Accuracy of testing for antibodies to synthetic gliadin-related peptides in celiac disease

What is the role of serologic testing in celiac disease? A prospective, biopsy-confirmed study with economic analysis

BACKGROUND & AIMS

The optimal serologic tests for the detection of celiac disease and follow-up assessment remains controversial. Our aim was to evaluate all current immunologic assays for diagnosing celiac disease using the gold standard of duodenal biopsy. We also assessed whether tissue transglutaminase (tTG) antibody is a quantitative marker for histologic severity.

METHODS

Consecutive adult patients referred for gastroscopy without a previous known diagnosis of celiac disease were recruited (group 1). Concurrently, patients with a known diagnosis of celiac disease on a gluten-free diet for more than 1 year undergoing repeat duodenal biopsy were identified (group 2). All patients had duodenal biopsies and serologic analysis performed for immunoglobulin(Ig) A and antibodies to human immunoglobulin (Ig)A-tTG, IgA-gliadin, IgG-gliadin, and IgA-endomysial antibody.

RESULTS

Two thousand patients were recruited in the first group. Seventy-seven (3.9%) patients were diagnosed with new celiac disease. The sensitivity, specificity, positive predictive value, and negative predictive value for IgA tTG were 90.9%, 90.9%, 28.6%, and 99.6%. When adopting a 2-step approach using tTG first and then EMA the sensitivity, specificity, positive predictive value, and negative predictive value was 85.7%, 98.6%, 71.7%, and 99.7%, respectively. The use of nondeamidated IgA/IgG gliadin antibodies conferred no additional diagnostic benefit when considering the detection of adult celiac disease. In the second group 48 patients with celiac disease on a gluten-free diet were identified. Sixteen of 48 of these patients had persisting villous atrophy, but 7 of 16 (44%) had a normal tTG level.

CONCLUSIONS

IgA tTG alone is a sensitive marker for celiac disease. A normal tTG level does not predict recovery of villous atrophy in patients with celiac disease on a gluten-free diet.

Coeliac disease screening in children: assessment of a novel anti-gliadin antibody assay

Coeliac disease (CD) screening has progressed rapidly with tissue transglutaminase (TTG), the screening tool of choice. However, TTG may be unreliable in young children and advances in CD etiology understanding have seen improvements in anti-gliadin (AGA) assay technology. The aim of this study was to investigate the utility of an updated and refined AGA (Neogliadin) assay for CD screening in children with gastrointestinal symptoms. Children attending the Sydney Children's Hospital, Randwick, with gastrointestinal symptoms had sera collected and assayed by Neogliadin and commercial TTG assays in addition to the usual clinical work-up. One hundred and fifteen children were recruited in which 32 were diagnosed with CD. AGA-IgA screening by Neogliadin showed improved sensitivity (83%) and specificity (91%) but did not eclipse the sensitivity (93%) and specificity (90%) of TTG-IgA screening. In the children diagnosed with CD, 7 were identified as younger than 5 years of age with 4/7 AGA-IgA positive, 5/7 AGA-IgG positive, and 6/7 TTG-IgA positive. The updated Neogliadin IgA assay does not improve on the accuracy achieved by TTG screening. TTG appears to be a suitable screening tool for children younger than 5 years of age although this preliminary finding requires confirmation.

Resurrection of gliadin antibodies in coeliac disease. Deamidated gliadin peptide antibody test provides additional diagnostic benefit

OBJECTIVE

Circulating antibodies against naive, whole gliadin have been replaced by more accurate endomysial and tissue transglutaminase antibody tests in the diagnosis of coeliac disease. The purpose of this study was to compare these serological tests with a new test recognizing antibodies against deamidated and defined gliadin peptides.

MATERIAL AND METHODS

The study population comprised selected coeliac disease patients in a tertiary clinic: newly detected patients before and after a gluten-free diet, patients with persistent small-bowel mucosal villous atrophy despite a strict gluten-free diet and non-coeliac controls reporting abdominal symptoms after ingestion of cereals. Comparisons were made between serum IgA-class gliadin peptide, endomysial, tissue transglutaminase and conventional gliadin antibodies.

RESULTS

The deamidated gliadin peptide antibody test showed a sensitivity of 91% and a specificity of 98% in coeliac disease. The tissue transglutaminase antibody test performed equally well. The specificity of endomysial antibody was just as high, but its sensitivity was lower, 80%. The conventional gliadin antibody test showed poor sensitivity and specificity. Combination of the deamidated gliadin peptide and tissue transglutaminase tests offered the best sensitivity without loss of specificity in the diagnosis of coeliac disease. All antibody levels declined in line with mucosal recovery. The deamidated gliadin peptide antibody test showed six of the nine cases with small-bowel mucosal damage persisting on a gluten-free diet, whereas tissue transglutaminase detected only two cases and endomysial antibody none.

