A linkage study of the N-methyl-D-aspartate receptor subunit gene loci and schizophrenia in southern African Bantu-speaking families

Family, twin and adoption studies of severe mental disorders in sub-Saharan Africa: a scoping review

PURPOSE

The traditional genetic epidemiological studies are necessary to improve accurate risk communication to service users and their families. This scoping review aimed to describe the volume and scope of existing research evidence on family, twin and adoption studies of severe mental disorders (SMDs) in SSA. This is with a view to identifying gaps in the literature and the adequacy of data for a systematic review and meta-analysis.

METHODS

Literature search was done for all original peer-reviewed research articles on the topic in SSA using PubMed and MEDLINE. Publications included were peer-reviewed original articles, irrespective of their quality, carried out in the region from the 1970s till 9th March, 2022, which were available in English or translated to English. Case reports, abstracts, and studies among populations living outside the region were excluded.

RESULTS

A total of five studies that met the inclusion criteria across the 46 countries in the region were identified. Of the three thematic areas of focus, only family studies on SMDs had research work in SSA. These studies provided evidence of familial clustering of SMDs in SSA. There were no twin and adoption studies on SMDs in the region. However, the review noted the establishment of two twin registries in Guinea-Bissau and Nigeria. A huge gap exists in the area of twin and adoption studies on SMDs in SSA.

CONCLUSION

The volume of research evidence on traditional family genetic studies of SMDs is grossly inadequate to consider a systematic review in SSA. We have suggested studies to remedy the situation.

The effect of human GRIN1 gene 5' functional region on gene expression regulation in vitro

INTRODUCTION

Abnormal expression of ionotropic glutamate receptor NMDA type subunit 1, the key subunit of the NMDA receptor, may be related to many neuropsychiatric disorders. In this study, we explored the functional sequence of the 5' regulatory region of the human GRIN1 gene and discussed the transcription factors that may regulate gene expression.

MATERIALS AND METHODS

Twelve recombinant pGL3 vectors with gradually truncated fragment lengths were constructed, transfected into HEK-293, U87, and SK-N-SH cell lines, and analyzed through the luciferase reporter gene assay. JASPAR database is used to predict transcription factors.

RESULTS

In SK-N-SH and U87 cell lines, regions from -337 to -159 bp, -704 to -556 bp inhibited gene expression, while -556 to -337 bp upregulated gene expression. In HEK-293 and U87 cell lines, the expression of fragment -1703 to + 188 bp was significantly increased compared to adjacent fragments -1539 to + 188 bp and -1843 to + 188 bp. The protein expressions of fragments -2162 to + 188 bp and -2025 to + 188 bp, -1539 to + 188 bp and -1215 to + 188 bp, -1215 to + 188 bp and -1066 to + 188 bp were significantly different in HEK-293 and SK-N-SH cells. According to the predictions of the JASPAR database, the transcription factors REST, EGR1, and CREB1/HIC2 may bind the DNA sequences of GRIN1 gene from the -337 to -159, -556 to -337, and -704 to -556, respectively. In addition, zinc finger transcription factors may regulate the expression of other differentially expressed fragments.

CONCLUSIONS

Abnormal transcription regulation in the proximal promoter region of GRIN1 (-704 to + 188 bp) may be involved in the course of neuropsychiatric diseases.

Association of the dopamine β-hydroxylase 19 bp insertion/deletion polymorphism with positive symptoms but not tardive dyskinesia in schizophrenia

OBJECTIVE

Overactivity of dopaminergic neurotransmission is a putative mechanism of tardive dyskinesia (TD). Dopamine beta-hydroxylase (DBH) is a key enzyme in the conversion of dopamine to norepinephrine, and plasma DBH activity is altered in TD patients. This study examined whether the functional DBH 5'-Ins/Del polymorphism was associated with TD severity in Chinese patients with schizophrenia.

