The genetics of schizophrenia and bipolar disorder: dissecting psychosis

A genome-wide scan for schizophrenia and psychosis susceptibility loci in families of Mexican and Central American ancestry

Schizophrenia is a complex psychiatric disorder, likely to be caused in part by multiple genes. In this study, linkage analyses were performed to identify chromosomal regions most likely to be associated with schizophrenia and psychosis in multiplex families of Mexican and Central American origin. Four hundred and fifty-nine individuals from 99 families, containing at least two siblings with hospital diagnoses of schizophrenia or schizoaffective disorder, were genotyped. Four hundred and four microsatellite markers were genotyped for all individuals and multipoint non-parametric linkage analyses were performed using broad (any psychosis) and narrow (schizophrenia and schizoaffective disorder) models. Under the broad model, three chromosomal regions (1pter-p36, 5q35, and 18p11) exhibited evidence of linkage with non-parametric lod (NPL) scores greater than 2.7 (equivalent to empirical P values of less than 0.001) with the peak multipoint NPL = 3.42 (empirical P value = 0.00003), meeting genomewide evidence for significant linkage in the 1pter-p36 region. Under the narrow model, the same three loci showed (non-significant) evidence of linkage. These linkage findings (1pter-p36, 18p11, and 5q35) highlight where genes for psychosis and schizophrenia are most likely to be found in persons of Mexican and Central American ancestry, and correspond to recent linkages of schizophrenia or psychosis in other populations which were formed in part from emigrants from the Spanish empire of the 15th and 16th centuries.

[Schizophrenia, human genetics and genetic counselling. Human genetic counselling as part of the psychiatric/psychotherapeutic treatment concept]

The human genome project has substantially increased our knowledge about the genetic basis of psychiatric diseases. In daily clinical practice the physician is asked about the diagnosis of genetically dependent diseases with an increased psychiatric risk, particularly schizophrenia group disorders, about the recurrence risk of psychiatric diseases in the relatives and children of the patients, on the use of psychopharmaceuticals during pregnancy and their potential consequences for the offspring, as well as psychopharmacogenetics. These questions will be dealt with in this contribution. At present, they receive too little attention, although genetic counselling might play an important role within the framework of psychiatric treatment, especially for schizophrenia. Such counselling should be seen as a component of the psychiatric/psychotherapeutic treatment concept and performed according to human genetic guidelines.

Phenotypic and genetic complexity of psychosis. Invited commentary on ... Schizophrenia: a common disease caused by multiple rare alleles

Psychosis, like other major psychiatric disorders, is both genetically and clinically complex. Increasingly powerful molecular genetic studies have the potential to identify DNA variation that influences susceptibility to genetically complex disorders. There is a need to use a range of genetic approaches appropriate to identifying a spectrum of risk variants from the common through to the rare. Some variants might have large effects at the level of the individual but most are likely to have modest or small effects at both population and individual level. Extensive clinical heterogeneity is likely to have a significant impact on the power of even the largest studies and, more importantly, will lead to extensive variability between studies and hamper attempts at replication. If we are to realise the potential of molecular genetics, we need to overcome the major limitations imposed by current psychiatric diagnostic classifications and identify clinical phenotypes that reflect the presence of underlying entities with biological validity.

Neuropsychological symptom dimensions in bipolar disorder and schizophrenia

BACKGROUND

While neurocognitive (NC) impairments have been well documented in schizophrenia (SZ), there is limited data as to whether similar impairments are present in other persistent mental illnesses. Recent data indicate that NC impairments may be manifested in bipolar disorder (BPD) and that they persist across disease states, including euthymia. An important question is whether a comparable structure of NC impairments is present in the 2 diagnostic groups.

OBJECTIVE

In a previous factor analytic study, we identified 6 factors to describe the basic underlying structure of neuropsychological (NP) functioning in SZ: Attention, Working Memory, Learning, Verbal Knowledge, Non-Verbal Functions, Ideational Fluency. The goal of this study was to investigate whether this factor structure is generalizable for BPD.

METHODS

The BPD sample included patients (n = 155) from an ongoing longitudinal study evaluating BPD at the time of hospitalization for relapse and at multiple time points over the following 2 years. The SZ sample included patients (n = 250) from a 3-year study. For the current examination the baseline NP evaluations were selected for both samples.

RESULTS

Exploratory and confirmatory factor analyses in the BPD sample yielded factors similar to those identified in the SZ sample. The coefficients of congruence ranged between 0.66-0.90 for the individual factors, indicating a good overall correspondence between the factor structures in the 2 diagnostic groups. Analysis of covariance (ANCOVA) analysis with education level, full scale-IQ, gender and ethnicity as covariates indicated that SZ patients had markedly worse performance on the Attention and Non-Verbal Functioning factors compared to the BPD patients.

CONCLUSIONS

Together, these data suggest that while the same underlying factor structure describes NP functioning in both groups, the profile of impairments appears to vary with the diagnosis.

The schizophrenias, the neuroses and the covered wagon; a critical review

OBJECTIVE

In order to compare their validity, this review applies scientific standards for sustaining the neuroses, the schizophrenias and bipolar disorders as separate "bona-fide" psychiatric diseases. The standards for disease validation demand specific and unique symptoms.

METHOD

We review a wide variety of clinical and basic science comparisons between schizophrenia and psychotic bipolar in a select English-language literature.

RESULTS

Like covered wagons, the neuroses once served us well but became obsolete and were discarded or reorganized based on what was known about commonalities of symptoms, causation and pharmacological responsivity. Bipolar patients meet unique and specific diagnostic criteria and demonstrate consistent results across a variety of scientific disciplines. Neither the neuroses nor the schizophrenias have such unique or disease specific diagnostic criteria. Psychotic mood disorders account for the DSM diagnostic criteria for schizophrenia. A recent, selected but diverse basic science literature demonstrates surprising similarities between schizophrenia and psychotic bipolar which should not exist if these disorders are distinct.

CONCLUSIONS

Like the neuroses, there is stigma, confusion and misunderstanding about the condition called schizophrenia, resulting in substantial negative impact on bipolar patients misdiagnosed as having schizophrenia. The psychoses, including the schizophrenias, likely are explained by a single disease, psychotic bipolar disorder, that has demonstrated a wide spectrum of severity of symptoms and chronicity of course, not traditionally recognized.

