Persistence criteria for susceptibility genes for schizophrenia: a discussion from an evolutionary viewpoint

A biocultural approach to psychiatric illnesses

RATIONALE

As a species, humans are vulnerable to numerous mental disorders, including depression and schizophrenia. This susceptibility may be due to the evolution of our large, complex brains, or perhaps because these illnesses counterintuitively confer some adaptive advantage. Additionally, cultural and biological factors may contribute to susceptibility and variation in mental illness experience and expression. Taking a holistic perspective could strengthen our understanding of these illnesses in diverse cultural contexts.

OBJECTIVES

This paper reviews some of these potential factors and contextualizes mental disorders within a biocultural framework.

RESULTS

There is growing evidence that suggests cultural norms may influence inflammation, neurotransmitters, and neurobiology, as well as the illness experience. Specific examples include variation in schizophrenia delusions between countries, differences in links between inflammation and emotion between the United States and Japan, and differences in brain activity between Caucasian and Asian participants indicating that cultural values may moderate cognitive processes related to social cognition and interoception.

CONCLUSIONS

Research agendas that are grounded in an appreciation of biocultural diversity as it relates to psychiatric illness represent key areas for truly interdisciplinary research that can result in culturally sensitive treatments and highlight possible biological variation affecting medical treatment.

Proteostasis and Mitochondrial Role on Psychiatric and Neurodegenerative Disorders: Current Perspectives

Proteostasis involves processes that are fundamental for neural viability. Thus, protein misfolding and the formation of toxic aggregates at neural level, secondary to dysregulation of the conservative mechanisms of proteostasis, are associated with several neuropsychiatric conditions. It has been observed that impaired mitochondrial function due to a dysregulated proteostasis control system, that is, ubiquitin-proteasome system and chaperones, could also have effects on neurodegenerative disorders. We aimed to critically analyze the available findings regarding the neurobiological implications of proteostasis on the development of neurodegenerative and psychiatric diseases, considering the mitochondrial role. Proteostasis alterations in the prefrontal cortex implicate proteome instability and accumulation of misfolded proteins. Altered mitochondrial dynamics, especially in proteostasis processes, could impede the normal compensatory mechanisms against cell damage. Thereby, altered mitochondrial functions on regulatory modulation of dendritic development, neuroinflammation, and respiratory function may underlie the development of some psychiatric conditions, such as schizophrenia, being influenced by a genetic background. It is expected that with the increasing evidence about proteostasis in neuropsychiatric disorders, new therapeutic alternatives will emerge.

Neuropsychiatric Features in Primary Mitochondrial Disease

Mitochondrial diseases are a clinically heterogeneous group of disorders that ultimately result from dysfunction of the mitochondrial respiratory chain. There is some evidence to suggest that mitochondrial dysfunction plays a role in neuropsychiatric illness; however, the data are inconclusive. This article summarizes the available literature published in the area of neuropsychiatric manifestations in both children and adults with primary mitochondrial disease, with a focus on autism spectrum disorder in children and mood disorders and schizophrenia in adults.

Mitochondrial dysfunction in schizophrenia: an evolutionary perspective

Schizophrenia (SCZ) is a severe psychiatric illness with a lifetime prevalence of 0.4 %. A disturbance of energy metabolism has been suggested as part of the etiopathogenesis of the disorder. Several lines of evidence have proposed a connection between etiopathogenesis of SCZ and human brain evolution, which was characterized by an increase in the energy requirement, demanding a co-evolution of the mitochondrial system. Mitochondria are key players in brain energy homeostasis and multiple lines of evidence suggest that the system is disrupted in SCZ. In this review, we will describe the current knowledge on pathways/system involved in the human brain evolution as well as the main theories regarding the evolutionary origin of SCZ. We will furthermore discuss the role of mitochondria in the context of brain energy metabolism and its role in the etiopathogenesis of SCZ. Understanding SCZ in the context of human brain evolution opens a new perspective to elucidate pathophysiological mechanisms involved in the origin and/or portions of the complex symptomatology of this severe mental disorder.

