Relevance of HLA-DQB1*02 Allele in the Genetic Predisposition of Children with Celiac Disease: Additional Cues from a Meta-Analysis

Association of the HLA-DQB1*02 allele with lower tauopathy in Alzheimer's disease

Although many studies have investigated the influence of HLA on the risk of Alzheimer's Disease (AD), there have been inconsistent results. Part of this problem has been attributed to limitations of a clinical assessment in the absence of histopathological confirmation or other quantitative assessments. This study employed a subset of the AD Sequencing Project, representing 2663 cases with histopathological confirmation of AD and confirmation of 881 cognitively normal cases. Two HLA allelic subtypes, DQB1*02:01 and DQB1*02:02, were associated with lower Braak staging, a measure of tauopathy in the brain. These HLA subtypes were also associated with a later age of onset. There was a lower occurrence of HLA-DQB1*02:01 and HLA-DQB1*02:02 in AD cases compared to cognitively normal cases. For all of the above results, replicative sets were confirmatory. The above results were also maintained for both HLA-DQB1*02:01 and HLA-DQB1*02:02 when removing the effect of APOE4 or APOE2. Interestingly, the HLA-DQB1*02 allele binds tau better than all other HLA-DQB1 alleles tested, per an in silico assessment, raising the question of whether deletion of tau binding, auto-reactive T-cells in the thymus could reduce the likelihood of the onset of AD?

Micronutrient deficiencies in patients with celiac disease: A systematic review and meta-analysis

This study aimed to characterize micronutrient deficiencies, including iron, ferritin, folic acid, vitamin D, zinc (Zn), vitamin B12, and copper, in patients with celiac disease, and evaluated the effects of these deficiencies on selected hematological parameters, including hemoglobin and mean corpuscular volume (MCV). Celiac disease (CeD), an immune-mediated disorder affecting the small bowel, is associated with genetic factors and micronutrient deficiencies. This meta-analysis was performed in accordance with the PRISMA guidelines. Literature searches of multiple databases retrieved 4140 studies, of which 45 were selected. Risk of Bias was performed in accordance with the STROBE checklist. Meta-analysis revealed a significant difference in hemoglobin levels between patients with CeD and controls (standardized mean difference (SMD) -0.59 (95% confidence interval (CI) -0.8459 to -0.3382); P = 0.0003). Iron levels were lower in patients with CeD (SMD ≈ -0.4 (95% CI -0.7385 to -0.0407); P = 0.0334), as were ferritin (SMD -0.6358 (95% CI -0.8962 to -0.3755); P = 0.0002), folic acid (SMD -0.5446 (95% CI -0.9749 to -0.1142); P = 0.0187), and vitamin D (SMD -0.4011 (95% CI -0.8020 to -0.0001); P = 0.0499) levels, while Zn levels were significantly reduced (SMD -1.1398 (95% CI -2.0712 to -0.2084); P = 0.0242). No significant differences were found in MCV, or copper or vitamin B12 levels between patients with CeD and controls. This study highlighted significantly higher micronutrient deficiencies in patients diagnosed with CeD than in controls, underscoring the importance of systematic nutritional assessment and multidisciplinary management to address micronutrient deficiencies and minimize negative health impact(s).

Saliva direct PCR protocol for HLA-DQB1*02 genotyping

Celiac disease (CD) is an immune disorder, that is triggered by gluten ingestion in genetically predisposed individuals. The HLA-DQB1*02 allele is the main predisposing genetic factor and a candidate for first-line genotyping screening. We designed and validated a simple, DNA purification-free PCR protocol directly from crude saliva, enabling the detection of the DQB1*02 allele. This assay also distinguishes homozygous from heterozygous carriers. We propose this method for use in mass screening and/or epidemiological studies.

Total serum IgA levels and HLA-DQB1*02:01 allelic status

Immunoglobulin A Deficiency (IgAD) is the most common primary immunodeficiency and is significantly associated with Celiac Disease (CD), which recognizes a specific background of human leukocyte antigens (HLA) predisposition (including HLA-DQB1*02:01 allele). A number of studies investigated the role of HLA in IgAD etiopathogenesis: HLA-DQB1*02 alleles are included in the main haplotypes linked to this primary immunodeficiency. In this preliminary study, we investigated the potential impact of HLA-DQB1*02:01 allelic status on total serum IgA levels: 108 serum samples from the bone marrow donors' registry were analyzed for total IgA concentration with respect to the HLA-DQB1*02:01 status. Although total serum IgA levels between HLA-DQB1*02:01 carriers and HLA-DQB1*02:01 negative donors were not different, we observed a statistically significant difference (p=0.0118) in total serum IgA levels among donors with low IgA concentration (<80mg/dL) in the sub-analysis between HLA-DQB1*02:01 positive group (including both homozygous and heterozygous carriers) compared to HLA-DQB1*02:01 negative donors. Our results might suggest a role of HLA-DQB1*02:01 allelic variant in the determination of total serum IgA levels, at least in patients affected with IgA deficiency and/or otherwise predisposed to it; however, larger and more standardized studies are needed to confirm this speculation.

