Neutrophils form the most abundant leukocyte subset and are central to many disease processes. Technical challenges in transcriptomic profiling have prohibited genetical genomic approaches to date. Here, we map expression quantitative trait loci (eQTL) in peripheral blood CD16+ neutrophils from 101 healthy European adults. We identify cis-eQTL for 3281 neutrophil-expressed genes including many implicated in neutrophil function, with 450 of these not previously observed in myeloid or lymphoid cells. Paired comparison with monocyte eQTL demonstrates nuanced conditioning of genetic regulation of gene expression by cellular context which relates to cell type specific DNA methylation and histone modifications. Neutrophil eQTL are markedly enriched for trait-associated variants particularly autoimmune, allergy and infectious disease. We further demonstrate how eQTL in PADI4 and NOD2 delineate risk variant function in rheumatoid arthritis, leprosy and Crohn’s disease (CD). Taken together, these data help advance understanding of the genetics of gene expression, neutrophil biology and immune-related diseases.
Common Variable Immunodeficiency Disorders (CVIDs) are the most prevalent cause of primary antibody failure. CVIDs are highly variable and a genetic causes have been identified in <5% of patients. Here, we performed whole genome sequencing (WGS) of 34 CVID patients (94% sporadic) and combined them with transcriptomic profiling (RNA-sequencing of B cells) from three patients and three healthy controls. We identified variants in CVID disease genes TNFRSF13B, TNFRSF13C, LRBA and NLRP12 and enrichment of variants in known and novel disease pathways. The pathways identified include B-cell receptor signalling, non-homologous end-joining, regulation of apoptosis, T cell regulation and ICOS signalling. Our data confirm the polygenic nature of CVID and suggest individual-specific aetiologies in many cases. Together our data show that WGS in combination with RNA-sequencing allows for a better understanding of CVIDs and the identification of novel disease associated pathways.
Common variable immunodeficiency; Whole genome sequencing; Transcriptome; Polygenic; B-cell
An exploratory genome-wide copy number variant (CNV) study was performed in 127 independent cases with specific language impairment (SLI), their first-degree relatives (385 individuals) and 269 population controls. Language-impaired cases showed an increased CNV burden in terms of the average number of events (11.28 vs 10.01, empirical P=0.003), the total length of CNVs (717 vs 513 Kb, empirical P=0.0001), the average CNV size (63.75 vs 51.6 Kb, empirical P=0.0005) and the number of genes spanned (14.29 vs 10.34, empirical P=0.0007) when compared with population controls, suggesting that CNVs may contribute to SLI risk. A similar trend was observed in first-degree relatives regardless of affection status. The increased burden found in our study was not driven by large or de novo events, which have been described as causative in other neurodevelopmental disorders. Nevertheless, de novo CNVs might be important on a case-by-case basis, as indicated by identification of events affecting relevant genes, such as ACTR2 and CSNK1A1, and small events within known micro-deletion/-duplication syndrome regions, such as chr8p23.1. Pathway analysis of the genes present within the CNVs of the independent cases identified significant overrepresentation of acetylcholine binding, cyclic-nucleotide phosphodiesterase activity and MHC proteins as compared with controls. Taken together, our data suggest that the majority of the risk conferred by CNVs in SLI is via common, inherited events within a ‘common disorder–common variant' model. Therefore the risk conferred by CNVs will depend upon the combination of events inherited (both CNVs and SNPs), the genetic background of the individual and the environmental factors.
The ratio of monocytes and lymphocytes (ML ratio) in peripheral blood is associated with tuberculosis and malaria disease risk and cancer and cardiovascular disease outcomes. We studied anti-mycobacterial function and the transcriptome of monocytes in relation to the ML ratio.
Mycobacterial growth inhibition assays of whole or sorted blood were performed and mycobacteria were enumerated by liquid culture. Transcriptomes of unstimulated CD14 + monocytes isolated by magnetic bead sorting were characterised by microarray. Transcript expression was tested for association with ML ratio calculated from leucocyte differential counts by linear regression.