Molecular evolution in the CREB1 signal pathway and a rare haplotype in CREB1 with genetic predisposition to schizophrenia

CREB1 is a cAMP responsive transcriptional factor which plays a key role in neural development. CREB1 signal pathway (CSP) has been implicated repeatedly in studies of predisposition for schizophrenia. We speculated that CSP has undergone positive selection during evolution of modern human and some genes that have undergone natural selection in the past may predispose to schizophrenia (SCZ) in modern time. Positive selection and association analysis were employed to explore the molecular evolution of CSP and association with schizophrenia. Our results showed a pan-ethnic selection event on NRG1 and CREB1, as confirmed in all 14 ethnic populations studied, which also suggested a selection process occurred before the "Out of Africa" scenario. Analysis of 62 SNPs covering 6 CSP genes in 2019 Han Chinese (976 SCZ patients and 1043 healthy individuals) showed an association of two SNPs (rs4379857, P = 0.009, OR [95% CI]: 1.200 [1.379-1.046]; rs2238751, P = 0.023, OR [95% CI]: 1.253 [1.522-1.032]) with SCZ. However, none of these significances survived after multiple testing corrections. Nonetheless, we observed an association of a rare CREB1 haplotype CCGGC (Bonferroni corrected P = 1.74 × 10(-5)) with SCZ. Our study showed that there was substantial population heterogeneity in genetic predisposition to SCZ, and different genes in the CSP pathway may predispose to SCZ in different populations.

TMPRSS9 and GRIN2B are associated with neuroticism: a genome-wide association study in a European sample

Major depression disorder (MDD) is a complex and chronic disease that ranks fourth as cause of disability worldwide. About 14 million adults in the USA are believed to have MDD, and an estimated 75 % attempt suicide making MDD a major public health problem. Neuroticism has been recognized as an endophenotype of MDD; however, few genome-wide association (GWA) analyses of neuroticism as a quantitative trait have been reported to date. The aim of this study is to identify genome-wide genetic variants affecting neuroticism using a European sample. A linear regression model was used to analyze the association with neuroticism as a continuous trait in the Netherlands Study of Depression and Anxiety and Netherlands Twin Registry population-based sample of 2,748 individuals with Perlegen 600K single nucleotide polymorphisms (SNPs). In addition, the neuroticism-associated genes/loci of the top 20 SNPs (p < 10⁻⁴) were examined with anti-social personality disorder (ASPD) in an Australian twin family study. Through GWA analysis, 32 neuroticism-associated SNPs (p < 10⁻⁴) were identified. The most significant association was observed with SNP rs4806846 within the TMPRSS9 gene (p = 7.79 × 10⁻⁶) at 19p13.3. The next best signal was in GRIN2B gene (rs220549, p = 1.05 × 10⁻⁵) at 12p12. In addition, several SNPs within GRIN2B showed borderline associations with ASPD in the Australian sample. In conclusion, these results provide a possible genetic basis for the association with neuroticism. Our findings provide a basis for replication in other populations to elucidate the potential role of these genetic variants in neuroticism and MDD along with a possible relationship between ASPD and neuroticism.

Association study of OPRM1 polymorphisms with Schizophrenia in Han Chinese population

BACKGROUND

The expression of μ-opioid receptor has important role in cognitive dysfunction in Schizophrenia (SZ). The results of studies about the association of polymorphisms of μ-opioid receptor gene (OPRM1) with SZ were inconsistent.

METHODS

We conducted a case-control study to investigate the genetic association between OPRM1 polymorphisms and SZ among the Han chinese population. 264 SZ patients and 264 age-matched control subjects were recruited. Four SNPs of OPRM1 were successfully genotyped by using PCR-RFLP.

RESULTS

Of four polymorphisms, rs1799971 and rs2075572 were shown to associate with SZ. Compared with the A allele of rs1799971 and C allele of rs2075572, the G allele of rs1799971 and rs2075572 was associated with an almost 0.46-fold risk (OR=0.46, 95% CI: 0.357-0.59, P<0.01) and 0.7-fold risk (OR=0.707, 95% CI: 0.534-0.937, P=0.015) of the occurrence of SZ,. When subjects were divided by gender, rs1799971 remained significant difference only in males (OR=0.309, 95% CI: 0.218-0.439 for G allele, P<0.01), and rs2075572 only in females (OR=0.399, 95% CI: 0.246-0.648 for G allele, P<0.01). In secondary analysis with subsets of patients, the G allele of rs1799971 (compared to the A allele) was associated with a decreased risk of all patients and male patients with apathy symptoms (OR=0.086, 95% CI: 0.048-0.151, P=0.01; OR=0.083, 95% CI: 0.045-0.153, P<0.01), and the G allele of rs2075572 (compared to the C allele) was associated with a decreased risk of all patients and female patients with positive family history (OR=0.468, 95% CI: 0.309-0.71, P<0.01; OR=0.34, 95% CI: 0.195-0.593, P<0.01). In addition, haplotype analysis revealed that two SNP haplotypes (A-C-C-G and G-C-C-A) were associated with decreased risks of SZ (P<0.01). The other two (G-C-C-G and G-G-C-G) with increased risks of SZ (P<0.01).