METHODS

We compared the rate of this polymorphism in patients with (n = 312) and without TD (n = 435), and healthy controls (n = 625). The severity of TD was assessed using the Abnormal Involuntary Movement Scale (AIMS) and psychopathology using the Positive and Negative Syndrome Scale (PANSS).

RESULTS

There were no significant differences in the distribution of the allele and genotype frequencies between the patients and controls, or between the patients with and without TD. Also, there was no significant difference in the AIMS total score between the three genotype groups. However, the PANSS positive symptom subscore was significantly higher in patients with Del/Del genotype (13.2 ± 5.2) than those with Ins/Del (11.2 ± 4.9) and Ins/Ins (11.1 ± 3.1) genotypes (both p < 0.05).

CONCLUSION

These results suggest that although the DBH 5'-Ins/Del polymorphism was not associated with susceptibility to TD in patients with schizophrenia, it might be related to positive symptoms of schizophrenia.

Toward a modern search for schizophrenia genes

Genetic epidemiology has provided consistent evidence that schizophrenia has a genetic component It is now clear that this genetic component is complex and polygenic, with several genes interacting in epistasis. Although molecular studies have failed to identify any DNA variant that clearly contributes to vulnerability to schizophrenia, several regions have been implicated by linkage studies. To overcome the difficulties in the search for schizophrenia genes, it is necessary (i) to use methods of analysis that are appropriate for complex multifactorial disorders; (ii) to gather large enough clinical samples; and (iii) in the absence of genetic validity of the diagnostic classification currently used, to apply new strategies in order to better define the affected phenotypes. For this purpose, we describe here two strategies: (i) the candidate symptom approach, which concerns affected subjects and uses proband characteristics as the affected phenotype, such as age at onset, severity, and negative/positive symptoms; and (ii) the endophenotypic approach, which concerns unaffected relatives and has already provided positive findings with phenotypes, such as P50 inhibitory gating or eye-movement dysfunctions.

The dopamine b-hydroxylase 19 bp insertion/deletion polymorphism was associated with first-episode but not medicated chronic schizophrenia

BACKGROUND

Numerous studies report dysfunctional dopaminergic and noradrenergic neurotransmission in the pathogenesis of schizophrenia. Dopamine beta-hydroxylase (DBH) is an intracellular enzyme catalyzing the conversion of dopamine to noradrenaline. Functional polymorphisms have been reported in the promoter region of DBH gene, including a 19 bp insertion/deletion polymorphism. The purpose of this study was to investigate whether there was an association between the functional polymorphism (DBH5'-Ins/Del) and schizophrenia in a Han Chinese population.

METHODS

This polymorphism was genotyped in 221 first-episode schizophrenics, 360 chronic schizophrenics and 318 healthy controls using a case-control design. We assessed their psychopathology using the Positive and Negative Syndrome Scale (PANSS).

RESULTS

We showed that the DBH5'-Ins/Del deletion (Del) allelic and genotypic frequencies were significantly lower in controls than first-episode of schizophrenics (FES) (both p < 0.001), but controls were not different from chronic schizophrenics. Furthermore, the PANSS positive symptom and total scores were significantly higher in FES with the Del/Del genotype than those with Ins/Del and Ins/Ins genotypes (all p < 0.05).

CONCLUSIONS

The DBH5'-Ins/Del polymorphism may play a role in susceptibility to the positive symptoms of FES and to these FES not progressing on to chronic schizophrenia.

Stage II follow-up on a linkage scan for bipolar disorder in the Ashkenazim provides suggestive evidence for chromosome 12p and the GRIN2B gene

PURPOSE

We had previously performed a genome-wide linkage scan for bipolar affective disorder in an Ashkenazi Jewish sample, a population likely to have reduced genetic heterogeneity. This study is a second stage follow-up focusing on regions that showed positive linkage scores in our previous scan but were not fine-mapped at that time.

METHODS

We genotyped an additional 145 highly polymorphic microsatellites and conducted linkage analyses using standard laboratory and analytical methods.

