Hylke M Blauw

University Medical Center Utrecht, Utrecht, Provincie Utrecht, Netherlands

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Publications (28)211.67 Total impact

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    ABSTRACT: Genomic copy number variations (CNVs) and increased parental age are both associated with the risk to develop a variety of clinical neuropsychiatric disorders such as autism, schizophrenia and bipolar disorder. At the same time, it has been shown that the rate of transmitted de novo single nucleotide mutations is increased with paternal age. To address whether paternal age also affects the burden of structural genomic deletions and duplications, we examined various types of CNV burden in a large population sample from the Netherlands. Healthy participants with parental age information (n = 6,773) were collected at different University Medical Centers. CNVs were called with the PennCNV algorithm using Illumina genome-wide SNP array data. We observed no evidence in support of a paternal age effect on CNV load in the offspring. Our results were negative for global measures as well as several proxies for de novo CNV events in this unique sample. While recent studies suggest de novo single nucleotide mutation rate to be dominated by the age of the father at conception, our results strongly suggest that at the level of global CNV burden there is no influence of increased paternal age. While it remains possible that local genomic effects may exist for specific phenotypes, this study indicates that global CNV burden and increased father's age may be independent disease risk factors.
    Human Genetics 01/2013; · 4.63 Impact Factor
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    ABSTRACT: The exact pathway leading to neuron death and muscle atrophy in amyotrophic lateral sclerosis (ALS) has not yet been elucidated. Gene expression profile of spinal cord, blood and muscle could provide signalling pathways and systemic alterations useful for future biomarker development. In our study we compared whole genome expression profiles of lumbar spinal cord with peripheral blood and tibialis anterior muscle in 16 mutant SOD1-G93A mice and 15 wild-type littermates. In SOD1-G93A mice, 11 genes were significantly differentially expressed in spinal cord, and 16 genes in blood, while much larger transcriptional changes were noted in muscle (1745 genes significant; six overlapping with spinal cord (0.3%)) probably due to muscle atrophy. Overlap with spinal cord was enriched for significant genes in blood (six of 16 overlapping with spinal cord (37.5%)). Three genes were significantly down-regulated in all three tissues, and were closely related to mitochondrial function. Furthermore, clustering the significant genes in spinal cord and in blood, but not in muscle, could identify the SOD1-G93A mice. We conclude that blood gene expression profile overlapped with profile of spinal cord, allowing differentiation of SOD1-G93A mice from wild-type littermates. Blood gene expression profiling may be a promising biomarker for ALS patients.
    Amyotrophic lateral sclerosis and frontotemporal degeneration. 01/2013;
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    ABSTRACT: Mutations in NIPA1 cause Hereditary Spastic Paraplegia type 6, a neurodegenerative disease characterized by an (upper) motor neuron phenotype. Deletions of NIPA1 have been associated with a higher susceptibility to amyotrophic lateral sclerosis (ALS). The exact role of genetic variation in NIPA1 in ALS susceptibility and disease course is, however, not known. We sequenced the entire coding sequence of NIPA1 and genotyped a polyalanine repeat located in the first exon of NIPA1. A total of 2292 ALS patients and 2777 controls from three independent European populations were included. We identified two sequence variants that have a potentially damaging effect on NIPA1 protein function. Both variants were identified in ALS patients; no damaging variants were found in controls. Secondly, we found a significant effect of 'long' polyalanine repeat alleles on disease susceptibility: odds ratio = 1.71, P = 1.6 × 10(-4). Our analyses also revealed a significant effect of 'long' alleles on patient survival [hazard ratio (HR) = 1.60, P = 4.2 × 10(-4)] and on the age at onset of symptoms (HR = 1.37, P = 4.6 × 10(-3)). In patients carrying 'long' alleles, median survival was 3 months shorter than patients with 'normal' genotypes and onset of symptoms occurred 3.6 years earlier. Our data show that NIPA1 polyalanine repeat expansions are a common risk factor for ALS and modulate disease course.
