Enhanced Learning and Memory in Patients with CRB1 Retinopathy.

Mutations in the CRB1 gene are associated with a diverse spectrum of retinopathies with phenotypic variability causing severe visual impairment. The CRB1 gene has a role in retinal development and is expressed in the cerebral cortex and hippocampus, but its role in cognition has not been described before. This study compares cognitive function in CRB1 retinopathy individuals with subjects with other retinopathies and the normal population. METHODS: Neuropsychological tests of cognitive function were used to test individuals with CRB1 and non-CRB1 retinopathies and compare results with a standardised normative dataset. RESULTS: CRB1 retinopathy subjects significantly outperformed those with non-CRB1 retinopathy in list learning tasks of immediate (p = 0.001) and delayed memory (p = 0.007), tests of semantic verbal fluency (p = 0.017), verbal IQ digit span subtest (p = 0.037), and estimation test of higher execution function (p = 0.020) but not in the remaining tests of cognitive function (p > 0.05). CRB1 retinopathy subjects scored significantly higher than the normal population in all areas of memory testing (p < 0.05) and overall verbal IQ tests (p = 0.0012). Non-CRB1 retinopathy subjects scored significantly higher than the normal population in story recall, verbal fluency, and overall verbal IQ tests (p = 0.0016). CONCLUSIONS: Subjects with CRB1 retinopathy may have enhanced cognitive function in areas of memory and learning. Further work is required to understand the role of CRB1 in cognition.

Transcriptomic and genetic analyses reveal potential causal drivers for intractable partial epilepsy.

Mesial temporal lobe epilepsy with hippocampal sclerosis represents the most common epilepsy syndrome in adult patients with medically intractable partial epilepsy. Mesial temporal lobe epilepsy is usually regarded as a polygenic and complex disorder, still poorly understood but probably caused and perpetuated by dysregulation of numerous biological networks and cellular functions. The study of gene expression changes by single nucleotide polymorphisms in regulatory elements (expression quantitative trait loci, eQTLs) has been shown to be a powerful complementary approach to the detection and understanding of risk loci by genome-wide association studies. We performed a whole (gene and exon-level) transcriptome analysis on cortical tissue samples (Brodmann areas 20 and 21) from 86 patients with mesial temporal lobe epilepsy with hippocampal sclerosis and 75 neurologically healthy controls. Genome-wide genotyping data from the same individuals (patients and controls) were analysed and paired with the transcriptome data. We report potential epilepsy-risk eQTLs, some of which are specific to tissue from patients with mesial temporal lobe epilepsy with hippocampal sclerosis. We also found large transcriptional and splicing deregulation in mesial temporal lobe epilepsy with hippocampal sclerosis tissue as well as gene networks involving neuronal and glial mechanisms that provide new insights into the cause and maintenance of the seizures. These data (available via the 'Seizubraineac' web-tool resource, www.seizubraineac.org) will facilitate the identification of new therapeutic targets and biomarkers as well as genetic risk variants that could influence epilepsy and pharmacoresistance.

The impact of brain-derived neurotrophic factor Val66Met polymorphism on cognition and functional brain networks in patients with intractable partial epilepsy.

INTRODUCTION: Medial temporal lobe epilepsy (mTLE) is the most common refractory focal epilepsy in adults. Around 30%-40% of patients have prominent memory impairment and experience significant postoperative memory and language decline after surgical treatment. BDNF Val66Met polymorphism has also been associated with cognition and variability in structural and functional hippocampal indices in healthy controls and some patient groups. AIMS: We examined whether BDNF Val66Met variation was associated with cognitive impairment in mTLE. METHODS: In this study, we investigated the association of Val66Met polymorphism with cognitive performance (n = 276), postoperative cognitive change (n = 126) and fMRI activation patterns during memory encoding and language paradigms in 2 groups of patients with mTLE (n = 37 and 34). RESULTS: mTLE patients carrying the Met allele performed more poorly on memory tasks and showed reduced medial temporal lobe activation and reduced task-related deactivations within the default mode networks in both the fMRI memory and language tasks than Val/Val patients. CONCLUSIONS: Although cognitive impairment in epilepsy is the result of a complex interaction of factors, our results suggest a role of genetic factors on cognitive impairment in mTLE.

Genetic variability in response to amyloid beta deposition influences Alzheimer's disease risk.

