Linkage analysis of candidate regions for coeliac disease genes

Artificial Intelligence Analysis of Celiac Disease Using an Autoimmune Discovery Transcriptomic Panel Highlighted Pathogenic Genes including BTLA

Celiac disease is a common immune-related inflammatory disease of the small intestine caused by gluten in genetically predisposed individuals. This research is a proof-of-concept exercise focused on using Artificial Intelligence (AI) and an autoimmune discovery gene panel to predict and model celiac disease. Conventional bioinformatics, gene set enrichment analysis (GSEA), and several machine learning and neural network techniques were used on a publicly available dataset (GSE164883). Machine learning and deep learning included C5, logistic regression, Bayesian network, discriminant analysis, KNN algorithm, LSVM, random trees, SVM, Tree-AS, XGBoost linear, XGBoost tree, CHAID, Quest, C&R tree, random forest, and neural network (multilayer perceptron). As a result, the gene panel predicted celiac disease with high accuracy (95–100%). Several pathogenic genes were identified, some of the immune checkpoint and immuno-oncology pathways. They included CASP3, CD86, CTLA4, FASLG, GZMB, IFNG, IL15RA, ITGAX, LAG3, MMP3, MUC1, MYD88, PRDM1, RGS1, etc. Among them, B and T lymphocyte associated (BTLA, CD272) was highlighted and validated at the protein level by immunohistochemistry in an independent series of cases. Celiac disease was characterized by high BTLA, expressed by inflammatory cells of the lamina propria. In conclusion, artificial intelligence predicted celiac disease using an autoimmune discovery gene panel.

Acute Oral Lesions

A variety of acute oral lesions may be encountered in the scope of dermatology. Oral lesions may be single or multiple; may arise secondary to infectious, immune, congenital, medication use, or idiopathic causes; and may take a variety of forms. A thorough evaluation of the oral cavity is required to assess patients with oral lesions. Affected patients may be monitored, treated, or referred to an appropriate specialist for further management as needed. Many acute oral lesions are self-limiting in nature and patients may require only assessment and reassurance. Several common acute oral lesions are discussed in this article.

Evaluation of adult celiac disease from a tertiary reference center: a retrospective analysis

OBJECTIVE

It has been observed that celiac disease (CD) is not restricted to a single type characterized by diarrhea but also has atypical, asymptomatic (silent), and latent forms. The prevalence of this autoimmune disease, which affects approximately 1% of the world, is estimated to be around 3%, including atypical and asymptomatic cases. In our study, we aimed to evaluate adult celiac patients.

METHODS

Between December 2008-2015, patients diagnosed with CD over the age of 18 years old were included in the study. Patients' symptoms at admission, frequency and type of anemia, transaminase levels, and celiac antibody positivity, and autoimmune diseases diagnosed at follow up were evaluated retrospectively.

RESULTS

Of 195 patients, 151 (77.4%) were female. The mean age of the patients was 35.73 ± 12.19 years (range, 18-71 years). A hundred patients (51.3%) had gastrointestinal symptoms. At the time of admission, 118 patients (60.5%) had anemia, and 52 (26.7%) had hypertransaminasemia. During the mean follow-up period of 58 months (36-120 months), 84 (43.1%) of the patients presented at least one autoimmune disease, and this rate was 96.6% in individuals diagnosed above the age of 50 years.

CONCLUSION

In adult CD, resistant anemia, dyspepsia, and hypertransaminasemia are very common findings at the time of diagnosis, and the association with other autoimmune diseases, especially Hashimoto's thyroiditis, is high.

Chronic autoimmune disorders are increased in coeliac disease: A case-control study

Coeliac disease (CD) is an autoimmune disorder of the small bowel associated with increased risk of additional autoimmune diseases (ADs).To investigate the prevalence of ADs in a population of adult coeliac patients.This was a retrospective case-control study. Data from coeliac patients and controls referred to a tertiary center between 2013 and 2016 were collected. The frequency of ADs and the unadjusted and adjusted odds ratios (ORs) for age, gender, disease duration, and body mass index with their 95% confidence intervals (CIs) were evaluated.Two hundred fifty-five patients with CD (median age 37.1 years; 206 women) were matched with 250 controls. ADs were more frequent (35.3%) in coeliac patients than in controls (15.2%). Adjusted ORs for the presence of only 1, at least 1, and more than 1 AD were 3.13 (95% CI 1.81-5.42, P < .0001), 3.31 (95% CI 2.00-5.46, P < .0001), and 3.93 (95% CI 1.49-10.36, P = .006), respectively. Hashimoto thyroiditis was the most prevalent AD (24.3% vs. 10%) OR = 2.55 (95% CI 1.39-4.70, P < .0001), followed by psoriasis (4.3% vs. 1.6%), type 1 diabetes (2.7% vs. 0.4%), and Sjögren syndrome (2.4% vs. 0.4%).These findings suggest a need for a careful surveillance of autoimmune status, especially for Hashimoto thyroiditis in patients with celiac disease.

No association observed between schizophrenia and non-HLA coeliac disease genes: integration with the initial MYO9B association with coeliac disease

Schizophrenia is a severe psychotic illness with a heterogeneous presentation and a devastating impact on social and occupational function. Worldwide variations in schizophrenia incidence rates suggest that local conditions may modify disease risk. The human leukocyte antigen (HLA) region has been confirmed to be associated with schizophrenia by genome-wide association studies in populations across the world. While the presence of autoimmune processes in a subgroup of schizophrenia cases is contentious, the immune system could allow environmental exposures to lead to schizophrenia by generating improper immune response. To investigate this topic, we reviewed the current evidence of the relationship between schizophrenia and coeliac disease. Based on this review, we performed genetic analysis of the MYO9B gene and the IL-2/IL-21 locus by genotyping SNPs that have been previously associated with coeliac disease or schizophrenia in 223 families, 108 unrelated individuals with schizophrenia and 120 controls. Finding no evidence for association with these two loci in our study samples, we applied meta-analytic techniques to combine our findings with previous reports. This synthesis, in light of our review of previous reports, suggests a differing developmental trajectory for schizophrenia and coeliac disease. It is possible that these two conditions do not share any functional overlap.

Heterogeneity of vitamin D receptor gene association with celiac disease and type 1 diabetes mellitus

OBJECTIVE

Vitamin D has been shown to exert multiple immunomodulatory effects and is known to suppress T-cell activation by binding to the vitamin D receptor (VDR). To determine whether VDR gene polymorphisms are related to the susceptibility to celiac disease, we investigated its implication as a candidate gene in the Basque population. Because celiac disease and type 1 diabetes share common susceptibility loci, we also analyzed families with type 1 diabetes mellitus.

METHODS

A total of 37 families with celiac disease and 64 type 1 diabetic families of Basque origin with at least one affected offspring were genotyped for four VDR restriction-site polymorphisms (Fok I, Bsm I, Apa I and Taq I). The AFBAC approach was used to test for association.

