Update on chromosomal locations for psychiatric disorders: report of the interim meeting of chromosome workshop chairpersons from the VIIth World Congress of Psychiatric Genetics, Monterey, California, October 14-18, 1999

Expression of NPAS3 in the human cortex and evidence of its posttranscriptional regulation by miR-17 during development, with implications for schizophrenia

NPAS3 is a developmentally important transcription factor that has been associated with psychiatric illness. Our aim is to better define the regulation of NPAS3 mRNA (messenger RNA) levels during normal human prefrontal cortical development and in schizophrenia. Utilizing postmortem tissue from 134 human brains, we assessed: 60 normal brains ranging in age from birth to adulthood, 37 chronic individuals with schizophrenia, and 37 matched controls. mRNA and microRNA (miRNA) expressions were measured by microarray and quantitative real-time PCR. Protein expression was measured by Western blotting. During human postnatal cortical development (neonate to adult), we found decreased NPAS3 mRNA yet increased NPAS3 protein expression, suggesting the involvement of posttranscriptional regulation. Through screening, we identified one NPAS-targeted miRNA (miR-17) that changed in a pattern consistent with the developmental regulation of NPAS3. Using luciferase reporter assays, we assessed the impact of miR-17 on NPAS3 translation and demonstrated that miR-17 alters NPAS3 biosynthesis by binding to the NPAS3 3'untranslated region (UTR). In schizophrenia prefrontal cortex, we found significant elevations in miR-17 expression. While NPAS3 mRNA was unaltered, reduced NPAS3 protein expression was detected in a subpopulation of people with schizophrenia. The reciprocal expression of NPAS3 mRNA and protein during postnatal development mediated by a schizophrenia-associated change in miR-17 suggests that there is complex control over NPAS3 synthesis in the human prefrontal cortex and that if NPAS3 is dysregulated in schizophrenia, it is not evident by large changes in NPAS3 expression. Further studies into how changes in NPAS3 or its miRNA regulator may influence the development of schizophrenia are warranted.

Searching for the true genetic vulnerability for schizophrenia

The search for a genetic basis for schizophrenia has taken a new turn recently with the publication of three reports of various rare copy-number variations that are associated with schizophrenia. While some of the findings may simply disappear as spurious reports, others remain interesting: that is, deletions in the Velocardiofacial syndrome region of chromosome 22, and regions of chromosome 1q21.1 and 15q13.3. These results will gain greater significance if future validation in family studies shows their segregation with illness within families, and when it is understood how the genes containing these variants affect the underlying neurochemistry and neuropathology characteristic of schizophrenia.

Schizophrenia research in the era of the genome, 2007

PURPOSE OF REVIEW

The field of molecular genetics has now provided new technology to discover causes, mechanisms and targets for the development of treatments for even the complex inherited disorders, such as schizophrenia and other major psychiatric diseases.

RECENT FINDINGS

As of the end of the year 2006, schizophrenia research has advanced a long way from epidemiological family surveys to examining the sequenced whole human genome.

SUMMARY

Whether entering a new era of the genome will lead to prevention and/or cures will depend on our ability to make sense of the many positive and confusing findings that are now emerging, several of which will not stand the test of time. Going beyond genetic linkage and association studies to pathways, mechanisms and what changes gene expression will be the key.

Abnormal neurodevelopment, neurosignaling and behaviour in Npas3-deficient mice

Npas3 is a member of the bHLH-PAS superfamily of transcription factors that is expressed broadly in the developing neuroepithelium. To study the function of this gene, mice deficient in Npas3 were generated and characterized. Npas3-/- mice were growth-retarded and exhibited developmental brain abnormalities that included a reduction in size of the anterior hippocampus, hypoplasia of the corpus callosum and enlargement of the ventricles. A number of behavioural abnormalities were identified in Npas3-/- mice including locomotor hyperactivity, subtle gait defects, impairment of prepulse inhibition of acoustic startle, deficit in recognition memory and altered anxiety-related responses. Characterization of neurosignaling pathways using several pharmacological agents revealed dysfunctional glutamate, dopamine and serotonin neurotransmitter signaling. Consistent with these findings, we identified a significant alteration in cortical PSD-95 expression, a PDZ-containing protein that has been shown to be involved in postsynaptic signal transduction. Together, our observations indicate an important role for Npas3 in controlling normal brain development and neurosignaling pathways.

Genetic models of schizophrenia and bipolar disorder: overlapping inheritance or discrete genotypes?

