No association between 5HT‐2A and bipolar disorder irrespective of genomic imprinting

Recent evidence that 5HT‐2A may be subjected to genomic imprinting prompted us to examine a collection of Irish family trios (an affected individual and both parents) for evidence of an association between 5HT‐2A and bipolar disorder. Family trios offer an advantage over case control studies in regard to genomic imprinting since with family trios it is possible to trace the path of alleles from the parents to the offspring. Using haplotype‐based haplotype relative risk (HHRR) and transmission/disequilibrium (TDT) analyses, no evidence was found for an association of 5HT‐2A with bipolar affective disorder under the assumption of no imprinting and of imprinting. © 2001 Wiley‐Liss, Inc.     

hSKCa3: no association of the polymorphic CAG repeat with bipolar affective disorder and schizophrenia

hSKCa3 is a neuronal small conductance calcium-activated potassium channel, which contains a polyglutamine tract, encoded by a polymorphic CAG repeat in the gene. Since an association between longer alleles of this CAG repeat and bipolar disorder or schizophrenia has been reported, we genotyped the polymorphic CAG repeat in 91 German family trios of patients with bipolar disorder I and used the transmission disequilibrium test (TDT) to test for association. Applying a dichotomized model (< or = 19 or > 19 CAG triplets), we found no evidence for an association of longer alleles with bipolar disorder (TDT = 0.75, P = 0.386). Regarding the whole range of alleles, there was no preference in transmitting the larger of the two observed alleles from parents to the affected offspring. In parallel we performed an independent case-control study on German patients with bipolar disorder and schizophrenia. Again we did not detect an overrepresentation of longer CAG repeats in patients. Thus, our data do not support the hypothesis that longer CAG repeats in the hSkCa3 gene contribute to the susceptibility for bipolar disorder and schizophrenia.     

Manic-depressive illness: an association study with the inositol polyphosphate 1-phosphatase and serotonin transporter genes

Association studies with candidate genes may contribute towards the understanding of the etiopathogenesis of bipolar disorder. Candidate genes in bipolar disorders are those related to aminergic neurotransmission, which is the target of the effects of antipsychotics and antidepressants, as well as genes related to signal transduction pathways, reporting the target for the mood-stabilizing effects of lithium. Association with such candidate genes may provide clues towards the understanding of the biological components of bipolar disorder. An association study was performed between the 5' regulatory region of the serotonin transporter gene (5-HTTLPR), the inositol polyphosphate 1-phosphatase gene (INPP1) and bipolar disorder using our sample of proband/parent trios. A total of 101 bipolar probands were considered eligible for the study. Since both parents had to be available, mean age at onset of bipolar disorder in probands was relatively young. However, the mean duration of illness and the number of episodes were consistent with a stable diagnosis. In our trios sample, the transmission disequilibrium test revealed no preferential transmission of alleles of the 5-HTTLPR and INPP1 from heterozygous parents to probands. Therefore, additional family-based data are warranted, possibly with a more complete subdivision of 5-HTTLPR alleles, since short and long alleles have recently been divided into four and six kinds of allelic variant, respectively, with significant ethnic differences in allele and genotype distributions.     

Genetic association between monoamine oxidase and manic-depressive illness: Comparison of relative risk and haplotype relative risk data

There have been several conflicting reports of association of monoamine oxidase (MAO) A gene polymorphisms and bipolar affective disorder. In order to determine the possible role of the MAO region in susceptibility to affective disorders in an independent sample, we have genotyped 83 probands of bipolar affective disorder families, 56 sets of parents of bipolar probands, and 84 normal controls for intronic simple sequence repeat polymorphisms of the MAO-A and MAO-B genes. For MAO-A there were no significant differences in allele frequencies between bipolar and normal control groups for both genders. However, for MAO-B there were significant differences between groups for both genders. In contrast, allele-wise haplotype relative risk analysis for the 56 bipolar proband-parent trios found no significant differences between transmitted and non-transmitted allele frequencies for MAO-A or B. These data do not support the association of MAO-A or B with bipolar affective disorder but do demonstrate that undetected population stratification can be an important source of bias in case-control studies. Am. J. Med. Genet. 74:475–479, 1997. © 1997 Wiley-Liss, Inc.     