    Human Molecular Genetics 03/2012; 21(11):2497-502. · 7.69 Impact Factor
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    ABSTRACT: To investigate the role of SMN1 and SMN2 copy number variation and point mutations in amyotrophic lateral sclerosis (ALS) pathogenesis in a large population. We conducted a genetic association study including 847 patients with ALS and 984 controls. We used multiplexed ligation-dependent probe amplification (MLPA) assays to determine SMN1 and SMN2 copy numbers and examined effects on disease susceptibility and disease course. Furthermore, we sequenced SMN genes to determine if SMN mutations were more prevalent in patients with ALS. A meta-analysis was performed with results from previous studies. SMN1 duplications were associated with ALS susceptibility (odds ratio [OR] 2.07, 95% confidence interval [CI] 1.34-3.20, p = 0.001). A meta-analysis with previous data including 3,469 individuals showed a similar effect: OR 1.85, 95% CI 1.18-2.90, p = 0.008). SMN1 deletions and SMN2 copy number status were not associated with ALS. SMN1 or SMN2 copy number variants had no effect on survival or the age at onset of the disease. We found no enrichment of SMN point mutations in patients with ALS. Our data provide firm evidence for a role of common SMN1 duplications in ALS, and raise new questions regarding the disease mechanisms involved.
    Neurology 02/2012; 78(11):776-80. · 8.25 Impact Factor
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    ABSTRACT: Amyotrophic lateral sclerosis (ALS) is a progressive, neurodegenerative disease characterized by loss of upper and lower motor neurons. ALS is considered to be a complex trait and genome-wide association studies (GWAS) have implicated a few susceptibility loci. However, many more causal loci remain to be discovered. Since it has been shown that genetic variants associated with complex traits are more likely to be eQTLs than frequency-matched variants from GWAS platforms, we conducted a two-stage genome-wide screening for eQTLs associated with ALS. In addition, we applied an eQTL analysis to finemap association loci. Expression profiles using peripheral blood of 323 sporadic ALS patients and 413 controls were mapped to genome-wide genotyping data. Subsequently, data from a two-stage GWAS (3,568 patients and 10,163 controls) were used to prioritize eQTLs identified in the first stage (162 ALS, 207 controls). These prioritized eQTLs were carried forward to the second sample with both gene-expression and genotyping data (161 ALS, 206 controls). Replicated eQTL SNPs were then tested for association in the second-stage GWAS data to find SNPs associated with disease, that survived correction for multiple testing. We thus identified twelve cis eQTLs with nominally significant associations in the second-stage GWAS data. Eight SNP-transcript pairs of highest significance (lowest p = 1.27 × 10(-51)) withstood multiple-testing correction in the second stage and modulated CYP27A1 gene expression. Additionally, we show that C9orf72 appears to be the only gene in the 9p21.2 locus that is regulated in cis, showing the potential of this approach in identifying causative genes in association loci in ALS. This study has identified candidate genes for sporadic ALS, most notably CYP27A1. Mutations in CYP27A1 are causal to cerebrotendinous xanthomatosis which can present as a clinical mimic of ALS with progressive upper motor neuron loss, making it a plausible susceptibility gene for ALS.
    PLoS ONE 01/2012; 7(4):e35333. · 3.53 Impact Factor
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    ABSTRACT: Several studies have suggested an increased frequency of variants in the gene encoding angiogenin (ANG) in patients with amyotrophic lateral sclerosis (ALS). Interestingly, a few ALS patients carrying ANG variants also showed signs of Parkinson disease (PD). Furthermore, relatives of ALS patients have an increased risk to develop PD, and the prevalence of concomitant motor neuron disease in PD is higher than expected based on chance occurrence. We therefore investigated whether ANG variants could predispose to both ALS and PD. We reviewed all previous studies on ANG in ALS and performed sequence experiments on additional samples, which allowed us to analyze data from 6,471 ALS patients and 7,668 controls from 15 centers (13 from Europe and 2 from the USA). We sequenced DNA samples from 3,146 PD patients from 6 centers (5 from Europe and 1 from the USA). Statistical analysis was performed using the variable threshold test, and the Mantel-Haenszel procedure was used to estimate odds ratios. Analysis of sequence data from 17,258 individuals demonstrated a significantly higher frequency of ANG variants in both ALS and PD patients compared to control subjects (p = 9.3 × 10(-6) for ALS and p = 4.3 × 10(-5) for PD). The odds ratio for any ANG variant in patients versus controls was 9.2 for ALS and 6.7 for PD. The data from this multicenter study demonstrate that there is a strong association between PD, ALS, and ANG variants. ANG is a genetic link between ALS and PD.
