Genetic association studies of schizophrenia using the 8p21-22 genes: prepronociceptin (PNOC), neuronal nicotinic cholinergic receptor alpha polypeptide 2 (CHRNA2) and arylamine N-acetyltransferase 1 (NAT1)

The alpha2 nicotinic acetylcholine receptor, a subunit with unique and selective expression in inhibitory interneurons associated with principal cells

Nicotinic acetylcholine receptors (nAChRs) play crucial roles in various human disorders, with the α7, α4, α6, and α3-containing nAChR subtypes extensively studied in relation to conditions such as Alzheimer's disease, Parkinson's disease, nicotine dependence, mood disorders, and stress disorders. In contrast, the α2-nAChR subunit has received less attention due to its more restricted expression and the scarcity of specific agonists and antagonists for studying its function. Nevertheless, recent research has shed light on the unique expression pattern of the Chrna2 gene, which encodes the α2-nAChR subunit, and its involvement in distinct populations of inhibitory interneurons. This review highlights the structure, pharmacology, localization, function, and disease associations of α2-containing nAChRs and points to the unique expression pattern of the Chrna2 gene and its role in different inhibitory interneuron populations. These populations, including the oriens lacunosum moleculare (OLM) cells in the hippocampus, Martinotti cells in the neocortex, and Renshaw cells in the spinal cord, share common features and contribute to recurrent inhibitory microcircuits. Thus, the α2-nAChR subunit's unique expression pattern in specific interneuron populations and its role in recurrent inhibitory microcircuits highlight its importance in various physiological processes. Further research is necessary to uncover the comprehensive functionality of α2-containing nAChRs, delineate their specific contributions to neuronal circuits, and investigate their potential as therapeutic targets for related disorders.

Nicotinic Receptors in Sleep-Related Hypermotor Epilepsy: Pathophysiology and Pharmacology

Sleep-related hypermotor epilepsy (SHE) is characterized by hyperkinetic focal seizures, mainly arising in the neocortex during non-rapid eye movements (NREM) sleep. The familial form is autosomal dominant SHE (ADSHE), which can be caused by mutations in genes encoding subunits of the neuronal nicotinic acetylcholine receptor (nAChR), Na⁺-gated K⁺ channels, as well as non-channel signaling proteins, such as components of the gap activity toward rags 1 (GATOR1) macromolecular complex. The causative genes may have different roles in developing and mature brains. Under this respect, nicotinic receptors are paradigmatic, as different pathophysiological roles are exerted by distinct nAChR subunits in adult and developing brains. The widest evidence concerns α4 and β2 subunits. These participate in heteromeric nAChRs that are major modulators of excitability in mature neocortical circuits as well as regulate postnatal synaptogenesis. However, growing evidence implicates mutant α2 subunits in ADSHE, which poses interpretive difficulties as very little is known about the function of α2-containing (α2*) nAChRs in the human brain. Planning rational therapy must consider that pharmacological treatment could have different effects on synaptic maturation and adult excitability. We discuss recent attempts towards precision medicine in the mature brain and possible approaches to target developmental stages. These issues have general relevance in epilepsy treatment, as the pathogenesis of genetic epilepsies is increasingly recognized to involve developmental alterations.

Helicid Reverses Lipopolysaccharide-Induced Inflammation and Promotes GDNF Levels in C6 Glioma Cells through Modulation of Prepronociceptin

Helicid suppresses inflammatory factors and protects nerve cells in the hippocampus of rats with depression, but the mechanisms underlying its protective effects are unclear at present. In this investigation, we conducted gene silencing, Helicid intervention and rescue experiments to explore the protective actions of PNOC, the prepronociceptin gene known to regulate inflammatory processes, and Helicid on a C6 cell model of inflammation induced by LPS. Collective data from Western blots, ELISA, immunofluorescence and flow cytometry experiments showed that PNOC silencing or administration of Helicid led to reduced inflammatory factor levels, oxidative stress and expression of glial fibrillary acidic protein (GFAP), along with increased glial cell lines-derived neurotrophic factor (GDNF) expression. Furthermore, expression of p-Akt in the Akt signaling pathway was increased. Interestingly, overexpression of PNOC in the Helicid treatment group partially reversed the Helicid-induced changes in the above biochemical indexes. Our collective results provide strong evidence of Helicid-mediated regulation of the Akt signaling pathway through PNOC to improve cell inflammation and oxidative stress.