CONCLUSIONS

The present study demonstrated for the first time that the OPRM1 polymorphism may be a risk factor for schizophrenia in the Han Chinese. Further studies are needed to give a global view of this polymorphism in pathogenesis of schizophrenia in a large-scale sample, family-based association design or well-defined subgroups of schizophrenia.

No evidence that major mtDNA European haplogroups confer risk to schizophrenia

Previous studies suggest that genetic factors could be involved in mitochondrial dysfunction observed in schizophrenia (SZ), some of them claiming a role of mtDNA common variants (mtSNPs) and/or haplogroups (hgs) in developing this disorder. These studies, however, have mainly been undertaken on relatively small cohorts of patients and control individuals and most have not yet been replicated. To further analyze the role of mtSNPs in SZ risk, we have carried out the largest genotyping effort to date using two Spanish case-control samples comprising a total of 942 schizophrenic patients and 1,231 unrelated controls: 454 patients and 616 controls from Santiago de Compostela (Galicia) and 488 patients and 615 controls from Reus (Catalonia). A set of 25 mtSNPs representing main branches of the European mtDNA phylogeny were genotyped in the Galician cohort and a subset of 16 out of these 25 mtSNPs was genotyped in the Catalan cohort. These 16 common variants characterize the most common European branches of the mtDNA phylogeny. We did not observe any positive association of mtSNPs and hgs with SZ. We discuss several deficiencies of previous studies that might explain the false positive nature of previous findings, including the confounding effect of population sub-structure and deficient statistical methodologies. It is unlikely that mtSNPs defining the most common European mtDNA haplogroups are related to SZ.

Paradox of schizophrenia genetics: is a paradigm shift occurring?

BACKGROUND

Genetic research of schizophrenia (SCZ) based on the nuclear genome model (NGM) has been one of the most active areas in psychiatry for the past two decades. Although this effort is ongoing, the current situation of the molecular genetics of SCZ seems disappointing or rather perplexing. Furthermore, a prominent discrepancy between persistence of the disease at a relatively high prevalence and a low reproductive fitness of patients creates a paradox. Heterozygote advantage works to sustain the frequency of a putative susceptibility gene in the mitochondrial genome model (MGM) but not in the NGM.

METHODS

We deduced a criterion that every nuclear susceptibility gene for SCZ should fulfill for the persistence of the disease under general assumptions of the multifactorial threshold model. SCZ-associated variants listed in the top 45 in the SZGene Database (the version of the 23rd December, 2011) were selected, and the distribution of the genes that could meet or do not meet the criterion was surveyed.

RESULTS

19 SCZ-associated variants that do not meet the criterion are located outside the regions where the SCZ-associated variants that could meet the criterion are located. Since a SCZ-associated variant that does not meet the criterion cannot be a susceptibility gene, but instead must be a protective gene, it should be linked to a susceptibility gene in the NGM, which is contrary to these results. On the other hand, every protective gene on any chromosome can be associated with SCZ in the MGM. Based on the MGM we propose a new hypothesis that assumes brain-specific antioxidant defenses in which trans-synaptic activations of dopamine- and N-methyl-d-aspartate-receptors are involved. Most of the ten predictions of this hypothesis seem to accord with the major epidemiological facts and the results of association studies to date.

CONCLUSION

The central paradox of SCZ genetics and the results of association studies to date argue against the NGM, and in its place the MGM is emerging as a viable option to account for genomic and pathophysiological research findings involving SCZ.

Molecular links between mitochondrial dysfunctions and schizophrenia

Schizophrenia is a complex neuropsychiatric disorder with both neurochemical and neurodevelopmental components in the pathogenesis. Growing pieces of evidence indicate that schizophrenia has pathological components that can be attributable to the abnormalities of mitochondrial function, which is supported by the recent finding suggesting mitochondrial roles for Disrupted-in-Schizophrenia 1 (DISC1). In this minireview, we briefly summarize the current understanding of the molecular links between mitochondrial dysfunctions and the pathogenesis of schizophrenia, covering recent findings from human genetics, functional genomics, proteomics, and molecular and cell biological approaches.