Genome-wide association studies of late-onset Alzheimer's disease risk have previously identified genes primarily expressed in microglia that form a transcriptional network. Using transgenic mouse models of amyloid deposition, we previously showed that many of the mouse orthologues of these risk genes are co-expressed and associated with amyloid pathology. In this new study, we generate an improved RNA-seq-derived network that is expressed in amyloid-responsive mouse microglia and we statistically compare this with gene-level variation in previous human Alzheimer's disease genome-wide association studies to predict at least four new risk genes for the disease (OAS1, LAPTM5, ITGAM/CD11b and LILRB4). Of the mouse orthologues of these genes Oas1a is likely to respond directly to amyloid at the transcriptional level, similarly to established risk gene Trem2, because the increase in Oas1a and Trem2 transcripts in response to amyloid deposition in transgenic mice is significantly higher than both the increase of the average microglial transcript and the increase in microglial number. In contrast, the mouse orthologues of LAPTM5, ITGAM/CD11b and LILRB4 (Laptm5, Itgam/CD11b and Lilra5) show increased transcripts in the presence of amyloid plaques similar in magnitude to the increase of the average microglial transcript and the increase in microglia number, except that Laptm5 and Lilra5 transcripts increase significantly quicker than the average microglial transcript as the plaque load becomes dense. This work suggests that genetic variability in the microglial response to amyloid deposition is a major determinant for Alzheimer's disease risk, and identification of these genes may help to predict the risk of developing Alzheimer's disease. These findings also provide further insights into the mechanisms underlying Alzheimer's disease for potential drug discovery.

Soluble Fibrinogen Triggers Non-cell Autonomous ER Stress-Mediated Microglial-Induced Neurotoxicity.

Aberrant or chronic microglial activation is strongly implicated in neurodegeneration, where prolonged induction of classical inflammatory pathways may lead to a compromised blood-brain barrier (BBB) or vasculature, features of many neurodegenerative disorders and implicated in the observed cognitive decline. BBB disruption or vascular disease may expose the brain parenchyma to "foreign" plasma proteins which subsequently impact on neuronal network integrity through neurotoxicity, synaptic loss and the potentiation of microglial inflammation. Here we show that the blood coagulation factor fibrinogen (FG), implicated in the pathogenesis of dementias such as Alzheimer's disease (AD), induces an inflammatory microglial phenotype as identified through genetic microarray analysis of a microglial cell line, and proteome cytokine profiling of primary microglia. We also identify a FG-mediated induction of non-cell autonomous ER stress-associated neurotoxicity via a signaling pathway that can be blocked by pharmacological inhibition of microglial TNFα transcription or neuronal caspase-12 activity, supporting a disease relevant role for plasma components in neuronal dysfunction.

Doublecortin-expressing cell types in temporal lobe epilepsy.

Doublecortin (DCX) is widely regarded as a marker of immature and migrating neurons during development. While DCX expression persists in adults, particularly in the temporal lobe and neurogenic regions, it is unknown how seizures influence its expression. The aim of the present study was to explore the distribution and characteristics of DCX-expressing cells in surgical and postmortem samples from 40 adult and paediatric patients, with epilepsy and with or without hippocampal sclerosis (HS), compared to post mortem controls. The hippocampus (pes and body), parahippocampal gyrus, amygdala, temporal pole and temporal cortex were examined with DCX immunohistochemistry using four commercially-available DCX antibodies, labelled cells were quantified in different regions of interest as well as their co-expression with cell type specific markers (CD68, Iba1, GFAP, GFAP∂, nestin, SOX2, CD34, OLIG2, PDGFRß, NeuN) and cell cycle marker (MCM2). Histological findings were compared with clinical data, as well as gene expression data obtained from the temporal cortex of 83 temporal lobe epilepsy cases with HS. DCX immunohistochemistry identified immature (Nestin-/NeuN-) neurons in layer II of the temporal neocortex in patients with and without epilepsy. Their number declined significantly with age but was not associated with the presence of hippocampal sclerosis, seizure semiology or memory dysfunction. DCX+ cells were prominent in the paralaminar nuclei and periamygdalar cortex and these declined with age but were not significantly associated with epilepsy history. DCX expressing cells with ramified processes were prominent in all regions, particularly in the hippocampal subgranular zone, where significantly increased numbers were observed in epilepsy samples compared to controls. DCX ramified cells co-expressed Iba1, CD68 and PDGFRß, and less frequently MCM2, OLIG2 and SOX2, but no co-localization was observed with CD34, nestin or GFAP/GFAP ∂. Gene expression data from neocortical samples in patients with TLE and HS supported ongoing DCX expression in adults. We conclude that DCX identifies a range of morphological cell types in temporal lobe epilepsy, including immature populations, glial and microglial cell types. Their clinical relevance and biological function requires further study but we show some evidence for alteration with age and in epilepsy.

