)(p24;q23). Gene content analyses of the breakpoint junctions revealed disruption of a gene (DIBD1 ) at 11q23, a genomic region that has also been implicated in schizophrenia and Tourette syndrome. DIBD1 is predicted to encode a mannosyltransferase similar to Saccaromyces cerevisiae Alg9p of the protein N-glycosylation pathway. The in-born errors of protein N-glycosylation cause congenital disorders of glycosylation in humans. DIBD1 shows uniform expression in the tested subregions of the brain by Northern analysis. Sequence analysis revealed four intragenic single nucleotide polymorphisms. The valine residue at V289I was conserved in other eukaryotic species, whereas its frequency was approximately 65% in humans. We performed linkage and linkage disequilibrium analyses in two NIMH bipolar pedigree series using four tightly linked simple tandem repeat polymorphisms (STRPs) and the V289I. These analyses overall failed to support a role for DIBD1 in disease susceptibility. The most-significant finding was a lod score of 1.18 (P=0.0098), obtained by an intronic STRP D11S5025, in the subset of 22 multiplex pedigrees. In conclusion, we found that a mannosyltransferase gene at 11q23 is disrupted by a translocation breakpoint co-segregating with BPAD in a family. However, its role in the disease susceptibility remains unconfirmed.

A human glucocorticoid receptor gene variant that increases the stability of the glucocorticoid receptor beta-isoform mRNA is associated with rheumatoid arthritis

OBJECTIVE

To study the occurrence and function of polymorphism in the human glucocorticoid receptor (hGR) gene in rheumatoid arthritis (RA) and systemic lupus erythematosus (SLE).

METHODS

We used single stranded conformation polymorphism (SSCP) and direct sequencing to study the hGR gene in 30 patients with RA, 40 with SLE, and 24 controls. A newly identified polymorphism was transfected in COS-1 cells and the stability of the mRNA containing the polymorphism was tested using real-time PCR.

RESULTS

A polymorphism in the hGR gene in exon9beta, in an "ATTTA" motif, was found to be significantly associated with RA. Introduction of this polymorphism in the hGRb mRNA was found to significantly increase stability in vitro compared to the wild-type sequence.

CONCLUSION

Our findings show an association between RA and a previously unreported polymorphism in the hGR gene. This polymorphism increased stability of hGRbeta mRNA, which could contribute to an altered glucocorticoid sensitivity since the hGRbeta is thought to function as an inhibitor of hGRalpha activity.

Fine mapping supports previous linkage evidence for a bipolar disorder susceptibility locus on 13q32

A region between D13S71 and D13S274 on 13q32 showed linkage to bipolar disorder (BP) based on a genome scan using markers with an average spacing of approximately 6 cM and an average heterozygosity of approximately 60% [Detera-Wadleigh et al., 1999: Proc Natl Acad Sci USA 96:5604-5609]. In an attempt to confirm this finding and achieve fine mapping of the susceptibility region, nine additional microsatellite markers with average heterozygosity of approximately 86%, located between D13S71 and D13S274, were typed in the same sample. The strongest linkage evidence was detected by multipoint linkage analysis (ASPEX program) around D13S779-D13S225 with maximum LOD score of 3.25 under Affection Status Model II (ASM II; P = 0.0000546). Data from additional nine markers resulted in a decrease of the 95% confidence interval of the linkage region. Association analyses with GASSOC TDT and ASPEX/sib_tdt detect potential linkage disequilibrium with several markers, including D13S280 (ASPEX TDT P = 0.0033, ASM I). These data generated using a higher marker density within the proposed susceptibility region strengthen the validity of our previous findings and suggest a finer localization of the susceptibility gene(s) on 13q32.

Lithium-related genetics of bipolar disorder

Lithium is a potent prophylactic medication and mood stabilizer in bipolar disorder. However, clinical outcome is variable, and its therapeutic effect manifests after a period of chronic treatment, implying a progressive and complex biological response process. Signal transduction systems known to be perturbed by lithium involve phosphoinositide (PI) turnover, activation of the Wnt pathway via inhibition of glycogen synthase kinase-3beta (GSK-3beta), and a growth factor-induced, Akt-mediated signalling that promotes cell survival. These pathways, acting in synergy, probably prompt the amplification of lithium signal causing such immense impact on the neuronal network. The sequencing of the human genome presents an unparallelled opportunity to uncover the full molecular repertoire involved in lithium action. Interrogation of high-resolution expression microarrays and protein profiles represents a strategy that should help accomplish this goal. A recent microarray analysis on lithium-treated versus untreated PC12 cells identified multiple differentially altered transcripts. Lithium-perturbed genes, particularly those that map to susceptibility regions, could be candidate risk-conferring factors for mood disorders. Transcript and protein profiling in patients could reveal a lithium fingerprint for responsiveness or nonresponsiveness, and a signature motif that may be diagnostic of a specific phenotype. Similarly, lithium-sensitive gene products could provide a new generation of pharmacological targets.