Schizophrenia: maternal inheritance and heteroplasmy of mtDNA mutations

Role of mitochondrial pathology in schizophrenia has not been fully clarified. We searched for distinctive variants in mtDNA extracted from the gray matter of postmortem brains and from peripheral blood samples. We screened mtDNA region containing 5 genes encoding subunits of cytochrome c oxidase and ATPases. Polymorphisms not already reported in databases are recorded as unregistered rare variants. Four unregistered, non-synonymous rare variants were detected in 4 schizophrenic samples. Seven registered non-synonymous variants were not previously detected in non-psychotic Japanese samples registered in the mtSNP database. These variants may contribute to disease pathophysiology. In one family, compound mutations showed co-segregation with schizophrenia. MtDNA mutations could confer a risk for schizophrenia in the Japanese population, although further analyses are needed.

Genomics and pharmacogenomics of schizophrenia

Schizophrenia (SCZ) is among the most disabling of mental disorders. Several neurobiological hypotheses have been postulated as responsible for SCZ pathogenesis: polygenic/multifactorial genomic defects, intrauterine and perinatal environment-genome interactions, neurodevelopmental defects, dopaminergic, cholinergic, serotonergic, gamma-aminobutiric acid (GABAergic), neuropeptidergic and glutamatergic/N-Methyl-D-Aspartate (NMDA) dysfunctions, seasonal infection, neuroimmune dysfunction, and epigenetic dysregulation. SCZ has a heritability estimated at 60-90%. Genetic studies in SCZ have revealed the presence of chromosome anomalies, copy number variants, multiple single-nucleotide polymorphisms of susceptibility distributed across the human genome, aberrant single nucleotide polymorphisms (SNPs) in microRNA genes, mitochondrial DNA mutations, and epigenetic phenomena. Pharmacogenetic studies of psychotropic drug response have focused on determining the relationship between variation in specific candidate genes and the positive and adverse effects of drug treatment. Approximately, 18% of neuroleptics are major substrates of CYP1A2 enzymes, 40% of CYP2D6, and 23% of CYP3A4; 24% of antidepressants are major substrates of CYP1A2 enzymes, 5% of CYP2B6, 38% of CYP2C19, 85% of CYP2D6, and 38% of CYP3A4; 7% of benzodiazepines are major substrates of CYP2C19 enzymes, 20% of CYP2D6, and 95% of CYP3A4. About 10-20% of Western populations are defective in genes of the CYP superfamily. Only 26% of Southern Europeans are pure extensive metabolizers for the trigenic cluster integrated by the CYP2D6+CYP2C19+CYP2C9 genes. The pharmacogenomic response of SCZ patients to conventional psychotropic drugs also depends on genetic variants associated with SCZ-related genes. Consequently, the incorporation of pharmacogenomic procedures both to drugs in development and drugs on the market would help to optimize therapeutics in SCZ and other central nervous system (CNS) disorders.

Association study of RELN polymorphisms with schizophrenia in Han Chinese population

Schizophrenia (SZ) is a common and complex psychiatric disorder with a strong genetic component. Previous research suggests that mutations altering genes in neurodevelopmental pathways contribute to SZ. Reelin gene (RELN) maps to chromosome 7q22.1, the encoded protein plays a pivotal role in guiding neuronal migration, lamination and connection during embryonic brain development. Several reports had indicated that reduced RELN expression is associated with human mental illnesses such as SZ, mood disorders and autism. In this study, case-control association analyses were performed in the Han Chinese population to determine if the RELN gene is a susceptibility gene for SZ. Thirty-seven single nucleotide polymorphisms (SNPs) were genotyped in 528 paranoid SZ patients and 528 control subjects. A significant association was found between rs12705169 and SZ (p=0.001). Moreover, the haplotypes constructed from five SNPs showed significant differences between cases and controls (p=0.041). When subjects were divided by gender, rs12705169 remained significant difference only in females (OR=0.24, 95%CI=0.14-0.40 for CC and OR=0.40, 95%CI=0.27-0.58 for AC), both in the allele and genotype (p=0.0001 for both). This study describes a positive association between RELN and SZ in the Han Chinese population, and provides genetic evidence to support the gender difference of SZ.