Peripheral Serotonin 1B Receptor Transcription Predicts the Effect of Acute Tryptophan Depletion on Risky Decision-Making.

Background: The effects of acute tryptophan depletion on human decision-making suggest that serotonin modulates the processing of rewards and punishments. However, few studies have assessed which of the many types of serotonin receptors are responsible. Methods: Using a within-subject, double-blind, sham-controlled design in 26 subjects, we examined whether individual differences in serotonin system gene transcription, measured in peripheral blood, predicted the effect of acute tryptophan depletion on decision-making. Participants performed a task in which they chose between successive pairs of fixed, lower-stakes (control) and variable, higher-stakes (experimental) gambles, each involving wins or losses. In 21 participants, mRNA from 9 serotonin system genes was measured in whole blood prior to acute tryptophan depletion: 5-HT1B, 5-HT1F, 5-HT2A, 5-HT2B, 5-HT3A, 5-HT3E, 5-HT7 (serotonin receptors), 5-HTT (the serotonin transporter), and tryptophan hydroxylase 1. Results: Acute tryptophan depletion did not significantly influence participants' sensitivity to probability, wins, or losses, although there was a trend for a lower tendency to choose experimental gambles overall following depletion. Significant positive correlations, which survived correction for multiple comparisons, were detected between baseline 5-HT1B mRNA levels and acute tryptophan depletion-induced increases in both the overall tendency to choose the experimental gamble and sensitivity to wins. No significant relationship was observed with any other peripheral serotonin system markers. Computational analyses of decision-making data provided results consistent with these findings. Conclusions: These results suggest that the 5-HT1B receptor may modulate the effects of acute tryptophan depletion on risky decision-making. Peripheral levels of serotonin markers may predict response to treatments that act upon the serotonin system, such as selective serotonin reuptake inhibitors.

PAX6, brain structure and function in human adults: advanced MRI in aniridia.

OBJECTIVE: PAX6 is a pleiotropic transcription factor essential for the development of several tissues including the eyes, central nervous system, and some endocrine glands. Recently it has also been shown to be important for the maintenance and functioning of corneal and pancreatic tissues in adults. We hypothesized that PAX6 is important for the maintenance of brain integrity in humans, and that adult heterozygotes may have abnormalities of cortical patterning analogous to those found in mouse models. METHODS: We used advanced magnetic resonance imaging techniques, including surface-based morphometry and region-of-interest analysis in adult humans heterozygously mutated for PAX6 mutations (n = 19 subjects and n = 21 controls). Using immunohistochemistry, we also studied PAX6 expression in the adult brain tissue of healthy subjects (n = 4) and patients with epilepsy (n = 42), some of whom had focal injuries due to intracranial electrode track placement (n = 17). RESULTS: There were significant reductions in frontoparietal cortical area after correcting for age and intracranial volume. A greater decline in thickness of the frontoparietal cortex with age, in subjects with PAX6 mutations compared to controls, correlated with age-corrected, accelerated decline in working memory. These results also demonstrate genotypic effects: those subjects with the most severe genotypes have the most widespread differences compared with controls. We also demonstrated significant increases in PAX6-expressing cells in response to acute injury in the adult human brain. INTERPRETATION: These findings suggest a role for PAX6 in the maintenance and consequent functioning of the adult brain, homologous to that found in other tissues. This has significant implications for the understanding and treatment of neurodegenerative diseases.

Variants in KCNJ11 and BAD do not predict response to ketogenic dietary therapies for epilepsy.