RESULTS

We saw an improvement of the evidence for linkage in most regions, with the most notable change on chromosome 12p13.1-p12.3, where the evidence of linkage is now suggestive. This region harbors the gene encoding the ionotropic glutamate receptor subunit 2B (GRIN2B), a gene that previously yielded evidence for association in a candidate gene study on 323 Ashkenazi Jewish bipolar case-parent trios. We find that the evidence for linkage is significantly correlated with the presence of the putative high-risk allele identified in our candidate gene study.

CONCLUSIONS

Following up weaker signals can significantly improve linkage signals even after relatively small increases in information content. Our results on chromosome 12p support GRIN2B as a candidate gene for bipolar disorder that needs further investigation.

Association study between the NMDA receptor 2B subunit gene (GRIN2B) and schizophrenia: a HuGE review and meta-analysis

Schizophrenia is a severe mental illness to which hypofunction of the N-methyl-D-aspartate receptors has been linked. Association studies have implicated the N-methyl-D-aspartate receptor 2B subunit gene (GRIN2B) as a candidate for schizophrenia. Subsequent studies have attempted to replicate the association, but the results have been mixed and thus inconclusive. It is necessary to explain the inconsistency of these results and to clarify the contribution of the GRIN2B gene to schizophrenia. The current meta-analysis covers all published association studies up to January 2006 using systematic allelic and genotypic analyses involving five polymorphisms. The results show evidence of a statistically significant association for GRIN2B. The association seems weaker, but nonetheless interesting. The meta-analysis supports the involvement of the glutamate system of the brain in the pathogenesis of schizophrenia. This may be the first systematic meta-analysis study focusing on GRIN2B.

Glutamate and schizophrenia: phencyclidine, N-methyl-D-aspartate receptors, and dopamine-glutamate interactions

Schizophrenia is a serious mental disorder that affects up to 1% of the population worldwide. As of yet, neurochemical mechanisms underlying schizophrenia remain unknown. To date, the most widely considered neurochemical hypothesis of schizophrenia is the dopamine hypothesis, which postulates that symptoms of schizophrenia may result from excess dopaminergic neurotransmission particularly in striatal brain regions, along with dopaminergic deficits in prefrontal brain regions. Alternative neurochemical models of schizophrenia, however, have been proposed involving glutamatergic mechanisms in general and N-methyl-D-aspartate (NMDA) receptors in particular. A potential role for glutamatergic mechanisms in schizophrenia was first proposed approximately 15 years ago based on the observation that the psychotomimetic agents phencyclidine (PCP) and ketamine induce psychotic symptoms and neurocognitive disturbances similar to those of schizophrenia by blocking neurotransmission at NMDA-type glutamate receptors. Since that time, significant additional evidence has accumulated supporting a role for NMDA hypofunction in the pathophysiology of schizophrenia. Clinical challenge studies with PCP and ketamine have confirmed the close resemblance between NMDA antagonist-induced symptoms and neurocognitive deficits and those observed in schizophrenia, and suggest that NMDA dysfunction may lead to secondary dopaminergic dysregulation in striatal and prefrontal brain regions. As compared to dopaminergic agents, NMDA antagonists induce negative and cognitive symptoms of schizophrenia, as well as positive symptoms. Treatment studies with NMDA modulators, such as glycine, d-serine, and glycine transport inhibitors (GTIs), have yielded encouraging findings, although results remain controversial. Finally, genetic linkage and in vivo neurochemical studies in schizophrenia highlight potential etiological mechanisms giving rise to glutamatergic/NMDA dysfunction in schizophrenia.

Inherited auditory-cortical dysfunction in twin pairs discordant for schizophrenia

BACKGROUND

Information on the inheritance of neurophysiological abnormalities might help elucidate the molecular genetic basis of schizophrenia. We used magnetoencephalography (MEG) and electroencephalography (EEG) to investigate the inheritance of auditory-cortical deficiencies in twin pairs discordant for schizophrenia.

