Association analysis of NOTCH4 loci in schizophrenia using family and population-based controls

Polymorphisms and gene expression of Notch4 in pulmonary tuberculosis

Background

Tuberculosis (TB) is a serious public health problem to human health, but the pathogenesis of TB remains elusive.

Methods

To identify novel candidate genes associated with TB susceptibility, we performed a population-based case control study to genotype 41SNPs spanning 21 genes in 435 pulmonary TB patients and 375 health donors from China.

Results

We found Notch4 gene rs206018 and rs422951 polymorphisms were associated with susceptibility to pulmonary tuberculosis. The association was validated in another independent cohort including 790 TB patients and 1,190 healthy controls. Moreover, we identified that the rs206018 C allele was associated with higher level of Notch4 in PBMCs from pulmonary TB patients. Furthermore, Notch4 expression increased in TB patients and higher Notch4 expression correlated with the severer pulmonary TB. Finally, we explored the origin and signaling pathways involved in the regulation of Notch4 expression in response to Mycobacterium tuberculosis (Mtb) infection. We determine that Mtb induced Notch4 and its ligand Jagged1expression in macrophages, and Notch4 through TLR2/P38 signaling pathway and Jagged1 through TLR2/ERK signaling pathway.

Conclusion

Our work further strengthens that Notch4 underlay an increased risk of TB in humans and is involved in the occurrence and development of TB, which could serve as a novel target for the host-targeted therapy of TB.

Convergent lines of evidence support NOTCH4 as a schizophrenia risk gene

The association between NOTCH4 and schizophrenia has been repeatedly reported. However, the results from different genetic studies are inconsistent, and the role of NOTCH4 in schizophrenia pathogenesis remains unknown. Here, we provide convergent lines of evidence that support NOTCH4 as a schizophrenia risk gene. We first performed a meta-analysis and found that a genetic variant (rs2071287) in NOTCH4 was significantly associated with schizophrenia (a total of 125 848 subjects, p=8.31×10^-17), with the same risk allele across all tested samples. Expression quantitative trait loci (eQTL) analysis showed that rs2071287 was significantly associated with NOTCH4 expression (p=1.08×10^-14) in human brain tissues, suggesting that rs2071287 may confer schizophrenia risk through regulating NOTCH4 expression. Sherlock integrative analysis using a large-scale schizophrenia GWAS and eQTL data from human brain tissues further revealed that NOTCH4 was significantly associated with schizophrenia (p=4.03×10^-7 in CMC dataset and p=3.06×10^-6 in xQTL dataset), implying that genetic variants confer schizophrenia risk through modulating NOTCH4 expression. Consistently, we found that NOTCH4 was significantly downregulated in brains of schizophrenia patients compared with controls (p=2.53×10^-3), further suggesting that dysregulation of NOTCH4 may have a role in schizophrenia. Finally, we showed that NOTCH4 regulates proliferation, self-renewal, differentiation and migration of neural stem cells, suggesting that NOTCH4 may confer schizophrenia risk through affecting neurodevelopment. Our study provides convergent lines of evidence that support the involvement of NOTCH4 in schizophrenia. In addition, our study also elucidates a possible mechanism for the role of NOTCH4 in schizophrenia pathogenesis.

On the diagnostic and neurobiological origins of bipolar disorder

Psychiatry is constructed around a taxonomy of several hundred diagnoses differentiated by nuances in the timing, co-occurrence, and severity of symptoms. Bipolar disorder (BD) is notable among these diagnoses for manic, depressive, and psychotic symptoms all being core features. Here, we trace current understanding of the neurobiological origins of BD and related diagnoses. To provide context, we begin by exploring the historical origins of psychiatric taxonomy. We then illustrate how key discoveries in pharmacology and neuroscience gave rise to a generation of neurobiological hypotheses about the origins of these disorders that facilitated therapeutic innovation but failed to explain disease pathogenesis. Lastly, we examine the extent to which genetics has succeeded in filling this void and contributing to the construction of an objective classification of psychiatric disturbance.

Regulation of striatal dopamine responsiveness by Notch/RBP-J signaling

Dopamine signaling is essential for reward learning and fear-related learning, and thought to be involved in neuropsychiatric diseases. However, the molecular mechanisms underlying the regulation of dopamine responsiveness is unclear. Here we show the critical roles of Notch/RBP-J signaling in the regulation of dopamine responsiveness in the striatum. Notch/RBP-J signaling regulates various neural cell fate specification, and neuronal functions in the adult central nervous system. Conditional deletion of RBP-J specifically in neuronal cells causes enhanced response to apomorphine, a non-selective dopamine agonist, and SKF38393, a D1 agonist, and impaired dopamine-dependent instrumental avoidance learning, which is corrected by SCH23390, a D1 antagonist. RBP-J deficiency drastically reduced dopamine release in the striatum and caused a subtle decrease in the number of dopaminergic neurons. Lentivirus-mediated gene transfer experiments showed that RBP-J deficiency in the striatum was sufficient for these deficits. These findings demonstrated that Notch/RBP-J signaling regulates dopamine responsiveness in the striatum, which may explain the mechanism whereby Notch/RBP-J signaling affects an individual's susceptibility to neuropsychiatric disease.

Heterogeneity of schizophrenia: Genetic and symptomatic factors

Schizophrenia may have etiological heterogeneity, and may reflect common symptomatology caused by many genetic and environmental factors. In this review, we show the potential existence of heterogeneity in schizophrenia based on the results of our previous studies. In our study of the NOTCH4 gene, there were no significant associations between any single nucleotide polymorphisms (SNPs) of NOTCH4 and schizophrenia. However, exploratory analyses suggested that the SNP, rs3134928 may be associated with early-onset schizophrenia, and that rs387071 may be associated with schizophrenia characterized by negative symptoms. In our highly familial schizophrenia study, the African-American cohort without environmental exposure showed a possible linkage at marker 8p23.1 in the dominant model and in the European-American cohort, a marker at 22q13.32 showed a probable linkage in the recessive model. In the less familial schizophrenia families, these linkages were not shown. Based on our eye movement study, a putative subtype of schizophrenia with severe symptoms related to excitement/hostility, negative symptoms and disorganization may be associated with chromosome 22q11. We consider that a sample stratification approach may clarify the heterogeneity of schizophrenia. Therefore, this approach may lead to a more straightforward way of identifying susceptibility genes of schizophrenia.

