NOX1 loss-of-function genetic variants in patients with inflammatory bowel disease.

Genetic defects that affect intestinal epithelial barrier function can present with very early-onset inflammatory bowel disease (VEOIBD). Using whole-genome sequencing, a novel hemizygous defect in NOX1 encoding NAPDH oxidase 1 was identified in a patient with ulcerative colitis-like VEOIBD. Exome screening of 1,878 pediatric patients identified further seven male inflammatory bowel disease (IBD) patients with rare NOX1 mutations. Loss-of-function was validated in p.N122H and p.T497A, and to a lesser degree in p.Y470H, p.R287Q, p.I67M, p.Q293R as well as the previously described p.P330S, and the common NOX1 SNP p.D360N (rs34688635) variant. The missense mutation p.N122H abrogated reactive oxygen species (ROS) production in cell lines, ex vivo colonic explants, and patient-derived colonic organoid cultures. Within colonic crypts, NOX1 constitutively generates a high level of ROS in the crypt lumen. Analysis of 9,513 controls and 11,140 IBD patients of non-Jewish European ancestry did not reveal an association between p.D360N and IBD. Our data suggest that loss-of-function variants in NOX1 do not cause a Mendelian disorder of high penetrance but are a context-specific modifier. Our results implicate that variants in NOX1 change brush border ROS within colonic crypts at the interface between the epithelium and luminal microbes.

International cancer seminars: a focus on esophageal squamous cell carcinoma.

The International Agency for Research on Cancer (IARC) and the US National Cancer Institute (NCI) have initiated a series of cancer-focused seminars [Scelo G, Hofmann JN, Banks RE et al. International cancer seminars: a focus on kidney cancer. Ann Oncol 2016; 27(8): 1382-1385]. In this, the second seminar, IARC and NCI convened a workshop in order to examine the state of the current science on esophageal squamous cell carcinoma etiology, genetics, early detection, treatment, and palliation, was reviewed to identify the most critical open research questions. The results of these discussions were summarized by formulating a series of 'difficult questions', which should inform and prioritize future research efforts.

Defective macrophage handling of Escherichia coli in Crohn's disease.

BACKGROUND AND AIM: Escherichia coli can be isolated from lamina propria macrophages in Crohn's disease (CD), and their intramacrophage persistence may provide a stimulus for inflammation. To further determine the contributions of macrophage dysfunction and E. coli pathogenicity to this, we aimed to compare in vitro functioning of macrophages from patients with CD and healthy controls (HC) in response to infection with CD-derived adherent-invasive E. coli (AIEC) and less pathogenic E. coli strains. METHODS: Monocyte-derived macrophages were cultured from patients with CD and HC. Intramacrophage survival of E. coli strains (CD-derived adherent-invasive [AI] and non-AI strains and laboratory strain K-12) was compared. Macrophage cytokine release (tumor necrosis factor alpha [TNFα], interleukin [IL]-23, IL-8 and IL-10) and monocyte phagoctyosis and respiratory burst function were measured after E. coli infection. For CD patients, laboratory data were correlated with clinical phenotype, use of immunomodulation, and CD risk alleles (NOD2, IL-23R, ATG16L1 and IRGM). RESULTS: Attenuated TNFα and IL-23 release from CD macrophages was found after infection with all E. coli strains. There was prolonged survival of CD-derived AIEC, CD-derived non-AIEC and E. coli K-12 in macrophages from CD patients compared to within those from HC. No abnormality of monocyte phagocytosis or respiratory burst function was detected in CD. Macrophage dysfunction in CD was not influenced by phenotype, use of immunomodulation or genotype. CONCLUSIONS: CD macrophage responses to infection with E. coli are deficient, regardless of clinical phenotype, CD genotype or E. coli pathogenicity. This suggests host immunodeficiency is an important contributor to intramacrophage E. coli persistence in CD.

FANCG promotes formation of a newly identified protein complex containing BRCA2, FANCD2 and XRCC3.