RESULTS

Comparison of VDR genotypes of the patients with those of 88 healthy individuals identified "ff" as a risk genotype for celiac disease [p = 0.01; OR = 3.45 (1.12-10.79)]. On the other hand, a significantly higher frequency of haplotype "fBAt" was observed in the type 1 diabetic group [p(c) = 0.02; OR = 4.4 (1.5-15.3)].

CONCLUSION

Our findings suggest that polymorphisms within the vitamin D receptor gene are markers of susceptibility to or protection from autoimmune diseases, although, at least in the Basque population, association of VDR variants with celiac disease and type 1 diabetes seems to be heterogeneous.

Variants within protectin (CD59) and CD44 genes linked to an inherited haplotype in a family with coeliac disease

Coeliac disease (CD) is an autoimmune disorder characterised by inflammation, villous atrophy and hyperplasia of the small intestinal mucosa that affects genetically susceptible individuals. A genome-wide scan was performed in 17 family members with high incidence of CD. Highest nonparametric linkage (NPL) and logarithm of odds (LOD) scores were of 6.21 (P = 0.0107) and 2.57, respectively, to a region on chromosome 11p13-12. Following fine mapping, NPL and LOD scores did not change, but the linkage interval on chromosome 11 was narrowed to a region that is approximately 50.94 cM from pTer. Two inherited haplotypes on chromosomes 11p13-12 and 9q21 were observed in all affected members but not in the majority of clinically normal individuals. Sequencing of genes at region 11p13-12 showed a number of sequence variants, two of which were linked with the inherited haplotype. One of these variants in the CD59 gene was found at a very low frequency in the population and could possibly affect pre-messenger RNA splicing. This study is of particular importance for the identification of novel genes that might be responsible for CD other than human leukocyte antigen.

The pathogenesis of coeliac disease

Coeliac disease is a common condition and its prevalence in UK is now thought to be approximately 1:100. It is being diagnosed and treated more frequently as awareness at the primary care level has increased. Coeliac disease is a complex disorder and is frequently associated with other disease processes. The management of these patients needs to take on a holistic approach, whilst the physician needs to be aware of the rare complications. This article gives an up-to-date review of the literature written on the pathogenesis of coeliac disease. We have attempted to paint a picture from beginning to end, whilst clarifying the grey areas in between. General epidemiological factors are reviewed before looking at genetic risk factors. We assess the sensitivity and specificity of the investigative modalities available for clinical use and comment on optimum management of these patients thereafter. The future of coeliac disease looks promising for patients with several novel therapies on the horizon. Whilst further work is still needed to breed out the toxic epitopes from wheat, novel therapies may come from other areas such as the work aimed at restoring normal tolerance to gluten.

Natural course of autoimmune thyroiditis in type 1 diabetes: association with gender, age, diabetes duration, and puberty

AIMS

To investigate the natural history and incidence of autoimmune thyroiditis (AIT) in paediatric patients with type 1 diabetes (T1D).

METHODS

Since 1990, annual screening for thyroid disease has been performed in children and adolescents with T1D. Antibodies against thyroperoxidase (anti-TPO) and thyroglobulin (anti-TG) as well as TSH were measured in 659 patients (54.3% boys). In 126 patients, anti-TPO and anti-TG levels were followed at yearly intervals from onset up to five years of T1D. Anti-TPO above 30 U/ml and anti-TG above 20 U/ml were considered positive, values above 100 U/ml as significantly raised and indicative of AIT. L-thyroxine treatment was started if TSH was higher than 4.5 microU/ml and/or thyroid gland enlargement on thyroid ultrasound was present.

RESULTS

At initial screening, 15.4% of patients had raised anti-TPO and 14.4% anti-TG. Girls had more frequently raised antibodies than boys. Sixty two patients (9.4%, 61% girls) required treatment with L-thyroxine. The cumulative incidence (SE) of AIT after 10 years of diabetes was 0.14 (0.02), being significantly higher in females (0.18 (0.03)), particularly after the age of 12 years. At T1D onset, positive anti-TPO and anti-TG were present in 21 of 126 patients (16.7%), each. All patients with significantly increased values of anti-TPO (n = 17, 148-5340 U/ml) and anti-TG (n = 11, 140-2000 U/ml) at T1D onset remained positive during the following five years.

CONCLUSIONS

For early detection of autoimmune thyroiditis in children with T1D, measurement of anti-TPO and TSH at T1D onset and in yearly intervals after the age of 12 years is recommended.

[Genetics and immunopathogenics aspects of the celiac disease: a recent vision]

BACKGROUND

Celiac disease, or gluten-sensitive enteropathy, is a strongly inherited condition. Although the genetic association of CD with the DQ2 and DQ8 HLA haplotypes has been known for long, others HLA and non-HLA genes are also important in the development of the disease. Celiac disease results of the combined effect of different normally functioning genes' products. The tissue damage in celiac disease is immunologically mediated and several effector mechanisms are responsible for the disease expression. The interplay between genetic, immunological and environmental factors explains the large spectrum of clinical, histological and serological alterations observed in the different stages of the disease development, pointing out to the polygenic nature of celiac disease.

CONCLUSION

The recent advances in the understanding of the immunopathogenesis, genetics and diagnoses of celiac disease have allowed the revision of strict concepts and previous criteria and their adequation to the new evidences, aiming a better diagnostic and orientation to celiac patients and relatives.

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.

Haplotype variation at the IBD5/SLC22A4 locus (5q31) in coeliac disease in the Irish population

In addition to the well-established association of coeliac disease (CD) with HLA-DQ (6p21) and possibly CTLA4 (2q33), there is considerable evidence for a susceptibility locus on chromosome 5q, which contains many potential candidates for inflammatory disease, including a cluster of cytokine genes in 5q31. CD cases and controls were genotyped for four single-nucleotide polymorphism (SNP) markers that together characterize >90% of the haplotype variation at the IBD5 locus encoding, among others, the SLC22A4 gene. IBD5 and SLC22A4 map to 5q31 and have recently been associated with Crohn's disease and rheumatoid arthritis. Haplotype frequencies do not differ significantly between CD cases and controls in the Irish population, and therefore the chromosome 5 CD susceptibility locus most likely lies elsewhere on 5q.

