Genome-Wide Copy Number Variation Scan Identifies Complement Component C4 as Novel Susceptibility Gene for Crohn's Disease.
; ; et al
in Inflammatory bowel diseases (2015)
BACKGROUND: The genetic component of Crohn's disease (CD) is well known, with 140 susceptibility loci identified so far. In addition to single nucleotide polymorphisms typically studied in genome-wide ... [more ▼]
BACKGROUND: The genetic component of Crohn's disease (CD) is well known, with 140 susceptibility loci identified so far. In addition to single nucleotide polymorphisms typically studied in genome-wide scans, copy number variation is responsible for a large proportion of human genetic variation. METHODS: We performed a genome-wide search for copy number variants associated with CD using array comparative genomic hybridization. One of the found regions was validated independently through real-time PCR. Serum levels of the found gene were measured in patients and control subjects. RESULTS: We found copy number differences for the C4S and C4L gene variants of complement component C4 in the central major histocompatibility complex region on chromosome 6p21. Specifically, we saw that CD patients tend to have lower C4L and higher C4S copies than control subjects (P = 5.00 x 10 and P = 9.11 x 10), which was independent of known associated classical HLA I and II alleles (P = 7.68 x 10 and P = 6.29 x 10). Although C4 serum levels were not different between patients and control subjects, the relationship between C4 copy number and serum level was different for patients and control subjects with higher copy numbers leading to higher serum concentrations in control subjects, compared with CD patients (P < 0.001). CONCLUSIONS: C4 is part of the classical activation pathway of the complement system, which is important for (auto)immunity. Low C4L or high C4S copy number, and corresponding effects on C4 serum level, could lead to an exaggerated response against infections, possibly leading to (auto)immune disease. [less ▲]Detailed reference viewed: 17 (0 ULg)
Host-microbe interactions have shaped the genetic architecture of inflammatory bowel disease.
; ; et al
in Nature (2012), 491(7422), 119-24
Crohn's disease and ulcerative colitis, the two common forms of inflammatory bowel disease (IBD), affect over 2.5 million people of European ancestry, with rising prevalence in other populations. Genome ... [more ▼]
Crohn's disease and ulcerative colitis, the two common forms of inflammatory bowel disease (IBD), affect over 2.5 million people of European ancestry, with rising prevalence in other populations. Genome-wide association studies and subsequent meta-analyses of these two diseases as separate phenotypes have implicated previously unsuspected mechanisms, such as autophagy, in their pathogenesis and showed that some IBD loci are shared with other inflammatory diseases. Here we expand on the knowledge of relevant pathways by undertaking a meta-analysis of Crohn's disease and ulcerative colitis genome-wide association scans, followed by extensive validation of significant findings, with a combined total of more than 75,000 cases and controls. We identify 71 new associations, for a total of 163 IBD loci, that meet genome-wide significance thresholds. Most loci contribute to both phenotypes, and both directional (consistently favouring one allele over the course of human history) and balancing (favouring the retention of both alleles within populations) selection effects are evident. Many IBD loci are also implicated in other immune-mediated disorders, most notably with ankylosing spondylitis and psoriasis. We also observe considerable overlap between susceptibility loci for IBD and mycobacterial infection. Gene co-expression network analysis emphasizes this relationship, with pathways shared between host responses to mycobacteria and those predisposing to IBD. [less ▲]Detailed reference viewed: 78 (26 ULg)
Meta-analysis identifies 29 additional ulcerative colitis risk loci, increasing the number of confirmed associations to 47.
; ; et al
in Nature Genetics (2011), 43(3), 246-52
Genome-wide association studies and candidate gene studies in ulcerative colitis have identified 18 susceptibility loci. We conducted a meta-analysis of six ulcerative colitis genome-wide association ... [more ▼]
Genome-wide association studies and candidate gene studies in ulcerative colitis have identified 18 susceptibility loci. We conducted a meta-analysis of six ulcerative colitis genome-wide association study datasets, comprising 6,687 cases and 19,718 controls, and followed up the top association signals in 9,628 cases and 12,917 controls. We identified 29 additional risk loci (P < 5 x 10(-8)), increasing the number of ulcerative colitis-associated loci to 47. After annotating associated regions using GRAIL, expression quantitative trait loci data and correlations with non-synonymous SNPs, we identified many candidate genes that provide potentially important insights into disease pathogenesis, including IL1R2, IL8RA-IL8RB, IL7R, IL12B, DAP, PRDM1, JAK2, IRF5, GNA12 and LSP1. The total number of confirmed inflammatory bowel disease risk loci is now 99, including a minimum of 28 shared association signals between Crohn's disease and ulcerative colitis. [less ▲]Detailed reference viewed: 32 (10 ULg)
Resequencing of positional candidates identifies low frequency IL23R coding variants protecting against inflammatory bowel disease.
Momozawa, Yukihide ; Mni, Myriam ; Nakamura, Kayo et al
in Nature Genetics (2011), 43(1), 43-7
Genome-wide association studies (GWAS) have identified dozens of risk loci for many complex disorders, including Crohn's disease. However, common disease-associated SNPs explain at most approximately 20 ... [more ▼]
Genome-wide association studies (GWAS) have identified dozens of risk loci for many complex disorders, including Crohn's disease. However, common disease-associated SNPs explain at most approximately 20% of the genetic variance for Crohn's disease. Several factors may account for this unexplained heritability, including rare risk variants not adequately tagged thus far in GWAS. That rare susceptibility variants indeed contribute to variation in multifactorial phenotypes has been demonstrated for colorectal cancer, plasma high-density lipoprotein cholesterol levels, blood pressure, type 1 diabetes, hypertriglyceridemia and, in the case of Crohn's disease, for NOD2 (refs. 14,15). Here we describe the use of high-throughput resequencing of DNA pools to search for rare coding variants influencing susceptibility to Crohn's disease in 63 GWAS-identified positional candidate genes. We identify low frequency coding variants conferring protection against inflammatory bowel disease in IL23R, but we conclude that rare coding variants in positional candidates do not make a large contribution to inherited predisposition to Crohn's disease. [less ▲]Detailed reference viewed: 99 (38 ULg)