The ML ratio was associated with mycobacterial growth in vitro (β = 2.23, SE 0.91, p = 0.02). Using sorted monocytes and lymphocytes, in vivo ML ratio (% variance explained R2 = 11%, p = 0.02) dominated over in vitro ratios (R2 = 5%, p = 0.10) in explaining mycobacterial growth. Expression of 906 genes was associated with the ML ratio and 53 with monocyte count alone. ML-ratio associated genes were enriched for type-I and -II interferon signalling (p = 1.2 × 10− 8), and for genes under transcriptional control of IRF1, IRF2, RUNX1, RELA and ESRRB. The ML-ratio-associated gene set was enriched in TB disease (3.11-fold, 95% CI: 2.28–4.19, p = 5.7 × 10− 12) and other inflammatory diseases including atopy, HIV, IBD and SLE.
The ML ratio is associated with distinct transcriptional and anti-mycobacterial profiles of monocytes that may explain the disease associations of the ML ratio.
•A pathophysiological basis for involvement of the ML ratio in infectious, malignant and cardiovascular diseases is unclear.•Monocytes from individuals with high ML ratio have impaired control of mycobacterial growth and a distinctive transcriptome.•These monocytes are characterised by enhanced interferon signalling, and intermediate transcription factors.•The ML-ratio associated transcript signature is enriched in TB and other diseases including atopy, IBD and SLE.•Ontogeny-specific function of monocytes may be the possible mechanism for the prognostic value of the ML ratio.
Enumeration of the absolute count of white blood cell subsets is one of the most frequently performed tests in clinical practice. Recently, elevation in the monocytes:lymphocytes (ML) ratio was linked to increased risk of tuberculosis and malaria disease, and poorer outcomes for many cancers and cardiovascular diseases. We sought to understand the mechanism of these disease associations. We found that the ML ratio reflects the functional capacity of monocytes and that genes that are differentially expressed in monocytes from donors with a high ML ratio are similar to those in other diseases such as HIV and inflammatory bowel disease. Because a specific type of blood-making stem cell regulates the ML ratio, it is plausible that the ratio reflects monocyte function because it is a clue to different monocyte origins. Our findings offer a mechanism for the predictive value of the ML ratio that may help improve its clinical utility.
ML ratio; Monocyte; Transcriptome; Interferon signalling; Tuberculosis
Neutrophils form the most abundant leukocyte subset and are central to many disease processes. Technical challenges in transcriptomic profiling have prohibited genomic approaches to date. Here we map expression quantitative trait loci (eQTL) in peripheral blood CD16+ neutrophils from 101 healthy European adults. We identify cis-eQTL for 3281 neutrophil-expressed genes including many implicated in neutrophil function, with 450 of these not previously observed in myeloid or lymphoid cells. Paired comparison with monocyte eQTL demonstrates nuanced conditioning of genetic regulation of gene expression by cellular context, which relates to cell-type-specific DNA methylation and histone modifications. Neutrophil eQTL are markedly enriched for trait-associated variants particularly autoimmune, allergy and infectious disease. We further demonstrate how eQTL in PADI4 and NOD2 delineate risk variant function in rheumatoid arthritis, leprosy and Crohn's disease. Taken together, these data help advance understanding of the genetics of gene expression, neutrophil biology and immune-related diseases.
Neutrophils are the most abundant subset of leukocyte and central to many diseases. Here by mapping expression quantitative trait loci (eQTL) in the context of epigenetic marks in neutrophils and monocytes of 101 healthy European adults, the authors provide a resource to advance understanding of immune-related trait-associated genetic variants.
Over several decades, various forms of genomic analysis of the human major histocompatibility complex (MHC) have been extremely successful in picking up many disease associations. This is to be expected, as the MHC region is one of the most gene-dense and polymorphic stretches of human DNA. It also encodes proteins critical to immunity, including several controlling antigen processing and presentation. Single-nucleotide polymorphism genotyping and human leukocyte antigen (HLA) imputation now permit the screening of large sample sets, a technique further facilitated by high-throughput sequencing. These methods promise to yield more precise contributions of MHC variants to disease. However, interpretation of MHC-disease associations in terms of the functions of variants has been problematic. Most studies confirm the paramount importance of class I and class II molecules, which are key to resistance to infection. Infection is likely driving the extreme variation of these genes across the human population, but this has been difficult to demonstrate. In contrast, many associations with autoimmune conditions have been shown to be specific to certain class I and class II alleles. Interestingly, conditions other than infections and autoimmunity are also associated with the MHC, including some cancers and neuropathies. These associations could be indirect, owing, for example, to the infectious history of a particular individual and selective pressures operating at the population level.