DISC1 regulates the transport of the NUDEL/LIS1/14-3-3epsilon complex through kinesin-1

Disrupted-In-Schizophrenia 1 (DISC1) is a candidate gene for susceptibility to schizophrenia. DISC1 is reported to interact with NudE-like (NUDEL), which forms a complex with lissencephaly-1 (LIS1) and 14-3-3epsilon. 14-3-3epsilon is involved in the proper localization of NUDEL and LIS1 in axons. Although the functional significance of this complex in neuronal development has been reported, the transport mechanism of the complex into axons and their functions in axon formation remain essentially unknown. Here we report that Kinesin-1, a motor protein of anterograde axonal transport, was identified as a novel DISC1-interacting molecule. DISC1 directly interacted with kinesin heavy chain of Kinesin-1. Kinesin-1 interacted with the NUDEL/LIS1/14-3-3epsilon complex through DISC1, and these molecules localized mainly at cell bodies and partially in the distal part of the axons. DISC1 partially colocalized with Kinesin family member 5A, NUDEL, LIS1, and 14-3-3epsilon in the growth cones. The knockdown of DISC1 by RNA interference or the dominant-negative form of DISC1 inhibited the accumulation of NUDEL, LIS1, and 14-3-3epsilon at the axons and axon elongation. The knockdown or the dominant-negative form of Kinesin-1 inhibited the accumulation of DISC1 at the axons and axon elongation. Furthermore, the knockdown of NUDEL or LIS1 inhibited axon elongation. Together, these results indicate that DISC1 regulates the localization of NUDEL/LIS1/14-3-3epsilon complex into the axons as a cargo receptor for axon elongation.

Evidence of linkage to psychosis on chromosome 5q33-34 in pedigrees ascertained for bipolar disorder

It is hypothesized that the presence of psychotic features may define a subtype of bipolar disorder that is more homogeneous in its genetic predisposition than bipolar disorder as a whole. We used psychosis as an alternative phenotype definition in a re-analysis of the NIMH Bipolar Genetics Initiative data sets. In this analysis we selected only those families in which at least two members were diagnosed with bipolar disorder type 1 with psychotic features. This analysis identified a linkage signal on chromosome 5q33-q34, a region previously implicated in independent linkage studies of schizophrenia and of psychosis, broadly defined. This finding is consistent with the hypothesis that susceptibility to psychosis may characterize at least a subtype of bipolar disorder.

Family-based association study between brain-derived neurotrophic factor gene polymorphisms and attention deficit hyperactivity disorder in UK and Taiwanese samples

Brain-derived neurotrophic factor (BDNF) plays an important role in normal neuronal development. Several lines of evidence implicate the involvement of BDNF in attention-deficit hyperactivity disorder (ADHD). This study investigated the role of two common BDNF variants (Val66Met, C270T) in two samples of ADHD probands from the United Kingdom (n = 180) and Taiwan (n = 212). We found evidence of increased transmission of the C allele of the C270T in Taiwanese samples (TDT: chi(2) = 6.78, P = 0.009) and the two samples pooled together (TDT: chi(2) = 7.24, P = 0.007). No association was found between the Val66Met polymorphism and ADHD in either of the two populations. Analysis of haplotypes demonstrated a significant decreased transmission of haplotypes containing the Val66 allele and the 270T allele in the Taiwanese samples (TDT: chi(2) = 4.57, P = 0.032) and the pooled sample set (TDT: chi(2) = 5.82, P = 0.016). This study provides evidence for the possible involvement of BDNF in susceptibility to ADHD.

DISC1 regulates neurotrophin-induced axon elongation via interaction with Grb2

Disrupted-in-Schizophrenia-1 (DISC1) is a candidate gene for susceptibility of schizophrenia. In the accompanying paper (Taya et al., 2006), we report that DISC1 acts as a linker between Kinesin-1 and DISC1-interacting molecules, such as NudE-like, lissencephaly-1, and 14-3-3epsilon. Here we identified growth factor receptor bound protein 2 (Grb2) as a novel DISC1-interacting molecule. Grb2 acts as an adaptor molecule that links receptor tyrosine kinases and the Ras-extracellular signal-regulated kinase (ERK) pathway. DISC1 formed a ternary complex with Grb2 and kinesin heavy chain KIF5A of Kinesin-1. In cultured rat hippocampal neurons, both DISC1 and Grb2 partially colocalized at the distal part of axons. Knockdown of DISC1 or kinesin light chains of Kinesin-1 by RNA interference inhibited the accumulation of Grb2 from the distal part of axons. Knockdown of DISC1 also inhibited the neurotrophin-3 (NT-3)-induced phosphorylation of ERK-1/2 at the distal part of axons and inhibited NT-3-induced axon elongation. These results suggest that DISC1 is required for NT-3-induced axon elongation and ERK activation at the distal part of axons by recruiting Grb2 to axonal tips.

Chasing genes for mood disorders and schizophrenia in genetically isolated populations

Major affective disorders and schizophrenia are among the most common brain diseases worldwide and their predisposition is influenced by a complex interaction of genetic and environmental factors. So far, traditional linkage mapping studies for these complex disorders have not achieved the same success as the positional cloning of genes for Mendelian diseases. The struggle to identify susceptibility genes for complex disorders has stimulated the development of alternative approaches, including studies in genetically isolated populations. Since isolated populations are likely to have both a reduced number of genetic vulnerability factors and environmental background and are therefore considered to be more homogeneous compared to outbred populations, the use of isolated populations in genetic studies is expected to improve the chance of finding susceptibility loci and genes. Here we review the role of isolated populations, based on linkage and association studies, in the identification of susceptibility genes for bipolar disorder and schizophrenia.

Variance in neurocognitive performance is associated with dysbindin-1 in schizophrenia: A preliminary study

Susceptibility genes for schizophrenia have been hypothesised to mediate liability for the disorder at least partly by influencing cognitive performance. We investigated the association between genotype and cognitive performance for a Dysbindin risk haplotype which is associated with schizophrenia in our sample. Fifty-two patients with schizophrenia or schizoaffective disorder (24 risk haplotypes carriers versus 28 non-risk haplotype carriers) were assessed in areas of cognition showing evidence of familial deficits in schizophrenia. Verbal and spatial memory, working memory, and attentional control was assessed using selected measures from the Weschler memory scale (WMS), Cambridge automated test battery (CANTAB), continuous performance test (CPT), and a simple go/no-go task. Pre-morbid IQ was also assessed using the Weschler Test of Adult Reading (WTAR). Patients carrying the Dysbindin risk haplotype showed significantly lower spatial working memory performance than patients who were non-risk carriers, with genotype explaining 12% of variance in performance. Our study suggests that the increased risk for schizophrenia associated with dysbindin may be partly mediated by its influence on pre-frontal function.