5'-Insulin gene VNTR polymorphism is specific for type 1 diabetes: no association with celiac or Addison's disease

The VNTR region located at the 5'-end of the insulin gene on chromosome 11p15.5 is linked to susceptibility to type 1 diabetes mellitus (T1DM), and class I alleles have been associated with increased risk of disease, whereas class III alleles are considered to be protective. Although a potential effect on the expression level of thymic insulin and a consequent abnormal tolerance have been proposed as an explanation, it is still not clear whether the association is specific for T1DM or whether it is shared by other autoimmune disorders. To investigate the contribution of INS-VNTR to the genetic susceptibility to autoimmune disorders, we analyzed 102 autoantibody-positive T1DM patients, 59 patients with celiac disease (CD), and 57 patients with Addison's disease (ADD), as well as 111 unrelated healthy individuals from the general population. When analyzing the results, class I allele frequencies were 85.8% in the T1DM group, 77% among CD patients, 71% in the ADD group, and 76.1% in the general population. Association with increased risk was seen only in the T1DM group (pc = 0.015). Risk to T1DM was associated with the class I/class I homozygous genotype (RR, 1.92; 95% CI, 1.03-3.6). In conclusion, INS-VNTR does not seem to be involved in the susceptibility to autoimmune diseases other than T1DM and can be considered a diabetes-specific locus.

Pediatric celiac disease: clinicopathologic and genetic aspects

Evaluation for celiac disease (CD), an autoimmune enteropathy triggered by grain proteins in wheat, barley, rye, and possibly oats, is a common indication for pediatric endoscopy and biopsy. Duodenal or jejunal biopsy remains key for the initial diagnosis of CD. Small intestinal pathology may be diffuse or focal in CD, and histologic findings are nonspecific and must be interpreted in conjunction with clinical and serologic findings. A standardized grading system for CD biopsies is recommended. This review article summarizes the epidemiology, clinical manifestations, genetics, pathogenesis, and serologic and histologic findings of CD. Clinical management of CD and general handling of small intestinal biopsies are also addressed.

Prevalence of celiac disease among relatives of sib pairs with celiac disease in U.S. families

OBJECTIVE

Celiac disease is a familial malabsorptive disorder with an estimated prevalence in first-degree relatives of 10-12%. The prevalence for first-degree and more distant relatives has not been determined in families where there are two affected first-degree relatives. The aim of our investigation was to estimate the prevalence and relative risk for celiac disease in relatives of two siblings diagnosed with celiac disease.

METHODS

We ascertained sib pairs with celiac disease, and then identified all living first-degree relatives and available second-degree relatives to minimize ascertainment bias. We measured IgA endomysial antibodies, a highly specific and sensitive assay for celiac disease, in all subjects without a confirmed biopsy diagnosis. For those individuals with positive serologic tests, IgA tissue transglutaminase antibody tests and human leukocyte antigen DQA1 and DQB1 genotyping were performed for additional confirmation. Individuals with positive biopsy and/or serology were considered affected. We calculated the relative risk of being affected with celiac disease using the lambda(R) statistic.

RESULTS

The prevalence of celiac disease in relatives of affected sib pairs was as follows: 21.3% (13/61) of siblings (lambda(S) = 53); 14.7% (10/68) of offspring (lambda(O) = 37); 17.2% (28/163) of first-degree relatives; 19.5% (16/82) of second-degree relatives; and 17.8% (52/292) of all relatives (lambda(R) = 44.5).

CONCLUSIONS

In these families, we identified a sibling risk approximately double that found in previous reports, as well as significant risk for more distant relatives, probably because of sharing of a common gene. In families where at least two siblings have been diagnosed with celiac disease, relatives are at high risk for celiac disease. Screening should be considered for all family members.

Celiac disease and HLA DQ in patients with IgA nephropathy

OBJECTIVES

Despite some reports on an association between celiac disease and IgA nephropathy, the evidence is still sparse. Celiac disease is strongly associated with the HLA DQ2 and DQ8 haplotypes, which might explain the potential risk of patients to contract various autoimmune conditions. In this study, we sought to establish how common celiac disease is in patients with IgA nephropathy, and whether the possible association can be explained by similar HLA DQ status.

METHODS

A total of 223 consecutive adult patients with IgA nephropathy were studied; 95 cadaver organ transplant donors served as controls for HLA DQ analysis. The diagnosis of celiac disease was based on small bowel mucosal biopsy. All known celiac cases were recorded, and eligible patients (n = 168) underwent serological screening for celiac disease as well as HLA DQ2 and DQ8 analysis. Screening methods were serum endomysium and tissue transglutaminase antibodies; patients who tested positive underwent mucosal biopsy.

RESULTS

Eight patients (3.6%, 95% CI = 1.6-7.0%) with IgA nephropathy were found to have celiac disease; three of them were identified by serological screening. All celiac cases had the HLA DQ2 or DQ8 haplotype, but these were not more common in patients with IgA nephropathy than in controls. As many as 14% of HLA DQ2 positive patients with IgA nephropathy had celiac disease. Gluten-free diet had no apparent influence on the course of nephropathy.

CONCLUSIONS

Although there is no increase in celiac-type HLA DQ, patients with IgA nephropathy carry a risk of contracting celiac disease. It can be hypothesized that the increased intestinal permeability in IgA nephropathy may predispose genetically susceptible patients to celiac disease.

Coeliac disease: dissecting a complex inflammatory disorder

The disease mechanisms of complex inflammatory disorders are difficult to define because of extensive interactions between genetic and environmental factors. Coeliac disease is a typical complex inflammatory disorder, but this disease is unusual in that crucial genetic and environmental factors have been identified. This knowledge has allowed functional studies of the predisposing HLA molecules, the identification of antigenic epitopes and detailed studies of disease-relevant T cells in coeliac disease. This dissection of the pathogenic mechanisms of coeliac disease has uncovered principles that are relevant to other chronic inflammatory diseases.

Endocrinological disorders and celiac disease

Celiac disease is a permanent intolerance to dietary gluten. Its well known features are abdominal symptoms, malabsorption of nutrients, and small-bowel mucosal inflammation with villous atrophy, which recover on a gluten-free diet. Diagnosis is challenging in that patients often suffer from subtle, if any, symptoms. The risk of clinically silent celiac disease is increased in various autoimmune conditions. The endocrinologist, especially, should maintain high suspicion and alertness to celiac disease, which is to be found in 2-5% of patients with insulin-dependent diabetes mellitus or autoimmune thyroid disease. Patients with multiple endocrine disorders, Addison's disease, alopecia, or hypophysitis may also have concomitant celiac disease. Similar heredity and proneness to autoimmune conditions are considered to be explanations for these associations. A gluten-free diet is essential to prevent celiac complications such as anemia, osteoporosis, and infertility. The diet may also be beneficial in the treatment of the underlying endocrinological disease; prolonged gluten exposure may even contribute to the development of autoimmune diseases. The diagnosis of celiac disease requires endoscopic biopsy, but serological screening with antiendomysial and antitissue transglutaminase antibody assays is an easy method for preliminary case finding. Celiac disease will be increasingly detected provided the close association with autoimmune endocrinological diseases is recognized.

