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John D Rioux

Publications and source records attributed to John D Rioux.

At least 37 records · Page 2Linked to original sources
PubMed2005

Paths to understanding the genetic basis of autoimmune disease.

Some people inherit an unfortunate combination of genetic sequences, such that exposure to an external trigger causes their immune response to turn on their own tissues. Although mutations in a single gene can cause autoimmunity, most autoimmune diseases are associated with several sequence variants. Marked advances in genetic resources and tools are now making it possible to identify the sequence variants that contribute to autoimmune diseases--promising a better understanding of how we normally remain tolerant of our own tissue components, and how this goes wrong in autoimmune disease.

Autoimmune Diseases↗
PubMed2005

A high-resolution linkage-disequilibrium map of the human major histocompatibility complex and first generation of tag single-nucleotide polymorphisms.

Autoimmune, inflammatory, and infectious diseases present a major burden to human health and are frequently associated with loci in the human major histocompatibility complex (MHC). Here, we report a high-resolution (1.9 kb) linkage-disequilibrium (LD) map of a 4.46-Mb fragment containing the MHC in U.S. pedigrees with northern and western European ancestry collected by the Centre d'Etude du Polymorphisme Humain (CEPH) and the first generation of haplotype tag single-nucleotide polymorphisms (tagSNPs) that provide up to a fivefold increase in genotyping efficiency for all future MHC-linked disease-association studies. The data confirm previously identified recombination hotspots in the class II region and allow the prediction of numerous novel hotspots in the class I and class III regions. The region of longest LD maps outside the classic MHC to the extended class I region spanning the MHC-linked olfactory-receptor gene cluster. The extended haplotype homozygosity analysis for recent positive selection shows that all 14 outlying haplotype variants map to a single extended haplotype, which most commonly bears HLA-DRB1*1501. The SNP data, haplotype blocks, and tagSNPs analysis reported here have been entered into a multidimensional Web-based database (GLOVAR), where they can be accessed and viewed in the context of relevant genome annotation. This LD map allowed us to give coordinates for the extremely variable LD structure underlying the MHC.

Haplotypes↗
PubMed2005

Association analysis of the R620W polymorphism of protein tyrosine phosphatase PTPN22 in systemic lupus erythematosus families: increased T allele frequency in systemic lupus erythematosus patients with autoimmune thyroid disease.

OBJECTIVE: Recent case-control studies show associations of the minor T allele (of the C1858T single-nucleotide polymorphism corresponding to the R620W amino acid substitution) of PTPN22 with multiple autoimmune diseases, including systemic lupus erythematosus (SLE). We performed family-based association studies of this polymorphism in 4 independent cohorts containing SLE patients and their parents and/or other family members. METHODS: A total of 2,689 individuals from 902 independent Caucasian families with SLE were genotyped using polymerase chain reaction pyrosequencing (cohorts 1 and 2) and the Sequenom MassArray system (cohorts 3 and 4). The transmission disequilibrium test (TDT) and the pedigree disequilibrium test (PDT) were conducted to assess the evidence of association. RESULTS: The 1858 C > T allele frequencies of the parents showed no deviation from Hardy-Weinberg equilibrium within each cohort. No evidence of preferential transmission of the T allele from heterozygous parents to their affected offspring was observed in each of the 4 cohorts or in the combined sample. Consistent with the TDT result, the PDT analysis revealed no significant association between the T allele and SLE. In 54 of the 661 SLE patients (cohorts 1 and 3) with documented autoimmune thyroid disease, the T allele frequency was higher than in individuals with SLE alone (16.7% versus 8.5%; P = 0.008, odds ratio 2.16 [95% confidence interval 1.25-3.72]). CONCLUSION: The R620W polymorphism of the PTPN22 gene is not a major risk allele for SLE susceptibility in our sample of Caucasian individuals from northern America, the UK, or Finland, but it appears to be a risk factor for the concurrent autoimmune diseases of autoimmune thyroid disease and SLE.

Arginine↗
PubMed2005

Haplotype structure of TNFRSF5-TNFSF5 (CD40-CD40L) and association analysis in systemic lupus erythematosus.

