A single nucleotide polymorphism fine mapping study of chromosome 1q42.1 reveals the vulnerability genes for schizophrenia, GNPAT and DISC1: Association with impairment of sustained attention.

BACKGROUND: The marker D1S251 of chromosome 1q42.1 showed significant association with schizophrenia in a Taiwanese sample. We used single nucleotide polymorphism (SNP) fine mapping to search for the vulnerability genes of schizophrenia. METHODS: We selected 120 SNPs covering 1 Mb around D1S251 from the public database. These selected SNPs were initially validated if allele frequency was >10%. Forty-seven validated SNPs were genotyped in 102 families with at least 2 siblings affected with schizophrenia. RESULTS: Two SNP blocks showed significant association with schizophrenia. Block 1 (five-SNP), located between intron 2 and intron 13 of the glyceronephosphate O-acyltransferase (GNPAT) gene, showed the most significant associations using single-locus TDT (z = -2.07, p = .038, df = 1) and haplotype association analyses (z = -1.99, p = .046, df = 1). Block 2 (two-SNP), located between intron 4 and intron 5 of the disrupted-in-schizophrenia 1 (DISC1) gene, also showed the most significant results in both the single-locus (z = -3.22, p = .0013, df = 1) and haplotype association analyses (z = 3.35, p = .0008, df = 1). The association of the DISC1 gene with schizophrenia was mainly in the patient group with sustained attention deficits as assessed by the Continuous Performance Test. CONCLUSIONS: Chromosome 1q42.1 harbors GNPAT and DISC1 as candidate genes for schizophrenia, and DISC1 is associated with sustained attention deficits.     

Association of DISC1 with autism and Asperger syndrome

The DISC1 gene at 1q42 has generated considerable interest in various psychiatric diseases, since a balanced translocation interrupting the gene was found to cosegregate with schizophrenia and related mental illnesses in a large Scottish pedigree. To date, linkage and association findings to this locus have been replicated in several study samples ascertained for psychotic disorders. However, the biological function of DISC1 in neuronal development would suggest a potential role for this gene also in other, early onset neuropsychiatric disorders. Here we have addressed the allelic diversity of the DISC1, DISC2 and TRAX genes, clustered in 1q42, in Finnish families ascertained for infantile autism (97 families, n(affected)=138) and Asperger syndrome (29 families, n(affected)=143). We established association between autism and a DISC1 intragenic microsatellite (D1S2709; P=0.004). In addition, evidence for association to Asperger syndrome was observed with an intragenic single nucleotide polymorphism (SNP) of DISC1 (rs1322784; P=0.0058), as well as with a three-SNP haplotype (P=0.0013) overlapping the HEP3 haplotype, that was previously observed to associate with schizophrenia in Finnish families. The strongest associations were obtained with broad diagnostic categories for both disorders and with affected males only, in agreement with the previous sex-dependent effects reported for DISC1. These results would further support the involvement of DISC1 gene also in the etiopathogenesis of early onset neuropsychiatric disorders.     

Replication of 1q42 linkage in Finnish schizophrenia pedigrees

Chromosome 1q has been implicated in the etiology of schizophrenia in several independent studies. However, the peak linkage findings have been dispersed over a large chromosomal region, with negative findings in this region also being reported. Our group has previously observed linkage on chromosome 1q42, maximizing within the DISC1 gene, which has also been implied in the etiology of schizophrenia based on functional studies. In the study presented here, we genotyped 300 polymorphic markers on chromosome 1 using a study sample of 70 families with multiple individuals affected with schizophrenia or related conditions, independent of the study samples in our previous reports. We again found evidence for linkage on 1q42 maximizing within the DISC1 gene (rs1000731, lod=2.70). Further, a haplotype containing the most strongly linked markers showed some evidence of association with the disease. This replicates the previous linkage finding in the same region and constitutes supportive evidence for a susceptibility gene in this region.     

Association analysis of FEZ1 variants with schizophrenia in Japanese cohorts.