Genome-wide association study of African and European Americans implicates multiple shared and ethnic specific loci in sarcoidosis susceptibility

Sarcoidosis is a systemic inflammatory disease characterized by the formation of granulomas in affected organs. Genome-wide association studies (GWASs) of this disease have been conducted only in European population. We present the first sarcoidosis GWAS in African Americans (AAs, 818 cases and 1,088 related controls) followed by replication in independent sets of AAs (455 cases and 557 controls) and European Americans (EAs, 442 cases and 2,284 controls). We evaluated >6 million SNPs either genotyped using the Illumina Omni1-Quad array or imputed from the 1000 Genomes Project data. We identified a novel sarcoidosis-associated locus, NOTCH4, that reached genome-wide significance in the combined AA samples (rs715299, P(AA-meta) = 6.51 × 10(-10)) and demonstrated the independence of this locus from others in the MHC region in the same sample. We replicated previous European GWAS associations within HLA-DRA, HLA-DRB5, HLA-DRB1, BTNL2, and ANXA11 in both our AA and EA datasets. We also confirmed significant associations to the previously reported HLA-C and HLA-B regions in the EA but not AA samples. We further identified suggestive associations with several other genes previously reported in lung or inflammatory diseases.

Investigation of NOTCH4 coding region polymorphisms in sporadic inclusion body myositis

The NOTCH4 gene, located within the MHC region, is involved in cellular differentiation and has varying effects dependent on tissue type. Coding region polymorphisms haplotypic of the sIBM-associated 8.1 ancestral haplotype were identified in NOTCH4 and genotyped in two different Caucasian sIBM cohorts. In both cohorts the frequency of the minor allele of rs422951 and the 12-repeat variation for rs72555375 was increased and was higher than the frequency of the sIBM-associated allele HLA-DRB1*0301. These NOTCH4 polymorphisms can be considered to be markers for sIBM susceptibility, but require further investigation to determine whether they are directly involved in the disease pathogenesis.

Notch signaling: simplicity in design, versatility in function

Notch signaling is evolutionarily conserved and operates in many cell types and at various stages during development. Notch signaling must therefore be able to generate appropriate signaling outputs in a variety of cellular contexts. This need for versatility in Notch signaling is in apparent contrast to the simple molecular design of the core pathway. Here, we review recent studies in nematodes, Drosophila and vertebrate systems that begin to shed light on how versatility in Notch signaling output is generated, how signal strength is modulated, and how cross-talk between the Notch pathway and other intracellular signaling systems, such as the Wnt, hypoxia and BMP pathways, contributes to signaling diversity.

Association evidence of schizophrenia with distal genomic region of NOTCH4 in Taiwanese families

Evidence for association with schizophrenia has been reported for NOTCH4, although results have been inconsistent. Previous studies have focused on polymorphisms in the 5' promoter region and first exon of NOTCH4. Our aim was to test the association of the entire genomic region of NOTCH4 in 218 families with at least two siblings affected by schizophrenia in Taiwan. We genotyped seven single nucleotide polymorphisms (SNPs) of this gene, with average intermarker distances of 5.3 kb. Intermarker linkage disequilibrium (LD) was calculated using gold software, and single-locus and haplotype association analyses were performed using transmit software. We found that the T allele of SNP rs2071285 (P= 0.035) and the G allele of SNP rs204993 (P= 0.0097) were significantly preferentially transmitted to the affected individuals in the single-locus association analysis. The two SNPs were in high LD (D' > 0.8). Trend for overtransmission was shown for the T-G haplotype of the two SNPs to affected individuals (P= 0.053), with the A-A haplotype significantly undertransmitted (P= 0.034). The associated region distributed across the distal portion of the NOTCH4 gene and overlapped with the genomic region of the G-protein signaling modulator 3 and pre-B-cell leukemia transcription factor 2. In summary, we found modest association evidence between schizophrenia and the distal genomic region of NOTCH4 in this Taiwanese family sample. Further replication for association with the distal genomic region of NOTCH4 is warranted.

Association study between the TNXB locus and schizophrenia in a Japanese population

The chromosome 6p21-24 region, which contains the human leukocyte antigen (HLA) region, has been suggested as an important locus for a susceptibility gene for schizophrenia. Recently, a significant association between schizophrenia and the TNXB locus, located immediately telomeric of the NOTCH4 locus in the HLA region, was observed. Few studies have further investigated the region in schizophrenia. In the present study, we investigated the region in a Japanese population. Subjects included 241 patients with schizophrenia and 290 controls. Twenty-six single nucleotide polymorphisms (SNPs) and the corresponding haplotypes were analyzed. As a result, exactly the same SNPs in the TNXB locus (rs1009382 and rs204887) as in the previous study were associated with schizophrenia (P = 0.034 and 0.034, respectively, uncorrected). A SNP (rs2071287) in the NOTCH4 locus and haplotype around it were also suggested to associate with the disease, consistent with another previous study (P = 0.041 and permutation P = 0.024, respectively, uncorrected). Although these associations became insignificant after Bonferroni correction, the findings might provide support for the association of the TNXB locus or its adjacent region of the NOTCH4 locus with schizophrenia.

A review and re-evaluation of an association between the NOTCH4 locus and schizophrenia

This work reviewed all the reports on the NOTCH4 gene in schizophrenia, which have been published since the gene was found to be associated with illness among a British population in 2000. The results from independent studies were inconsistent. Allelic heterogeneity, clinical diagnosis, ethnical backgrounds, and linkage disequilibrium (LD) structures in the human genome may be major reasons for poor replication. A couple of studies suggested that the NOTCH4 gene could play a role in a subgroup of the disease, such as early-onset schizophrenia and negative symptoms. A single study revealed a weak association of the NOTCH4 gene with frontal lobe brain volumes and a strong association with frontal lobe cognitive performance. A meta-analysis showed stronger evidence of the NOTCH4 association in family-based studies than in case-control studies. In a previous study, we found that rs520692, a single nucleotide polymorphism (SNP) at the NOTCH4 locus, was associated with schizophrenia in a Chinese population. In the present study, we applied a large sample size to re-evaluate our initial findings and then confirmed the rs520692 association with illness. The pairwise measures did not show strong LD between paired SNPs although the SNPs tested are located within a 34-kb region, suggesting that LD within the NOTCH4 gene has been broken rapidly by historical recombination in the Chinese population. Taken together, the NOTCH4 gene may be associated with schizophrenia but how the gene contributes to the etiology of the illness needs a further investigation.