METHODS

Auditory EEG/MEG responses to frequent standard and occasional deviant tones were measured in mono- and dizygotic (MZ and DZ) twin pairs discordant for schizophrenia and demographically matched healthy twin pairs, recruited from a total population cohort. The MEG/EEG results were regressed against the genetic resemblance to patients with schizophrenia across the patients' unaffected MZ/DZ co-twins and control subjects (with genetic correlations of 1, .5, and 0 to schizophrenia patients, respectively).

RESULTS

The EEG responses P50, N100, and mismatch negativity (MMN), as well as the MEG response P50m, were reduced in the schizophrenic patients. P50 and N100 were significantly decreased also in their unaffected co-twins, as compared with the control subjects. Importantly, the P50 and N100 decrease correlated with the unaffected subjects' genetic resemblance to schizophrenia patients.

CONCLUSIONS

Our results suggest inherited abnormalities in cortical auditory processing in schizophrenia, reflected by the decreased P50/P50m and N100 amplitudes, whereas the MMN abnormalities might reflect predominantly state-dependent neurodegeneration.

Significant association between the genetic variations in the 5' end of the N-methyl-D-aspartate receptor subunit gene GRIN1 and schizophrenia

BACKGROUND

N-methyl-D-aspartate (NMDA) receptors play important roles in many neurophysiological processes. Evidence from previous studies indicate that NMDA receptors contribute to the pathophysiology of schizophrenia. Two NMDA receptor subunit genes, GRIN1 and GRIN2A, are both good candidate genes for schizophrenia.

METHOD

We genotyped five single nucleotide polymorphisms (SNPs) in GRIN1 and two in GRIN2A in 2455 Han Chinese subjects, including population- and family-based samples, and performed case-control and transmission disequilibrium test (TDT) analyses. A microsatellite in GRIN2A was genotyped in population-based samples and a Mann-Whitney U test was performed.

RESULTS

A highly significant association was detected at the 5' end of GRIN1. Analyses of single variants and multiple-locus haplotypes indicate that the association is mainly generated by rs11146020 (case-control study: p = .0000013, odds ratio = .61, 95% confidence interval .50-.74; TDT: p = .0019, T/NT = 79/123). No association was found in the GRIN2A polymorphisms.

CONCLUSIONS

Our results provide support for the hypothesis that NMDA receptors are an important factor in schizophrenia. Moreover, rs11146020 is located in 5' untranslated region where several functional elements have been found. Hence, the SNP is a potential candidate in altering risk for schizophrenia and worthy of further replication and functional study.

Linkage analysis of ordinal traits for pedigree data

Linkage analysis is used routinely to map genes for human diseases and conditions. However, the existing linkage-analysis methods require that the diseases or conditions either be dichotomized or measured by a quantitative trait, such as blood pressure for hypertension. In the latter case, normality is generally assumed for the trait. However, many diseases and conditions, such as cancer and mental and behavioral conditions, are rated on ordinal scales. The objective of this study was to establish a framework to conduct linkage analysis for ordinal traits. We propose a latent-variable, proportional-odds logistic model that relates inheritance patterns to the distribution of the ordinal trait. We use the likelihood-ratio test for testing evidence of linkage. By means of simulation studies, we find that the power of our proposed model is substantially higher than that of the binary-trait-based linkage analysis and that our test statistic is robust with regard to certain parameter misspecifications. By using our proposed method, we performed a genome scan of the hoarding phenotype in a data set with 53 nuclear families, which were collected by the Tourette Syndrome Association International Consortium for Genetics (TSAICG). Standard linkage scans using hoarding as a dichotomous trait were also performed by using GENEHUNTER and ALLEGRO. Both GENEHUNTER and ALLEGRO failed to reveal any marker significantly linked to the binary hoarding phenotypes. However, our method identified three markers at 4q34-35 (P = 0.0009), 5q35.2-35.3 (P = 0.0001), and 17q25 (P = 0.0005) that manifest significant allele sharing.