Systems Biology Analysis of the Antagonizing Effects of HIV-1 Tat Expression in the Brain over Transcriptional Changes Caused by Methamphetamine Sensitization

Methamphetamine (Meth) abuse is common among humans with immunodeficiency virus (HIV). The HIV-1 regulatory protein, trans-activator of transcription (Tat), has been described to induce changes in brain gene transcription that can result in impaired reward circuitry, as well as in inflammatory processes. In transgenic mice with doxycycline-induced Tat protein expression in the brain, i.e., a mouse model of neuroHIV, we tested global gene expression patterns induced by Meth sensitization. Meth-induced locomotor sensitization included repeated daily Meth or saline injections for seven days and Meth challenge after a seven-day abstinence period. Brain samples were collected 30 min after the Meth challenge. We investigated global gene expression changes in the caudate putamen, an area with relevance in behavior and HIV pathogenesis, and performed pathway and transcriptional factor usage predictions using systems biology strategies. We found that Tat expression alone had a very limited impact in gene transcription after the Meth challenge. In contrast, Meth-induced sensitization in the absence of Tat induced a global suppression of gene transcription. Interestingly, the interaction between Tat and Meth broadly prevented the Meth-induced global transcriptional suppression, by maintaining regulation pathways, and resulting in gene expression profiles that were more similar to the controls. Pathways associated with mitochondrial health, initiation of transcription and translation, as well as with epigenetic control, were heavily affected by Meth, and by its interaction with Tat in anti-directional ways. A series of systems strategies have predicted several components impacted by these interactions, including mitochondrial pathways, mTOR/RICTOR, AP-1 transcription factor, and eukaryotic initiation factors involved in transcription and translation. In spite of the antagonizing effects of Tat, a few genes identified in relevant gene networks remained downregulated, such as sirtuin 1, and the amyloid precursor protein (APP). In conclusion, Tat expression in the brain had a low acute transcriptional impact but strongly interacted with Meth sensitization, to modify effects in the global transcriptome.

Association between NAT2 polymorphisms and the risk of schizophrenia in a Northern Chinese Han population

The gene that encodes N-acetyltransferase 2 (NAT2), an enzyme that plays a crucial role in the metabolism of many drugs and xenobiotics, is located on chromosome 8p22, one of the most convictive susceptibility loci of schizophrenia. NAT2 genetic polymorphisms lead to various enzyme acetylation phenotypes. In the present study, six selected NAT2 exonic single nucleotide polymorphisms were genotyped in an independent case-control sample of a Northern Chinese Han population to verify the possible association between NAT2 and schizophrenia. Three (rs1801280T/341C, rs1799930/G590A, and rs1208/A803G) of the six single nucleotide polymorphisms showed significant allele frequency differences between the case and the control groups after rigorous Bonferroni correction. One protective fast-acetylation haplotype (NAT2*4) and two risk slow acetylation haplotypes (NAT2*5B and NAT2*6A) were discovered to be associated with schizophrenia. Our results indicate that NAT2 may be a susceptibility gene for schizophrenia in this Chinese Han population, and the risk haplotypes might cause the impairment of NAT2 in metabolizing neurotoxic substances.

The Role of Nicotine in Schizophrenia

Schizophrenia is associated with by severe disruptions in thought, cognition, emotion, and behavior. Patients show a marked increase in rates of smoking and nicotine dependence relative to nonaffected individuals, a finding commonly ascribed to the potential ameliorative effects of nicotine on symptom severity and cognitive impairment. Indeed, many studies have demonstrated improvement in patients following the administration of nicotine. Such findings have led to an increased emphasis on the development of therapeutic agents to target the nicotinic system as well as increasing the impetus to understand the genetic basis for nicotinic dysfunction in schizophrenia. The goal of this review article is to provide a critical summary of evidence for the role of the nicotinic system in schizophrenia. The first part will review the role of nicotine in normalization of primary dysfunctions and endophenotypical changes found in schizophrenia. The second part will provide a summary of genetic evidence linking polymorphisms in nicotinic receptor genes to smoking and schizophrenia. The third part will summarize attempts to treat schizophrenia using agents specifically targeting nicotinic and nicotinic receptor subtypes. Although currently available antipsychotic treatments are generally able to manage some aspects of schizophrenia (e.g., positive symptoms) they fail to address several other critically effected aspects of the disease. As such, the search for novel mechanisms to treat this disease is necessary.