MHC; HLA; polymorphism; antigen presentation; antigen processing; imputation
The functional consequences of trait associated SNPs are often investigated using expression quantitative trait locus (eQTL) mapping. While trait-associated variants may operate in a cell-type specific manner, eQTL datasets for such cell-types may not always be available. We performed a genome-environment interaction (GxE) meta-analysis on data from 5,683 samples to infer the cell type specificity of whole blood cis-eQTLs. We demonstrate that this method is able to predict neutrophil and lymphocyte specific cis-eQTLs and replicate these predictions in independent cell-type specific datasets. Finally, we show that SNPs associated with Crohn’s disease preferentially affect gene expression within neutrophils, including the archetypal NOD2 locus.
Many variants in the genome, including variants associated with disease, affect the expression of genes. These so-called expression quantitative trait loci (eQTL) can be used to gain insight in the downstream consequences of disease. While it has been shown that many disease-associated variants alter gene expression in a cell-type dependent manner, eQTL datasets for specific cell types may not always be available and their sample size is often limited. We present a method that is able to detect cell type specific effects within eQTL datasets that have been generated from whole tissues (which may be composed of many cell types), in our case whole blood. By combining numerous whole blood datasets through meta-analysis, we show that we are able to detect eQTL effects that are specific for neutrophils and lymphocytes (two blood cell types). Additionally, we show that the variants associated with some diseases may preferentially alter the gene expression in one of these cell types. We conclude that our method is an alternative method to detect cell type specific eQTL effects, that may complement generating cell type specific eQTL datasets and that may be applied on other cell types and tissues as well.
Sepsis continues to be a major cause of death, disability, and health-care expenditure worldwide. Despite evidence suggesting that host genetics can influence sepsis outcomes, no specific loci have yet been convincingly replicated. The aim of this study was to identify genetic variants that influence sepsis survival.
We did a genome-wide association study in three independent cohorts of white adult patients admitted to intensive care units with sepsis, severe sepsis, or septic shock (as defined by the International Consensus Criteria) due to pneumonia or intra-abdominal infection (cohorts 1–3, n=2534 patients). The primary outcome was 28 day survival. Results for the cohort of patients with sepsis due to pneumonia were combined in a meta-analysis of 1553 patients from all three cohorts, of whom 359 died within 28 days of admission to the intensive-care unit. The most significantly associated single nucleotide polymorphisms (SNPs) were genotyped in a further 538 white patients with sepsis due to pneumonia (cohort 4), of whom 106 died.
In the genome-wide meta-analysis of three independent pneumonia cohorts (cohorts 1–3), common variants in the FER gene were strongly associated with survival (p=9·7 × 10−8). Further genotyping of the top associated SNP (rs4957796) in the additional cohort (cohort 4) resulted in a combined p value of 5·6 × 10−8 (odds ratio 0·56, 95% CI 0·45–0·69). In a time-to-event analysis, each allele reduced the mortality over 28 days by 44% (hazard ratio for death 0·56, 95% CI 0·45–0·69; likelihood ratio test p=3·4 × 10−9, after adjustment for age and stratification by cohort). Mortality was 9·5% in patients carrying the CC genotype, 15·2% in those carrying the TC genotype, and 25·3% in those carrying the TT genotype. No significant genetic associations were identified when patients with sepsis due to pneumonia and intra-abdominal infection were combined.
We have identified common variants in the FER gene that associate with a reduced risk of death from sepsis due to pneumonia. The FER gene and associated molecular pathways are potential novel targets for therapy or prevention and candidates for the development of biomarkers for risk stratification.
European Commission and the Wellcome Trust.