Analysis of candidate genes on chromosome 19 in coeliac disease: an association study of the KIR and LILR gene clusters

Coeliac disease is strongly heritable, with more than half of the genetic susceptibility estimated to come from genes outside the HLA region. Several candidate regions have been suggested from genome-wide linkage studies including chromosome 19q13.4 where linkage has been replicated between populations. The natural killer (NK) cell immunoglobulin-like receptors (KIRs) and leukocyte immunoglobulin-like receptor (LILR, also known as ILT and LIR) gene clusters lie within this region in the leukocyte receptor cluster (LRC). KIR molecules are involved in cytotoxic lymphocyte function and expressed by intraepithelial T and NK cells in the duodenum. We studied 132 unrelated UK Caucasian coeliac patients and their parents together with a control group of 171 UK Caucasians. PCR-SSP for KIR2DL1, KIR2DL2, KIR2DL3, KIR2DL5, LILRA3 (ILT6), LILRA3 deletion and an LILRA3 exon 3 single nucleotide polymorphism (SNP) allowed classification of KIR genotypes into five categories and determination of homozygosity or heterozygosity for the common A and B type KIR haplotypes (as defined in the text) and for the LILRA3 deletion. Case-control analysis found no association of the five KIR genotype categories, the A or B KIR haplotypes, the LILRA3 gene deletion or the LILRA3 exon 3 SNP with coeliac disease. A transmission disequilibrium test also found no association of the A and B KIR haplotypes or the LILRA3 gene deletion with coeliac disease.

Genome-wide linkage analysis for celiac disease in North American families

Celiac disease (CD) is an autoimmune disease caused by sensitivity to the dietary protein gluten. It has a prevalence of 1 in 250 in the United States. Multiple-case families are common with a risk to siblings from 10-12%. Previous linkage studies have found no significant evidence for linkage other than to HLA. In this study, we performed a genome-wide search on 62 families with at least two cases of CD to identify non-HLA loci for CD. Two-point and multipoint parametric and nonparametric analyses were performed on the entire set of families and on sets stratified by the HLA genotype. Accounting for multiple testing, we found genome-wide intermediate linkage evidence at 18q (heterogeneity LOD (HLOD) = 3.6) and at 3p (HLOD = 3.2) and suggestive evidence at 5p (HLOD = 2.7). Good consensus between two-point and multipoint evidence was not found, and after genotyping with new markers in these regions, our results were inconclusive. The 18q region had intermediate two-point evidence, but weak multipoint evidence. At 3p and 5p, the addition of follow-up markers added flanking support, yet multipoint evidence was still lacking. Our results indicate that multipoint analyses may be hindered by the complexity of CD. Multipoint analyses are not robust to model misspecification, and further development of models is needed. Additional study of these and other families is necessary to validate or rule out the regions implicated in this study.

HLA-DRB1 and MHC class 1 chain-related A haplotypes in Basque families with celiac disease

The contribution of HLA genes to the genetic risk for celiac disease (CD) has been known for a long time. Recent publications have pointed to the possibility that a second, independent susceptibility locus could be located in the same genomic region, and a triplet repeat polymorphism in exon 5 of the gene MHC class I chain-related protein A (MICA; located between TNFA and HLA-B) has been associated with several autoimmune disorders, including type 1 diabetes mellitus (DM1) and Addison's disease. On the other hand, a single amino acid change in exon 3 of MICA (M129V) has been shown to strongly reduce MICA binding to NKG2D, an activating natural killer receptor expressed also on T cells, and this could have significant effects on autoimmune reactions. In this study, we have analyzed the contribution of these polymorphisms to CD in 37 Basque families, and have constructed MICA-HLA-DRB1 haplotypes to determine whether MICA has an effect independent from the HLA class II conferred risk. In our population, HLA-DRB1*0301 was associated with an increased risk for CD, while HLA-DRB1*1501 conferred protection from the disease (OR: 7.38 and 0.06, respectively). On the other hand, MICA allele A4 was positively associated with the disease (OR: 4.69) whereas allele A9 showed a trend towards protection (OR: 0.18), although significance did not hold after correction. No association of the exon 3 biallelic polymorphism was observed. A positive allelic association was found for haplotypes A5.1-DRB1*0301 (associated with risk for disease), A4-DRB1*0301 and A6-DRB1*07. In view of our results, both HLA-DRB1 and MICA are associated with CD, but stratification analysis did not show any independent contribution of the MICA polymorphisms analyzed to CD risk. Besides, MICA allele A4 (also A5.1 was associated with risk for CD and other diseases) is in strong linkage disequilibrium with HLA-DRB1*0301. Finally, the major histocompatibility complex region's conferred susceptibility to CD, at least in Basque, is very similar to that observed for DM1, with shared risk and protective haplotypes.

Human genome search in celiac disease: mutated gliadin T-cell-like epitope in two human proteins promotes T-cell activation

Discovery of a number of novel and known human genes whose protein products bear striking similarity to two or more wheat gliadin domains raised the possibility that human intestinal non-HLA peptides homologous to celiac T-cell epitopes could play a role in non-HLA gene specification in celiac disease. Database searching of the entire human genome identified only 11 gut-expressed proteins with high T-cell epitope homology, particularly to the DQ2-gamma-I-gliadin epitope (i.e. TFIIA, FOXJ2 and IgD; mean BestFit quality score=40 versus random value of 24). Others were similar to DQ2-alpha-I-gliadin (i.e. PAX9; BestFit quality 46 versus 20 for random), or DQ2-alpha-II-gliadin (PHLDA1, known in mice as the T-cell death-associated gene; BestFit quality 43 versus 30 for random) epitopes. Among proteins previously screened for gliadin homology, noteworthy was achaete scute homologous protein (DQ2-alpha-I-gliadin; BestFit quality 41 versus 22 for random). With the exception of IgD, all are nuclear factors. Paying particular attention to the position of potential major histocompatibility complex (MHC) anchor residues, several were selected for testing in a DQ2-gamma-I-gliadin-restricted T-cell system. All native 10-mer peptides were inactive, even when deamidated, but V96F substitution of deamidated TFIIA amino acid residues 91-100 stimulated IL-2 release at levels exceeding the wheat gliadin positive control. Also active, but only slightly, was L1009F substitution of AIB3 amino acid residues 1004-1013. PlotSimilarity alignment of TFIIAs from eight species revealed subthreshold similarity score in the peptide region, in contrast to the highly conserved amino and carboxy termini. Molecular modeling of TFIIA[V96F] peptide points to an important juxtaposition of an upwardly projecting phenylalanine residue at peptide position 6 that likely contacts a receptor complementarity-determining region, and a downwardly projecting glutamic acid residue that fits into the shallow MHC P7 pocket. These observations tentatively point to a new multi-gene hypothesis for the initiation of celiac disease in which deamidated free human peptides with T-cell epitope homology (particularly those made more homologous by mutation) escape negative selection, as per deamidation of the HEL(48-62) peptide in the hen egg lysozyme model of autoimmunity. Deamidation following peptide release due to injury triggers inflammation, thereafter repeatedly provoked by dietary gliadin immunodominant peptides concentrated in the proximal small intestine.

