Susceptibility to develop celiac disease is primarily associated with HLA-DQ alleles

Genetic risk variants for membranous nephropathy: extension of and association with other chronic kidney disease aetiologies

Background

Membranous nephropathy (MN) is a common cause of nephrotic syndrome in adults. Previous genome-wide association studies (GWAS) of 300 000 genotyped variants identified MN-associated loci at HLA-DQA1 and PLA2R1.

Methods

We used a combined approach of genotype imputation, GWAS, human leucocyte antigen (HLA) imputation and extension to other aetiologies of chronic kidney disease (CKD) to investigate genetic MN risk variants more comprehensively. GWAS using 9 million high-quality imputed genotypes and classical HLA alleles were conducted for 323 MN European-ancestry cases and 345 controls. Additionally, 4960 patients with different CKD aetiologies in the German Chronic Kidney Disease (GCKD) study were genotyped for risk variants at HLA-DQA1 and PLA2R1.

Results

In GWAS, lead variants in known loci [rs9272729, HLA-DQA1, odds ratio (OR) = 7.3 per risk allele, P = 5.9 × 10^-27 and rs17830558, PLA2R1, OR = 2.2, P = 1.9 × 10^-8] were significantly associated with MN. No novel signals emerged in GWAS of X-chromosomal variants or in sex-specific analyses. Classical HLA alleles (DRB1*0301-DQA1*0501-DQB1*0201 haplotype) were associated with MN but provided little additional information beyond rs9272729. Associations were replicated in 137 GCKD patients with MN (HLA-DQA1: P = 6.4 × 10^-24; PLA2R1: P = 5.0 × 10^-4). MN risk increased steeply for patients with high-risk genotype combinations (OR > 79). While genetic variation in PLA2R1 exclusively associated with MN across 19 CKD aetiologies, the HLA-DQA1 risk allele was also associated with lupus nephritis (P = 2.8 × 10^-6), type 1 diabetic nephropathy (P = 6.9 × 10^-5) and focal segmental glomerulosclerosis (P = 5.1 × 10^-5), but not with immunoglobulin A nephropathy.

Conclusions

PLA2R1 and HLA-DQA1 are the predominant risk loci for MN detected by GWAS. While HLA-DQA1 risk variants show an association with other CKD aetiologies, PLA2R1 variants are specific to MN.

Celiac disease as a model for the evolution of multifactorial disease in humans

Celiac disease (CD) is a multifactorial chronic inflammatory condition that results in injury of the mucosal lining of the small intestine upon ingestion of wheat gluten and related proteins from barley and rye. Although the exact mechanisms leading to CD are not fully understood, the genetic basis of CD has been relatively well characterized. In this review we briefly review the history of discovery, clinical presentation, pathophysiology, and current understanding of the genetics underlying CD risk. Then, we discuss what is known about the current distribution and evolutionary history of genes underlying CD risk in light of other evolutionary models of disease. Specifically, we conclude that the set of loci underlying CD risk did not cohesively evolve as a response to a single past selection event such as the development of agriculture. Rather, deterministic and stochastic evolutionary processes have both contributed to the present distribution of variation in CD risk loci. Selection has shaped some components of this network, but this selection appears to have occurred at different points in the past. Other parts of the CD risk network have likely arisen due to stochastic processes such as genetic drift.

Intestinal microbiota and probiotics in celiac disease

Celiac disease (CD) is a common chronic autoimmune enteropathy caused by gluten intake. To date, the only therapy for CD is the complete exclusion of dietary sources of grains and any food containing gluten. It has been hypothesized that the intestinal microbiota is somehow involved in CD. For this reason, probiotics are appearing as an interesting adjuvant in the dietetic management of CD. This review aims to discuss the characteristics of the microbiota in CD subjects and the use of probiotics as a novel therapy for CD. Comparisons between children with CD and controls show that their microbiota profiles differ; the former have fewer lactobacilli and bifidobacteria. Specific probiotics have been found to digest or alter gluten polypeptides. It has also been demonstrated that some bacterial species belonging to the genera Lactobacillus and Bifidobacterium exert protective properties on epithelial cells from damage caused by gliadin.

An update on celiac disease histopathology and the road ahead

CONTEXT

Celiac disease (CD) is a common immune-mediated disorder that occurs in genetically predisposed individuals (carriers of HLA-DQ2 and DQ8 haplotypes) on consumption of wheat (gluten). It is characterized by inflammation of the small-intestinal mucosa and myriad gastrointestinal and systemic manifestations. Celiac disease is common in the general population (prevalence, 0.5%-1%). Currently, small-bowel biopsy is considered the gold standard for diagnosing CD. However, the role of serologic testing in the diagnosis of CD has evolved, from being a supportive test to supplanting intestinal biopsies in certain patient populations.

OBJECTIVE

To summarize key aspects of histopathologic assessment, discuss the benefit of standardized pathology reports, impact of the site and number of small-bowel biopsy samples on diagnosis, and recommendations regarding serologic testing.

DATA SOURCES

Literature review of publications on CD and experience with histopathologic review of biopsies at the Department of Pathology and Cell Biology, Columbia University Medical Center, New York-Presbyterian Hospital, New York.

CONCLUSIONS

Intraepithelial lymphocytosis in the context of villous atrophy is considered a characteristic histologic finding of CD; however, it is a rather nonspecific finding. A growing list of publications has also indicated that the detection of intraepithelial lymphocytosis in the absence of villous atrophy has rather low specificity for CD. Therefore, communication between pathologists and gastroenterologists is paramount, as is knowledge regarding the pertinent clinical and laboratory data, in distinguishing between CD and other disorders with similar histopathologic and clinical manifestations.

On the perils of poor editing: regulation of peptide loading by HLA-DQ and H2-A molecules associated with celiac disease and type 1 diabetes

This review discusses mechanisms that link allelic variants of major histocompatibility complex (MHC) class II molecules (MHCII) to immune pathology. We focus on HLA (human leukocyte antigen)-DQ (DQ) alleles associated with celiac disease (CD) and type 1 diabetes (T1D) and the role of the murine DQ-like allele, H2-Ag7 (I-Ag7 or Ag7), in murine T1D. MHCII molecules bind peptides, and alleles vary in their peptide-binding specificity. Disease-associated alleles permit binding of disease-inducing peptides, such as gluten-derived, Glu-/Pro-rich gliadin peptides in CD and peptides from islet autoantigens, including insulin, in T1D. In addition, the CD-associated DQ2.5 and DQ8 alleles are unusual in their interactions with factors that regulate their peptide loading, invariant chain (Ii) and HLA-DM (DM). The same alleles, as well as other T1D DQ risk alleles (and Ag7), share nonpolar residues in place of Asp at β57 and prefer peptides that place acidic side chains in a pocket in the MHCII groove (P9). Antigen-presenting cells from T1D-susceptible mice and humans retain CLIP because of poor DM editing, although underlying mechanisms differ between species. We propose that these effects on peptide presentation make key contributions to CD and T1D pathogenesis.