Linkage studies of schizophrenia

The study of schizophrenia genetics has revealed much about the disease but none of the essential secrets of its etiology, so far, for numerous reasons. First, schizophrenia is a complex trait, influenced by both genes and environment. Second, it appears to be a highly heterogeneous disease, with locus and allelic heterogeneity both between and within families likely. Third, since it is common, it is likely that the genetic liability variants are common, and so are found with relatively high frequency in the general population. Fourth, linkage methods, which deliver rapid coverage of the genome, have great power to identify single genes causing Mendelian disorders but are poorly suited to the genetic architecture of complex traits. Although association methods are undeniably more powerful in such situations, affordable technologies to deliver the much higher density whole genome coverage required are not yet available and candidate gene studies of schizophrenia have not produced robust and replicable results. In spite of these limitations, there are now sufficient data to support several conclusions. Numerous regions of the human genome give consistent, though by no means unanimous, support for linkage. The precise nature of these signals is not yet understood, and power to position the effects is poor, but metanalyses show the co-occurrence is unlikely to be due to chance. Combined approaches utilizing linkage for rapid genome coverage and association for fine-scale follow-up have identified several promising candidate genes. Although the definition of replication in a complex trait is itself complex, a number of these candidates have been supported by numerous studies. These converging lines of evidence suggest that the genetics of schizophrenia, long considered a most intractable problem, are at last beginning to be unraveled.

Identification of candidate genes for schizophrenia based on natural resistance to infectious diseases

BACKGROUND

Identification of candidate genes for schizophrenia may be more successful than genome screens as the latter have not found consistent linkages.

OBJECTIVE

To assist in the gene search, a model of schizophrenia based on resistance to infectious diseases, rather than susceptibility, is proposed. The theory blends the geography of schizophrenia with the assumption that genes that cause schizophrenia likely evolved and persist from selection pressure. The theory includes the notion that schizophrenia enhances biological survival at the cost of psychological and social functioning.

METHOD

To demonstrate the utility of using this model, the Medline literature was searched for resistance genes, mostly identified in mice.

RESULTS

Based on homologous locations in the human genome, these resistance genes are shown to be located in human chromosome regions linked significantly, in at least one genome screen, with schizophrenia or some physiologically related function or condition associated with schizophrenia.

CONCLUSIONS

The infectious disease resistance theory of schizophrenia is offered as a viable model for understanding the origins of schizophrenia. The theory also allows for the inclusion of persistent infections, seasonal variability and translational pathophysiology to contribute to the etiology of schizophrenia.

Identification of a high-risk haplotype for the dystrobrevin binding protein 1 (DTNBP1) gene in the Irish study of high-density schizophrenia families

A recent report showed significant associations between several SNPs in a previously unknown EST cluster with schizophrenia. (1). The cluster was identified as the human dystrobrevin binding protein 1 gene (DTNBP1) by sequence database comparisons and homology with mouse DTNBP1. (2). However, the linkage disequilibrium (LD) among the SNPs in DTNBP1 as well as the pattern of significant SNP-schizophrenia association was complex. This raised several questions such as the number of susceptibility alleles that may be involved and the size of the region where the actual disease mutation(s) could be located. To address these questions, we performed different single-marker tests on the 12 previously studied and 2 new SNPs in DTNBP1 that were re-scored using an improved procedure, and performed a variety of haplotype analyses. The sample consisted of 268 Irish multiplex families selected for high density of schizophrenia. Results suggested a simple structure where the LD in the target region could be explained by 6 haplotypes that together accounted for 96% of haplotype diversity in the whole sample. From these six, a single high-risk haplotype was identified that showed a significant association with schizophrenia and explained the pattern of significant findings in the analyses with individual markers. This haplotype was 30 kb long, had a large effect, could be measured with two tag SNPs only, had a frequency of 6% in our sample, seemed to be of relatively recent origin in evolutionary terms, and was equally distributed over Ireland. Implications of these findings for follow-up and replication studies are discussed.

