A possible vulnerability locus for bipolar affective disorder on chromosome 21q22.3

A genome-wide scan points to a susceptibility locus for bipolar disorder on chromosome 12

Our previous results pointed to a putative gene for susceptibility to bipolar affective disorder located on the chromosomal region 12q23-q24 that segregated in the Saguenay-Lac-St-Jean population of Quebec. We report here results from a second genome-wide scan based on the analysis of 380 polymorphic microsatellite markers. For the purpose of this analysis, an additional 18 families were recruited from the Saguenay-Lac-St-Jean region and pooled to our previous sample to improve its statistical power, giving a total of 394 sampled individuals. This work confirms the presence of a susceptibility locus for affective disorder on chromosome 12q24 with parametric LOD score value of 3.35 at D12S378 when pedigrees were broken into nuclear families and analysed under a recessive segregation model. This result was supported by neighbouring markers and by a LOD score value of 5.05 at D12S378 under model-free analysis. Other regions of lower interest were indicated on chromosomes 2, 5, 7, 9, 10, 17 and 20.

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.

Shared and specific susceptibility loci for schizophrenia and bipolar disorder: a dense genome scan in Eastern Quebec families

The goal of this study was to identify susceptibility loci shared by schizophrenia (SZ) and bipolar disorder (BP), or specific to each. To this end, we performed a dense genome scan in a first sample of 21 multigenerational families of Eastern Quebec affected by SZ, BP or both (N=480 family members). This probably constitutes the first genome scan of SZ and BP that used the same ascertainment, statistical and molecular methods for the concurrent study of the two disorders. We genotyped 607 microsatellite markers of which 350 were spaced by 10 cM and 257 others were follow-up markers in positive regions at the 10 cM scan. Lander and Kruglyak thresholds were conservatively adjusted for multiple testings. We maximized the lod scores (mod score) over eight combinations (2 phenotype severity levels x 2 models of transmission x 2 analyses, affected/unaffected vs affected-only). We observed five genomewide significant linkages with mod score >4.0: three for BP (15q11.1, 16p12.3, 18q12-q21) and two for the shared phenotype, that is, the common locus (CL) phenotype (15q26,18q12-q21). Nine mod scores exceeded the suggestive threshold of 2.6: three for BP (3q21, 10p13, 12q23), three for SZ (6p22, 13q13, 18q21) and three for the CL phenotype (2q12.3, 13q14, 16p13). Mod scores >1.9 might represent confirmatory linkages of formerly reported genomewide significant findings such as our finding in 6p22.3 for SZ. Several regions appeared to be shared by SZ and BP. One linkage signal (15q26) appeared novel, whereas others overlapped formerly reported susceptibility regions. Despite the methodological limitations we raised, our data support the following trends: (i) results from several genome scans of SZ and BP in different populations tend to converge in specific genomic regions and (ii) some of these susceptibility regions may be shared by SZ and BP, whereas others may be specific to each. The present results support the relevance of investigating concurrently SZ and BP within the same study and have implications for the modelling of genetic effects.

Expression of mitochondria-related genes in lymphoblastoid cells from patients with bipolar disorder

OBJECTIVES

Several studies have suggested mitochondrial abnormality in bipolar disorder. We reported the association of mitochondrial complex I subunit gene, NDUFV2 at 18p11, with bipolar disorder. A decrease in the mRNA expression of this gene was found in patients with bipolar disorder compared with controls. However, it was unclear whether only the NDUFV2 gene exhibited the decreased expression level in bipolar disorder. The aim of this study was to clarify the association of other nuclear-encoded complex I subunit genes and mitochondria-related genes with bipolar disorder.

METHODS

We quantified the mRNA expression level of five nuclear-encoded mitochondrial complex I subunit genes located at the chromosomal regions linked with bipolar disorder other than NDUFV2, three complex IV subunit genes, and four mitochondrial transcription-related genes using a real-time quantitative reverse transcription polymerase chain reaction method in the lymphoblastoid cell lines from 21 patients with bipolar disorder and 11 controls.

RESULTS

Decreased mRNA expression in patients with bipolar I disorder compared with control subjects was found in most of the complex I subunit genes. In addition, decreased expression levels of these genes correlated with that of NDUFV2. No statistically significant alterations of mRNA expression levels were found between bipolar patients and controls among two of three complex IV subunit genes and all transcription-related genes.

CONCLUSIONS

Our study suggests that the decreased expression of NDUFV2 has a considerable effect on other subunit genes in the mitochondrial respiratory chain and presents further evidence of the biological significance of NDUFV2 in bipolar disorder.

Characterization of human and mouse TRPM2 genes: Identification of a novel N-terminal truncated protein specifically expressed in human striatum

Transient receptor potential melastatin 2 (TRPM2) is a calcium-permeable cation channel activated by ADP-ribose or reactive oxygen species. In human, a major transcript of 6.5 kb is expressed in various tissues, whereas a minor transcript of 5.5 kb is detected only in striatum (caudate nucleus and putamen). We found that the 5.5-kb shorter transcript is transcribed from the intron 4 of the TRPM2 gene and encodes the striatum short form protein (SSF-TRPM2) with 1289 amino acid residues as compared to the long form protein (LF-TRPM2), in which the N-terminal 214 amino acid residues are removed. The SSF-TRPM2 protein still maintained H2(O2)-induced Ca2+ influx activity. In addition, we found that the major transcripts in human and mouse start from a novel 5' non-coding exon; however, we could not detect any striatum short transcript in mouse brain. These new findings are invaluable to further study the regulation of TRPM2 gene expression and to examine the possible involvement of the TRPM2 gene in the pathophysiology of bipolar disorder.