Systemic lupus erythematosus (SLE) is a prototypic autoimmune disease that is caused by genetic and environmental factors. The tumour necrosis factor (TNF) superfamily of genes play a central role in immune regulation and have been proposed to be involved in the development of SLE. TNFRSF5 (CD40) falls on 20q11-13, a region linked with SLE in three independent genome-wide studies. TNFSF5 (CD40L) falls on Xq26 and is the ligand for TNFRSF5. Seven single-nucleotide polymorphisms (SNPs) in CD40 and eight SNPs in CD40L were looked at for linkage disequilibrium (LD) and haplotype analysis in European-Caucasians. Limited haplotype diversity was observed across CD40 and CD40L, and >97% of the diversity was captured. We also examined the association of SNPs and haplotypes in CD40 and CD40L with SLE in European-Caucasians. There was no evidence of association for CD40 or CD40L in 408 European-Caucasian families with SLE from UK. Haplotype tagging SNPs (htSNPs) are made known, which will facilitate analysis for susceptibility in other autoimmune diseases and risk for infectious disease.

CD40 Antigens↗
PubMed2005

Association of DLG5 R30Q variant with inflammatory bowel disease.

Crohn's disease (CD) and ulcerative colitis (UC) are chronic inflammatory diseases of the gastrointestinal system known as the inflammatory bowel diseases (IBD). Recently, Stoll and colleagues reported a novel finding of genetic variation in the DLG5 gene that is associated with IBD (CD and UC combined). We present here a study of the genetic variation described in that report in two well-powered, independent case-control cohorts and one family-based collection, and confirm the proposed association between IBD and the R30Q variant of DLG5 in two of the three studies. We are, however, unable to replicate the other proposed association to the common haplotype described in Stoll et al and suggest that this other finding could conceivably have been partially a statistical fluctuation and partially a result of LD with the replicated R30Q association. This study provides support for the hypothesis that DLG5 constitutes a true IBD risk factor of modest effect.

Case-Control Studies↗
PubMed2005

Mapping autoimmune disease genes in humans: lessons from IBD and SLE.

The inflammatory bowel diseases (IBD) and systemic lupus erythematosus (SLE) are common autoimmune diseases that affect 2-3 million people in the USA alone. Crohn's disease (CD) and ulcerative colitis (UC), the inflammatory bowel diseases, are idiopathic, chronic inflammatory disorders of the gastrointestinal tract. SLE is a chronic, multi-system autoimmune disease that generally presents in women of childbearing age as fatigue, arthralgia and rash. Although the aetiology of these two diseases is not fully known, it is believed that genetic, hormonal and environmental influences contribute to susceptibility. Genomewide linkage scans in IBD have revealed significant loci that, upon comprehensive association mapping strategies, yield what are believed to be causal susceptibility alleles. Human linkage studies performed to date in SLE have not been as informative, although genetic mapping in mouse models of SLE as well as candidate gene approaches have provided important clues to the genetic susceptibility in humans. We will examine how some of the recent advances in our understanding of genetic variation in the human genome are greatly improving our ability to map autoimmune disease genes in humans.

Autoimmune Diseases↗
PubMed2004

Genomewide search and association studies in a Finnish celiac disease population: Identification of a novel locus and replication of the HLA and CTLA4 loci.

It has been reported that celiac disease (CD) is strongly associated with the HLA-DQ2 alleles DQA1*0501 and DQB1*0201. However, this association only accounts for a portion of the genetic component of CD. Several non-HLA loci and candidate genes that potentially contribute to CD susceptibility have been reported, but have not been confirmed. The aim of this study was to identify loci that contribute to disease susceptibility in a CD population from Finland. We performed a genomewide linkage scan and identified two regions of significant linkage to CD (6p and 2q23-32) and one region of suggestive linkage (10p). We also performed targeted typing and analyses that replicated the associations of the HLA and CTLA4 loci.

Adolescent↗
PubMed2004

Enhancing linkage analysis of complex disorders: an evaluation of high-density genotyping.

To explore the potential value of recently developed high-density linkage mapping methods in the analysis of complex disease we have regenotyped five nuclear families first studied in the 1996 UK multiple sclerosis linkage genome screen, using Applied Biosystems high-density microsatellite linkage mapping set, the Illumina BeadArray linkage mapping panel (version 3) and the Affymetrix GeneChip Human Mapping 10K array. We found that genotyping success, information extraction and genotyping accuracy were improved with all systems. These improvements were particularly marked with the SNP-based methods (Illumina and Affymetrix), with little difference between these. The extent of additional information extracted is considerable, indicating that reanalysis of existing multiplex families using these newer systems would substantially increase power.

Chromosome Mapping↗
PubMed2004

Inflammatory bowel disease susceptibility loci defined by genome scan meta-analysis of 1952 affected relative pairs.