Disruption of the neuronal PAS3 gene in a family affected with schizophrenia

Schizophrenia and its subtypes are part of a complex brain disorder with multiple postulated aetiologies. There is evidence that this common disease is genetically heterogeneous, with many loci involved. In this report, we describe a mother and daughter affected with schizophrenia, who are carriers of a t(9;14)(q34;q13) chromosome. By mapping on flow sorted aberrant chromosomes isolated from lymphoblast cell lines, both subjects were found to have a translocation breakpoint junction between the markers D14S730 and D14S70, a 683 kb interval on chromosome 14q13. This interval was found to contain the neuronal PAS3 gene (NPAS3), by annotating the genomic sequence for ESTs and performing RACE and cDNA library screenings. The NPAS3 gene was characterised with respect to the genomic structure, human expression profile, and protein cellular localisation to gain insight into gene function. The translocation breakpoint junction lies within the third intron of NPAS3, resulting in the disruption of the coding potential. The fact that the bHLH and PAS domains are disrupted from the remaining parts of the encoded protein suggests that the DNA binding and dimerisation functions of this protein are destroyed. The daughter (proband), who is more severely affected, has an additional microdeletion in the second intron of NPAS3. On chromosome 9q34, the translocation breakpoint junction was defined between D9S752 and D9S972 and no genes were found to be disrupted. We propose that haploinsufficiency of NPAS3 contributes to the cause of mental illness in this family.

Linkage and associated studies of schizophrenia

Genetic epidemiology has provided consistent evidence over many years that schizophrenia has a genetic component, and that this genetic component is complex, polygenic, and involves epistatic interaction between loci. Molecular genetics studies have, however, so far failed to identify any DNA variant that can be demonstrated to contribute to either liability to schizophrenia or to any identifiable part of the underlying pathology. Replication studies of positive findings have been difficult to interpret for a variety of reasons. First, few have reproduced the initial findings, which may be due either to random variation between two samples in the genetic inputs involved, or to a lack of power to replicate an effect at a given alpha level. Where positive data have been found in replication studies, the positioning of the locus has been unreliable, leading no closer to positional cloning of genes involved. However, an assessment of all the linkage studies performed over the past ten years does suggest a number of regions where positive results are found numerous times. These include regions on chromosomes 1, 2, 4, 5, 6, 7, 8, 9, 10, 13, 15, 18, 22 and the X. All of these data are critically reviewed and their locations compared. Reasons for the difficulty in obtaining consistent results and possible strategies for overcoming them are discussed. Am. J. Med. Genet. (Semin. Med. Genet.) 97:23-44, 2000.

Chromosomal abnormalities and mental illness

Linkage studies of mental illness have provided suggestive evidence of susceptibility loci over many broad chromosomal regions. Pinpointing causative gene mutations by conventional linkage strategies alone is problematic. The breakpoints of chromosomal abnormalities occurring in patients with mental illness may be more direct pointers to the relevant gene locus. Publications that describe patients where chromosomal abnormalities co-exist with mental illness are reviewed along with supporting evidence that this may amount to an association. Chromosomal abnormalities are considered to be of possible significance if (a) the abnormality is rare and there are independent reports of its coexistence with psychiatric illness, or (b) there is colocalisation of the abnormality with a region of suggestive linkage findings, or (c) there is an apparent cosegregation of the abnormality with psychiatric illness within the individual's family. Breakpoints have been described within many of the loci suggested by linkage studies and these findings support the hypothesis that shared susceptibility factors for schizophrenia and bipolar disorder may exist. If these abnormalities directly disrupt coding regions, then combining molecular genetic breakpoint cloning with bioinformatic sequence analysis may be a method of rapidly identifying candidate genes. Full karyotyping of individuals with psychotic illness especially where this coexists with mild learning disability, dysmorphism or a strong family history of mental disorder is encouraged.