Evidence for association of the myo-inositol monophosphatase 2 (IMPA2) gene with schizophrenia in Japanese samples

In our search for candidate genes for affective disorder on the short arm of chromosome 18, we cloned IMPA2, a previously unreported myo-inositol monophosphatase gene, that maps to 18p11.2. We determined its genomic structure and detected three new single nucleotide polymorphisms (SNPs). In the present study, we screened the gene further to search for additional polymorphisms in Japanese samples and identified seven other SNPs, including a novel missense mutation. These polymorphisms clustered into three regions of the gene. Three relatively informative SNPs, 58G>A, IVS1--15G>A and 800C>T from clusters 1, 2 and 3, respectively, were selected for association tests using a case-control design. The Japanese cohort included 302 schizophrenics, 205 patients with affective disorder and 308 controls. Genotyping was done either by melting curve analysis on the LightCycler or by sequencing. All three SNPs showed significant genotypic association (nominal P = 0.031--0.0001) with schizophrenia, but not with affective disorder. These findings increase the relevance of 18p11.2 to schizophrenia susceptibility because GNAL, which has been shown previously to be implicated in schizophrenia in an independent study, is in close physical proximity to IMPA2. Our findings suggest that IMPA2 or a gene nearby may contribute to the overall genetic risk for schizophrenia among Japanese.

Refinement of regions with allelic loss on chromosome 18p11.2 and 18q12.2 in esophageal squamous cell carcinoma

Esophageal cancer ranks among the 10 most common cancers worldwide and is almost invariably fatal. The detailed genetic repertoire involved in esophageal carcinogenesis has not been defined. We have shown previously that the esophageal squamous cell carcinoma genome exhibits a frequent loss of heterozygosity (LOH) in the pericentromeric region of chromosome 18. To construct a fine deletion map, we screened 76 new samples composed of microdissected esophageal squamous cell carcinoma and matched morphologically normal epithelial cells using closely spaced markers. Maximal LOH frequency (54%) was displayed by D18S542 on 18p11.2. The pattern of LOH in selected patients indicated that the short region of overlap extends 3 cM on either side of D18S542. On the long arm of chromosome 18, the highest frequency of allelic loss (42%) was detected by D18S978 on 18q12.2-q21.1. This analysis revealed a short region of overlap of approximately 0.8 cM. These findings further implicate unreported tumor suppressor genes encoded by 18p11.2 and 18q12.2 in esophageal squamous cell carcinogenesis and they indicate a refinement of their map location.

Association study on the DUSP6 gene, an affective disorder candidate gene on 12q23, performed by using fluorescence resonance energy transfer-based melting curve analysis on the LightCycler

We introduced a new genotyping method, fluorescence resonance energy transfer-based melting curve analysis on the LightCycler, for the analysis of the gene, DUSP6 (dual specificity MAP kinase phosphatase 6), in affective disorder patients. The DUSP6 gene is located on chromosome 12q22-23, which overlaps one of the reported bipolar disorder susceptibility loci. Because of its role in intracellular signalling pathways, the gene may be involved in the pathogenesis of affective disorders not only on the basis of its position but also of its function. We performed association analysis using a T>G polymorphism that gives rise to a missense mutation (Leu114Val). No evidence for a significant disease-causing effect was found in Japanese unipolars (n = 132) and bipolars (n = 122), when compared with controls (n = 299). More importantly, this study demonstrates that melting curve analysis on the LightCycler is an accurate, rapid and robust method for discriminating genotypes from biallelic markers. This strategy has the potential for use in high throughput scanning for and genotyping of single nucleotide polymorphisms (SNPs).