The master transactivator CIITA is essential to the regulation of Major Histocompatibility Complex (MHC) class II genes and an effective immune response. CIITA is known to modulate a small number of non-MHC genes involved in antigen presentation such as CD74 and B2M but its broader genome-wide function and relationship with underlying genetic diversity has not been resolved.
We report the first genome-wide ChIP-seq map for CIITA and complement this by mapping inter-individual variation in CIITA expression as a quantitative trait. We analyse CIITA recruitment for pathophysiologically relevant primary human B cells and monocytes, resting and treated with interferon-gamma, in the context of the epigenomic regulatory landscape and DNA-binding proteins associated with the CIITA enhanceosome including RFX, CREB1/ATF1 and NFY. We confirm recruitment to proximal promoter sequences in MHC class II genes and more distally involving the canonical CIITA enhanceosome. Overall, we map 843 CIITA binding intervals involving 442 genes and find 95% of intervals are located outside the MHC and 60% not associated with RFX5 binding. Binding intervals are enriched for genes involved in immune function and infectious disease with novel loci including major histone gene clusters. We resolve differentially expressed genes associated in trans with a CIITA intronic sequence variant, integrate with CIITA recruitment and show how this is mediated by allele-specific recruitment of NF-kB.
Our results indicate a broader role for CIITA beyond the MHC involving immune-related genes. We provide new insights into allele-specific regulation of CIITA informative for understanding gene function and disease.
Electronic supplementary material
The online version of this article (doi:10.1186/s13059-014-0494-z) contains supplementary material, which is available to authorized users.
Despite increases in vaccination coverage, reductions in influenza-related mortality have not been observed. Better vaccines are therefore required and influenza challenge studies can be used to test the efficacy of new vaccines. However, this requires the accurate post-challenge classification of subjects by outcome, which is limited in current methods that use artificial thresholds to assign ‘symptomatic’ and ‘asymptomatic’ phenotypes. We present data from an influenza challenge study in which 22 healthy adults (11 vaccinated) were inoculated with H3N2 influenza (A/Wisconsin/67/2005). We generated genome-wide gene expression data from peripheral blood taken immediately before the challenge and at 12, 24 and 48 h post-challenge. Variation in symptomatic scoring was found amongst those with laboratory confirmed influenza. By combining the dynamic transcriptomic data with the clinical parameters this variability can be reduced. We identified four subjects with severe laboratory confirmed influenza that show differential gene expression in 1103 probes 48 h post-challenge compared to the remaining subjects. We have further reduced this profile to six genes (CCL2, SEPT4, LAMP3, RTP4, MT1G and OAS3) that can be used to define these subjects. We have used this gene set to predict symptomatic infection from an independent study. This analysis gives further insight into host-pathogen interactions during influenza infection. However, the major potential value is in the clinical trial setting by providing a more quantitative method to better classify symptomatic individuals post influenza challenge.
Differential gene expression signatures are seen following influenza challenge.Expression of six predictive genes can classify response to influenza challenge.The genomic influenza response classification replicates in an independent dataset.
Electronic supplementary material
The online version of this article (doi:10.1007/s00109-014-1212-8) contains supplementary material, which is available to authorized users.
Influenza; Challenge; Transcriptome; Expression; RNA; Microarray
To systematically investigate the impact of immune stimulation upon regulatory variant activity, we exposed primary monocytes from 432 healthy Europeans to interferon-γ (IFN-γ) or differing durations of lipopolysaccharide and mapped expression quantitative trait loci (eQTLs). More than half of cis-eQTLs identified, involving hundreds of genes and associated pathways, are detected specifically in stimulated monocytes. Induced innate immune activity reveals multiple master regulatory trans-eQTLs including the major histocompatibility complex (MHC), coding variants altering enzyme and receptor function, an IFN-β cytokine network showing temporal specificity, and an interferon regulatory factor 2 (IRF2) transcription factor–modulated network. Induced eQTL are significantly enriched for genome-wide association study loci, identifying context-specific associations to putative causal genes including CARD9, ATM, and IRF8. Thus, applying pathophysiologically relevant immune stimuli assists resolution of functional genetic variants.