    Annals of Neurology 12/2011; 70(6):964-73. · 11.19 Impact Factor
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    ABSTRACT: To investigate whether submicroscopic copy number variants (CNVs) on the X chromosome can be identified in women with primary ovarian insufficiency (POI), defined as spontaneous secondary amenorrhea before 40 years of age accompanied by follicle-stimulating hormone levels above 40 IU/L on at least two occasions. Analysis of intensity data of single nucleotide polymorphism (SNP) probes generated by genomewide Illumina 370k CNV BeadChips, followed by the validation of identified loci using a custom designed ultra-high-density comparative genomic hybridization array containing 48,325 probes evenly distributed over the X chromosome. Multicenter genetic cohort study in the Netherlands. 108 Dutch Caucasian women with POI, 97 of whom passed quality control, who had a normal karyogram and absent fragile X premutation, and 235 healthy Dutch Caucasian women as controls. None. Amount and locus of X chromosomal microdeletions or duplications. Intensity differences between SNP probes identify microdeletions and duplications. The initial analysis identified an overrepresentation of deletions in POI patients. Moreover, CNVs in two genes on the Xq21.3 locus (i.e., PCDH11X and TGIF2LX) were statistically significantly associated with the POI phenotype. Mean size of identified CNVs was 262 kb. However, in the validation study the identified putative Xq21.3 deletions samples did not show deviations in intensities in consecutive probes. X chromosomal submicroscopic CNVs do not play a major role in Caucasian POI patients. We provide guidelines on how submicroscopic cytogenetic POI research should be conducted.
    Fertility and sterility 02/2011; 95(5):1584-8.e1. · 3.97 Impact Factor
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    ABSTRACT: Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease selectively affecting motor neurons in the brain and spinal cord. Recent genome-wide association studies (GWASs) have identified several common variants which increase disease susceptibility. In contrast, rare copy-number variants (CNVs), which have been associated with several neuropsychiatric traits, have not been studied for ALS in well-powered study populations. To examine the role of rare CNVs in ALS susceptibility, we conducted a CNV association study including over 19,000 individuals. In a genome-wide screen of 1875 cases and 8731 controls, we did not find evidence for a difference in global CNV burden between cases and controls. In our association analyses, we identified two loci that met our criteria for follow-up: the DPP6 locus (OR = 3.59, P = 6.6 × 10(-3)), which has already been implicated in ALS pathogenesis, and the 15q11.2 locus, containing NIPA1 (OR = 12.46, P = 9.3 × 10(-5)), the gene causing hereditary spastic paraparesis type 6 (HSP 6). We tested these loci in a replication cohort of 2559 cases and 5887 controls. Again, results were suggestive of association, but did not meet our criteria for independent replication: DPP6 locus: OR = 1.92, P = 0.097, pooled results: OR = 2.64, P = 1.4 × 10(-3); NIPA1: OR = 3.23, P = 0.041, pooled results: OR = 6.20, P = 2.2 × 10(-5)). Our results highlight DPP6 and NIPA1 as candidates for more in-depth studies. Unlike other complex neurological and psychiatric traits, rare CNVs with high effect size do not play a major role in ALS pathogenesis.
    Human Molecular Genetics 10/2010; 19(20):4091-9. · 7.69 Impact Factor
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    ABSTRACT: We conducted a genome-wide association study among 2,323 individuals with sporadic amyotrophic lateral sclerosis (ALS) and 9,013 control subjects and evaluated all SNPs with P < 1.0 x 10(-4) in a second, independent cohort of 2,532 affected individuals and 5,940 controls. Analysis of the genome-wide data revealed genome-wide significance for one SNP, rs12608932, with P = 1.30 x 10(-9). This SNP showed robust replication in the second cohort (P = 1.86 x 10(-6)), and a combined analysis over the two stages yielded P = 2.53 x 10(-14). The rs12608932 SNP is located at 19p13.3 and maps to a haplotype block within the boundaries of UNC13A, which regulates the release of neurotransmitters such as glutamate at neuromuscular synapses. Follow-up of additional SNPs showed genome-wide significance for two further SNPs (rs2814707, with P = 7.45 x 10(-9), and rs3849942, with P = 1.01 x 10(-8)) in the combined analysis of both stages. These SNPs are located at chromosome 9p21.2, in a linkage region for familial ALS with frontotemporal dementia found previously in several large pedigrees.