Schizophrenia and affective disorder have been considered to be nosologically and etiologically distinct disorders. This postulate is challenged by progress in new biological research. Both disorders are strongly influenced by genetic factors; thus genetic research is a main contributor to this discussion. We review current evidence of the genetic relationship between schizophrenia and affective disorders, mainly bipolar disorder (the various genetic research methods have been particularly applied to bipolar disorder). Recent family and twin studies reveal a growing consistency in demonstrating cosegregation between both disorders which is difficult to detect with certainty given the low base rates. Systematic molecular genetic search for specific genes impacting on either disorder has now identified one gene which is apparently involved in both disorders (G72/G30); other candidate genes reveal some evidence to present as susceptibility genes with very modest effects for each of both disorders, although not consistently so (e. g., COMT, BDNF). There is room for speculation about other common susceptibility genes, given the overlap between candidate regions for schizophrenia and those for bipolar disorder emerging from linkage studies.

Expression of mitochondria-related genes in lymphoblastoid cells from patients with bipolar disorder

OBJECTIVES

Several studies have suggested mitochondrial abnormality in bipolar disorder. We reported the association of mitochondrial complex I subunit gene, NDUFV2 at 18p11, with bipolar disorder. A decrease in the mRNA expression of this gene was found in patients with bipolar disorder compared with controls. However, it was unclear whether only the NDUFV2 gene exhibited the decreased expression level in bipolar disorder. The aim of this study was to clarify the association of other nuclear-encoded complex I subunit genes and mitochondria-related genes with bipolar disorder.

METHODS

We quantified the mRNA expression level of five nuclear-encoded mitochondrial complex I subunit genes located at the chromosomal regions linked with bipolar disorder other than NDUFV2, three complex IV subunit genes, and four mitochondrial transcription-related genes using a real-time quantitative reverse transcription polymerase chain reaction method in the lymphoblastoid cell lines from 21 patients with bipolar disorder and 11 controls.

RESULTS

Decreased mRNA expression in patients with bipolar I disorder compared with control subjects was found in most of the complex I subunit genes. In addition, decreased expression levels of these genes correlated with that of NDUFV2. No statistically significant alterations of mRNA expression levels were found between bipolar patients and controls among two of three complex IV subunit genes and all transcription-related genes.

CONCLUSIONS

Our study suggests that the decreased expression of NDUFV2 has a considerable effect on other subunit genes in the mitochondrial respiratory chain and presents further evidence of the biological significance of NDUFV2 in bipolar disorder.

CALCYON gene variation, schizophrenia, and cocaine dependence

Calcyon is a brain-specific D1 dopamine receptor-interacting protein, with a potential role in D1-mediated physiological processes, including motor control, reward mechanisms, and cognitive processes. Our objective was to investigate the relationship between polymorphism of the CALCYON gene and (1) schizophrenia and (2) cocaine dependence in African-American (AA) and European-American (EA) subjects. Two single nucleotide polymorphisms (SNPs) at the CALCYON locus were genotyped in 70 AA and 206 EA individuals with schizophrenia and 90 AA and 118 EA individuals with cocaine dependence. The control group was comprised of 46 AA and 207 EA subjects screened to exclude those with psychiatric or substance use disorders. The specific polymorphisms studied were markers +295214G/A and +297151T/G. Comparisons of allele and haplotype frequencies between cases and controls were performed with the Fisher's Exact Test. Linkage disequilibrium (LD) between these two SNPs was calculated with the 3LOCUS program. No alleles or haplotypes were found to be associated with schizophrenia or cocaine dependence either in AA or EA subjects. The markers +295214G/A and +297151T/G are in the same haplotype block in all subgroups. Allele and haplotype frequencies differed significantly between EA and AA subjects. These results suggest that these two genetic variants in the CALCYON gene do not play a major role in predisposition to either schizophrenia or cocaine dependence in AA or EA subjects. Furthermore, these findings begin to establish a haplotype map for this gene in the AA and EA populations.

A rare polymorphism affects a mitogen-activated protein kinase site in synapsin III: possible relationship to schizophrenia

BACKGROUND

Synapsin III plays a role in neuronal plasticity and maps to chromosome 22q12-13, a region suggested to be linked to schizophrenia. To determine if synapsin III plays a role in this disease, we searched for polymorphisms in this gene in patients with schizophrenia and controls.

METHODS

The synapsin III gene was initially sequenced from 10 individuals with schizophrenia to identify polymorphisms. Association analysis was then performed using 118 individuals with schizophrenia and 330 population controls. Synapsin III expression was studied by immunoblot analyses, and phosphorylation sites were mapped by sequencing trypsin-digested synapsin III fragments phosphorylated with phosphorus-32.