In the absence of specific metabolic disorders, predictors of response to ketogenic dietary therapies (KDT) are unknown. We aimed to determine whether variants in established candidate genes KCNJ11 and BAD influence response to KDT. We sequenced KCNJ11 and BAD in individuals without previously-known glucose transporter type 1 deficiency syndrome or other metabolic disorders, who received KDT for epilepsy. Hospital records were used to obtain demographic and clinical data. Two response phenotypes were used: ≥ 50% seizure reduction and seizure-freedom at 3-month follow-up. Case/control association tests were conducted with KCNJ11 and BAD variants with minor allele frequency (MAF)>0.01, using PLINK. Response to KDT in individuals with variants with MAF<0.01 was evaluated. 303 Individuals had KCNJ11 and 246 individuals had BAD sequencing data and diet response data. Six SNPs in KCNJ11 and two in BAD had MAF>0.01. Eight variants in KCNJ11 and seven in BAD (of which three were previously-unreported) had MAF<0.01. No significant results were obtained from association analyses, with either KDT response phenotype. P-values were similar when accounting for ethnicity using a stratified Cochran-Mantel-Haenszel test. There did not seem to be a consistent effect of rare variants on response to KDT, although the cohort size was too small to assess significance. Common variants in KCNJ11 and BAD do not predict response to KDT for epilepsy. We can exclude, with 80% power, association from variants with a MAF of >0.05 and effect size >3. A larger sample size is needed to detect associations from rare variants or those with smaller effect sizes.

First effects of rising amyloid-ß in transgenic mouse brain: synaptic transmission and gene expression.

Detecting and treating Alzheimer's disease, before cognitive deficits occur, has become the health challenge of our time. The earliest known event in Alzheimer's disease is rising amyloid-ß. Previous studies have suggested that effects on synaptic transmission may precede plaque deposition. Here we report how relative levels of different soluble amyloid-ß peptides in hippocampus, preceding plaque deposition, relate to synaptic and genomic changes. Immunoprecipitation-mass spectrometry was used to measure the early rise of different amyloid-ß peptides in a mouse model of increasing amyloid-ß ('TASTPM', transgenic for familial Alzheimer's disease genes APP/PSEN1). In the third postnatal week, several amyloid-ß peptides were above the limit of detection, including amyloid-ß40, amyloid-ß38 and amyloid-ß42 with an intensity ratio of 6:3:2, respectively. By 2 months amyloid-ß levels had only increased by 50% and although the ratio of the different peptides remained constant, the first changes in synaptic currents, compared to wild-type mice could be detected with patch-clamp recordings. Between 2 and 4 months old, levels of amyloid-ß40 rose by ∼7-fold, but amyloid-ß42 rose by 25-fold, increasing the amyloid-ß42:amyloid-ß40 ratio to 1:1. Only at 4 months did plaque deposition become detectable and only in some mice; however, synaptic changes were evident in all hippocampal fields. These changes included increased glutamate release probability (P < 0.001, n = 7-9; consistent with the proposed physiological effect of amyloid-ß) and loss of spontaneous action potential-mediated activity in the cornu ammonis 1 (CA1) and dentate gyrus regions of the hippocampus (P < 0.001, n = 7). Hence synaptic changes occur when the amyloid-ß levels and amyloid-ß42:amyloid-ß40 ratio are still low compared to those necessary for plaque deposition. Genome-wide microarray analysis revealed changes in gene expression at 2-4 months including synaptic genes being strongly affected but often showing significant changes only by 4 months. We thus demonstrate that, in a mouse model of rising amyloid-ß, the initial deposition of plaques does not occur until several months after the first amyloid-ß becomes detectable but coincides with a rapid acceleration in the rise of amyloid-ß levels and the amyloid-ß42:amyloid-ß40 ratio. Prior to acceleration, however, there is already a pronounced synaptic dysfunction, reflected as changes in synaptic transmission and altered gene expression, indicating that restoring synaptic function early in the disease progression may represent the earliest possible target for intervention in the onset of Alzheimer's disease.

A genome-wide gene-expression analysis and database in transgenic mice during development of amyloid or tau pathology.

We provide microarray data comparing genome-wide differential expression and pathology throughout life in four lines of "amyloid" transgenic mice (mutant human APP, PSEN1, or APP/PSEN1) and "TAU" transgenic mice (mutant human MAPT gene). Microarray data were validated by qPCR and by comparison to human studies, including genome-wide association study (GWAS) hits. Immune gene expression correlated tightly with plaques whereas synaptic genes correlated negatively with neurofibrillary tangles. Network analysis of immune gene modules revealed six hub genes in hippocampus of amyloid mice, four in common with cortex. The hippocampal network in TAU mice was similar except that Trem2 had hub status only in amyloid mice. The cortical network of TAU mice was entirely different with more hub genes and few in common with the other networks, suggesting reasons for specificity of cortical dysfunction in FTDP17. This Resource opens up many areas for investigation. All data are available and searchable at http://www.mouseac.org.