Susceptibility genes for schizophrenia: Characterisation of mutant mouse models at the level of phenotypic behaviour

A wealth of evidence indicates that schizophrenia is heritable. However, the genetic mechanisms involved are poorly understood. Furthermore, it may be that genes conferring susceptibility interact with one another and with non-genetic factors to modulate risk status and/or the expression of symptoms. Genome-wide scanning and the mapping of several regions linked with risk for schizophrenia have led to the identification of several putative susceptibility genes including neuregulin-1 (NRG1), dysbindin (DTNBP1), regulator of G-protein signalling 4 (RGS4), catechol-o-methyltransferase (COMT), proline dehydrogenase (PRODH) and disrupted-in-schizophrenia 1 (DISC1). Genetic animal models involving targeted mutation via gene knockout or transgenesis have the potential to inform on the role of a given susceptibility gene on the development and behaviour of the whole organism and on whether disruption of gene function is associated with schizophrenia-related structural and functional deficits. This review focuses on data regarding the behavioural phenotype of mice mutant for schizophrenia susceptibility genes identified by positional candidate analysis and the study of chromosomal abnormalities. We also consider methodological issues that are likely to influence phenotypic effects, as well as the limitations associated with existing molecular techniques.

The genetics of bipolar affective disorder

PURPOSE OF REVIEW

Molecular genetic studies of bipolar affective disorder are beginning to show some positive and reproducible findings. The most relevant of these will be reviewed.

RECENT FINDINGS

Obtaining consistent findings from whole genome scans has been hampered by small sample sizes and phenotypic heterogeneity. Recently, there have been concerted efforts to overcome these problems by combining data for meta-analysis. What has become increasingly clear is that several regions that are likely to contain genes contributing to bipolar affective disorder are also relevant to schizophrenia, a finding supported by recent twin data. Studies to date have implicated the D-amino acid oxidase activator complex (also known as G72/G30), disrupted in schizophrenia-1 and neuregulin, and have pointed to several promising linkage regions in which the genes have not yet been identified. In addition, there is some evidence to support the involvement of genetic variants in catechol-o-methyl transferase and brain-derived neurotrophic factor in the aetiology of bipolar affective disorder.

SUMMARY

Molecular genetic research in bipolar affective disorder may lead to the development of new diagnostic paradigms for classifying the psychoses and affective states. In addition, determining the functional significance of the susceptibility genes will pave the way for enhanced diagnostic accuracy and improved treatments.

Genome-wide scan supports the existence of a susceptibility locus for schizophrenia and bipolar disorder on chromosome 15q26

Schizophrenia (SZ) and bipolar disorder (BPD) are two severe psychiatric diseases with a strong genetic component. In agreement with the 'continuum theory', which suggests an overlap between these disorders, the existence of genes that affect simultaneously susceptibility to SZ and BPD has been hypothesized. In this study we performed a 7.5 cM genome scan in a sample of 16 families affected by SZ and BPD, all originating from the same northeast Italian population. Using both parametric and non-parametric analyses we identified linkage peaks on four regions (1p, 1q, 4p and 15q), which were then subjected to a follow-up study with an increased marker density. The strongest linkage was obtained on chromosome 15q26 with a non-parametric linkage of 3.05 for marker D15S1014 (nominal P=0.00197). Interestingly, evidence for linkage with the same marker has been reported previously by an independent study performed on SZ and BPD families from Quebec. In this region, the putative susceptibility gene ST8SIA2 (also known as SIAT8B) was recently associated with SZ in a Japanese sample. However, our allele frequency analyses of the two single-nucleotide polymorphisms (SNPs) with putative functional outcome (rs3759916 and rs3759914) suggest that these polymorphisms are unlikely to be directly involved in SZ in our population. In conclusion, our results support the presence of a gene in 15q26 that influences the susceptibility to both SZ and BPD.

Evidence of linkage and association on 18p11.2 for psychosis

The genetic basis of bipolar disorder (BPD) and schizophrenia (SCZ) has been established through numerous clinical and molecular studies. Although often considered separate nosological entities, evidence now suggests that the two syndromes may share some genetic liability. Recent studies have used a composite phenotype (psychosis) that includes BPD, SCZ, psychosis not otherwise specified, and schizoaffective disorder, to identify shared susceptibility loci. Several chromosomal regions are reported to be shared between these syndromes (18p, 6q, 10p, 13q, 22q). As a part of our endeavor to scan these regions, we report a positive linkage and association finding at 18p11.2 for psychosis. Two-point linkage analysis performed on a series of 52 multiplex pedigrees with 23 polymorphic markers yielded a LOD score of 2.02 at D18S37. An independent set of 159 parent offspring trios was used to confirm this suggestive finding. The TDT analysis yielded support for association between the marker D18S453 and the disease allele (chi2 = 4.829, P < 0.028). This region has been implicated by several studies on BPD [Sjoholt et al. (2004); Mol Psychiatry 9(6):621-629; Washizuka et al. (2004); Biol Psychiatry 56(7):483-489; Pickard et al. (2005); Psychiatr Genet 15(1):37-44], SCZ [Kikuchi et al. (2003); J Med Dent Sci 50(3):225-229; Babovic-Vuksanovic et al. (2004); Am J Med Genet 124(3):318-322] and also as a shared region between the two diseases [Ishiguro et al. (2001); J Neural Transm 108(7):849-854; Reyes et al. (2002); Mol Psychiatry 7(4):337-339; Craddock et al. (2005); J Med Genet 42(3):193-204]. Our findings provide an independent validation of the above reports, and suggest the presence of susceptibility loci for psychoses in this region.

Polypharmacy in oligopopulations: what psychiatric genetics can teach biological psychiatry

Psychiatric genetics and genomics have made major strides in recent years. Some of that knowledge has yet to permeate in the clinical practice of biological psychiatry. The example of cancer-genetics, biology and clinical treatments may be profitable in terms of accelerating translational integration in psychiatry. We propose that current developments in genetics and genomics point to an Early Low-Dose Rational Polypharmacy in Oligopopulations model for psychiatric pharmacotherapy.

Evidence implicating BRD1 with brain development and susceptibility to both schizophrenia and bipolar affective disorder

Linkage studies suggest that chromosome 22q12-13 may contain one or more shared susceptibility genes for schizophrenia (SZ) and bipolar affective disorder (BPD). In a Faeroese sample, we previously reported association between microsatellite markers located at 22q13.31-qtel and both disorders. The present study reports an association analysis across five genes (including 14 single nucleotide and two microsatellite polymorphisms) in this interval using a case-control sample of 162 BPD, 103 SZ patients and 200 controls. The bromodomain-containing 1 gene (BRD1), which encodes a putative regulator of transcription showed association with both disorders with minimal P-values of 0.0046 and 0.00001 for single marker and overall haplotype analysis, respectively. A specific BRD1 2-marker 'risk' haplotype showed a frequency of approximately 10% in the combined case group versus approximately 1% in controls (P-value 2.8 x 10(-7)). Expression analysis of BRD1 mRNA revealed widespread expression in mammalian brain tissue, which was substantiated by immunohistochemical detection of BRD1 protein in the nucleus, perikaryal cytosol and proximal dendrites of the neurons in the adult rat, rabbit and human CNS. Quantitative mRNA analysis in developing fetal pig brain revealed spatiotemporal differences with high expression at early embryonic stages, with intense nuclear and cytosolar immunohistochemical staining of the neuroepithelial layer and early neuroblasts, whilst more mature neurons at later embryonic stages had less nuclear staining. The results implicate BRD1 with SZ and BPD susceptibility and provide evidence that suggests a role for BRD1 in neurodevelopment.

