Chromosomal abnormalities and mental illness

Whole Genome Sequencing Revealed Inherited Rare Oligogenic Variants Contributing to Schizophrenia and Major Depressive Disorder in Two Families

Schizophrenia and affective disorder are two major complex mental disorders with high heritability. Evidence shows that rare variants with significant clinical impacts contribute to the genetic liability of these two disorders. Also, rare variants associated with schizophrenia and affective disorders are highly personalized; each patient may carry different variants. We used whole genome sequencing analysis to study the genetic basis of two families with schizophrenia and major depressive disorder. We did not detect de novo, autosomal dominant, or recessive pathogenic or likely pathogenic variants associated with psychiatric disorders in these two families. Nevertheless, we identified multiple rare inherited variants with unknown significance in the probands. In family 1, with singleton schizophrenia, we detected four rare variants in genes implicated in schizophrenia, including p.Arg1627Trp of LAMA2, p.Pro1338Ser of CSMD1, p.Arg691Gly of TLR4, and Arg182X of AGTR2. The p.Arg691Gly of TLR4 was inherited from the father, while the other three were inherited from the mother. In family 2, with two affected sisters diagnosed with major depressive disorder, we detected three rare variants shared by the two sisters in three genes implicated in affective disorders, including p.Ala4551Gly of FAT1, p.Val231Leu of HOMER3, and p.Ile185Met of GPM6B. These three rare variants were assumed to be inherited from their parents. Prompted by these findings, we suggest that these rare inherited variants may interact with each other and lead to psychiatric conditions in these two families. Our observations support the conclusion that inherited rare variants may contribute to the heritability of psychiatric disorders.

Lumateperone tosylate, A Selective and Concurrent Modulator of Serotonin, Dopamine, and Glutamate, in the Treatment of Schizophrenia

Purpose of Review

This is a comprehensive review of the literature regarding the use of Lumateperone tosylate for schizophrenia. This review presents the background, evidence, and indications for the use of lumateperone tosylate in the treatment of schizophrenia.

Recent Findings

Schizophrenia is a chronic mental health disorder that affects approximately 3.3 million people in the United States. Its symptoms, which must be present more than six months, are comprised of disorganized behavior and speech, a diminished capacity to comprehend reality, hearing voices unheard by others, seeing things unseen by others, delusions, decreased social commitment, and decreased motivation. The majority of these symptoms can be managed with antipsychotic medication. Lumateperone is a selective and concurrent modulator of serotonin, dopamine, and glutamate, which all mediate or modulate serious mental illness.

Summary

Schizophrenia is a complex, severe mental illness that affects how the brain processes information. There are many medications used to treat schizophrenia. One antipsychotic agent, lumateperone tosylate, is a newer agent that the FDA recently approved. The most common adverse effects are shown to be mild such as somnolence, constipation, sedation, and fatigue, with the 42 mg recommended dose. Lumateperone tosylate is an FDA-approved drug that can be given only at the 42mg dose once daily with no titration requirements.

LDB2 locus disruption on 4p16.1 as a risk factor for schizophrenia and bipolar disorder

We had previously reported the case of a male patient with schizophrenia, having de-novo balanced translocation. Here, we determined the exact breakpoints in chromosomes 4 and 13. The breakpoint within chromosome 4 was mapped to a region 32.6 kbp upstream of the LDB2 gene encoding Lim domain binding 2. Variant screening in LDB2 revealed a rare novel missense variant in patients with psychiatric disorder.

The many roads to psychosis: recent advances in understanding risk and mechanisms

Schizophrenia is a chronic and severe mental illness which frequently leads to substantial lifelong disability. The past five years have seen major progress in our understanding of the complex genetic architecture of this disorder. Two major barriers to understanding the core biological processes that underlie schizophrenia and developing better interventions are (1) the absence of etiologically defined biomarkers and (2) the clinical and genetic heterogeneity of the disorder. Here, we review recent advances that have led to changes in our understanding of risk factors and mechanisms involved in the development of schizophrenia. In particular, mechanistic and clinically oriented approaches have now converged on a focus on disruptions in early neurodevelopment and synaptic plasticity as being critical for both understanding trajectories and intervening to change them. Translating these new findings into treatments that substantively change the lives of patients is the next major challenge for the field.

A balanced translocation disrupting BCL2L10 and PNLDC1 segregates with affective psychosis

Affective psychoses are a group of severe psychiatric disorders, including schizoaffective disorder and bipolar I disorder, together affecting ∼1% of the population. Despite their high heritability, the molecular genetics and neurobiology of affective psychosis remain largely elusive. Here, we describe the identification of a structural genetic variant segregating with affective psychosis in a family with multiple members suffering from bipolar I disorder or schizoaffective disorder, bipolar type. A balanced translocation involving chromosomes 6 and 15 was detected by karyotyping and fluorescence in-situ hybridization (FISH). Using whole-genome sequencing, we rapidly delineated the translocation breakpoints as corresponding intragenic events disrupting BCL2L10 and PNLDC1. These data warrant further consideration for BCL2L10 and PNLDC1 as novel candidates for affective psychosis. © 2016 The Authors. American Journal of Medical Genetics Part B: Neuropsychiatric Genetics Published by Wiley Periodicals, Inc.

A Mutation in NPAS3 That Segregates with Schizophrenia in a Small Family Leads to Protein Aggregation

Schizophrenia and other major mental illnesses result from a complex interplay of genetic and environmental factors. We previously identified a mutation in NPAS3 that results in a valine to isoleucine (V304I) amino acid substitution segregating with schizophrenia in a small family. The amino acid change occurs in a potentially critical region for protein function. Furthermore, the same amino acid substitution in proteins related to familial Alzheimer's disease and transthyretin amyloidosis has been associated with protein aggregation. In this study, we demonstrate that NPAS3 is prone to aggregation, and that the V304I mutation in NPAS3 increases this propensity in both bacterial and mammalian expression systems. We also show that NPAS3-V304I reduces soluble endogenous NPAS3, and increases insoluble endogenous NPAS3 and leads to alteration of transcriptional activity. These results suggest that protein aggregation, potentially leading to cell dysfunction via a loss of protein function through sequestration, may contribute to the pathogenesis of schizophrenia and other forms of mental illness. Further exploration of the mechanisms leading to abnormal protein quality control could lead to new therapeutic targets.

The Vitamin E Analog Gamma-Tocotrienol (GT3) Suppresses Radiation-Induced Cytogenetic Damage

Purpose

Ionizing radiation (IR) generates reactive oxygen species (ROS), which cause DNA double-strand breaks (DSBs) that are responsible for cytogenetic alterations. Because antioxidants are potent ROS scavengers, we determined whether the vitamin E isoform γ-tocotrienol (GT3), a radio-protective multifunctional dietary antioxidant, can suppress IR-induced cytogenetic damage.