Fanconi anemia (FA) is a human disorder characterized by cancer susceptibility and cellular sensitivity to DNA crosslinks and other damages. Thirteen complementation groups and genes are identified, including BRCA2, which is defective in the FA-D1 group. Eight of the FA proteins, including FANCG, participate in a nuclear core complex that is required for the monoubiquitylation of FANCD2 and FANCI. FANCD2, like FANCD1/BRCA2, is not part of the core complex, and we previously showed direct BRCA2-FANCD2 interaction using yeast two-hybrid analysis. We now show in human and hamster cells that expression of FANCG protein, but not the other core complex proteins, is required for co-precipitation of BRCA2 and FANCD2. We also show that phosphorylation of FANCG serine 7 is required for its co-precipitation with BRCA2, XRCC3 and FANCD2, as well as the direct interaction of BRCA2-FANCD2. These results argue that FANCG has a role independent of the FA core complex, and we propose that phosphorylation of serine 7 is the signalling event required for forming a discrete complex comprising FANCD1/BRCA2-FANCD2-FANCG-XRCC3 (D1-D2-G-X3). Cells that fail to express either phospho-Ser7-FANCG, or full length BRCA2 protein, lack the interactions amongst the four component proteins. A role for D1-D2-G-X3 in homologous recombination repair (HRR) is supported by our finding that FANCG and the RAD51-paralog XRCC3 are epistatic for sensitivity to DNA crosslinking compounds in DT40 chicken cells. Our findings further define the intricate interface between FANC and HRR proteins in maintaining chromosome stability.

Psoriasis is associated with pleiotropic susceptibility loci identified in type II diabetes and Crohn disease.

BACKGROUND: Psoriasis is an immune-mediated skin disorder that is inherited as a multifactorial trait. Linkage analyses have clearly mapped a primary disease susceptibility locus to the major histocompatibility complex (MHC) region on chromosome 6p21. More recently, whole-genome association studies have identified two non-MHC disease genes (IL12B and IL23R), both of which also confer susceptibility to Crohn disease (CD). OBJECTIVE AND METHODS: To ascertain the genetic overlap between these two inflammatory conditions further, we investigated 15 CD-associated loci in a psoriasis case-control dataset. RESULTS: The analysis of 1256 patients and 2938 unrelated controls found significant associations for loci mapping to chromosomes 1q24 (rs12035082, p = 0.009), 6p22 (rs6908425, p = 0.00015) and 21q22 (rs2836754, p = 0.0003). Notably, the marker showing the strongest phenotypic effect (rs6908425) maps to CDKAL1, a gene also associated with type 2 diabetes. CONCLUSIONS: These results substantiate emerging evidence for a pleiotropic role for s genes that contribute to the pathogenesis of immune-mediated disorders.

Estimating risks of common complex diseases across genetic and environmental factors: the example of Crohn disease.

BACKGROUND: Progress has been made in identifying mutations that confer susceptibility to complex diseases, with the prospect that these genetic risks might be used in determining individual disease risk. AIM: To use Crohn disease (CD) as a model of a common complex disorder, and to develop methods to estimate disease risks using both genetic and environmental risk factors. METHODS: The calculations used three independent risk factors: CARD15 genotype (conferring a gene dosage effect on risk), smoking (twofold increased risk for smokers), and residual familial risk (estimating the effect of unidentified genes, after accounting for the contribution of CARD15). Risks were estimated for high-risk people who are siblings, parents and offspring of a patient with CD. RESULTS: The CD risk to the sibling of a patient with CD who smokes and carries two CARD15 mutations is approximately 35%, which represents a substantial increase on the population risk of 0.1%. In contrast, the risk to a non-smoking sibling of a patient with CD who carries no CARD15 mutations is 2%. Risks to parents and offspring were lower. CONCLUSIONS: High absolute risks of CD disease can be obtained by incorporating information on smoking, family history and CARD15 mutations. Behaviour modification through smoking cessation may reduce CD risk in these people.

Fanconi anaemia genes and susceptibility to cancer.

Fanconi anaemia (FA) is a rare recessive disorder associated with chromosomal fragility, aplastic anaemia, congenital abnormalities and a high risk of cancer, including acute myeloid leukaemia and squamous cell carcinomas. The identification of 11 different FA genes has revealed a complex web of interacting proteins that are involved in the recognition or repair of DNA interstrand crosslinks and perhaps other forms of DNA damage. Bi-allelic mutations in BRCA2 are associated with a rare and highly cancer-prone form of FA, and the DNA helicase BRIP1 (formerly BACH1) is mutated in FA group J. There is little convincing evidence that FA heterozygotes are at increased risk of cancer, but larger studies are needed to address the possibility of modest risk effects. Somatic inactivation of the FA pathway by mutation or epigenetic silencing has been observed in several different types of sporadic cancer, and this may have important implications for targeted chemotherapy. Inhibition of this pathway represents a possible route to sensitization of tumours to DNA crosslinking drugs such as cisplatin.

Sequence variation, linkage disequilibrium and association with Crohn's disease on chromosome 5q31.