    Nature Genetics 09/2009; 41(10):1083-7. · 35.21 Impact Factor
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    BMC Genomics 09/2009; · 4.40 Impact Factor
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    ABSTRACT: Amyotrophic lateral sclerosis is a degenerative disorder of motor neurons that typically develops in the 6th decade and is uniformly fatal, usually within 5 years. To identify genetic variants associated with susceptibility and phenotypes in sporadic ALS, we performed a genome-wide SNP analysis in sporadic ALS cases and controls. A total of 288,357 SNPs were screened in a set of 1,821 sporadic ALS cases and 2,258 controls from the U.S. and Europe. Survival analysis was performed using 1,014 deceased sporadic cases. Top results for susceptibility were further screened in an independent sample set of 538 ALS cases and 556 controls. SNP rs1541160 within the KIFAP3 gene (encoding a kinesin-associated protein) yielded a genome-wide significant result (P = 1.84 x 10(-8)) that withstood Bonferroni correction for association with survival. Homozygosity for the favorable allele (CC) conferred a 14.0 months survival advantage. Sequence, genotypic and functional analyses revealed that there is linkage disequilibrium between rs1541160 and SNP rs522444 within the KIFAP3 promoter and that the favorable alleles of rs1541160 and rs522444 correlate with reduced KIFAP3 expression. No SNPs were associated with risk of sporadic ALS, site of onset, or age of onset. We have identified a variant within the KIFAP3 gene that is associated with decreased KIFAP3 expression and increased survival in sporadic ALS. These findings support the view that genetic factors modify phenotypes in this disease and that cellular motor proteins are determinants of motor neuron viability.
    Proceedings of the National Academy of Sciences 06/2009; 106(22):9004-9. · 9.81 Impact Factor
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    ABSTRACT: Illumina genotyping arrays provide information on DNA copy number. Current methodology for their analysis assumes linkage equilibrium across adjacent markers. This is unrealistic, given the markers high density, and can result in reduced specificity. Another limitation of current methods is that they cannot be directly applied to the analysis of multiple samples with the goal of detecting copy number polymorphisms and their association with traits of interest. We propose a new Hidden Markov Model for Illumina genotype data, that takes into account linkage disequilibrium between adjacent loci. Our framework also allows for location specific deletion/duplication rates. When multiple samples are available, we describe a methodology for their analysis that simultaneously reconstructs the copy number states in each sample and identifies genomic locations with increased variability in copy number in the population. This approach can be extended to test association between copy number variants and a disease trait. We show that taking into account linkage disequilibrium between adjacent markers can increase the specificity of a HMM in reconstructing copy number variants, especially single copy deletions. Our multisample approach is computationally practical and can increase the power of association studies.
    Human Heredity 05/2009; 68(1):1-22. · 1.57 Impact Factor
  • Neurology 04/2009; 72(13):1184-5. · 8.25 Impact Factor
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    ABSTRACT: The recent identification of copy-number variation in the human genome has opened up new avenues for the discovery of positional candidate genes underlying complex genetic disorders, especially in the field of psychiatric disease. One major challenge that remains is pinpointing the susceptibility genes in the multitude of disease-associated loci. This challenge may be tackled by reconstruction of functional gene-networks from the genes residing in these loci. We applied this approach to autism spectrum disorder (ASD), and identified the copy-number changes in the DNA of 105 ASD patients and 267 healthy individuals with Illumina Humanhap300 Beadchips. Subsequently, we used a human reconstructed gene-network, Prioritizer, to rank candidate genes in the segmental gains and losses in our autism cohort. This analysis highlighted several candidate genes already known to be mutated in cognitive and neuropsychiatric disorders, including RAI1, BRD1, and LARGE. In addition, the LARGE gene was part of a sub-network of seven genes functioning in glycobiology, present in seven copy-number changes specifically identified in autism patients with limited co-morbidity. Three of these seven copy-number changes were de novo in the patients. In autism patients with a complex phenotype and healthy controls no such sub-network was identified. An independent systematic analysis of 13 published autism susceptibility loci supports the involvement of genes related to glycobiology as we also identified the same or similar genes from those loci. Our findings suggest that the occurrence of genomic gains and losses of genes associated with glycobiology are important contributors to the development of ASD.