Reduced fertility in patients' families is consistent with the sexual selection model of schizophrenia and schizotypy

Background

Schizophrenia is a mental disorder marked by an evolutionarily puzzling combination of high heritability, reduced reproductive success, and a remarkably stable prevalence. Recently, it has been proposed that sexual selection may be crucially involved in the evolution of schizophrenia. In the sexual selection model (SSM) of schizophrenia and schizotypy, schizophrenia represents the negative extreme of a sexually selected indicator of genetic fitness and condition. Schizotypal personality traits are hypothesized to increase the sensitivity of the fitness indicator, thus conferring mating advantages on high-fitness individuals but increasing the risk of schizophrenia in low-fitness individuals; the advantages of successful schzotypy would be mediated by enhanced courtship-related traits such as verbal creativity. Thus, schizotypy-increasing alleles would be maintained by sexual selection, and could be selectively neutral or even beneficial, at least in some populations. However, most empirical studies find that the reduction in fertility experienced by schizophrenic patients is not compensated for by increased fertility in their unaffected relatives. This finding has been interpreted as indicating strong negative selection on schizotypy-increasing alleles, and providing evidence against sexual selection on schizotypy.

Methodology

A simple mathematical model is presented, showing that reduced fertility in the families of schizophrenic patients can coexist with selective neutrality of schizotypy-increasing alleles, or even with positive selection on schizotypy in the general population. If the SSM is correct, studies of patients' families can be expected to underestimate the true fertility associated with schizotypy.

Significance

This paper formally demonstrates that reduced fertility in the families of schizophrenic patients does not constitute evidence against sexual selection on schizotypy-increasing alleles. Futhermore, it suggests that the fertility estimates derived from extant studies may be biased to an unknown extent. These results have important implications for the evolutionary genetics of psychosis.

Mitochondrial DNA (mtDNA) and schizophrenia

The poorly understood aetiology of schizophrenia is known to involve a major genetic contribution even though the genetic factors remain elusive. Most genetic studies are based on Mendelian rules and focus on the nuclear genome, but current studies indicate that other genetic mechanisms are probably involved. This review focuses on mitochondrial DNA (mtDNA), a maternally inherited, 16.6-Kb molecule crucial for energy production that is implicated in numerous human traits and disorders. The aim of this review is to summarise the studies that have explored mtDNA in schizophrenia patients and those which provide evidence for its implication in this illness. Alterations in mitochondrial morphometry, brain energy metabolism, and enzymatic activity in the mitochondrial respiratory chain suggest a mitochondrial dysfunction in schizophrenia that could be related to the genetic characteristics of mtDNA. Moreover, evidence of maternal inheritance and the presence of schizophrenia symptoms in patients suffering from a mitochondrial disorder related to an mtDNA mutation suggest that mtDNA is involved in schizophrenia. The association of specific variants has been reported at the molecular level; however, additional studies are needed to determine whether the mitochondrial genome is involved in schizophrenia.

SMARCA2 and other genome-wide supported schizophrenia-associated genes: regulation by REST/NRSF, network organization and primate-specific evolution

The SMARCA2 gene, which encodes BRM in the SWI/SNF chromatin-remodeling complex, was recently identified as being associated with schizophrenia (SZ) in a genome-wide approach. Polymorphisms in SMARCA2, associated with the disease, produce changes in the expression of the gene and/or in the encoded amino acid sequence. We show here that an SWI/SNF-centered network including the Smarca2 gene is modified by the down-regulation of REST/NRSF in a mouse neuronal cell line. REST/NRSF down-regulation also modifies the levels of Smarce1, Smarcd3 and SWI/SNF interactors (Hdac1, RcoR1 and Mecp2). Smarca2 down-regulation generates an abnormal dendritic spine morphology that is an intermediate phenotype of SZ. We further found that 8 (CSF2RA, HIST1H2BJ, NOTCH4, NRGN, SHOX, SMARCA2, TCF4 and ZNF804A) out of 10 genome-wide supported SZ-associated genes are part of an interacting network (including SMARCA2), 5 members of which encode transcription regulators. The expression of 3 (TCF4, SMARCA2 and CSF2RA) of the 10 genome-wide supported SZ-associated genes is modified when the REST/NRSF-SWI/SNF chromatin-remodeling complex is experimentally manipulated in mouse cell lines and in transgenic mouse models. The REST/NRSF-SWI/SNF deregulation also results in the differential expression of genes that are clustered in chromosomes suggesting the induction of genome-wide epigenetic changes. Finally, we found that SMARCA2 interactors and the genome-wide supported SZ-associated genes are considerably enriched in genes displaying positive selection in primates and in the human lineage which suggests the occurrence of novel protein interactions in primates. Altogether, these data identify the SWI/SNF chromatin-remodeling complex as a key component of the genetic architecture of SZ.