Chromosome 5q31 contains a cluster of genes involved in immune response, including a 250 kb risk haplotype associated with Crohn's disease (CD) susceptibility. Recently, two functional variants in SLC22A4 and SLC22A5 (L503F and G-207C), encoding the cation transporters OCTN1 and OCTN2, were proposed as causal variants for CD, but with conflicting genetic evidence regarding their contribution. We investigated this locus by resequencing the coding regions of 10 genes in 24 CD cases and deriving a linkage disequilibrium (LD) map of the 27 single nucleotide polymorphisms (SNPs) detected. Ten SNPs representative of the LD groups observed, were tested for CD association. L503F in SLC22A4 was the only nonsynonymous SNP significantly associated with CD (P=0.003), but was not associated with disease in the absence of other markers of the 250 kb risk haplotype. Two other SNPs, rs11242115 in IRF1 and rs17166050 in RAD50, lying outside the 250 kb risk haplotype, also showed CD association (P=0.019 and P=0.0080, respectively). The RAD50 gene contains a locus control region regulating expression of the Th2 cytokine genes at this locus. Other as yet undiscovered SNPs in this region may therefore modulate gene expression and contribute to the risk of CD, and perhaps of other inflammatory phenotypes.

A general autoimmunity gene (PTPN22) is not associated with inflammatory bowel disease in a British population.

A single-nucleotide polymorphism (C1858T) causing an amino acid substitution (R620W) in the lymphoid protein tyrosine phosphatase gene PTPN22 has been implicated in type 1 diabetes, rheumatoid arthritis, systemic lupus erythematosus, Graves' disease, juvenile idiopathic arthritis and Hashimoto's thyroiditis, thus revealing a general role for this gene in autoimmune disease. We investigated the association of the C1858T variant in an additional autoimmune disease population by performing a case-control study of 514 British individuals with inflammatory bowel disease (IBD) [294 with Crohn's disease (CD) and 220 with ulcerative colitis (UC)] and 374 normal controls. No significant differences in genotype or allele frequencies were observed between IBD, CD or UC and controls, indicating that PTPN22 does not influence risk of IBD.

Synergy between TLR9 and NOD2 innate immune responses is lost in genetic Crohn's disease.

BACKGROUND: Nucleotide binding oligomerisation domain 2 (NOD2; also known as CARD15) mutations are associated with Crohn's disease but how mutations cause disease is poorly understood. Innate immune responses are reportedly enhanced by combined NOD2 ligand (muramyl dipeptide, MDP) and Toll-like receptor 4 ligand (TLR4, lipopolysaccharide) stimulation. Intestinal TLR signalling has a dual role-maintaining intestinal homeostasis and protection from injury as well as initiating inflammatory responses. TLR9 is functional in the intestinal epithelium where it is most strongly expressed in Paneth cells. AIMS: To study possible interactions between CpG DNA (TLR9 ligand) and MDP using primary human cells of differing NOD2 genotypes. SUBJECTS: NOD2 wild-type healthy controls (n = 7) and NOD2 homozygous Crohn's disease patients (n = 19), age and sex matched. METHODS: Peripheral blood mononuclear cells were stimulated with CpG DNA and MDP. Cytokines were measured by enzyme linked immunosorbent assay. RESULTS: Tumour necrosis factor alpha (TNF-alpha) and interleukin 8 (IL-8) responses to CpG DNA were similar in NOD2 wild-type and homozygous mutant cells. Concomitant NOD2 stimulation had a marked synergistic effect on CpG DNA induced TNF-alpha responses at 10-100 ng/ml MDP. A mean 2.1-fold increase in CpG DNA induced TNF-alpha responses and a mean 3.7-fold increase in IL-8 responses were observed in NOD2 wild-type cells with 10 ng/ml MDP. This effect was abolished in NOD2 homozygous cells. CONCLUSIONS: NOD2 stimulation normally enhances innate immune responses to CpG DNA. This marked synergistic effect is lost in Crohn's disease patients homozygous for NOD2 mutations, with implications for TLR mediated intestinal homeostasis and inflammation.

Nijmegen breakage syndrome diagnosed as Fanconi anaemia.