Identifying the downstream effects of disease-associated single nucleotide polymorphisms (SNPs) is challenging: the causal gene is often unknown or it is unclear how the SNP affects the causal gene, making it difficult to design experiments that reveal functional consequences. To help overcome this problem, we performed the largest expression quantitative trait locus (eQTL) meta-analysis so far reported in non-transformed peripheral blood samples of 5,311 individuals, with replication in 2,775 individuals. We identified and replicated trans-eQTLs for 233 SNPs (reflecting 103 independent loci) that were previously associated with complex traits at genome-wide significance. Although we did not study specific patient cohorts, we identified trait-associated SNPs that affect multiple trans-genes that are known to be markedly altered in patients: for example, systemic lupus erythematosus (SLE) SNP rs49170141 altered C1QB and five type 1 interferon response genes, both hallmarks of SLE2-4. Subsequent ChIP-seq data analysis on these trans-genes implicated transcription factor IKZF1 as the causal gene at this locus, with DeepSAGE RNA-sequencing revealing that rs4917014 strongly alters 3’ UTR levels of IKZF1. Variants associated with cholesterol metabolism and type 1 diabetes showed similar phenomena, indicating that large-scale eQTL mapping provides insight into the downstream effects of many trait-associated variants.
ZFP57 is an important transcriptional regulator involved in DNA methylation and genomic imprinting during development. Here we demonstrate that gene expression also occurs at a low level in adult peripheral blood cells and other tissues including the kidney and thymus, but is critically dependent on underlying local genetic variation within the MHC. We resolve a highly significant expression quantitative trait locus for ZFP57 involving single-nucleotide polymorphisms (SNPs) in the first intron of the gene co-localizing with a DNase I hypersensitive site and evidence of CTCF recruitment. These data identify ZFP57 as a candidate gene underlying reported MHC disease associations, notably for putative regulatory variants associated with cancer and HIV-1. The work highlights the role that ZFP57 may play in DNA methylation and epigenetic regulation beyond early development into adult life dependent on genetic background, with important potential implications for disease.
ZFP57; expression quantitative trait; genetic variation; MHC; disease susceptibility
Asthma is a common, chronic inflammatory airway disease of major public health importance with multiple genetic determinants. Previously, we found by positional cloning that PHD finger protein 11 (PHF11) on chromosome 13q14 modifies serum immunoglobulin E (IgE) concentrations and asthma susceptibility. No coding variants in PHF11 were identified.
Here we investigate the 3 single nucleotide polymorphisms (SNPs) in this gene most significantly associated with total serum IgE levels—rs3765526, rs9526569, and rs1046295—for a role in transcription factor binding.
We used electrophoretic mobility shift assays to examine the effect of the 3 SNPs on transcription factor binding in 3 cell lines relevant to asthma pathogenesis. Relative preferential expression of alleles was investigated by using the allelotyping method.
Electrophoretic mobility shift assays show that rs1046295 modulates allele-specific binding by the octamer-binding transcription factor 1 (Oct-1). Analysis of the relative expression levels of the 2 alleles of this SNP in heterozygous individuals showed a modest, but highly significant (P = 6.5 × 10−16), preferential expression of the A allele consistent with a functional role for rs1046295.
These results suggest a mechanism by which rs1046295 may act as a regulatory variant modulating transcription at this locus and altering asthma susceptibility.
Asthma genetics; PHF11; IgE; rs1046295; electrophoretic mobility shift assay; Oct-1; gene expression
The Vitamin D Receptor (VDR) gene encodes a transcription factor which, on activation by vitamin D, modulates diverse biological processes including calcium homeostasis and immune function. Genetic variation involving VDR shows striking differences in allele frequency between populations and has been associated with disease susceptibility including tuberculosis and autoimmunity, although results have often been conflicting. We hypothesized that methylation of VDR may be population specific and that the combination of differential methylation and genetic variation may characterise TB predisposition. We use bisulphite conversion and/or pyrosequencing to analyse the methylation status of 17 CpGs of VDR and to genotype 7 SNPs in the 3′ CpG Island (CGI 1060), including the commonly studied SNPs ApaI (rs7975232) and TaqI (rs731236). We show that for lymphoblastoid cell lines from two ethnically diverse populations (Yoruba from HapMap, n=30 and Caucasians, n=30) together with TB cases (n=32) and controls (n=29) from the Venda population of South Africa there are methylation variable positions (MVPs) in the 3′ end that significantly distinguish ethnicity (9/17 CpGs) and TB status (3/17 CpGs). Moreover methylation status shows complex association with TaqI genotype highlighting the need to consider both genetic and epigenetic variants in genetic studies of VDR association with disease.