BACKGROUND: DISC1 has been suggested as a causative gene for psychoses in a large Scottish family. We recently identified FEZ1 as an interacting partner for DISC1. To investigate the role of FEZ1 in schizophrenia and bipolar disorder, case-control association analyses were conducted in Japanese cohorts. METHODS: We performed a mutation screen of the FEZ1 gene and detected 15 polymorphisms. Additional data on informative polymorphisms were obtained from public databases. Eight single nucleotide polymorphisms (SNPs) were analyzed in 119 bipolar disorder and 360 schizophrenic patients and age- and gender-matched control subjects. All genotypes were determined with the TaqMan assay, and selected samples were confirmed by sequencing. RESULTS: The two adjacent polymorphisms displayed a nominally significant association with schizophrenia (IVS2+ 1587G>A, p = .014; 396T   

Functional genomics in postmortem human brain: abnormalities in a DISC1 molecular pathway in schizophrenia

The disrupted in schizophrenia 1 (DISC1) gene has been identified as a schizophrenia susceptibility gene based on linkage and single nucleotide polymorphism (SNP) association studies and clinical data, suggesting that risk SNPs impact on hippocampal structure and function. We hypothesized that altered expression of DISC1 and/or its molecular partners (nuclear distribution element-like [NUDEL], fasciculation and elongation protein zeta-i [FEZ1], and lissencephaly 1 [LIS1]) may underlie its pathogenic role in schizophrenia and explain its genetic association. We examined the expression of DISC1 and its binding partners in the hippocampus and dorsolateral prefrontal cortex of postmortem human brains of schizophrenic patients and controls. We found no difference in the expression of DISC1 mRNA in schizophrenia, and no association with previously identified risk SNPs. However, the expression of NUDEL, FEZ1, and LIS1 was significantly reduced in tissue from schizophrenic subjects, and the expression of each showed association with high-risk DISC1 polymorphisms. These data suggest involvement of genetically linked abnormalities in the DISC1 molecular pathway in the pathophysiology of schizophrenia.     

A haplotype within the DISC1 gene is associated with visual memory functions in families with a high density of schizophrenia

We have previously reported evidence of linkage and association between markers on 1q42 and schizophrenia in a study sample of 498 multiply affected Finnish nuclear families, leading to the recent identification of four significantly associated haplotypes that specifically implicate the Translin-Associated Factor X (TRAX) and Disrupted in Schizophrenia 1 and 2 (DISC1 and DISC2) genes in the genetic etiology of schizophrenia. Previously, the DISC genes were found to be disrupted by a balanced translocation (1;11)(q42.1;q14.3) that cosegregated with schizophrenia and related disorders in a large Scottish pedigree. Interestingly, we also reported earlier suggestive linkage between endophenotypic quantitative traits of visual and verbal memory and microsatellite markers in close proximity to TRAX/DISC, on 1q41. Here, we tested if the identified allelic haplotypes of TRAX/DISC would be associated with visual and/or verbal memory function impairments that are known to aggregate with schizophrenia in families. One haplotype of DISC1, HEP3, displayed association with poorer performance on tests assessing short-term visual memory and attention. Analysis of affected and unaffected offspring separately revealed that both samples contribute to the observed association to visual working memory. These results provide genetic support to the view that the DISC1 gene contributes to sensitivity to schizophrenia and associated disturbances and affects short-term visual memory functions. This finding should stimulate studies aiming at the molecular characterization of how the specific alleles of DISC1 affect the visual memory functions and eventually participates in the development of schizophrenia.     

Disrupted-in-Schizophrenia-1 SNPs and Susceptibility to Schizophrenia: Evidence from Malaysia

Objective

Even though the role of the DICS1 gene as a risk factor for schizophrenia is still unclear, there is substantial evidence from functional and cell biology studies that supports the connection of the gene with schizophrenia. The studies associating the DISC1 gene with schizophrenia in Asian populations are limited to East-Asian populations. Our study examined several DISC1 markers of schizophrenia that were identified in the Caucasian and East-Asian populations in Malaysia and assessed the role of rs2509382, which is located at 11q14.3, the mutual translocation region of the famous DISC1 translocation [t (1; 11) (p42.1; q14.3)].