A genomic profile of the immune response to stroke with implications for stroke recovery.

OBJECTIVES: The objectives of this study were to determine the change in gene expression between two time points following stroke and to identify biomarkers of stroke recovery through gene expression profiling and pathway analysis. METHODS: Peripheral blood was collected from 34 ischemic stroke patients (confirmed by magnetic resonance imaging) ≥18 years of age, within 24 hr of symptom onset and 24-48 hr later, and from healthy controls. The Modified Rankin Scale (MRS) was used to determine 30-day recovery. Total RNA was extracted from whole blood in Paxgene RNA tubes, amplified, and hybridized to Illumina HumanRef-8v2 bead chips. Gene expression was compared in a univariate manner between stroke patients at both time points and good versus bad outcome using t-test in GeneSpring. Inflation of Type 1 error was corrected by false discovery rate (FDR), and Ingenuity Systems Pathway analysis (IPA) was performed. A secondary validation cohort was recruited from a local hospital. RESULTS: Three genes were significantly downregulated over time (LY96, IL8, and SDPR; FDR corrected p < .05). This finding was confirmed in a validation cohort of stroke patients (n = 8). IPA revealed cytotoxic T-lymphocyte antigen 4 (CTLA4) signaling was the most significant pathway present in the peripheral whole blood of stroke patients 24-48 hr after onset. When controlling for age and National Institutes of Health Stroke Scale score, high baseline expression of TLR2 and TLR4 significantly predicted worse scores on the MRS. CONCLUSION: CTLA4 signaling is a novel pathway for the study of stroke-induced immune suppression. Markers of immune dysfunction early after stroke may prove useful for identifying patients with increased risk of poor recovery.

Disruption of SATB2 or its long-range cis-regulation by SOX9 causes a syndromic form of Pierre Robin sequence.

Heterozygous loss-of-function (LOF) mutations in the gene encoding the DNA-binding protein, SATB2, result in micrognathia and cleft palate in both humans and mice. In three unrelated individuals, we show that translocation breakpoints (BPs) up to 896 kb 3' of SATB2 polyadenylation site cause a phenotype which is indistinguishable from that caused by SATB2 LOF mutations. This syndrome comprises long nose, small mouth, micrognathia, cleft palate, arachnodactyly and intellectual disability. These BPs map to a gene desert between PLCL1 and SATB2. We identified three putative cis-regulatory elements (CRE1-3) using a comparative genomic approach each of which would be placed in trans relative to SATB2 by all three BPs. CRE1-3 each bind p300 and mono-methylated H3K4 consistent with enhancer function. In silico analysis suggested that CRE1-3 contain one or more conserved SOX9-binding sites, and this binding was confirmed using chromatin immunoprecipitation on cells derived from mouse embryonic pharyngeal arch. Interphase bacterial artificial chromosome fluorescence in situ hybridization measurements in embryonic craniofacial tissues showed that the orthologous region in mice exhibits Satb2 expression-dependent chromatin decondensation consistent with Satb2 being a target gene of CRE1-3. To assess their in vivo function, we made multiple stable reporter transgenic lines for each enhancer in zebrafish. CRE2 was shown to drive SATB2-like expression in the embryonic craniofacial region. This expression could be eliminated by mutating the SOX9-binding site of CRE2. These observations suggest that SATB2 and SOX9 may be acting together via complex cis-regulation to coordinate the growth of the developing jaw.

Epilepsy, hippocampal sclerosis and febrile seizures linked by common genetic variation around SCN1A.