No evidence for association between NOTCH4 and schizophrenia in a large family-based and case–control association analysis

OBJECTIVES

An analysis of 80 British parent-offspring trios by Wei and Hemmings in 2000 revealed thre1e out of five markers within the NOTCH4 locus to be strongly associated with schizophrenia. In our present study, we have examined NOTCH4 markers in large samples of German and Palestinian-Arab origin.

METHODS

Our study population comprised a German case-control sample (n=512 schizophrenia patients and n=232 controls) and two independent parent-offspring trio samples of German (n=159 trios) and Palestinian-Arab (n=208 trios) descent. We examined a total of ten single nucleotide polymorphisms within the NOTCH4 locus and the adjacent loci, spanning a region of approximately 100 kb.

RESULTS

Neither single marker nor haplotype analyses showed association with schizophrenia. In addition, analyses of the German case-control and trio samples revealed no significant association between NOTCH4 polymorphisms and early-onset schizophrenia.

CONCLUSIONS

Our results suggest that NOTCH4 is unlikely to play a major role in the genetic predisposition to schizophrenia in the German or the Palestinian-Arab population.

Genetic association between Notch4 polymorphisms and Japanese schizophrenics

The objective of this study was to investigate whether three single nucleotide polymorphisms of the Notch4 gene are associated with the onset of schizophrenia. To confirm the linkage disequilibrium among these three single nucleotide polymorphisms of the gene, the three single nucleotide polymorphisms were genotyped by a polymerase chain reaction-restriction-fragment length polymorphism method for all samples. The genotypic frequencies of each single nucleotide polymorphism in the schizophrenic were compared with respective controls using a chi method. To check linkage disequilibrium, the haplotype frequency program was utilized. No statistical association between the two single nucleotide polymorphisms of the Notch4 gene and schizophrenia was observed in our Japanese samples. Although one nonsynonymous single nucleotide polymorphism did show a weakly significant P-value, its allelic frequencies are not positive. Two of the single nucleotide polymorphisms showed strong linkage disequilibrium in our Japanese samples. The single nucleotide polymorphism between the other two single nucleotide polymorphisms showed a weaker linkage disequilibrium with the others. Our study suggests that the three single nucleotide polymorphisms are not associated with the onset of schizophrenia. The linkage disequilibrium of this locus indicates that there is genetic heterogeneity in the Notch4 gene. Linkage disequilibrium may differ among ethnic groups, and so a larger study should be performed in this region.

Genetic investigation of chromosome 5q GABAA receptor subunit genes in schizophrenia

We previously performed a genome-wide linkage scan in Portuguese schizophrenia families that identified a risk locus on chromosome 5q31-q35. This finding was supported by meta-analysis of 20 other schizophrenia genome-wide scans that identified 5q23.2-q34 as the second most compelling susceptibility locus in the genome. In the present report, we took a two-stage candidate gene association approach to investigate a group of gamma-aminobutyric acid (GABA) A receptor subunit genes (GABRA1, GABRA6, GABRB2, GABRG2, and GABRP) within our linkage peak. These genes are plausible candidates based on prior evidence for GABA system involvement in schizophrenia. In the first stage, associations were detected in a Portuguese patient sample with single nucleotide polymorphisms (SNPs) and haplotypes in GABRA1 (P=0.00062-0.048), GABRP (P=0.0024-0.042), and GABRA6 (P=0.0065-0.0088). The GABRA1 and GABRP findings were replicated in the second stage in an independent German family-based sample (P=0.0015-0.043). Supportive evidence for association was also obtained for a previously reported GABRB2 risk haplotype. Exploratory analyses of the effects of associated GABRA1 haplotypes on transcript levels found altered expression of GABRA6 and coexpressed genes of GABRA1 and GABRB2. Comparison of transcript levels in schizophrenia patients and unaffected siblings found lower patient expression of GABRA6 and coexpressed genes of GABRA1. Interestingly, the GABRA1 coexpressed genes include synaptic and vesicle-associated genes previously found altered in schizophrenia prefrontal cortex. Taken together, these results support the involvement of the chromosome 5q GABAA receptor gene cluster in schizophrenia, and suggest that schizophrenia-associated haplotypes may alter expression of GABA-related genes.

Association of common variation in the HNF1alpha gene region with risk of type 2 diabetes

It is currently unclear how often genes that are mutated to cause rare, early-onset monogenic forms of disease also harbor common variants that contribute to the more typical polygenic form of each disease. The gene for MODY3 diabetes, HNF1alpha, lies in a region that has shown linkage to late-onset type 2 diabetes (12q24, NIDDM2), and previous association studies have suggested a weak trend toward association for common missense variants in HNF1alpha with glucose-related traits. Based on genotyping of 79 common SNPs in the 118 kb spanning HNF1alpha, we selected 21 haplotype tag single nucleotide polymorphisms (SNPs) and genotyped them in >4,000 diabetic patients and control subjects from Sweden, Finland, and Canada. Several SNPs from the coding region and 5' of the gene demonstrated nominal association with type 2 diabetes, with the most significant marker (rs1920792) having an odds ratio of 1.17 and a P value of 0.002. We then genotyped three SNPs with the strongest evidence for association to type 2 diabetes (rs1920792, I27L, and A98V) in an additional 4,400 type 2 diabetic and control subjects from North America and Poland and compared our results with those of the original sample and of Weedon et al. None of the results were consistently observed across all samples, with the possible exception of a modest association of the rare (3-5%) A98V variant. These results indicate that common variants in HNF1alpha either play no role in type 2 diabetes, a very small role, or a role that cannot be consistently observed without consideration of as yet unmeasured genetic or environmental modifiers.

Association testing of variants in the hepatocyte nuclear factor 4alpha gene with risk of type 2 diabetes in 7,883 people

Two recent publications reported association of common polymorphisms in the P2 promoter of hepatocyte nuclear factor 4alpha (HNF4alpha) (the MODY1 gene) with risk for type 2 diabetes. We attempted to reproduce this putative association by genotyping 11 single nucleotide polymorphism (SNPs) spanning the HNF4alpha coding region and the P2 promoter in >3,400 patients and control subjects from Sweden, Finland, and Canada. One SNP that was consistently associated in the two previous reports (rs1884613, in the P2 promoter region) also trended in the same direction in our sample, albeit with a lower estimated odds ratio (OR) of 1.11 (P = 0.05, one-tailed). We genotyped this SNP (rs1884613) in an additional 4,400 subjects from North America and Poland. In this sample, the association was not confirmed and trended in the opposite direction (OR 0.88). Meta-analysis of our combined sample of 7,883 people (three times larger than the two initial reports combined) yielded an OR of 0.97 (P = 0.27). Finally, we provide an updated analysis of haplotype structure in the region to guide any further investigation of common variation in HNF4alpha. Although our combined results fail to replicate the previously reported association of common variants in HNF4alpha with risk for type 2 diabetes, we cannot exclude an effect smaller than that originally proposed, heterogeneity among samples, variation in as-yet-unmeasured genotypic or environmental modifiers, or true association secondary to linkage disequilibrium (LD) with as-yet-undiscovered variant(s) in the region.