Methods

We genotyped eleven single-neucleotide polymorphism (SNPs) within or related to DISC1 (rs821597, rs821616, rs4658971, rs1538979, rs843979, rs2812385, rs1407599, rs4658890, and rs2509382) using the PCR-RFLP methods.

Results

In all, there were 575 participants (225 schizophrenic patients and 350 healthy controls) of either Malay or Chinese ethnicity. The case-control analyses found two SNPs that were associated with schizophrenia [rs4658971 (p=0.030; OR=1.43 (1.35-1.99) and rs1538979-(p=0.036; OR=1.35 (1.02-1.80)] and rs2509382-susceptibility among the males schizophrenics [p=0.0082; OR=2.16 (1.22-3.81)]. This is similar to the meta-analysis findings for the Caucasian populations.

Conclusion

The study supports the notion that the DISC1 gene is a marker of schizophrenia susceptibility and that rs2509382 in the mutual DISC1 translocation region is a susceptibility marker for schizophrenia among males in Malaysia. However, the finding of the study is limited due to possible genetic stratification and the small sample size.     

Association between the TRAX/DISC locus and both bipolar disorder and schizophrenia in the Scottish population

The Translin-associated factor X/Disrupted in Schizophrenia 1 (TRAX/DISC) region was first implicated as a susceptibility locus for schizophrenia by analysis of a large Scottish family in which a t(1;11) translocation cosegregates with schizophrenia, bipolar disorder and recurrent major depression. We now report evidence for association between bipolar disorder and schizophrenia and this locus in the general Scottish population. A systematic study of linkage disequilibrium in a representative sample of the Scottish population was undertaken across the 510 kb of TRAX and DISC1. SNPs representing each haplotype block were selected for case-control association studies of both schizophrenia and bipolar disorder. Significant association with bipolar disorder in women P=0.00026 (P=0.0016 in men and women combined) was detected in a region of DISC1. This same region also showed nominally significant association with schizophrenia in both men and women combined, P=0.0056. Two further regions, one in TRAX and the second in DISC1, showed weaker evidence for sex-specific associations of individual haplotypes with bipolar disorder in men and women respectively, P<0.01. Only the association between bipolar women and DISC1 remained significant after correction for multiple testing. This result provides further supporting evidence for DISC1 as a susceptibility factor for both bipolar disorder and schizophrenia, consistent with the diagnoses in the original Scottish translocation family.     

Association of schizophrenia with the rs821633 polymorphism in the DISC1 gene among Han Chinese

Background

Previous studies report that various single nucleotide polymorphisms (SNP) in the Disrupted-in Schizophrenia 1 (DISC1) gene are closely associated with schizophrenia, but there are no studies that assess the relationship of age of onset of schizophrenia with these SNPs.

Objective

Investigate the relationship between the rs821633 SNP in the DISC1 gene and the occurrence and age of onset of schizophrenia in Han Chinese.

Methods

We used the TaqMan genotyping technology to examine the rs821633 SNP in the DISC1 gene among 315 individuals who developed schizophrenia prior to 19 years of age (‘early-onset’), 407 individuals who developed schizophrenia when 19 years of age or older (‘late-onset’), and 482 healthy controls. We used survival analyses to investigate the relationship between the rs821633(C) risk allele and the age of onset of schizophrenia.

Results

Compared to the prevalence in healthy controls, the prevalence of the C/C genotype of rs821633 and of the C allele in rs821633 were significantly greater in individuals with early-onset schizophrenia (X²=7.17, df=1, p=0.007; X²=7.20, df=2, p=0.032) and significantly greater in individuals with late-onset schizophrenia (X²=5.36, df=1, p=0.022; X²=6.58, df=2, p=0.041). However, there were no significant differences in the prevalence of the C/C genotype or the C allele between individuals with early-onset and late-onset schizophrenia. Kaplan-Meier survival analyses found no significant association between the rs821633(C) risk allele and age of onset in schizophrenia.

Conclusion

We confirm the association of polymorphism in the rs821633 SNP in the DISC1 gene with schizophrenia among Han Chinese, but we found no association between the rs821633(C) risk allele and the age of onset in individuals with schizophrenia.     