VDR (vitamin D (1,25- dihydroxyvitamin D3) receptor); gene polymorphism; CpG methylation; TB (tuberculosis); ethnic differences
There is substantial genetic and epidemiological evidence implicating vitamin D in the pathogenesis of many common diseases. A number of studies have sought to define an association for disease with sequence variation in the VDR gene, encoding the ligand-activated nuclear hormone receptor for vitamin D. The results of such studies have been difficult to replicate and are likely to need to account for specific environmental exposures. Here, we review recent work that has begun to study the interactions between VDR gene polymorphisms, vitamin D blood levels, and complex disease susceptibility, notably in the context of major clinical outcomes. We highlight the challenges moving forward in this area and its importance for effective clinical translation of current research.
Human leukocyte antigen (HLA) loci have been implicated in several neurodevelopmental disorders in which language is affected. However, to date, no studies have investigated the possible involvement of HLA loci in specific language impairment (SLI), a disorder that is defined primarily upon unexpected language impairment. We report association analyses of single-nucleotide polymorphisms (SNPs) and HLA types in a cohort of individuals affected by language impairment.
We perform quantitative association analyses of three linguistic measures and case-control association analyses using both SNP data and imputed HLA types.
Quantitative association analyses of imputed HLA types suggested a role for the HLA-A locus in susceptibility to SLI. HLA-A A1 was associated with a measure of short-term memory (P = 0.004) and A3 with expressive language ability (P = 0.006). Parent-of-origin effects were found between HLA-B B8 and HLA-DQA1*0501 and receptive language. These alleles have a negative correlation with receptive language ability when inherited from the mother (P = 0.021, P = 0.034, respectively) but are positively correlated with the same trait when paternally inherited (P = 0.013, P = 0.029, respectively). Finally, case control analyses using imputed HLA types indicated that the DR10 allele of HLA-DRB1 was more frequent in individuals with SLI than population controls (P = 0.004, relative risk = 2.575), as has been reported for individuals with attention deficit hyperactivity disorder (ADHD).
These preliminary data provide an intriguing link to those described by previous studies of other neurodevelopmental disorders and suggest a possible role for HLA loci in language disorders.
Specific language impairment (SLI); HLA; Neurodevelopmental disorders; Genetic association
Our understanding of immunity has historically been informed by studying heritable mutations in both the adaptive and innate immune responses, including primary immunodeficiency and autoimmune diseases. Recent advances achieved through the application of genomic and epigenomic approaches are reshaping the study of immune dysfunction and opening up new avenues for therapeutic interventions. Moreover, applying genomic techniques to resolve functionally important genetic variation between individuals is providing new insights into immune function in health. This review describes progress in the study of rare variants and primary immunodeficiency diseases arising from whole-exome sequencing (WES), and discusses the application, success, and challenges of applying genome-wide association studies (GWAS) to disorders of immune function and how they may inform more rational use of therapeutics. In addition, the application of expression quantitative-trait mapping to immune phenotypes, progress in understanding MHC disease associations, and insights into epigenetic mechanisms at the interface of immunity and the environment are reviewed.
immunity; major histocompatibility complex; gene regulation; autoimmunity; immunodeficiency; leukocyte
Trans-acting genetic variants play a substantial, albeit poorly characterized, role in the heritable determination of gene expression. Using paired purified primary monocytes and B-cells we identify novel, predominantly cell-specific, cis- and trans-eQTL (expression quantitative trait loci). These include multi-locus trans-associations to LYZ in monocytes and to KLF4 in B-cells. Additionally, we observe B-cell specific trans-association of rs11171739 at 12q13.2, a known autoimmune disease locus, to IP6K2 (pB-cell=5.8×10−15), PRIC285 (pB-cell=3.0×10−10) and an upstream region of CDKN1A (pB-cell=2×10−52; pmonocyte=1.8×10−4), suggesting roles for cell cycle regulation and PPARγ signaling in disease pathogenesis. We also find specific HLA alleles forming trans-association with the expression of AOAH and ARHGAP24 in monocytes but not in B-cells. In summary, we demonstrate that mapping gene expression in defined primary cell populations identifies new cell-specific trans-regulated networks and provides insights into the genetic basis of disease susceptibility.