Co-expression network of neural-differentiation genes shows specific pattern in schizophrenia

Background

Schizophrenia is a neurodevelopmental disorder with genetic and environmental factors contributing to its pathogenesis, although the mechanism is unknown due to the difficulties in accessing diseased tissue during human neurodevelopment. The aim of this study was to find neuronal differentiation genes disrupted in schizophrenia and to evaluate those genes in post-mortem brain tissues from schizophrenia cases and controls.

Methods

We analyzed differentially expressed genes (DEG), copy number variation (CNV) and differential methylation in human induced pluripotent stem cells (hiPSC) derived from fibroblasts from one control and one schizophrenia patient and further differentiated into neuron (NPC). Expression of the DEG were analyzed with microarrays of post-mortem brain tissue (frontal cortex) cohort of 29 schizophrenia cases and 30 controls. A Weighted Gene Co-expression Network Analysis (WGCNA) using the DEG was used to detect clusters of co-expressed genes that werenon-conserved between adult cases and controls brain samples.

Results

We identified methylation alterations potentially involved with neuronal differentiation in schizophrenia, which displayed an over-representation of genes related to chromatin remodeling complex (adjP = 0.04). We found 228 DEG associated with neuronal differentiation. These genes were involved with metabolic processes, signal transduction, nervous system development, regulation of neurogenesis and neuronal differentiation. Between adult brain samples from cases and controls there were 233 DEG, with only four genes overlapping with the 228 DEG, probably because we compared single cell to tissue bulks and more importantly, the cells were at different stages of development. The comparison of the co-expressed network of the 228 genes in adult brain samples between cases and controls revealed a less conserved module enriched for genes associated with oxidative stress and negative regulation of cell differentiation.

Conclusion

This study supports the relevance of using cellular approaches to dissect molecular aspects of neurogenesis with impact in the schizophrenic brain. We showed that, although generated by different approaches, both sets of DEG associated to schizophrenia were involved with neocortical development. The results add to the hypothesis that critical metabolic changes may be occurring during early neurodevelopment influencing faulty development of the brain and potentially contributing to further vulnerability to the illness.

Electronic supplementary material

The online version of this article (doi:10.1186/s12920-015-0098-9) contains supplementary material, which is available to authorized users.

Detection of SNP-SNP interactions in trios of parents with schizophrenic children

Schizophrenia (SZ) is a heritable and complex psychiatric disorder with an estimated worldwide prevalence of about 1%. Research on the risk factors for SZ has thus far yielded few clues to causes, but has pointed to a heterogeneous etiology that likely involves multiple genes and gene-environment interactions. In this manuscript, we apply a novel method (trio logic regression, Li et al., 2009) to case-parent trio data from a SZ candidate gene study conducted on families of Ashkenazi Jewish descent, and demonstrate the method's ability to detect multi-gene models for SZ risk in the family-based design. In particular, we demonstrate how this method revealed a genotype-phenotype association that includes an allele without marginal effect.

Association of the NPAS3 gene and five other loci with response to the antipsychotic iloperidone identified in a whole genome association study

A whole genome association study was performed in a phase 3 clinical trial conducted to evaluate a novel antipsychotic, iloperidone, administered to treat patients with schizophrenia. Genotypes of 407 patients were analyzed for 334,563 single nucleotide polymorphisms (SNPs). SNPs associated with iloperidone efficacy were identified within the neuronal PAS domain protein 3 gene (NPAS3), close to a translocation breakpoint site previously observed in a family with schizophrenia. Five other loci were identified that include the XK, Kell blood group complex subunit-related family, member 4 gene (XKR4), the tenascin-R gene (TNR), the glutamate receptor, inotropic, AMPA 4 gene (GRIA4), the glial cell line-derived neurotrophic factor receptor-alpha2 gene (GFRA2), and the NUDT9P1 pseudogene located in the chromosomal region of the serotonin receptor 7 gene (HTR7). The study of these polymorphisms and genes may lead to a better understanding of the etiology of schizophrenia and of its treatment. These results provide new insight into response to iloperidone, developed with the ultimate goal of directing therapy to patients with the highest benefit-to-risk ratio.