Genomic structure and novel variants of myo-inositol monophosphatase 2 (IMPA2)

Recently, we cloned the human myo-inositol monophosphatase 2 (IMPA2) cDNA and established its map location to chromosome 18p11.2, a region previously implicated in bipolar disorder. Because the myo-inositol monophosphatase enzyme has been shown to be inhibited by lithium, an effective therapeutic agent for bipolar disorder, IMPA2 is a plausible positional and functional candidate gene. To permit comprehensive screening for variants we characterized the genomic structure and isolated the potential promoter of IMPA2. The gene was found to encode eight exons spanning;27 kb. The proximal 1-kb 5' flanking region did not contain an obvious TATA box but multiple potential binding sites for Sp1 and consensus motifs for AP2 and other transcription factors were evident. Sequencing of the coding region and splice junctions in unrelated bipolar disorder patients detected novel variants. A missense mutation in exon 2, His76Tyr, was found in one patient. His76 is evolutionarily conserved and replacement with Tyr introduces a potential site for phosphorylation. The other polymorphisms included an RsaI polymorphism, IVS1-15G>A, and a T --> C silent mutation in the third nucleotide of codon 53 in exon 2. By Fisher's exact test the silent mutation showed a trend for association (P = 0.051) with bipolar disorder suggesting that further scrutiny of this gene is warranted.

Suggestive evidence of a locus on chromosome 10p using the NIMH genetics initiative bipolar affective disorder pedigrees

As part of a four-center NIMH Genetics Initiative on Bipolar Disorder, a genome screen using 365 markers was performed on 540 DNAs from 97 families, enriched for affected relative pairs. This is the largest uniformly ascertained and assessed linkage sample for this disease, and includes 232 subjects diagnosed with bipolar I (BPI), 32 with schizo-affective, bipolar type (SABP), 72 with bipolar II (BPII), and 88 with unipolar recurrent depression (UPR). A hierarchical set of definitions of affected status was examined. Under Model I, affected individuals were those with a diagnosis of BPI or SABP, Model II included as affected those fitting Model I plus BPII, and Model III included those fitting Model II plus UPR. This data set was previously analyzed using primarily affected sib pair methods. We report the results of nonparametric linkage analyses of the extended pedigree structure using the program Genehunter Plus. The strongest finding was a lod score of 2.5 obtained on chromosome 10 near the marker D10S1423 with diagnosis as defined under Model II. This region has been previously implicated in genome-wide studies of schizophrenia and bipolar disorder. Other chromosomal regions with lod scores over 1.50 for at least one Model Included chromosomes 8 (Model III), 16 (Model III), and 20 (Model I). Am. J. Med. Genet. (Neuropsychiatr. Genet.) 96:18-23, 2000

Mutation analysis of oculopharyngeal muscular dystrophy in Hispanic American families

BACKGROUND

Oculopharyngeal muscular dystrophy (OPMD) is a late-onset autosomal dominant muscular dystrophy characterized by progressive ptosis, swallowing difficulties, and proximal limb weakness. Recently, the genetic basis of this disease has been characterized by mutations in the PABP2 gene that involve short expansions of the trinucleotide repeat GCG.

OBJECTIVES

To independently confirm the presence and study the meiotic stability of the GCG expansion mutations in a distinct ethnic population with OPMD.

SETTINGS

Hospital and university research laboratories in Los Angeles, Calif.

SUBJECTS AND METHODS

Three unrelated families of Hispanic American descent were identified in whom OPMD was transmitted in an autosomal dominant pattern. All of these families can trace affected ancestors to the southwestern United States or to the bordering states of Mexico. In these families, 14 persons with OPMD were identified and studied.

RESULTS

Our results confirm that in these families, expansion mutations characterized by a gain of 3 GCG repeats in the wild-type allele result in an abnormal nucleotide length of 9 GCG repeats in the PABP2 gene. In these families, these mutations are associated with the OPMD phenotype. The identical repeat mutation ([GCG]9) is found in all affected members of these unrelated families and shows relative meiotic stability.

CONCLUSIONS

These results support and extend our study of haplotype analysis and suggest that a founder effect may have occurred for OPMD in this Hispanic American population.

Do schizophrenia and affective disorder share susceptibility genes?

Schizophrenia and affective disorders are relatively common neuropsychiatric diseases with a complex genetic etiology. A multigenic inheritance with variable influence of unknown environmental factors may be involved. Family studies have demonstrated the existence of both phenotypes in the same kindreds, and in certain cases, a transition from one phenotype to another occurs. In addition, intermediate phenotypes such as schizoaffective disorders are found in families with schizophrenia and affective illness. Recent genome and chromosomal scans appear to support these epidemiologic data, since susceptibility regions for both schizophrenia and affective disorders have been found to overlap, on chromosomes 10p13-p12, 13q32, 18p and 22q11-q13. These studies were performed in independently ascertained family samples with index patients afflicted either with schizophrenia or bipolar disorder. Taken together, these findings imply shared loci for schizophrenia and affective disorders among those required for the full expression of the phenotype. Identification and molecular characterization of the genetic components conferring risk to both disorders would impact positively on diagnosis, prevention, and treatment.