Neurobiology of schizophrenia

With its hallucinations, delusions, thought disorder, and cognitive deficits, schizophrenia affects the most basic human processes of perception, emotion, and judgment. Evidence increasingly suggests that schizophrenia is a subtle disorder of brain development and plasticity. Genetic studies are beginning to identify proteins of candidate genetic risk factors for schizophrenia, including dysbindin, neuregulin 1, DAOA, COMT, and DISC1, and neurobiological studies of the normal and variant forms of these genes are now well justified. We suggest that DISC1 may offer especially valuable insights. Mechanistic studies of the properties of these candidate genes and their protein products should clarify the molecular, cellular, and systems-level pathogenesis of schizophrenia. This can help redefine the schizophrenia phenotype and shed light on the relationship between schizophrenia and other major psychiatric disorders. Understanding these basic pathologic processes may yield novel targets for the development of more effective treatments.

Applications and limitations of empiric data in provision of recurrence risks for schizophrenia: a practical review for healthcare professionals providing clinical psychiatric genetics consultations

Schizophrenia is a common disorder that may frequently be encountered when taking family histories in the genetics clinic, whether or not the referral is for a psychiatric indication. Like in other common disorders, the provision of recurrence risks for schizophrenia is a complex clinical issue because empiric recurrence risks (while reasonably well established) can rarely be used without individual tailoring. This review seeks to identify and detail some pertinent issues surrounding the clinical utility of empiric recurrence risks for schizophrenia, and to provide an overview of important factors to consider when tailoring empiric risks for individual patients.

Genetic counselling for psychiatric disorders

Family, adoption and twin studies demonstrate that many adult psychiatric disorders, including schizophrenia, major depression and bipolar disorder, have a clear genetic component. The aetiology of psychiatric disorders is a complex combination of both genetic and environmental components. While potential susceptibility genes for psychiatric disorders have been identified, interaction with the environment is a crucial component in disease development. Pharmacogenetics and genetic testing have the potential to play key roles in the future of clinical psychiatry. At present, an increased risk of psychiatric disorders can be identified through a detailed family history. The empirical risk of developing a disorder has been determined for many psychiatric disorders and can be used as a general guide. Genetic counselling can extend and enhance patient care by providing information to patients about the complexities of inheriting psychiatric disorders and the associated risks of recurrence. The genetic counselling process can facilitate informed decision making, alleviate misconceptions and reduce stigma through an improved understanding of the genetic cause of psychiatric disorders, and offer support to patients and their families.

Longitudinal stability of the CBCL-juvenile bipolar disorder phenotype: A study in Dutch twins

BACKGROUND

The Child Behavior Checklist-juvenile bipolar disorder phenotype (CBCL-JBD) is a quantitative phenotype that is based on parental ratings of the behavior of the child. The phenotype is predictive of DSM-IV characterizations of BD and has been shown to be sensitive and specific. Its genetic architecture differs from that for inattentive, aggressive, or anxious-depressed syndromes. The purpose of this study is to assess the developmental stability of the CBCL-JBD phenotype across ages 7, 10, and 12 years in a large population-based twin sample and to examine its genetic architecture.

METHODS

Longitudinal data on Dutch mono- and dizygotic twin pairs (N = 8013 pairs) are analyzed to decompose the stability of the CBCL-JBD phenotype into genetic and environmental contributions.

RESULTS

Heritability of the CBCL-JBD increases with age (from 63% to 75%), whereas the effects of shared environment decrease (from 20% to 8%). The stability of the CBCL-JBD phenotype is high, with correlations between .66 and .77 across ages 7, 10, and 12 years. Genetic factors account for the majority of the stability of this phenotype. There were no sex differences in genetic architecture.

CONCLUSIONS

Roughly 80% of the stability in childhood CBCL-JBD is a result of additive genetic effects.

No association between Ala9Val functional polymorphism of MnSOD gene and schizophrenia in a representative Italian sample

Reactive oxygen species (ROS) have been suggested to play an important role in physiopathology of schizophrenia. The polymorphisms in the genes encoding antioxidant enzymes, such as manganese superoxide dismutase (MnSOD) should, thus, result in predisposition to this psychiatric disorder. A functional amino acid polymorphism (Ala9Val) has been described in the signal sequence of enzyme associated with a decreased defense capacity against oxidative stress. Preliminary evidence in a Turkey population indicated that this polymorphism contributes to physiopathogenesis of schizophrenia. The object of this study was to verify the association between Ala9Val and schizophrenia in a representative Italian sample. The polymorphism was genotyped by PCR amplification and Single-Stranded Conformational Polymorphism (SSCP) analysis in 212 DSMIV schizophrenic patients and 257 healthy volunteers. No association was observed between cases and controls (genotype and allele frequencies: p = 0.72, p = 0.55, respectively) even when a sample stratification for gender, age at onset and diagnostic subtypes was performed. This suggests that the gene variant could not be a risk factor for schizophrenia susceptibility in an Italian sample.

The G72/G30 gene locus in psychiatric disorders: a challenge to diagnostic boundaries?

In follow-up from evidence obtained in linkage studies, systematic linkage disequilibrium mapping within chromosomal region 13q33 has led to the identification of a schizophrenia susceptibility locus which harbors the genes G72 and G30. These association findings have been replicated in several independent schizophrenia samples. Association has also been found between genetic variants at the G72/G30 locus and bipolar affective disorder (BPAD), with replication in independent studies. Results from studies of more detailed psychiatric phenotypes show that association exists with symptom clusters that are common to several disorders as well as with specific psychiatric diagnoses. These findings may indicate that the association lies not with the diagnostic categories per se but with more specific aspects of the phenotype, such as affective symptoms and cognitive effects, which cross traditional psychiatric diagnostic boundaries. At the molecular level, the picture remains far from clear. No putative functional variants have been identified in the coding regions of G72 or G30, and it is therefore likely that disease susceptibility is caused by as yet unidentified variants which alter gene expression or splicing. A further complication is the fact that inconsistencies are evident in the risk alleles and haplotypes observed to be associated across different samples and studies, which may suggest the presence of multiple susceptibility variants at this locus. Functional analyses indicate that the G72 gene product plays a role in the activation of N-methyl-D-aspartate receptors, a molecular pathway implicated in both schizophrenia and BPAD, making it the most plausible candidate gene at this locus.