Initial characterization of an uromodulin-like 1 gene on human chromosome 21q22.3

We have isolated a novel gene, designated UMODL1, similar to uromodulin (UMOD)/Tamm-Horsfall glycoprotein, on human chromosome 21q22.3. Uromodulin like-1 (UMODL1) consists of 22 exons and spans approximately 80 kb in a direction from centromere to telomere. Two major transcripts produced by alternative splicing have been identified. These transcripts contain open reading frames of 4125 and 3741 bp encoding proteins of 1374 and 1246 amino acids, respectively. Expression of UMODL1 mRNA was detected only in 14 human tissues, e.g., kidney, testis, and fetal thymus at low level. Interestingly, two gene products (UMODL1L and UMODL1S) contain multiple domains including whey acidic protein, sea urchin sperm protein, enterokinase, and agrin, zona pellucida domain, and so on. Both proteins seemed to localize in cytoplasm, but UMODL1 is likely to be ubiquitinated and rapidly degraded in HEK293 cells. This gene may be a potent candidate for Down syndrome or bipolar affective disorder.

Molecular genetics of affective disorders

Evidence for familial aggregation in Affective Disorders (AD) has been provided in classical studies. Linkage and association genetic studies have been proposed to detect genetic factors implicated in AD. However, findings from molecular genetic studies remain inconclusive. Nevertheless, current research is focusing on the phenotypes, both sub- and endophenotypes. In addition, recent advances in technology, such as microarrays, provide new tools in psychiatric genetics. These different approaches offer a new optimism era in the search of genetic factors in AD.

Sequence analysis of ADARB1 gene in patients with familial bipolar disorder

BACKGROUND

The ADARB1 gene is located in 21q22.3 region, previously linked to familial bipolar disorder, and its product has a documented action in the editing of the pre-mRNA of glutamate receptor B subunit. Dysfunction of glutamatergic neurotransmission could play an important role in the pathophysiology of bipolar disorder (BD). Glutamate excitatory neurotransmission regulation is a possible mechanism of the initial effect of anticonvulsants in regulating mood.

METHODS

To investigate the hypothesis of an involvement of ADARB1 gene in the BD, the ADARB1 cDNA has been cloned and sequenced in seven selected bipolar I disorder patients with evidence of familiarity of mood disorders. A detailed investigation of the gene nucleotide sequence in the open reading frame has been performed.

RESULTS

No alteration in the sequence of the ADARB1 gene cDNA was found in any patient, except a common neutral polymorphism in three out of seven patients.

CONCLUSIONS

Mutations in ADARB1 gene are not commonly associated with bipolar I disorder, therefore other genes in the 21q22 region could be associated with bipolar illness in some families, likely in the context of a multifactorial transmission model.

Analysis of SYNJ1, a candidate gene for 21q22 linked bipolar disorder: a replication study

Linkage analysis has shown that chromosome 21q22 may contain a candidate gene for bipolar disorder (BPD). One potential 21q22 candidate gene we previously analyzed is SYNJ1, which encodes synaptojanin 1, an inositol 5-phosphatase. Previous mutation screening of SYNJ1 identified three rare functional variants, one of which is a polymorphic variant near the intron 12-oxon 12 border. The rare variants were found only in a total of four BPD patients and no controls, and a trend toward significance was found for the intron 12 polymorphism. In an analysis of a new set of 84 bipolar patients, none of the rare variants were detected. There was an increase in allele 2 for the intron 12 polymorphism, similar to our original study, but the result was not significant. The combined data from both studies continue to show a trend toward significance for allele 2 homozygotes in BPD.

Linkage analysis in bipolar pedigrees adds support for a susceptibility locus on 21q22

Several studies provide suggestive evidence of a susceptibility locus for bipolar disorder at chromosome 21q22-23. In an attempt to replicate these findings, we have analyzed linkage to 11 polymorphic markers from this region in 18 Bulgarian pedigrees with affective disorder. Two-point linkage analysis under assumption of homogeneity and a dominant model with reduced penetrance produced modest positive values for some of the markers tested under a 'narrow' phenotype definition, including bipolar I and II, and schizoaffective disorder. The maximum two-point score (lod=1.76, theta=0.00) was at marker D21S1919. Non-parametric linkage analysis under the same phenotype model, yielded positive NPLall values (P<0.05) over the region between markers D21S211 and D21S416, with a peak at D21S1252 (NPL Zall=2.32, P=0.0003). The multipoint lod score (GENEHUNTER) reached a suggestive value for linkage (lod=2.10) also at marker D21S1252. The results under a recessive model were completely negative. These data add to the evidence for the existence of a susceptibility locus for bipolar affective disorder on chromosome 21q22.

Identification of PIK3C3 promoter variant associated with bipolar disorder and schizophrenia

BACKGROUND

Genes involved in phosphoinositide (PI) lipid metabolism are excellent candidates to consider in the pathogenesis of bipolar disorder (BD) and schizophrenia (SZ). One is PIK3C3, a member of the phosphatidylinositide 3-kinase family that maps closely to markers on 18q linked to both BD and SZ in a few studies.

METHODS

The promoter region of PIK3C3 was analyzed for mutations by single-strand conformation polymorphism analysis and sequencing. A case-control association study was conducted to determine the distribution of variant alleles in unrelated patients from three cohorts. Electromobility gel shift assays (EMSA) were performed to assess the functional significance of variants.