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

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

Prioritization of positional candidate genes using multiple web-based software tools

The prioritization of genes within a candidate genomic region is an important step in the identification of causal gene variants affecting complex traits. Surprisingly, there have been very few reports of bioinformatics tools to perform such prioritization. The purpose of this article is to investigate the performance of 3 positional candidate gene software tools available, PosMed, GeneSniffer and SUSPECTS. The comparison was made for 40, 20 and 10 Mb regions in the human genome centred around known susceptibility genes for the common diseases breast cancer, Crohn's disease, age-related macular degeneration and schizophrenia. The known susceptibility gene was not always ranked highly, or not ranked at all, by 1 or more of the software tools. There was a large variation between the 3 tools regarding which genes were prioritized, and their rank order. PosMed and GeneSniffer were most similar in their prioritization gene list, whereas SUSPECTS identified the same candidate genes only for the narrowest (10 Mb) regions. Combining 2 or all of the candidate gene finding tools was superior in terms of ranking positional candidates. It is possible to reduce the number of candidate genes from a starting set in a region of interest by combining a variety of candidate gene finding tools. Conversely, we recommend caution in relying solely on single positional candidate gene prioritization tools. Our results confirm the obvious, that is, that starting with a narrower positional region gives a higher likelihood that the true susceptibility gene is selected, and that it is ranked highly. A narrow confidence interval for the mapping of complex trait genes by linkage can be achieved by maximizing marker informativeness and by having large samples. Our results suggest that the best approach to classify a minimum set of candidate genes is to take those genes that are prioritized by multiple prioritization tools.

FZD3 is not a risk gene for schizophrenia: a case-control study in a Caucasian sample

BACKGROUND

Polymorphisms in the human frizzeled-3 (FZD3) gene have been associated with schizophrenia in an Asian population sample. However, this finding could not be confirmed in subsequent studies investigating other populations. Here we attempted to replicate this finding in a sample of 192 German chronically ill schizophrenic subjects.

METHODS

Three single nucleotide polymorphisms in the FZD3 gene have been genotyped by primer extension and MALDI-TOF measurement. Subsequently, associations for single markers as well as haplotypes were tested.

RESULTS

In German patients, neither single markers nor haplotypes in FZD3 were associated with schizophrenia. Further exploratory analyses using a different diagnostic approach did also not yield significant results.

CONCLUSIONS

FZD3 is unlikely to play a role in the genetic predisposition towards schizophrenia in the Caucasian population.

Genetic association and brain morphology studies and the chromosome 8p22 pericentriolar material 1 (PCM1) gene in susceptibility to schizophrenia

CONTEXT

There is evidence of linkage to a schizophrenia susceptibility locus on chromosome 8p21-22 found by several family linkage studies.

OBJECTIVES

To fine map and identify a susceptibility gene for schizophrenia on chromosome 8p22 and to investigate the effect of this genetic susceptibility on an endophenotype of abnormal brain structure using magnetic resonance imaging.

DESIGN

Fine mapping and identification of a chromosome 8p22 susceptibility gene was carried out by finding linkage disequilibrium between genetic markers and schizophrenia in multiply affected families, a case-control sample, and a trio sample. Variation in brain morphology associated with pericentriolar material 1 (PCM1) alleles was examined using voxel-based morphometry and statistical parametric mapping with magnetic resonance imaging. Setting and Patients A family sample of 13 large families multiply affected with schizophrenia, 2 schizophrenia case-control samples from the United Kingdom and Scotland, and a sample of schizophrenic trios from the United States containing parents and 1 affected child with schizophrenia.

MAIN OUTCOME MEASURES

Tests of transmission disequilibrium between PCM1 locus polymorphisms and schizophrenia using a family sample and tests of allelic association in case-control and trio samples. Voxel-based morphometry using statistical parametric mapping.

RESULTS

The family and trio samples both showed significant transmission disequilibrium between marker D85261 in the PCM1 gene locus and schizophrenia. The case-control sample from the United Kingdom also found significant allelic association between PCM1 gene markers and schizophrenia. Voxel-based morphometry of cases who had inherited a PCM1 genetic susceptibility showed a significant relative reduction in the volume of orbitofrontal cortex gray matter in comparison with patients with non-PCM1-associated schizophrenia, who, by contrast, showed gray matter volume reduction in the temporal pole, hippocampus, and inferior temporal cortex.