Radiation hybrid mapping of genes in the lithium-sensitive wnt signaling pathway

Lithium, an effective drug in the treatment of bipolar disorder, has been proposed to disrupt the Wnt signaling pathway. To facilitate analysis of the possible involvement of elements of the Wnt pathway in human bipolar disorder, a high resolution radiation hybrid mapping (RHM) of these genes was performed. A fine physical location has been obtained for Wnt 7A, frizzled 3, 4 and 5, dishevelled 1, 2 and 3, GSK3beta, axin, alpha-catenin, the Armadillo repeat-containing genes (delta-catenin and ARVCF), and a frizzled-like protein (frpHE) using the Stanford Human Genome Center (SHGC) G3 panel. Most of these genes were previously mapped by fluorescence in situ hybridization (FISH). Frizzled 4, axin and frpHE did not have a previous chromosomal assignment and were linked by RHM to chromosome markers, SHGC-35131 at 11q22.1, NIB1488 at 16p13.3 and D7S2919 at 7p15.2, respectively. Interestingly, some of these genes were found to map within potential regions underlying susceptibility to bipolar disorder and schizophrenia as well as disorders of neurodevelopmental origin. This alternative approach of establishing the precise location of selected genetic components of a candidate pathway and determining if they map within previously defined susceptibility loci should help to identify plausible candidate genes that warrant further analysis through association and mutational scanning.

Molecular cytogenetic fingerprinting of esophageal squamous cell carcinoma by comparative genomic hybridization reveals a consistent pattern of chromosomal alterations

Esophageal cancer is the third most prevalent gastrointestinal malignancy in the world. The tumor responds poorly to various therapeutic regimens and the genetic events underlying esophageal carcinogenesis are not well understood. To identify overall chromosomal aberrations in esophageal squamous cell carcinoma, we performed comparative genomic hybridization (CGH). All 17 tumor samples were found to exhibit multiple gains and losses involving different chromosomal regions. The frequency of chromosomal loss associated with this type of tumor was as follows: in 2q (100%), 3p (100%), 13q (100%), Xq (94%), 4 (82%), 5q (82%), 18q (76%), 9p (76%), 6q (70%), 12q (70%), 14q (65%), 11q (59%), and 1p (53%). Interstitial deletions on 1p, 3p, 5q, 6q, 11q, and 12q were detected also. Chromosomal gains were displayed by chromosomes and chromosome areas: 19 (100%), 20q (94%), 22 (94%), 16p (65%), 17 (59%), 12q (59%), 8q (53%), 9q (53%), and 3q (50%). Two sites showing apparent amplification were 11q (70%) and 5p15 (47%). To validate the CGH data, we isolated a BAC clone mapping to 18q12.1. This clone was used as a probe in interphase fluorescence in situ hybridization of tumor touch preparations and allelic loss was clearly revealed. This study represents the first whole-genome analysis in esophageal squamous cell carcinoma for associated chromosomal aberrations that may be involved in either the genesis or progression of this malignancy.

Chromosomes 12 and 16 workshop

Recent linkage results independently derived from a large French Canadian pedigree and Danish kindreds coupled with supportive data from other studies provide compelling evidence for a bipolar disorder susceptibility locus on chromosome 12q23-q24. The idea is further strengthened by the finding that Darier's disease, which maps to this region, has been shown to cosegregate with affective disorder in a family. This linkage finding, however, was not supported in other independent genome scans. On chromosome 16, bipolar families from Denmark exhibited suggestive linkage with D16S510, on 16p13. Multipoint nonparametric analysis on the NIMH Genetics Initiative bipolar pedigrees yielded increased allele sharing that maximized approximately 18 cM proximal to the latter locus. In contrast, evidence of linkage was not detected in other panels of bipolar families that were presented. At 16p13, a maximum multipoint lod score of 4 for a latent class-derived phenotype that has aspects of alcohol dependence was found in a genome scan of 105 families from the Collaborative Study of the Genetics of Alcoholism, identifying a potential vulnerability locus.