Epilepsy comprises several syndromes, amongst the most common being mesial temporal lobe epilepsy with hippocampal sclerosis. Seizures in mesial temporal lobe epilepsy with hippocampal sclerosis are typically drug-resistant, and mesial temporal lobe epilepsy with hippocampal sclerosis is frequently associated with important co-morbidities, mandating the search for better understanding and treatment. The cause of mesial temporal lobe epilepsy with hippocampal sclerosis is unknown, but there is an association with childhood febrile seizures. Several rarer epilepsies featuring febrile seizures are caused by mutations in SCN1A, which encodes a brain-expressed sodium channel subunit targeted by many anti-epileptic drugs. We undertook a genome-wide association study in 1018 people with mesial temporal lobe epilepsy with hippocampal sclerosis and 7552 control subjects, with validation in an independent sample set comprising 959 people with mesial temporal lobe epilepsy with hippocampal sclerosis and 3591 control subjects. To dissect out variants related to a history of febrile seizures, we tested cases with mesial temporal lobe epilepsy with hippocampal sclerosis with (overall n = 757) and without (overall n = 803) a history of febrile seizures. Meta-analysis revealed a genome-wide significant association for mesial temporal lobe epilepsy with hippocampal sclerosis with febrile seizures at the sodium channel gene cluster on chromosome 2q24.3 [rs7587026, within an intron of the SCN1A gene, P = 3.36 × 10(-9), odds ratio (A) = 1.42, 95% confidence interval: 1.26-1.59]. In a cohort of 172 individuals with febrile seizures, who did not develop epilepsy during prospective follow-up to age 13 years, and 6456 controls, no association was found for rs7587026 and febrile seizures. These findings suggest SCN1A involvement in a common epilepsy syndrome, give new direction to biological understanding of mesial temporal lobe epilepsy with hippocampal sclerosis with febrile seizures, and open avenues for investigation of prognostic factors and possible prevention of epilepsy in some children with febrile seizures.

Apolipoprotein E genotype, cardiovascular biomarkers and risk of stroke: systematic review and meta-analysis of 14,015 stroke cases and pooled analysis of primary biomarker data from up to 60,883 individuals.

BACKGROUND: At the APOE gene, encoding apolipoprotein E, genotypes of the ε2/ε3/ε4 alleles associated with higher LDL-cholesterol (LDL-C) levels are also associated with higher coronary risk. However, the association of APOE genotype with other cardiovascular biomarkers and risk of ischaemic stroke is less clear. We evaluated the association of APOE genotype with risk of ischaemic stroke and assessed whether the observed effect was consistent with the effects of APOE genotype on LDL-C or other lipids and biomarkers of cardiovascular risk. METHODS: We conducted a systematic review of published and unpublished studies reporting on APOE genotype and ischaemic stroke. We pooled 41 studies (with a total of 9027 cases and 61,730 controls) using a Bayesian meta-analysis to calculate the odds ratios (ORs) for ischaemic stroke with APOE genotype. To better evaluate potential mechanisms for any observed effect, we also conducted a pooled analysis of primary data using 16 studies (up to 60,883 individuals) of European ancestry. We evaluated the association of APOE genotype with lipids, other circulating biomarkers of cardiovascular risk and carotid intima-media thickness (C-IMT). RESULTS: The ORs for association of APOE genotypes with ischaemic stroke were: 1.09 (95% credible intervals (CrI): 0.84-1.43) for ε2/ε2; 0.85 (95% CrI: 0.78-0.92) for ε2/ε3; 1.05 (95% CrI: 0.89-1.24) for ε2/ε4; 1.05 (95% CrI: 0.99-1.12) for ε3/ε4; and 1.12 (95% CrI: 0.94-1.33) for ε4/ε4 using the ε3/ε3 genotype as the reference group. A regression analysis that investigated the effect of LDL-C (using APOE as the instrument) on ischaemic stroke showed a positive dose-response association with an OR of 1.33 (95% CrI: 1.17, 1.52) per 1 mmol/l increase in LDL-C. In the separate pooled analysis, APOE genotype was linearly and positively associated with levels of LDL-C (P-trend: 2 × 10(-152)), apolipoprotein B (P-trend: 8.7 × 10(-06)) and C-IMT (P-trend: 0.001), and negatively and linearly associated with apolipoprotein E (P-trend: 6 × 10(-26)) and HDL-C (P-trend: 1.6 × 10(-12)). Associations with lipoprotein(a), C-reactive protein and triglycerides were non-linear. CONCLUSIONS: In people of European ancestry, APOE genotype showed a positive dose-response association with LDL-C, C-IMT and ischaemic stroke. However, the association of APOE ε2/ε2 genotype with ischaemic stroke requires further investigation. This cross-domain concordance supports a causal role of LDL-C on ischaemic stroke.

Are myocardial infarction--associated single-nucleotide polymorphisms associated with ischemic stroke?

