Analysis of variations in the NAPG gene on chromosome 18p11 in bipolar disorder

Progress and Implications from Genetic Studies of Bipolar Disorder

With the advancements in gene sequencing technologies, including genome-wide association studies, polygenetic risk scores, and high-throughput sequencing, there has been a tremendous advantage in mapping a detailed blueprint for the genetic model of bipolar disorder (BD). To date, intriguing genetic clues have been identified to explain the development of BD, as well as the genetic association that might be applied for the development of susceptibility prediction and pharmacogenetic intervention. Risk genes of BD, such as CACNA1C, ANK3, TRANK1, and CLOCK, have been found to be involved in various pathophysiological processes correlated with BD. Although the specific roles of these genes have yet to be determined, genetic research on BD will help improve the prevention, therapeutics, and prognosis in clinical practice. The latest preclinical and clinical studies, and reviews of the genetics of BD, are analyzed in this review, aiming to summarize the progress in this intriguing field and to provide perspectives for individualized, precise, and effective clinical practice.

Chromosome 18p11.2 harbors susceptibility marker: D18S452, for bipolar affective disorder

AIM

The aim of our study was to investigate whether the tandem repeat polymorphism in D18S452 microsatellite marker at locus 18p11.2 is a risk factor of bipolar affective disorder (BPAD) in Kashmiri population.

MATERIALS AND METHODS

The repeat polymorphism in D18S452 was evaluated by polymerase chain reaction (PCR) analysis of in 74 diagnosed BPAD patients and 74 controls subjects.

RESULTS

Tandem repeat (300 bp*) allele frequency was found to be 1.35% in controls and 8.108% in cases. The tandem repeat (250 bp*) allele frequency was found to be in 91.89% in cases and 98.65% in controls. The 252 bp/252 bp genotype was found to be present in 89.18% of cases and 98.64% of controls, the 300 bp/300 bp genotype in 5.40% of cases and 1.35% of controls and the 252 bp/300 bp variant in 5.40% of cases and none among the controls. Although the proportion of patients homozygous for tandem repeat (300 bp/300 bp) was higher in cases than in controls, the difference was not statistically significant when 252 bp/252 bp genotype was taken as reference (odds ratio [OR]=4.4242; 95% confidence interval [CI] 0.4822-40.5924); P=0.1529). However, when the frequency of heterozygous genotype (252 bp/300 bp) was compared with 252 bp/252 bp statistical significance was observed (OR=8.0603; 95% CI 1.1112-58.4646; P=0.0383).

CONCLUSION

This is the first study reporting a significant association between D18S452 maker with tandem repeat polymorphism in heterozygous condition (252 bp/300 bp) and the development of BPAD in Kashmiri population.

Evaluation of candidate genes from orphan FEB and GEFS+ loci by analysis of human brain gene expression atlases

Febrile seizures, or febrile convulsions (FEB), represent the most common form of childhood seizures and are believed to be influenced by variations in several susceptibility genes. Most of the associated loci, however, remain ‘orphan’, i.e. the susceptibility genes they contain still remain to be identified. Further orphan loci have been mapped for a related disorder, genetic (generalized) epilepsy with febrile seizures plus (GEFS+).

We show that both spatially mapped and ‘traditional’ gene expression data from the human brain can be successfully employed to predict the most promising candidate genes for FEB and GEFS+, apply our prediction method to the remaining orphan loci and discuss the validity of the predictions. For several of the orphan FEB/GEFS+ loci we propose excellent, and not always obvious, candidates for mutation screening in order to aid in gaining a better understanding of the genetic origin of the susceptibility to seizures.