RESULTS

A rare, missense polymorphism, S470N, was identified in the synapsin III gene and appeared more frequently in individuals with schizophrenia than in controls (p =.0048). The site affected by the polymorphism, Ser470, was determined to be a substrate for mitogen-activated protein kinase, a downstream effector of neurotrophin action. Phosphorylation at Ser470 was increased during neonatal development and in response to neurotrophin-3 in cultured hippocampal neurons.

CONCLUSIONS

Our observations suggest an association of a rare polymorphism in synapsin III with schizophrenia, but further studies will be required to clarify its role in this disease.

beta-1,3-Glucuronyltransferase-1 gene implicated as a candidate for a schizophrenia-like psychosis through molecular analysis of a balanced translocation

We have mapped and sequenced both chromosome breakpoints of a balanced t(6;11)(q14.2;q25) chromosome translocation that segregates with a schizophrenia-like psychosis. Bioinformatics analysis of the regions revealed a number of confirmed and predicted transcripts. No confirmed transcripts are disrupted by either breakpoint. The chromosome 6 breakpoint region is gene poor, the closest transcript being the serotonin receptor 1E (HTR1E) at 625 kb telomeric to the breakpoint. The chromosome 11 breakpoint is situated close to the telomere. The closest gene, beta-1,3-glucuronyltransferase (B3GAT1 or GlcAT-P), is 299 kb centromeric to the breakpoint. B3GAT1 is the key enzyme during the biosynthesis of the carbohydrate epitope HNK-1, which is present on a number of cell adhesion molecules important in neurodevelopment. Mice deleted for the B3GAT1 gene show defects in hippocampal long-term potentiation and in spatial memory formation. We propose that the translocation causes a positional effect on B3GAT1, affecting expression levels and making it a plausible candidate for the psychosis found in this family. More generally, regions close to telomeres are highly polymorphic in both sequence and length in the general population and several studies have implicated subtelomeric deletions as a common cause of idiopathic mental retardation. This leads us to the hypothesis that polymorphic or other variation of the 11q telomere may affect the activity of B3GAT1 and be a risk factor for schizophrenia and related psychoses in the general population.

Association of mitochondrial complex I subunit gene NDUFV2 at 18p11 with bipolar disorder

Linkage of bipolar disorder with 18p11 has been replicated by several investigators. A nuclear-encoded mitochondrial complex I subunit gene, NDUFV2, is one of the candidate genes in this locus, since the possible pathophysiological significance of mitochondrial dysfunction in bipolar disorder has been suggested. The objective of our study was to clarify the association between the NDUFV2 gene and bipolar disorder. We performed the real-time quantitative reverse transcription polymerase chain reaction (RT-PCR) for NDUFV2 mRNA expression in lymphoblastoid cell lines derived from patients with bipolar disorder and healthy controls. We also screened novel polymorphisms using denaturing high performance liquid chromatography (D-HPLC) and PCR-direct sequencing method. Detected five single nucleotide polymorphisms (SNPs) were genotyped. A decrease of the expression level of NDUFV2 gene was found in patients with bipolar I disorder compared with controls (P = 0.006). We also found that the haplotype frequencies of the four polymorphisms in the upstream region of NDUFV2 were significantly different between bipolar disorders and controls (P = 0.0001). Our findings suggest that polymorphisms of the NDUFV2 gene may be one of the genetic risk factors for bipolar disorder.

TNFB polymorphism may be associated with schizophrenia in the Korean population

This study was conducted to test the association between the tumor necrosis factor (TNF)-beta gene (B) polymorphism and schizophrenia in the Korean population. 127 patients with schizophrenia according to the DSM-IV criteria and 202 healthy controls were enrolled in this study. Patients and controls were biologically unrelated age and sex-matched native Koreans. Genotyping for the TNFB polymorphism was performed by polymerase chain reaction-restriction fragment length polymorphism. Genotype and allele distributions of the TNFB polymorphism in patients with schizophrenia were significantly different from those of the controls. Subjects with the TNFB*2 allele had an increased risk for schizophrenia (Odds Ratio=1.76, 95% CI=1.27-2.45). The present study suggests that the TNFB polymorphism may confer susceptibility to schizophrenia in the Korean population.

Sib-pairs in multifactorial disorders: the sib-similarity problem

Common disorders are, by definition, the major cause of ill health and death. Most can be modified by avoiding or shielding an environment, as in sunburn and coeliac disease, by replacing some deficient substance, as in diabetes or myxoedema, or by empirical methods of evident effect as in schizophrenia and depressive illness. As expected, all show an increased incidence in relatives and the identification of the more influential loci involved may define unexpected links in the metabolic map: these may be amenable to therapy, or, in autoimmune disorders and asthma, define precipitating factors by sequencing the receptor involved. The major investment in trawling the genotype for influential loci has been by affected sib-pairs with parents (ASPs). Over a hundred major studies have been published with very limited success. No substantial study of normal sib-pairs has been undertaken, making this family of surveys one of the largest undertaken in the absence of controls. Possible reasons for this limited success and the many suggestive false positives are considered.