Methods

We measured DSB formation in irradiated primary human umbilical vein endothelial cells (HUVECs) by quantifying the formation of γ-H2AX foci. Chromosomal aberrations (CAs) were analyzed in irradiated HUVECs and in the bone marrow cells of irradiated mice by conventional and fluorescence-based chromosome painting techniques. Gene expression was measured in HUVECs with quantitative reverse transcriptase polymerase chain reaction (qRT-PCR).

Results

GT3 pretreatment reduced DSB formation in HUVECS, and also decreased CAs in HUVECs and mouse bone marrow cells after irradiation. Moreover, GT3 increased expression of the DNA-repair gene RAD50 and attenuated radiation-induced RAD50 suppression.

Conclusions

GT3 attenuates radiation-induced cytogenetic damage, possibly by affecting RAD50 expression. GT3 should be explored as a therapeutic to reduce the risk of developing genetic diseases after radiation exposure.

Analysis of t(9;17)(q33.2;q25.3) chromosomal breakpoint regions and genetic association reveals novel candidate genes for bipolar disorder

OBJECTIVES

Breakpoints of chromosomal abnormalities facilitate identification of novel candidate genes for psychiatric disorders. Genome-wide significant evidence supports the linkage between chromosome 17q25.3 and bipolar disorder (BD). Co-segregation of translocation t(9;17)(q33.2;q25.3) with psychiatric disorders has been reported. We aimed to narrow down these chromosomal breakpoint regions and to investigate the associations between single nucleotide polymorphisms within these regions and BD as well as schizophrenia (SZ) in large genome-wide association study samples.

METHODS

We cross-linked Danish psychiatric and cytogenetic case registers to identify an individual with both t(9;17)(q33.2;q25.3) and BD. Fluorescent in situ hybridization was employed to map the chromosomal breakpoint regions of this proband. We accessed the Psychiatric Genomics Consortium BD (n = 16,731) and SZ (n = 21,856) data. Genetic associations between these disorders and single nucleotide polymorphisms within these breakpoint regions were analysed by BioQ, FORGE, and RegulomeDB programmes.

RESULTS

Four protein-coding genes [coding for (endonuclease V (ENDOV), neuronal pentraxin I (NPTX1), ring finger protein 213 (RNF213), and regulatory-associated protein of mammalian target of rapamycin (mTOR) (RPTOR)] were found to be located within the 17q25.3 breakpoint region. NPTX1 was significantly associated with BD (p = 0.004), while ENDOV was significantly associated with SZ (p = 0.0075) after Bonferroni correction.

CONCLUSIONS

Prior linkage evidence and our findings suggest NPTX1 as a novel candidate gene for BD.

Incomplete penetrance of NRXN1 deletions in families with schizophrenia

Neurexin 1 (NRXN1) is a presynaptic neuronal adhesion molecule that interacts with postsynaptic neuroligins in both glutamatergic and GABAergic synapses and is important in synaptic formation and function. NRXN1 deletions increase the risk of schizophrenia, so our aims were to explore this in our family sample, to distinguish de novo from inherited mutations, to examine transmission to affected and unaffected siblings and to estimate penetrance. We performed copy number analyses in NRXN1 using data from Illumina BeadArrays from 635 subjects with schizophrenia (276 in genotyped families), 487 of their unaffected parents and 309 unaffected siblings as well as 635 normal controls, all from the CBDB/NIMH Genetic Study of Schizophrenia. Deletions called by software were confirmed by quantitative PCR and comparative genome hybridization. There were deletions in 15 individuals in 11 families, including de novo exonic deletions in one case and one unaffected sibling. We observed no deletions in controls, 7 deletions in cases (1.10%), and an unexpectedly high deletion frequency in parents (n=5, 1.02%) and siblings (n=3, 0.97%). Three families showed inheritance from an unaffected parent, and in two families an unaffected parent did not transmit to the affected offspring. Thus we have added to the evidence that NRXN1 deletions are more frequent in patients with schizophrenia than in healthy individuals. However, the presence of de novo deletions in unaffected relatives and transmission from and to unaffected family members demonstrated that while the deletions may well have been necessary for some carriers to develop schizophrenia, they were not always sufficient.

Developmental psychopathology: The role of structural variation in the genome

A wide range of developmental disorders present with characteristic psychopathologies and behaviors, with diagnoses including, inter alia, cognitive disorders and learning disabilities, epilepsies, autism, and schizophrenia. Each, to varying extent, has a genetic component to etiology and is associated with cytogenetic abnormalities. Technological developments, particularly array-based comparative genome hybridization and single nucleotide polymorphism chips, has revealed a wide range of rare recurrent and de novo copy number variants (CNVs) to be associated with disorder and psychopathology. It is surprising that many apparently similar CNVs are identified across two or more disorders hitherto considered unrelated. This article describes the characteristics of CNVs and current technological restrictions that make accurately identifying small events difficult. It summarizes the latest discoveries for individual diagnostic categories and considers the implications for a shared neurobiology. It examines likely developments in the knowledge base as well as addressing the clinical implications going forward.

Genetics of schizophrenia from a clinicial perspective

Schizophrenia (SZ) is a common disorder that runs in families. It has a relatively high heritability, i.e., inherited factors account for the major proportion of its etiology. The high heritability has motivated gene mapping studies that have improved in sophistication through the past two decades. Belying earlier expectations, it is now becoming increasingly clear that the cause of SZ does not reside in a single mutation, or even in a single gene. Rather, there are multiple DNA variants, not all of which have been identified. Additional risk may be conferred by interactions between individual DNA variants, as well as 'gene-environment' interactions. We review studies that have accounted for a fraction of the heritability. Their relevance to the practising clinician is discussed. We propose that continuing research in DNA variation, in conjunction with rapid ongoing advances in allied fields, will yield dividends from the perspective of diagnosis, treatment prediction through pharmacogenetics, and rational treatment through discoveries in pathogenesis.

