Javier Costas

Common variants conferring risk of schizophrenia

Schizophrenia is a complex disorder, caused by both genetic and environmental factors and their interactions. Research on pathogenesis has traditionally focused on neurotransmitter systems in the brain, particularly those involving dopamine. Schizophrenia has been considered a separate disease for over a century, but in the absence of clear biological markers, diagnosis has historically been based on signs and symptoms. A fundamental message emerging from genome-wide association studies of copy number variations (CNVs) associated with the disease is that its genetic basis does not necessarily conform to classical nosological disease boundaries. Certain CNVs confer not only high relative risk of schizophrenia but also of other psychiatric disorders. The structural variations associated with schizophrenia can involve several genes and the phenotypic syndromes, or the ‘genomic disorders’, have not yet been characterized. Single nucleotide polymorphism (SNP)-based genome-wide association studies with the potential to implicate individual genes in complex diseases may reveal underlying biological pathways. Here we combined SNP data from several large genome-wide scans and followed up the most significant association signals. We found significant association with several markers spanning the major histocompatibility complex (MHC) region on chromosome 6p21.3-22.1, a marker located upstream of the neurogranin gene (NRGN) on 11q24.2 and a marker in intron four of transcription factor 4 (TCF4) on 18q21.2. Our findings implicating the MHC region are consistent with an immune component to schizophrenia risk, whereas the association with NRGN and TCF4 points to perturbation of pathways involved in brain development, memory and cognition.

Common Variants at VRK2 and TCF4 Conferring Risk of Schizophrenia

Common sequence variants have recently joined rare structural polymorphisms as genetic factors with strong evidence for association with schizophrenia. Here we extend our previous genome-wide association study and meta-analysis (totalling 7 946 cases and 19 036 controls) by examining an expanded set of variants using an enlarged follow-up sample (up to 10 260 cases and 23 500 controls). In addition to previously reported alleles in the major histocompatibility complex region, near neurogranin (NRGN) and in an intron of transcription factor 4 (TCF4), we find two novel variants showing genome-wide significant association: rs2312147[C], upstream of vaccinia-related kinase 2 (VRK2) [odds ratio (OR) = 1.09, P = 1.9 × 10(-9)] and rs4309482[A], between coiled-coiled domain containing 68 (CCDC68) and TCF4, about 400 kb from the previously described risk allele, but not accounted for by its association (OR = 1.09, P = 7.8 × 10(-9)).

Identification of new putative susceptibility genes for several psychiatric disorders by association analysis of regulatory and non-synonymous SNPs of 306 genes involved in neurotransmission and neurodevelopment†‡

A fundamental difficulty in human genetics research is the identification of the spectrum of genetic variants that contribute to the susceptibility to common/complex disorders. We tested here the hypothesis that functional genetic variants may confer susceptibility to several related common disorders. We analyzed five main psychiatric diagnostic categories (substance‐abuse, anxiety, eating, psychotic, and mood disorders) and two different control groups, representing a total of 3,214 samples, for 748 promoter and non‐synonymous single nucleotide polymorphisms (SNPs) at 306 genes involved in neurotransmission and/or neurodevelopment. We identified strong associations to individual disorders, such as growth hormone releasing hormone (GHRH) with anxiety disorders, prolactin regulatory element (PREB) with eating disorders, ionotropic kainate glutamate receptor 5 (GRIK5) with bipolar disorder and several SNPs associated to several disorders, that may represent individual and related disease susceptibility factors. Remarkably, a functional SNP, rs945032, located in the promoter region of the bradykinin receptor B2 gene (BDKRB2) was associated to three disorders (panic disorder, substance abuse, and bipolar disorder), and two additional BDKRB2 SNPs to obsessive‐compulsive disorder and major depression, providing evidence for common variants of susceptibility to several related psychiatric disorders. The association of BDKRB2 (odd ratios between 1.65 and 3.06) to several psychiatric disorders supports the view that a common genetic variant could confer susceptibility to clinically related phenotypes, and defines a new functional hint in the pathophysiology of psychiatric diseases.