Balancing selection and heterogeneity across the classical human leukocyte antigen loci: a meta-analytic review of 497 population studies

This paper presents a meta-analysis of high-resolution human leukocyte antigen (HLA) allele frequency data describing 497 population samples. Most of the datasets were compiled from studies published in eight journals from 1990 to 2007; additional datasets came from the International Histocompatibility Workshops and from the AlleleFrequencies.net database. In all, these data represent approximately 66,800 individuals from throughout the world, providing an opportunity to observe trends that may not have been evident at the time the data were originally analyzed, especially with regard to the relative importance of balancing selection among the HLA loci. Population genetic measures of allele frequency distributions were summarized across populations by locus and geographic region. A role for balancing selection maintaining much of HLA variation was confirmed. Further, the breadth of this meta-analysis allowed the ranking of the HLA loci, with DQA1 and HLA-C showing the strongest balancing selection and DPB1 being compatible with neutrality. Comparisons of the allelic spectra reported by studies since 1990 indicate that most of the HLA alleles identified since 2000 are very-low-frequency alleles. The literature-based allele-count data, as well as maps summarizing the geographic distributions for each allele, are available online.

Gene dose effect of the DQB1*0201 allele contributes to severity of coeliac disease

OBJECTIVE

Coeliac disease (CD) susceptibility has been shown to be associated with the HLA alleles DQA1*0501 and DQB1*0201. This HLA-associated risk has been estimated to account for 29-40% of the genetic component of CD. Conflicting data have been published on the gene dose effect of these HLA alleles on the risk and severity of CD. In this study the aim was to investigate the association between the number of HLA risk alleles and the severity of CD.

MATERIAL AND METHODS

Fifty-four Finnish CD families, including 144 CD patients mainly diagnosed in adulthood (94.4%), were enrolled in the study. The association between the number of DQA1*0501 and DQB1*0201 alleles and villous atrophy, symptoms and laboratory parameters at the time of diagnosis, and the association with villous atrophy after one year of treatment on a gluten-free diet were studied.

RESULTS

The homozygosity for the DQB1*0201 allele was associated with a more severe form of CD assessed by more severe villous atrophy (p=0.011), younger age (p=0.036), more severe diarrhoea (p=0.048) and a lower level of blood haemoglobin at the time of diagnosis (p=0.010). Furthermore, the homozygosity for the DQB1*0201 allele was associated with a slower recovery of villous atrophy after a gluten-free diet (p=0.041). In contrast, the DQA1*0501 allele did not have a significant association with the severity of CD.

CONCLUSIONS

Our results demonstrate a gene dose effect of the DQB1*0201 allele on the clinical heterogeneity of CD and on the rate of recovery from villous atrophy in patients on a gluten-free diet.

Fluctuating transglutaminase autoantibodies are related to histologic features of celiac disease

BACKGROUND & AIMS

Asymptomatic children at risk for celiac disease (CD) and seropositive for immunoglobulin A anti-TG autoantibodies (TGAA) may lack small intestinal mucosal changes characteristic of CD. We have followed a group of children with serial testing for TGAA.

METHODS

Subjects were a group of at-risk children comprised of infants expressing HLA-DR3 on newborn screening, those with type 1A diabetes, or a first-degree relative of someone with type 1 diabetes. All children participating in the prospective study for development of CD underwent serial testing for TGAA. Data from clinical evaluation and small intestinal biopsy were compared to the TGAA levels followed over time.

RESULTS

In 42 children, serial TGAA determinations while on a gluten-containing diet showed levels fluctuating 10-100-fold over 3-12 months. A TGAA index more than 0.5 had a positive predictive value (PPV) for histologic confirmation of CD of 96% (22/23). A TGAA index above the usual cutoff for positivity (0.05) had a PPV of only 76% (28/37).

CONCLUSIONS

In children with TGAA seropositivity, the TGAA level varied over time and a higher titer predicted an abnormal biopsy characteristic of CD. A threshold for biopsy for diagnosis of CD could be set higher for screening-identified cases than for clinically identified cases to decrease the frequency of performing "normal" biopsies.

Azathioprine in refractory sprue: results from a prospective, open-label study

OBJECTIVE

Refractory sprue is a rare and severe malabsorptive disorder that mimics celiac disease but is refractory to a gluten-free diet and is without initial evidence of overt lymphoma. Treatment is largely empiric and often ineffective, with steroids and immunosuppression being the mainstream therapeutic options. The aim of this study was to evaluate prospectively the effect of azathioprine on a group of patients diagnosed with refractory sprue.

METHODS

We studied seven consecutive patients (five women and two men) with a well-defined diagnosis of refractory sprue and a lack of response to oral or parenteral steroids. At diagnosis, five patients had endoscopic evidence of ulcerative jejunitis, and five underwent exploratory laparotomy for exclusion of malignancies. The characteristic monoclonal TCRgamma gene rearrangement was shown in five of six patients studied. Patients were treated for a mean of 11 months (range 8-12 months), and clinical, biochemical, molecular, and histological parameters were reassessed at the end of the trial. The study was a prospective, open-label, non-placebo-controlled study using azathioprine (2 mg/kg/ day) plus oral prednisone (1 mg/kg/day). A gluten-free diet (n = 7) as well as enteral (n = 6) and parenteral nutrition (n = 5) were administered during the trial.

RESULTS

After treatment, five patients had a complete clinical remission, and biochemical and nutritional parameters were significantly improved. Steroids were tapered after the onset of azathioprine, and no patient was on steroids at the end of the trial. Intestinal histology improved significantly in all cases (normal histology in three cases and minor infiltration in the lamina propria in two). Two patients did not respond to treatment at any time and died in months 10 and 9, of an irreversible ventricular fibrillation and sepsis, respectively. No overt lymphoma was demonstrated during the follow-up.

CONCLUSIONS

The present study confirms earlier anecdotal reports on the efficacy of azathioprine in refractory sprue, with clear clinical and histological improvement shown in most patients. However, monoclonality persisted after treatment. We consider that a larger number of patients should be evaluated before a definitive recommendation is adopted for use of this drug in refractory sprue.