CONCLUSIONS

The new gliadin peptide antibody test proved highly accurate in the diagnostic work-up and follow-up of coeliac disease and can be endorsed in combination with the tissue transglutaminase test.

Antibodies against synthetic deamidated gliadin peptides and tissue transglutaminase for the identification of childhood celiac disease

BACKGROUND & AIMS

Children with celiac disease have antibodies against gliadin, tissue transglutaminase (tTG), or both antigens. The aim was to evaluate immunoglobulin (Ig)A and IgG antibodies to synthetic deamidated gliadin peptides (DGP) and human tTG as screening markers for childhood celiac disease.

METHODS

Antibodies were detected in enzyme-linked immunosorbent assay using anti-human IgA, IgG, or a combined conjugate of IgA and IgG (IgAG) against DGP, tTG, or both (DGP/tTG), in sera from 119 children with celiac disease, 57 disease controls, and 398 blood donors. Treatment with a gluten-free diet was evaluated in 20 children with celiac disease who were followed up for 6 months from diagnosis.

RESULTS

The highest sensitivity was accounted for IgAG-DGP/tTG at 100% (119 of 119), followed by IgA-tTG at 97% (115 of 119), IgG-DGP at 95% (113 of 119), IgA-DGP at 91% (108 of 119), and IgG-tTG at 13% (15 of 119). With respect to disease controls and blood donors, specificity was for IgAG-DGP/tTG at 89% (51 of 57) and at 97% (385 of 398), IgA-tTG at 96% (55 of 57) and at 98% (392 of 398), IgG-DGP at 86% (49 of 57) and at 99% (395 of 398), IgA-DGP at 91% (52 of 57) and at 92% (366 of 398), and IgG-tTG at 100%, respectively. The concordances between antibody assays were 87%-98%, except for comparisons with IgG-tTG (39%-41%). After 6 months of a gluten-free diet, the mean antibody levels decreased for all test results (P < .001).

CONCLUSIONS

The combined IgAG-DGP/tTG assay is recommended as a front-line screening test for the identification of childhood celiac disease and also could be used as a marker of dietary compliance.

A prospective comparative study of five measures of gluten-free diet adherence in adults with coeliac disease

BACKGROUND

Increasing numbers of individuals are now being diagnosed with coeliac disease. The only accepted treatment for coeliac disease is lifelong adherence to a strict gluten-free diet (GFD). Individuals' ability to adhere to the GFD varies, but systematic studies guiding the assessment of adherence are currently lacking.

AIM

We sought to compare the predictive value of self-report and four serologic tests compared to expert nutritionist evaluation.

METHODS

In all, 154 individual adults with biopsy-proven coeliac disease rated their adherence to the GFD on a Likert scale. Serum antibody titres of IgA anti-tissue transglutaminase, and IgA and IgG anti-deamidated gliadin peptides were determined. Using anova and ROC analyses, results were compared to a standardized evaluation by an expert nutritionist blinded to the participants' self-rated adherence and serology results.

RESULTS

All serologic measures as well as participant reported adherence were significantly associated with GFD adherence as assessed by expert nutritionist evaluation. However, on ROC analysis no measure performed satisfactorily. The performance of serologic testing, but not self-report, improved with increased time on the GFD.

CONCLUSION

Although current serologic tests have very high sensitivities and specificities for the diagnosis of coeliac disease, they cannot replace trained nutritionist evaluation in the assessment of GFD adherence.

Antibodies against synthetic deamidated gliadin peptides as predictors of celiac disease: prospective assessment in an adult population with a high pretest probability of disease

BACKGROUND

Noninvasive serologic tests have shown high diagnostic accuracy for celiac disease (CD) in selected populations. Our aim was to determine prospectively the performance of CD-related serology in individuals undergoing intestinal biopsy because of clinical suspicion of small-bowel disorders.

METHODS

We enrolled 141 unselected consecutive adult patients attending a small-bowel disease clinic. Patients underwent endoscopy and biopsy; serum samples were obtained at that time for measurements of anti-tissue transglutaminase (a-tTG), IgA and IgG anti-deamidated gliadin-related peptide (a-DGP), and IgA antiactin antibodies (AAAs). Characterization of patients was based on histological criteria (Marsh type II lesion or greater).

RESULTS

The prevalence of CD was 42.5%. Sensitivity, specificity, and positive and negative predictive values were >90% for most assays. Diagnostic accuracy based on ROC curve analysis was similar for all assays [area under the curve (95% CI): 0.996 (0.967-0.998) for a-tTG, 0.995 (0.964-0.998) for IgA a-DGP, 0.989 (0.954-0.999) for IgG a-DGP, 0.996 (0.966-0.998) for blended conjugated of IgA + IgG a-DGP in a single assay, and 0.967 (0.922-0.990) for AAA]. The combinations of 2 tests, IgG a-DGP plus IgA a-tTG or the single blended conjugate detecting IgA + IgG a-DGP plus IgA a-tTG had 100% positive and negative predictive values if concentrations of both tests in either combination were above or below the cutoff.