Caught in the trio trap? Potential selection bias inherent to association studies usings parent‐offspring trios

During the last years, the validity of classic case control studies in psychiatric genetic research has been increasingly under question due to the risk of population stratification problems inherent to this type of association study. By consequence, the application of family‐based association studies using parent‐offspring trios has been strongly advocated. Recently, however, in a study comparing clinical characteristics between index patients from parent‐offspring trios and singleton patients with bipolar affective disorder, the question was raised whether a systematic neglect of case control association studies could lead to a selection bias of susceptibility genes. In a similar approach, we compared demographic and clinical characteristics of 122 singleton bipolar patients with those of 54 bipolar patients derived from parent‐offspring trios. The singleton patients did not only present with a higher age of onset, but also with a higher frequency of suicidal behavior and a higher familial loading for suicidality. These findings suggest that the genetic mechanism for disease might be different between trio‐based and classic case control samples, where patients are examined whose parents are not available for genetic studies. Thus, giving up case control designs for the sake of family‐based association studies could be at the risk of selecting against several genetically determined factors. © 2001 Wiley‐Liss, Inc.     

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.     

Association of mitochondrial complex I subunit gene NDUFV2 at 18p11 with schizophrenia in the Japanese population.

Schizophrenia and bipolar disorder share common genetic background. Several loci such as 18p11, 13q32, and 22q11-13 were commonly linked with these diseases. Since mitochondrial dysfunction has been suggested in both of these disorders, NDUFV2 at 18p11, encoding a subunit of the complex I, NADH ubiquinone oxidoreductase, is a candidate gene for these diseases. We previously reported that single nucleotide polymorphisms (SNPs) in the upstream region of NDUFV2 were associated with bipolar disorder in Japanese. The association of haplotype consisting of two SNPs, -3542G > A and -602G > A, with bipolar disorder was also seen both in Japanese and the National Institute of Mental Health Pedigrees trios. In this study, 2 polymorphisms, -3542G > A and -602G > A, were investigated in 229 schizophrenic patients as compared with controls. Individual genotypes were not associated with schizophrenia. However, the haplotype consisting of these two SNPs were significantly associated with schizophrenia. These results suggested that inter-individual variation of the genomic sequence of the promoter region of NDUFV2 might be a genetic risk factor common to bipolar disorder and schizophrenia.     

Haplotype association study between DRD1 gene and bipolar type I affective disorder in two samples from Canada and Sardinia.

Based on the dopaminergic hypothesis, the dopamine D(1) receptor gene (DRD1) is considered to be a good candidate gene involved in the susceptibility of bipolar disorder (BP). Genetic association between three DRD1 single nucleotide polymorphisms (SNPs) (-800T/C, -48A/G, and 1403T/C) and bipolar type I (BP I) disorder was performed in a case-control sample of Sardinian origin (170 BP I and 209 controls) and in an enlarged sample (229 families) of BP I trios from Toronto. The haplotype analyses generated significant global chi-square in both samples (P-value 0.024 in Toronto and 0.00042 in Sardinian). The main representative haplotypes in both samples were the -800T/-48A/1403C and the -800C/-48G/1403T. Considering each group individually, the -800C/-48G/1403T was transmitted more frequently from parents to BP I probands in Toronto sample (nominally P-value = 0.047) and was more frequent in cases than in control subjects in Sardinian sample although showing no significant evidence of association (nominally P-value = 0.16) When the estimated haplotype counts of both samples were combined, the global chi(2) was significant (P-value = 0.00085) and the nominal P-value for the haplotype -800C/-48G/1403T was 0.01. The fact that the same haplotype shows a similar trend for association in samples originating from different ethnic backgrounds seems to imply that the -800C/-48G/1403T haplotype may be considered as a risk factor for BP I disorder.     

Analysis of BDNF Val66Met allele-specific mRNA levels in bipolar disorder

We have previously reported an association between the BDNF Val66Met polymorphism and bipolar disorder (BD). However, the possibility that genomic imprinting in BDNF gene affects risk for BD has not been investigated. To examine the possibility of genomic imprinting in the BDNF gene in BD, we analyzed the parent-of-origin effect (POE) and differential expression of the BDNF Val66Met alleles in BD. We performed a family-based association study and ETDT analyses of the Val66Met polymorphism in 312 BD nuclear families, and compared allele-specific mRNA levels in both post-mortem brain samples and B lymphoblasts from BD patients and controls. The BDNF Val66 allele was transmitted significantly more often to patients with BD (maternal transmissions: 46/22, p=0.003; paternal transmissions: 55/30, p=0.006). There was no significant difference between maternal and paternal transmission ratios. There was no significant difference in the ratio of Val/Met-specific mRNA expression between BD and controls, in either brain or B lymphoblasts. The Val/Met ratio was much lower in the brain vs. B lymphoblasts. These data do not support a role for genomic imprinting as a modifier of the contribution of BDNF gene to risk of susceptibility to BD.     