HLA-DQ typing in the diagnosis of celiac disease

OBJECTIVE

More than 95% of celiac patients share the major histocompatibility complex II class human leukocyte antigen (HLA) DQ2 or DQ8 haplotype; patients negative for both types are unlikely to suffer from celiac disease. Our aim was to investigate whether HLA-DQ2 and -DQ8 typing is helpful when diagnosis is uncertain because of the absence of unequivocal small bowel villous atrophy.

METHODS

HLA-DQ2 and -DQ8 typing was carried out in 59 patients evincing nondiagnostic small bowel mucosal lesion or positive celiac serology, and in 17 patients maintaining a gluten-free diet without biopsy-proven celiac disease. HLA findings were compared to small bowel mucosal morphology; intraepithelial lymphocytes; and serum endomysial (EmA), reticulin, tissue transglutaminase (anti-tTG) and gliadin antibodies.

RESULTS

Of the 59 patients evincing only minor small bowel mucosal changes or positive celiac disease serology, 22 (37%) were negative for DQ2 and DQ8. All EmA-positive patients had celiac-type HLA, but antireticulin antibody, anti-tTg, and antigliadin antibody were also present in HLA-DQ2- and -DQ8-negative individuals. Eleven of 17 patients (65%) observing a gluten-free diet before small bowel biopsy did not share celiac-type HLA. None of the 17 had apparent villous atrophy. Serum EmA and anti-tTG were negative in all. HLA-DQ typing is less expensive than follow-up biopsy in the exclusion of celiac disease.

CONCLUSIONS

HLA-DQ2 and -DQ8 determination is useful in exclusion, probably lifelong, of celiac disease in individuals with an equivocal small bowel histological finding. The low specificity of this test must, however, be borne in mind.

Genomewide linkage analysis of celiac disease in Finnish families

Celiac disease (CD), or gluten-sensitive enteropathy, is a common multifactorial disorder resulting from intolerance to cereal prolamins. The only established genetic susceptibility factor is HLA-DQ, which appears to explain only part of the overall genetic risk. We performed a genomewide scan of CD in 60 Finnish families. In addition to strong evidence for linkage to the HLA region at 6p21.3 (Z(max)>5), suggestive evidence for linkage was found for six other chromosomal regions--1p36, 4p15, 5q31, 7q21, 9p21-23, and 16q12. We further analyzed the three most convincing regions--4p15, 5q31, and 7q21--by evaluation of dense marker arrays across each region and by analysis of an additional 38 families. Although multipoint analysis with dense markers provided supportive evidence (multipoint LOD scores 3.25 at 4p15, 1.49 at 5q31, and 1.04 at 7q21) for the initial findings, the additional 38 families did not strengthen evidence for linkage. The role that HLA-DQ plays was studied in more detail by analysis of DQB1 alleles in all 98 families. All but one patient carried one or two HLA-DQ risk alleles, and 65% of HLA-DQ2 carriers were affected. Our study indicates that the HLA region harbors a predominant CD-susceptibility locus in these Finnish families.

Genome-wide linkage analysis of Scandinavian affected sib-pairs supports presence of susceptibility loci for celiac disease on chromosomes 5 and 11

Celiac disease (CD) is a common chronic inflammatory disorder of the small intestine with a multifactorial aetiology. HLA is a well-known risk factor, but other genetic factors also influence disease susceptibility. To identify the genes involved in this disorder, we performed a genome-wide scan on 106 well-defined Swedish and Norwegian families with at least two affected siblings. We investigated familial segregation of 398 microsatellite markers, and utilised non-parametric linkage analysis. The strongest linkage with disease was found to the HLA locus (6p) (P<0.000006). There were eight regions besides HLA with a point wise P value below 0.05. Among these eight regions were 11q and 5q, both of which have been suggested in several linkage studies of independent celiac disease families. We also performed a stratification analysis of families according to their HLA genotypes. This resulted in significant differences on chromosome 2q. These results indicate that 11q, 5q and possibly also 2q are true susceptibility regions in CD.

The tissue transglutaminase gene is not a primary factor predisposing to celiac disease

OBJECTIVES

The aim of this study was to determine whether the tissue transglutaminase (tTG) gene is a causal factor in the pathogenesis of celiac disease (CD).

METHODS

A total of 147 Dutch families with at least one patient with biopsy-proven CD were available for this study. In all patients, CD was diagnosed according to the revised European Society for Pediatric Gastroenterology and Nutrition criteria. A microsatellite marker in a noncoding region of the tTG gene was investigated for both linkage and association. Linkage was tested by determining the amount of allele sharing between affected brothers and sisters (affected sibling [sib] pair analysis). Association was determined by comparing transmission of certain tTG alleles from parents to CD patients to the nontransmitted alleles by the transmission/disequilibrium test.

RESULTS

Linkage analysis did not show cosegregation of the tTG gene with celiac disease in our families, and there was no association between certain tTG alleles and celiac disease. Furthermore, the tTG gene could be excluded as a CD susceptibility gene.

CONCLUSION

Our results indicate that the tTG gene can be excluded as a major primary genetic factor in CD pathogenesis.

Linkage analysis of HLA and candidate genes for celiac disease in a North American family-based study

BACKGROUND

Celiac disease has a strong genetic association with HLA. However, this association only explains approximately half of the sibling risk for celiac disease. Therefore, other genes must be involved in susceptibility to celiac disease. We tested for linkage to genes or loci that could play a role in pathogenesis of celiac disease.

METHODS

DNA samples, from members of 62 families with a minimum of two cases of celiac disease, were genotyped at HLA and at 13 candidate gene regions, including CD4, CTLA4, four T-cell receptor regions, and 7 insulin-dependent diabetes regions. Two-point and multipoint heterogeneity LOD (HLOD) scores were examined.

RESULTS

The highest two-point and multipoint HLOD scores were obtained in the HLA region, with a two-point HLOD of 3.1 and a multipoint HLOD of 5.0. For the candidate genes, we found no evidence for linkage.

CONCLUSIONS

Our significant evidence of linkage to HLA replicates the known linkage and association of HLA with CD. In our families, likely candidate genes did not explain the susceptibility to celiac disease.

Genetic factors underlying gluten-sensitive enteropathy

Genetic epidemiology clearly has shown that there is a genetic predisposition to gluten-sensitive enteropathy (GSE), or celiac disease. The strong genetic component, as determined by the lambda sib (lambda s), has been calculated to lie in the range of 7.5 to 30, based on a 5% to 10% recurrence risk for siblings. Ninety-five percent of northern European patients with GSE carry a particular HLA-DQ alpha beta heterodimer. Studies support the concept that the HLA-DQ gene acts as a dominant gene, and they also found that, in addition to HLA-DQ, a second locus within the major histocompatibility complex (MHC) is involved in the predisposition to GSE in the Dutch population. Genome scans conducted so far suggest that MHC and non-MHC loci collectively contribute to disease susceptibility. Since one, and probably even two, gene(s) from the MHC region itself determine at least 40% to 50% of the genetic predisposition to GSE, it is expected that the other loci each contribute only a little to the total genetic variation. The exact role of these additional genes (i.e., whether they are involved in the initiation or the progression of the disease) remains to be determined.