Crohn's disease and ulcerative colitis (the inflammatory bowel diseases) have a strong genetic component. Although over 20 putative susceptibility loci have been identified by individual genome scans, the majority of these loci have not been replicated. Many individual studies are at the lower limit of acceptable power for complex disease linkage analysis. Genome scan meta-analysis (GSMA), by use of sample sizes an order of magnitude greater than individual linkage studies, has increased power to detect novel loci, may confirm or refute regions detected in smaller individual studies, and enables regions to be prioritized for further gene identification efforts. Genome scan data (markers, significance scores) were obtained from 10 separate studies and meta-analysis was performed using the GSMA method. These studies comprised 1952 inflammatory bowel disease, 1068 Crohn's disease and 457 ulcerative colitis affected relative pairs. Study results were divided into 34 cM chromosomal bins, ranked, weighted by study size, summed across studies and bin-by-bin significance obtained by simulation. A region on chromosome 6p (containing the HLA) met genome wide significance for inflammatory bowel disease. Loci meeting suggestive significance for inflammatory bowel disease were 2q, 3q, 5q, 7q and 16 (NOD2/CARD15 region); Crohn's disease, 2q, 3q, 6p, 16 (NOD2/CARD15 region), 17q, 19p; and ulcerative colitis, 2q. Clustering of adjacent bins was observed for chromosomes 6p, 16, 19p. The meta-analysis has identified novel loci and prioritized genomic regions for further gene identification studies.

Chromosomes↗
PubMed2004

Genome scan analyses and positional cloning strategy in IBD: successes and limitations.

The past decade has witnessed a tremendous expansion of our knowledge-base of genetics of inflammatory bowel disease. To a large extent, this progress reflects the scientific innovation and impact of the human genome project, which has fueled many laboratory-based studies focusing on the molecular genetics of Crohn's disease and ulcerative colitis. The complementary strategies of genome-wide linkage scanning and candidate gene analysis uncovered a number of genetic loci associated with IBD susceptibility. Notably, the identification of the IBD1 and IBD5 loci is a major scientific discovery. Although many issues related to the function and expression of these genes await elucidation, there is a shared optimism that pivotal clinical applications will emerge from these investigations.

Carrier Proteins↗
PubMed2004

New approaches to gene hunting in IBD.

Without a doubt, one of the greatest promises of the human genome project has been the expectation that its completion will rapidly accelerate the discovery of the heritable components of complex disease. Such discoveries will educate us as to the underlying causes of disease and hold out great promise for medicine in the future by potentially enabling the prediction of individual risk, the selection of therapy based on genetic profile, and a more rational approach to designing drugs. Unfortunately, discovering these genetic components of complex disease has been much more difficult than initially hoped and, to date, very few positive results have been conclusively confirmed. We review here approaches to tackling the problem of gene finding in complex disease with an emphasis on new approaches that may complement and supplement existing methods that have been making only slow progress toward the elucidation of the genetic architecture of disease. Along the way we highlight the successful work by many groups in studying the genetics of IBD, where significant successes have arrived earlier than in most other complex human diseases.

Chromosome Mapping↗
PubMed2004

Progress towards identifying inflammatory bowel disease susceptibility genes.

Genomewide searches have identified about a dozen genomic regions potentially containing inflammatory bowel disease (IBD) susceptibility loci. Although some were observed in more than one genome scan or in replication studies, no one locus has been identified in all studies. This apparent lack of consistency is explained by the modest effect of most genetic loci in complex traits and by the modest power and the sampling variance of individual family-based studies. Despite these challenges, the field of IBD genetics found convincing evidence of linkage and, more recently, of genetic sequence variants that are strongly associated with disease. The first example was that of the IBD1 locus on chromosome 16, a linkage region confirmed by a large multicentre study, for which the CARD 15 gene was identified--using independent association strategies-as being a gene contributing to Crohn's disease susceptibility. Despite these advances, a number of questions still remain: (1) What is the best approach to identify the remaining IBD susceptibility loci? (2) How do we prove causality for any given gene or genetic variant? (3) How can we best use this information to obtain an understanding of the biological mechanisms underlying disease susceptibility and to identify useful markers of disease progression and response to therapy?

Chromosomes, Human, Pair 16↗
PubMed2003

An integrated haplotype map of the human major histocompatibility complex.