Pediatric celiac disease in India is associated with multiple DR3-DQ2 haplotypes

The role of human leukocyte antigen (HLA) DQ2 heterodimer (DQA1*0501-DQB1*0201) in presenting gluten peptides to effector T cells in celiac disease (CD) has been well documented. Because HLA-DQ2 is carried on DR3 haplotypes due to linkage disequilibrium, such haplotypes are encountered more frequently in patients with autoimmune disease. This study analyzed 35 North Indian children below 15 years of age and diagnosed to have CD as per the ESPGAN criteria, which included histopathologic alterations in duodenal biopsies, clinical response to gluten withdrawal, and presence of antiendomysial antibodies. The HLA class I and class II alleles were determined by polymerase chain reaction-sequence-specific primers, sequence-specific oligonucleotide probe, and reverse line strip molecular techniques. A statistically significant positive association of the disease with HLA-DRB1*03 (94.2% versus 22.1% in controls, chi(2) = 73.4, p = 7.54E-11), and a negative association with DRB1*15 (chi(2) = 7.4, p = 6.5E-03) and DRB1*13 alleles was observed. The HLA-DQB1*0201 was observed in all the 35 patients (100%), whereas the DQ2 heterodimer alpha(0)beta(0) occurred in 97.1% of CD patients (31.4% in double dose, 65.7% in single dose) and revealed significant deviation from healthy controls (chi(2) = 102.08, p = 7.56E-11). Further analysis revealed involvement of multiple DR3+ve haplotypes with CD in Indians, of which A26-B8-DR3 was the most common DR3 haplotype among patients (34.28%, chi(2) = 40.57, p = 2.65E-10) followed by Ax-B21-DR3 (11.4%) (chi(2) = 13.8, p = 2E-04) and the classical Caucasian haplotype A1-B8-DR3 (5.7%). The former two haplotypes are characteristic of Asian Indians and are involved in the development of CD. We conclude that the high risk DR3 haplotypes that play a crucial role in the development of CD are unique in Asian Indians. Detailed analysis of these haplotypes in Indian patients with autoimmune diseases may help understand the influence of other intervening genes within the major histocompatibility complex.

The genetics of autoimmune polyendocrine syndrome type II

A series of autoimmune disorders, often Addison's disease, type 1 diabetes mellitus, and thyroid autoimmunity, frequently occurs together in patients with the autoimmune polyendocrine syndrome type II (APS-II). The highest risk HLA genotype for Addison's disease, either as a single disease or in APS-II patients, consists of the genotype DR3/4, DQ2/DQ8 with DRB1*0404. As many as 30% of patients with Addison's disease have this genotype versus less than 0.5% of controls. An additional and important associated locus within the HLA region is the class I related gene, MIC-A. Patients who develop Addison's disease often have a delayed diagnosis and may die from Addisonian crisis; therefore, improved genetic testing combined with testing for 21-hydroxylase autoantibodies might allow the identification of relatively high-risk populations (greater than 1 in 200 defined genetic risk compared with 1 in 10,000 population risk).

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.

Celiac disease-like abnormalities in a subgroup of patients with irritable bowel syndrome

BACKGROUND & AIMS

Abdominal symptoms in the absence of mucosal abnormalities are features of both the irritable bowel syndrome (IBS) and latent/potential celiac disease (cd). To identify a possible subgroup of IBS patients with latent/potential cd, surrogate markers of cd were investigated in IBS patients.

METHODS

IBS patients suffering from diarrhea (n = 102), and patients with active cd (n = 10), treated cd (n = 26), and latent cd (n = 5) were included in the study. We measured serum immunoglobulin (Ig) A against gliadin and tissue-transglutaminase, and IgA and IgM against gliadin, tissue-transglutaminase (intestinal cd-associated antibodies), and the dietary proteins beta-lactoglobulin and ovalbumin in duodenal aspirate by enzyme-linked immunosorbent assay. Intraepithelial lymphocytes (IELs) were counted in histology sections, and the expression of HLA-DQ2 (A1*0501/B1*0201) was investigated by polymerase chain reaction. In 26 IBS patients, the effect of 6 months of gluten withdrawal was examined.

RESULTS

Most cd patients expressed HLA-DQ2 and had increased intestinal cd-associated antibodies, whereas cd-associated serum IgA and IEL counts were increased in active cd in contrast to treated or latent cd. In IBS patients, 35% were HLA-DQ2-positive, 23% had increased IEL counts, and 0% and 30% had increased cd-associated antibodies in serum and duodenal aspirate, respectively. Furthermore, stool frequency and intestinal IgA decreased significantly under a gluten-free diet in the subgroups of HLA-DQ2-positive and intestinal antibody-positive IBS patients when compared with IBS patients without these markers.

CONCLUSIONS

HLA-DQ2 expression and increased intestinal cd-associated antibodies are markers that can identify latent/potential cd in a subgroup of IBS patients who consequently appear to profit from a gluten-free diet.

Commentary: advances in the laboratory diagnosis of celiac disease

Anti-endomysial autoantibodies are very useful in the diagnosis and monitoring of celiac disease (gluten-sensitive enteropathy) due to their high sensitivity and specificity for that disorder. The recent discovery that the autoantigen responsible for the endomysial pattern is tissue transglutaminase (tTG) has led to the commercial development of automated enzyme immunoassays for quantitation of that autoantibody. These assays are standardized to provide highly accurate and comparable testing between laboratories for anti-tTG autoantibodies. Celiac disease is a common genetic disease in populations of Europe and the United States. It has a spectrum of expression ranging from silent or mild to severe, with resulting malabsorption that produces multiple-organ system effects due to malnutrition. Many cases miss the diagnosis because the symptoms are not classic or the clinical syndrome is not severe. Because the treatment of celiac disease (avoidance of wheat products) is so effective and inexpensive and because celiac disease is so common in selective populations, a highly reliable test for its detection such as anti-tTG should find wide application in clinical practice.

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.

Refractory celiac disease

Celiac disease is a gluten-sensitive enteropathy, characterized by villous atrophy, which is reversed by gluten withdrawal. A minority of patients with celiac-like enteropathy are resistant to gluten-free diet, so-called refractory sprue, or unclassified sprue. Refractory sprue is a diagnosis of exclusion; all other causes of a celiac-like enteropathy must be eliminated before a diagnosis of refractory sprue can be made. Recent evidence suggests that refractory sprue comprises a heterogenous group of patients with diverse underlying causes. A small proportion of these patients seem to have an adult form of autoimmune enteropathy, characterized by the presence of antienterocyte antibodies. However, a larger group of patients with refractory sprue now seem to have a cryptic intestinal T-cell lymphoma, characterized by the presence of phenotypically abnormal, monoclonal intraepithelial lymphocytes, despite benign cytology. Current therapeutic options include nutritional support and immunosuppressive therapy, but response is variable. The prognosis of refractory sprue may be poor; patients may die of severe malabsorption, or through synchronous or metachronous development of an enteropathy-associated T-cell lymphoma. Based on this recent evidence, patients with refractory sprue should be screened for antienterocyte antibodies and have T-cell receptor and monoclonal antibody studies performed; this could facilitate identification of cases of adult-onset autoimmune enteropathy and those of cryptic T-cell lymphoma. Moreover, early recognition of the malignant nature of the intestinal infiltrate in some cases of refractory sprue could permit the development of novel chemotherapeutic regimens for this condition.