Meta-Analysis and Systematic Review of HLA DQ2/DQ8 in Adults with Celiac Disease

Although people with human leukocyte antigens (HLA) DQ2 and/or DQ8 are more likely to develop celiac disease (CD), the condition cannot be fully explained by this genetic predisposition alone. Multiple, as yet unidentified, factors contribute to the genesis of CD, including genetics, the environment, and the immune system. In order to provide insight into a prospective possibility and an expanded screening technique, we aim to undertake a comprehensive and meta-analytical study of the assessment and distribution of HLA class II (HLA-DQ2/DQ8) in adult CD patients. A systematic review was conducted using an electronic search of databases (PubMed, Google Scholar, Embase, and Direct Science) from January 2004 to February 2022. DQ2/DQ2 homozygotes have the highest risk of developing CD. DQ2/DQ8 typing is an effective test to exclude CD from the differential diagnosis of a patient with CD symptoms. Although other non-HLA genes have been associated with CD, they are rarely considered at diagnosis because they account for only a small proportion of the heritability of CD. This finding, together with the information gathered previously, may be useful in considering widely available and economically feasible screening options for celiac disease in young people.

The Role of HLA in the Association between IgA Deficiency and Celiac Disease

Selective IgA deficiency (SIgAD) is the most frequent primary immune defect. Since SIgAD is not characterized by relevant infectious issues in most cases, it is often diagnosed during the diagnostic work up of several and different autoimmune disorders, which are associated with this primary immune defect. The genetic background of SIgAD is complex and three HLA haplotypes resulted to be more frequently associated with it; in detail, two of them include HLA-DQB1∗02 allelic variants, which are essential predisposing factors to develop Celiac Disease (CD). Here, we discuss the evidence regarding the role of HLA in the etiopathogenesis of SIgAD and its association with CD. Actually, the HLA region seems to play a modest role in the genetic predisposition to SIgAD and we may speculate that the association with the HLA-DQB1∗02 alleles (or haplotypes including them) could derive from its link with CD. Indeed, SIgAD and some related immunological alterations are likely to predispose to several autoimmune diseases (with and despite different HLA backgrounds), including CD, which is relatively common and directly associated with the HLA-DQB1∗02 allelic variants coding the DQ2 heterodimer. Further and specific studies are needed to make final conclusions in this regard.

Distribution of HLA Alleles and Genotypes in Patients with Chronic Inflammatory Demyelinating Polyneuropathy

Chronic inflammatory demyelinating polyneuropathy (CIDP) is an acquired immunological disorder. Although the precise pathoetiology of CIDP has not been clarified yet, it is believed that both B and T cells of immune system contribute in this disorder. Based on the importance of human leukocyte antigen (HLA) cluster in the regulation of immune responses, this family of proteins is putative determinants of risk of CIDP. We conducted the current investigation to appraise association between HLA alleles/genotypes/haplotypes and risk of CIDP in Iranian patients. HLA-DQB1*02 allele was significantly more prevalent among cases compared with controls (OR [95% CI] = 4.82 [2.06, 11.3], P value = 0.000215, adjusted P value = 0.0124). A*01-B*52-C*12-DRB1*15-DQB1*02 and A*23-B*35-C*04-DRB1*11-DQB1*03 haplotypes with frequency of 0.03 were the most frequent HLA haplotypes. These haplotypes were not detected among healthy controls. The present study introduces HLA-DQB1*02 allele as a risk allele for CIDP among Iranian patients and further supports the importance of HLA region in this immunological condition.

Fecal and Duodenal Microbiota in Pediatric Celiac Disease

Background and Objective: The gut microbiota plays a role in regulating the host immunity. Therefore, alterations in gut microbiota (or dysbiosis) have been investigated in several gastrointestinal diseases, including Celiac Disease (CD). The aim of this study is to summarize the main characteristics of the gut microbiota in pediatric CD. Methods: We performed a systematic review to retrieve the available studies investigating the gut microbiota in pediatric CD patients and controls. In detail, after the screening of >2,200 titles from the medical literature, 397 articles were assessed for eligibility based on the abstracts: of those, 114 full-text original articles were considered as eligible according to the aim of this systematic review. Results: The final search output consisted of 18 articles describing the gut microbiota of CD children and including one or more control groups. Eleven pediatric studies provided information on the duodenal microbiota and as many investigated the fecal microbiota; three articles analyzed the microbiota on both fecal and duodenal samples from the same cohorts of patients. Conclusion: Due to the heterogeneity of the experimental procedures and study design, it is not possible to evidence any specific celiac signature in the fecal and/or duodenal microbiota of CD children. However, some specific components of the fecal microbiota and, in detail, Bifidobacterium spp. (e.g., Bifidobacterium longum) may deserve additional research efforts, in order to understand their potential value as both probiotic therapy and diagnostic/prognostic biomarker.

