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Table 1 Increased circulating levels of insulin-related peptides in schizophrenia subjects
Schizophrenia 1 Glucose Insulin
FC
P-value
1.07 3.77
0.520 0.034
Schizophrenia 2 Glucose Insulin Proinsulin des31,32-proinsulin
0.92 2.36 2.01 1.78
0.169 0.020 0.015 0.023
Schizophrenia 3 Glucose Insulin Proinsulin des31,32-proinsulin C-peptide
1.30 4.00 2.67 5.48 2.26
0.017 0.030 0.033 0.010 0.019
Schizophrenia 4 Glucose Proinsulin C-peptide Chromogranin A
ND 2.59 1.54 1.52
ND 0.003 0.006 0.043
Bipolar disorder Glucose Proinsulin des31,32-proinsulin
0.89 0.80 0.78
0.453 0.484 0.582
ND, not determined. Subjects were matched for age (schizophrenia (S)1 (serum) = 25±7 years; S2 (plasma) = 23±4 years; S3 (plasma) = 34±12 years; S4 (serum) = 30±7 years; bipolar disorder (BD) (serum) = 37±11 years) and body mass index (24±5 kg m2 across all cohorts). Cohorts were comprised (male/female) of the following: S1—controls (cont) = 12/5, schiz = 10/0; S2—cont = 21/0, schiz = 26/0; S3—cont = 6/4, schiz = 7/3; S4—cont = 9/11, schiz = 10/10; BD—cont = 5/5; BD = 5/5. Glucose was determined using the Dimension RXL system (Dade Behring, Dallas, TX, USA) (control levels = 4.6±0.8 mM). Insulin was determined using a two-step time-resolved fluorometric (TRF) assay9 (control levels = 75.1±58.6 pM). Proinsulin and des31,32-proinsulin were determined using two-site TRF assays7 (control levels = 4.9±4.4 and 5.9±5.2 pM, respectively). C-peptide was measured using the Immulite system (DPC Diagnostic Products Corp, Los Angeles, CA, USA) (control levels = 1.9±1.3 nM). Chromogranin A was measured using a two-site immunoassay kit (ALPCO Diagnostics, Salem, NH, USA) (control levels = 29.6±21.3 ng ml1). Fold change (FC) was calculated as the disease:control ratio of analyte levels. Statistical significance (P-value) was determined by two-tailed t-tests. Significant FC values are indicated in bold font.
disorder patients (Table 1), suggesting that these molecules are not altered in all neuropsychiatric disorders. Taken together, these findings show that hyperinsulinemia may have a role in the onset of schizophrenia. This has important implications, as elevated insulin levels can have deleterious effects on brain function.8 In addition, this suggests the possibility
that drugs that improve insulin signaling may represent a novel treatment strategy. In this regard, the insulin-related molecules identified here, and potentially other co-secreted insulin-secretory granule proteins, may have utility as biomarkers for patient stratification and for monitoring the responses to existing and novel therapeutic treatment strategies.
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PC Guest1, L Wang1, LW Harris1, K Burling2, Y Levin1, A Ernst1, MT Wayland1, Y Umrania1, M Herberth1, D Koethe3, JM van Beveren4, M Rothermundt5, G McAllister6, FM Leweke3,7, J Steiner8 and S Bahn1 1 Institute of Biotechnology, University of Cambridge, Cambridge, UK; 2NIHR Biomedical Research Centre, Department of Clinical Biochemistry, University of Cambridge, Cambridge, UK; 3 Department of Psychiatry and Psychotherapy, University of Cologne, Cologne, Germany; 4 Department of Psychiatry, Erasmus University Medical Centre, Rotterdam, Netherlands; 5 Department of Psychiatry, University Medical Faculty, Mu¨nster, Germany; 6Psynova Neurotech Ltd, St John’s Innovation Centre, Cambridge, UK; 7Central Institute of Mental Health, University of Heidelberg, Mannheim, Germany and 8Department of Psychiatry, University of Magdeburg, Magdeburg, Germany E-mail:
[email protected]
References 1 Holmes E, Tsang TM, Huang JT et al. PLoS Med 2006; 3: e327. 2 Spelman LM, Walsh PI, Sharifi N, Collins P, Thakore JH. Diabet Med 2007; 24: 481–485. 3 Newcomer JW. Am J Manag Care 2007; 13(Suppl): S170–S177. 4 Shanik MH, Xu Y, Skrha J, Dankner R, Zick Y, Roth J. Diabetes Care 2008; 31: S262–S268. 5 Guest PC, Bailyes EM, Rutherford NG, Hutton JC. J Biol Chem 1992; 274: 73–78. 6 Ferrier IN, Stanton BR, Kelly TP, Scott J. Br J Psychiatry 1999; 175: 246–251. 7 Sobey WJ, Beer SF, Carrington CA et al. Biochem J 1989; 260: 535–541. 8 Taguchi A, Wartschow LM, White MF. Science 2007; 317: 369–372. 9 Andersen L, Dinesen B, Jørgensen P, Poulson F, Røder M. Clin Chem 1993; 39: 578–582.