CONCLUSIONS

In a population with high pretest probability, the newly developed a-DGP tests have diagnostic accuracy that is at least equivalent to that of established assays.

Antibody responses to deamidated gliadin peptide show high specificity and parallel antibodies to tissue transglutaminase in developing coeliac disease

Coeliac disease (CD) is an enteropathy induced in genetically susceptible individuals by gluten components, gliadin, hordein and secalin, polypeptides present in cereals such as wheat, barley and rye, respectively. Although the disease starts as intolerance to gliadins, antibodies to tissue transglutaminase (tTG) in the gut epithelium are characteristic of the disease. Whereas serum autoantibodies against tTG (tTGA) are highly specific for CD, antibodies to gliadin are less informative as they can also be detected in other enteropathies, and even in healthy individuals. However, it was shown recently that antibodies to certain gliadin peptides occur with high specificity in CD patient sera. We developed a solid phase lanthanide-based immunofluorometric assay for simultaneous detection of serum IgA and IgG antibodies to a synthetic peptide derived from gamma gliadin of wheat comprising amino acids 86-103. Three glutamine residues of this native 18-mer peptide were replaced by glutamic acids and the peptide was biotinylated. Sera from 87 individuals who had undergone duodenal biopsy and were diagnosed with CD and from 81 healthy individuals were analysed for the presence of both IgA and IgG anti-gliadin peptide antibodies. The performance of the peptide AGA assay was excellent, showing a specificity and sensitivity of 90% and 92% for IgA, and 98% and 75% for IgG, respectively. The corresponding values for conventional anti-gliadin antibody (AGA) enzyme-linked immunosorbent assay (ELISA) tests were 72% specificity and 87% sensitivity for IgA, and 64% specificity and 78% sensitivity for IgG. In a prospective study, almost all the tTGA-positive sera drawn from children who later developed CD were also positive for gliadin peptide antibodies.

Natural history of antibodies to deamidated gliadin peptides and transglutaminase in early childhood celiac disease

INTRODUCTION

Gliadin proteins play a key role in the pathogenesis of celiac disease; however, as a screen for celiac disease, anti-gliadin antibody testing has been replaced by the more sensitive and specific serological assays for transglutaminase autoantibodies (TGAA). A new generation of anti-gliadin antibody assays has been developed to detect synthetic, deamidated homologous gliadin peptides (DGP) with high sensitivity and specificity.

METHODS

Sera were collected prospectively from children with an increased risk for celiac disease as part of an ongoing study at Denver, and studied for the development of celiac autoimmunity. We investigated the high-performance DGP antibody assay in 50 TGAA-positive children both before the development of celiac autoimmunity and following the institution of a gluten-free diet to determine the relationship of DGP antibodies to TGAA. TGAA were measured by an in-house radioassay.

RESULTS

DGP antibodies and TGAA parallel each other over the period of years children were studied. DGP antibodies resolved sooner than TGAA in subjects on a gluten-free diet. DGP antibodies appeared earlier than TGAA in 9 children.

CONCLUSIONS

Measuring DGP antibodies may be more useful than TGAA in monitoring children on a gluten-free diet. DGP antibodies can precede the appearance of TGAA in some at-risk children.

Deamidated Gliadin Peptides as Targets for Celiac Disease‐Specific Antibodies

Celiac disease (CD) is an (auto)immunologically mediated intestinal intolerance against proteins from wheat (gluten) and related cereal proteins. Tissue transglutaminase (tTG) has been identified as the autoantigen in CD. Although ultimate diagnosis is based on histological analysis of small intestinal mucosa obtained via tissue biopsy, assessment of autoantibodies can provide substantial help in the evaluation of CD. Gliadin antibodies are directed against the native disease-provoking cereal proteins. Despite their initial usefulness, these antibodies have lost diagnostic importance due to their poor specificity and sensitivity as CD markers. Recently, it was found, however, that gliadin antibodies from sera of patients with active CD preferentially recognized deamidated gliadin peptides. The use of deamidated gliadin peptides in immunoassays has significantly improved the usefulness of gliadin antibodies in diagnosis of CD to that observed with autoantibody assay methods (endomysium antibodies, antibodies against tTG). The antibody epitopes (B-cell epitopes) reflect substrate specificity of tTG and resemble peptide sequences known to be strongly T-cell stimulatory (T-cell epitopes) in CD. The assay applying deamidated gliadin peptides measures a new species of antibodies, which is different from conventional gliadin antibodies as well as from autoantibodies and will likely provide new information on pathophysiological mechanisms of CD.