Absolute linkage of celiac disease and dermatitis herpetiformis to HLA-DQ

This report shows the absolute genetic linkage of celiac disease (CD) to the HLA-DQ region, and supports the fact that dermatitis herpetiformis (DH) follows the same pattern of HLA-mediated susceptibility in extensive series of Caucasian Spanish patients. Ninety-five percent of CD (201 of 212) and 100% of DH (55) patients could produce DQ alpha 1*0501-DQ beta 1*02 heterodimers. Negative CD patients for this combination were mostly DR4-DQ8 (DQA1*03-DQB1*0302) (9 OF 11), along with a restricted number of complementary chromosomes. Comparison of observed and expected DQA1-DQB1 genotype distributions (Hardy-Weinberg equilibrium) showed that the excess of patients with DQB1*02 in double doses would be the consequence for which this allele should be complemented by DQA1*0501. Homozygosity for DQA1*0501 would restrain susceptibility to CD and DH.

Celiac patients predominantly inherit HLA-DPB1*0101 positive haplotype from HLA-DQ2 homozygous parent

The DQA1*0501 and DQB1*0201 alleles (hereafter DQ2) confer genetic susceptibility to celiac disease (CD). Some studies have indicated that the DPB1, DMB, and TAP loci, that are located close to the DQ genes, could also together with DQ or independently confer genetic susceptibility to CD. Some others have claimed that these associations result merely from linkage disequilibrium, a hallmark of the MHC, that often makes the precise mapping of susceptibility genes difficult. To evaluate further the role of class II genes in CD, we analyzed segregation of DPB1 alleles in families with CD. In particular, we analyzed families where one of the parents was homozygous for the DQ2 risk allele but heterozygous for DPB1*0101, an allele claimed to be an additional risk allele. We reasoned that if DPB1*0101 would not play a role in CD, then patients should inherit the DQ2 haplotypes randomly from a homozygous parent. We here present evidence that, in all 6 informative families, those DQ2 positive haplotypes that also include the DPB1*0101 allele, rather than those without DPB1*0101, are predominantly segregated to the index patient from the parent homozygous for the DQ2 risk marker (p = 0.03 as compared to their healthy siblings). If confirmed in larger studies the results indicate that despite DQ2 other genes in or near the MHC may associate with CD.

Dermatitis herpetiformis and celiac disease are both primarily associated with the HLA-DQ (alpha 1*0501, beta 1*02) or the HLA-DQ (alpha 1*03, beta 1*0302) heterodimers

HLA-DRB1,-DQA1, and -DQB1 genomic typing of 50 patients with dermatitis herpetiformis and of 290 healthy blood donors was performed. Genes encoding the DQ (alpha 1*0501, beta 1*02) heterodimer were carried by 43 (86%) of the patients and 72 (25%) of the controls. Of the remaining seven patients six (12% of all the patients) carried genes encoding the DQ (alpha 1*03, beta 1*0302) heterodimer. These HLA associations are very similar to those observed in patients with celiac disease. We thus conclude that dermatitis herpetiformis and celiac disease are associated to the very same HLA-DQ alpha beta heterodimers.

Celiac disease in Down's syndrome with HLA serological and molecular studies

The association between Down's syndrome (DS) and celiac disease (CD) has been confirmed by several authors. The sensitivity and specificity of antigliadin antibodies (AGAs), the clinical features of subjects with DS and CD (DS-CD+), the incidence of CD, and the results of serological and molecular class I and II HLA typing were determined in a sample of 57 Sicilian subjects with DS. Six (10.5%) and 17 subjects (29.8%) showed high levels of IgA AGAs and IgG AGAs, respectively. AGAs sensitivity and specificity were lower than in the population without DS. Ten people with DS were submitted to jejunal biopsy, and seven (12.2%) showed CD according to ESPGAN criteria. All seven patients were put on gluten-free diet, followed by rapid disappearance of symptoms. Class I and II HLA serological and molecular typing was carried out in seven DS-CD + subjects, 22 people with DS without CD (DS-CD-), five subjects with CD without DS, and 20 controls. Between DS-CD + and DS-CD- subjects, no statistically significant difference regarding serum HLA class I antigens was found. DQA1*0101 allele appears significantly in DS-CD + patients and deserves to be searched for in a larger sample to assess its meaning in the DS-CD association.

Cytokine mRNA expression in the mucosa of treated coeliac patients after wheat peptide challenge

This study investigated the presence of mRNA coding for interferon gamma (IFN gamma), tumour necrosis factor alpha (TNF alpha), and interleukins 2 (IL2) and 6 (IL6), in the mucosa of four coeliac patients in remission who had been challenged with either gliadin or synthetic gliadin oligopeptides. Jejunal biopsy specimens from these patients, taken before and at two, four, and six hours after challenge, were hybridised with specific 35S-labelled DNA oligonucleotide probes. The lamina propria of all the patients contained significantly increased numbers of cytokine mRNA expressing cells four hours after challenge with gliadin or an oligopeptide corresponding to amino acids 31-49 of A-gliadin (peptide A). No significant changes were seen with the peptides corresponding to aminoacids 202-220 (peptide B) or 3-21 (peptide C) of A-gliadin, with the exception of one patient who showed a significant increase in the number of TNF alpha mRNA expressing cells four hours after challenge with peptide B. In vivo studies in coeliac disease have shown that significant histological changes occur in the mucosa of treated coeliac patients four hours after challenge with either gliadin or peptide A. These findings suggest that the histological changes seen previously in the mucosa of coeliac patients after wheat peptide challenge may be caused by increased expression of cytokines within the mucosa.