Five NOTCH4 polymorphisms show weak evidence for association with schizophrenia: evidence from meta-analyses

NOTCH4 initially received consideration as a risk gene for schizophrenia based on its location within a region on chromosome 6p that had previously shown strong evidence for genetic linkage with the illness. The initial published test for allelic association found strong evidence for involvement of this gene in schizophrenia, but subsequent studies failed to confirm this finding. Presently, we have used meta-analysis to derive a best estimate of the nature and magnitude of the associations between schizophrenia and five polymorphisms in and around the NOTCH4 gene. No significant association was detected between schizophrenia and repeat length of alleles at the (TAA)n, (CTG)n, or (TTAT)n polymorphisms, or between the disease and specific risk alleles at these polymorphisms or at the SNP1 or SNP2 polymorphisms. Heterogeneity and stronger evidence of association with the putative risk alleles of the (TAA)n, (CTG)n, SNP1, and SNP2 polymorphisms was observed in family-based studies than in case-control studies, suggesting that these polymorphisms may reliably influence risk for schizophrenia under certain circumstances. Since more consistent and robust associations with schizophrenia risk have been observed for haplotypes of these polymorphisms [especially those containing SNP2 and (CTG)n], additional large family-based or genomic-controlled studies would be helpful for definitively specifying the role of NOTCH4 haplotypes in risk for schizophrenia.

A NOTCH4 association with multiple sclerosis is secondary to HLA-DR*1501

Multiple sclerosis (MS) is a chronic inflammatory disease of the central nervous system (CNS) with supposedly autoimmune features known to be associated with a specific HLA DR-DQ haplotype (DR15, DQ6, or HLDRB1*1501,DRB5*0101,DQA1*0102,DQB1*0602). We have previously reported that the associated haplotype extends to HLA-B and described an independent association with HLA-A alleles in MS. Owing to a complex situation with extensive linkage disequilibria, it is still unclear whether classical HLA genes are responsible or whether associations may be due to other genes in this region. Here, we analyzed an association in MS with the NOTCH4 and TNFalpha (tumor necrosis factor-alpha) genes, located between the HLA-DRB1 gene and the HLA-A gene. For NOTCH4, located 0.4 Mb telomeric to HLA-DRB1, an SNP at position -25 and a trinucleotide repeat were investigated in 181 MS patients, and 180 controls also typed P = 0.027 for HLA-DRB and HLA-A. A modest association was observed (OR = 3.44) with the C-25 allele. However, two-locus analysis revealed that this association was secondary to the classical association with HLA-DRB1. For TNF, located 0.7 Mb telomeric of NOTCH4, SNPs at positions -308 and -238 were studied in the same dataset. We found no association between these TNFalpha gene polymorphisms and MS in this dataset, although there was linkage disequilibrium (LD) between DRB1 and TNF and between HLA-A and TNF. We conclude that alleles of the NOTCH4 and TNFalpha genes are unlikely to be of importance for the susceptibility to MS, although specific alleles of these genes are often carried on the same haplotype as DR15, DQ6.

Association analysis of NOTCH 4 polymorphisms with schizophrenia among two independent family based samples

The present study investigated polymorphisms of the NOTCH 4 gene in two independent samples from India and USA, consisting of patients with schizophrenia and their parents (n = 182, and n = 148 'trios,' respectively). Five DNA markers, namely (GAAG)(n), (TAA)(n), SNP1, SNP2, and (CTG)(n) were evaluated. Transmission distortion, consistent with a modest association was detected among both samples. Additional association studies at this locus are warranted.

Neither single-marker nor haplotype analyses support an association between genetic variation near NOTCH4 and bipolar disorder

Markers near the NOTCH4 locus on chromosome 6p21.3 have been reported to be associated with schizophrenia in some studies. Since schizophrenia and bipolar affective disorder (BPAD) may share genetic determinants, we tested markers in and near NOTCH4 in a sample of 153 parent-offspring triads ascertained through a sibling pair with BPAD for evidence of association. This sample would have 80% power to detect an association at or above a genotype relative risk of 2.4 at the 10(-7) level of significance. In addition to the two markers previously showing the most significant association with schizophrenia, three additional nearby markers were studied. The five markers were genotyped using validated methods. Both single-marker and 3-marker haplotype data was analyzed using family-based association methods. No genome-wide significant association was detected between any of the five SNP-markers and BPAD in this sample. One marker showed nominal evidence of association (P = 0.049), but this evidence was not supported by haplotype analyses including nearby flanking markers or by case-control analysis using 93 Caucasian controls. These results do not support an association between genetic variation near NOTCH4 and BPAD in this sample.

Is NOTCH4 associated with schizophrenia?

The NOTCH4 locus was reported to be associated with schizophrenia in our previous study but the subsequent replication by other workers has been inconsistent. To find out possible reasons for the poor replication, the present work was undertaken to analyse four functional single nucleotide polymorphisms (SNPs) (rs367398, rs915894, rs520692 and rs422951) at the NOTCH4 locus among 141 schizophrenic family trios of Chinese Han descent. Of these four SNPs, rs520692 was the only one associated with schizophrenia (P = 0.017); the other three, however, did not show any association with the illness, including rs367398 located in the promoter region, which had shown a strong association with the illness in our previous study conducted with British samples. Although these four SNPs analysed lie within a less than 4 kb segment of genomic DNA, the pattern of linkage disequilibrium between them was unexpected. The strongest linkage disequilibrium was shown only between rs367398 and rs520692 and between rs520692 and rs422951 in both parent and patient groups. This study raises the possibility that there might be two or more disease-underlying variants at the NOTCH4 locus or at a nearby locus, and that the allelic or locus heterogeneity may be one of the possible reasons for the poor replication of the NOTCH4 finding.