Identification and characterization of three inherited genomic copy number variations associated with familial schizophrenia

Schizophrenia is a complex mental disorder with high degree of genetic influence in its etiology. Several recent studies revealed that copy number variations (CNVs) of genomic DNA contributed significantly to the genetic architecture of sporadic schizophrenia. This study aimed to investigate whether CNVs also contribute to the familial forms of schizophrenia. Using array-based comparative genomic hybridization technology, we searched for pathogenic CNV associated with schizophrenia in a sample of 60 index cases from multiplex schizophrenia families. We detected three inherited CNVs that were associated with schizophrenia in three families, including a microdeletion of ~4.4Mb at chromosome 6q12-q13, a microduplication of ~1Mb at chromosome 18q12.3, and an interstitial duplication of ~5Mb at chromosome 15q11.2-q13.1. Our data indicate that CNVs contribute to the genetic underpinnings of the familial forms of schizophrenia as well as of the sporadic form. As 15q11-13 duplication is a well-known recurrent CNV associated with autism in the literature, the detection of the 15q11.2-q13.1 duplication in our schizophrenia patients provides additional support to other studies reporting that schizophrenia is part of the clinical spectrum of 15q11-q13 duplication syndrome.

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.

Copy number variants of schizophrenia susceptibility loci are associated with a spectrum of speech and developmental delays and behavior problems

PURPOSE

: Recently, molecular cytogenetic techniques have identified novel copy number variants in individuals with schizophrenia. However, no large-scale prospective studies have been performed to characterize the broader spectrum of phenotypes associated with such copy number variants in individuals with unexplained physical and intellectual disabilities encountered in a diagnostic setting.

METHODS

: We analyzed 38,779 individuals referred to our diagnostic laboratory for microarray testing for the presence of copy number variants encompassing 20 putative schizophrenia susceptibility loci. We also analyzed the indications for study for individuals with copy number variants overlapping those found in six individuals referred for schizophrenia.

RESULTS

: After excluding larger gains or losses that encompassed additional genes outside the candidate loci (e.g., whole-arm gains/losses), we identified 1113 individuals with copy number variants encompassing schizophrenia susceptibility loci and 37 individuals with copy number variants overlapping those present in the six individuals referred to our laboratory for schizophrenia. Of these, 1035 had a copy number variant of one of six recurrent loci: 1q21.1, 15q11.2, 15q13.3, 16p11.2, 16p13.11, and 22q11.2. The indications for study for these 1150 individuals were diverse and included developmental delay, intellectual disability, autism spectrum, and multiple congenital anomalies.

CONCLUSION

: The results from our study, the largest genotype-first analysis of schizophrenia susceptibility loci to date, suggest that the phenotypic effects of copy number variants associated with schizophrenia are pleiotropic and imply the existence of shared biologic pathways among multiple neurodevelopmental conditions.

Evidence of aberrant DNA damage response signalling but normal rates of DNA repair in dividing lymphoblasts from patients with schizophrenia

OBJECTIVES

Cancer incidence in schizophrenia is not increased commensurate with higher rates of risk exposures. Here we report an investigation of the DNA damage response, an anti-tumorigenic defence, in immortalised lymphoblasts from patients with schizophrenia.

METHODS

Unirradiated and irradiated (5Gy) lymphoblasts from schizophrenia patients (n = 28) and healthy controls (n = 28) were immunostained for the phosphorylated histone variant H2AX (γH2AX), an index of DNA double-strand breaks. Flow cytometry was used to assess cell cycle distribution and γH2AX immunofluorescence. Rate of DNA repair was quantified by determining the temporal change in γH2AX values following irradiation.

RESULTS

In unirradiated lymphoblasts, γH2AX levels were significantly increased in the schizophrenia group compared with controls (effect size = 0.86). This increase was most evident in patients with cognitive deficits. In irradiated lymphoblasts, peak radiation-induced γH2AX levels were significantly reduced in patients. No differences between patients and controls were found in the rate of DNA repair or in cell cycle distribution.

CONCLUSIONS

The significant differences in DNA damage response signalling observed involve modification of histone variant H2AX and thereby implicate regulatory processes determining chromatin structure in dividing lymphoblasts from patients with schizophrenia. The role that aberrant DNA damage response signalling plays in protecting patients from cancer is unclear.

Isochromosome 13 in a patient with childhood-onset schizophrenia, ADHD, and motor tic disorder

BACKGROUND

A small percentage of all cases of schizophrenia have a childhood onset. The impact on the individual and family can be devastating. We report the results of genetic analyses from a patient with onset of visual hallucinations at 5 years, and a subsequent diagnosis at 9 years of schizophrenia, attention deficit hyperactivity disorder (ADHD) with hyperactivity and impulsivity, and chronic motor tic disorder.

RESULTS

Karyotypic analysis found 45,XX,i(13)(q10) in all cells examined. Alpha satellite FISH of isochromosome 13 revealed a large unsplit centromeric region, interpreted as two centromeres separated by minimal or undetectable short-arm material or as a single monocentric centromere, indicating that the isochromosome likely formed post-zygotically by a short arm U-type or centromeric exchange. Characterization of chromosome 13 simple tandem repeats and Affymetrix whole-genome 6.0 SNP array hybridization found homozygosity for all markers, and the presence of only a single paternal allele in informative markers, consistent with an isodisomic isochromosome of paternal origin. Analysis of two chromosome 13 schizophrenia candidate genes, D-amino acid oxidase activator (DAOA) and 5-hydroxytryptamine (serotonin) receptor 2A (5-HTR2A), failed to identify non-synonymous coding mutations but did identify homozygous risk polymorphisms.

CONCLUSIONS

We report a female patient with childhood-onset schizophrenia, ADHD, and motor tic disorder associated with an isodisomic isochromosome 13 of paternal origin and a 45,XX,i(13)(q10q10) karyotype. We examined two potential mechanisms to explain chromosome 13 involvement in the patient's pathology, including reduction to homozygosity of a paternal mutation and reduction to homozygosity of a paternal copy number variation, but were unable to identify any overtly pathogenic abnormality. Future studies may consider whether epigenetic mechanisms resulting from uniparental disomy (UPD) and the lack of chromosome 13 maternal alleles lead to the patient's features.

Genome arrays for the detection of copy number variations in idiopathic mental retardation, idiopathic generalized epilepsy and neuropsychiatric disorders: lessons for diagnostic workflow and research

We review the contributions and limitations of genome-wide array-based identification of copy number variants (CNVs) in the clinical diagnostic evaluation of patients with mental retardation (MR) and other brain-related disorders. In unselected MR referrals a causative genomic gain or loss is detected in 14-18% of cases. Usually, such CNVs arise de novo, are not found in healthy subjects, and have a major impact on the phenotype by altering the dosage of multiple genes. This high diagnostic yield justifies array-based segmental aneuploidy screening as the initial genetic test in these patients. This also pertains to patients with autism (expected yield about 5-10% in nonsyndromic and 10-20% in syndromic patients) and schizophrenia (at least 5% yield). CNV studies in idiopathic generalized epilepsy, attention-deficit hyperactivity disorder, major depressive disorder and Tourette syndrome indicate that patients have, on average, a larger CNV burden as compared to controls. Collectively, the CNV studies suggest that a wide spectrum of disease-susceptibility variants exists, most of which are rare (<0.1%) and of variable and usually small effect. Notwithstanding, a rare CNV can have a major impact on the phenotype. Exome sequencing in MR and autism patients revealed de novo mutations in protein coding genes in 60 and 20% of cases, respectively. Therefore, it is likely that arrays will be supplanted by next-generation sequencing methods as the initial and perhaps ultimate diagnostic tool in patients with brain-related disorders, revealing both CNVs and mutations in a single test.