The association between coeliac disease, dermatitis herpetiformis and certain HLA-antigens in Icelanders

Twenty-eight cases of coeliac disease (CD) and seven of dermatitis herpetiformis (DH) have been verified in Iceland. Standard serological techniques were used for HLA typing. Twenty-five individuals with CD were typed, 21 (84%) of whom carried DR3,DQ2. Twelve of these 25 (48%) had DR3,DR7, DQ2, which makes them possibly homozygous for DQ2, and suggests that homozygosity of DQ2 increases the risk for CD. The four DH patients that were typed all had HLA-B8,DR3,DQ2. It is concluded that CD and DH are associated with DR3, DQZ in Icelanders.

A gene dosage effect of the DQA1*0501/DQB1*0201 allelic combination influences the clinical heterogeneity of celiac disease

This study reports the HLA-DR and DQ molecular characterization of 62 CD patients of Sardinian descent. Patients were divided in two groups (36 in group I and 26 in group II) according to the clinical features at the disease onset. Among the patients of group I, having the fully expressed form of CD and a mean age of 3 years at disease onset, a significant increase of DRB1*0301, DQA1*0501, DQB1*0201 homozygotes, encoding in cis two DQ (alpha 1*0501, beta 1*0201) susceptibility heterodimers, was observed when compared either with the patients of group II (pIII < 0.012) or with healthy individuals (pI < 10(-6)). On the other hand, in the patients of group II, presenting oligosymptomatic forms and a mean age of 5.7 years at the disease onset, the haplotype combinations encoding in cis or in trans only one DQ (alpha 1*0501, beta 1*0201) heterodimer were significantly increased in comparison either with the patients of group I (pIII < 0.026) or with controls (pII < 10(-6)). These findings suggest that a double dose of DQA1*0501, DQB1*0201 genes may predispose a person to an earlier onset and to more severe disease manifestations. Genotype analysis showed that only three patients (all in group I) failed to form in trans or in cis the DQ (alpha 1*0501, beta 1*0201) heterodimer and carried the DQA1*0101,DQB1*0501 haplotype, suggesting its possible role in CD susceptibility. In addition, a significant increment of DQB1*0501 gene (pc < 0.0065) was found comparing the frequency of DQB1 alleles in CD patients and healthy controls, after exclusion of DQB1*0201 chromosomes.(ABSTRACT TRUNCATED AT 250 WORDS)

T cells from the peripheral blood of coeliac disease patients recognize gluten antigens when presented by HLA-DR, -DQ, or -DP molecules

Coeliac disease (CD) is a T-cell mediated immunological disease of the small intestine which is precipitated in susceptible individuals by ingestion of gluten. We recently reported that gliadin-specific T cells can be found in the small intestinal mucosa of CD patients, and that a preponderance of these T cells was restricted by the CD-associated DQ(alpha 1*0501,beta 1*0201) heterodimer. Here we report studies on whether the same is found for gliadin specific T cells in the peripheral blood of CD patients. T-cell responses towards gluten antigens in vitro were found for both most CD patients and healthy controls. Gluten-specific T-cell clones (TCC) were established from four CD patients. Although a large proportion of these TCC were restricted by DQ molecules, including the CD-associated DQ(alpha 1*0501,beta 1*0201) heterodimer, several were restricted instead by DR or DP molecules. Thus, gluten-derived peptides can be presented to T cells by several different HLA class-II molecules, and the preferential DQ(alpha 1*0501,beta 1*0201) restriction of gluten-specific T cells in the small intestinal mucosa of CD patients is less pronounced than for similar T cells in the peripheral blood.

T cells recognize a peptide derived from alpha-gliadin presented by the celiac disease-associated HLA-DQ (alpha 1*0501, beta 1*0201) heterodimer

CD is unique among the HLA-associated diseases since (a) the disease-promoting agent (gliadin) is known and (b) the disease is precipitated mainly in individuals carrying a particular cis- or trans-encoded HLA-DQ heterodimer; i.e., DQ(alpha 1*0501, beta 1*0201). Further, a preponderance of gliadin-specific T cells derived from the small intestinal mucosa of CD patients are restricted by this DQ heterodimer. T-cell recognition of gliadin peptides presented by the DQ(alpha 1*0501, beta 1*0201) heterodimer may thus be of importance in CD. Here we report that a T-cell clone from a patient with CD recognizes a synthetic alpha-gliadin peptide, when presented by the cis- or trans-encoded CD-associated DQ(alpha 1*0501, beta 1*0201) heterodimer. The minimal peptide recognized by the T-cell clone corresponds to residues 31-47 of alpha-gliadin, which is included in the part of alpha-gliadin previously shown to have disease-promoting activity. When testing analogue peptides derived from other alpha-gliadin sequences, one peptide differing by one amino acid was recognized by the T-cell clone, whereas the other peptide differing by two amino acids was not recognized. Our findings demonstrate that the CD-associated DQ(alpha 1*0501, beta 1*0201) heterodimer may serve as an antigen-presenting molecule to T cells for certain gliadin peptides.

Celiac disease: clinical features and pathogenesis

Celiac disease is a fascinating illness, from both a clinical and research perspective. Most clinicians consider a diagnosis of celiac disease when a young patient has classic signs and symptoms of steatorrhea and severe malabsorption. However, the typical gastrointestinal symptoms often are absent. The patient may only have subtle signs of chronic malnutrition or nonspecific gastrointestinal complaints. Celiac disease is not diagnosed commonly in the United States, at least in part because of a low clinical index of suspicion. A diagnosis of celiac disease is confirmed by a small bowel mucosa biopsy. A dramatic clinical response to a gluten-free diet verifies the diagnosis, and provides a cost-effective treatment free of significant side effects. Strict adherence to the prescribed diet usually results in a complete resolution of the symptoms and mucosal histopathologic changes. The serious, long-term complication of intestinal lymphoma also may be prevented. To the clinical investigator, celiac disease is an important model of the HLA-associated immune-mediated illnesses. A specific HLA-DQ heterodimer is found in 95% of patients, representing perhaps the strongest association of any illness with a specific class II HLA molecule. In addition, an important environmental trigger (gluten) has been identified, providing a unique opportunity to study the interaction of gene products and environmental factors in the pathogenesis of an immune-mediated disease.

Molecular characterization of HLA class II genes in celiac disease patients of Latin American Caucasian origin

In the present study, the polymorphic domain of HLA class II genes present in a pediatric population of Argentinian celiac disease patients was analyzed by hybridization to sequence-specific oligonucleotides and DNA sequencing. Sixteen out of 16 DR5/7 heterozygous patients bore the DQA1*0501 and DQB1*0201 alleles implicated in the DQ2 risk specificity. The second exon of DQA1, DQB1 and DRB1 genes from 2 DR5/7 patients was characterized by DNA sequencing. The following alleles were found in both patients: DRB1*1101 and DRB1*0701; DQB1*0301 and DQB1*0201; DQA1*0501 and DQA1*0201. Previous serological analysis in this population had shown the presence of DQ2 in 95% of the patients (40% in controls) and a negative association with DQ1 haplotypes, suggesting the presence of other "permissive" or neutral alleles. The following HLA-DQB1 alleles, besides DQB1*0201, were identified in 31 CD patients: DQB1*0301, 0302, 0401 and 0402. All these alleles share a common pattern of residues between positions 84 and 90, and distinct from that present in DQ1-related alleles.