Current research status of HLA in immune-related diseases

Human leukocyte antigen (HLA), also known as human major histocompatibility complex (MHC), is encoded by the HLA gene complex, and is currently known to have the highest gene density and the most polymorphisms among human chromosomal areas. HLA is divided into class I antigens, class II antigens, and class III antigens according to distribution and function. Classical HLA class I antigens include HLA-A, HLA-B, and HLA-C; HLA class II antigens include HLA-DP, HLA-DQ, and HLA-DR; nonclassical HLA class I and II molecules include HLA-F, E, H, X, DN, DO, and DM; and others, such as complement, are class III antigens. HLA is closely related to the body's immune response, regulation, and surveillance and is of great significance in the study of autoimmune diseases, tumor immunity, organ transplantation, and reproductive immunity. HLA is an important research topic that bridges immunology and clinical diseases. With the development of research methods and technologies, there will be more discoveries and broader prospects.

Salivary Microbiome in Pediatric and Adult Celiac Disease

The human salivary microbiota includes hundreds of bacterial species. Alterations in gut microbiota have been explored in Celiac Disease (CD), but fewer studies investigated the characteristics of salivary microbiome in these patients, despite the potential implications in its pathogenesis. Indeed, some recent studies suggested that the partial digestion of gluten proteins by some bacteria may affect the array of gluten peptides reaching the gut and the way by which those are presented to the intestinal immune system. The available clinical studies investigating the salivary microbiota in children and adults, are insufficient to make any reliable conclusion, even though some bacterial species/phyla differences have been reported between celiac patients and controls. However, the salivary microbiome could correlate better with the duodenal microbiota, than the fecal one. Therefore, further clinical studies on salivary microbiome by different and independent research groups and including different populations, are advisable in order to explore the usefulness of the salivary microbiome analysis and understand some aspects of CD pathogenesis with potential clinical and practical implications.

HLA class II genes in precision-based care of childhood diseases: what we can learn from celiac disease

Celiac disease (CeD) is a chronic immuno-mediated enteropathy caused by dietary gluten with marked autoimmunity traits. The human leukocyte antigen (HLA) class II heterodimers represent the main predisposing factor, although environmental agents, as viral infection, gut microbiota, and dietary regimen, also contribute to CeD risk. These molecules are involved in autoimmunity as they present self-antigens to autoreactive T cells that have escaped the thymic negative selection. In CeD, the HLA class II risk alleles, DQA1*05-DQB1*02 and DQA1*03-DQB1*03, encode for DQ2.5 and DQ8 heterodimers, and, furthermore, disease susceptibility was found strictly dependent on the dose of these genes. This finding questioned how the expression of HLA-DQ risk genes, and of relative surface protein on antigen-presenting cells, might be relevant for the magnitude of anti-gluten inflammatory response in CeD patients, and impact the natural history of disease, its pathomechanisms, and compliance to dietary treatment. In this scenario, new personalized medical approaches will be desirable to support an early, accurate, and non-invasive diagnosis, and to define genotype-guided preventive and therapeutic strategies for CeD. To reach this goal, a stratification of genetic risk, disease outcome, and therapy compliance based on HLA genotypes, DQ2.5/DQ8 expression measurement and magnitude of T cell response to gluten is mandatory. IMPACT: This article revises the current knowledge on how different HLA haplotypes, carrying the DQ2.5/DQ8 risk alleles, impact the onset of CeD. This review discusses how the expression of susceptibility HLA-DQ genes can determine the risk assessment, outcome, and prevention of CeD. The recent insights on the environmental factors contributing to CeD in childhood are reviewed. This review discusses the use of HLA risk gene expression as a tool to support medical precision approaches for an early and non-invasive diagnosis of CeD, and to define genotype-guided preventive and therapeutic strategies.

Carrier frequency of HLA-DQB1*02 allele in patients affected with celiac disease: A systematic review assessing the potential rationale of a targeted allelic genotyping as a first-line screening

BACKGROUND

Celiac Disease (CD) is an immune-mediated disorder, in which the HLA immunogenetic background (DQ2 and DQ8 heterodimers) and environmental trigger (gluten) are well established. Indeed, both factors are necessary - but not sufficient - to develop CD. However, it is very likely that CD is underdiagnosed in both developing and developed countries, due to several aspects, including the fact that a lot of patients present mild and/or atypical symptoms, without the presence of any recognized risk factors. Therefore, the possibility and feasibility of widened screening strategies to identify CD patients are debated.