RESULTS

Two polymorphisms in complete linked disequilibrium with each other were identified, -432C- > T and a "C" insert at position -86. The -432T allele occurs within an octamer containing an ATTT motif resembling members of the POU family of transcription factors. In each population analyzed, an increase in -432T was found in patients. EMSAs showed that a -432T containing oligonucleotide binds to brain proteins that do not recognize -432C.

CONCLUSIONS

A promoter mutation in a PI regulator affecting the binding of a POU-type transcription factor may be involved in BD and SZ in a subset of patients.

Sequence variants and haplotype analysis of serotonin transporter gene and association with bipolar affective disorder in Taiwan

OBJECTIVES

Serotonin transporter (SLC6A4) is responsible for serotonin re-uptake into presynaptic terminals, thus fine-tuning brain serotonergic neurotransmission. Current studies have found associations of SLC6A4 polymorphisms with several psychiatric traits including bipolar affective disorder (BPD) in various populations; however, studies with contradictory results were also reported. This study examined the role of SLC6A4 in etiology of BPD in a Taiwanese population.

METHODS

Ten markers including two variable number tandem repeat and eight single nucleotide polymorphisms (SNPs) on the SLC6A4 gene were used to study the genetic association with 90 unrelated BPD, type I patients and 103 controls.

RESULTS

Two SNPs were not informative in a Taiwanese population and the other eight polymorphic markers were analyzed by Fisher's exact test and haplotype analysis. No association was detected for any single SLC6A4 marker and BPD. Additional statistic analyses including other factors also showed lack of association between the SLC6A4 gene polymorphisms and BPD. Significant linkage disequilibrium was obtained among eight SLC6A4 markers and eight common haplotypes were constructed that can be found in 95% of the total subjects. The four commonest haplotypes in both patients and controls were identical. However, the fifth commonest haplotype differed in patients and controls and was significantly associated with a protection from BPD.

CONCLUSIONS

This study suggested that a particular SLC6A4 haplotype harboring functional sequence variant could play a significant role in BPD etiology in Taiwan. However, due to its modest sample size, the conclusion is not final and should be confirmed in the future studies.

An overview of the genetics of psychotic mood disorders

This article presents a conceptual review of the genetic underpinnings of psychotic mood disorders. Both unipolar and bipolar forms of mood disorder sometimes feature psychotic symptoms. Some evidence from epidemiological research suggests that psychotic forms of mood disorder specifically might be heritable. Linkage studies of mood disorders in general have also provided some support for that notion, as have associated studies involving serotonin and dopamine genes and psychotic mood disorder. Some research suggests there might be a genetic connection between schizophrenia and bipolar disorder, undermining the Kraepelinian dichotomous classification of the psychoses. Future research should continue to examine psychotic forms of mood disorder using both epidemiological and molecular approaches.

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.

Polymorphism screening of PIP5K2A: a candidate gene for chromosome 10p-linked psychiatric disorders

Lithium is a potent noncompetitive inhibitor of inositol monophosphatases, enzymes involved in phosphoinositide (PI) and inositol phosphate metabolism. A critical component of the PI pathway is phosphatidylinositol 4,5-bisphosphate (PtdIns(4,5)P(2)), which is hydrolyzed to second messengers and has a direct role in synaptic vesicle function. Interestingly, a number of genes involved in the synthesis and dephosphorylation of PtdIns(4,5)P(2) are found in regions of the genome previously mapped in bipolar disorder (BD) including 10p12, 21q22, and 22q11, among others. Some of these regions overlap with loci mapped in schizophrenia (SZ). One gene involved in PI metabolism that maps to a region of interest is 10p12-linked PIP5K2A, a member of the phosphatidylinositol 4-phosphate 5-kinase family. Polymorphism screening revealed the existence of an imperfect CT repeat polymorphism located near the exon 9-intron 9 splice donor site. A modest difference was found in the distribution of alleles from this highly polymorphic variant when bipolar and schizophrenic subjects were compared with controls; relatively rare short repeat variants were found more commonly in patients and homozygosity for a common long repeat variant was found more commonly in controls. These data suggest that the imperfect CT repeat in PIP5K2A intron 9 should be further investigated as a possible candidate allele for 10p12-linked psychiatric disorders.

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.

Genome wide scan using homozygosity mapping and linkage analyses of a single pedigree with affective disorder suggests oligogenic inheritance

The present study reports results from a genome scan on a family with bipolar affective disorder in which the parents are first cousins and four of the offsprings and one grandchild have affective disorder. The study searched for risk loci for affective disorder by searching for homozygous segments or more complex inherited loci using parametric and non-parametric multipoint linkage analysis. In addition dominant, multipoint, affecteds-only linkage analyses were performed as a supplement to previous analyses. On chromosomes 2q31.3, 10, 12q24, and 21q22.3 evidence for a risk locus was obtained by parametric and/or non-parametric linkage analyses and by haplotype sharing. As other studies have found significant or suggestive linkage to bipolar disorder in these chromosome regions this suggests that an oligogenic mode of inheritance is possible in this family involving at least some of the loci. Finally, the work discusses whether homozygosity mapping using parametric and non-parametric linkage analyses may be of value for complex diseases including rare subphenotypes of such disorders.