Caught in the trio trap? Potential selection bias inherent to association studies using parent-offspring trios

During the last years, the validity of classic case control studies in psychiatric genetic research has been increasingly under question due to the risk of population stratification problems inherent to this type of association study. By consequence, the application of family-based association studies using parent-offspring trios has been strongly advocated. Recently, however, in a study comparing clinical characteristics between index patients from parent-offspring trios and singleton patients with bipolar affective disorder, the question was raised whether a systematic neglect of case control association studies could lead to a selection bias of susceptibility genes. In a similar approach, we compared demographic and clinical characteristics of 122 singleton bipolar patients with those of 54 bipolar patients derived from parent-offspring trios. The singleton patients did not only present with a higher age of onset, but also with a higher frequency of suicidal behavior and a higher familial loading for suicidality. These findings suggest that the genetic mechanism for disease might be different between trio-based and classic case control samples, where patients are examined whose parents are not available for genetic studies. Thus, giving up case control designs for the sake of family-based association studies could be at the risk of selecting against several genetically determined factors.     

Association analysis of HSP90B1 with bipolar disorder

Pathophysiological role of endoplasmic reticulum (ER) stress response signaling has been suggested for bipolar disorder. The goal of this study was to test the genetic association between bipolar disorder and an ER chaperone gene, HSP90B1 (GRP94/gp96), which is located on a candidate locus, 12q23.3. We tested the genetic association between bipolar disorder and HSP90B1 by case-control studies in two independent Japanese sample sets and by a transmission disequilibrium test (TDT) in NIMH Genetics initiative bipolar trio samples (NIMH trios). We also performed gene expression analysis of HSP90B1 in lymphoblastoid cells. Among the 11 SNPs tested, rs17034977 showed significant association in both Japanese sample sets. The frequency of the SNP was lower in NIMH samples than in Japanese samples and there was no significant association in NIMH trios. Gene expression analysis of HSP90B1 in lymphoblastoid cells suggested a possible relationship between the associated SNP and mRNA levels. HSP90B1 may have a pathophysiological role in bipolar disorder in the Japanese population, though further study will be needed to understand the underlying functional mechanisms.     

Family environment patterns in families with bipolar children

BACKGROUND: We studied the characteristics of family functioning in bipolar children and healthy comparison children. We hypothesized that the family environment of bipolar children would show greater levels of dysfunction as measured by the Family Environment Scale (FES). METHODS: We compared the family functioning of 36 families that included a child with DSM-IV bipolar disorder versus 29 comparison families that included only healthy children. All subjects and their parents were assessed with the K-SADS-PL interview. The parents completed the FES to assess their current family functioning. Multivariate analysis of variance was used to compare the family environment of families with and without offspring with bipolar disorder. RESULTS: Parents of bipolar children reported lower levels of family cohesion (p<0.001), expressiveness (p=0.005), active-recreational orientation (p<0.001), intellectual-cultural orientation (p=0.04) and higher levels of conflict (p<0.001) compared to parents with no bipolar children. Secondary analyses within the bipolar group revealed lower levels of organization (p=0.031) and cohesion (p=0.014) in families where a parent had a history of mood disorders compared to families where parents had no history of mood disorders. Length of illness in the affected child was inversely associated with family cohesion (r=-0.47, p=0.004). LIMITATIONS: Due to the case-control design of the study, we cannot comment on the development of these family problems or attribute their cause specifically to child bipolar disorder. CONCLUSION: Families with bipolar children show dysfunctional patterns related to interpersonal interactions and personal growth. A distressed family environment should be addressed when treating children with bipolar disorder.     

Polymorphisms in the neuronal isoform of tryptophan hydroxylase 2 are associated with bipolar disorder in French Canadian pedigrees

OBJECTIVE: Tryptophan hydroxylase is the rate-limiting enzyme in the serotonin biosynthetic pathway and plays an important role in the regulation of serotonin levels. Recently, a brain-specific isoform, tryptophan hydroxylase 2 or n-tryptophan hydroxylase, has been discovered. Some studies reported genetic and functional associations between this isoform and bipolar disorder and/or major depressive disorder. The aim of this study was to investigate further association of genetic variants in French Canadian samples with bipolar disorders. METHODS: Genetic variants in the tryptophan hydroxylase 2 gene were genotyped in a case-control sample consisting of 225 affected individuals (191 bipolar I and 34 bipolar II) and 221 controls and in a collection of extended pedigrees and trios from the same population 357 nuclear families (201 bipolar I, 64 bipolar II, 79 recurrent major depressive disorder). RESULTS: We determined linkage disequilibrium structure in our isolated population and analyzed six tagged single nucleotide polymorphisms in the case-control sample. Whereas no single, single nucleotide polymorphism gave any significant result, a three single nucleotide polymorphism haplotype gave a global P=0.01. Family-based association showed significant association (P=0.004) of one polymorphism (rs4290270) with the major allele overtransmitted to affected offspring. CONCLUSIONS: Case-control and family-based association studies further support the presence of a susceptibility locus for bipolar disorder in tryptophan hydroxylase 2 by showing statistically significant associations with both, single nucleotide polymorphism alone and haplotype of single nucleotide polymorphism markers.     