Global visual scanning abnormalities in schizophrenia and bipolar disorder

Visual scanning of face images is widely reported to be abnormal in schizophrenia. This impaired processing has been proposed to be partly responsible for patients' disturbance in social interactions. The present study was designed to determine whether abnormal scanning is specific to images with social content or extends to other types of stimuli. Individuals with schizophrenia (n=22), bipolar disorder (n=19) and healthy controls (n=37) were asked to view a series of 28 images with or without socially important content (i.e. faces, landscapes, fractals and noise patterns) while their eye movements were recorded video-oculographically. Temporal and spatial characteristics of scan paths were compared for each patient group and picture type. Independent of image content, patients with schizophrenia exhibited fewer fixations, longer fixation duration, longer saccade duration and peak velocity, and smaller saccade amplitude compared with healthy controls. Patients with schizophrenia and bipolar disorder did not differ significantly from one another on any of the temporal variables recorded. Fixation location distributions of participants with schizophrenia differed significantly from that of healthy controls on all picture types and from patients with bipolar disorder on all but face images. Abnormal scanning in schizophrenia and also bipolar disorder was independent of stimulus type and therefore reflects a global visual scanning impairment not specific to faces. Spatial scanning characteristics but not temporal ones may serve as biomarkers in the functional psychoses.

Psychosis pathways converge via D2high dopamine receptors

The objective of this review is to identify a target or biomarker of altered neurochemical sensitivity that is common to the many animal models of human psychoses associated with street drugs, brain injury, steroid use, birth injury, and gene alterations. Psychosis in humans can be caused by amphetamine, phencyclidine, steroids, ethanol, and brain lesions such as hippocampal, cortical, and entorhinal lesions. Strikingly, all of these drugs and lesions in rats lead to dopamine supersensitivity and increase the high-affinity states of dopamine D2 receptors, or D2High, by 200-400% in striata. Similar supersensitivity and D2High elevations occur in rats born by Caesarian section and in rats treated with corticosterone or antipsychotics such as reserpine, risperidone, haloperidol, olanzapine, quetiapine, and clozapine, with the latter two inducing elevated D2High states less than that caused by haloperidol or olanzapine. Mice born with gene knockouts of some possible schizophrenia susceptibility genes are dopamine supersensitive, and their striata reveal markedly elevated D2High states; suchgenes include dopamine-beta-hydroxylase, dopamine D4 receptors, G protein receptor kinase 6, tyrosine hydroxylase, catechol-O-methyltransferase, the trace amine-1 receptor, regulator of G protein signaling RGS9, and the RIIbeta form of cAMP-dependent protein kinase (PKA). Striata from mice that are not dopamine supersensitive did not reveal elevated D2High states; these include mice with knockouts of adenosine A2A receptors, glycogen synthase kinase GSK3beta, metabotropic glutamate receptor 5, dopamine D1 or D3 receptors, histamine H1, H2, or H3 receptors, and rats treated with ketanserin or aD1 antagonist. The evidence suggests that there are multiple pathways that convergetoelevate the D2High state in brain regions and that this elevation may elicit psychosis. This proposition is supported by the dopamine supersensitivity that is a common feature of schizophrenia and that also occurs in many types of genetically altered, drug-altered, and lesion-altered animals. Dopamine supersensitivity, in turn, correlates with D2High states. The finding that all antipsychotics, traditional and recent ones, act on D2High dopamine receptors further supports the proposition.

Convergent linkage evidence from two Latin-American population isolates supports the presence of a susceptibility locus for bipolar disorder in 5q31-34

We performed a whole genome microsatellite marker scan in six multiplex families with bipolar (BP) mood disorder ascertained in Antioquia, a historically isolated population from North West Colombia. These families were characterized clinically using the approach employed in independent ongoing studies of BP in the closely related population of the Central Valley of Costa Rica. The most consistent linkage results from parametric and non-parametric analyses of the Colombian scan involved markers on 5q31-33, a region implicated by the previous studies of BP in Costa Rica. Because of these concordant results, a follow-up study with additional markers was undertaken in an expanded set of Colombian and Costa Rican families; this provided a genome-wide significant evidence of linkage of BPI to a candidate region of approximately 10 cM in 5q31-33 (maximum non-parametric linkage score=4.395, P<0.00004). Interestingly, this region has been implicated in several previous genetic studies of schizophrenia and psychosis, including disease association with variants of the enthoprotin and gamma-aminobutyric acid receptor genes.

Tryptophan hydroxylase-1 gene variants associated with schizophrenia

BACKGROUND

Serotonin (5-HT) has been implicated in the pathophysiology of schizophrenia. Tryptophan hydroxylase (TPH) is the rate-limiting enzyme in the biosynthesis of serotonin (5-HT), and as such it might be related to the pathogenesis of schizophrenia. Two isoforms are known, TPH-1 and TPH-2. TPH-1 association with schizophrenia is debated.

METHODS

A case-control design was employed for gene-disease association in 155 schizophrenic psychosis patients and 253 healthy controls, all North European Caucasians. Six single nucleotide polymorphisms (SNPs) with a haplotype block structure spanning over 23 kb of the total TPH-1 29 kb were analyzed. Linkage disequilibrium and haplotype analyses were performed. Bonferroni correction was used for multiple testing.

RESULTS

Single marker association analyses showed two SNPs significantly associated with schizophrenia. Several haplotypes were associated with the disease. A "sliding window" analysis attributed the strongest disease association to a haplotype configuration localized between the promoter region and intron 3.

CONCLUSIONS

Our data indicate that TPH-1 associates with schizophrenia. It appears that specific combinations of promoter variants vis-à-vis gene transcript variants contribute to genetic predisposition to the disease.

Critical factors in gene expression in postmortem human brain: Focus on studies in schizophrenia

BACKGROUND

Studies of postmortem human brain are important for investigating underlying pathogenic molecular mechanisms of neuropsychiatric disorders. They are, however, confounded by pre- and postmortem factors. The purpose of this study was to identify sources of variation that will enable a better design of gene expression studies and higher reliability of gene expression data.

METHODS

We assessed the contribution of multiple variables to messenger RNA (mRNA) expression of reference (housekeeping) genes measured by reverse transcriptase-polymerase chain reaction (RT-PCR) by multiple regression analysis in a large number (N = 143) of autopsy samples from the hippocampus and white and grey matter of the dorsolateral prefrontal cortex (DLPFC) of patients with schizophrenia and normal control subjects.