Reconsidering the classification of schizophrenia and manic depressive illness--a critical analysis and new conceptual model

The idea of 'disease entity' in psychiatry and the nosologic map of insanity with the distinction between dementia praecox (schizophrenia since Bleuler 1911) and manic depressive insanity, originally developed by Emil Kraepelin (1986), is an important landmark in the history of psychiatry (Jablensky 1995). This classification, however, has been vigorously debated throughout the years, and new evidence emerging from epidemiological, clinical, genetic and biological research demonstrates that the two nosological categories have distinct features as well as share many similarities in their risk factors, genetic predisposition, brain pathology, neurophysiology, clinical phenomenology and response to treatment, thus raising questions about the validity of the categorical classification of psychoses. In this paper we examine some of the similarities and differences between schizophrenia and bipolar illness emerging from recent biological and clinical research and attempt to clarify major inherent logical contradictions in the application of the 'disease' model of psychiatric diagnosis to the categorical classification of schizophrenia and bipolar illness. Then we examine how similar predicaments have been resolved in other natural classification systems, namely the biological classification of species and the periodic table of the elements. Finally we propose a hypothetical conceptual approach to the classification of psychoses that has been greatly informed by the organizing principle underlying the periodic table of the elements, and is distinct from the 'disease' model of psychiatric classification.

Chromosomal abnormalities and mental illness

Linkage studies of mental illness have provided suggestive evidence of susceptibility loci over many broad chromosomal regions. Pinpointing causative gene mutations by conventional linkage strategies alone is problematic. The breakpoints of chromosomal abnormalities occurring in patients with mental illness may be more direct pointers to the relevant gene locus. Publications that describe patients where chromosomal abnormalities co-exist with mental illness are reviewed along with supporting evidence that this may amount to an association. Chromosomal abnormalities are considered to be of possible significance if (a) the abnormality is rare and there are independent reports of its coexistence with psychiatric illness, or (b) there is colocalisation of the abnormality with a region of suggestive linkage findings, or (c) there is an apparent cosegregation of the abnormality with psychiatric illness within the individual's family. Breakpoints have been described within many of the loci suggested by linkage studies and these findings support the hypothesis that shared susceptibility factors for schizophrenia and bipolar disorder may exist. If these abnormalities directly disrupt coding regions, then combining molecular genetic breakpoint cloning with bioinformatic sequence analysis may be a method of rapidly identifying candidate genes. Full karyotyping of individuals with psychotic illness especially where this coexists with mild learning disability, dysmorphism or a strong family history of mental disorder is encouraged.

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.

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 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.

Family-based association study of 76 candidate genes in bipolar disorder: BDNF is a potential risk locus. Brain-derived neutrophic factor

Identification of the genetic bases for bipolar disorder remains a challenge for the understanding of this disease. Association between 76 candidate genes and bipolar disorder was tested by genotyping 90 single-nucleotide polymorphisms (SNPs) in these genes in 136 parent-proband trios. In this preliminary analysis, SNPs in two genes, brain-derived neurotrophic factor (BDNF) and the alpha subunit of the voltage-dependent calcium channel were associated with bipolar disorder at the P<0.05 level. In view of the large number of hypotheses tested, the two nominally positive associations were then tested in independent populations of bipolar patients and only BDNF remains a potential risk gene. In the replication samples, excess transmission of the valine allele of amino acid 66 of BDNF was observed in the direction of the original result in an additional sample of 334 parent-proband trios (T/U=108/87, P=0.066). Resequencing of 29 kb surrounding the BDNF gene identified 44 additional SNPs. Genotyping eight common SNPs identified three additional markers transmitted to bipolar probands at the P < 0.05 level. Strong LD was observed across this region and all adjacent pairwise haplotypes showed excess transmission to the bipolar proband. Analysis of these haplotypes using TRANSMIT revealed a global P value of 0.03. A single haplotype was identified that is shared by both the original dataset and the replication sample that is uniquely marked by both the rare A allele of the original SNP and a novel allele 11.5 kb 3'. Therefore, this study of 76 candidate genes has identified BDNF as a potential risk allele that will require additional study to confirm.

Additional, physically ordered markers increase linkage signal for bipolar disorder on chromosome 18q22

BACKGROUND

We recently reported evidence of linkage of bipolar disorder to chromosome 18q, with a paternal logarithm of odds (LOD) score of 4.67 (p =.004) in a clinically defined subset of families. Like other linkage studies, we had to rely on imprecise genetic maps to establish the marker order. Here, we test for linkage in the same sample with a denser set of markers, now physically ordered according to the draft sequence of the human genome.

METHODS

Families were ascertained through probands with bipolar I disorder and diagnosed with reliable methods. Genotypes were generated for 12 microsatellite markers within an 11-centimorgan (cM) region of chromosome 18q22. Multipoint affected sib-pair linkage analysis was performed in a set of 16 nuclear families.

RESULTS

The additional markers significantly increased the total genetic information extracted from our sample. We also observed an increase in the LOD score (to 5.42, p =.0066) and linkage resolution. The approximate 1-LOD support interval is now 9 male cM.

CONCLUSIONS

The results strengthen our previous findings and further define a region suitable for genetic fine-mapping analysis on chromosome 18q. Our data suggest that a dense set of markers, when physically ordered, can increase the informational value of genetic linkage signals.

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.