Linkage analysis in psychiatric disorders: the emerging picture

Gene finding in genetically complex diseases has been difficult as a result of many factors that have diagnostic and methodologic considerations. For bipolar disorder and schizophrenia, numerous family, twin, and adoption studies have identified a strong genetic component to these behavioral psychiatric disorders. Despite difficulties that include diagnostic differences between sample populations and the lack of statistical significance in many individual studies, several promising patterns have emerged, suggesting that true susceptibility loci for schizophrenia and bipolar disorder may have been identified. In this review, the genetic epidemiology of these disorders is covered as well as linkage findings on chromosomes 4, 12, 13, 18, 21, and 22 in bipolar disorder and on chromosomes 1, 6, 8, 10, 13, 15, and 22 in schizophrenia. The sequencing of the human genome and identification of numerous single nucleotide polymorphisms (SNP) should substantially enhance the ability of investigators to identify disease-causing genes in these areas of the genome.

Manic-depression genes and the new millennium: poised for discovery

Manic-depressive illness is a common psychiatric disorder with complex etiology that likely involves multiple genes and non-genetic influences. The uncertain path to gene discovery has spurred considerable debate over genetic findings and gene-finding strategies. In this article, I review the main findings, with a focus on: (1) putative linked loci on chromosomes 1q31-32, 4p16, 6pter-p24, 10p14, 10q21-26, 12q23-24, 13q31-32, 18p11, 18q21-23, 21q22, 22q11-13, and Xq24-28; and (2) association studies with candidate genes, dynamic mutations, mitochondrial mutations, and chromosomal aberrations. Although no gene has been identified, promising findings are emerging. I then discuss the challenges and opportunities ahead, with special emphasis on gene-finding methods-in particular, questions pertaining to phenotype definition, linkage and association mapping, gene markers, sampling, study population, multigene systems, lessons from other disorders, animal models, and bioinformatics. The progress to date, together with rapid advances in genomics, analytical and computational methods, and bioinformatics, holds promise for new insights into the genetics of manic-depression, in the new millennium.

Future of genetics of mood disorders research

This report summarizes the deliberations of a panel with representation from diverse disciplines of relevance to the genetics of mood disorders. The major charge to the panel was to develop a strategic plan to employ the tools of genetics to advance the understanding, treatment, and outcomes for mood disorders. A comprehensive review of the evidence for the role of genetic factors in the etiology of mood disorders was conducted, and the chief impediments for progress in gene identification were identified. The National Institute of Mental Health (NIMH) portfolios in the Genetics Research Branch and the Division of Mental Disorders, Behavioral Sciences, AIDS, and all genetics training activities were reviewed. Despite some promising leads, there are still no confirmed linkage findings for mood disorders. Impediments to gene finding include the lack of phenotypic validity, variation in ascertainment sources and methodology across studies, and genetic complexity. With respect to linkage, the committee recommended that a large-scale, integrated effort be undertaken to examine existing data from linkage and association studies of bipolar disorders using identical phenotypes and statistical methods across studies to determine whether the suggestive linkage findings at some loci can be confirmed. Confirmation would justify more intensive approaches to gene finding. The committee recommended that the NIMH support continued efforts to identify the most heritable subtypes and endophenotypes of major depression using the tools of genetic epidemiology, neuroscience, and behavioral science. The field of genetic epidemiology was identified as an important future direction because population-based, epidemiologic studies of families and unrelated affected individuals assume increasing importance for common chronic diseases. To prepare for shifts to more complex genetic models, the committee recommended that the NIMH develop new interdisciplinary training strategies to prepare for the next generation of genetics research.