RESULTS

The strongest predictor of gene expression was total RNA quality. Other significant factors included pH, postmortem interval, age and the duration of the agonal state, but the importance of these factors depended on transcript measured, brain region analyzed, and diagnosis. The quality of RNA obtained from the DLPFC white matter was also adversely affected by smoking.

CONCLUSIONS

Our results show that normalization of expression data of target genes with a geometric mean of multiple housekeeping genes should be used to control for differences in RNA quality between samples. The results also suggest that accurate assessment of other confounding factors and their inclusion as regressors in the analysis is critical for obtaining reliable and accurate quantification of mRNA expression.

Common variations in ALG9 are not associated with bipolar I disorder: a family-based study

Background

A mannosyltransferase gene (ALG9, DIBD1) at chromosome band 11q23 was previously identified to be disrupted by a balanced chromosomal translocation t(9;11)(p24;q23) co-segregating with bipolar affective disorder in a small family. Inborn ALG9 deficiency (congenital disorders of glycosylation type IL) is associated with progressive microcephaly, seizures, developmental delay, and hepatomegaly. It is unknown whether common variations of ALG9 predispose to bipolar affective disorder.

Methods

We tested five polymorphic markers spanning ALG9 (three intragenic and one upstream microsatellite repeats and one common missense variation, V289I (rs10502151) for their association with bipolar I disorder in two pedigree series. The NIMH (National Institute of Mental Health) pedigrees had a total of 166 families showing transmissions to 250 affected offspring, whereas The PITT (The University of Pittsburgh) pedigrees had a total of 129 families showing transmissions to 135 cases. We used transmission disequilibrium test for the association analyses.

Results

We identified three common and distinct haplotypes spanning the ALG9 gene. We found no statistically-significant evidence of transmission disequilibrium of marker alleles or multi-marker haplotypes to the affected offspring with bipolar I disorder.

Conclusion

These results suggest that common variations in ALG9 do not play a major role in predisposition to bipolar affective disorder.

Family-based association study between G72/G30 genetic polymorphism and schizophrenia

Genetic variations in G72/G30 have been reported to be associated with schizophrenia and bipolar disorders in several case-control studies. This gene is located in a genomic region known to contain susceptibility genes for schizophrenia. As case-control studies carry an increased risk of confounding through population stratification, we investigate whether the rs947267 (A/C) polymorphism is associated with schizophrenia in a family-based association study. This polymorphism is located within the G72/G30 gene and has been previously associated with bipolar disorders. The sample consisted of a total of 216 Chinese families that included an affected offspring and parents. Transmission disequilibrium analysis revealed a significant association between the G72/G30 rs947267 polymorphism and schizophrenia (P=0.016), with the A allele more commonly transmitted to patients. Further analysis stratified by sex showed that the A allele was significantly more overtransmitted than nontransmitted in the trios of male probands (P=0.031), but not in the trios of female probands. Our family-based association study supports the suggestion that the G72/G30 gene may be implicated in susceptibility to schizophrenia and there may be an interaction between this gene and sex in the pathogenesis of schizophrenia.

Toward constructing an endophenotype strategy for bipolar disorders

Research aimed at elucidating the underlying neurobiology and genetics of bipolar disorder, and factors associated with treatment response, have been limited by a heterogeneous clinical phenotype and lack of knowledge about its underlying diathesis. We used a survey of clinical, epidemiological, neurobiological, and genetic studies to select and evaluate candidate endophenotypes for bipolar disorder. Numerous findings regarding brain function, brain structure, and response to pharmacological challenge in bipolar patients and their relatives deserve further investigation. Candidate brain function endophenotypes include attention deficits, deficits in verbal learning and memory, cognitive deficits after tryptophan depletion, circadian rhythm instability, and dysmodulation of motivation and reward. We selected reduced anterior cingulate volume and early-onset white matter abnormalities as candidate brain structure endophenotypes. Symptom provocation endophenotypes might be based on bipolar patients' sensitivity to sleep deprivation, psychostimulants, and cholinergic drugs. Phenotypic heterogeneity is a major impediment to the elucidation of the neurobiology and genetics of bipolar disorder. We present a strategy constructed to improve the phenotypic definition of bipolar disorder by elucidating candidate endophenotypes. Studies to evaluate candidate endophenotypes with respect to specificity, heritability, temporal stability, and prevalence in unaffected relatives are encouraged.

Behavioral and biochemical characterization of a mutant mouse strain lacking D-amino acid oxidase activity and its implications for schizophrenia

D-amino acid oxidase (DAO) degrades D-serine, a co-agonist at the NMDA receptor (NMDAR). Hypofunction of the NMDAR has been suggested to contribute to the pathophysiology of schizophrenia. Intriguingly, DAO has been recently identified as a risk factor for schizophrenia through genetic association studies. A naturally occurring mouse strain (ddY/DAO-) has been identified which lacks DAO activity. We have characterized this strain both behaviorally and biochemically to evaluate DAO as a target for schizophrenia. We have confirmed that this strain lacks DAO activity and shown for the first time it has increased occupancy of the NMDAR glycine site due to elevated extracellular D-serine levels and has enhanced NMDAR function in vivo. Furthermore, the ddY/DAO- strain displays behaviors which suggest that it will be a useful tool for evaluation of the clinical benefit of DAO inhibition in schizophrenia.

Genetics of affective (mood) disorders

The enormous public health importance of mood disorders, when considered alongside their substantial heritabilities, has stimulated much work, predominantly in bipolar disorder but increasingly in unipolar depression, aimed at identifying susceptibility genes using both positional and functional molecular genetic approaches. Several regions of interest have emerged in linkage studies and, recently, evidence implicating specific genes has been reported; the best supported include BDNF and DAOA but further replications are required and phenotypic relationships and biological mechanisms need investigation. The complexity of psychiatric phenotypes is demonstrated by (a) the evidence accumulating for an overlap in genetic susceptibility across the traditional classification systems that divide disorders into schizophrenia and mood disorders, and (b) evidence suggestive of gene-environment interactions.