Mood changes after delivery: role of the serotonin transporter gene

BACKGROUND Polymorphic variations in the serotonin transporter gene (5-HTT) moderate the depressogenic effects of tryptophan depletion. After childbirth there is a sharp reduction in brain tryptophan availability, thus polymorphic variations in 5-HTT may play a similar role in the post-partum period. AIMS To study the role of 5-HTT polymorphic variations in mood changes after delivery. METHOD One thousand, eight hundred and four depression-free Spanish women were studied post-partum. We evaluated depressive symptoms at 2-3 days, 8 weeks and 32 weeks post-partum. We used diagnostic interview to confirm major depression for all probable cases. Based on two polymorphisms of 5-HTT (5-HTTLPR and STin2 VNTR), three genotype combinations were created to reflect different levels of 5-HTT expression. RESULTS One hundred and seventy-three women (12.7%) experienced major depression during the 32-week post-partum period. Depressive symptoms were associated with the high-expression 5-HTT genotypes in a dose-response fashion at 8 weeks post-partum, but not at 32 weeks. CONCLUSIONS High-expression 5-HTT genotypes may render women more vulnerable to depressive symptoms after childbirth.

Heterozygosity at catechol-O-methyltransferase Val158Met and schizophrenia: New data and meta-analysis

Catechol-O-methyltransferase (COMT) has been largely studied in relation to schizophrenia susceptibility. Most studies focused on the functional single nucleotide polymorphism (SNP) rs4680 that causes a substitution of Val by Met at codon 158 of the COMT protein. Recent meta-analyses do not support an association between allelic variants at rs4680 and schizophrenia. However, the putative role of overdominance has not been tested in meta-analyses, despite its biological plausibility. In this work, we tested the overdominant model in two Spanish samples (from Valencia and Santiago de Compostela), representing a total of 762 schizophrenic patients and 1042 controls, and performed a meta-analysis of the available studies under this model. A total of 51 studies comprising 13,894 schizophrenic patients and 16,087 controls were included in the meta-analysis, that revealed a small but significant protective effect for heterozygosity at rs4680 (pooled OR=0.947, P=0.023). Post-hoc analysis on southwestern European samples suggested a stronger effect in these populations (pooled OR=0.813, P=0.0009). Thus, the COMT functional polymorphism rs4680 contributes to schizophrenia genetic susceptibility under an overdominant model, indicating that both too high and too low levels of dopamine (DA) signalling may be risk factors. This effect can be modulated by genetic background.

Interaction between COMT haplotypes and cannabis in schizophrenia: A case-only study in two samples from Spain

Cannabis use is one of the environmental factors with more solid evidence contributing to schizophrenia risk, especially in genetically susceptible individuals. One of the genes that may interact with cannabis is COMT, although available data are scarce. Here, we present a case-only study of the putative COMT-cannabis interaction in schizophrenia. Two Spanish samples from Santiago de Compostela and Valencia were screened for cannabis use. One hundred and fifty five individuals from a total of 748 patients were identified as cannabis users. Five SNPs in COMT, defining three common functional haplotypes with different enzymatic activities, were genotyped and analyzed for association at the SNP, haplotype and genotype levels. An association was detected between cannabis use and low activity variants (P<0.01) in the joint analysis and results were consistent between the two samples. Schizophrenic subjects homozygous for the Met allele at rs4680 doubled the probability of lifetime prevalence of cannabis use in comparison to Val homozygous (Mantel-Haenszel OR=2.07, 95% CI: 1.27-3.26, P=0.0031, in the combined sample). These data are in contrast to those from Caspi et al. (Biol. Psychiatry 57 (2005)1117-1127) who found association between schizophrenia/schizophreniform disorder and homozygosity at the high activity Val variant of rs4680. The results of our study are discussed in the context of previous findings, suggesting the involvement of COMT polymorphisms in the association between cannabis use and schizophrenia as well as the existence of additional factors mediating this association. However, further research is needed to confirm the COMT-cannabis interaction.

Association Study of Nonsynonymous Single Nucleotide Polymorphisms in Schizophrenia

BACKGROUND Genome-wide association studies using several hundred thousand anonymous markers present limited statistical power. Alternatively, association studies restricted to common nonsynonymous single nucleotide polymorphisms (nsSNPs) have the advantage of strongly reducing the multiple testing problem, while increasing the probability of testing functional single nucleotide polymorphisms (SNPs). METHODS We performed a case-control association study of common nsSNPs in Galician (northwest Spain) samples using the Affymetrix GeneChip Human 20k cSNP Kit, followed by a replication study of the more promising results. After quality control procedures, the discovery sample consisted of 5100 nsSNPs at minor allele frequency >5% analyzed in 476 schizophrenia patients and 447 control subjects. The replication sample consisted of 4069 cases and 15,128 control subjects of European origin. We also performed multilocus analysis, using aggregated scores of nsSNPs at liberal significance thresholds and cross-validation procedures. RESULTS The 5 independent nsSNPs with false discovery rate q ≤ .25, as well as 13 additional nsSNPs at p < .01 and located in functional candidate genes, were genotyped in the replication samples. One SNP, rs13107325, located at the metal ions transporter gene SLC39A8, reached significance in the combined sample after Bonferroni correction (trend test, p = 2.7 × 10(-6), allelic odds ratio = 1.32). This SNP presents minor allele frequency of 5% to 10% in many European populations but is rare outside Europe. We also confirmed the polygenic component of susceptibility. CONCLUSIONS Taking into account that another metal ions transporter gene, SLC39A3, is associated to bipolar disorder, our findings reveal a role for brain metal homeostasis in psychosis.