Subcellular targeting of DISC1 is dependent on a domain independent from the Nudel binding site

Disrupted in schizophrenia 1 (DISC1) has been identified as a putative risk factor for schizophrenia and affective disorders through study of a Scottish family with a balanced (1;11) (q42.1;q14.3) translocation, which results in the disruption of the DISC1 locus and cosegregates with major psychiatric disease. Several other reports of genetic linkage and association between DISC1 and schizophrenia in a range of patient populations have added credibility to the DISC1-schizophrenia theory, but the function of the DISC1 protein is still poorly understood. Recent studies have suggested that DISC1 plays a role in neuronal outgrowth, possibly through reported interactions with the molecules Nudel and FEZ1. Here we have analyzed the DISC1 protein sequence to identify previously unknown regions that are important for the correct targeting of the protein and conducted imaging studies to identify DISC1 subcellular location. We have identified a central coiled-coil region and show it is critical for the subcellular targeting of DISC1. This domain is independent from the C-terminal Nudel binding domain highlighting the multidomain nature/functionality of the DISC1 protein. Furthermore, we have been able to provide the first direct evidence that DISC1 is localized to mitochondria in cultured cortical neurons that are dependent on an intact cytoskeleton. Surprisingly, Nudel is seen to differentially associate with mitochondrial markers in comparison to DISC1. Disruption of the cytoskeleton results in colocalization of Nudel and mitochondrial markers-the first observation of such a direct relationship. Mitochondrial dysfunction has been implicated to play a role in schizophrenia so we speculate that mutations in DISC1 or Nudel may impair mitochondrial transport or function, initiating a cascade of events culminating in psychiatric illness.     

No association between the PCM1 gene and schizophrenia: a multi-center case-control study and a meta-analysis

Alterations in centrosomal function have been suggested in the pathology of schizophrenia. The molecule pericentriolar material 1 (PCM1) is involved in maintaining centrosome integrity and in the regulation of the microtubule cytoskeleton. PCM1 forms a complex at the centrosome with the disrupted-in-schizophrenia 1 (DISC1) protein, which is a major susceptibility factor for schizophrenia. The association between genetic variants in the PCM1 gene and schizophrenia has been reported by several case-control studies, linkage studies and a meta-analysis. The aims of this study are to replicate the association between four single-nucleotide polymorphisms (SNPs) in the PCM1 gene and schizophrenia in a Japanese population (1496 cases and 1845 controls) and to perform a meta-analysis of the combined sample groups (3289 cases and 3567 controls). We failed to find a significant association between SNPs or haplotypes of the PCM1 gene and schizophrenia in the Japanese population (P>0.28). The meta-analysis did not reveal an association between the four examined SNPs and schizophrenia. Our data did not support genetic variants in the PCM1 gene as a susceptibility locus for schizophrenia.     

Association between a disrupted-in-schizophrenia 1 (DISC1) single nucleotide polymorphism and schizophrenia in a combined Scandinavian case-control sample

Disrupted-in-schizophrenia-1 (DISC1), located on chromosome 1q42.1, is linked to rare familial schizophrenia in a large Scottish family. The chromosomal translocation that segregates with the disease results in a truncated protein that impairs neurite outgrowth and proper development of the cerebral cortex, suggesting that lost DISC1 function may underlie neurodevelopmental dysfunction in schizophrenia. DISC1 has been associated with schizophrenia in multiple populations, but there is little evidence of convergence across populations. In the present case-control study three Scandinavian samples of 837 individuals affected with schizophrenia and 1473 controls, were used in an attempt to replicate previously reported associations between single nucleotide polymorphisms (SNPs) in DISC1 and schizophrenia. No SNP with allele frequency above 10% was significantly associated with the disease after correction for multiple testing. However, the minor allele of rs3737597 (frequency 2%) in the 3'-untranslated region (UTR), previously identified as a risk allele in Finnish families, was significantly and consistently associated with the disorder across the three samples, (p-value corrected for multiple testing was 0.002). Our results suggest that a relatively uncommon DISC1 mutation, which increases the susceptibility for schizophrenia may be segregating in the Scandinavian population, and support the view that common DISC1 SNP alleles are unlikely to account for a substantial proportion of the genetic risk of the disease across populations of European descent.     