BACKGROUND AND PURPOSE: Ischemic stroke (IS) shares many common risk factors with coronary artery disease (CAD). We hypothesized that genetic variants associated with myocardial infarction (MI) or CAD may be similarly involved in the etiology of IS. To test this hypothesis, we evaluated whether single-nucleotide polymorphisms (SNPs) at 11 different loci recently associated with MI or CAD through genome-wide association studies were associated with IS. METHODS: Meta-analyses of the associations between the 11 MI-associated SNPs and IS were performed using 6865 cases and 11 395 control subjects recruited from 9 studies. SNPs were either genotyped directly or imputed; in a few cases a surrogate SNP in high linkage disequilibrium was chosen. Logistic regression was performed within each study to obtain study-specific ßs and standard errors. Meta-analysis was conducted using an inverse variance weighted approach assuming a random effect model. RESULTS: Despite having power to detect odds ratio of 1.09-1.14 for overall IS and 1.20-1.32 for major stroke subtypes, none of the SNPs were significantly associated with overall IS and/or stroke subtypes after adjusting for multiple comparisons. CONCLUSIONS: Our results suggest that the major common loci associated with MI risk do not have effects of similar magnitude on overall IS but do not preclude moderate associations restricted to specific IS subtypes. Disparate mechanisms may be critical in the development of acute ischemic coronary and cerebrovascular events.

X-linked megalocornea caused by mutations in CHRDL1 identifies an essential role for ventroptin in anterior segment development.

X-linked megalocornea (MGC1) is an ocular anterior segment disorder characterized by an increased cornea diameter and deep anterior chamber evident at birth and later onset of mosaic corneal degeneration (shagreen), arcus juvenilis, and presenile cataracts. We identified copy-number variation, frameshift, missense, splice-site and nonsense mutations in the Chordin-like 1 gene (CHRDL1) on Xq23 as the cause of the condition in seven MGC1 families. CHRDL1 encodes ventroptin, a bone morphogenic protein antagonist with a proposed role in specification of topographic retinotectal projections. Electrophysiological evaluation revealed mild generalized cone system dysfunction and, in one patient, an interhemispheric asymmetry in visual evoked potentials. We show that CHRDL1 is expressed in the developing human cornea and anterior segment in addition to the retina. We explored the impact of loss of ventroptin function on brain function and morphology in vivo. CHRDL1 is differentially expressed in the human fetal brain, and there is high expression in cerebellum and neocortex. We show that MGC1 patients have a superior cognitive ability despite a striking focal loss of myelination of white matter. Our findings reveal an unexpected requirement for ventroptin during anterior segment development and the consequences of a lack of function in the retina and brain.

Siblings with ischemic stroke study: results of a genome-wide scan for stroke loci.

BACKGROUND AND PURPOSE: Ischemic stroke has a strong familial component to risk. The Siblings With Ischemic Stroke Study (SWISS) is a genome-wide, family-based analysis that included use of imputed genotypes. The Siblings With Ischemic Stroke Study was conducted to examine the associations between single-nucleotide polymorphisms (SNPs) and risk of stroke and stroke subtypes within pairs. METHODS: The Siblings With Ischemic Stroke Study enrolled 312 probands with ischemic stroke from 70 US and Canadian centers. Affected siblings were ascertained by centers and confirmed by central record review; unaffected siblings were ascertained by telephone contact. Ischemic stroke was subtyped according to Trial of Org 10172 in Acute Stroke Treatment criteria. Genotyping was performed with an Illumina 610 quad array (probands) and an Illumina linkage V array (affected siblings). SNPs were imputed by using 1000 Genomes Project data and MACH software. Family-based association analyses were conducted by using the sibling transmission-disequilibrium test. RESULTS: For all pairs, the correlation of age at stroke within pairs of affected siblings was r=0.83 (95% CI, 0.78-0.86; P<2.2×10(-16)). The correlation did not differ substantially by subtype. The concordance of stroke subtypes among affected pairs was 33.8% (kappa=0.13; P=5.06×10(-4)) and did not differ by age at stroke in the proband. Although no SNP achieved genome-wide significance for risk of ischemic stroke, there was clustering of the most associated SNPs on chromosomes 3p (neuronal nitric oxide synthase) and 6p. CONCLUSIONS: Stroke subtype and age at stroke in affected sibling pairs exhibit significant clustering. No individual SNP reached genome-wide significance. However, 2 promising candidate loci were identified, including 1 that contains neuronal nitric oxide synthase, although these risk loci warrant further examination in larger sample collections.

Genomic risk profiling of ischemic stroke: results of an international genome-wide association meta-analysis.