AIM

To provide further evidence of the main epidemiological importance of HLA-DQB1*02 allele in the population of CD patients.

METHODS

We performed a systematic search in PubMed, EMBASE, Cochrane, Web of Science and Scopus databases, in order to produce a systematic review assessing the carrier frequency of HLA-DQB1*02 allele in the celiac population. Following the PRISMA guidelines, we retrieved all the original articles describing CD patients' HLA-DQB1 genotype in such a way that could allow to assess the HLA-DQB1*02 carrier frequency among CD patients, along with the evidence of the appropriate diagnostic work-up to achieve a correct and final diagnosis of CD.

RESULTS

The final output of this systematic search in the medical literature consisted of 38 studies providing the appropriate HLA-DQB1 genotype information of the respective CD population. According to this systematic review, including a pool of 4945 HLA-DQ genotyped CD patients, the HLA-DQB1*02 carrier frequency was 94.94%, meaning that only 5.06% of CD patients were completely lacking this allelic variant. Interestingly, if we consider only the studies whereby the prevalence of CD patients affected with type 1 diabetes mellitus was supposed or clearly established to be very low, the frequency of non-HLA-DQB1*02 carriers among CD patients dropped to 3.65%.

CONCLUSION

Such a high carrier frequency of the HLA-DQB1*02 allelic variant (which is > 95%-96% in CD patients without risk factors, like type 1 diabetes mellitus comorbidity) might be exploited to consider a cost-effective and widened screening approach. If a sustainable strategy could be implemented through a low-cost targeted genetic test to detect the individual presence of HLA-DQB1*02 allele, an appropriate algorithm for serological screening in individuals resulting to be genetically predisposed to CD, might be considered.

Genetic predisposition to celiac disease in Kazakhstan: Potential impact on the clinical practice in Central Asia

BACKGROUND

Celiac disease (CD) is a systemic immune-mediated disorder developing in HLA genetically predisposed individuals carrying HLA-DQ2 and/or HLA-DQ8 molecules. Recent evidences supported a predominant importance of HLA-DQB1 locus and, in particular, HLA-DQB1*02 alleles. This diagnosis is poorly considered in Kazakhstan, because of the assumption that CD is not prevalent in this population.

OBJECTIVE

To demonstrate that the genetic predisposition to CD in Kazakhstan is not negligible and is actually comparable to Western populations.

METHODS

Through the analysis of HLA-DQ genotypes of healthy bone marrow donors from Kazakhstan's national registry, we estimated the HLA-related genetic predisposition to CD in the country.

RESULTS

We demonstrated that the frequency of CD-related HLA-DQB1 alleles and, as a consequence, of predisposed individuals to CD in Kazakhstan is significant and comparable to countries with the highest disease prevalence.

CONCLUSION

Considering the dietary style in Kazakhstan, including wheat as a staple food, these results provided a preliminary background of knowledge to expect a significant CD prevalence in Kazakhstan and Central Asia by implementing appropriate and cost-effective diagnostic strategies.

Micronutrients Dietary Supplementation Advices for Celiac Patients on Long-Term Gluten-Free Diet with Good Compliance: A Review

Background and objective: Often micronutrient deficiencies cannot be detected when patient is already following a long-term gluten-free diet with good compliance (LTGFDWGC). The aim of this narrative review is to evaluate the most recent literature that considers blood micronutrient deficiencies in LTGFDWGC subjects, in order to prepare dietary supplementation advice (DSA). Materials and methods: A research strategy was planned on PubMed by defining the following keywords: celiac disease, vitamin B12, iron, folic acid, and vitamin D. Results: This review included 73 studies. The few studies on micronutrient circulating levels in long-term gluten-free diet (LTGFD) patients over 2 years with good compliance demonstrated that deficiency was detected in up to: 30% of subjects for vitamin B12 (DSA: 1000 mcg/day until level is normal, then 500 mcg), 40% for iron (325 mg/day), 20% for folic acid (1 mg/day for 3 months, followed by 400–800 mcg/day), 25% for vitamin D (1000 UI/day or more-based serum level or 50,000 UI/week if level is <20 ng/mL), 40% for zinc (25–40 mg/day), 3.6% of children for calcium (1000–1500 mg/day), 20% for magnesium (200–300 mg/day); no data is available in adults for magnesium. Conclusions: If integration with diet is not enough, starting with supplements may be the correct way, after evaluating the initial blood level to determine the right dosage of supplementation.