Characterization of MICA gene polymorphism of HLA complex in the Slovak population

The function of the MHC class I polypeptide-related sequence A (MICA) gene, which belongs to the MHC class I chain-related genes, is to trigger cytolysis of target cells mediated by NKG2D receptor recognition in NK (Natural Killer) cells and CD8 T-lymphocytes. The MICA gene has a high degree of polymorphism, especially observed in exons 2-5. MICA allelic diversity has been reported in association with some autoimmune diseases such Behcet's disease, psoriasis and diabetes, as well as with organ rejections.

The aim of this study was to analyse MICA gene polymorphism in the Slovak population, to establish frequencies of MICA alleles and to compare the results with those found in other Western Eurasian populations. No such study has been performed previously in the Slovak population.

This study examined DNA samples from 124 unrelated Slovak individuals (51 women and 73 men with an average age of 40.3 years) using direct sequencing of MICA exons 2-5. Allele and genotype frequencies were calculated by direct counting and statistical analysis was carried out using Arlequin software.

This study identified 15 out of 71 MICA alleles. The most frequent allele was MICA(*)008 (37.1%) followed by alleles MICA(*)002 (16.5%) and MICA(*)009 (11.3%). The rarest alleles were MICA(*)027, MICA(*)006 (both 0.8%) and MICA(*)057 (0.4%), respectively. The most frequent genotypes were 008/008 and 008/002, both with a frequency of 13.7%. Exon 5 microsatellite polymorphism screening revealed five MICA alleles, namely A4, A5, A5.1, A6 and A9. The most frequent was allele A5.1 (37.1%) and the rarest A5 (8.1%). Finally it was found that haplotype MICA*008 A5.1 was the most frequent (37.1%).

A comparison of these results with those reported in the literature revealed similarity in MICA polymorphism to that found in other Western Eurasian populations. The data will be useful for further association studies on MICA polymorphism and its function.