CONCLUSIONS

The PCM1 gene is implicated in susceptibility to schizophrenia and is associated with orbitofrontal gray matter volumetric deficits.

Failure to confirm allelic association between markers at the CAPON gene locus and schizophrenia in a British sample

BACKGROUND

Linkage studies have confirmed that chromosome 1q23.3 is a susceptibility locus for schizophrenia. It was then claimed that markers at the carboxyl-terminal PDZ ligand of neuronal nitric oxide synthase (CAPON) gene showed allelic association with schizophrenia in Canadian families. A second Chinese study found a base pair polymorphism at the CAPON gene also associated with schizophrenia.

METHODS

We attempted replication using eight markers from the Canadian study in a UK based sample of 450 cases and 450 supernormal controls.

RESULTS

We found no evidence for allelic or haplotypic association with schizophrenia for any of the markers found to be associated in the Canadian sample.

CONCLUSIONS

The negative results might reflect genetic heterogeneity between the Canadian, Chinese and UK samples or be due to methodological problems. The present finding weakens the evidence that mutations or variation in the CAPON gene are causing genetic susceptibility to schizophrenia in European populations.

Extreme population differences across Neuregulin 1 gene, with implications for association studies

Neuregulin 1 (NRG1) is one of the most exciting candidate genes for schizophrenia in recent years since its first association with the disease in an Icelandic population. Since then, many association studies have analysed allele and haplotype frequencies in distinct populations yielding varying results: some have replicated the association, although with different alleles or haplotypes being associated, whereas others have failed to replicate the association. These contradictory results might be attributed to population differences in allele and haplotype frequencies. In order to approach this issue, we have typed 13 SNPs across this large 1.4 Mb gene, including two of the SNPs originally found associated with schizophrenia in the Icelandic population, the objective being to discover if the underlying cause of the association discrepancies to date may be due to population-specific genetic variation. The analyses have been performed in a total of 1088 individuals from 39 populations, covering most of the genetic diversity in the human species. Most of the SNPs analysed displayed differing frequencies according to geographical region. These allele differences are especially relevant in two SNPs located in a large intron of the gene, as shown by the extreme F(ST) values, which reveal genetic stratification correlated to broad continental areas. This finding may be indicative of the influence of some local selective forces on this gene. Furthermore, haplotype analysis reveals a clear clustering according to geographical areas. In summary, our findings suggest that NRG1 presents extreme population differences in allele and haplotype frequencies. We have given recommendations for taking this into account in future association studies since this diversity could give rise to erroneous results.

Bipolar I disorder and schizophrenia: a 440-single-nucleotide polymorphism screen of 64 candidate genes among Ashkenazi Jewish case-parent trios

Bipolar, schizophrenia, and schizoaffective disorders are common, highly heritable psychiatric disorders, for which familial coaggregation, as well as epidemiological and genetic evidence, suggests overlapping etiologies. No definitive susceptibility genes have yet been identified for any of these disorders. Genetic heterogeneity, combined with phenotypic imprecision and poor marker coverage, has contributed to the difficulty in defining risk variants. We focused on families of Ashkenazi Jewish descent, to reduce genetic heterogeneity, and, as a precursor to genomewide association studies, we undertook a single-nucleotide polymorphism (SNP) genotyping screen of 64 candidate genes (440 SNPs) chosen on the basis of previous linkage or of association and/or biological relevance. We genotyped an average of 6.9 SNPs per gene, with an average density of 1 SNP per 11.9 kb in 323 bipolar I disorder and 274 schizophrenia or schizoaffective Ashkenazi case-parent trios. Using single-SNP and haplotype-based transmission/disequilibrium tests, we ranked genes on the basis of strength of association (P<.01). Six genes (DAO, GRM3, GRM4, GRIN2B, IL2RB, and TUBA8) met this criterion for bipolar I disorder; only DAO has been previously associated with bipolar disorder. Six genes (RGS4, SCA1, GRM4, DPYSL2, NOS1, and GRID1) met this criterion for schizophrenia or schizoaffective disorder; five replicate previous associations, and one, GRID1, shows a novel association with schizophrenia. In addition, six genes (DPYSL2, DTNBP1, G30/G72, GRID1, GRM4, and NOS1) showed overlapping suggestive evidence of association in both disorders. These results may help to prioritize candidate genes for future study from among the many suspected/proposed for schizophrenia and bipolar disorders. They provide further support for shared genetic susceptibility between these two disorders that involve glutamate-signaling pathways.