Association analysis between polymorphisms in the myo-inositol monophosphatase 2 (IMPA2) gene and bipolar disorder

Linkage studies in bipolar disorder (BPD) suggest that a susceptibility locus exists on chromosome 18p11. The myo-inositol monophosphatase 2 gene (IMPA2) maps to this genomic region. Myo-inositol monophosphatase dephosphorylates inositol monophosphate, regenerating free inositol. Lithium, a common treatment for BPD, has been shown to inhibit IMPA2 activity and decrease levels of inositol. It is hypothesized that lithium conveys its therapeutic effect for BPD patients partially through inositol regulation. Hence, dysfunction of inositol caused by IMPA2 irregularity may contribute to the pathophysiology of BPD. In this study, we hypothesize that genetic variations in the IMPA2 gene contributes to increased susceptibility to BPD. We tested this hypothesis by genotyping 9 SNPs (rs1787984; rs585247; rs3974759; rs650727; rs589247; rs669838; rs636173; rs3786285; rs613993) in BPD patients (n=556) and controls (n=735). Genotype 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. Single marker analysis revealed several associations between IMPA2 variations and BPD, which were subsequently rendered non-significant after correction for multiple testing. Although our study did not show strong support for an association between the tested IMPA2 polymorphisms and susceptibility to BPD, additional larger studies are necessary to comprehensively investigate a role of the IMPA2 gene in the pathophysiology of BPD.

Association between polymorphisms in the metallophosphoesterase (MPPE1) gene and bipolar disorder

Genetic linkage studies in bipolar disorder (BPD) suggest that a susceptibility locus exists on chromosome 18p11. The metallophosphoesterase (MPPE1) gene maps to this region. Dysregulation of protein phosphorylation and subsequent abnormal cellular signaling has been postulated to be involved in neuropsychiatric disorders thus making MPPE1 a plausible biological candidate gene for BPD. In this study, we hypothesized that genetic variation in the MPPE1 gene contributes to BPD. We tested this hypothesis by genotyping four SNPs (rs871044; rs3974590; rs593713; rs602201) in BPD patients (n = 570) and healthy controls (n = 725). 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. Single marker analysis revealed an association of rs3974590 with BPD (P = 0.009; permutation corrected P = 0.046). Haplotype analysis did not show any significant association with disease after permutation correction. Our results provide evidence of an association between a polymorphism in the MPPE1 gene and BPD. Additional studies are necessary to confirm and elucidate the role of MPPE1 as a susceptibility gene for BPD on chromosome 18p.

Psychiatric syndromes in individuals with chromosome 18 abnormalities

Chromosome 18 abnormalities are associated with a range of physical abnormalities such as short stature and hearing impairments. Psychiatric manifestations have also been observed. This study focuses on the presentations of psychiatric syndromes as they relate to specific chromosomal abnormalities of chromosome 18. Twenty-five subjects (13 with an 18q deletion, 9 with 18p tetrasomy, and 3 with an 18p deletion), were interviewed by psychiatrists (blind to specific chromosomal abnormality) using the DIGS (subjects 18 and older) or KSADS-PL (subjects under 18). A consensus best estimation diagnostic process was employed to determine psychiatric syndromes. Oligonucleotide Array Comparative Genomic Hybridization (Agilent Technologies) was utilized to define specific regions of chromosome 18 that were deleted or duplicated. These data were further analyzed to determine critical regions of the chromosome as they relate to phenotypic manifestations in these subjects. 58.3% of the chromosome 18q- deletion subjects had depressive symptoms, 58.3% had anxiety symptoms, 25% had manic symptoms, and 25% had psychotic symptoms. 66.6% of the chromosome 18p- deletion subjects had anxiety symptoms, and none had depressive, manic, or psychotic symptoms. Fifty percent of the chromosome 18p tetrasomy subjects had anxiety symptoms, 12.5% had psychotic symptoms, and 12.5% had a mood disorder. All three chromosomal disorders were associated with high anxiety rates. Psychotic, manic and depressive disorders were seen mostly in 18q- subjects and this may be helpful in narrowing regions for candidate genes for these psychiatric conditions.

Case-control association study of 65 candidate genes revealed a possible association of a SNP of HTR5A to be a factor susceptible to bipolar disease in Bulgarian population

BACKGROUND

Bipolar affective disorder (BAD) is a psychiatric illness characterized by episodes of mania and depression. Although the etiology is not clear, epidemiological studies suggest it is a result of an interaction of genetic and environmental factors. Despite of enormous efforts and abundant studies conducted, none has yet been identified definitively a gene susceptible to bipolar disorder.

METHODS

Ninety-four Bulgarian patients diagnosed with bipolar disorder and 184 Bulgarian healthy individuals, were used for genotyping of 191 single nucleotide polymorphisms (SNPs) by TaqMan and/or Invader assays. Seventeen SNPs that revealed P value less than 0.05 in the first screening were genotyped using an additional independent set of samples, consisting of 78 BAD cases and 372 controls.