CACNA1C (rs1006737) is associated with schizophrenia Molecular Psychiatry (2010) 15, 119–121; doi:10.1038/mp.2009.69
In a large collaborative study combining three separate whole-genome association studies, the CACNA1C gene (rs1006737) was recently found to display a genome-wide significant association with bipolar disorder (BPD). Here, we report for the first time the Molecular Psychiatry
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significant association of the same SNP with schizophrenia (SZ), with the same risk allele and odds ratio as observed for BPD. Sklar et al.1 reported the association between CACNA1C and BPD for rs1006737 (P-value = 3.15 106) in a combined analysis of two genome-wide association studies (WTCCC and STEP-UCL dataset). Further evidence of the involvement of rs1006737 in BPD was found combining the WTCCC/STEP-UCL sample with a third genome-wide association study (ED-DUB-STEP2) (P = 7.0 10–8).2 The involvement of CACNA1C in BPD is therefore established with a high degree of certainty due to rs1006737 passing genomewide significance. Accumulating evidence suggests that BPD and SZ have some genetic risk factors in common.3,4 These results motivated us to test rs1006737 for association with SZ in a sample of 986 patients and 1501 control individuals collected in three Danish studies. All the studies were approved by the Danish Data Protection Agency and by the ethics committees in Denmark. Denmark I: This sample included 385 SZ patients and 780 controls matched on the basis of gender and date of birth. The patients were recruited to the Danish Psychiatric Biobank and diagnosed with SZ according to the ICD-10 criteria. The control individuals were ethnically Danish blood donors. Denmark II: This sample consisted of 366 SZ patients recruited from the Danish Newborn Screening Biobank.5 The patients, all born in Denmark, were diagnosed with SZ according to ICD-10 criteria. The patients are matched on the basis of gender and date of birth to at least one control individual from the Biobank. In total, 435 controls with no record of mental illness were included. Denmark III: This sample included 235 incident SZ patients and 286 medical student volunteers as controls. The patients were diagnosed according to ICD-10-DCR using SCAN interviews and a best estimate procedure. The patients and controls were of Danish parentage for three generations. Genotyping of individuals from the studies Denmark I and III was performed using genomic DNA isolated from blood samples. Individuals from the Denmark II
study were genotyped using whole genome-amplified DNA from neonatal dried blood spot samples.6 Rs1006737 was genotyped using the Sequenom MassARRAY System (Sequenom, San Diego, CA, USA) (primer sequences available on request). Call rate was 0.991, and no deviation from Hardy-Weinberg Equilibrium was observed among patients (P = 0.677) or controls (P = 0.448). A total of 22 individuals (10 patients and 12 controls) were removed from the analysis due to failed genotyping. A stratified association analysis was performed using the Cochran–Mantel–Haenszel test in the open-source software PLINK (http://pngu.mgh.harvard.edu/~purcell/plink/).7 For the Denmark I and Denmark II samples, each patient and their matched control(s) were treated as one cluster. The unmatched patients and controls from the Denmark III sample were analyzed as a single cluster. Significant association was found between rs1006737 and SZ: odds ratio (OR) = 1.16 and P = 0.015 (Table 1). In our combined Danish sample, the odds ratio and risk allele frequency of rs1006737 for SZ were similar to the results reported for BPD in the WTCCC/ STEP-UCL/ED-DUB-STEP2 study2 (Table 1). Thus, our finding suggests that CACNA1C is a common risk gene for both BPD and SZ. However, replication analyses in both BPD and SZ are warranted. It is unknown whether rs1006737 is the causal variant or