Gene profiling--chances and challenges

Microarray analysis has been emerged as a tool to characterize the overall reaction of cells in culture or tissue to different stimuli e.g. stressful events by analysing bulk RNA present at a particular time point. It has supplemented or even replaced more traditional methods like cDNA-bank sequencing or conventional differential display. The commercial availability of several different precoated arrays and the ease of handling has supported the broad distribution of this new technique. The basic protocol involves the hybridization of complementary strands of labelled DNA or RNA from cells/tissue with representations of known genes spotted onto a solid support (nylon, glass). Labelling can be radioactive (p32/33), by a hapten group (biotin, digoxigenin, aminoallyl) or by fluorescent (Cy3, Cy5 etc.) nucleotides. Detection is performed by autoradiography, chemiluminescence or fluorescence scanning. There are different setups of arrays available: either known genes/gene-groups (apoptosis, cytokines etc.) are spotted as PCR fragments, plasmids or synthetic oligonucleotides or representations of the known genome are directly synthesized as short sequence tags of 20-70 oligonucleotides on glass chips. The latter allow the identification of newly expressed genes whereas the former deal with known genes. Ideally, the intensity of the signal can be correlated with the relative expression of a known gene and allows the comparison with a standard. Problems arise from the quality of the sample material, the standardization of the protocols and the data management. Nevertheless, gene profiling by cDNA-arrays will definitely be integrated into routine screening programs.

Association of six polymorphisms of the NOTCH4 gene with schizophrenia in the Japanese population

The NOTCH4 gene is located at 6p21.3 and involved in the development and patterning of the central nervous systems. Recently, Wei and Hemmings [2000] observed that the gene was associated with schizophrenia. Subsequent to the report, several studies investigated the gene in schizophrenia, with controversial and inconclusive results. In the present study, we investigated six polymorphisms (SNPs 1-5 and a CTG repeat) of the gene in Japanese subjects with schizophrenia (n = 284) and the same number of controls. The polymorphisms include SNP5, which has been observed to be associated with schizophrenia in a Chinese population and two new SNPs 3-4 adjacent to SNP5, in addition to the SNPs 1-2 and the CTG repeat, which were suggested for the association with the disease in the previous study. As a result, no significant difference in genotypic distributions or allelic frequencies of the six polymorphisms of the gene was observed between the patients and the controls. Also, no significant difference was found in frequencies of haplotypes of the six polymorphisms between the patients and the controls. However, the distribution of SNP2 was significantly deviated from Hardy-Weinberg equilibrium in the patients (P = 0.000986), not in the controls, which could be a chance or due to an association of SNP2 with the disease. In conclusion, the present study provided no clear evidence for an association between the NOTCH4 gene and schizophrenia in the Japanese population.

Molecular characterization of bipolar disorder by comparing gene expression profiles of postmortem brains of major mental disorders

We performed the oligonucleotide microarray analysis in bipolar disorder, major depression, schizophrenia, and control subjects using postmortem prefrontal cortices provided by the Stanley Foundation Brain Collection. By comparing the gene expression profiles of similar but distinctive mental disorders, we explored the uniqueness of bipolar disorder and its similarity to other mental disorders at the molecular level. Notably, most of the altered gene expressions in each disease were not shared by one another, suggesting the molecular distinctiveness of these mental disorders. We found a tendency of downregulation of the genes encoding receptor, channels or transporters, and upregulation of the genes encoding stress response proteins or molecular chaperons in bipolar disorder. Altered expressions in bipolar disorder shared by other mental disorders mainly consisted of upregulation of the genes encoding proteins for transcription or translation. The genes identified in this study would be useful for the understanding of the pathophysiology of bipolar disorder, as well as the common pathophysiological background in major mental disorders at the molecular level. In addition, we found the altered expression of LIM and HSPF1 both in the brains and lymphoblastoid cells in bipolar disorder. These genes may have pathophysiological importance and would be novel candidate genes for bipolar disorder.

Transmission disequilibrium test and haplotype analysis of the NOTCH4 gene in Japanese patients with schizophrenia

A recent study reported that the NOTCH4 gene was highly associated with schizophrenia in the British population. To confirm this association for another population, a case-control study was conducted and a transmission disequilibrium test (TDT) analysis was performed on a group of Japanese subjects (235 pairs of schizophrenia patients and controls, and 78 trios consisting of probands and their parents) using two single nucleotide polymorphisms and three microsatellite markers for the NOTCH4 gene. Haplotype analysis was also studied in case-control and family based data sets. In all markers except for (CTG)n (P = 0.012, before correction for multiple testing), no differences were found in the case-control study. The TDT analysis also revealed only a weak transmission disequilibrium in (TTAT)n (genotype-wise P = 0.012). The finding of the present study could not support the original findings that the NOTCH4 gene itself is associated with susceptibility to schizophrenia.

TNXB locus may be a candidate gene predisposing to schizophrenia

We report here on the detection of nine single nucleotide polymorphisms (SNPs) near to the NOTCH4 locus in the search for schizophrenia susceptibility genes in the class III region of the human major histocompatibility complex (MHC). We totally analyzed 122 family trios recruited in the UK. The TDT analysis demonstrated that of the nine SNPs, three were associated with schizophrenia, including rs1009382 (P = 0.00047), rs204887 (P = 0.007), and rs8283 (P = 0.015). Both rs1009382 and rs204887 are present in the TNXB locus. The rs1009382 is a non-synonymous SNP located in exon 23 of the gene and its A to G base change causes a Glu2578Gly substitution. The goodness-of-fit test showed that genotypic distribution of rs1009382 was deviated from Hardy-Weinberg equilibrium due to homozygote excess in the patient group (P = 0.01), suggesting that a double dose of a genetic risk may be involved. Possibly, rs1009382 is a candidate SNP predisposing to a schizophrenic illness. Moreover, the test for linkage disequilibrium (LD) between paired SNPs showed that the nine SNPs studied may be in the same LD block with an unexpected pattern as the strength of LD was not correlated with the distance between paired SNPs. The haplotype analysis suggested that there might be more than one disease-related allele located in the class III region of the MHC, and that these alleles possibly confer either susceptibility or resistance to schizophrenia.

NOTCH4 gene haplotype is associated with schizophrenia in African Americans

BACKGROUND

The goal of this study was to investigate the relationship between the NOTCH4 gene and schizophrenia in African American (AA) and European American (EA) subjects.

METHODS

Two single nucleotide polymorphisms (SNPs) at the NOTCH4 locus were genotyped in 123 AA schizophrenia patients, 223 EA schizophrenia patients, 85 AA healthy control subjects, and 211 EA healthy control subjects. The specific markers studied were -1725T/G and -25T/C. Comparisons of allele and haplotype frequencies between patients and control subjects were performed with the chi-square test, the Fisher's Exact Test, and CLUMP software. Linkage disequilibrium (LD) between these two SNPs was calculated with the 3LOCUS program.