Endotoxin tolerance is characterized by the suppression of further TNF release upon recurrent exposure to LPS. This phenomenon is proposed to act as a homeostatic mechanism preventing uncontrolled cytokine release such as that observed in bacterial sepsis. The regulatory mechanisms and inter-individual variation of endotoxin tolerance induction in man remain poorly characterized. Here we describe a genetic association study of variation in endotoxin tolerance amongst healthy individuals. We identify a common promoter haplotype in TNFRSF1B (encoding TNFR2) to be strongly associated with reduced tolerance to LPS (P = 5.82×10−6). This identified haplotype is associated with increased expression of TNFR2 (P = 4.9 ×10−5) and we find basal expression of TNFR2, irrespective of genotype and unlike TNFR1, is associated with secondary TNF release (P <0.0001). Functional studies demonstrate a positive feedback loop via TNFR2 of LPS induced TNF release, confirming this previously unrecognized role for TNFR2 in the modulation of LPS response.
There is growing evidence that genetic variation plays an important role in the determination of individual susceptibility to complex disease traits. In contrast to coding sequence polymorphisms, where the consequences of non-synonymous variation may be resolved at the level of the protein phenotype, defining specific functional regulatory polymorphisms has proved problematic. This has arisen for a number of reasons, including difficulties with fine mapping due to linkage disequilibrium, together with a paucity of experimental tools to resolve the effects of non-coding sequence variation on gene expression. Recent studies have shown that variation in gene expression is heritable and can be mapped as a quantitative trait. Allele-specific effects on gene expression appear relatively common, typically of modest magnitude and context specific. The role of regulatory polymorphisms in determining susceptibility to a number of complex disease traits is discussed, including variation at the VNTR of INS, encoding insulin, in type 1 diabetes and polymorphism of CTLA4, encoding cytotoxic T lymphocyte antigen, in autoimmune disease. Examples where regulatory polymorphisms have been found to play a role in mongenic traits such as factor VII deficiency are discussed, and contrasted with those polymorphisms associated with ischaemic heart disease at the same gene locus. Molecular mechanisms operating in an allele-specific manner at the level of transcription are illustrated, with examples including the role of Duffy binding protein in malaria. The difficulty of resolving specific functional regulatory variants arising from linkage disequilibrium is demonstrated using a number of examples including polymorphism of CCR5, encoding CC chemokine receptor 5, and HIV-1 infection. The importance of understanding haplotypic structure to the design and interpretation of functional assays of putative regulatory variation is highlighted, together with discussion of the strategic use of experimental tools to resolve regulatory polymorphisms at a transcriptional level. A number of examples are discussed including work on the TNF locus which demonstrate biological and experimental context specificity. Regulatory variation may also operate at other levels of control of gene expression and the modulation of splicing at PTPRC, encoding protein tyrosine phosphatase receptor-type C, and of translational efficiency at F12, encoding factor XII, are discussed.
Gene expression; Genetics; Gene polymorphism; Promoter; Transcription
Objective To assess the evidence for a genetic basis to magic.
Design Literature review.
Setting Harry Potter novels of J K Rowling.
Participants Muggles, witches, wizards, and squibs.
Main outcome measures Family and twin studies, magical ability, and specific magical skills.
Results Magic shows strong evidence of heritability, with familial aggregation and concordance in twins. Evidence suggests magical ability to be a quantitative trait. Specific magical skills, notably being able to speak to snakes, predict the future, and change hair colour, all seem heritable.
Conclusions A multilocus model with a dominant gene for magic might exist, controlled epistatically by one or more loci, possibly recessive in nature. Magical enhancers regulating gene expressionmay be involved, combined with mutations at specific genes implicated in speech and hair colour such as FOXP2 and MCR1.