Molecular cytogenetics and cytogenomics of brain diseases

Molecular cytogenetics is a promising field of biomedical research that has recently revolutionized our thinking on genome structure and behavior. This is in part due to discoveries of human genomic variations and their contribution to biodiversity and disease. Since these studies were primarily targeted at variation of the genome structure, it appears apposite to cover them by molecular cytogenomics. Human brain diseases, which encompass pathogenic conditions from severe neurodegenerative diseases and major psychiatric disorders to brain tumors, are a heavy burden for the patients and their relatives. It has been suggested that most of them, if not all, are of genetic nature and several recent studies have supported the hypothesis assuming them to be associated with genomic instabilities (i.e. single-gene mutations, gross and subtle chromosome imbalances, aneuploidy). The present review is focused on the intriguing relationship between genomic instability and human brain diseases. Looking through the data, we were able to conclude that both interindividual and intercellular genomic variations could be pathogenic representing, therefore, a possible mechanism for human brain malfunctioning. Nevertheless, there are still numerous gaps in our knowledge concerning the link between genomic variations and brain diseases, which, hopefully, will be filled by forthcoming studies. In this light, the present review considers perspectives of this dynamically developing field of neurogenetics and genomics.

Inherited balanced translocation t(9;17)(q33.2;q25.3) concomitant with a 16p13.1 duplication in a patient with schizophrenia

We report two rare genetic aberrations in a schizophrenia patient that may act together to confer disease susceptibility. A previously unreported balanced t(9;17)(q33.2;q25.3) translocation was observed in two schizophrenia-affected members of a small family with diverse psychiatric disorders. The proband also carried a 1.5 Mbp microduplication at 16p13.1 that could not be investigated in other family members. The duplication has been reported to predispose to schizophrenia, autism and mental retardation, with incomplete penetrance and variable expressivity. The t(9;17) (q33.2;q25.3) translocation breakpoint occurs within the open reading frames of KIAA1618 on 17q25.3, and TTLL11 (tyrosine tubulin ligase like 11) on 9q33.2, causing no change in the expression level of KIAA1618 but leading to loss of expression of one TTLL11 allele. TTLL11 belongs to a family of enzymes catalyzing polyglutamylation, an unusual neuron-specific post-translational modification of microtubule proteins, which modulates microtubule development and dynamics. The 16p13.1 duplication resulted in increased expression of NDE1, encoding a DISC1 protein partner mediating DISC1 functions in microtubule dynamics. We hypothesize that concomitant TTLL11-NDE1 deregulation may increase mutation load, among others, also on the DISC1 pathway, which could contribute to disease pathogenesis through multiple effects on neuronal development, synaptic plasticity, and neurotransmission. Our data illustrate the difficulties in interpreting the contribution of multiple potentially pathogenic changes likely to emerge in future next-generation sequencing studies, where access to extended families will be increasingly important.

Association of common copy number variants at the glutathione S-transferase genes and rare novel genomic changes with schizophrenia

Copy number variants (CNVs) are a substantial source of human genetic diversity, influencing the variable susceptibility to multifactorial disorders. Schizophrenia is a complex illness thought to be caused by a number of genetic and environmental effects, few of which have been clearly defined. Recent reports have found several low prevalent CNVs associated with the disease. We have used a multiplex ligation-dependent probe amplification-based (MLPA) method to target 140 previously reported and putatively relevant gene-containing CNV regions in 654 schizophrenic patients and 604 controls for association studies. Most genotyped CNVs (95%) showed very low (<1%) population frequency. A few novel rare variants were only present in patients suggesting a possible pathogenic involvement, including 1.39 Mb overlapping duplications at 22q11.23 found in two unrelated patients, and duplications of the somatostatin receptor 5 gene (SSTR5) at 16p13.3 in three unrelated patients. Furthermore, among the few relatively common CNVs observed in patients and controls, the combined analysis of gene copy number genotypes at two glutathione S-transferase (GST) genes, GSTM1 (glutathione S-transferase mu 1) (1p13.3) and GSTT2 (glutathione S-transferase theta 2) (22q11.23), showed a statistically significant association of non-null genotypes at both loci with an additive effect for increased vulnerability to schizophrenia (odds ratio of 1.92; P=0.0008). Our data provide complementary evidences for low prevalent, but highly penetrant chromosomal variants associated with schizophrenia, as well as for common CNVs that may act as susceptibility factors by disturbing glutathione metabolism.

Copy number variation of the SELENBP1 gene in schizophrenia

Background

Schizophrenia is associated with rare copy-number (CN) mutations. Screening for such alleles genome-wide, though comprehensive, cannot study in-depth the causality of particular loci, therefore cannot provide the functional interpretation for the disease etiology. We hypothesized that CN mutations in the SELENBP1 locus could associate with the disorder and that these mutations could alter the gene product's activity in patients.

Methods

We analyzed SELENBP1 CN variation (CNV) in blood DNA from 49 schizophrenia patients and 49 controls (cohort A). Since CN of genes may vary among tissues, we investigated SELENBP1 CN in age- sex- and postmortem interval-matched cerebellar DNA samples from 14 patients and 14 controls (cohort B). Since CNV may either be de-novo or inherited we analyzed CNV of the SELENBP1 locus in blood DNA from 26 trios of schizophrenia probands and their healthy parents (cohort C). SELENBP1 mRNA levels were measured by real-time PCR.

Results

In cohort A reduced CN of the SELENBP1 locus was found in four patients but in none of the controls. In cohort B we found reduced CN of the SELENBP1 locus in two patients but in none of the controls. In cohort C three patients exhibited drastic CN reduction, not present in their parents, indicating de-novo mutation. A reduction in SELENBP1 mRNA levels in the postmortem cerebellar samples of schizophrenia patients was found.

Conclusions

We report a focused study of CN mutations in the selenium binding-protein1 (SELENBP1) locus previously linked with schizophrenia. We provide evidence for recurrence of decreased CN of the SELENBP1 locus in three unrelated patients' cohorts but not in controls, raising the possibility of functional involvement of these mutations in the etiology of the disease.

