Objectives: Polymorphisms in the major histocompatibility complex class I chain-related gene A may influence its binding to the Natural Killer Cell Receptor G2D (NKG2D). We looked for polymorphisms in major histocompatibility complex class I chain-related gene A exon 5 and in Human Leukocyte Antigen (HLA)-DQ/DR in adult coeliac disease patients to determine whether they affected coeliac disease phenotypes.
Methods: Adult coeliac disease patients with (n=98) and without (n=93) gastrointestinal symptoms (gastrointestinal symptoms+/gastrointestinal symptoms-) and 108 control subjects from Campania (Italy) were characterized by Polymerase Chain Reaction (PCR) sequence specific oligonucleotide followed by PCR sequence specific primer assays for HLA DQ/DR, and by PCR followed by capillary electrophoresis for major histocompatibility complex class I chain-related gene A exon 5 polymorphisms. Immunoglobulin A (IgA) anti-transglutaminase antibodies were also evaluated by immunosorbent assay.
Results: Five different major histocompatibility complex class I chain-related gene A alleles were detected in both coeliac disease patients and control subjects. The major histocompatibility complex class I chain-related gene A 5.1 allele occurred more frequently in patients than in controls (p<0.05), and the major histocompatibility complex class I chain-related gene A 5.1/5.1 homozygous genotype increased the risk of gastrointestinal symptoms- coeliac disease (OR=2.79, 95% CI 1.15-6.79). Gastrointestinal symptoms- coeliac disease patients bearing major histocompatibility complex class I chain-related gene A 5.1/5.1 alleles showed lower anti-transglutaminase levels (18U/L) than the gastrointestinal symptoms+ coeliac disease patients (35U/L). HLA-DQ2/DQ8 genotypes did not differ between gastrointestinal symptoms+ and gastrointestinal symptoms- coeliac disease, although DQ8 tended to be more frequent in gastrointestinal symptoms- coeliac disease (11.7%) than in gastrointestinal symptoms+ coeliac disease (6%).
Conclusions: Our study shows that a double dose of the major histocompatibility complex class I chain-related gene A 5.1 allele could predispose to the onset of gastrointestinal symptoms- coeliac disease. We can hypothesize that a lower level of immunological involvement in gastrointestinal symptoms- coeliac disease patients is associated with absence of gastrointestinal symptoms. This test could represent a second step in the genetic typing of high-risk subjects such as first-degree relatives of coeliac disease patients positive for the DQ2/DQ8 molecule.