Celiac disease-associated autoimmune endocrinopathies

Celiac disease (CD) is an autoimmune disorder induced by gluten intake in genetically susceptible individuals. It is characterized by the presence of serum antibodies to endomysium, reticulin, gliadin, and tissue transglutaminase. The incidence of CD in various autoimmune disorders is increased 10- to 30-fold in comparison to the general population, although in many cases CD is clinically asymptomatic or silent. The identification of such cases with CD is important since it may help in the control of type I diabetes or endocrine functions in general, as well as in the prevention of long-term complications of CD, such as lymphoma. It is believed that CD may predispose an individual to other autoimmune disorders such as type I diabetes, autoimmune thyroid, and other endocrine diseases and that gluten may be a possible trigger. The onset of type I diabetes at an early age in patients with CD, compared to non-CD, and the prevention or delay in onset of diabetes by gluten-free diet in genetically predisposed individuals substantiates this antigen trigger hypothesis. Early identification of CD patients in highly susceptible population may result in the treatment of subclinical CD and improved control of associated disorders.

Candidate gene regions and genetic heterogeneity in gluten sensitivity

BACKGROUND

Gluten sensitivity is a common multifactorial disorder, manifested in the small intestine or on the skin as typical coeliac disease or dermatitis herpetiformis, respectively. The only established genetic risk factor is HLA DQ2.

AIMS

We tested genetic linkage of previously reported chromosomal loci 5q and 11q in Finnish families with gluten sensitivity. We also tested if genetic linkage to candidate loci on 5q, 11q, 2q33, and HLA DQ differed with respect to clinical manifestations or sex.

SUBJECTS

We studied 102 Finnish families with affected sibpairs. For heterogeneity analysis, families were divided into subgroups according to sex and the presence of dermatitis herpetiformis, the skin manifestation of gluten sensitivity.

METHODS

Non-parametric linkage between microsatellite markers and disease was tested. Linkage heterogeneity between subgroups was tested using the M test. The transmission/disequilibrium test and association analysis were performed.

RESULTS

Evidence of linkage to 11q (MLS 1.37), but not to 5q, was found in the entire dataset of 102 families. Heterogeneity between subgroups was suggested: families with only the intestinal disease showed linkage mainly to 2q33 whereas families with dermatitis herpetiformis showed linkage to 11q and 5q, but not to 2q33. Linkage in all three non-HLA loci was strongest in families with predominantly male patients. HLA DQ2 conferred much stronger susceptibility to females than males.

CONCLUSIONS

Independent evidence for the suggested genetic linkage between 11q and gluten sensitivity was obtained. The possible linkage heterogeneity suggests genetic differences between intestinal and skin manifestations, and the gender dependent effect of HLA DQ2.

Comparative analysis of organ-specific autoantibodies and celiac disease--associated antibodies in type 1 diabetic patients, their first-degree relatives, and healthy control subjects

OBJECTIVE

In type 1 diabetes the coexistence with other endocrine diseases and organ-specific autoantibodies has been frequently reported leading to the concept of autoimmune polyendocrine syndrome (APS). In addition, an association of type 1 diabetes with celiac disease has been described. These disorders share a similar genetic background, and first-degree relatives of type 1 diabetic patients may also be affected significantly. Screening for specific antibodies allows early diagnosis of these disorders.

RESEARCH DESIGN AND METHODS

In the present cross-sectional study, we analyzed sera from 197 recent-onset type 1 diabetic patients at the time of diagnosis, 882 first-degree relatives, and sera of 150 healthy control subjects for prevalence and co-occurence of the following antibodies (method): insulin autoantibodies (radioimmunoassay); GAD and IA-2 antibodies (radioligand assay); islet cell antibody, anti-adrenal cortex antibodies, and anti-gastric parietal cell antibodies (indirect immunofluorescence); anti-thyroglobulin and anti-thyroid peroxidase antibodies; and gliadin IgG/A and tissue-transglutaminase IgA (enzyme-linked immunosorbent assay).

RESULTS

The overall frequency of gastric patietal cell antibodies and adrenal antibodies did not differ significantly among groups. In contrast, type 1 diabetes-associated antibodies and thyroid antibodies were significantly more frequent both in recent-onset type 1 diabetic patients and in the group of first-degree relatives (P < 0.05). The prevalence of gliadin IgG/IgA and transglutaminase IgA was significantly higher in the group of recent-onset type 1 diabetic patients (P < 0.05), but the difference between first-degree relatives and control subjects did not reach statistical significance. Focusing on the coexistence of antibodies, the group of recentonset type 1 diabetic patients presented with 27.4% of the subjects testing antibody-positive-specific for two or more of the envisaged disorders (i.e., type 1 diabetes, autoimmune thyroiditis, and celiac disease) compared with 3.1% in the group of first-degree relatives and 0 of 150 in the control population (P < 0.05).

CONCLUSIONS

We conclude that, in an active case-finding strategy, recent-onset type 1 diabetic patients should be routinely screened at least for concomitant autoimmune thyroid disease and additionally for celiac disease. Screening in their first-degree relatives should include at a minimum the search for thyroid autoimmunity in addition to screening for pre-type 1 diabetes.

The CTLA4/CD28 gene region on chromosome 2q33 confers susceptibility to celiac disease in a way possibly distinct from that of type 1 diabetes and other chronic inflammatory disorders

The effect of the gene region on chromosome 2q33 containing the CD28 and the cytotoxic T-lymphocyte associated (CTLA4) genes has been investigated in several diseases with chronic inflammatory nature. In addition to celiac disease (CD), type I diabetes, Grave's disease, rheumatoid arthritis and multiple sclerosis have all demonstrated associations to the A/G single nucleotide polymorphism (SNP) in exon 1, position +49 of the CTLA4 gene. The purpose of this study was to investigate this gene region in a genetically homogeneous population consisting of 107 Swedish and Norwegian families with CD using genetic association and linkage methods. We found a significant association with preferential transmission of the A-allele of the exon 1 +49 polymorphism by using the transmission disequilibrium test (TDT). Suggestive linkage of this region to CD was moreover demonstrated by non-parametric linkage (NPL) analysis giving a NPL-score of 2.1. These data strongly indicates that the CTLA4 region is a susceptibility region in CD. Interestingly, of the several chronic inflammatory diseases that exhibit associations to the CTLA4 +49 A/G dimorphism, CD appears to be the only disease associated to the A allele. This suggests that the +49 alleles of the CTLA4 gene are in linkage disequilibrium with two distinct disease predisposing alleles with separate effects. The peculiar association found in the gut disorder CD may possibly relate to the fact that the gastrointestinal immune system, in contrast to the rest of the immune system, aims to establish tolerance to foreign proteins.