Evolutionary Dynamics of the Human Endogenous Retrovirus Family HERV-K Inferred from Full-Length Proviral Genomes

Abstract. Several distinct families of endogenous retroviruses exist in the genomes of primates. Most of them are remnants of ancient germ-line infections. The human endogenous retrovirus family HERV-K represents the unique known case of endogenous retrovirus that amplified in the human genome after the divergence of human and chimpanzee lineages. There are two types of HERV-K proviral genomes differing by the presence or absence of 292 bp in the pol-env boundary. Human-specific insertions exist for both types. The analyses shown in the present work reveal that several lineages of type 1 and type 2 HERV-K proviruses remained transpositionally active after the human/chimpanzee split. The data also reflect the important role of mosaic evolution (either by recombination or gene conversion) during the evolutionary history of HERV-K.

Association study of 44 candidate genes with depressive and anxiety symptoms in post-partum women

The post-partum period is a time of extreme vulnerability for a whole spectrum of psychiatric disorders. Delivery may be considered an important risk factor in genetically susceptible women. Five hundred and eight SNPs in 44 genes at candidate pathways putatively related to mood changes after delivery were genotyped in a multicenter cohort of 1804 women from Spain. Participants completed two scales at 2-3 days, 8 weeks, and 32 weeks post-partum, the Edinburgh Post-partum Depression Scale (EPDS) and the Spielberger State-Trait Anxiety Inventory (STAI). Those women who scored 9 or more on EPDS were evaluated for major depression using the Diagnostic Interview for Genetics Studies (DIGS) adapted for post-partum depression. Association with major depression was assessed using likelihood ratio tests under a codominant genotype model. Association with scale scores was tested using linear mixed models to take into account repeated measures over time. Two intronic SNPs, one at the serotonin transporter gene (SLC6A4) and another at dopa decarboxylase (DDC), were significantly associated to STAI anxiety scores after multiple testing correction (nominal P=0.0000513 and 0.000097, respectively). In addition, post hoc analysis at the unphased haplotype level using nominal significant SNPs revealed an association with a combination of three SNPs at protein kinase C, beta (PRKCB) with major depression, significant after multiple testing correction (nominal global P=0.0001596). In conclusion, we detected a role of SLC6A4 in mood changes after stressful events, and revealed new putative associations involving DDC and PRKCB. Therefore, these genes deserve further investigation to confirm these results.

Genetic variation in the nuclear factor κB pathway in relation to susceptibility to rheumatoid arthritis

Objective: To examine genetic association between rheumatoid arthritis (RA) and known polymorphisms in core genes of the nuclear factor (NF)κB pathway, the major intracellular pathway in RA pathogenesis. Methods: Discovery and replication sample sets of Spanish patients with RA and controls were studied. A total of 181 single nucleotide polymorphisms (SNPs) uniformly spaced along the genomic sequences of 17 core genes of the NFκB pathway (REL, RELA, RELB, NFKB1, NFKB2, NFKBIA, NFKBIB, NFKBIE, IKBKA, IKBKB, IKBKE, IKBKAP, KBRAS1, KBRAS2, MAP3K1, MAP3K14, TAX1BP1) were studied by mass spectrometry analysis complemented with 5′-nuclease fluorescence assays in the discovery set, 458 patients with RA and 657 controls. SNPs showing nominal significant differences were further investigated in the replication set of 1189 patients with RA and 1092 controls. Results: No clear reproducible association was found, although 12 SNPs in IKBKB, IKBKE and REL genes showed significant association in the discovery set. Interestingly, two of the SNPs in the IKBKE gene, weakly associated in the discovery phase, showed a trend to significant association in the replication phase. Pooling both sample sets together, the association with these two SNPs was significant. Conclusion: We did not find any major effect among the explored members of the NFκB pathway in RA susceptibility. However, it is possible that variation in the IKBKE gene could have a small effect that requires replication in additional studies.