Candidate gene analysis of 21q22 Support for S100B as a susceptibility gene for bipolar affective disorder with psychosis.код для вставкиСкачать
American Journal of Medical Genetics Part B (Neuropsychiatric Genetics) 144B:1094 –1096 (2007) Brief Research Communication Candidate Gene Analysis of 21q22: Support for S100B as a Susceptibility Gene for Bipolar Affective Disorder With Psychosis S. Roche,1* F. Cassidy,1 C. Zhao,2 J. Badger,2 E. Claffey,3 L. Mooney,3 C. Delaney,3 S. Dobrin,5 and P. McKeon3,4 1 Smurfit Institute of Genetics, Trinity College, Dublin, Ireland The Marshfield Clinic Center for Human Genetics, Marshfield, Wisconsin 3 St. Patrick’s Hospital, James’s Street, Dublin, Ireland 4 Department of Psychiatry, Trinity College, Dublin, Ireland 5 Monsanto Company, 3302 SE Convenience Blvd, Ankeny, Iowa 2 A genome-wide scan in 60 bipolar affective disorder (BPAD) affected sib-pairs (ASPs) identified linkage on chromosome 21 at 21q22 (D21S1446, NPL ¼ 1.42, P ¼ 0.08), a BPAD susceptibility locus supported by multiple studies. Although this linkage only approaches significance, the peak marker is located 12 Kb upstream of S100B, a neurotrophic factor implicated in the pathology of psychiatric disorders, including BPAD and schizophrenia. We hypothesized that the linkage signal at 21q22 may result from pathogenic disease variants within S100B and performed an association analysis of this gene in a collection of 125 BPAD type I trios. S100B single nucleotide polymorphisms (SNPs) rs2839350 (P ¼ 0.022) and rs3788266 (P ¼ 0.031) were significantly associated with BPAD. Since variants within S100B have also been associated with schizophrenia susceptibility, we reanalyzed the data in trios with a history of psychosis, a phenotype in common between the two disorders. SNPs rs2339350 (P ¼ 0.016) and rs3788266 (P ¼ 0.009) were more significantly associated in the psychotic subset. Increased significance was also obtained at the haplotype level. Interestingly, SNP rs3788266 is located within a consensus-binding site for Six-family transcription factors suggesting that this variant may directly affect S100B gene expression. Fine-mapping analyses of 21q22 have previously identified transient receptor potential gene melastatin 2 (TRPM2), which is 2 Mb upstream of S100B, as a possible BPAD susceptibility gene at 21q22. We also performed a family-based association analysis of TRPM2 which did not reveal any evidence for association of this gene with BPAD. Overall, our findings suggest that variants within the S100B gene predispose to a psychotic subtype of BPAD, possibly via alteration of gene expression. ß 2007 Wiley-Liss, Inc. Grant sponsor: AWARE; Grant sponsor: National Heart Lung and Blood Institute (NHLBI). *Correspondence to: S. Roche, Smurfit Institute of Genetics, Trinity College, Dublin 2, Ireland. E-mail: firstname.lastname@example.org Received 24 October 2006; Accepted 2 April 2007 DOI 10.1002/ajmg.b.30556 ß 2007 Wiley-Liss, Inc. KEY WORDS: schizophrenia; association; single nucleotide polymorphisms (SNPs); haplotype; TRPM2; linkage; disease variant Please cite this article as follows: Roche S, Cassidy F, Zhao C, Badger J, Claffey E, Mooney L, Delaney C, Dobrin S, McKeon P. 2007. Candidate Gene Analysis of 21q22: Support for S100B as a Susceptibility Gene for Bipolar Affective Disorder with Psychosis. Am J Med Genet Part B 144B:1094–1096. Whole genome linkage scans of bipolar affective disorder (BPAD) have identified numerous potential susceptibility loci, including region 21q22. Linkage of BPAD to 21q22 is highly replicated with positive findings extending from 35 to 45 Mb [McQuillin et al., 2006]. Fine-mapping and candidate gene analyses of this region have identified the transient receptor potential gene melastatin 2 (TRPM2) as a candidate susceptibility gene at 21q22 [McQuillin et al., 2006; Xu et al., 2006]. The TRPM2 gene is implicated in regulating calcium homeostasis, a disturbance of which has been identified in bipolar patients. We recently performed a whole genome scan for linkage to BPAD in a collection of 60 Irish BPAD affected sib-pairs (ASPs) and also obtained evidence for linkage at 21q22 at a slightly more distal region (D21S1446/47 Mb, multipoint NPL ¼ 1.42, P ¼ 0.078, bipolar I disease model) [Cassidy et al., 2007]. Interestingly, marker D21S1446 is located 12 Kb upstream of the S100B gene which encodes a glial cell-derived neurotrophic factor that has been implicated in both neurological and psychiatric diseases [Rothermundt et al., 2003]. Increased levels of the S100B