Molecular genetic studies of schizophrenia: challenges and insights

Schizophrenia (SCZ) is a mental disease that affects approximately 1% of the population with life-long devastating consequences. Based on evidence for a major contribution of genetic factors, a decade of extensive efforts has been dedicated to the search of DNA sequence variations that increase the risk to SCZ. Search for genes in rare multiplex SCZ families with a large number of affected individuals and quasi-Mendelian mode of inheritance using genetic linkage methodology has been one of the favorite strategies in psychiatric genetics. Although several genomic regions were suggested for linkage to SCZ, not a single gene causing or predisposing to SCZ has been identified thus far. Furthermore, it is not clear whether the genes of familial SCZ are also involved in sporadic cases that represent the overwhelming majority of SCZ patients. For sporadic cases, genetic association studies comparing the distribution of allelic frequencies of candidate genes in SCZ patients and controls have been performed but the outcome of such studies has also been quite modest. Several factors such as possible involvement of numerous interactive genes of minor effect, yet unknown environmental effects and diagnostic ambiguities of the disease have made genetic studies in SCZ quite unproductive. In terms of future studies, a genome-wide association search is a promising approach; however, this approach requires genotyping of thousands of genetic markers in large samples. In addition, a detailed analysis of the genes, expression of which changes under the influence of environmental factors, can indicate good candidates for genetic association studies. In this connection, investigations of the epigenetic regulation of genes and not only the DNA sequence variation, may be necessary for complete understanding of the etiopathogenic mechanisms of SCZ.

Genetic basis of anxiety-like behaviour: a critical review

The way genetic and/or environmental factors influence psychiatric disorders is an enduring question in the field of human psychiatric diseases. Anxiety-related disorders provide a relevant example of how such an interaction is involved in the aetiology of a psychiatric disease. In this paper we review the literature on that subject, reporting data derived from human and rodent studies. We present in a critical way the animal models used in the studies aimed at investigating the genetic basis of anxiety, including inbred mice, selected lines, multiple marker strains, or knockout mice and review data reporting environmental components influencing anxiety-related behaviours. We conclude that anxiety is a complex behaviour, underlined not only by genetic or environmental factors but also by multiple interactions between these two factors.

Molecular genetics of bipolar disorder

Alteration of monoaminergic neurotransmission is implicated in the pathophysiology of bipolar disorder (manic-depressive illness). Candidate genes participating in monoaminergic neurotransmission, especially serotonin transporter and monoamine oxidase A, may be associated with bipolar disorder. And the regulating regions of these genes and the molecules participating in intracellular signal transduction are now under investigation. To date, 13 whole genome positional cloning studies have been performed and many candidate loci identified. Using patients from a pedigree in which schizophrenia, depression or bipolar disorder have been linked with a balanced translocation at 1 and 11, candidate pathogenetic genes were cloned as DISC1 (disrupted in schizophrenia-1) and DISC2. Recently, pathogenetic mutations have been identified in two genetic diseases frequently co-morbid with mood disorder; WFS1 for Wolfram syndrome and ATP2A2 (SERCA2) for Darier's disease. Transmission of bipolar disorder may be characterized by anticipation and parent-of-origin effect, and extended CTG repeat at SEF2-1B gene was identified from a bipolar patient. However, its pathogenetic role was not supported by subsequent studies. Association of bipolar disorder with mitochondrial DNA has also been suggested. The role of genomic imprinting is also possible because linkage to 18p11 is limited to paternally transmitted pedigrees. These results warrant further study of molecular genetics of bipolar disorder.

Nuts and bolts of psychiatric genetics: building on the Human Genome Project

Schizophrenia and bipolar affective disorder are chronic, disabling illnesses that together affect 2% of the population. Genetic factors are known to be important in their development, but there are, as yet, no confirmed susceptibility genes. Here we discuss important issues in terms of alternative genetic strategies (linkage, association and/or cytogenetics) in the identification of candidate genes for the major psychoses. We discuss the impact of the Human Genome Project, the role of comparative genetics in finding and testing positional candidates, and the prospects for rational drug design and personalized medicine.

Mutation analysis of the N-methyl-D-aspartate receptor NR1 subunit gene (GRIN1) in schizophrenia

Dysfunction of N-methyl-D-aspartate (NMDA) type ionotropic glutamate receptors has been implicated in the etiology of schizophrenia based on psychotomimetic properties of the antagonist phencyclidine (PCP) and observation that mice expressing low levels of the N-methyl-D-aspartate receptor NR1 subunit exhibit behavioral alterations that may be ameliorated by neuroleptic drugs. Based on the hypothesis that some schizophrenic patients have functionally deficient mutation(s) of the gene encoding N-methyl-D-aspartate receptor NR1 subunit (GRIN1), we screened 48 Japanese patients with schizophrenia for mutations in the coding region of the GRIN1 gene. Four variants, IVS2-22T>C, IVS2-12G>A, IVS4-34C>T, and 1719G/A (Pro516Pro), were identified. No non-synonymous mutation was detected. No significant association was suggested by case-control comparisons. Results indicate that genomic variations of the GRIN1 gene are not likely to be involved substantially in the etiology of schizophrenia.