    PLoS ONE 02/2009; 4(5):e5324. · 3.53 Impact Factor
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    ABSTRACT: Amyotrophic lateral sclerosis (ALS) is an unrelenting neurodegenerative condition characterized by adult-onset loss of motor neurons. Genetic risk factors have been implicated in ALS susceptibility. Copy number variants (CNVs) account for more inter-individual genetic variation than SNPs and have the capacity to alter gene dose and phenotype. We sought to identify the contribution both of commonly polymorphic CNVs and rare ALS-specific CNVs to sporadic ALS (SALS). Using high-density genome-wide data from 408 Irish individuals and 868 Dutch individuals and the QuantiSNP CNV-detection algorithm, we showed that no common CNV locus is significantly associated with ALS risk. However, we identified 39 recurrent CNV loci and 16 replicated ALS-specific gene dose alterations that occur exclusively in patients with ALS and do not occur in more than 11 000 previously identified CNVs in the Database of Genomic Variation. Ataxin genes and the hereditary haemochromatosis locus were implicated along with ENSG00000176605, an uncharacterized gene on chromosome 14. Our data support the hypothesis that multiple rare CNVs may contribute risk for SALS. Future work should seek to profile the contribution of CNVs located in regions not covered on the present SNP platforms.
    Human Molecular Genetics 09/2008; 17(21):3392-8. · 7.69 Impact Factor
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    ABSTRACT: Copy-number variation (CNV) is a major contributor to human genetic variation. Recently, CNV associations with human disease have been reported. Many genome-wide association (GWA) studies in complex diseases have been performed with sets of biallelic single-nucleotide polymorphisms (SNPs), but the available CNV methods are still limited. We present a new method (TriTyper) that can infer genotypes in case-control data sets for deletion CNVs, or SNPs with an extra, untyped allele at a high-resolution single SNP level. By accounting for linkage disequilibrium (LD), as well as intensity data, calling accuracy is improved. Analysis of 3102 unrelated individuals with European descent, genotyped with Illumina Infinium BeadChips, resulted in the identification of 1880 SNPs with a common untyped allele, and these SNPs are in strong LD with neighboring biallelic SNPs. Simulations indicate our method has superior power to detect associations compared to biallelic SNPs that are in LD with these SNPs, yet without increasing type I errors, as shown in a GWA analysis in celiac disease. Genotypes for 1204 triallelic SNPs could be fully imputed, with only biallelic-genotype calls, permitting association analysis of these SNPs in many published data sets. We estimate that 682 of the 1655 unique loci reflect deletions; this is on average 99 deletions per individual, four times greater than those detected by other methods. Whereas the identified loci are strongly enriched for known deletions, 61% have not been reported before. Genes overlapping with these loci more often have paralogs (p = 0.006) and biologically interact with fewer genes than expected (p = 0.004).