INTRODUCTION: Familial aggregation of ischemic stroke derives from shared genetic and environmental factors. We present a meta-analysis of genome-wide association scans (GWAS) from 3 cohorts to identify the contribution of common variants to ischemic stroke risk. METHODS: This study involved 1464 ischemic stroke cases and 1932 controls. Cases were genotyped using the Illumina 610 or 660 genotyping arrays; controls, with Illumina HumanHap 550Kv1 or 550Kv3 genotyping arrays. Imputation was performed with the 1000 Genomes European ancestry haplotypes (August 2010 release) as a reference. A total of 5,156,597 single-nucleotide polymorphisms (SNPs) were incorporated into the fixed effects meta-analysis. All SNPs associated with ischemic stroke (P<1×10(-5)) were incorporated into a multivariate risk profile model. RESULTS: No SNP reached genome-wide significance for ischemic stroke (P<5×10(-8)). Secondary analysis identified a significant cumulative effect for age at onset of stroke (first versus fifth quintile of cumulative profiles based on SNPs associated with late onset, ß = 14.77 [10.85,18.68], P = 5.5×10(-12)), as well as a strong effect showing increased risk across samples with a high propensity for stroke among samples with enriched counts of suggestive risk alleles (P<5×10(-6)). Risk profile scores based only on genomic information offered little incremental prediction. DISCUSSION: There is little evidence of a common genetic variant contributing to moderate risk of ischemic stroke. Quintiles based on genetic loading of alleles associated with a younger age at onset of ischemic stroke revealed a significant difference in age at onset between those in the upper and lower quintiles. Using common variants from GWAS and imputation, genomic profiling remains inferior to family history of stroke for defining risk. Inclusion of genomic (rare variant) information may be required to improve clinical risk profiling.

Effect modification by population dietary folate on the association between MTHFR genotype, homocysteine, and stroke risk: a meta-analysis of genetic studies and randomised trials.

BACKGROUND: The MTHFR 677C→T polymorphism has been associated with raised homocysteine concentration and increased risk of stroke. A previous overview showed that the effects were greatest in regions with low dietary folate consumption, but differentiation between the effect of folate and small-study bias was difficult. A meta-analysis of randomised trials of homocysteine-lowering interventions showed no reduction in coronary heart disease events or stroke, but the trials were generally set in populations with high folate consumption. We aimed to reduce the effect of small-study bias and investigate whether folate status modifies the association between MTHFR 677C→T and stroke in a genetic analysis and meta-analysis of randomised controlled trials. METHODS: We established a collaboration of genetic studies consisting of 237 datasets including 59,995 individuals with data for homocysteine and 20,885 stroke events. We compared the genetic findings with a meta-analysis of 13 randomised trials of homocysteine-lowering treatments and stroke risk (45,549 individuals, 2314 stroke events, 269 transient ischaemic attacks). FINDINGS: The effect of the MTHFR 677C→T variant on homocysteine concentration was larger in low folate regions (Asia; difference between individuals with TT versus CC genotype, 3·12 µmol/L, 95% CI 2·23 to 4·01) than in areas with folate fortification (America, Australia, and New Zealand, high; 0·13 µmol/L, -0·85 to 1·11). The odds ratio (OR) for stroke was also higher in Asia (1·68, 95% CI 1·44 to 1·97) than in America, Australia, and New Zealand, high (1·03, 0·84 to 1·25). Most randomised trials took place in regions with high or increasing population folate concentrations. The summary relative risk (RR) of stroke in trials of homocysteine-lowering interventions (0·94, 95% CI 0·85 to 1·04) was similar to that predicted for the same extent of homocysteine reduction in large genetic studies in populations with similar folate status (predicted RR 1·00, 95% CI 0·90 to 1·11). Although the predicted effect of homocysteine reduction from large genetic studies in low folate regions (Asia) was larger (RR 0·78, 95% CI 0·68 to 0·90), no trial has evaluated the effect of lowering of homocysteine on stroke risk exclusively in a low folate region. INTERPRETATION: In regions with increasing levels or established policies of population folate supplementation, evidence from genetic studies and randomised trials is concordant in suggesting an absence of benefit from lowering of homocysteine for prevention of stroke. Further large-scale genetic studies of the association between MTHFR 677C→T and stroke in low folate settings are needed to distinguish effect modification by folate from small-study bias. If future randomised trials of homocysteine-lowering interventions for stroke prevention are undertaken, they should take place in regions with low folate consumption. FUNDING: Full funding sources listed at end of paper (see Acknowledgments).