Gluten stimulation of coeliac mucosa in vitro induces activation (CD25) of lamina propria CD4+ T cells and macrophages but no crypt-cell hyperplasia

Jejunal biopsy specimens from 10 patients with treated coeliac disease and seven non-coeliac controls were challenged in vitro with peptic-tryptic gluten digest. Mucosal T cells were examined in situ by three-colour immunofluorescence staining for expression of the activation marker CD25 (the p55 alpha-chain of interleukin-2 receptor) and the nuclear proliferation marker revealed by monoclonal antibody Ki-67. Intraepithelial T cells expressed CD25 rarely whereas the proportion of activated lamina propria T cells increased (P < 0.002) from median 2.8% (cultured with 20% fetal calf serum alone for 24-48 h) to 10.0% after 24 h with gluten (n = 10; range 1.1-17.4%) and to 10.4% after 48 h (n = 7; range 1.4-17.5%). Such gluten-induced increase of CD25+ T cells was not observed in specimens from non-coeliac control subjects. Crypt-cell hyperplasia and T-cell proliferation (Ki-67+) were observed neither in the coeliac nor in the control mucosae after gluten stimulation. Three-colour staining combining a polyclonal antibody reagent to CD3 and a monoclonal antibody to CD25 with a monoclonal antibody to CD45R0, CD4, CD8, the p75 beta-chain of interleukin-2 receptor, integrin alpha E beta 7, or HLA-DR showed that most of the CD25+ T cells (> 90%) were CD4+CD8-, co-expressed CD45R0 and the p75 beta-chain, and often also the integrin alpha E beta 7 but not HLA-DR. In addition to these activated T cells, a dominating population of CD25+CD3-CD4+ subepithelial pan-HLA-class II+ macrophages (CD68+) with variable expression of the p75 beta-chain was often induced by gluten challenge.

T-cell receptor variable genes and genetic susceptibility to celiac disease: an association and linkage study

BACKGROUND

Genetic susceptibility of celiac disease is primarily associated with a particular combination of and HLA-DQA1/DQB1 gene; however, this does not fully account for the genetic predisposition. Therefore, the aim of this study was to examine whether T-cell receptor (TCR) genes may be susceptibility genes in celiac disease.

METHODS

HLA class II typing was performed by polymerase chain reaction amplification in combination with sequence-specific oligonucleotide hybridization. TCR alpha (TCRA), TCR gamma (TCRG), and TCR beta (TCRB) loci were investigated by restriction fragment length polymorphism analysis.

RESULTS

Allelic frequencies of TCRA, TCRG, and TCRB variable genes were compared between patients with celiac disease (n = 53) and control patients (n = 67), and relative risk (RR) estimates were calculated. The RR was 1.67 for allele C1 at TCRA1, 3.35 for allele D2 at TCRA2, 1.66 for allele B2 at TCRG, and 1.35 for allele B at TCRB, showing no significant association. Additionally, linkage analysis was performed in 23 families. The logarithm of odd scores for celiac disease vs. the TCR variable genes at TCRA, TCRG, and TCRB showed no significant linkage.

CONCLUSIONS

These data suggest that the analyzed TCR variable gene segments V alpha 1.2, V gamma 11, and V beta 8 do not play a major role in susceptibility to celiac disease.

HLA susceptibility genes in celiac disease: genetic mapping and role in pathogenesis

The overrepresentation of particular HLA alleles in patients with celiac disease was first noted two decades ago. Several lines of evidence obtained during the last years strongly suggest that a particular HLA-DQ heterodimer, encoded by the DQA1*0501 and DQB1*0201 genes in cis or trans configuration, confers the primary disease susceptibility. This paper reviews the evidence behind this concept and discusses how this particular DQ molecule may be involved in the pathogenesis.

DNA typing for HLA-DPB1-alleles in German patients with systemic lupus erythematosus using the polymerase chain reaction and DIG-ddUTP-labelled oligonucleotide probes. Members of SLE Study Group

Genomic DNA of 178 German Caucasian patients with systemic lupus erythematosus are studied for HLA-DP locus by using PCR and DIG-ddUTP-labelled oligonucleotide probes. A significant increase of DPB1*0101 is observed in SLE patients compared with healthy controls (chi 2 = 15.27, p.c. < 0.004). DPB1*0501 and *0901 are also slightly increased (chi 2 = 5.85, P < 0.05, p.c. = NS; chi 2 = 5.64, P < 0.05, p.c. = NS). There is no significant difference in frequency of DP alleles between male and female patients. Since a linkage disequilibrium between HLA-B, DR and DP loci is found in our SLE patients, an analysis is performed assessing the relative importance of these HLA-markers to SLE. The results show that the increase of DPB1*0101 in SLE patients is associated with the HLA-B8, DR3 haplotype and it suggests a more important role for HLA-B8, DR3 or genes within this haplotype than for DPB1*0101 in the genetic predisposition for SLE.

Associations of HLA-DR and HLA-DQ types with anti-GBM nephritis by sequence-specific oligonucleotide probe hybridization

Twenty-three patients from the United States with anti-glomerular basement membrane nephritis (Goodpasture's syndrome) were HLA class I and class II typed by serology and HLA-DR and HLA-DQB typed using sequence-specific oligonucleotide (SSO) probes. Protocols used were those of the 11th International HLA Workshop. We were able to confirm the strong association of DR2 with the disease and, using the molecular techniques, showed that all DR2 patients were restricted to DRB1-1501 and DQB1-0602 alleles. We also found highly significant associations between disease and the alleles of DRB1-0301 and DQB1-0201. DR4 alleles as a group were not significantly more frequent among patients, but the allele DRB1-0404 did appear to be associated with the disease. The use of SSO typing provides an expanded opportunity for refined analysis of HLA and disease associated alleles.