What have the genomics ever done for the psychoses?

BACKGROUND

Despite the substantial heritability of the psychoses and their genuine public health burden, the applicability of the genomic approach in psychiatry has been strongly questioned or prematurely dismissed.

METHODS

selective review of the recent literature on molecular genetic and genomic approaches to the psychoses including the early output from genome-wide association studies and the genomic analysis of DNA structural variation.

RESULTS

Susceptibility variants at strong candidate genes have been identified including neuregulin, dysbindin, DISC1 and neurexin 1. Rare but highly penetrant copy number variants and new mutations affecting genes involved in neurodevelopment, cell signalling and synaptic function have been described showing some overlapping genetic architecture with other developmental disorders including autism. The de-novo mutations described offer an explanation for the familial sporadic divide and the persistence of schizophrenia in the population. The functional effects of risk variants at the level of cognition and connectivity has been described and recently, ZNF804A has been identified, and the MHC re-identified as risk loci, and it has been shown that at least a third of the variation in liability is due to multiple common risk variants of small effect with a substantial shared genetic liability between schizophrenia and bipolar affective disorder.

CONCLUSIONS

The genomics have done much for the psychoses to date and more is anticipated.

The role of DNA copy number variation in schizophrenia

Schizophrenia is a major psychiatric disease with strong evidence of genetic risk factors. Recent studies based on genome-wide study of copy number variations (CNVs) have detected novel recurrent submicroscopic copy number changes, including recurrent deletions at 1q21.11, 15q11.3, 15q13.3, and the recurrent CNV at the 2p16.3 neurexin 1 locus. These schizophrenia susceptibility CNV loci demonstrate that schizophrenia is, at least in part, genetic in origin and provide the basis for further investigation of mutations associated with the disease. The studies combined have also established the role of rare and-in sporadic cases-de novo variants in schizophrenia. Furthermore, neuronal-related genes and genetic pathways are starting to emerge from the CNV loci associated with schizophrenia. Here, we review the major findings in the recent literature, which begin to unravel the genetic and biological architecture of this complex human neuropsychiatric disorder.

The role of genetic variation in the causation of mental illness: an evolution-informed framework

The apparently large genetic contribution to the aetiology of mental illness presents a formidable puzzle. Unlike common physical disorders, mental illness usually has an onset early in the reproductive age and is associated with substantial reproductive disadvantage. Therefore, genetic variants associated with vulnerability to mental illness should be under strong negative selection pressure and be eliminated from the genetic pool through natural selection. Still, mental disorders are common and twin studies indicate a strong genetic contribution to their aetiology. Several theories have been advanced to explain the paradox of high heritability and reproductive disadvantage associated with the same common phenotype, but none provides a satisfactory explanation for all types of mental illness. At the same time, identification of the molecular substrate underlying the large genetic contribution to the aetiology of mental illness is proving more difficult than expected. The quest for genetic variants associated with vulnerability to mental illness is predicated upon the common disease/common variant (CDCV) hypothesis. On the basis of a summary of evidence, it is concluded that the CDCV hypothesis is untenable for most types of mental illness. An alternative evolution-informed framework is proposed, which suggests that gene-environment interactions and rare genetic variants constitute most of the genetic contribution to mental illness. Common mental illness with mild reproductive disadvantage is likely to have a large contribution from interactions between common genetic variants and environmental exposures. Severe mental illness that confers strong reproductive disadvantage is likely to have a large and pleiotropic contribution from rare variants of recent origin. This framework points to a need for a paradigm change in genetic research to enable major progress in elucidating the aetiology of mental illness.

Chromosome 8p as a potential hub for developmental neuropsychiatric disorders: implications for schizophrenia, autism and cancer

Defects in genetic and developmental processes are thought to contribute susceptibility to autism and schizophrenia. Presumably, owing to etiological complexity identifying susceptibility genes and abnormalities in the development has been difficult. However, the importance of genes within chromosomal 8p region for neuropsychiatric disorders and cancer is well established. There are 484 annotated genes located on 8p; many are most likely oncogenes and tumor-suppressor genes. Molecular genetics and developmental studies have identified 21 genes in this region (ADRA1A, ARHGEF10, CHRNA2, CHRNA6, CHRNB3, DKK4, DPYSL2, EGR3, FGF17, FGF20, FGFR1, FZD3, LDL, NAT2, NEF3, NRG1, PCM1, PLAT, PPP3CC, SFRP1 and VMAT1/SLC18A1) that are most likely to contribute to neuropsychiatric disorders (schizophrenia, autism, bipolar disorder and depression), neurodegenerative disorders (Parkinson's and Alzheimer's disease) and cancer. Furthermore, at least seven nonprotein-coding RNAs (microRNAs) are located at 8p. Structural variants on 8p, such as copy number variants, microdeletions or microduplications, might also contribute to autism, schizophrenia and other human diseases including cancer. In this review, we consider the current state of evidence from cytogenetic, linkage, association, gene expression and endophenotyping studies for the role of these 8p genes in neuropsychiatric disease. We also describe how a mutation in an 8p gene (Fgf17) results in a mouse with deficits in specific components of social behavior and a reduction in its dorsomedial prefrontal cortex. We finish by discussing the biological connections of 8p with respect to neuropsychiatric disorders and cancer, despite the shortcomings of this evidence.

Analysis of a t(18;21)(p11.1;p11.1) translocation in a family with schizophrenia

It is suggested that chromosome 18p11 is a susceptibility region for both bipolar disorder and schizophrenia. Aiming to identify susceptibility gene(s), we investigated a family whose members have either schizophrenia or schizophrenia-spectrum psychosis and carried a t(18;21)(p11.1;p11.1) translocation. Fluorescence in situ hybridization showed that the breakpoint on chromosome 21 was localized to a bacterial artificial chromosome (BAC) clone RP11-2503J9, which contained coding sequences for transmembrane phosphatase with tensin homology, although this gene was not disrupted. On chromosome 18p, the break point was narrowed to BAC clone RP11-527H14. In silico sequence analysis of this clone identified possible pseudo genes and gene fragments but no intact genes. RP11-527H14 also showed sites of cross hybridization, including 21p11.1. To test for a position effect on 18p11 sequences translocated to 21p11, we performed quantitative RT-PCR to measure the expression of the candidate gene C18orf1 in translocation carriers, but found no significant differences from controls in lymphoblastoid cells.