Polymorphism screening of PIK4CA: possible candidate gene for chromosome 22q11-linked psychiatric disorders

Lithium is potent non-competitive inhibitor of an enzyme involved in the metabolism of phosphatidylinositol 4,5-bisphosphate (PtdIns-4,5-P(2)), a critical phosphoinositide (PI) that regulates signal transduction and synaptic vesicle function. Interestingly, a number of genes involved in the regulation of PtdIns-4,5-P(2) synthesis and dephosphorylation are found in regions of the genome previously mapped in bipolar disorder (BPD) including 10p, 18q, 21q, and 22q. One is PIK4CA, a member of the phosphatidylinositol 4-kinase family that phosphorylates PtdIns at the D4 position of the inositol ring as part of the PtdIns-4,5-P(2) synthetic pathway. PIK4CA maps to 22q11 in a region believed to contain a susceptibility gene for psychiatric disorders. Screening of two functional domains of PIK4CA and the promoter region resulted in the identification of 15 different polymorphisms. Rare variants at a consensus splice donor site and the promoter region were found in a total of three patients with BPD, three with schizophrenia (SZ) and only one control. Several common non-synonymous changes and a common single nucleotide polymorphism (SNP) at position -31 in the putative promoter were identified and analyzed in patients with BPD, SZ, and controls. There was no difference in the allele distribution in mentally ill subjects and controls for two variants, R2259C and E2079Q, both located in the PIK4CA catalytic domain. There was, however, a trend toward significance in the distribution of the -31 promoter genotypes in bipolar subjects and controls. Although the results of this analysis were modest, considering the heterogeneity of BPD and SZ and the hypothesis that BPD may be caused by abnormalities in genes that regulate PI-mediated phenomena in the brain, the polymorphisms we detected in the PIK4CA gene should be analyzed in a larger data set to help determine their significance in 22q11-linked mental disorders.

Bipolar disorder susceptibility region on Xq24-q27.1 in Finnish families

Bipolar disorder (BPD) is a common disorder characterized by episodes of mania, hypomania and depression. The genetic background of BPD remains undefined, although several putative loci predisposing to BPD have been identified. We have earlier reported significant evidence of linkage for BPD to chromosome Xq24-q27.1 in an extended pedigree from the late settlement region of the genetically isolated population of Finland. Further, we established a distinct chromosomal haplotype covering a 19 cM region on Xq24-q27.1 co-segregating with the disorder. Here, we have further analyzed this X-chromosomal region using a denser marker map and monitored X-chromosomal haplotypes in a study sample of 41 Finnish bipolar families. Only a fraction of the families provided any evidence of linkage to this region, suggesting that a relatively rare gene predisposing to BPD is enriched in this linked pedigree. The genome-wide scan for BPD predisposing loci in this large pedigree indicated that this particular X-chromosomal region provides the best evidence of linkage genome-wide, suggesting an X-chromosomal gene with a major role for the genetic predisposition of BPD in this family.

Linkage analysis in psychiatric disorders: the emerging picture

Gene finding in genetically complex diseases has been difficult as a result of many factors that have diagnostic and methodologic considerations. For bipolar disorder and schizophrenia, numerous family, twin, and adoption studies have identified a strong genetic component to these behavioral psychiatric disorders. Despite difficulties that include diagnostic differences between sample populations and the lack of statistical significance in many individual studies, several promising patterns have emerged, suggesting that true susceptibility loci for schizophrenia and bipolar disorder may have been identified. In this review, the genetic epidemiology of these disorders is covered as well as linkage findings on chromosomes 4, 12, 13, 18, 21, and 22 in bipolar disorder and on chromosomes 1, 6, 8, 10, 13, 15, and 22 in schizophrenia. The sequencing of the human genome and identification of numerous single nucleotide polymorphisms (SNP) should substantially enhance the ability of investigators to identify disease-causing genes in these areas of the genome.

The human genome project and its impact on psychiatry

There has been substantial evidence for more than three decades that the major psychiatric illnesses such as schizophrenia, bipolar disorder, autism, and alcoholism have a strong genetic basis. During the past 15 years considerable effort has been expended in trying to establish the genetic loci associated with susceptibility to these and other mental disorders using principally linkage analysis. Despite this, only a handful of specific genes have been identified, and it is now generally recognized that further advances along these lines will require the analysis of literally hundreds of affected individuals and their families. Fortunately, the emergence in the past three years of a number of new approaches and more effective tools has given new hope to those engaged in the search for the underlying genetic and environmental factors involved in causing these illnesses, which collectively are among the most serious in all societies. Chief among these new tools is the availability of the entire human genome sequence and the prospect that within the next several years the entire complement of human genes will be known and the functions of most of their protein products elucidated. In the meantime the search for susceptibility loci is being facilitated by the availability of single nucleotide polymorphisms (SNPs) and by the beginning of haplotype mapping, which tracks the distribution of clusters of SNPs that segregate as a group. Together with high throughput DNA sequencing, microarrays for whole genome scanning, advances in proteomics, and the development of more sophisticated computer programs for analyzing sequence and association data, these advances hold promise of greatly accelerating the search for the genetic basis of most mental illnesses while, at the same time, providing molecular targets for the development of new and more effective therapies.