Numerous studies have clearly indicated a role for the major histocompatibility complex (MHC) in susceptibility to autoimmune diseases. Such studies have focused on the genetic variation of a small number of classical human-leukocyte-antigen (HLA) genes in the region. Although these genes represent good candidates, given their immunological roles, linkage disequilibrium (LD) surrounding these genes has made it difficult to rule out neighboring genes, many with immune function, as influencing disease susceptibility. It is likely that a comprehensive analysis of the patterns of LD and variation, by using a high-density map of single-nucleotide polymorphisms (SNPs), would enable a greater understanding of the nature of the observed associations, as well as lead to the identification of causal variation. We present herein an initial analysis of this region, using 201 SNPs, nine classical HLA loci, two TAP genes, and 18 microsatellites. This analysis suggests that LD and variation in the MHC, aside from the classical HLA loci, are essentially no different from those in the rest of the genome. Furthermore, these data show that multi-SNP haplotypes will likely be a valuable means for refining association signals in this region.

Chromosome Mapping↗
PubMed2003

IBD5 is a general risk factor for inflammatory bowel disease: replication of association with Crohn disease and identification of a novel association with ulcerative colitis.

Inflammatory bowel disease (IBD) refers to complex chronic relapsing autoimmune disorders of the gastrointestinal tract that have been traditionally classified into Crohn disease (CD) and ulcerative colitis (UC). We have previously reported that genetic variation within a 250-kb haplotype (IBD5) in the 5q31 cytokine gene cluster confers susceptibility to CD in a Canadian population. In the current study, we first replicated this association by examining 368 German trios with CD and demonstrating, by transmission/disequilibrium testing (TDT), that the same haplotype is associated with CD (chi2=5.97; P=.007). Our original association study focused on the role of IBD5 in CD; we next explored the potential contribution of this locus to UC susceptibility in 187 German trios. Given the TDT results in the present cohort with UC, IBD5 may also act as a susceptibility locus for UC (chi2=8.10; P=.002). We then examined locus-locus interactions between IBD5 and CARD15, a locus reported elsewhere to confer risk exclusively to CD. Our current results indicate that the two loci act independently to confer risk to CD but that these two loci may behave in an epistatic fashion to promote the development of UC. Moreover, IBD5 was not associated with particular clinical manifestations upon phenotypic stratification in the current cohort with CD. Taken together, our results suggest that IBD5 may act as a general risk factor for IBD, with loci such as CARD15 modifying the clinical characteristics of disease.

Colitis, Ulcerative↗
PubMed2003

Identification of a gene causing human cytochrome c oxidase deficiency by integrative genomics.

Identifying the genes responsible for human diseases requires combining information about gene position with clues about biological function. The recent availability of whole-genome data sets of RNA and protein expression provides powerful new sources of functional insight. Here we illustrate how such data sets can expedite disease-gene discovery, by using them to identify the gene causing Leigh syndrome, French-Canadian type (LSFC, Online Mendelian Inheritance in Man no. 220111), a human cytochrome c oxidase deficiency that maps to chromosome 2p16-21. Using four public RNA expression data sets, we assigned to all human genes a "score" reflecting their similarity in RNA-expression profiles to known mitochondrial genes. Using a large survey of organellar proteomics, we similarly classified human genes according to the likelihood of their protein product being associated with the mitochondrion. By intersecting this information with the relevant genomic region, we identified a single clear candidate gene, LRPPRC. Resequencing identified two mutations on two independent haplotypes, providing definitive genetic proof that LRPPRC indeed causes LSFC. LRPPRC encodes an mRNA-binding protein likely involved with mtDNA transcript processing, suggesting an additional mechanism of mitochondrial pathophysiology. Similar strategies to integrate diverse genomic information can be applied likewise to other disease pathways and will become increasingly powerful with the growing wealth of diverse, functional genomics data.

Amino Acid Sequence↗
PubMed2003

Genetic analysis of multiple sclerosis.

Multiple sclerosis (MS) is a complex disease with a significant genetic contribution. Similar to other complex diseases, the genetic risk for MS results from a combination of many genetic variants which individually confer only modest effects. Here we review the results of the complementary genetic approaches of linkage and association in MS, highlighting the challenges of identifying loci of modest effect. We describe meta-analytical approaches that provide additional statistical power necessary for detecting such loci and further apply this approach to evaluate the association of a CTLA-4 variant with MS. Lastly, we review recent important advances in our understanding of the patterns of genetic variation in the human genome and speculate about how these advances will aid in future studies of the genetic causes of MS.

Genetic Linkage↗