Strong association of de novo copy number mutations with sporadic schizophrenia

Schizophrenia is an etiologically heterogeneous psychiatric disease, which exists in familial and nonfamilial (sporadic) forms. Here, we examine the possibility that rare de novo copy number (CN) mutations with relatively high penetrance contribute to the genetic component of schizophrenia. We carried out a whole-genome scan and implemented a number of steps for finding and confirming CN mutations. Confirmed de novo mutations were significantly associated with schizophrenia (P = 0.00078) and were collectively approximately 8 times more frequent in sporadic (but not familial) cases with schizophrenia than in unaffected controls. In comparison, rare inherited CN mutations were only modestly enriched in sporadic cases. Our results suggest that rare de novo germline mutations contribute to schizophrenia vulnerability in sporadic cases and that rare genetic lesions at many different loci can account, at least in part, for the genetic heterogeneity of this disease.

Rare structural variants disrupt multiple genes in neurodevelopmental pathways in schizophrenia

Schizophrenia is a devastating neurodevelopmental disorder whose genetic influences remain elusive. We hypothesize that individually rare structural variants contribute to the illness. Microdeletions and microduplications >100 kilobases were identified by microarray comparative genomic hybridization of genomic DNA from 150 individuals with schizophrenia and 268 ancestry-matched controls. All variants were validated by high-resolution platforms. Novel deletions and duplications of genes were present in 5% of controls versus 15% of cases and 20% of young-onset cases, both highly significant differences. The association was independently replicated in patients with childhood-onset schizophrenia as compared with their parents. Mutations in cases disrupted genes disproportionately from signaling networks controlling neurodevelopment, including neuregulin and glutamate pathways. These results suggest that multiple, individually rare mutations altering genes in neurodevelopmental pathways contribute to schizophrenia.

The schizophrenia brain exhibits low-level aneuploidy involving chromosome 1

OBJECTIVE

Genetic instability manifested as loss or gain of whole chromosomes (aneuploidy) is a newly described feature of the human brain. Aneuploidy in the brain was hypothesized to be involved in schizophrenia pathogenesis. To gain further insights into the relationship between aneuploidy in the brain and schizophrenia pathogenesis, a molecular-cytogenetic study of chromosome 1 aneuploidy was performed.

METHODS

Interphase multiprobe fluorescence in situ hybridization (FISH) with quantitative FISH (QFISH) and interphase chromosome-specific multicolor banding (ICS-MCB) were used to define aneuploidy rate in 12 unaffected and 12 schizophrenia brains.

RESULTS

In the unaffected brain (n=12; 22,794 cells analyzed), average frequencies of stochastic chromosome 1 loss and gain were 0.3% (95%CI 0.2-0.4%) and 0.3% (95%CI 0.2-0.4%), respectively. The threshold level for stochastic chromosome gain and loss (the mean+3SD) in the normal brain was 0.7%. Average rate of aneuploidy in the schizophrenia brain (n=12; 28,482 cells analyzed) was 0.9% (95%CI 0.3-1.5%) for chromosome 1 loss and 0.9% (95%CI 0.2-1.7%) for chromosome 1 gain. Significantly increased level of mosaic aneuploidy involving chromosome 1 was revealed in two schizophrenia brains (3.6% and 4.7% of cells with chromosome 1 loss and gain, respectively). Stochastic aneuploidy rate for chromosome 1 in the schizophrenia brain without two outliers (n=10) reached 0.6% (95%CI 0.3-0.9%) for loss and 0.5% (0.2-0.9%) for gain and was higher than in controls (P=0.005 and P=0.001, respectively).

CONCLUSIONS

Our findings support the hypothesis suggesting that subtle genomic imbalances manifesting as low-level mosaic aneuploidy may contribute to schizophrenia pathogenesis.

Functional genomics and schizophrenia: endophenotypes and mutant models

This article summarizes the rationale, methods, and results of gene discovery programs in schizophrenia research and describes functional methods of investigating potential candidate genes. It focuses next on the most prominent current candidate genes and describes (1) evidence for their association with schizophrenia and research into the function of each gene; (2) investigation of the clinical phenotypes and endophenotypes associated with each gene, at the levels of psychopathologic, neurocognitive, electrophysiologic, neuroimaging, and neuropathologic findings; and (3) research into the ethologic, cognitive, social, and psychopharmacologic phenotype of mutants with targeted deletion of each gene. It examines gene-gene and gene-environment interactions. Finally, it looks at future directions for research.

Disrupted in Schizophrenia 1 Interactome: evidence for the close connectivity of risk genes and a potential synaptic basis for schizophrenia

Disrupted in Schizophrenia 1 (DISC1) is a schizophrenia risk gene associated with cognitive deficits in both schizophrenics and the normal ageing population. In this study, we have generated a network of protein-protein interactions (PPIs) around DISC1. This has been achieved by utilising iterative yeast-two hybrid (Y2H) screens, combined with detailed pathway and functional analysis. This so-called 'DISC1 interactome' contains many novel PPIs and provides a molecular framework to explore the function of DISC1. The network implicates DISC1 in processes of cytoskeletal stability and organisation, intracellular transport and cell-cycle/division. In particular, DISC1 looks to have a PPI profile consistent with that of an essential synaptic protein, which fits well with the underlying molecular pathology observed at the synaptic level and the cognitive deficits seen behaviourally in schizophrenics. Utilising a similar approach with dysbindin (DTNBP1), a second schizophrenia risk gene, we show that dysbindin and DISC1 share common PPIs suggesting they may affect common biological processes and that the function of schizophrenia risk genes may converge.

Cytogenetic and genetic evidence supports a role for the kainate-type glutamate receptor gene, GRIK4, in schizophrenia and bipolar disorder

In the search for the biological causes of schizophrenia and bipolar disorder, glutamate neurotransmission has emerged as one of a number of candidate processes and pathways where underlying gene deficits may be present. The analysis of chromosomal rearrangements in individuals diagnosed with neuropsychiatric disorders is an established route to candidate gene identification in both Mendelian and complex disorders. Here we describe a set of genes disrupted by, or proximal to, chromosomal breakpoints (2p12, 2q31.3, 2q21.2, 11q23.3 and 11q24.2) in a patient where chronic schizophrenia coexists with mild learning disability (US: mental retardation). Of these disrupted genes, the most promising candidate is a member of the kainate-type ionotropic glutamate receptor family, GRIK4 (KA1). A subsequent systematic case-control association study on GRIK4 assessed its contribution to psychiatric illness in the karyotypically normal population. This identified two discrete regions of disease risk within the GRIK4 locus: three single single nucleotide polymorphism (SNP) markers with a corresponding underlying haplotype associated with susceptibility to schizophrenia (P=0.0005, odds ratio (OR) of 1.453, 95% CI 1.182-1.787) and two single SNP markers and a haplotype associated with a protective effect against bipolar disorder (P=0.0002, OR of 0.624, 95% CI 0.485-0.802). After permutation analysis to correct for multiple testing, schizophrenia and bipolar disorder haplotypes remained significant (P=0.0430, s.e. 0.0064 and P=0.0190, s.e. 0.0043, respectively). We propose that these convergent cytogenetic and genetic findings provide molecular evidence for common aetiologies for different psychiatric conditions and further support the 'glutamate hypothesis' of psychotic illness.