protein have been detected in the serum of patients with BPAD and major depression [Machado-Vieira et al., 2002; Schroeter et al., 2002; Arolt et al., 2003] and both CSF and serum of schizophrenic patients [Rothermundt et al., 2001, 2004] and may predict course of illness and treatment outcome. Furthermore, variants within the S100B gene are associated with schizophrenia [Liu et al., 2005]. It is currently unknown whether the same is true for BPAD. As this gene had previously been implicated in the pathology of BPAD, we hypothesized that linkage at 21q22 could result from pathogenic variants within the S100B gene instead of or in addition to TRPM2. Here, we report the novel finding that variants within S100B are associated with BPAD. Single nucleotide polymorphisms (SNPs) spanning the S100B and TRPM2 genes were genotyped in a collection of 125 bipolar type I trios of Irish ethnicity. Participants were diagnosed according to DSM-IV criteria and information S100B and Bipolar Affective Disorder obtained from the Schedule for Affective Disorders and Schizophrenia (Lifetime version: SADS-LB) or Structured Clinical Interview for DSM-IV-TR Axis I Disorders (SCID). Genotyping was performed at KBiosciences, Hoddesdon, UK using competitive allele-specific PCR (proprietary KASPar and Applied Biosystems TaqmanTM technologies, Warrington, UK). Single- and multi-marker association tests were performed using the transmission disequilibrium test (TDT) implemented in Haploview and Transmit, respectively. All SNPs were in Hardy–Weinberg equilibrium. There was modest evidence for association of S100B SNPs M2, M3, and M9 with BPAD (M2: P ¼ 0.022; M3: P ¼ 0.052; M9: P ¼ 0.031; Table I). Markers M2 and M3 are in strong linkage disequilibrium (LD) and are included within a single haplotype block that extends from M1 to M5 but not to M9 (data not shown). A sliding window haplotype analysis also revealed borderline evidence for association of haplotypes comprised of alleles from M3 and M4 with BPAD (Table I: global P ¼ 0.047). As S100B variants may also increase susceptibility to schizophrenia, we restricted the association analysis to trios with a proband that had experienced at least one psychotic episode of mania or depression (86 trios). Psychotic features reported by probands included grandiose delusions (56%), persecutory delusions (12%), both grandiose and persecutory delusions (24%), and other forms of delusions (8%). Both delusions and hallucinations occurred in 23% of probands. Despite the decreased power due to the reduced sample size, markers M2 and M9 were more significantly associated (M2: P ¼ 0.0159; M9: P ¼ 0.009; Table I: BPI þ psychosis). Furthermore, the global P-value for M3_M4 haplotypes was reduced from 0.047 (Table I: BPI) to 0.016 (Table I: BPI þ psychosis) and haplotypes comprised of alleles from M8 and M9 were now significantly associated (BPI: P ¼ 0.075; BPI þ psychosis: P ¼ 0.025; Table I). It should be noted that protective haplotypes were the most significantly associated individual haplotypes in the BPI analysis. However, the most significantly associated individual M8_9 haplotype (GG) in the BPI þ psychosis analysis confers risk consistent with the single allele TDT result for M9. Overall, the data suggest that variants within S100B predispose to a psychotic subtype of BPAD. Fourteen SNPs spanning the TRPM2 gene were also tested for association. There was no evidence for association in either 1095 the single- or multi-marker association analyses (Table II). Markers M5, a nonsynonymous SNP in exon 11 of TRMP2, and M8 were previously associated with BPAD [McQuillin et al., 2006; Xu et al., 2006]. The discovery that S100B variants are associated with BPAD is interesting given the elevation of the protein in serum from patients with manic and depressive episodes and the influence of anti-depressive treatments [Schroeter et al., 2002], such as fluoxetine [Manev et al., 2001], on these levels. S100B protein levels are also increased in the ouabain-induced rat model of mania [Machado-Vieira et al., 2004]. Transgenic mice overexpressing S100B are hyperactive and exhibit possible memory defects [Gerlai and Roder 1995], both phenotypes of relevance to BPAD, and mutant mice lacking S100B exhibit enhanced synaptic plasticity, learning, and memory [Nishiyama et al., 2002]. Finally, S100B is primarily secreted by glial cells which are implicated in the pathology of both schizophrenia and BPAD. It is unclear whether the altered levels of S100B in psychiatric patients are due to increased secretion