Neuropsychological functioning in adolescents and young adults at genetic risk for schizophrenia and affective psychoses: results from the Harvard and Hillside Adolescent High Risk Studies

Siblings and offspring of persons with schizophrenia carry elevated genetic risk for the illness and manifest attentional and memory impairments. Because less is known about other neuropsychological functions and their specificity in adolescents, we conducted a genetic high-risk (HR) study of schizophrenia (HR-SCZ) and affective psychosis (HR-AFF). Participants (ages 12-25) were from the Harvard Adolescent High-Risk and Hillside Family studies, including 73 HR-SCZ, 18 HR-AFF, and 84 community controls (CCs) recruited in metropolitan Boston and New York. Groups were compared on overall neurocognitive functioning, 6 domains, and 13 test scores, controlling for age, parental education, and correlated data within families. The HR-SCZ group was significantly impaired overall, while the HR-AFF group demonstrated a trend toward overall impairment. HR-SCZ subjects showed significantly lower Verbal Ability (d = .73) and Executive Functioning/Working Memory (d = .47) than CCs. HR-AFF subjects showed reduced Verbal Ability (d = .64) compared to CCs. Excluding 12 CCs with a parental history of depression (without psychosis) led to larger differences between HR and CC groups across domains. Moreover, HR-SCZ and CC group differences in Verbal Memory (d = .39) and Visual-Spatial (d = .34) became statistically significant. There were no significant differences between HR-SCZ and HR-AFF groups. Data support a modest neuropsychological deficit in persons at genetic HR for psychosis, with a broader range of deficits in HR-SCZ. Future work should assess the relationship of neurocognition to adaptive functioning and possible onset of psychosis in HR samples. Ascertainment criteria for controls may markedly influence results and interpretation of group differences.

Use of phenotypic covariates in association analysis by sequential addition of cases

Optimal use of phenotype information is important in complex disease gene mapping. We describe a method, sequential addition, for the analysis of case-control data by taking into account of a quantitative trait that is measured in cases but not in controls. The method also provides an estimate of the best phenotype definition for future studies. We demonstrate proof of principle, using an example of incorporation of age-at-onset data into a study of a small sample for association between APOE and late-onset Alzheimer's disease. The sequential addition method finds evidence of association when conventional case-control methods fail. We also illustrate the use of the method for taking account of a dimensional measure of psychosis in a study of the schizophrenia susceptibility gene, dysbindin, in bipolar disorder.

Lithium increases nerve growth factor levels in the rat hippocampus in an animal model of mania

Pharmacological studies suggest that neurotrophins may play a role in the effects of lithium and valproate on mood regulation. In this study, we tested the hypotheses that lithium and valproate would reverse and prevent the behavioral and biochemical effects of amphetamine, using a rat model of mania. In the reversal treatment, male Wistar rats were first administered D-amphetamine or saline for 14 days, and then, between days 8-14, rats were treated with lithium, valproate or saline. In the prevention treatment, rats were pretreated with lithium, valproate or saline, and then, between days 8-14, rats were administered D-amphetamine or saline. Locomotor behavior was assessed using the open-field task and hippocampal nerve growth factor levels were determined by enzyme-linked immunosorbent assay. Both lithium and valproate reversed and prevented D-amphetamine-induced hyperactivity. Lithium increased nerve growth factor content in rat hippocampus in both experiments, but this effect was blocked with the co-administration of D-amphetamine. No significant effects on nerve growth factor levels were observed with valproate or D-amphetamine alone. These findings suggest that nerve growth factor may play a role in the neurotrophic effects of lithium but do not support the hypotheses that the nerve growth factor/TrkA pathway is involved in the pathophysiology of bipolar disorder.

The role of phospholipases A2 in schizophrenia

A range of neurotransmitter systems have been implicated in the pathogenesis of schizophrenia based on the antidopaminergic activities of antipsychotic medications, and chemicals that can induce psychotic-like symptoms, such as ketamine or PCP. Such neurotransmitter systems often mediate their cellular response via G-protein-coupled release of arachidonic acid (AA) via the activation of phospholipases A2 (PLA2s). The interaction of three PLA2s are important for the regulation of the release of AA--phospholipase A2 Group 2 A, phospholipase A2 Group 4A and phospholipase A2 Group 6A. Gene variations of these three key enzymes have been associated with schizophrenia with conflicting results. Preclinical data suggest that the activity of these three enzymes are associated with monoaminergic neurotransmission, and may contribute to the differential efficacy of antipsychotic medications, as well as other biological changes thought to underlie schizophrenia, such as altered neurodevelopment and synaptic remodelling. We review the evidence and discuss the potential roles of these three key enzymes for schizophrenia with particular emphasis on published association studies.

Duplication 8q22.1-q24.1 associated with bipolar disorder and speech delay

OBJECTIVE

To report a case of a child with bipolar disorder found to have an unbalanced translocation involving the long arm of chromosome 8, a region that has been previously implicated in genome-wide linkage scans.

CASE REPORT

A 7-year-old boy with a complex psychiatric symptom presentation including attention deficits, distractibility, impulsivity, pressured speech, sleep disturbance, aggressive behavior, and hypersexuality diagnosed with bipolar disorder. He also showed evidence of borderline intellectual and adaptive functioning and had mild dysmorphic features with a duplication of distal 8q that arose as an unbalanced chromosomal translocation due to a maternal 15p;8q insertion.

CONCLUSION

This finding of an unbalanced translocation provides further evidence to support previous linkage studies of a potential causative gene on 8q for bipolar disorder.

A summary statistic approach to sequence variation in noncoding regions of six schizophrenia-associated gene loci

In order to explore the role of noncoding variants in the genetics of schizophrenia, we sequenced 27 kb of noncoding DNA from the gene loci RAC-alpha serine/threonine-protein kinase (AKT1), brain-derived neurotrophic factor (BDNF), dopamine receptor-3 (DRD3), dystrobrevin binding protein-1 (DTNBP1), neuregulin-1 (NRG1) and regulator of G-protein signaling-4 (RGS4) in 37 schizophrenia patients and 25 healthy controls. To compare the allele frequency spectrum between the two samples, we separately computed Tajima's D-value for each sample. The results showed a smaller Tajima's D-value in the case sample, pointing to an excess of rare variants as compared to the control sample. When randomly permuting the affection status of sequenced individuals, we observed a stronger decrease of Tajima's D in 2400 out of 100,000 permutations, corresponding to a P-value of 0.024 in a one-sided test. Thus, rare variants are significantly enriched in the schizophrenia sample, indicating the existence of disease-related sequence alterations. When categorizing the sequenced fragments according to their level of human-rodent conservation or according to their gene locus, we observed a wide range of diversity parameter estimates. Rare variants were enriched in conserved regions as compared to nonconserved regions in both samples. Nevertheless, rare variants remained more common among patients, suggesting an increased number of variants under purifying selection in this sample. Finally, we performed a heuristic search for the subset of gene loci, which jointly produces the strongest difference between controls and cases. This showed a more prominent role of variants from the loci AKT1, BDNF and RGS4. Taken together, our approach provides promising strategy to investigate the genetics of schizophrenia and related phenotypes.

Emotional processing in schizophrenia

INTRODUCTION

Persons with schizophrenia have impaired emotional processing, involving experience, expression, and recognition of emotions.

METHODS

This article reviews the historical descriptions and more recent work on emotion processing in schizophrenia.

RESULTS

Although abilities of emotional processing relate directly to interpersonal communication and psychosocial functioning, methodological issues exist in the current body of studies and resultant knowledge, which limit translation to novel treatment options.