Linkage disequilibrium mapping of bipolar affective disorder at 12q23-q24 provides evidence for association at CUX2 and FLJ32356.

Chromosome 12q23-q24 has been implicated by several linkage studies as harboring a gene for bipolar affective disorder. We performed linkage disequilibrium (LD) mapping with 17 microsatellite markers across a 1.6 Mb-wide segment forming the central part of our narrowest linkage region. A significant signal (P = 0.0016) was identified for one microsatellite marker in our UK Caucasian case-control sample (347 cases, 374 controls). Genes, including regulatory elements, around this marker were screened for mutations and the LD structure of the region determined by genotyping 22 SNPs and insertion/deletion polymorphisms in 94 individuals. A set of 11 haplotype tagging (ht) SNPs was genotyped in our sample using a two-stage procedure. Two SNPs (rs3847953 and rs933399) and an insertion/deletion with putative functional relevance (which are in high LD with each other and with the microsatellite marker) showed significant or nearly significant association with bipolar disorder after Bonferroni-correction (reaching nominal P values from P = 0.002 to P = 0.005). In a sample of 110 UK Caucasian parent-offspring trios there was a trend for an over transmission in the same direction that failed to meet conventional levels of statistical significance. Our data provide evidence for association between bipolar mood disorder and markers on chromosome 12q23-q24 but need replication in independent samples.     

Multimarkerhaplotypes within the serotonin transporter gene suggest evidence of an association with bipolar disorder

Previously we obtained modest linkage evidence implicating 17q11. 1-12 in bipolar disorder. A modified genome screen, based on gene-rich regions, on a collection of Irish sib-pair nuclear families revealed excess allele sharing at markers flanking the gene encoding the serotonin transporter (5-HTT; hSERT). Here we describe a study designed to combine the advantages of family-based association studies with the consideration of multiple polymorphic markers within a candidate gene. Ninety-two Irish families, with a total of 106 proband-parent trios, have been genotyped for 3 previously known polymorphisms within hSERT (5-HTTLPR, intron 2 VNTR, and 3' UTR G/T). Data from two and three polymorphic marker haplotypes revealed a number of marker combinations that showed evidence supportive of association; the most significant being for polymorphisms 5-HTTLPR and 3' UTR G/T (global chi(2), 12.91, df 3, P = 0.005). In addition, modest evidence of association also was observed for 5-HTTLPR alone. Am. J. Med. Genet. (Neuropsychiatr. Genet.) 96:845-849, 2000.     

5-羟色胺转运体基因VNTR位点与双相情感性障碍的关联分析

目的探讨５－羟色胺转运体基因第２内含子ＶＮＴＲ区域在中国人群中的群体遗传学背景，以及与双相情感障碍的关系。方法利用ＰＣＲ等方法在１７０个随机健康中国人中对５－羟色胺转运体基因第２内含子的ＶＮＴＰ多态性位点进行了群体遗传学研究，并就该位点与双相情感障碍的关系进行了关联分析。结果该位点在中国人群中的多态信息含量为０．１２，杂合度为１２％，且符合孟德尔遗传方式；其基因型分布、等位片段频率在中国汉族人群与高加索人种间存在着极显著性差异（Ｐ＜１０－８）；在与情感性障碍的关联分析中发现该多态性位点的等位片段１０与双相情感障碍女性群体存在着显著的关联（Ｐ＝０．０４３）。结论该结果表明：５－羟色胺转运体基因ＶＮＴＲ的位点多态性在中国人群与高加索人群间存在极显著的差异；同时，在男女性双相情感障碍群体中的差别可能暗示了该疾病的发病机理在性别上的差异。     

Serotonin transporter (5-HTT) gene variants associated with autism?