Celiac disease: strongly heritable, oligogenic, but genetically complex

Celiac disease, or gluten-sensitive enteropathy, is a small intestinal disorder which affects up to 1:250 people in the United States. Disease development has a strong genetic component, with a sibling relative risk (lambda(s)) of 30. One susceptibility locus is the MHC region, with a particular association with the HLA-DQ alleles DQA1*0501 and DQB1*0201. However, haplotype sharing studies suggest that genes within the MHC complex contribute no more than 40% to the sibling familial risk of disease. This means that the stronger genetic risk is likely to be conferred by a small number of non-HLA-linked genes. Genome-wide linkage studies, plus linkage and association studies of candidate loci have been used to try to identify these genes. However, these studies have either failed to detect loci, or produced inconsistent results. Such difficulties in identifying susceptibility genes are encountered when investigating any complex genetic disorder. Information from the Human Genome Project, coupled with new technology for high throughput single nucleotide polymorphism typing may help to identify the non-HLA determinants of celiac disease in the future.

Genetics of celiac disease

Celiac disease (CD) is a chronic inflammatory disease of the gut resulting from ingestion of gluten, occurring in genetically susceptible individuals. The strong genetic association of CD with the DQ2 and DQ8 HLA heterodimers has been known for long, but others non-HLA genes are involved. In order to identify susceptibility genes to CD, several studies have been performed, based on either linkage analyses or candidate gene approaches. This review describes these different studies and their results. The hypothesis of the implication of the DR53 heterodimer in the HLA region has been proposed. The existence of a susceptibility locus on chromosome 5q has been evidenced through linkage analysis and candidate gene strategies have revealed the role of CTLA-4 and of the immunoglobulin gamma genes in the disease.

Human genome search in celiac disease using gliadin cDNA as probe

Celiac disease is a wheat gliadin-promoted disorder that displays a complex genetic susceptibility associated with HLA-DQ2, and one or more unknown factor(s), possibly gliadin-like. The presence of mammalian proteins with partial gliadin similarity was suggested by transglutaminase-independent multi-tissue reactivity of gliadin-immunopurified antibodies from celiac patients. No non-plant sequence, however, was identified in gliadin peptide epitope searches of non-redundant and EST databanks via TBLASTN, BLASTP and FASTA, even at E values as high as 20. Therefore, an alpha-gliadin cDNA screen of human cDNA and genomic libraries was undertaken, an approach in keeping with positive human Northern and Southern analyses with the same probe. Four distinct cDNA clones were obtained, the most stringent of which (3.2 and 5.1 kb) were novel, and featured potential open reading frames with high gliadin domain II and domain IV homologies (BestFit quality scores >/=295 and 322, respectively, versus random value 126-127). Both were also homologous to ESTs. An additional 5' gliadin oligonucleotide screen identified the widely distributed cytoplasmic protein acyl coA hydrolase whose homology was restricted to the oligonucleotide probe (BestFit quality=215 versus 100 for random); and achaete-scute homologous protein, which displays particularly high gliadin domain II homology (BestFit quality 316 versus 111 for random). Genomic screening uncovered 16 positives, one of which was the ALR gene, whose similarity to three of gliadin's five domains (I, II and IV; BestFit quality 322-473 versus 121-154 for random) was remarkable. More extensive was novel genomic clone 2, with fragments hybridizing to cDNA probes approximating gliadin domains I, II+IV, V and the gliadin 5' untranslated region, and mapping by FISH to 19q13.11-13. 12. Two fragments were sequenced; one was exonic, as predicted by four different programs; and test oligonucleotides suggested widespread 4 and/or 2 kb mRNA expression, even at high stringency (t(m)-8.8 deg. C). Taken together, it is apparent that several genes with partial gliadin homology exist in the human genome. Many bear gliadin-like T-cell epitopes, are expressed in intestine and, like transglutaminase, are cytoplasmic. Glutamine to glutamic acid or other mutation within such epitopes followed by injury or infection-related release could explain enhanced disease susceptibility in affected families.

Molecular basis of celiac disease

Celiac disease (CD) is an intestinal disorder with multifactorial etiology. HLA and non-HLA genes together with gluten and possibly additional environmental factors are involved in disease development. Evidence suggests that CD4(+) T cells are central in controlling an immune response to gluten that causes the immunopathology, but the actual mechanisms responsible for the tissue damage are as yet only partly characterized. CD provides a good model for HLA-associated diseases, and insight into the mechanism of this disease may well shed light on oral tolerance in humans. The primary HLA association in the majority of CD patients is with DQ2 and in the minority of patients with DQ8. Gluten-reactive T cells can be isolated from small intestinal biopsies of celiac patients but not of non-celiac controls. DQ2 or DQ8, but not other HLA molecules carried by patients, are the predominant restriction elements for these T cells. Lesion-derived T cells predominantly recognize deamidated gluten peptides. A number of distinct T cell epitopes within gluten exist. DQ2 and DQ8 bind the epitopes so that the glutamic acid residues created by deamidation are accommodated in pockets that have a preference for negatively charged side chains. Evidence indicates that deamidation in vivo is mediated by the enzyme tissue transglutaminase (tTG). Notably, tTG can also cross-link glutamine residues of peptides to lysine residues in other proteins including tTG itself. This may result in the formation of complexes of gluten-tTG. These complexes may permit gluten-reactive T cells to provide help to tTG-specific B cells by a mechanism of intramolecular help, thereby explaining the occurrence of gluten-dependent tTG autoantibodies that is a characteristic feature of active CD.

Current concepts of celiac disease pathogenesis

Our knowledge of celiac disease pathogenesis has recently made rapid progress. The disorder is now considered the result of a complex interplay of intrinsic (genetic) and variable extrinsic (environmental) factors that explain the wide spectrum of clinical manifestations ranging from asymptomatic to severe malabsorption. Gluten peptides are efficiently presented by celiac disease-specific HLA-DQ2- and HLA-DQ8-positive antigen-presenting cells, and thus drive the immune response, predominantly in the connective tissue of the lamina propria. Tissue transglutaminase, which has been identified as the highly specific endomysial autoantigen, is released from cells during inflammation. It may potentiate antigen presentation by HLA-DQ2 and HLA-DQ8 by deamidating or cross-linking gluten peptides. The result is lamina propria T-cell activation and mucosal transformation by activated intestinal fibroblasts. In the future, manipulation of the gut-associated lymphoid tissue may allow reduced sensitivity or even generate oral tolerance to gluten. Long-standing untreated celiac disease, even if clinically silent, predisposes for other autoimmune diseases. Therefore, population screening for immunoglobulin A antibodies to tissue transglutaminase seems justified.