No association between common variations in the neuronal nicotinic acetylcholine receptor alpha2 subunit gene (CHRNA2) and bipolar I disorder

The neuronal nicotinic acetylcholine receptor alpha2 subunit gene (CHRNA2) maps to the bipolar susceptibility locus on chromosome 8p21-22. Given the biological role of the neuronal nicotinic acetylcholine receptors and the substantial comorbidity of nicotine dependence in psychiatric disorders, the CHRNA2 gene is a plausible candidate gene for bipolar disorder (BPD). We tested the hypothesis that variations in the CHRNA2 gene confer susceptibility to bipolar I disorder in a case-control association study. Genotypes of one amino acid substitution polymorphism (Ala125Thr) and five non-coding variations across the CHRNA2 gene were obtained from 345 unrelated bipolar I patients and 273 control samples. Genotypes and allele frequencies were compared between groups using chi-square contingency analysis. Linkage disequilibrium (LD) between markers was calculated, and estimated haplotype frequencies were compared between groups. We observed no statitistically significant difference in genotype and allele frequencies for all six variations between bipolar patients and controls, but we did demonstrate strong LD throughout the gene. Haplotype analysis showed that no combinations of alleles were associated with illness. Our results suggest that common variations in the CHRNA2 gene are unlikely to confer susceptibility to BPD in this sample. Further studies are required to elucidate the susceptibility locus for BPD on chromosome 8p21-22.

A Girl with Pervasive Developmental Disorder and Complex Chromosome Rearrangement Involving 8p and 10p

We report a 4-year-old girl with a de novo, apparently balanced complex chromosome rearrangement. She initially presented for assessment of velopharyngeal insufficiency due to hypernasal speech. She has distinctive facial features (long face, broad nasal bridge, and protuberant ears with simplified helices), bifid uvula, strabismus, and joint laxity. She is developmentally delayed, with language and cognitive skills approximately 2 SD below the mean expected for her age, and meets ADI, ADOS, and DSM-IV criteria for pervasive developmental disorder. She has poor eye contact, atypical communication and social interaction, repetitive behaviours and significant difficulties with processing sensory input. Her karyotype is characterized by the presence of two derivative chromosomes; 46,XX, der(8)(10pter- >10pl2.32::8p12- >8qter), der(l0)(8pter- >8p21.3::10p12.32- >10p11.23::8p21.3- > 8p12::10p11.23- >l0qter). The der(8) is a result of translocation of the segment 10p12.32-pter onto 8p12. The der(l0) has two 8p segments collectively from 8p12-pter in that the segment 8p21.3-pter is translocated onto 10p12.32 and the segment 8p12-p21.3 is inserted at 10p11.23. FISH analysis showed no microdeletion of the major locus at 22q11.2 nor for the minor locus at 10p13p14. This case suggests that aberrations at 8p12, 8p21.3, 10p11.23 and/or 10p12.32 may result in pervasive developmental disorder, associated with mild cognitive delay and specific facial anomalies.

Linkage evidence of schizophrenia to loci near neuregulin 1 gene on chromosome 8p21 in Taiwanese families

Positive linkage of schizophrenia to chromosome 8p22-21 loci had been reported in the Caucasian samples. This study was designed to replicate this finding by using eleven microsatellite markers on chromosome 8p22-21 in 52 Taiwanese schizophrenic families with at least two affected siblings. Two phenotype models (narrow: DSM-IV schizophrenia only; and broad: including schizophrenia, schizoaffective, and other non-affective psychotic disorders) were used to define the disease phenotype. Maximum non-parametric linkage scores (NPL score) of 2.45 (P = 0.008) and 1.89 (P = 0.02) were obtained for the marker D8S1222 under the broad and narrow models, respectively. Positive linkage was found across about a 4-cM region. The marker D8S1222 was about 400 kbp distal to the exon 1 of glial growth factor 2 (GGF2), an isoform of Neuregulin 1 gene (NRG1), which has been highly suggested to be a candidate gene for schizophrenia. The results provide suggestive linkage evidence of schizophrenia to loci near NRG1 on chromosome 8p21 in an ethnically distinct Taiwanese sample. Further exploration of the candidate gene and nearby chromosome regions is warranted.