An association study was performed to elucidate the role of the serotonin transporter (5-HTT) gene as a susceptibility factor for autism as treatment of patients with antidepressant drugs which selectively target 5-HTT reduced autistic or concomitant symptoms, such as repetitive behavior and aggression, and ameliorate language use. Using the transmission/disequilibrium test (TDT) an analysis was done for a common polymorphism in the upstream regulatory region (5-HTTLPR), a VNTR in intron 2 of the gene and a haplotype of both loci in 52 trios fulfilling stringent criteria for autism and an extended group of 65 trios including patients showing no language delay in their first 3 years of life. A higher frequency and preferential transmission of the long allele of the 5-HTTLPR was observed, but the TDT gave a statistically significant value ( P = 0. 032) only for the extended patient group. This result is in contrast to a recent study by a US group presenting preliminary evidence for preferential transmission of the short allele of 5-HTTLPR in 86 trios. Both studies failed to reveal significant linkage disequilibrium between the VNTR in intron 2 of the gene and autism. In our study haplotype analysis of the 5-HTTLPR and the VNTR in intron 2 supplied evidence for an association of 5-HTT and autism in the stringent ( P = 0.069) and extended patient group ( P = 0.049). Overall, we were not able to replicate the findings of the first study on 5-HTT and autism and instead observed a tendency for association of the opposite genetic variant of the gene with the disorder. The implications for genetic variants of the serotonin transporter in the etiology of autism and possible subgroups of patients, therefore, needs clarification in further studies with other and larger patient samples.      

Parent-of-origin effect in transmission of bipolar disorder

Recently, possible involvement of a parent-of-origin effect in the transmission of bipolar disorder has been suggested. We examined the possible contribution of parent-of-origin effect by using data from a large family and family history study of bipolar patients in the Collaborative Depression Study. In 276 probands with bipolar I disorder, family histories were examined using three diagnostic criteria: (1) bipolar I disorder, (2) bipolar I or bipolar II disorder, and (3) bipolar disorders or recurrent unipolar depression for parents and siblings. An excess of affected mothers was not observed when unipolar depression was excluded. Age-at-onset was significantly lower in probands having a father with bipolar disorders or recurrent unipolar depression than in probands with an affected mother. This difference was not observed when unipolar depression was excluded. There was no significant difference of prevalence rate in children of affected mothers and those with affected fathers. These data do not support the contribution of parent-of-origin effect in the transmission of bipolar disorder. © 1996 Wiley-Liss, Inc.     

Association study of the tryptophan hydroxylase gene and bipolar affective disorder using family-based internal controls

The tryptophan hydroxylase (TPH) gene encodes for the rate-limiting enzyme of the serotonin metabolism and, therefore, has to be considered a major candidate for association studies in affective disorders. Recently, an association between this gene and bipolar affective disorder has been reported in a French population. We sought to replicate this finding in a German sample. Allele frequencies of a biallelic polymorphism (A218C) of the TPH gene were determined in 95 bipolar I patients and their parents. Preferential transmission of alleles from heterozygous parents to bipolar offspring was tested with the "transmission disequilibrium test" (TDT), which eliminates the contribution of population stratification to an association finding. Our sample yielded a power >90% to detect the originally reported effect. Neither allele 218A nor allele 218C were preferentially transmitted from heterozygous parents to bipolar offspring. Our results, therefore, do not support the hypothesis that the TPH gene is involved in the etiology of bipolar disorder.     

Molecular genetics of bipolar disorder

Alteration of monoaminergic neurotransmission is implicated in the pathophysiology of bipolar disorder (manic-depressive illness). Candidate genes participating in monoaminergic neurotransmission, especially serotonin transporter and monoamine oxidase A, may be associated with bipolar disorder. And the regulating regions of these genes and the molecules participating in intracellular signal transduction are now under investigation. To date, 13 whole genome positional cloning studies have been performed and many candidate loci identified. Using patients from a pedigree in which schizophrenia, depression or bipolar disorder have been linked with a balanced translocation at 1 and 11, candidate pathogenetic genes were cloned as DISC1 (disrupted in schizophrenia-1) and DISC2. Recently, pathogenetic mutations have been identified in two genetic diseases frequently co-morbid with mood disorder; WFS1 for Wolfram syndrome and ATP2A2 (SERCA2) for Darier's disease. Transmission of bipolar disorder may be characterized by anticipation and parent-of-origin effect, and extended CTG repeat at SEF2-1B gene was identified from a bipolar patient. However, its pathogenetic role was not supported by subsequent studies. Association of bipolar disorder with mitochondrial DNA has also been suggested. The role of genomic imprinting is also possible because linkage to 18p11 is limited to paternally transmitted pedigrees. These results warrant further study of molecular genetics of bipolar disorder.