Linkage disequilibrium between TAP2 variants and HLA class II alleles; no primary association between TAP2 variants and insulin-dependent diabetes mellitus

The TAP1 and TAP2 genes, located in the HLA class II region, encode subunits of a peptide transporter. Both genes display limited genetic variability; four different nucleotide substitutions have been found in the TAP2 gene. Here studies on linkage disequilibrium between TAP2 variants and HLA class II alleles are reported, in an attempt to evaluate whether TAP2 variants are associated with insulin-dependent diabetes mellitus (IDDM). As reported previously, a significant decrease of homozygosity for TAP2 alleles encoding alanine at residue 665 (665 Ala) and glutamine at 687 (687 Gln) paralleled by an increase in homozygosity for TAP2 alleles encoding threonine at residue 665 (665 Thr) and a stop codon at 687 (687 Stop), was found in both Finnish and Norwegian IDDM patients compared to random controls. However, a strong linkage disequilibrium between these TAP2 polymorphisms and given HLA-DR and -DQ genes was observed among healthy controls. The frequent 665 Thr and 687 Stop variants were in linkage disequilibrium both with the DR4-DQ8 and the DR3-DQ2 haplotypes, haplotypes which are strongly associated with IDDM. In contrast, the DR1-DQ5 and DR13-DQ6 (e.g. DQB1*0603) haplotypes, which are decreased among IDDM patients, were associated with the 665 Ala and 687 Gln variants. Thus, when DR- and DQ-matched patients and controls were compared, associations of the investigated TAP2 variants and IDDM were no longer detectable. These data, therefore, indicate that the associations previously found between certain TAP2 variants and IDDM are secondary to a primary association between this disease and particular DQ alpha beta heterodimers.

On the HLA-DQ(alpha 1*0501, beta 1*0201)-associated susceptibility in celiac disease: a possible gene dosage effect of DQB1*0201

The HLA-associated susceptibility to develop celiac disease (CD) seems mainly to be conferred by a particular HLA-DQ heterodimer encoded by the DQA1*0501 and DQB1*0201 genes either in cis or in trans position. To study the possible influence of DRB1 or other DQA1 and DQB1 alleles on the CD susceptibility conferred by these DQ genes, we performed genomic HLA typing of 94 CD patients, selected those who carried at least one copy of the DRB1*0301-DQA1*0501-DQB1*0201 haplotype (N = 89) and compared them to 47 random, healthy Norwegians matched with the patients to carry at least one copy of the above haplotype. We found an excess of DQB1*0201 homozygosity in the patients. This was due to an increased frequency of the DRB1*0301-DQA1*0501-DQB1*0201 and DRB1*0701-DQA1*0201-DQB1*0201 haplotypes present on the other chromosome. We propose that, in individuals carrying the DQA1*0501 and DQB1*0201 alleles, the presence of a second copy of the DQB1*0201 allele increases susceptibility to CD.

Different dose effect of HLA-DQ alpha beta heterodimers in insulin-dependent diabetes mellitus and celiac disease susceptibility

To compare the quantitative effect of the DQ alpha beta heterodimers DQ alpha 52 Arg+, beta 57 Asp- and DQ alpha 1*0501, beta 1*0201 on susceptibility to IDDM and CD, we characterized, at the genomic level, the DQ alpha 52 and DQ beta 57 residues of 50 IDDM Italian patients observed in Rome. The results were compared with those of a previous study concerning the oligotyping of DQ dimers in a group of CD children belonging to the same population. Our data confirm that both diseases are primarily associated with HLA-DQ alpha beta heterodimers, but the distributions of the respective susceptible DQA1 and DQB1 alleles in the two diseases were different. In fact, the highest risk of IDDM is for subjects alpha SS, beta SS that could express, by either cis- or trans-association, four susceptible heterodimers and decreases in proportion to the number of these; in regard to CD, the highest risk was found for individuals who carried only one predisposing heterodimer.

HLA-DR and -DQ genotypes of celiac disease patients serologically typed to be non-DR3 or non-DR5/7

The susceptibility to develop celiac disease (CD) seems to be primarily associated to a particular HLA-DQ alpha/beta heterodimer encoded by the DQA1*0501 and DQB1*0201 alleles, in cis position on the DR3-DQ2 haplotype or in trans position by DR5-DQ7/DR7-DQ2 heterozygotes. However, exceptional patients exist who are neither DR3 nor DR5/DR7, particularly among Southern European populations. We therefore examined the DRB1, DQA1, and DQB1 alleles of 13 Spanish CD patients who were serologically typed to be neither DR3 nor DR5/DR7. Five patients were found to carry the DQA1*0501 and DQB1*0201 alleles either in cis or in trans position, three of them had previously been serologically mistyped. However, two of these patients carried DQA1*0501 and DQB1*0201 on haplotypes other than DR3 or DR5 in combination with DR7. One of the latter patients carried an unusual DR4-DQ2 haplotype, while another had an unusual DR8-DQ2 haplotype. Four of the remaining eight patients carried DR4-DQ8 haplotypes. Taken together, our findings provide further evidence that the DQ alpha/beta heterodimer encoded by the DQA1*0501 and the DQB1*0201 alleles confers the primary HLA-associated susceptibility to develop CD. However, our studies also corroborate that a second (and "weaker") HLA-associated CD susceptibility gene may be present on some DR4-carrying haplotypes.

HLA-DP polymorphism in northern Italian celiac patients

The contribution of HLA-DP genes to celiac disease susceptibility has been investigated in 95 Italian patients, 41 with childhood and 54 with adult disease onset. Polymerase chain reaction amplification, sequence-specific oligonucleotide probe hybridization and restriction fragment length polymorphism analyses have been carried out. All celiac patients and 56 out of 128 random healthy controls were DQw2-positive. The frequency of the DPB1*0101 allele was significantly increased (pc = 0.002, relative risk 5.21) in patients with celiac disease (23.2%) compared to the whole panel of controls (5.5%), but not to the 56 controls bearing DQw2 (10.7%). No significant difference in the frequency of DPB1*0101 was found between celiac patients with pediatric (24.4%) or adult (22.2%) onset. The DPB1*0101 allele was associated with both the DR3-DQw2 and DR7-DQw2 haplotypes. Moreover, our study has not confirmed the association with DPB1*0402 and DPB1*0301 previously reported in celiac children from southern Italy. The linkage of the DPB1*0101 allele with the DQ locus and the observation that the DP but not the DQ association appears to be ethnically dependent strongly support a secondary role of DP molecules in celiac disease susceptibility.

Linkage disequilibrium between DPA1 and DPB1 alleles among Norwegian Caucasoids and Japanese

Associations between alleles at the DPA1 and DPB1 loci were analyzed in 181 Norwegian caucasoids. Associations were observed between the DPA1*0201 and the DPB1*0101, *0901, *1001 and *1101 alleles. An association between DPA1*0201 and the DPB1*0901 allele was also observed among 23 healthy Japanese and 24 Japanese MS patients. In addition, it appeared that among Japanese the DPA1*0201 allele may be associated to the DPB1*0501. In conclusion, alleles at the DPA1 and DPB1 loci display different associations among Norwegian caucasoids and Japanese.