BACKGROUND: Fanconi anaemia (FA) and Nijmegen breakage syndrome (NBS) are rare chromosomal instability disorders with overlapping clinical features. It has recently been shown that, like FA, NBS is also associated with increased chromosomal sensitivity to DNA cross-linking agents. PROCEDURE: We report a family that was initially diagnosed with FA on the basis of increased sensitivity to DNA cross-linking agents. They were atypical in that there were associated severe infection problems. In view of these features we performed immune function studies together with molecular analysis of the FA genes and subsequently the NBS1 gene. RESULTS: Two children in the kindred have died, one from sepsis, and the other with a plasma cell malignancy. A third child underwent bone marrow transplantation because of recurrent infections. All affected members had severe immunological abnormalities. The genetic defect was shown to be a novel mutation in the NBS1 gene, so the diagnosis was revised to that of NBS. CONCLUSIONS: This family illustrates the importance of awareness of the lack of specificity of DNA cross-linking agent tests for FA, particularly in situations where the clinical features are atypical. In addition, one of the cases represents the first use of bone marrow transplantation for NBS that we are aware of; this treatment may have a future role for other patients with the syndrome.

Quantitative PCR analysis reveals a high incidence of large intragenic deletions in the FANCA gene in Spanish Fanconi anemia patients.

Fanconi anaemia is an autosomal recessive disease characterized by chromosome fragility, multiple congenital abnormalities, progressive bone marrow failure and a high predisposition to develop malignancies. Most of the Fanconi anaemia patients belong to complementation group FA-A due to mutations in the FANCA gene. This gene contains 43 exons along a 4.3-kb coding sequence with a very heterogeneous mutational spectrum that makes the mutation screening of FANCA a difficult task. In addition, as the FANCA gene is rich in Alu sequences, it was reported that Alu-mediated recombination led to large intragenic deletions that cannot be detected in heterozygous state by conventional PCR, SSCP analysis, or DNA sequencing. To overcome this problem, a method based on quantitative fluorescent multiplex PCR was proposed to detect intragenic deletions in FANCA involving the most frequently deleted exons (exons 5, 11, 17, 21 and 31). Here we apply the proposed method to detect intragenic deletions in 25 Spanish FA-A patients previously assigned to complementation group FA-A by FANCA cDNA retroviral transduction. A total of eight heterozygous deletions involving from one to more than 26 exons were detected. Thus, one third of the patients carried a large intragenic deletion that would have not been detected by conventional methods. These results are in agreement with previously published data and indicate that large intragenic deletions are one of the most frequent mutations leading to Fanconi anaemia. Consequently, this technology should be applied in future studies on FANCA to improve the mutation detection rate.

Deletion and reduced expression of the Fanconi anemia FANCA gene in sporadic acute myeloid leukemia.

Fanconi anemia (FA) is an autosomal recessive chromosomal instability disorder caused by mutations in one of seven known genes (FANCA,C,D2,E,F,G and BRCA2). Mutations in the FANCA gene are the most prevalent, accounting for two-thirds of FA cases. Affected individuals have greatly increased risks of acute myeloid leukemia (AML). This raises the question as to whether inherited or acquired mutations in FA genes might be involved in the development of sporadic AML. Quantitative fluorescent PCR was used to screen archival DNA from sporadic AML cases for FANCA deletions, which account for 40% of FANCA mutations in FA homozygotes. Four heterozygous deletions were found in 101 samples screened, which is 35-fold higher than the expected population frequency for germline FANCA deletions (P<0.0001). Sequencing FANCA in the AML samples with FANCA deletions did not detect mutations in the second allele and there was no evidence of epigenetic silencing by hypermethylation. However, real-time quantitative PCR analysis in these samples showed reduced expression of FANCA compared to nondeleted AML samples and to controls. These findings suggest that gene deletions and reduced expression of FANCA may be involved in the promotion of genetic instability in a subset of cases of sporadic AML.

SNP subset selection for genetic association studies.

Association studies for disease susceptibility genes rely on the high density of SNPs within candidate genes. However, the linkage disequilibrium between SNPs imply that not all SNPs identified in the candidate region need be genotyped. Here we develop several approaches to SNP subset selection, which can substantially reduce the number of SNPs to be genotyped in an association study. We apply clustering algorithms to pairwise linkage disequilibrium measures, with SNP subsets determined for different cut-off values of Delta using nearest and furthest neighbour clusters. Alternatively, SNP subsets may be determined by the proportion of haplotypes they identify. We also show how power calculations, based on the average power to identify a SNP as the disease susceptibility mutation using haplotype-based or logistic regression based statistical analyses, can be used to choose SNP subsets. All these methods provide a ranking method for subsets of a specific size, but do not provide criteria for overall choice of SNP subset size. We develop such criteria by incorporating power calculations into a decision analysis, where the choice of SNP subset size depends on the genotyping costs and the perceived benefits of identifying association. These methods are illustrated using eleven SNPs in the MMP2 gene.

A Crohn's disease-associated insertion polymorphism (3020insC) in the NOD2 gene is not associated with psoriasis vulgaris, palmo-plantar pustular psoriasis or guttate psoriasis.