The genetics and biology of DISC1--an emerging role in psychosis and cognition

In the developing field of biological psychiatry, DISC1 stands out by virtue of there being credible evidence, both genetic and biological, for a role in determining susceptibility to schizophrenia and related disorders. We highlight the methodologic paradigm that led to identification of DISC1 and review the supporting genetic and biological evidence. The original finding of DISC1 as a gene disrupted by a balanced translocation on chromosome 1q42 that segregates with schizophrenia, bipolar disorder, and recurrent major depression has sparked a number of confirmatory linkage and association studies. These indicate that DISC1 is a generalizable genetic risk factor for psychiatric illness that also influences cognition in healthy subjects. DISC1 has also been shown to interact with a number of proteins with neurobiological pedigrees, including Ndel1 (NUDEL), a key regulator of neuronal migration with endo-oligopeptidase activity, and PDE4B, a phosphodiesterase that is critical for cyclic adenosine monophosphate signaling and that is directly linked to learning, memory, and mood. Both are potential "drug" targets. DISC1 has thus emerged as a key molecular player in the etiology of major mental illness and in normal brain processes.

Segmental uniparental isodisomy on 5q32-qter in a patient with childhood-onset schizophrenia

Schizophrenia is a severe mental disorder affecting approximately 1% of the world's population. Although the aetiology of schizophrenia is complex and multifactorial, with estimated heritabilities as high as 80%, genetic factors are the most compelling. Childhood-onset schizophrenia (COS), defined as onset of schizophrenia before the age of 13 years, is a rare and malignant form of the illness that may have more salient genetic influence. The first known case of paternal segmental uniparental isodisomy (iUPD) on 5q32-qter in a patient with COS is described, which adds to the previously known high rates of chromosomal abnormalities reported in this sample. iUPD is a rare genetic condition in which the offspring receives two chromosomal homologues from one parent. Segmental UPD is defined as UPD on a portion of a chromosome with biparental inheritance seen in the rest of the homologous pair. Complications owing to this abnormality may arise from malfunctioning imprinted genes or homozygosity of recessive disease-causing mutations. This aberration became apparent during whole-genomic screening of a COS cohort and is of particular interest because 5q has been implicated in schizophrenia by several genomewide linkage studies and positive gene associations. This report, therefore, presents more evidence that schizophrenia susceptibility gene, or genes, may be found on distal 5q.

Chromosomal abnormalities and psychosis

The search for susceptibility genes for schizophrenia and severe affective disorder has been enhanced by the study of cytogenetic abnormalities that disrupt genes directly. One such gene is DISCI and there is increasing evidence that it may be an important modulator of risk of psychosis.

Array-based genomic delineation of a familial duplication 11q14.1-q22.1 associated with recurrent depression

Detection of abnormal karyotypes with associated clinical manifestations is an important tool for the identification of genes that confer susceptibility to genetic disorders. We present a family with a duplication 11q14.1-q22.1 resulting from an unbalanced familial insertion, associated with a mild dysmorphic phenotype and mood disorders, mainly major depression. This relatively large duplication of a segment from chromosome 11 is associated with a surprisingly little physical phenotypic effect in this family. The finding of mood disorders in adult members of the family who carry the insertion supports the view that the duplication may be important for the identification of contributing gene(s) to mood disorders. Major depression is considered to be a complex trait with multiple genetic alterations interacting with environmental factors. Array-based comparative genome hybridization (array CGH) analysis with a 1 Mb genomic array, defined the duplication region that extended over 16 Mb from 11q14.1 to 11q22.1. Brain-expressed genes that map within this 16 Mb region, are considered worthy of further investigation as gene(s) contributing to the etiology of major depression.

The genetics of schizophrenia and bipolar disorder: dissecting psychosis

Much work has been done to identify susceptibility genes in schizophrenia and bipolar disorder. Several well established linkages have emerged in schizophrenia. Strongly supported regions are 6p24-22, 1q21-22, and 13q32-34, while other promising regions include 8p21-22, 6q16-25, 22q11-12, 5q21-q33, 10p15-p11, and 1q42. Genomic regions of interest in bipolar disorder include 6q16-q22, 12q23-q24, and regions of 9p22-p21, 10q21-q22, 14q24-q32, 13q32-q34, 22q11-q22, and chromosome 18. Recently, specific genes or loci have been implicated in both disorders and, crucially, replicated. Current evidence supports NRG1, DTNBP1, DISC1, DAOA(G72), DAO, and RGS4 as schizophrenia susceptibility loci. For bipolar disorder the strongest evidence supports DAOA(G72) and BDNF. Increasing evidence suggests an overlap in genetic susceptibility across the traditional classification systems that dichotomised psychotic disorders into schizophrenia or bipolar disorder, most notably with association findings at DAOA(G72), DISC1, and NRG1. Future identification of psychosis susceptibility genes will have a major impact on our understanding of disease pathophysiology and will lead to changes in classification and the clinical practice of psychiatry.

DNA copy-number analysis in bipolar disorder and schizophrenia reveals aberrations in genes involved in glutamate signaling

Using bacterial artificial chromosome (BAC) array comparative genome hybridization (aCGH) at approximately 1.4 Mbp resolution, we screened post-mortem brain DNA from bipolar disorder cases, schizophrenia cases and control individuals (n=35 each) for DNA copy-number aberrations. DNA copy number is a largely unexplored source of human genetic variation that may contribute risk for complex disease. We report aberrations at four loci which were seen in affected but not control individuals, and which were verified by quantitative real-time PCR. These aberrant loci contained the genes encoding EFNA5, GLUR7, CACNG2 and AKAP5; all brain-expressed proteins with known or postulated roles in neuronal function, and three of which (GLUR7, CACNG2 and AKAP5) are involved in glutamate signaling. A second cohort of psychiatric samples was also tested by quantitative PCR using the primer/probe sets for EFNA5, GLUR7, CACNG2 and AKAP5, and samples with aberrant copy number were found at three of the four loci (GLUR7, CACNG2 and AKAP5). Further scrutiny of these regions may reveal insights into the etiology and genetic risk factors for these complex psychiatric disorders.