Manic-depression genes and the new millennium: poised for discovery

Manic-depressive illness is a common psychiatric disorder with complex etiology that likely involves multiple genes and non-genetic influences. The uncertain path to gene discovery has spurred considerable debate over genetic findings and gene-finding strategies. In this article, I review the main findings, with a focus on: (1) putative linked loci on chromosomes 1q31-32, 4p16, 6pter-p24, 10p14, 10q21-26, 12q23-24, 13q31-32, 18p11, 18q21-23, 21q22, 22q11-13, and Xq24-28; and (2) association studies with candidate genes, dynamic mutations, mitochondrial mutations, and chromosomal aberrations. Although no gene has been identified, promising findings are emerging. I then discuss the challenges and opportunities ahead, with special emphasis on gene-finding methods-in particular, questions pertaining to phenotype definition, linkage and association mapping, gene markers, sampling, study population, multigene systems, lessons from other disorders, animal models, and bioinformatics. The progress to date, together with rapid advances in genomics, analytical and computational methods, and bioinformatics, holds promise for new insights into the genetics of manic-depression, in the new millennium.

Future of genetics of mood disorders research

This report summarizes the deliberations of a panel with representation from diverse disciplines of relevance to the genetics of mood disorders. The major charge to the panel was to develop a strategic plan to employ the tools of genetics to advance the understanding, treatment, and outcomes for mood disorders. A comprehensive review of the evidence for the role of genetic factors in the etiology of mood disorders was conducted, and the chief impediments for progress in gene identification were identified. The National Institute of Mental Health (NIMH) portfolios in the Genetics Research Branch and the Division of Mental Disorders, Behavioral Sciences, AIDS, and all genetics training activities were reviewed. Despite some promising leads, there are still no confirmed linkage findings for mood disorders. Impediments to gene finding include the lack of phenotypic validity, variation in ascertainment sources and methodology across studies, and genetic complexity. With respect to linkage, the committee recommended that a large-scale, integrated effort be undertaken to examine existing data from linkage and association studies of bipolar disorders using identical phenotypes and statistical methods across studies to determine whether the suggestive linkage findings at some loci can be confirmed. Confirmation would justify more intensive approaches to gene finding. The committee recommended that the NIMH support continued efforts to identify the most heritable subtypes and endophenotypes of major depression using the tools of genetic epidemiology, neuroscience, and behavioral science. The field of genetic epidemiology was identified as an important future direction because population-based, epidemiologic studies of families and unrelated affected individuals assume increasing importance for common chronic diseases. To prepare for shifts to more complex genetic models, the committee recommended that the NIMH develop new interdisciplinary training strategies to prepare for the next generation of genetics research.

Investigation of Notch3 as a candidate gene for bipolar disorder using brain hyperintensities as an endophenotype

The purpose of the study was to consider MRI hyperintensities as a potential endophenotype for bipolar disorder (BPD) and to investigate Notch3 (CADASIL) as a candidate gene for BPD. MRI scans were performed on 21 members of a family with a high incidence of BPD. Two-point and multipoint linkage analyses were performed and two exons of Notch3 were investigated with SSCP. Fifteen of 21 family members had MRI hyperintensities, including all bipolar patients and six family members with no affective illness. Two-point linkage analysis yielded negative results for all models. Multipoint linkage analysis yielded negative results except for Model 1a, in which a maximal LOD score was -1.24. A mutation screen of Exons 3 and 4 was negative. Notch3 does not appear to be a candidate gene for BPD in this family.

Genome scan for susceptibility loci for schizophrenia and bipolar disorder

BACKGROUND

Despite the widely accepted view that schizophrenia and bipolar disorder represent independent illnesses and modes of inheritance, some data in the literature suggest that the diseases may share some genetic susceptibility. The objective of our analyses was to search for vulnerability loci for the two disorders.

METHODS

A genomewide map of 388 microsatellite DNA markers was genotyped in five schizophrenia and three bipolar disorder Austrian families. Linkage analyses was used to compute the usual parametric logarithm of the likelihood of linkage (LOD) scores and nonparametric linkage analysis (NPL scores Z(all)) was used to assess the pattern of allele sharing at each marker locus relative to the presence of the disease (GENEHUNTER). Affected status was defined as severe affective disorder or schizophrenia.

RESULTS

Across the genome, p values associated with NPL scores resulted in evidence (i.e., p <.0007) for linkage at marker D3S1265 on chromosome 3q (NPL score Z (all) = 3.74, p =.0003). Two other markers (on 3q and 6q) showed p values of <.01.

CONCLUSIONS

We detected a potential susceptibility locus for bipolar disorder and schizophrenia on chromosome 3q, which has not been reported previously. The possibility of a false positive result has to be taken into account. Our data suggest shared loci for schizophrenia and bipolar affective disorders and are consistent with the continuum model of psychosis.

Nineteen additional unpredicted transcripts from human chromosome 21

The identification of all human chromosome 21 (HC21) genes is a necessary step in understanding the molecular pathogenesis of trisomy 21 (Down syndrome). The first analysis of the sequence of 21q included 127 previously characterized genes and predicted an additional 98 novel anonymous genes. Recently we evaluated the quality of this annotation by characterizing a set of HC21 open reading frames (C21orfs) identified by mapping spliced expressed sequence tags (ESTs) and predicted genes (PREDs), identified only in silico. This study underscored the limitations of in silico-only gene prediction, as many PREDs were incorrectly predicted. To refine the HC21 annotation, we have developed a reliable algorithm to extract and stringently map sequences that contain bona fide 3' transcript ends to the genome. We then created a specific 21q graphical display allowing an integrated view of the data that incorporates new ESTs as well as features such as CpG islands, repeats, and gene predictions. Using these tools we identified 27 new putative genes. To validate these, we sequenced previously cloned cDNAs and carried out RT-PCR, 5'- and 3'-RACE procedures, and comparative mapping. These approaches substantiated 19 new transcripts, thus increasing the HC21 gene count by 9.5%. These transcripts were likely not previously identified because they are small and encode small proteins. We also identified four transcriptional units that are spliced but contain no obvious open reading frame. The HC21 data presented here further emphasize that current gene prediction algorithms miss a substantial number of transcripts that nevertheless can be identified using a combination of experimental approaches and multiple refined algorithms.