Molecular cytogenetic fingerprinting of esophageal squamous cell carcinoma by comparative genomic hybridization reveals a consistent pattern of chromosomal alterations

Esophageal cancer is the third most prevalent gastrointestinal malignancy in the world. The tumor responds poorly to various therapeutic regimens and the genetic events underlying esophageal carcinogenesis are not well understood. To identify overall chromosomal aberrations in esophageal squamous cell carcinoma, we performed comparative genomic hybridization (CGH). All 17 tumor samples were found to exhibit multiple gains and losses involving different chromosomal regions. The frequency of chromosomal loss associated with this type of tumor was as follows: in 2q (100%), 3p (100%), 13q (100%), Xq (94%), 4 (82%), 5q (82%), 18q (76%), 9p (76%), 6q (70%), 12q (70%), 14q (65%), 11q (59%), and 1p (53%). Interstitial deletions on 1p, 3p, 5q, 6q, 11q, and 12q were detected also. Chromosomal gains were displayed by chromosomes and chromosome areas: 19 (100%), 20q (94%), 22 (94%), 16p (65%), 17 (59%), 12q (59%), 8q (53%), 9q (53%), and 3q (50%). Two sites showing apparent amplification were 11q (70%) and 5p15 (47%). To validate the CGH data, we isolated a BAC clone mapping to 18q12.1. This clone was used as a probe in interphase fluorescence in situ hybridization of tumor touch preparations and allelic loss was clearly revealed. This study represents the first whole-genome analysis in esophageal squamous cell carcinoma for associated chromosomal aberrations that may be involved in either the genesis or progression of this malignancy.

A high-density genome scan detects evidence for a bipolar-disorder susceptibility locus on 13q32 and other potential loci on 1q32 and 18p11.2

Bipolar disorder is a severe mental illness characterized by mood swings of elation and depression. Family, twin, and adoption studies suggest a complex genetic etiology that may involve multiple susceptibility genes and an environmental component. To identify chromosomal loci contributing to vulnerability, we have conducted a genome-wide scan on approximately 396 individuals from 22 multiplex pedigrees by using 607 microsatellite markers. Multipoint nonparametric analysis detected the strongest evidence for linkage at 13q32 with a maximal logarithm of odds (lod) score of 3.5 (P = 0. 000028) under a phenotype model that included bipolar I, bipolar II with major depression, schizoaffective disorder, and recurrent unipolar disorder. Suggestive linkage was found on 1q31-q32 (lod = 2. 67; P = 0.00022) and 18p11.2 (lod = 2.32; P = 0.00054). Recent reports have linked schizophrenia to 13q32 and 18p11.2. Our genome scan identified other interesting regions, 7q31 (lod = 2.08; P = 0. 00099) and 22q11-q13 (lod = 2.1; P = 0.00094), and also confirmed reported linkages on 4p16, 12q23-q24, and 21q22. By comprehensive screening of the entire genome, we detected unreported loci for bipolar disorder, found support for proposed linkages, and gained evidence for the overlap of susceptibility regions for bipolar disorder and schizophrenia.

Systematic screening of chromosome 18 for loss of heterozygosity in esophageal squamous cell carcinoma

Esophageal cancer ranks among the 10 most common cancers in the world, and is almost uniformly fatal. The genetic events leading to the development of esophageal carcinoma are not well established. To identify genomic regions involved in esophageal carcinogenesis, we performed a systematic screening for loss of heterozygosity (LOH) in 24 samples of squamous cell carcinomas, initially focusing the analysis on chromosome 18. Thirteen short tandem repeat markers spanning 18p and 18q were used. We found a broad peak of LOH spanning 18p11.2 and 18q21.1 with the most frequent LOH (72%) at D18S978 on 18q12.2, which coincides with a known fragile site FRA18A. This region is 4 cM proximal to known tumor suppressor genes and therefore suggests the possible existence of a yet undiscovered tumor suppressor gene.

Genetic mapping and haplotype analysis of oculopharyngeal muscular dystrophy

Oculopharyngeal muscular dystrophy (OPMD) is an autosomal dominant muscular dystrophy characterized by late onset ptosis, proximal muscle weakness and swallowing difficulties. This disease has been recently linked to chromosome 14q11.2-q13 in French-Canadian pedigrees. We studied three unrelated American families with OPMD of Hispanic descent and our results indicate that in this ethnic group, this disease also maps to chromosome 14q11.2-q13 (marker MYH7.24; Zmax = 3.98; theta max = 0). These results represent an independent demonstration of disease linkage in a second distinct ethnic group. Furthermore, our analysis demonstrates a unique haplotype that is shared by affected individuals from all three families suggesting a founder effect for OPMD in this population. Meiotic recombinants and radiation hybrid mapping permit the narrowing of the critical region to 1 Mb which will facilitate positional cloning of the OPMD disease gene.