whether the association is caused by a yet unidentified variant in linkage disequilibrium with rs1006737. In the Hapmap CEU data, the intronic rs1006737 shows complete linkage disequilibrium (r2 = 1), with five SNPs also positioned in the third intron of CACNA1C. Although rs1006737 may be used as a predictive marker, identification of the true susceptibility variant remains challenging and will involve replication, re-sequencing and functional studies. CACNA1C encodes the a 1C subunit (Cav 1.2) of the L-type voltage-dependent calcium channel. Calcium influx through such channels is coupled to signaling pathways that stimulate the expression of genes essential for neuronal survival and plasticity,8 and rare mutations in CACNA1C are known to cause cognitive abnormalities and autism.9 The association
Table 1 Association analysis of schizophrenia (SZ) and rs1006737 compared with the genome-wide association study of bipolar disorder (BPD) reported by Ferreira et al.2 Chromosome 12p13 (CACNA1C)
For comparison Schizophrenia (combined Denmark I, II and III)
Genotype counts (AA/AG/GG) SNP, minor allele
SZ (n = 976)
CON (n = 1489)
rs1006737, A
130/444/402
158/675/656
Bipolar disorder (combined WTCCC/STEP-UCL/ED-DUB-STEP2)
MAF SZ
CON
0.361 0.333
MAF P-value
OR
BPD (n = 4387)
CON (n = 6209)
P-value
OR
0.015
1.160
0.356
0.324
7.0 108
1.181
Abbreviations: BPD, bipolar disorder; CON, control individuals; MAF, minor allele frequency; OR, odds ratio; SNP, single nucleotide polymorphism; SZ, schizophrenia; WTCCC, Wellcome Trust Case-Control Consortium. Molecular Psychiatry
Letters to the Editor
of CACNA1C with BPD and SZ therefore suggests that the two disorders are partly ion-channelopathies. The possible involvement of calcium channels and CACNA1C is also intriguing, as some antiepileptic drugs used to manage symptoms in BPD and SZ are known to affect voltage-gated sodium or calcium channels.10
University, Copenhagen, Denmark; 7Research Institute of Biological Psychiatry, MHC Sct. Hans, Copenhagen University Hospital, Copenhagen, Denmark and 8National Centre for Register-based Research, University of Aarhus, Aarhus, Denmark E-mail:
[email protected]
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Conflict of interest The authors declare no conflict of interest.
References
M Nyegaard1, D Demontis1, L Foldager2,3, A Hedemand1, TJ Flint2, KM Sørensen4, PS Andersen5, M Nordentoft6, T Werge7, CB Pedersen8, DM Hougaard4, PB Mortensen8, O Mors2 and AD Børglum1,2 1 Department of Human Genetics, Aarhus University, Aarhus, Denmark; 2Centre for Psychiatric Research, Aarhus University Hospital, Risskov, Denmark; 3 BiRC - Bioinformatics Research Center, Aarhus University, Aarhus, Denmark; 4Department of Clinical Biochemistry and Immunology, Statens Serum Institut, Copenhagen, Denmark; 5National Center for Antimicrobials and Infection Control, Statens Serum Institut, Copenhagen, Denmark; 6Psychiatric Centre Bispebjerg, Faculty of Health Science, Copenhagen
1 Sklar P, Smoller JW, Fan J, Ferreira MA, Perlis RH, Chambert K et al. Mol Psychiatry 2008; 13: 558–569. 2 Ferreira MA, O’Donovan MC, Meng YA, Jones IR, Ruderfer DM, Jones L et al. Nat Genet 2008; 40: 1056–1058. 3 Craddock N, O’Donovan MC, Owen MJ. Schizophr Bull 2009; 35: 482–490. 4 Moskvina V, Craddock N, Holmans P, Nikolov I, Pahwa JS, Green E et al. Mol Psychiatry 2009; 14: 252–260. 5 Norgaard-Pedersen B, Hougaard DM. J Inherit Metab Dis 2007; 30: 530–536. 6 Sorensen KM, Jespersgaard C, Vuust J, Hougaard D, NorgaardPedersen B, Andersen PS. Genet Test 2007; 11: 65–71. 7 Purcell S, Neale B, Todd-Brown K, Thomas L, Ferreira MA, Bender D et al. Am J Hum Genet 2007; 81: 559–575. 8 Dolmetsch RE, Pajvani U, Fife K, Spotts JM, Greenberg ME. Science 2001; 294: 333–339. 9 Splawski I, Timothy KW, Sharpe LM, Decher N, Kumar P, Bloise R et al. Cell 2004; 119: 19–31. 10 Landmark CJ. CNS Drugs 2008; 22: 27–47.
Molecular Psychiatry