Endophenotypes in bipolar disorder

The search for genes in bipolar disorder has provided numerous genetic loci that have been linked to susceptibility to developing the disorder. However, because of the genetic heterogeneity inherent in bipolar disorder, additional strategies may need to be employed to fully dissect the genetic underpinnings. One such strategy involves reducing complex behaviors into their component parts (endophenotypes). Abnormal neurophysiological, biochemical, endocrinological, neuroanatomical, cognitive, and neuropsychological findings are characteristics that often accompany psychiatric illness. It is possible that some of these may eventually be useful in subdefining complex genetic disorders, allowing for improvements in diagnostic assessment, genetic linkage studies, and development of animal models. Findings in patients with bipolar disorder that may eventually be useful as endophenotypes include abnormal regulation of circadian rhythms (the sleep/wake cycle, hormonal rhythms, etc.), response to sleep deprivation, P300 event-related potentials, behavioral responses to psychostimulants and other medications, response to cholinergics, increase in white matter hyperintensities (WHIs), and biochemical observations in peripheral mononuclear cells. Targeting circadian rhythm abnormalities may be a particularly useful strategy because circadian cycles appear to be an inherent evolutionarily conserved function in all organisms and have been implicated in the pathophysiology of bipolar disorder. Furthermore, lithium has been shown to regulate circadian cycles in diverse species, including humans, possibly through inhibition of glycogen synthase kinase 3-beta (GSK-3beta), a known target of lithium.

Review of bipolar molecular linkage and association studies

This paper reviews the history of molecular genetic linkage and linkage disequilibrium (LD) or association studies of bipolar disorder (BPD). The topic is introduced with a brief discussion of various genetic concepts, including linkage and linkage disequilibrium. It is emphasized that criteria for declaring linkage must include independent confirmation by multiple groups of investigators. Given that the inherited susceptibility for BPD is most likely explained by multiple genes of small effect, simulations indicate that universal confirmation of valid linkages cannot be expected due to sampling variation and genetic heterogeneity. With this background, several valid linkages of BPD to genomic regions are reviewed, including some which may be shared with schizophrenia. These results suggest that nosology must be changed to reflect the genetic origins of the multiple disorders which are collectively described by the term, BPD. The history of BPD LD studies is reviewed, using monoamine oxidase as as an example. Some suggestions of improving these BPD LD are offered.

Association between a polymorphism in the pseudoautosomal X-linked gene SYBL1 and bipolar affective disorder

In the past decade, several chromosomal regions have been analyzed for linkage with bipolar affective disorder (BPAD). There have been conflicting results regarding the involvement of X-chromosomal regions in harboring susceptibility genes for BPAD. Recently, a new candidate gene (SYBL1) for BPAD has been described on Xq28. SYBL1, which maps to the Xq pseudoautosomal region (PAR), encodes a member of the synaptobrevin family of proteins involved in synaptic vesicle docking, exocytosis, and membrane transport. A subsequent case-control association study, including 110 US-American patients with BPAD and 119 unrelated controls, investigated a potential etiological role of a novel polymorphism (G-->C transversion) in a regulatory region of the SYBL1 gene. In this analysis, the C allele showed a statistical trend to be more frequent in males with BPAD than in respective controls (P=0.06). This finding prompted us to verify whether a similar effect was also present in a larger German sample of 164 unrelated patients with BPAD (148 patients with BP I disorder, 16 patients with BP II disorder) and 267 controls. We observed a significantly increased frequency of genotypes homozygous for the C allele in females with BPAD in comparison with controls (P=0.017). Thus, our data strengthen the role of the SYBL1 gene as a candidate gene for BPAD.

Population isolates: their special value for locating genes for bipolar disorder

OBJECTIVES

Population isolates offer several advantages for those hoping to identify predisposition genes for bipolar disorder (BP). In this review article, the rationale for performing gene mapping studies in this type of population and the results of genetic mapping studies performed to date in population isolates are presented.

METHODS

This article begins with a brief review of the concepts involved in mapping genes for BP. The concept of populations that show some degree of historical isolation and their special utility for certain types of gene mapping is presented. Methods of statistical analysis particularly relevant for gene mapping of complex diseases like BP are presented. Finally, several BP gene studies conducted to date in several population isolates are reviewed.

RESULTS

Genetic mapping studies of BP have occurred thus far in several isolates or sub-isolates, including the Amish population, Costa Ricans, Finnish, and Canadians (in Quebec), and significant linkage scores have been identified in the latter three isolates.

CONCLUSIONS

Possible greater homogeneity and greater consistency of diagnosis are factors that have been cited in several studies of BP done in isolates to date. Another special advantage of working in certain types of population isolate is their appropriateness for using certain types of association or linkage disequilibrium-based approaches at both the genome screening and fine mapping stages. These tests include mapping by linkage disequilibrium analyses, an approach that allows mapping to occur at the population, rather than the pedigree, level.