RESULTS

The haplotype -1725G/-25T associates to schizophrenia in AA subjects (p =.0008), but not in EA subjects. Alleles -1725G and allele -25T are in positive LD both in AAs and EAs. Allele and haplotype frequencies differ significantly between AAs and EAs.

CONCLUSIONS

The haplotype -1725G/-25T at the NOTCH4 locus, which results from SNPs of NOTCH4 that are in LD, may increase susceptibility to schizophrenia in AAs. Any effect of this locus on risk for schizophrenia is population-specific.

Notch signaling in development and disease

Notch receptors and ligands were first identified in flies and worms, where they were shown to regulate cell proliferation, cell differentiation, and, in particular, binary cell fate decisions in a variety of developmental contexts. The first mammalian Notch homolog was discovered to be a partner in a chromosomal translocation in a subset of human T-cell leukemias. Subsequent studies in mice and humans have shown that Notch signaling plays essential roles at multiple stages of hematopoiesis, and also regulates the development or homeostasis of cells in many tissues and organs. Thus, it is not surprising that mutations which disrupt Notch signaling cause a wide range of cancers and developmental disorders. Perhaps because it is so widely used, Notch signaling is subject to many unusual forms of regulation. In this review, we will first outline key aspects of Notch signaling and its regulation by endocytosis, glycosylation, and ubiquitination. We will then overview recent literature elucidating how Notch regulates cell-lineage decisions in a variety of developmental contexts. Finally, we will describe the roles of dysregulated Notch signaling in causing several types of cancer and other pathologies.

Human endogenous retroviruses with transcriptional potential in the brain

Genetic studies of neuropsychiatric disorders have often produced conflicting results, which might partly result from the involvement of epigenetic modifications. We intended to explore the possible implication of DNA methylation and human endogenous retroviruses (HERVs) in neuropsychiatric disorders. In the present study, we identified two HERV loci that are expected to retain the transcriptional activity in the brain. One was located on chromosome 1q21-q22 and the other on 22q12. Interestingly, these regions were overlapped with or included in those of schizophrenia-susceptible loci, SCZD9 and SCZD4, respectively. Particularly, the HERV on 22q12 was located in the opposite direction 4 kb downstream of the Synapsin III gene. These HERV loci could afford clear targets for methylation and expression analyses in postmortem brains of patients with psychiatric disorders such as schizophrenia. In addition, we confirmed our previous finding that only a few of particular HERV-K loci were activated among a number of highly homologous loci in teratocarcinoma cell lines. These activated loci included ones common to all teratocarcinoma cell lines analyzed and depending on their male or female origin.

Family-based association study of the NOTCH4 gene in schizophrenia using Japanese and Chinese samples

BACKGROUND

A family based association study in a British sample found the NOTCH4 gene to be associated with schizophrenia; however, all six replication studies failed to confirm the finding.

METHODS

We performed a family based association study of NOTCH4 and schizophrenia in 123 trios (16 Japanese and 107 Chinese). In addition to the original study's polymorphisms, we examined four new single nucleotide polymorphisms (SNPs)--SNPs_A, B, C and D--around SNP1 of the original study. We genotyped all samples for SNPs_A-D and for SNP1 and (CTG)n of the original study.

RESULTS

We found no significant associations between NOTCH4 and schizophrenia or its subtypes for all polymorphisms, regardless of gender. The finding remained negative when the Chinese sample was analyzed separately. Exploratory analyses suggested that SNP_A may be associated with early-onset schizophrenia and that SNP1 may be associated with schizophrenia characterized by numerous negative symptoms.

CONCLUSIONS

NOTCH4 is not a significant susceptibility gene for schizophrenia when clinical heterogeneity is ignored; however, NOTCH4 may be associated with early-onset schizophrenia or schizophrenia with many negative symptoms, but these findings should be interpreted cautiously.

Disrupted-In-Schizophrenia 1, a candidate gene for schizophrenia, participates in neurite outgrowth

Disrupted-In-Schizophrenia 1 (DISC1) was identified as a novel gene disrupted by a (1;11)(q42.1;q14.3) translocation that segregated with schizophrenia in a Scottish family. Predicted DISC1 product has no significant homology to other known proteins. Here, we demonstrated the existence of DISC1 protein and identified fasciculation and elongation protein zeta-1 (FEZ1) as an interacting partner of DISC1 by a yeast two-hybrid study. FEZ1 and its nematode homolog are reported to represent a new protein family involved in axonal outgrowth and fasciculation. In cultured hippocampal neurons, DISC1 and FEZ1 colocalized in growth cones. Interactions of these proteins were associated with F-actin. In the course of neuronal differentiation of PC12 cells, upregulation of DISC1/FEZ1 interaction was observed as along with enhanced extension of neurites by overexpression of DISC1. The present study shows that DISC1 participates in neurite outgrowth through its interaction with FEZ1. Recent studies have provided reliable evidence that schizophrenia is a neurodevelopmental disorder. As there is a high level of DISC1 expression in developing rat brain, dysfunction of DISC1 may confer susceptibility to psychiatric illnesses through abnormal development of the nervous system.

Linkage and association studies of schizophrenia

Recent twin studies confirm that schizophrenia is highly heritable, but attempts to locate and identify genes have proved to be difficult. This is largely because major genes appear to be rare or nonexistent. Instead, genetic liability almost certainly results from the combined effects of multiple susceptibility loci and most studies have been under-equipped to detect such effects. Nevertheless, several regions of the genome have been implicated by more than one linkage study and chromosome 22q has been implicated by linkage and by studies of patients with microdeletions. Recent work attempting to refine regions of interest using linkage dysequilibrium mapping has identified four promising and novel "positional candidates;" they are neuregulin-1 on chromosome 8p-p21, G72 located at chromosome 13q34, dysbindin at 6p22.3, and proline dehydrogenase, which is a gene that maps to chromosome 22q11. In addition, there is renewed interest in a fifth gene, catechol-O-methyltransferase, also on chromosome 22q11.