Mouse models for psychiatric disorders

Genes involved in psychiatric disorders are difficult to identify, and those that have been proposed so far remain ambiguous. As it is unrealistic to expect the development of, say, a 'schizophrenic' or 'autistic' mouse, mice are unlikely to have the same role in gene identification in psychiatry as circling mice did in the discovery of human deafness genes. However, many psychiatric disorders are associated with intermediate phenotypes that can be modeled and studied in mice, including physiological or anatomical brain changes and behavioral traits. Mouse models help to evaluate the effect of a human candidate gene mutation on an intermediate trait, and to identify new candidate genes. Once a gene or pathway has been identified, mice are also used to study the interplay of different genes in that system.

Molecular genetics of schizophrenia: past, present and future

Schizophrenia is a severe neuropsychiatric disorder with a polygenic mode of inheritance which is also governed by non-genetic factors. Candidate genes identified on the basis of biochemical and pharmacological evidence are being tested for linkage and association studies. Neurotransmitters, especially dopamine and serotonin have been widely implicated in its etiology. Genome scan of all human chromosomes with closely spaced polymorphic markers is being used for linkage studies. The completion and availability of the first draft of Human Genome Sequence has provided a treasure-trove that can be utilized to gain insight into the so far inaccessible regions of the human genome. Significant technological advances for identification of single nucleo-tide polymorphisms (SNPs) and use of microarrays have further strengthened research methodologies for genetic analysis of complex traits. In this review, we summarize the evolution of schizophrenia genetics from the past to the present, current trends and future direction of research.

A 3-Mb map of a large Segmental duplication overlapping the alpha7-nicotinic acetylcholine receptor gene (CHRNA7) at human 15q13-q14

Several neuropsychiatric disorders map to human 15q13-q14, which contains a strong candidate in the alpha7-nicotinic acetylcholine receptor subunit gene (CHRNA7) and is partly duplicated, complicating further genetic analysis. We have shown that the partial duplication is in a hybrid (CHRFAM7A)between CHRNA7 and one of many copies of a novel gene (FAM7A). We have constructed a 3-Mb map of 15q13-q14 showing that CHRFAM7A is part of a large segmental duplication in the opposite orientation to CHRNA7 and revealing several other duplications. The data support a model of recent evolutionary events including duplications, at least one large deletion, and an inversion. We have identified two individuals with a structure that lacks CHRFAM7A and therefore predates many steps in this model, suggesting an unstable region with other intermediates possibly still in existence. This instability may be relevant to the many neuropsychiatric disorders that map in this region.

Mutation analysis of the NMDAR2B (GRIN2B) gene in schizophrenia

NMDA receptor dysfunction may be involved in the pathophysiology of schizophrenia. Based on this hypothesis, we screened 48 Japanese patients with schizophrenia for mutations in the coding region of the NMDAR2B subunit gene (GRIN2B). An association study between the identified DNA sequence variants and schizophrenia was performed in 268 Japanese patients with schizophrenia and 337 Japanese control subjects. Eight single nucleotide polymorphisms were detected, all of which were synonymous. The association sample showed statistically significant excesses of homozygosity for the polymorphisms in the 3' region of the last exon in the patients with schizophrenia (P = 0.004) and higher frequency of the G allele of the 366C/G polymorphism (corrected P = 0.04) in the patients than in the controls. Although we did not detect NMDAR2B protein variants, our findings support the possibility that the GRIN2B gene or a locus in linkage disequilibrium with it may confer susceptibility to schizophrenia. Replication studies in independent samples are warranted.