A C-insertion polymorphism in the NOD2 gene (3020insC) on chromosome 16 is a rare mutation associated with Crohn's disease. Crohn's disease and psoriasis are more commonly observed together than expected by chance. Furthermore a susceptibility locus for psoriasis has been identified on chromosome 16q which overlaps the recently identified susceptibility locus for Crohn's disease. Thus, NOD2 may potentially be important as a candidate susceptibility gene for psoriasis. We tested this hypothesis by genotyping psoriasis patients for the C-insertion polymorphism using the Taqman ABI 7700 sequencing system. No statistically significant differences were observed between psoriasis vulgaris (n = 216), palmo-plantar pustular psoriasis (PPP) (n = 100), guttate psoriasis (n = 118) and the control group (n = 283). In both patient and control groups, no mutant homozygotes were observed and approximately 4% were heterozygotes. This particular insertion mutation in the NOD2 gene does not appear to contribute to the genetic susceptibility of psoriasis vulgaris, PPP or guttate psoriasis. However, other mutations exist in the NOD2 gene, which may potentially have a role in psoriasis susceptibility.

Genetic variation at the chromosome 16 chemokine gene cluster: development of a strategy for association studies in complex disease.

The chemokine gene cluster [CCL22, CX3CL1, CCL17] (previously known as [SCYA22, SCYD1, SCYA17]) is a candidate locus for one of the susceptibility genes for inflammatory bowel disease that are located in the peri-centromeric region of chromosome 16. Screening for sequence variation at this locus led to the detection of 14 single nucleotide polymorphisms (SNPs). An efficient experimental and computational approach was developed to estimate allele frequencies and pairwise linkage disequilibrium relationships between SNPs at this locus, and to test them for association with inflammatory bowel disease. The 12 common SNPs were assigned to 5 distinct linkage disequilibrium groups. Genotyping of one SNP from each linkage disequilibrium group in a large cohort of families with inflammatory bowel disease did not provide convincing evidence of association with either Crohn's disease or ulcerative colitis. We describe an efficient experimental design from SNP screening to association testing. This strategy can be used to test candidate genes for involvement in susceptibility to complex disease.

Genetic variation in the IGSF6 gene and lack of association with inflammatory bowel disease.

The immunoglobulin superfamily 6 gene (IGSF6) on chromosome 16p11-p12 has been investigated as a positional and functional candidate for inflammatory bowel disease (IBD) susceptibility. Screening of the six exons of IGSF6 for single nucleotide polymorphisms (SNPs) detected four novel SNPs, and validated three of six SNPs listed in the international SNP database (dbSNP). The seven SNPs in IGSF6 formed five distinct linkage disequilibrium groups. There was no evidence for association of the common SNPs with disease in a large cohort of patients with IBD. The novel SNPs and the linkage disequilibrium map will be a useful resource for the analysis of IGSF6 in other immune disorders.

Development of rheumatoid arthritis is not associated with two polymorphisms in the Crohn's disease gene CARD15.

INTRODUCTION: It has been proposed that genetic susceptibility loci for rheumatoid arthritis (RA) may be shared with other autoimmune/inflammatory diseases. Recently, common variation in the CARD15 (NOD2) gene on chromosome 16q12 has been associated with Crohn's disease (CD) in several independent populations. CARD15 is an excellent functional and positional candidate gene for RA. METHODS: Genomic DNA was obtained from 392 RA cases and 471 ethnically matched healthy controls. All samples were genotyped for two polymorphisms in CARD15, 1007fs and R702W, using 5' nuclease reporter assays. Allele frequencies were compared between cases and controls using the chi(2) test. Estimated haplotype frequencies across the two mutations were determined using the EH program. RESULTS: The allele frequency of the 1007fs variant in RA cases was 1.8% compared with 1.6% in normal controls (not significant). The frequency of the R702W variant was 4.0% in both cases and controls. Haplotypes carrying either of the two mutations accounted for 5.6% of possible haplotypes. A haplotype carrying both mutations was rare, with estimated frequency <0.01%. This study provided high power to detect an association of similar magnitude to that in Crohn's disease. These data therefore exclude the possibility that the contribution of these mutations to RA is comparable to that seen in CD. CONCLUSION: Within defined statistical parameters, we excluded a role for the CARD15 1007fs and R702W variants in RA susceptibility. These data do not preclude a role for other polymorphisms in the CARD15 gene in RA susceptibility. Results from other autoimmune and inflammatory diseases will reveal whether the CARD15 gene is in fact a common autoimmune susceptibility locus.