Linkage disequilibrium between intra-locus variants in the aminopeptidase n gene and test of their association with coeliac disease

The pathogenesis of coeliac disease

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

Identification of six new polymorphisms in the human coronavirus 229E receptor gene (aminopeptidase N/CD13)

Objective: Human aminopeptidase N (APN/CD13/ANPEP) has been identified as the receptor for human coronavirus (HCoV) 229E. In this study, we analyzed the region of the APN gene that encodes a stretch of amino acid residues, essential for its HCoV-229E receptor function (amino acids 260–353).

Methods: Full-length APN exon 3, intron 3 and exon 4, was PCR-amplified and sequenced in DNA samples from 100 unrelated Caucasian Belgian healthy volunteers.

Results: We identified seven polymorphisms, including four intron 3 and three exon 4 variations. Apart from the already known C956T exon 4 mutation, the six other polymorphisms have not yet been described. The most prevalent APN variations in this population (C956T leading to an alanine to valine substitution, G978T, G987A and intron3-C389T) always occurred together at an allele frequency of 8.5%. Haploid DNA sequencing demonstrated the presence of these four variations on the same allele. Three polymorphisms in intron 3, intron3-G395C, intron3-C86T, and intron3-C429T, were identified with an allele frequency of 3.5%, 1% and 0.5% respectively. Five haplotypes were identified in the population of 100 individuals.

Conclusion: These results demonstrate that there is a relatively broad spectrum of variations in the APN domain critical for coronavirus binding.

The nucleotide sequence reported here has been submitted to the GenBank database with the following accession number: AF527789.

Celiac disease

Celiac disease is more prevalent than it was previously thought to be, and screening of selected population groups may reveal many new cases. Tissue transglutaminase appears to have a significant role in the degradation of gliadin and antigen production. Specific gliadin epitopes have been defined using T-cell responses. Bone disease is a significant problem for patients with celiac disease but management guidelines are being developed. Refractory sprue (nonresponsive celiac disease) appears to be a manifestation of enteropathy-associated T-cell lymphoma in most cases.

Celiac disease: strongly heritable, oligogenic, but genetically complex

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

Genetics of celiac disease

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