Genetics of affective disorders

Despite substantial evidence for heritability in affective disorders the contributing genes have proven elusive. Here we discuss the genetic epidemiology of depression, as well as methodological issues and results from molecular genetic studies. There has been rapid advances in genetics, genomics and statistical modelling, facilitating the search for molecular mechanisms underlying affective disorders and several strategies reviewed in this paper hold promise to provide progress in the field. Considering the poorly understood biological basis of vulnerability to affective disorders, the identification of genes involved in the pathophysiology will unravel mechanisms and pathways that could permit more personalized therapeutic strategies and result in new targets for pharmacological intervention.

Molecular linkage studies of bipolar disorders

OBJECTIVES

To review the reports of linkage findings for bipolar disorder.

METHODS

Literature review of published linkage findings in bipolar disorder.

RESULTS

There are several regions of the human genome that have been implicated repeatedly by independent investigators. These include 4p16, 12q24, 18q22, 18p11, 21q21 and 22q11. Two of these regions (18p11 and 22q11) are also implicated in genome scans of schizophrenia, suggesting that these two distinct nosological categories may share some genetic susceptibility. This hypothesis can only be tested when the underlying genes are identified.

Screening ABCG1, the human homologue of the Drosophila white gene, for polymorphisms and association with bipolar affective disorder

ABCG1 encodes a transporter protein that may be involved in the cellular uptake of tryptophan. Tryptophan is the precursor for serotonin, which is implicated in the regulation of mood. The gene maps to chromosome 21q22.3, a region implicated in bipolar disorder I (BPI) in genetic linkage studies. ABCG1 is thus a suitable candidate gene for study in BP1. We screened all 15 exons and 700 bases of the 5' flanking region of ABCG1 for mutations, using Denaturing High Performance Liquid Chromatography (DHPLC). A total of 13 single nucleotide polymorphisms (SNPs) were identified. Ten of the SNPs were intronic, two lie within the 5' flanking region and one within the 3' UTR. We identified a GCC repeat within Exon 1 and two novel intronic VNTRs. Eight of the SNPs, the two VNTRs, the GCC repeat and two known microsatellite markers within the gene were tested for association with BP1 in a sample of 110 parent-offspring trios using the Extended Transmission Disequilibrium Test (ETDT). No alleles or haplotypes were significantly preferentially transmitted from parents to affected offspring. However, the trend for preferential transmission of markers in the 3'UTR is in the same direction as in a previous report for association with mood and panic disorders and therefore warrants attempts at replication. Marker-to-marker linkage disequilibrium (LD) showed that strong LD was present over relatively short distances of up to 20 kb and was present for SNPs as well as for polymorphic repeats. The polymorphisms identified in this study will be useful in examining the role of this gene in other neuropsychiatric disorders and behavioural traits.

A search for specific and common susceptibility loci for schizophrenia and bipolar disorder: a linkage study in 13 target chromosomes

We report the first stage of a genome scan of schizophrenia (SZ) and bipolar disorder (BP) covering 18 candidate chromosomal areas. In addition to testing susceptibility loci that are specific to each disorder, we tested the hypothesis that some susceptibility loci might be common to both disorders. A total of 480 individuals from 21 multigenerational pedigrees of Eastern Québec were evaluated by means of a consensus best-estimate diagnosis made blind to diagnoses in relatives and were genotyped with 220 microsatellite markers. Two-point and multipoint model-based linkage analyses were performed and mod scores (Z, for max Z(max)) are reported. The strongest linkage signals were detected at D18S1145 (in 18q12; Z = 4.03) for BP, and at D6S334 (in 6p 22-24; Z(het) = 3.47; alpha = 0.66) for SZ. Three other chromosomal areas (3q, 10p, and 21q) yielded linkage signals. Chromosomes 3p, 4p, 5p, 5q, 6q, 8p, 9q, 11q, 11p, 12q, 13q, 18p and 22q showed no evidence of linkage. The 18q12 results met the Lander and Kruglyak (1995) criterion for a genome-wide significant linkage and suggested that this susceptibility region may be shared by SZ and BP. The 6p finding provided confirmatory evidence of linkage for SZ. Our results suggest that both specific and common susceptibility loci must be searched for SZ and BP.

Altered TRPC7 gene expression in bipolar-I disorder

BACKGROUND

As altered storage-operated calcium (Ca(2+)) entry (SOCE) may affect Ca(2+) homeostasis in bipolar disorder (BD), we determined whether changes occur in the expression of TRPC7 and SERCA2s, proteins implicated or known to be involved in SOCE, in B lymphoblast cell lines (BLCLs) from BD-I patients and comparison subjects.

METHODS

mRNA levels were determined in BLCL lysates from BD-I, BD-II, and major depressive disorder patients, and healthy subjects by comparative reverse transcriptase-polymerase chain reaction, and BLCL basal intracellular Ca(2+) concentration ([Ca(2+)]B) was determined by ratiometric spectrophotometry using Fura-2, in aliquots of the same cell lines, at 13-16 passages in culture.

RESULTS

TRPC7 mRNA levels were significantly lower in BLCLs from BD-I patients with high BLCL [Ca(2+)]B compared with those showing normal [Ca(2+)]B (-33%, p =.017) and with BD-II patients (-48%, p =.003), major depressive disorder patients (-47%, p =.049) and healthy subjects (-33%, p =.038). [Ca(2+)]B also correlated inversely with TRPC7 mRNA levels in BLCLs from the BD-I group as a whole (r = -.35, p =.027).

CONCLUSIONS

Reduced TRPC7 gene expression may be a trait associated with pathophysiological disturbances of Ca(2+) homeostasis in a subgroup of BD-I patients.