RESULTS

After applying the Bonferonni correction on genotyping results of 172 cases and 556 controls, only one SNP, rs1800883, in the HTR5A gene revealed a significant level of P value (P=0.000097; odds ratio=1.80 (95%CI, 1.27-2.54); corrected P=0.017).

CONCLUSIONS

Our findings suggest that HTR5A gene could play an important role in the pathogenesis of bipolar disorder in our population. However these findings should be viewed with caution and replication studies in other populations are necessary in support of these findings.

Genetics of bipolar disorder

Bipolar disorder, especially the most severe type (type I), has a strong genetic component. Family studies suggest that a small number of genes of modest effect are involved in this disorder. Family-based studies have identified a number of chromosomal regions linked to bipolar disorder, and progress is currently being made in identifying positional candidate genes within those regions, À number of candidate genes have also shown evidence of association with bipolar disorder, and genome-wide association studies are now under way, using dense genetic maps. Replication studies in larger or combined datasets are needed to definitively assign a role for specific genes in this disorder. This review covers our current knowledge of the genetics of bipolar disorder, and provides a commentary on current approaches used to identify the genes involved in this complex behavioral disorder.

The genetics of bipolar disorder: genome 'hot regions,' genes, new potential candidates and future directions

Bipolar disorder (BP) is a complex disorder caused by a number of liability genes interacting with the environment. In recent years, a large number of linkage and association studies have been conducted producing an extremely large number of findings often not replicated or partially replicated. Further, results from linkage and association studies are not always easily comparable. Unfortunately, at present a comprehensive coverage of available evidence is still lacking. In the present paper, we summarized results obtained from both linkage and association studies in BP. Further, we indicated new potential interesting genes, located in genome 'hot regions' for BP and being expressed in the brain. We reviewed published studies on the subject till December 2007. We precisely localized regions where positive linkage has been found, by the NCBI Map viewer (http://www.ncbi.nlm.nih.gov/mapview/); further, we identified genes located in interesting areas and expressed in the brain, by the Entrez gene, Unigene databases (http://www.ncbi.nlm.nih.gov/entrez/) and Human Protein Reference Database (http://www.hprd.org); these genes could be of interest in future investigations. The review of association studies gave interesting results, as a number of genes seem to be definitively involved in BP, such as SLC6A4, TPH2, DRD4, SLC6A3, DAOA, DTNBP1, NRG1, DISC1 and BDNF. A number of promising genes, which received independent confirmations, and genes that have to be further investigated in BP, have been also systematically listed. In conclusion, the combination of linkage and association approaches provided a number of liability genes. Nevertheless, other approaches are required to disentangle conflicting findings, such as gene interaction analyses, interaction with psychosocial and environmental factors and, finally, endophenotype investigations.

Association analysis of the pituitary adenylate cyclase-activating polypeptide (PACAP/ADCYAP1) gene in bipolar disorder

BACKGROUND

Linkage studies in bipolar disorder (BPD) suggest that a susceptibility locus exists on chromosome 18p11. The pituitary adenylate cyclase-activating polypeptide/adenylate cyclase-activating polypeptide 1 (pituitary) (PACAP/ADCYAP1) gene maps to this region. PACAP is a neuropeptide involved in neurotransmission in both the peripheral nervous system and central nervous system and is required for catecholamine secretion. Animal models of PACAP mutations show remarkable behavioral defects, including hyperactivity and increased exploratory behavior.

OBJECTIVE

In this study we tested the hypothesis that genetic variations in the human PACAP gene contribute to BPD.

METHODS

Genotyping of seven single nucleotide polymorphisms (rs1893154; rs2846811; rs8192595; rs2856966; rs928978; rs2231187; rs1610037) was performed in BPD patients (n=570) and healthy controls (n=710). Genotypes and allele frequencies were compared between groups using chi contingency analysis. Linkage disequilibrium between markers was calculated and estimated haplotype frequencies were compared between groups.

MAIN RESULTS

There were no significant differences between groups on the allele, genotype or haplotype level for any of the tested single nucleotide polymorphisms.