Genetic studies of neuropsychiatric disorders in Costa Rica: a model for the use of isolated populations

The importance of genetics in understanding the etiology of mental illness has become increasingly clear in recent years, as more evidence has mounted that almost all neuropsychiatric disorders have a genetic component. It has also become clear, however, that these disorders are etiologically complex, and multiple genetic and environmental factors contribute to their makeup. So far, traditional linkage mapping studies have not definitively identified specific disease genes for neuropsychiatric disorders, although some potential candidates have been identified via these methods (e.g. the dysbindin gene in schizophrenia; Straub et al., 2002; Schwab et al., 2003). For this reason, alternative approaches are being attempted, including studies in genetically isolated populations. Because isolated populations have a high degree of genetic homogeneity, their use may simplify the process of identifying disease genes in disorders where multiple genes may play a role. Several areas of Latin America contain genetically isolated populations that are well suited for the study of neuropsychiatric disorders. Genetic studies of several major psychiatric illnesses, including bipolar disorder, major depression, schizophrenia, Tourette Syndrome, alcohol dependence, attention deficit hyperactivity disorder, and obsessive-compulsive disorder, are currently underway in these regions. In this paper we highlight the studies currently being conducted by our groups in the Central Valley of Costa Rica to illustrate the potential advantages of this population for genetic studies.

A Novel Permutation Testing Method Implicates Sixteen Nicotinic Acetylcholine Receptor Genes as Risk Factors for Smoking in Schizophrenia Families

Smoking is a common correlate of schizophrenia, which leads to medical morbidity. Although twin and adoption studies have consistently implicated genes in the etiology of both smoking and schizophrenia, finding genes has been difficult. Several authors have suggested that clinical or neurobiological features associated with schizophrenia, such as smoking, might improve the ability to detect schizophrenia susceptibility genes by identifying genes related to the etiology of that feature. The objective of this study is to assess evidence for linkage of sixteen nicotinic acetylcholine receptor genes and smoking in schizophrenia families, using data from the NIMH Genetics Initiative for schizophrenia. Sixteen nicotinic acetylcholine receptor genes were selected prior to analysis. We used a multipoint sibling pair linkage analysis program, SIBPAL2, with a smoking trait in schizophrenia families. The significance of the group of candidate genes, in addition to each individual candidate gene, was assessed using permutation testing, which adjusted for multiple comparisons. The group of genes showed significant linkage to the smoking trait after adjusting for multiple comparisons through permutation testing (p = 0.039). In addition, two of the individual candidate genes were significant (CHRNA2, p = 0.044) and (CHRNB2, p = 0.015) and two genes were marginally significant (CHRNA7, p = 0.095; CHRNA1, p = 0.076). The significance of the complex hypothesis, involving sixteen genes, implicates the nicotinic system in smoking for schizophrenic families. Individual gene analysis suggests that CHRNA2 and CHRNB2 may play a particular role in this involvement. Such findings help prioritize genes for future case control studies. In addition, we provide a novel permutation method that is useful in future analyses involving a single hypothesis, with multiple candidate genes.

Genetic linkage in bipolar disorder

Bipolar disorder is an etiologically complex syndrome that is clearly heritable. Multiple genes, working singly or in concert, are likely to cause susceptibility to bipolar disorder. Bipolar disorder genetics has progressed rapidly in the last few decades. However, specific causal genetic mutations for bipolar disorder have not been identified. Both candidate gene studies and complete genome screens have been conducted. They have provided compelling evidence for several potential bipolar disorder susceptibility loci in several regions of the genome. The strongest evidence suggests that bipolar disorder susceptibility loci may lie in one or more genomic regions on chromosomes 18, 4, and 21. Other regions of interest, including those on chromosomes 5 and 8, are also under investigation. New approaches, such as the use of genetically isolated populations and the use of endophenotypes for bipolar disorder, hold promise for continued advancement in the search to identify specific bipolar disorder genes.