Linkage analysis of candidate regions using a composite neurocognitive phenotype correlated with schizophrenia

As schizophrenia is genetically and clinically heterogeneous, systematic investigations are required to determine whether ICD-10 or DSM-IV categorical diagnoses identify a phenotype suitable and sufficient for genetic research, or whether correlated phenotypes incorporating neurocognitive performance and personality traits provide a phenotypic characterisation that accounts better for the underlying variation. We utilised a grade of membership (GoM) model (a mathematical typology developed for studies of complex biological systems) to integrate multiple cognitive and personality measurements into a limited number of composite graded traits (latent pure types) in a sample of 61 nuclear families comprising 80 subjects with ICD-10/DSM-IV schizophrenia or schizophrenia spectrum disorders and 138 nonpsychotic first-degree relatives. GoM probability scores, computed for all subjects, allowed individuals to be partly assigned to more than one pure type. Two distinct and contrasting neurocognitive phenotypes, one familial, associated with paranoid schizophrenia, and one sporadic, associated with nonparanoid schizophrenia, accounted for 74% of the affected subjects. Combining clinical diagnosis with GoM scores to stratify the entire sample into liability classes, and using variance component analysis (SOLAR), in addition to parametric and nonparametric multipoint linkage analysis, we explored candidate regions on chromosomes 6, 10 and 22. The results indicated suggestive linkage for the familial neurocognitive phenotype (multipoint MLS 2.6 under a low-penetrance model and MLS>3.0 under a high-penetrance model) to a 14 cM area on chromosome 6, including the entire HLA region. Results for chromosomes 10 and 22 were negative. The findings suggest that the familial neurocognitive phenotype may be a pleiotropic expression of genes underlying the susceptibility to paranoid schizophrenia. We conclude that use of composite neurocognitive and personality trait measurements as correlated phenotypes supplementing clinical diagnosis can help stratify the liability to schizophrenia across all members of families prior to linkage, allow the search for susceptibility genes to focus selectively on subsets of families at high genetic risk, and augment considerably the power of genetic analysis.

Modest evidence for linkage and possible confirmation of association between NOTCH4 and schizophrenia in a large Veterans Affairs Cooperative Study sample

Wei and Hemmings [2000: Nat Genet 25:376-377], using 80 British parent-offspring trios, identified a number of NOTCH4 variants and haplotypes that showed statistically significant evidence of association to schizophrenia. Specifically, the 10 repeat allele of a (CTG)(n) marker and the 8 repeat allele of a (TAA)(n) marker demonstrated excess transmission to affected individuals; SNP21 and haplotypes SNP2-(CTG)(n) and SNP12-SNP2-(CTG)(n) also showed significant associations. In an attempt to replicate these findings, we tested for linkage and association between the same five markers used by Wei and Hemmings in 166 families collected from a multi-center study conducted by the Department of Veterans Affairs (DVA) Cooperative Study Program (CSP). The families include 392 affected subjects (schizophrenia or schizoaffective disorder, depressed) and 216 affected sibling pairs. The families represent a mix of European Americans (n = 62, 37%), African Americans (n = 60, 36%), and racially mixed or other races (n = 44, 27%). We identified moderate evidence for linkage in the pooled race sample (LOD = 1.25) and found excess transmission of the 8 (P = 0.06) and 13 (P = 0.04) repeat alleles of the (TAA)(n) marker to African American schizophrenic subjects. The 8 and 13 repeat alleles were previously identified to be positively associated with schizophrenia by Wei and Hemmings [2000: Nat Genet 25:376-377] and Sklar et al. [2001: Nat Genet 28:126-128], respectively.

NOTCH4 and the frontal lobe in schizophrenia

NOTCH4 is a developmentally expressed gene recently reported to be in linkage disequilibrium (LD) with schizophrenia. We investigated this finding in our sample of subjects, focusing on an exonic (CTG)(n) polymorphism, examining not only the association of this polymorphism with the disease phenotype, but also its effect on frontal lobe brain morphology and cognitive function in both affected individuals and a psychiatrically normal comparison group. While we did not find any association or LD with schizophrenia, we identified striking effects of NOTCH4 variability on the trait measures. Within the respective schizophrenia and comparison groups, NOTCH4 allelic variability was correlated with differences in measures of frontal lobe cognitive performance and frontal lobe brain tissue volumes that were intuitively congruent. These within-group effects, however, were in opposite directions across groups. These findings may reflect the interaction of NOTCH4 with the underlying genetic and phenotypic complexity that characterizes both schizophrenia and normal cognition and brain development.

Notch4, a non-HLA gene in the MHC is strongly associated with the most severe form of alopecia areata

Alopecia areata (AA) is a disorder primarily affecting the hair and nails in which associated autoimmune or atopic disease is common. Genetically, it is a complex trait with evidence of a role for genes of the major histocompatibility complex (MHC), the interleukin-1 cluster and chromosome 21 in the pathogenesis. The strongest association is with HLA class II alleles, although whether this indicates a direct contribution to the pathogenesis or results merely from linkage disequilibrium with nearby disease genes is unknown. Notch4 is a recently defined gene in the HLA class III region. Notch signalling is a direct determinant of keratinocyte growth arrest and entry into differentiation. A possible role for Notch in hair growth has been indicated by transgenic mouse findings that activation of the Notch pathway in the hair cortex leads to aberrant differentiation of adjacent hair-shaft layers. Notch4 is therefore a plausible candidate gene for AA. We have examined two polymorphisms in the coding sequence of the Notch4 gene at positions +1297 and +3063 in a case-control study of 116 AA patients and 142 ethnically matched, healthy control subjects. The initial analysis showed a significant association of AA in the overall data set with the Notch4(T+1297C) polymorphism (P<0.001) but not with Notch4(A+3063G). To confirm this association, we genotyped an additional 62 patients and found that the risk for disease was higher in Notch4(+1297C) homozygotes [odds ratio (OR) 3.43 (1.63, 7.19)] than in heterozygotes [OR 2.58 (1.57, 4.24)]. On classifying the patients by severity of disease, the association appeared to be confined to the severest form (alopecia universalis) [OR 4.02 (1.64, 9.88), P=0.0014]. These results support previous findings showing that different HLA susceptibility alleles are associated with mild and severe AA.

Two NOTCH4 polymorphisms and their relation to schizophrenia susceptibility and different personality traits

BACKGROUND

Recently, linkage disequilibrium mapping of the major histocompatibility complex region on the short arm of human chromosome 6 suggested that the NOTCH4 locus is highly associated with schizophrenia.