Intraepithelial gamma delta T-cell-receptor lymphocytes and genetic susceptibility to coeliac disease

Although the proportion of gamma delta T-cell-receptor (TCR)-bearing intraepithelial lymphocytes is increased in the jejunum of patients with active coeliac disease, an abnormality thought to be specific among those with gluten-sensitive enteropathy, the factors influencing gamma delta TCR expression remain uncertain. We examined the relation between genetic factors associated with coeliac disease and intraepithelial gamma delta T lymphocyte distribution in both coeliac patients and their healthy first-degree relatives. 41% (45/109) of healthy relatives had an increased density of gamma delta T cells in their mucosa and 66% had an increased density of alpha beta T cells. By contrast with alpha beta T cells, the density of gamma delta cells was significantly associated with genetic markers for coeliac disease susceptibility (DR3, DQA, and DQB). We also found a dose effect of DQA and DQB genes on the number of intraepithelial gamma delta T cells. An increased density of gamma delta T cells in normal jejunal mucosa of a healthy individual with appropriate genetic determinants might be necessary for the development of the typical lesions of coeliac disease. Routine jejunal histological studies should include gamma delta T-cell counts, thus allowing early detection of coeliac disease latency.

Immunoglobulin and HLA-DP genes contribute to the susceptibility to juvenile dermatitis herpetiformis

HLA-DQ genes and gluten diet are the main factors involved in the pathogenesis of Dermatitis Herpetiformis (DH), as well as Coeliac Disease (CD). However other genetic factors are probably relevant, since about 10% of the patients with DH and CD lack the DQA1*0501/B1*0201 heterodimer while the majority of individuals presenting this genotype and also being exposed to gluten diets did not suffer from these diseases. To evaluate the role of other genes, 36 Northern Italian children with DH were analysed for DNA polymorphisms at HLA-DP and immunoglobulin (Ig) heavy chain loci. DPA1*0201 and DPB1*1301 frequencies were higher in patients than in controls (Pc = 0.0357 and Pc = 0.0273). With respect to immunoglobulin heavy chain restriction fragment length polymorphisms (RFLP), the 4.6 kb SacI RFLP at the switch alpha 2 gene was more frequent in patients (0.13) than in controls (0.019; Pc = 0.036). Moreover, rare alleles or duplications in the switch regions occurred more frequently in the patients than in the controls. These results support the hypothesis of a multifactorial inheritance of DH, the HLA and Ig constant heavy chain genes being some of the loci contributing to the susceptibility. In accordance with previous CD studies, these data also confirm that DP subregion is probably involved in the pathogenesis of DH.

HLA class II frequencies in celiac disease patients in the West of Ireland

Restriction fragment length polymorphism analysis, using a single restriction enzyme TaqI-multiple-probe system for HLA-DRB1-DQB1 and -DQA1, was used to determine HLA-DR and -DQ frequencies in 56 unrelated celiac patients and 47 unrelated controls from the west of Ireland. In addition, HLA-DPB1 allelic frequencies were determined in the same group of patients and controls by using the technique of enzymatic DNA amplification of the polymorphic second exon of HLA-DPB1 genes in conjunction with sequence-specific oligonucleotide probing. The results suggest that HLA-DQ rather than HLA-DR is more important in conferring susceptibility to celiac disease. Furthermore, no association between HLA-DP and celiac disease was found in this study.

A study of Italian pediatric celiac disease patients confirms that the primary HLA association is to the DQ(alpha 1*0501, beta 1*0201) heterodimer

Celiac disease (CD) has been recently reported to be primarily associated with the DQ(alpha 1*0501, beta 1*0201) heterodimer encoded in cis on DR3 haplotype and in trans in DR5,7 heterozygous individuals. The high incidence of DR5,7 heterozygotes, reflecting the high frequency of the DR5 allele in Italy, makes the analysis of the Italian CD patients critical. Polymerase chain reaction-amplified DNA from 50 CD patients and 50 controls, serologically typed for DR and DQw antigens, was hybridized with five DQA1-specific oligonucleotide probes detecting DQA1*0101 + 0102 + 0103, DQA1*0201, DQA1*0301 + 0302, DQA1*0401 + 0501 + 0601, and DQA1*0501 and a DQB1-sequence-specific oligonucleotide probe recognizing DQB1*0201 allele. As expected by the DR-DQ disequilibria, DQA1*0201 [62% in patients versus 26% in controls, relative risk (RR) = 5] and DQA1*0501 (96% versus 56%, RR = 19) show positive association with the disease. Of CD patients, 92% (50% DR3 and 42% DR5,7) compared to 18% of the controls carry both DQA1*0501 and DQB1*0201 alleles, so that the combination confers an RR of 52, higher than both the risks of the single alleles (DQA1*0501 RR = 19, DQB1*0201 RR = 30), confirming the primary role of the dimer in determining genetic predisposition to CD both in DR3 and in DR5,7 subjects.

A high frequency of the A30, B18, DR3, DRw52, DQw2 extended haplotype in Sardinian celiac disease patients: Further evidence that disease susceptibility is conferred by DQ A1*0501, B1*0201

This study characterizes by serological and molecular methods the HLA class I and class II alleles in a group of celiac disease children, their parents and a control group of Sardinian descent. We found the DR3-DQw2 haplotype in all patients which was, in almost all cases (84%), associated with the HLA-A30, B18, DR3, DRw52, DQw2 extended haplotype named "Sardinian haplotype" because of its frequency (12-15%) in this Caucasian population. This is the first time that this DQw2-linked haplotype has been reported with such a high frequency in CD. However, no different distribution of "Sardinian haplotype" was found comparing CD patients with 91 haplotyped DQw2-positive controls. This finding indicates that the DQw2 antigen in Sardinians is almost always associated with the A30, B18, DR3, DRw52, DQw2 extended haplotype. The DQA1 and DQB1 second exon sequence analysis of the B18,DR3 and B8,DR3 haplotypes showed the DQA1*0501 and DQB1*0201 alleles which shared the already published sequences. DPB1 subtyping showed the DPB1*0301 allele more frequently (p less than 0.005) in CD patients but this difference was no longer significant when patients and controls, both heterozygous for the DR3-DQw2 haplotype, were compared. We suggest that the divergent HLA extended haplotypes and DP allele associated with CD, described in different Caucasian populations, can be explained by the particular DQw2 linkage disequilibrium in each population.