CONCLUSIONS

Further improvement in emotion processing in persons with stable schizophrenia are unlikely to result from conventional pharmacotherapy of psychosis. New treatment modalities and behavioural interventions offer possible improvements in quality of life and psychosocial functioning.

Serum brain-derived neurotrophic factor is decreased in bipolar disorder during depressive and manic episodes

Genetic and pharmacological studies have suggested that brain-derived neurotrophic factor (BDNF) may be associated with the pathophysiology of bipolar disorder (BD). The present study investigated serum BDNF levels in manic, depressed, euthymic BD patients and in matched healthy controls, using an enzyme-linked immunosorbent assay (sandwich-ELISA). Serum BDNF levels were decreased in manic (p=0.019) and depressed (p=0.027) BD patients, as compared with euthymic patients and controls. Serum BDNF levels were negatively correlated with the severity of manic (r=-0.37, p=0.005) and depressive (r=-0.30, p=0.033) symptoms. These findings further support the hypothesis that the BDNF signaling system may play a role in the pathophysiology of BD.

The catechol-O-methyl transferase (COMT) gene as a candidate for psychiatric phenotypes: evidence and lessons

The enzyme catechol-O-methyl transferase (COMT), identified in the 1950s, is involved in catabolism of monoamines that are influenced by psychotropic medications, including neuroleptics and antidepressants. The COMT gene lies in a chromosomal region of interest for psychosis and bipolar spectrum disorder and a common polymorphism within the gene alters the activity of the enzyme. As a consequence, COMT has been one of the most studied genes for psychosis. On the basis of prior probabilities it would seem surprising if functional variation at COMT did not have some influence either on susceptibility to psychiatric phenotypes, modification of the course of illness or moderation of response to treatment. There is now robust evidence that variation at COMT influences frontal lobe function. However, despite considerable research effort, it has not proved straightforward to demonstrate and characterise a clear relationship between genetic variation at COMT and psychiatric phenotypes. It is of course, possible that COMT will turn out to be an unusually intractable case but it seems more likely that the experiences with this gene will provide a foretaste of the complexity of genotype-phenotype relationships that will be found for psychiatric traits. In this review, we consider the current state of evidence and the implications both for further studies of COMT and more generally for studies of other genes.

A Neuroscientist–Consumer Alliance to Transform Mental Health Care

The field of mental health has long suffered from a lack of convergence of disciplines that deal with the mind, the brain, and behavior. This mind-brain dualism has been particularly detrimental for consumers and their families who daily face stigma and discrimination. The understanding of the brain and its dysfunctions has benefited from the study of the human genome and, in particular, of the mutations and variations in its code. This analysis permits a better understanding of the biological basis of mental disease and will soon inform a generation of new diagnostic tools and individualized pharmacological therapies. A biological perspective on mental illness will be complemented by the analysis of the social factors influencing people's behavior and their impact on brain biology and gene function. Neurobiology has progressed to a level for which the knowledge that is generated, even if still colored with uncertainty, could represent a catalyst for the creation of an alliance between neuroscientists and consumers. This partnership has the potential to benefit both parties but will require some concrete steps that might be outside of the usual courses of action for both consumers and scientists. It is by building collaborations based on personal contact and information sharing that a transformation of the mental health care system can occur.

Association analysis of the chromosome 4p-located G protein-coupled receptor 78 (GPR78) gene in bipolar affective disorder and schizophrenia

The orphan G protein-coupled receptor 78 (GPR78) gene lies within a region of chromosome 4p where we have previously shown linkage to bipolar affective disorder (BPAD) in a large Scottish family. GPR78 was screened for single-nucleotide polymorphisms (SNPs) and a linkage disequilibrium map was constructed. Six tagging SNPs were selected and tested for association on a sample of 377 BPAD, 392 schizophrenia (SCZ) and 470 control individuals. Using standard chi(2) statistics and a backwards logistic regression approach to adjust for the effect of sex, SNP rs1282, located approximately 3 kb upstream of the coding region, was identified as a potentially important variant in SCZ (chi(2) P=0.044; LRT P=0.065). When the analysis was restricted to females, the strength of association increased to an uncorrected allele P-value of 0.015 (odds ratios (OR)=1.688, 95% confidence intervals (CI): 1.104-2.581) and uncorrected genotype P-value of 0.015 (OR=5.991, 95% CI: 1.545-23.232). Under the recessive model, the genotype P-value improved further to 0.005 (OR=5.618, 95% CI: 1.460-21.617) and remained significant after correcting for multiple testing (P=0.017). No single-marker association was detected in the SCZ males, in the BPAD individuals or with any other SNP. Haplotype analysis of the case-control samples revealed several global and individual haplotypes, with P-values <0.05, all but one of which contained SNP rs1282. After correcting for multiple testing, two haplotypes remained significant in both the female BPAD individuals (P=0.038 and 0.032) and in the full sample of affected female individuals (P=0.044 and 0.033). Our results provide preliminary evidence for the involvement of GPR78 in susceptibility to BPAD and SCZ in the Scottish population.

The role of the phosphatidylinositide 3-kinase–protein kinase B pathway in schizophrenia

Neuroanatomical studies of brains from schizophrenic patients report evidence for neuronal dystrophy, while in genetic studies in schizophrenia there is evidence for mutations in growth factors and the downstream enzymes phosphatidylinositide 3-kinase (PI3K) and protein kinase B (PKB). Since the PI3K-PKB pathway is involved in cellular growth and proliferation, reduced activity of this cascade in schizophrenia could at least partly explain the neuronal dystrophy. Risk factors for schizophrenia, such as corticosteroids and cannabis, suppress the activity of the PI3K-PKB pathway. Conversely, estrogen and vitamin D, 2 factors with a moderate protective activity in schizophrenia, electroconvulsive shock therapy, and chronic treatment with antipsychotic compounds stimulate the pathway. Reduced activity of the PI3K-PKB pathway makes the brain more susceptible to virus infections, anoxia, and obstetric complications (recognized risk factors for schizophrenia), whereas a diminution of growth factor levels towards the end of puberty could contribute to an increase in schizophrenia symptoms observed around that time. On the other hand, constitutive (over)activation of the PI3K-PKB pathway increases cancer risk. Consequently, the presumed hypoactivity of the PI3K-PKB cascade might provide a partial explanation for the remarkable epidemiological finding of a reduced cancer rate in schizophrenic patients. Recognition of the role of a dysfunctional PI3K-PKB pathway in schizophrenia might help in the discovery of hitherto undetected causative gene mutations and could also lead to novel therapeutic approaches. However, a major challenge that remains to be solved is how the PI3K-PKB pathway can be activated without increasing the risk of cancer.