OBJECTIVES AND METHODS

We analysed two polymorphisms in this gene in Swedish schizophrenic patients ( =74) and control subjects ( =135). The NOTCH4 variants were also analysed in schizophrenic patients with regard to subdiagnosis, age at first hospitalization, abuse/dependence of alcohol, solvents, or drugs, previous suicide attempts, extrapyramidal symptoms, treatment with anticholinergic drugs, and response to anti-psychotic drug treatment. Control subjects were scrutinized with regard to personality, another partially heritable trait suggested being of importance in schizophrenia. In addition, two intermediate endophenotypes suggested being of importance in schizophrenia, dopamine D(2) receptor density in striatum and monoamine metabolites in cerebrospinal fluid, respectively, were investigated with regard to the two NOTCH4 variants.

RESULTS

There was no significant association between the patients and the controls for the two investigated polymorphisms neither for the parameters analysed in the schizophrenia material. The NOTCH4 SNP2 variant, an A-->G substitution, was associated with the Karolinska Scales of Personality Irritability scale. The NOTCH4 (CTG)(n) variant was associated with the revised NEO personality inventory Extraversion and Activity (E4) scales. However, after correction for multiple testing, no difference remained significant. The results for the endophenotypes and the polymorphisms were non-significant.

CONCLUSIONS

The present study does not support that the investigated NOTCH4 variants have a major influence on susceptibility to schizophrenia or related neurobiological traits.

Association study between dopamine D3 receptor gene variant and personality traits

Dopamine receptor gene variation has been hypothesized to influence personality traits characterized by novelty seeking and related traits. We analyzed a dopamine D(3) receptor gene (DRD3) variant in a Swedish population (n = 373) investigated with one or more of several personality questionnaires. No significant relationships were found between DRD3 genotypes and any of the 15 Karolinska Scales of Personality (KSP) and five Health-relevant Personality 5 factor inventory (HP5i) scales. The DRD3 variant was associated with some scales related to novelty seeking: the Swedish universities Scales of Personality (SSP) Adventure Seeking and the revised NEO personality inventory (NEO-PI-R) Fantasy (O1) and Order (C2) scales. There were also associations with the Temperament and Character Inventory (TCI) Cooperativeness and Compassion (C4) scales. After correction for multiple testing, however, no significant difference remained. We conclude that the investigated DRD3 polymorphism does not have a major impact on personality in the investigated population.

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.

Genetics and etiopathophysiology of schizophrenia

Schizophrenia is one of the most common, devastating, and least understood neuropsychiatric illnesses present in the human population. Despite decades of research involving neurochemical, neuroanatomical, neuropathologic, neurodevelopmental, neuropsychological, and genetic approaches, no clear etiopathophysiology has been elucidated. Among the most robust findings, however, is the contribution of genetics to disease development. Statistical models suggest that susceptibility to the disorder is governed by the effects of multiple genes, coupled with environmental and stochastic factors. This review briefly summarizes recent etiopathologic findings and hypotheses, with special attention to genetics.

Organisation of the human genome and our tools for identifying disease genes

Determination of the sequence of the human genome has been a major undertaking. It provided powerful tools to explore the genetic component in complex diseases. To fully understand the genetic pathways contributing to complex disease traits, we must not only reveal the genomic locus of all genes involved, but also delineate the functionally relevant allelic variation in such genes and understand the patterns of gene expression leading up to the actual disease trait. Insight in the genetic contribution to clinical endpoints of complex disease and their biological risk factors, therefore, requires an understanding of both the structure and the biology of the genome. This paper constitutes a tutorial overview of the organisation of the human genome, the tools it provides for molecular genetic studies, and the genomic background of the current strategies for gene identification.

Genetic variation in the 6p22.3 gene DTNBP1, the human ortholog of the mouse dysbindin gene, is associated with schizophrenia

Prior evidence has supported the existence of multiple susceptibility genes for schizophrenia. Multipoint linkage analysis of the 270 Irish high-density pedigrees that we have studied, as well as results from several other samples, suggest that at least one such gene is located in region 6p24-21. In the present study, family-based association analysis of 36 simple sequence-length-polymorphism markers and of 17 SNP markers implicated two regions, separated by approximately 7 Mb. The first region, and the focus of this report, is 6p22.3. In this region, single-nucleotide polymorphisms within the 140-kb gene DTNBP1 (dystrobrevin-binding protein 1, or dysbindin) are strongly associated with schizophrenia. Uncorrected, empirical P values produced by the program TRANSMIT were significant (P<.01) for a number of individual SNP markers, and most remained significant when the data were restricted to include only one affected offspring per nuclear family per extended pedigree; multiple three-marker haplotypes were highly significant (P=.008-.0001) under the restricted conditions. The pattern of linkage disequilibrium is consistent with the presence of more than one susceptibility allele, but this important issue is unresolved. The number of markers tested in the adjacent genes, all of which are negative, is not sufficient to rule out the possibility that the dysbindin gene is not the actual susceptibility gene, but this possibility appears to be very unlikely. We conclude that further investigation of dysbindin is warranted.

Investigation of linkage and association/linkage disequilibrium of HLA A-, DQA1-, DQB1-, and DRB1-alleles in 69 sib-pair- and 89 trio-families with schizophrenia

The hypothesis that HLA antigens confer susceptibility to schizophrenic disorders has been tested by studying linkage and association in a family sample with 69 sib-pair families. Suggestive evidence for linkage was obtained by nonparametric multipoint LOD score analysis with a maximum around DQB CAR (P = 0.0004), a microsatellite marker that is in linkage disequilibrium with the HLA antigen DQB1. Spurious evidence for negative association as calculated by the transmission disequilibrium test was found for HLA- DRB1*11 (chi-square = 11.72, corrected P value = 0.03) and for the haplotype DQB1*301-DQA1*501-DRB1*11 (chi-square = 11.3, corrected P value = 0.043). No evidence of association with these alleles was obtained in a sample of 89 trios with schizophrenic offspring and parents. Our results are not in favor of a direct involvement of the HLA system in development of schizophrenia, but are compatible with the possible existence of a susceptibility gene in the MHC region at chromosome 6p 21.31.

Genetic analysis of the (CTG)n NOTCH4 polymorphism in 65 multiplex bipolar pedigrees

A strong genetic association between the NOTCH4 locus on chromosome 6 and schizophrenia was recently reported. Based on the data suggesting overlapping susceptibility for schizophrenia and bipolar disorder, we genotyped the polymorphic (CTG)n encoding polyleucine repeat in exon 1 of NOTCH4 in 65 pedigrees ascertained for a genetic linkage study of bipolar disorder. In addition, we analyzed a subset of our pedigrees with psychotic features at this locus. We failed to find any association between the (CTG)n NOTCH4 polymorphism and either the bipolar or the psychotic bipolar phenotype in our 65 pedigrees.