    The American Journal of Human Genetics 06/2008; 82(6):1316-33. · 11.20 Impact Factor
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    ABSTRACT: Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease characterised by the selective death of motor neurons in the brain and spinal cord. Genetic risk factors have been implicated in susceptibility to ALS. Like single nucleotide polymorphisms (SNPs), copy-number variants (CNVs) are a source of genetic variation that have important effects on gene expression and disease phenotypes, and our aim was to identify CNVs that predispose to sporadic ALS. We did a genome-wide screen for CNVs by analysis of Illumina 317K SNP arrays for 406 patients with sporadic ALS and 404 controls. We examined CNVs for association with ALS, and used the Kyoto Encyclopedia of Genes and Genomes database and the Gene Ontology database to investigate the functionality of genes that were deleted exclusively in patients with ALS. We detected 2328 CNVs in 810 individuals. No CNV locus was significantly associated with sporadic ALS. 406 genes were duplicated or deleted exclusively in patients with ALS and have not been reported in previous studies of CNVs. Of the 390 genes heterozygously deleted in patients with sporadic ALS, 155 (40%) deletions were recorded exclusively in patients. By contrast, of the 323 genes heterozygously deleted in control participants, only 51 (16%) were exclusive to the controls (p=2.15 x 10(-12) for difference between groups). Products of the genes deleted specifically in patients with sporadic ALS include proteins involved in oxidative phosphorylation, regulation of the actin cytoskeleton, and interactions between cytokines and their receptors. Common CNVs in the regions of the genome represented on the SNP array are unlikely to be associated with sporadic ALS. However, the high number of genes deleted specifically in patients with ALS strongly suggests that multiple rare deletions might have an important role in ALS pathogenesis.
    The Lancet Neurology 05/2008; 7(4):319-26. · 23.92 Impact Factor
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    ABSTRACT: We identified a SNP in the DPP6 gene that is consistently strongly associated with susceptibility to amyotrophic lateral sclerosis (ALS) in different populations of European ancestry, with an overall P value of 5.04 x 10(-8) in 1,767 cases and 1,916 healthy controls and with an odds ratio of 1.30 (95% confidence interval (CI) of 1.18-1.43). Our finding is the first report of a genome-wide significant association with sporadic ALS and may be a target for future functional studies.
    Nature Genetics 02/2008; 40(1):29-31. · 35.21 Impact Factor
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    ABSTRACT: Methods We did a genome-wide screen for CNVs by analysis of Illumina 317K SNP arrays for 406 patients with sporadic ALS and 404 controls. We examined CNVs for association with ALS, and used the Kyoto Encyclopedia of Genes and Genomes database and the Gene Ontology database to investigate the functionality of genes that were deleted exclusively in patients with ALS. Findings We detected 2328 CNVs in 810 individuals. No CNV locus was signifi cantly associated with sporadic ALS. 406 genes were duplicated or deleted exclusively in patients with ALS and have not been reported in previous studies of CNVs. Of the 390 genes heterozygously deleted in patients with sporadic ALS, 155 (40%) deletions were recorded exclusively in patients. By contrast, of the 323 genes heterozygously deleted in control participants, only 51 (16%) were exclusive to the controls (p=2·15x10 - ¹² for diff erence between groups). Products of the genes deleted specifi cally in patients with sporadic ALS include proteins involved in oxidative phosphorylation, regulation of the actin cytoskeleton, and interactions between cytokines and their receptors.
    01/2008;
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    ABSTRACT: Amyotrophic lateral sclerosis (ALS) is a devastating disease characterised by progressive degeneration of motor neurons in the brain and spinal cord. ALS is thought to be multifactorial, with both environmental and genetic causes. Our aim was to identify genetic variants that predispose for sporadic ALS. We did a three-stage genome-wide association study in 461 patients with ALS and 450 controls from The Netherlands, using Illumina 300K single-nucleotide polymorphism (SNP) chips. The SNPs that were most strongly associated with ALS were analysed in a further 876 patients and 906 controls in independent sample series from The Netherlands, Belgium, and Sweden. We also investigated the possible pathological functions of associated genes using expression data from whole blood of patients with sporadic ALS and of control individuals who were included in the genome-wide association study. A genetic variant in the inositol 1,4,5-triphosphate receptor 2 gene (ITPR2) was associated with ALS (p=0.012 after Bonferroni correction). Combined analysis of all samples (1337 patients and 1356 controls) confirmed this association (p=3.28x10(-6), odds ratio 1.58, 95% CI 1.30-1.91). ITPR2 expression was greater in the peripheral blood of 126 ALS patients than in that of 126 healthy controls (p=0.00016). Genetic variation in ITPR2 is a susceptibility factor for ALS. ITPR2 is a strong candidate susceptibility gene for ALS because it is involved in glutamate-mediated neurotransmission, is one of the main regulators of intracellular calcium concentrations, and has an important role in apoptosis.
    The Lancet Neurology 11/2007; 6(10):869-77. · 23.92 Impact Factor