of S100B from glial cells, glial-cell abnormalities, or possibly pathogenic disease variants in the S100B gene. Our findings suggest that S100B is a susceptibility gene for a psychotic subtype of BPAD. S100B is also a susceptibility factor for schizophrenia which may be more genetically related to psychotic than nonpsychotic forms of the BPAD. Illness susceptibility may occur via altered gene expression. The location of the associated variants within the promoter (M9) and 30 UTR (M2-3) regions of the gene suggests that they may affect gene expression. The lack of LD extending between these regions may indicate the existence of more than one disease variant within S100B. Bioinformatics analysis revealed that the disease-associated G allele of M9 disrupts a Trex/MEF3 consensus recognition site, which is bound by Six-family proteins [Himeda et al., 2004], suggesting that it could directly affect S100B expression and may represent a functional variant. Six-family proteins are expressed in the brain and regulate brain development and possibly differentiation/ maturation of neuronal cells [Ohto et al., 1998; Kawakami et al., 2000]. Although variants within TRPM2 have been associated with BPAD in both Canadian and British case–control analyses, this first family-based analysis of TRPM2 does not support TABLE I. Results of Association Analysis of S100B SNPs BPI þ psychosis BPI Marker M1: rs3804040 M2: rs2839350 M3: rs2839351 M4: rs9722 M5: rs881827 M6: rs2839355 M7: rs2839359 M8: rs2839363 M9: rs3788266 M1_2 M2_3 M3_4 M4_5 M5_6 M6_7 M7_8 M8_9 Allele T/NT w2df G G T T T C T G G 40:29 36:19 52:34 14:10 54:45 37:24 34:29 57:48 63:41 1.754 5.255 3.767 0.667 0.818 2.770 0.397 0.771 4.654 0.185 0.022 0.052 0.414 0.366 0.096 0.529 0.380 0.031 4.6802 4.7012 7.9533 3.4343 3.3193 1.8343 0.7953 6.9063 0.096 0.095 0.047 0.329 0.345 0.608 0.850 0.075 CA AC CC TC CT TT TA GA P-value T/NT w2df P-value 29:23 30:14 39:24 13:06 39:30 29:20 22:21 43:30 47:25 0.692 5.818 3.571 2.579 1.174 1.653 0.023 2.315 6.722 0.405 0.016 0.059 0.108 0.279 0.198 0.879 0.128 0.009 5.1002 5.0352 10.3823 5.5962 0.9252 0.6712 2.1233 9.3293 0.078 0.081 0.016 0.061 0.630 0.715 0.547 0.025 a CC TC a a GG T, transmitted; NT, not transmitted; df, degrees of freedom. P-values </¼0.05 are indicated in bold. Global P-values for haplotypes with frequencies >5% are shown. a Most significant individual haplotype in BPI þ psychosis analysis which differs from that in the BPI analysis (listed in allele column). 1096 Roche et al. TABLE II. Results of Association Analysis of TRPM2 SNPs Marker M1: rs734336 M2: rs2096860 M3: rs9984977 M4: rs4818917 M5: rs1556314 M6: rs9974831 M7: rs1785454 M8: rs933151 M9: rs8129542 M10: rs2238724 M11: rs2238725 M12: rs2010779 M13: rs6518189 M14: rs4818922 Allele T/NT w2 P-value Haplotype w2df P-value C T C C T T C C A G A A C A 38:26 36:30 45:44 46:39 40:36 45:39 42:40 46:41 28:23 35:23 47:43 43:43 39:29 31:26 2.250 0.545 0.011 0.576 0.211 0.429 0.049 0.287 0.490 2.483 0.178 0.000 1.471 0.439 0.134 0.460 0.916 0.448 0.646 0.513 0.825 0.592 0.484 0.115 0.673 1.000 0.225 0.508 M1_2 M2_3 M3_4 M4_5 M5_6 M6_7 M7_8 M8_9 M9_10 M10_11 M11_12 M12_13 M13_14 1.7062 1.1522 4.0512 4.2962 1.1343 2.8473 1.4762 1.3523 2.7622 3.8672 1.3583 2.7793 0.9922 0.426 0.562 0.132 0.117 0.769 0.416 0.478 0.717 0.251 0.145 0.715 0.427 0.609 T, transmitted; NT, not transmitted; df, degrees of freedom; Global P-values for haplotypes with frequencies >5% are shown. association of TRPM2 variants with BPAD in Irish families. It is possible that there is more than one susceptibility gene at 21q22 for BPAD which may explain the variance is linkage findings in this region and the identification of more than one candidate susceptibility gene. Although the resolution of the fine-mapping analysis of 21q22 performed by McQuillin et al.  was very high across a 500 Kb region containing the TRPM2 gene, the resolution outside of this region was very low for LD mapping and could have missed additional candidate genes, such as S100B. In summary, we have shown that variants within the S100B gene are associated with a psychotic subtype of BPAD. These data suggest that pathogenic disease variants within S100B may contribute to the altered protein levels observed in psychiatric disorders. ACKNOWLEDGMENTS We thank all of the families who kindly participated in these studies. This research was funded by the voluntary organisation, AWARE, and the National Heart Lung and Blood Institute (contract NO1-HV-48141). 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