Meta-analysis of genome-wide linkage studies in celiac disease

A review on the relationship between gluten and schizophrenia: Is gluten the cause?

INTRODUCTION

Schizophrenia is a chronic disease that possesses various clinical manifestations. It presents rather heterogeneous characteristics with respect to onset type, symptoms, and the course of the disease. Although the lifetime prevalence is as low as 1%, it can cause serious disability. Thus, it is very important to develop efficient treatment methods. In some studies, it is hypothesized that removing gluten from the diet leads to a significant improvement in disease symptoms. Epidemiological studies revealed that the prevalence of celiac disease among schizophrenic patients is almost two times higher than that of the general population.

OBJECTIVE

In this review, we evaluate the effects of gluten and celiac disease on the onset of schizophrenia. Efficacy of gluten-free diet applications, antibody response against gluten, and the interaction of the brain-gut axis and the presence of common genetic points are also investigated.

METHODS

Without any publication date restriction, Pubmed database searches were made for 'schizophrenia, gluten, gliadin, celiac disease, exorphin, brain-gut axis, psychiatric disorders.' The keywords and the articles about the schizophrenia-celiac disease relationship are included in our review.

RESULTS

Several studies presented evidence to suggest that symptoms associated with schizophrenia were minimized when gluten was excluded from patients' diets. Immunological searches revealed that most schizophrenic patients with increased anti-gliadin antibodies did not possess celiac disease; yet, the presence of increased antibodies against gliadin can be the share point of the immunological abnormalities found in both of the diseases.

DISCUSSION

There were no consistent results in the clinical, immunological, microbiological, and epidemiological studies that investigated the relationship between schizophrenia and celiac disease. This presents a need for a larger scale study to confirm the presence of this suggested correlation between schizophrenia and celiac disease. The underlying mechanisms between the two diseases should be explored.

Celiac disease screening in southern and East Asia

Until 1970s, celiac disease (CD) was considered to be an uncommon disease except in Western Europe. The global epidemiology of CD continues to evolve with improvement in the diagnostic tests, simplification of the diagnostic criteria and increase in awareness about the disease. The Asian region is currently at the crossroads of the frontier of knowledge and awareness of CD. In many Asian nations, CD is still considered to be either nonexistent or very rare. A notable exception is India, where CD has been well recognized, especially in the northern part, and 2 population-based studies have revealed a prevalence of 0.3-1.04%. Initial reports from Malaysia, China, Japan and Singapore suggest the existence of CD in these countries. Furthermore, a meta-analysis of the predisposing factors predicts a high probability of occurrence of CD in fair numbers in China. There are no formal reports on CD from Malaysia, Indonesia, Korea, Taiwan and many other nations in this region. With the impending CD epidemic in Asia, there are many challenges. Some of the efforts which are required include determination of prevalence of CD across the region, spreading of awareness among physicians and patients, training of dieticians for proper counseling and supervision of patients, creation of gluten-free food infrastructure in the food supply and creation of patient advocacy organizations. Although the absolute number of patients with CD at present is not very large, this number is expected to increase over the next few years/decades. It is thus appropriate that the medical community across Asia define the extent of the problem and get prepared to handle the impending CD epidemic.

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

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

Testing for gluten-related disorders in clinical practice: the role of serology in managing the spectrum of gluten sensitivity

Immunoglobulin A tissue transglutaminase is the single most efficient serological test for the diagnosis of celiac disease. It is well known that immunoglobulin A tissue transglutaminase levels correlate with the degree of intestinal damage, and that values can fluctuate in patients over time. Serological testing can be used to identify symptomatic individuals that need a confirmatory biopsy, to screen at-risk populations or to monitor diet compliance in patients previously diagnosed with celiac disease. Thus, interpretation of serological testing requires consideration of the full clinical scenario. Antigliadin tests are no longer recommended for the diagnosis of classical celiac disease. However, our understanding of the pathogenesis and spectrum of gluten sensitivity has improved, and gluten-sensitive irritable bowel syndrome patients are increasingly being recognized. Studies are needed to determine the clinical utility of antigliadin serology in the diagnosis of gluten sensitivity.

Meta-analysis of genome-wide linkage scans for renal function traits

BACKGROUND

Several genome scans have explored the linkage of chronic kidney disease phenotypes to chromosomic regions with disparate results. Genome scan meta-analysis (GSMA) is a quantitative method to synthesize linkage results from independent studies and assess their concordance.

METHODS

We searched PubMed to identify genome linkage analyses of renal function traits in humans, such as estimated glomerular filtration rate (GFR), albuminuria, serum creatinine concentration and creatinine clearance. We contacted authors for numerical data and extracted information from individual studies. We applied the GSMA nonparametric approach to combine results across 14 linkage studies for GFR, 11 linkage studies for albumin creatinine ratio, 11 linkage studies for serum creatinine and 4 linkage studies for creatinine clearance.

RESULTS

No chromosomal region reached genome-wide statistical significance in the main analysis which included all scans under each phenotype; however, regions on Chromosomes 7, 10 and 16 reached suggestive significance for linkage to two or more phenotypes. Subgroup analyses by disease status or ethnicity did not yield additional information.

CONCLUSIONS

While heterogeneity across populations, methodologies and study designs likely explain this lack of agreement, it is possible that linkage scan methodologies lack the resolution for investigating complex traits. Combining family-based linkage studies with genome-wide association studies may be a powerful approach to detect private mutations contributing to complex renal phenotypes.

Risk factors in familial forms of celiac disease

Celiac disease has been reported in up to 2% of some European populations. A similar risk has been identified in the America and Australia where immigration of Europeans has occurred. Moreover, an increasing number of celiac disease patients are being identified in many Asian countries, including China and India. Finally, celiac disease has also been detected in Asian immigrants and their descendants to other countries, such as Canada. Within these so-called "general" celiac populations, however, there are specific high risk groups that have an even higher prevalence of celiac disease. Indeed, the single most important risk factor for celiac disease is having a first-degree relative with already-defined celiac disease, particularly a sibling. A rate up to 20% or more has been noted. Risk is even greater if a specific family has 2 siblings affected, particularly if a male carries the human leukocyte antigen-DQ2. Both structural changes in the small bowel architecture occur along with functional changes in permeability, even in asymptomatic first-degree relatives. Even if celiac disease is not evident, the risk of other autoimmune disorders seems significantly increased in first-degree relatives as well as intestinal lymphoma. Identification of celiac disease is important since recent long-term studies have shown that the mortality of celiac disease is increased, if it is unrecognized and untreated.