CONCLUSION

Our results provide no evidence of an association of the PACAP gene with BPD in this group of patients and controls. Additional studies are necessary to elucidate the BPD susceptibility locus on chromosome 18p.

Dense SNP association study for bipolar I disorder on chromosome 18p11 suggests two loci with excess paternal transmission

Parent-of-origin effects have been implicated as mediators of genetic susceptibility for a number of complex disease phenotypes, including bipolar disorder. Specifically, evidence for linkage on chromosome 18 is modified when allelic parent-of-origin is accommodated in the analysis. Our goal was to characterize the susceptibility locus for bipolar I disorder on chromosome 18p11 and investigate this parent-of-origin hypothesis in an association context. This was achieved by genotyping single nucleotide polymorphisms (SNPs) at a high density (1 SNP/5 kb) along 13.6 megabases of the linkage region. To increase our ability to detect a susceptibility locus, we restricted the phenotype definition to include only bipolar I probands. We also restricted our study population to Ashkenazi Jewish individuals; this population has characteristics of a genetic isolate and may therefore facilitate detection of variants for complex disease. Three hundred and forty-four pedigrees (363 parent/child trios) where probands were affected with bipolar 1 disorder were genotyped. Transmission disequilibrium test analysis revealed no statistically significant association to SNPs or haplotypes within this region in this sample. However, when parent-of-origin of transmitted SNPs was taken into account, suggestive association was revealed for two separate loci.

Molecular genetics of bipolar disorder and depression

In this review, all papers relevant to the molecular genetics of bipolar disorder published from 2004 to the present (mid 2006) are reviewed, and major results on depression are summarized. Several candidate genes for schizophrenia may also be associated with bipolar disorder: G72, DISC1, NRG1, RGS4, NCAM1, DAO, GRM3, GRM4, GRIN2B, MLC1, SYNGR1, and SLC12A6. Of these, association with G72 may be most robust. However, G72 haplotypes and polymorphisms associated with bipolar disorder are not consistent with each other. The positional candidate approach showed an association between bipolar disorder and TRPM2 (21q22.3), GPR50 (Xq28), Citron (12q24), CHMP1.5 (18p11.2), GCHI (14q22-24), MLC1 (22q13), GABRA5 (15q11-q13), BCR (22q11), CUX2, FLJ32356 (12q23-q24), and NAPG (18p11). Studies that focused on mood disorder comorbid with somatic symptoms, suggested roles for the mitochondrial DNA (mtDNA) 3644 mutation and the POLG mutation. From gene expression analysis, PDLIM5, somatostatin, and the mtDNA 3243 mutation were found to be related to bipolar disorder. Whereas most previous positive findings were not supported by subsequent studies, DRD1 and IMPA2 have been implicated in follow-up studies. Several candidate genes in the circadian rhythm pathway, BmaL1, TIMELESS, and PERIOD3, are reported to be associated with bipolar disorder. Linkage studies show many new linkage loci. In depression, the previously reported positive finding of a gene-environmental interaction between HTTLPR (insertion/deletion polymorphism in the promoter of a serotonin transporter) and stress was not replicated. Although the role of the TPH2 mutation in depression had drawn attention previously, this has not been replicated either. Pharmacogenetic studies show a relationship between antidepressant response and HTR2A or FKBP5. New technologies for comprehensive genomic analysis have already been applied. HTTLPR and BDNF promoter polymorphisms are now found to be more complex than previously thought, and previous papers on these polymorphisms should be treated with caution. Finally, this report addresses some possible causes for the lack of replication in this field.

A ubiquitous membrane fusion protein αSNAP: a potential therapeutic target for cancer, diabetes and neurological disorders?

Alpha soluble NSF attachment protein (alphaSNAP) is a ubiquitous and indispensable component of membrane fusion machinery. Deletion of alphaSNAP is embryonically lethal. Yet, there is accumulating evidence that milder alterations in expression levels of alphaSNAP may be associated with a number of specific pathological conditions, such as several neurological disorders, Type 2 diabetes and aggressive neuroendocrine tumours. Here, the authors review the evidence available for animal models and for humans, and discuss possible therapeutic approaches that may target alphaSNAP.