Screening by anti-endomysium antibody for celiac disease in diabetic children and adolescents in Austria

BACKGROUND

Unrecognized celiac disease (CD) may be found in a substantial proportion of patients with type I diabetes mellitus.

METHODS

A cohort of 403 Austrian children and adolescents with type I diabetes mellitus (210 males and 193 females; age range, 1-22 years) was screened for celiac disease using the IgA anti-endomysium antibody test (EMA) and the immunoglobulin (Ig)G anti-gliadin (AGA-IgG) and IgA anti-gliadin (AGA-IgA) antibody test.

RESULTS

Twelve patients' sera (2.98%) yielded positive EMA results and two patients' sera (0.49%) with IgA deficiency had high AGA-IgG values. All but one of these patients underwent intestinal biopsy. Six (1.49%) had clear histologic evidence of CD (flat mucosa), whereas three (0.74%) showed minor histologic changes (increase in intraepithelial lymphocytes) and four (0.99%), including the EMA-negative patients with IgA deficiency, had a normal mucosa. When the cases with silent and potential CD were combined, the overall prevalence in the current cohort was 2.98%. There was no difference in the hemoglobin (Hb)A1c level between antibody-positive and -negative patients, and subsequent gluten-free diet did not change this metabolic parameter.

CONCLUSION

The prevalence of clinically unrecognized CD, found by EMA screening, is much higher in Austrian children with diabetes than in a comparable population without diabetes. The prevalence of CD in diabetic children in Austria is distinctly lower, however, than in several other countries.

A susceptibility locus for human systemic lupus erythematosus (hSLE1) on chromosome 2q

To identify chromosomal regions containing susceptibility loci for systemic lupus erythematosus (SLE), we performed genome scans in families with multiple SLE patients from Iceland, a geographical and genetic isolate, and from Sweden. A number of chromosomal regions showed maximum lod scores (Z) indicating possible linkage to SLE in both the Icelandic and Swedish families. In the Icelandic families, five regions showed lod scores greater than 2.0, three of which (4p15-13, Z=3.20; 9p22, Z=2.27; 19q13, Z=2.06) are homologous to the murine regions containing the lmb2, sle2 and sle3 loci, respectively. The fourth region is located on 19p13 (D19S247, Z=2.58) and the fifth on 2q37 (D2S125, Z=2.06). Only two regions showed lod scores above 2.0 in the Swedish families: on chromosome 2q11 (D2S436, Z=2. 13) and 2q37 (D2S125, Z=2.18). The combination of both family sets gave a highly significant lod score at D2S125 of Z=4.24 in favor of linkage for 2q37. This region represents a new locus for SLE. Our results underscore the importance of studying well-defined populations for genetic analysis of complex diseases such as SLE.

No polymorphism in the tissue transglutaminase gene detected in coeliac disease patients

BACKGROUND

The autoantigen for the anti-endomysial antibody (AEA) found in coeliac disease has recently been reported to be the enzyme tissue transglutaminase (tTG). Polymorphisms in the gene for tTG would result in different enzymic isoforms being expressed. Certain isoforms may interact with gliadin to create antigenic neoepitopes, which could then generate an immune response in genetically predisposed individuals possessing major histocompatibility complex (MHC) class II DQ2.

METHODS

We have sequenced the coding region of tTG in coeliac patients and normal controls. Total RNA was extracted from mucosal biopsies from eight AEA-positive histologically proven coeliac disease patients and four control patients with a histologically normal duodenum and a negative AEA. The 2-kb coding region of tTG was amplified in overlapping fragments by reverse transcription polymerase chain reaction (PCR), using five sets of PCR primers. Each overlapping PCR fragment was sequenced using the fmol DNA sequencing system.

RESULTS

tTG transcripts were detected in all samples. There was no difference in the coding sequence of tTG between the four control and eight coeliac patients, even though we observed differences in sequence between our study and the original published sequence. These differences have also been reported in sequences published subsequent to the original description.

CONCLUSIONS

Polymorphisms in the tTG gene have not been observed in coeliac disease patients and therefore cannot explain the creation of neoepitopes.

CD28/CTLA4 gene region on chromosome 2q33 confers genetic susceptibility to celiac disease. A linkage and family-based association study

Celiac disease (CD) is a common small intestinal injury caused by sensitivity to gliadin in genetically-predisposed individuals. The only susceptibility locus established is the HLA-DQ. We tested whether the chromosomal region of the CD28/CTLA4 genes on 2q33 is linked to CD. These genes encode receptors regulating the T-lymphocyte activation. Recently, this gene region was reported to be linked to the susceptibility to many autoimmune diseases, including insulin-dependent diabetes (IDDM12locus). It is thus an obvious candidate locus also for CD, since the intestinal injury is mediated by the immune system. Genetic linkage between seven marker loci in this gene region and CD was studied in 69 Finnish families. In the multipoint linkage analysis, the highest non-pararametric linkage score (NPL) was 1.75 (P=0.04) for D2S116, suggesting weak linkage for this candidate locus. To evaluate this finding, an additional 31 families were typed for all markers. In the combined set of 100 families the NPL score for marker D2S116 was 2.55 (P=0.006) and for other markers 1.90-2.47 (P=0.029-0.007), supporting genuine linkage at this region. Significantly, locus D2S116 also showed a clear allelic association in these 100 families (P=0.0001). The transmission/disequilibrium test (TDT) for locus D2S116 gave preliminary evidence for preferential maternal non-transmission of allele *136 to patients (TDTmax=8.3; P<0.05). No paternal deviation was found suggesting that the effect of the locus might be mediated by a sex-dependent factor protective against CD. Our results indicate that the CD28/CTLA4 gene region can contain a novel susceptibility locus for CD and support the hypothesis that CD has an immune system-mediated component. Like the HLA, the CD28/CTLA4 genes appear to be associated with genetic susceptibility to various autoimmune diseases.

Genome search in celiac disease

Celiac disease (CD), a malabsorption disorder of the small intestine, results from ingestion of gluten. The HLA risk factors involved in CD are well known but do not explain the entire genetic susceptibility. To determine the localization of other genetic risk factors, a systematic screening of the genome has been undertaken. The typing information of 281 markers on 110 affected sib pairs and their parents was used to test linkage. Systematic linkage analysis was first performed on 39 pairs in which both sibs had a symptomatic form of CD. Replication of the regions of interest was then carried out on 71 pairs in which one sib had a symptomatic form and the other a silent form of CD. In addition to the HLA loci, our study suggests that a risk factor in 5qter is involved in both forms of CD (symptomatic and silent). Furthermore, a factor on 11qter possibly differentiates the two forms. In contrast, none of the regions recently published was confirmed by the present screening.