Systematic re-examination of carriers of balanced reciprocal translocations: a strategy to search for candidate regions for common and complex diseases

Balanced reciprocal translocations associated with genetic disorders have facilitated the identification of a variety of genes for early-onset monogenic disorders, but only rarely the genes associated with common and complex disorders. To assess the potential of chromosomal breakpoints associated with common/ complex disorders, we investigated the full spectrum of diseases in 731 carriers of balanced reciprocal translocations without known early-onset disorders in a nation-wide questionnaire-based re-examination. In 42 families, one of the breakpoints at the cytogenetic level concurred with known linkage data and/or the translocation co-segregated with the reported phenotype, for example, we found a significant linkage (lod score=2.1) of dyslexia and a co-segregating translocation with a breakpoint in a previously confirmed locus for dyslexia. Furthermore, we identified 441 instances of at least two unrelated carriers with concordant breakpoints and traits. If applied to other populations, re-examination of translocation carriers may identify additional genotype-phenotype associations, some of which may be novel and others that may coincide with and provide additional support of data presented here.

Chromosomal fragility, structural rearrangements and mobile element activity may reflect dynamic epigenetic mechanisms of importance in neurobehavioural genetics

Advances in human genome analyses have not yet allowed identification of specific genetic mechanisms underlying the expression of human neurobehavioural disorders. There is an increasing awareness that several genes may contribute to behavioural phenotypes and these genes appear to interact in as yet undetermined ways. It has been suggested that the problem needs elucidation from an epigenetic, gene expression perspective. Cytogenetic instability manifesting as chromosomal fragile sites, translocations, duplications, deletions and inversions, when co-occurring with neurobehavioural disorders, may offer a doorway to the investigation of such chromatin level, regulatory region, epigenetic processes. Due to earlier indications of non-specificity of chromosomal aberrations, poor phenotype:genotype correlations and a shift to analysing candidate coding regions on high resolution map level, the only utility of chromosomal breakpoints came to be seen as harbouring possible candidate genes of interest when segregating together with particular neurobehavioural disorders. More recent findings of the expression of highly specific subsets of fragile sites in association with Tourette and Rett syndromes need to be extended to other neurobehavioural disorders to ascertain whether observed patterns can be considered representative of 'chromatin endophenotypes' correlating with discrete sets of neurobehavioural symptoms. Environmental/epigenetic factors could affect the chromatin characteristics of the genome arising through DNA strand breakage, mobile element activity and retroinsertion, establishing new architectural features of regulatory control networks very rapidly in comparison to coding region evolution rates. Microarray-based techniques for the genome-wide mapping of in vivo protein-DNA interactions offer increasingly comprehensive views of genetic and epigenetic regulatory networks. It may be informative to include functionally significant chromatin structural variation analyses when considering candidate genes for neurobehavioural disorders.

Schizophrenia: genes at last?

Genetic epidemiological studies suggest that individual variation in susceptibility to schizophrenia is largely genetic, reflecting alleles of moderate to small effect in multiple genes. Molecular genetic studies have identified several potential regions of linkage and two associated chromosomal abnormalities, and evidence is accumulating in favour of several positional candidate genes. Currently, the positional candidate genes for which we consider the evidence to be strong are those encoding dysbindin (DTNBP1) and neuregulin 1 (NRG1). For other genes, disrupted in schizophrenia 1 (DISC1), D-amino-acid oxidase (DAO), D-amino-acid oxidase activator (DAOA, formerly known as G72) and regulator of G-protein signalling 4 (RGS4), the data are promising but not yet compelling. The identification of these, and other susceptibility genes, will open up new avenues for research aimed at understanding the pathogenesis of schizophrenia, and will catalyse a re-appraisal of the classification of psychiatric disorders.

Finding schizophrenia genes

Genetic epidemiological studies suggest that individual variation in susceptibility to schizophrenia is largely genetic, reflecting alleles of moderate to small effect in multiple genes. Molecular genetic studies have identified a number of potential regions of linkage and 2 associated chromosomal abnormalities, and accumulating evidence favors several positional candidate genes. These findings are grounds for optimism that insight into genetic factors associated with schizophrenia will help further our understanding of this disease and contribute to the development of new ways to treat it.

Bipolar affective disorder in a male with a deletion of Y chromosome -- a case report

We report on a 25-year-old male with bipolar disorder, dysmorphic features and a deletion of the long arm of Y chromosome. A potential association between sex chromosome abnormalities and a susceptibility to major psychiatric disorders has been documented. However there have been very few reports on the coincidence of Y chromosome aberrations with bipolar disorder. Cytogenetic studies have contributed to the identification of several disease genes. Karyotyping of patients with bipolar disorder in order to identify candidate regions for linkage studies has been recommended.

Cytogenetics and gene discovery in psychiatric disorders

The disruption of genes by balanced translocations and other rare germline chromosomal abnormalities has played an important part in the discovery of many common Mendelian disorder genes, somatic oncogenes and tumour supressors. A search of published literature has identified 15 genes whose genomic sequences are directly disrupted by translocation breakpoints in individuals with neuropsychiatric illness. In these cases, it is reasonable to hypothesise that haploinsufficiency is a major factor contributing to illness. These findings suggest that the predicted polygenic nature of psychiatric illness may not represent the complete picture; genes of large individual effect appear to exist. Cytogenetic events may provide important insights into neurochemical pathways and cellular processes critical for the development of complex psychiatric phenotypes in the population at large.

Genética do transtorno bipolar

O Transtorno bipolar (TB) possui alta prevalência na população mundial e causa perdas significativas na vida dos portadores. É uma doença cuja herança genética se caracteriza por mecanismos complexos de transmissão envolvendo múltiplos genes. Na tentativa de identificar genes de vulnerabilidade para o TB, várias estratégias de investigação genética têm sido utilizadas. Estudos de ligação apontam diversas regiões cromossômicas potencialmente associadas ao TB, cujos marcadores ou genes podem ser candidatos para os estudos de associação. Genes associados aos sistemas monoaminérgicos e vias de sinalização intracelulares são candidatos para investigação da etiologia genética do TB. Novas técnicas de mapeamento de expressão gênica em tecidos especializados apontam para novos genes cujas mutações possam ser responsáveis pelo aparecimento da doença. Em virtude da complexidade do modo de transmissão do TB e de sua heterogeneidade fenotípica, muitas dificuldades são encontradas na determinação desses genes de vulnerabilidade. Até o momento, há apenas resultados preliminares identificando alguns genes associados à vulnerabilidade para desenvolver o TB. Entretanto, a compreensão crescente dos mecanismos epigenéticos de controle da expressão gênica e a abordagem dimensional dos transtornos mentais podem colaborar nas investigações futuras em genética psiquiátrica.