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

BACKGROUND: N-methyl-D-aspartate (NMDA) receptors play important roles in many neurophysiological processes. Evidence from previous studies indicate that NMDA receptors contribute to the pathophysiology of schizophrenia. Two NMDA receptor subunit genes, GRIN1 and GRIN2A, are both good candidate genes for schizophrenia. METHOD: We genotyped five single nucleotide polymorphisms (SNPs) in GRIN1 and two in GRIN2A in 2455 Han Chinese subjects, including population- and family-based samples, and performed case-control and transmission disequilibrium test (TDT) analyses. A microsatellite in GRIN2A was genotyped in population-based samples and a Mann-Whitney U test was performed. RESULTS: A highly significant association was detected at the 5' end of GRIN1. Analyses of single variants and multiple-locus haplotypes indicate that the association is mainly generated by rs11146020 (case-control study: p = .0000013, odds ratio = .61, 95% confidence interval .50-.74; TDT: p = .0019, T/NT = 79/123). No association was found in the GRIN2A polymorphisms. CONCLUSIONS: Our results provide support for the hypothesis that NMDA receptors are an important factor in schizophrenia. Moreover, rs11146020 is located in 5' untranslated region where several functional elements have been found. Hence, the SNP is a potential candidate in altering risk for schizophrenia and worthy of further replication and functional study.     

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.     

Association study between Disrupted-in-Schizophrenia-1 (DISC1) and Japanese patients with treatment-resistant schizophrenia (TRS)

Treating the 20-30% of patients with schizophrenia whose symptoms are resistant to antipsychotic treatment, a condition known as treatment-resistant schizophrenia (TRS), can be problematic. Recently, an association between Disrupted-in-Schizophrenia-1 (DISC1), a candidate susceptibility gene for schizophrenia, and TRS was reported. Associations between three missense SNPs, rs3738401 (Q264R), rs6675281 (L607F), and rs821616 (S704C) in DISC1, especially rs3738401, showed strong significance. Thus, the main aim of our current study was to examine if the reported possible functional polymorphisms in DISC1 were related to Japanese TRS. First, DISC1 was re-investigated in 485 Japanese patients with schizophrenia and 660 healthy controls with a case-control study using four candidate SNPs, rs751229, rs3738401, rs821597, and rs821616. DISC1 was not associated with schizophrenia in the Japanese population. Second, we investigated whether these SNPs contributed to TRS in 127 inpatients with schizophrenia (35 patients; TRS and 92 patients; non-TRS). The genotypic distributions of these four SNPs were not significantly different between TRS and non-TRS in either genotypic or recessive models of minor alleles. In addition, clinical variables, such as improvement in clinical symptoms, duration of hospitalization, and total antipsychotics dose amounts, were not different among the genotypes of these SNPs. Taken together, results showed that DISC1 had no apparent degree of association with Japanese patients with schizophrenia as a candidate susceptibility gene for disease per se or TRS.     

Association study of the DISC1/TRAX locus with schizophrenia in a Japanese population

Disrupted-in-Schizophrenia-1 (DISC1), identified by cytogenetic approaches in a pedigree with familial psychosis, is considered a candidate susceptibility gene for schizophrenia in some populations. In the pedigree, the TRAX gene, located adjacent to DISC1 on the disrupted chromosome 1, may also contribute to the pathophysiology of the familial schizophrenia. We studied association of the DISC1 and TRAX genes with schizophrenia in 338 Japanese by analyzing 15 single nucleotide polymorphisms (SNPs), including 12 SNPs in DISC1 and three in TRAX, respectively. No significant difference was observed between the patients and controls in allelic frequencies or genotypic distributions of 15 SNPs. A weak trend for the association in genotypic distribution of one SNP in TRAX (major homo/hetero/minor homo: 0.324/0.431/0.245 vs. 0.293/0.526/0.181 for patients vs controls, p = 0.039 in the 2 x 3 comparison) turned out to be insignificant after Bonferroni correction. Haplotype analysis did not support the association between the patients and controls. The present study suggests that the DISC1/TRAX locus may not have a major role in Japanese schizophrenia.     