Localization of genes modulating the predisposition to schizophrenia: a revision

The genetics of schizophrenia or bipolar affective disorder has advanced greatly at the molecular level since the introduction of probes for the localization of specific genes. Research on gene candidates for susceptibility to schizophrenia can broadly be divided into two types, i.e., linkage studies, where a gene is found near a specific DNA marker on a specific chromosome, and association studies, when a condition is associated with a specific allele of a specific gene. This review covers a decade of publications in this area, from the 1988 works of Bassett et al. and Sherrington et al. on a gene localized on the long arm of chromosome 5 at the 5q11-13 loci, to the 1997 work of Lin et al. pointing to the 13q14.1-q32 loci of chromosome 13 and to the 1998 work of Wright et al. on an HLA DRB1 gene locus on chromosome 6 at 6p21-3. The most replicated loci were those in the long arm of chromosome 22 (22q12-q13.1) and on the short arm of chromosome 6 (6p24-22). In this critical review of the molecular genetic studies involved in the localization of genes which modulate the predisposition to schizophrenia the high variability in the results obtained by different workers suggests that multiple loci are involved in the predisposition to this illness.

Development, disease and degeneration in schizophrenia: a unitary pathophysiological model

In recent years, several pathophysiological models of schizophrenia, i.e. the early and late brain neurodevelopmental and post-illness onset neurodegenerative models, have been proposed and theorists have often argued as if these explanations are mutually exclusive. We propose that all these mechanisms may interact cumulatively during successive critical 'windows of vulnerability' during brain development and during the early course of the illness to lead to the clinical manifestations of the illness. Early brain insults may lead to dysplasia of selective neural networks that account for the premorbid cognitive and psychosocial dysfunction seen in many patients. The onset of psychosis in adolescence may be related to an excessive elimination of synapses and secondarily, phasic dopaminergic overactivity. Following illness onset, these neurochemical alterations in relation to continuing untreated psychosis may lead to further neurodegenerative processes. A reduction in tonic glutamatergic neurotransmission and a phasic glutamatergic excess can potentially predispose to these processes and may have considerable explanatory power. This hypothesis is consistent with central characteristics of schizophrenia such as premorbid manifestations, adolescent onset, functional decline early in this illness, cognitive impairments, the role of dopamine and the role of genes and environment in pathophysiology. This 'three hit' model extends similar integrative conceptualization by other investigators and generates testable predictions of relevance to future pathophysiology and treatment research in schizophrenia.

A.E. Bennett Research Award. Reversal of phencyclidine-induced effects by glycine and glycine transport inhibitors

BACKGROUND

Phencycline (PCP, "angel dust") and other noncompetitive antagonists of N-methyl-D-aspartate (NMDA)-type glutamatergic neurotransmission induce psychotic effects in humans that closely resemble positive, negative, and cognitive symptoms of schizophrenia. Behavioral effects of PCP in rodents are reversed by glycine (GLY) and other NMDA augmenting agents. In rodents, behavioral effects of PCP are mediated, in part, by secondary dysregulation of subcortical dopaminergic neurotransmission. This study evaluates effects of GLY and GLY transport antagonists on behavioral and neurochemical consequences of PCP administration in rodents.

METHODS

Two separate experiments were performed. In the first, effects of GLY on PCP-induced stimulation of dopaminergic neurotransmission in nucleus accumbens were evaluated using in vivo microdialysis in awake animals. In the second, effects of a series of GLY transport antagonists were evaluated for potency in inhibiting PCP-induced hyperactivity.

RESULTS

In microdialysis studies, GLY significantly inhibited PCP-induced stimulation of subcortical DA release in a dose-dependent fashion. In behavioral studies, the potency of a series of GLY transport antagonists for inhibiting PCP-induced hyperactivity in vivo correlated significantly with their potency in antagonizing GLY transport in vitro.

CONCLUSIONS

These findings suggest, first, that GLY reverses not only the behavioral, but also the neurochemical, effects of PCP in rodents. Second, the findings suggest that GLY transport antagonists may induce similar effects to GLY, and may therefore represent an appropriate site for targeted drug development.