Major histocompatibility complex (MHC) class II molecules are central to adaptive immune responses and maintenance of self-tolerance. Since the early 1970s the MHC class II region at chromosome 6p21 has been shown to be associated with a remarkable number of autoimmune, inflammatory and infectious diseases. Given that a full explanation for most MHC class II disease associations has not been reached through analysis of structural variation alone, in this review we explore the role of genetic variation in modulating gene expression. We describe the intricate architecture of the MHC class II regulatory system, indicating how its unique characteristics may relate to observed associations with disease. There is evidence that haplotype-specific variation involving proximal promoter sequences can alter the level of gene expression, potentially modifying the emergence and expression of key phenotypic traits. Although much emphasis has been placed on cis-regulatory elements, we also explore the role of more distant enhancer elements together with the evidence of dynamic inter- and intra-chromosomal interactions and epigenetic processes. The role of genetic variation in such mechanisms may hold profound implications for susceptibility to common disease.
MHC; HLA; transcription; gene regulation; polymorphism; autoimmune
The number of significant genetic associations with common complex traits is constantly increasing. However, most of these associations have not been understood at molecular level. One of the mechanisms mediating the effect of DNA variants on phenotypes is gene expression, which has been shown to be particularly relevant for complex traits1.
This method tests in a cellular context the effect of specific DNA sequences on gene expression. The principle is to measure the relative abundance of transcripts arising from the two alleles of a gene, analysing cells which carry one copy of the DNA sequences associated with disease (the risk variants)2,3. Therefore, the cells used for this method should meet two fundamental genotypic requirements: they have to be heterozygous both for DNA risk variants and for DNA markers, typically coding polymorphisms, which can distinguish transcripts based on their chromosomal origin (Figure 1). DNA risk variants and DNA markers do not need to have the same allele frequency but the phase (haplotypic) relationship of the genetic markers needs to be understood. It is also important to choose cell types which express the gene of interest. This protocol refers specifically to the procedure adopted to extract nucleic acids from fibroblasts but the method is equally applicable to other cells types including primary cells.
DNA and RNA are extracted from the selected cell lines and cDNA is generated. DNA and cDNA are analysed with a primer extension assay, designed to target the coding DNA markers4. The primer extension assay is carried out using the MassARRAY (Sequenom)5 platform according to the manufacturer's specifications. Primer extension products are then analysed by matrix-assisted laser desorption/ionization time of-flight mass spectrometry (MALDI-TOF/MS). Because the selected markers are heterozygous they will generate two peaks on the MS profiles. The area of each peak is proportional to the transcript abundance and can be measured with a function of the MassARRAY Typer software to generate an allelic ratio (allele 1: allele 2) calculation. The allelic ratio obtained for cDNA is normalized using that measured from genomic DNA, where the allelic ratio is expected to be 1:1 to correct for technical artifacts. Markers with a normalised allelic ratio significantly different to 1 indicate that the amount of transcript generated from the two chromosomes in the same cell is different, suggesting that the DNA variants associated with the phenotype have an effect on gene expression. Experimental controls should be used to confirm the results.
The regulation of heat shock protein expression is of significant physiological and pathophysiological significance. Here we show that genetic diversity is an important determinant of heat shock protein 70 expression involving local, likely cis-acting, polymorphisms. We define DNA sequence variation for the highly homologous HSPA1A and HSPA1B genes in the major histocompatibility complex on chromosome 6p21 and establish quantitative and specific assays for determining transcript abundance. We show for lymphoblastoid cell lines established from individuals of African ancestry that following heat shock, expression of HSPA1B is associated with rs400547 (P 3.88 × 10−8) and linked single nucleotide polymorphisms (SNPs) located 62–93 kb telomeric to HSPA1B. This association was found to explain 31 and 29% of the variance in HSPA1B expression following heat shock or in resting cells, respectively. The associated SNPs show marked variation in minor allele frequency among populations, being more common in individuals of African ancestry, and are located in a region showing population-specific haplotypic block structure. The work illustrates how analysis of a heritable induced expression phenotype can be highly informative in defining functionally important genetic variation.