Bipolar disorder and polymorphisms in the dysbindin gene (DTNBP1).

BACKGROUND: Several studies support the dysbindin (dystrobrevin binding protein 1) gene (DTNBP1) as a susceptibility gene for schizophrenia. We previously reported that variation at a specific 3-locus haplotype influences susceptibility to schizophrenia in a large United Kingdom (UK) Caucasian case-control sample. METHODS: Using similar methodology to our schizophrenia study, we have investigated this same 3-locus haplotype in a large, well-characterized bipolar sample (726 Caucasian UK DSM-IV bipolar I patients; 1407 ethnically matched controls). RESULTS: No significant differences were found in the distribution of the 3-locus haplotype in the full sample. Within the subset of bipolar I cases with predominantly psychotic episodes of mood disturbance (n = 133) we found nominally significant support for association at this haploptype (p < .042) and at SNP rs2619538 (p = .003), with a pattern of findings similar to that in our schizophrenia sample. This finding was not significant after correction for multiple testing. CONCLUSIONS: Our data suggest that variation at the polymorphisms examined does not make a major contribution to susceptibility to bipolar disorder in general. They are consistent with the possibility that DTNBP1 influences susceptibility to a subset of bipolar disorder cases with psychosis. However, our subset sample is small and the hypothesis requires testing in independent, adequately powered samples.     

Genetic Association Study of the Alpha 7 Nicotinic Receptor (CHRNA7) with the Development of Schizophrenia and Bipolar Disorder in Korean Population

Objective

CHRNA7 has been shown to be a strong candidate gene for schizophrenia and bipolar disorder. It is located on chromosome 15q13-q14, which is one of the replicated linkage spots for schizophrenia and bipolar disorder.

Methods

We conducted an association study to determine whether previous positive association is replicable in the Korean population. We included 254 patients with schizophrenia, 193 patients with bipolar disorder type I, 38 patients with bipolar disorder type II, 64 schizoaffective disorder patients, and 349 controls. All subjects were ethnically Korean. A total of 898 subjects were included, and genotyping was done for three single nucleotide polymorphisms (SNPs) of CHRNA7. These three intronic SNPs were rs2337506 (A/G), rs6494223 (C/T), and rs12916879 (A/G).

Results

There was only one marginally significant association; this association was between rs12916879 and bipolar disorder type I in the male subgroup. In both the allele and genotype distributions, we found a weak signal (Chi-squared=3.57, df=1, p=0.06 for allele, Chi-squared=7.50, df=2, p=0.02 for genotype) only. Unphased haplotype analysis could not provide additional support for this finding. No SNP was associated with schizophrenia or any other affected groups in this Korean sample. The associative finding is marginal and inconclusive.

Conclusion

We could not replicate positive association in other ethnic groups previously studied. This suggests possible heterogeneity in the genes associated with schizophrenia and bipolar disorders. Because of structural complexity of the CHRNA7 gene and the limited statistical power of this study, further genetic studies with more SNPs and larger samples covering various populations, along with more fine molecular exploration of the CHRNA7 gene structure, are required.     

NCAM1 and neurocognition in schizophrenia.

BACKGROUND: Alterations in neurocognition may be fundamental to schizophrenia and may be endophenotypes. Neural cell adhesion molecule 1 (NCAM1, aliases NCAM and CD56) may be a candidate gene for schizophrenia or for neurocognition in schizophrenia as supported by linkage and functional findings. METHODS: Subjects were 641 patients with schizophrenia who participated in the Clinical Antipsychotic Trials of Intervention Effectiveness (CATIE) clinical trial. Neurocognition was assessed at study baseline. Nine NCAM1 single nucleotide polymorphisms (SNPs) were blindly genotyped. Analysis of covariance was used to test for single SNP associations and haplotype regression for multilocus associations. RESULTS: As there were suggestions of population stratification, all analyses were conducted stratified by inferred ancestry. In the "Europe only" stratum, there were nominally significant associations with five contiguous SNPs (rs1943620, rs1836796, rs1821693, rs686050, rs584427) with the strongest association at rs1836796 (p = .007). Via permutation testing, the probability of obtaining five consecutive statistically significant SNPs with p-values 相似文献