MICA gene polymorphisms in an Italian paediatric series of juvenile Behçet disease

The objective of this study was to investigate MICA (major histocompatibility complex MHC class I chain-related genes) polymorphisms in an Italian series of patients with juvenile Behcet disease (jBD) and to compare these genetic findings with the high prevalence of inflammatory mucosal disease, which occurs in Western populations. Ten families which included at least 1 affected patient were studied. We genotyped 18 patients (13 children and 5 adults) affected with the complete or incomplete form of jBD comparing the results to those found in a population of 20 apparently healthy individuals. The MICA transmembrane polymorphism was analysed by PCR and polyacrylamide gel electrophoresis. HLA typing was assessed by SSP-PCR technique. Statistical analysis was performed using chi2 based methods. In our series the prevalence of gastrointestinal disease was high (41%). Seven of 10 patients were HLA-B51 positive. MICA A6 allele was present in 70% of probands as compared to 25% of an ethnically matched control population. On the other hand, MICA A5.1 was present in 20% of probands as compared to 60% in controls. Out of 5 A6 homozygotes, 2 probands and 2 affected relatives developed a severe gut inflammatory disease. The study of MICA gene polymorphisms disclosed an independent association with genetic risk for jBD. The combination of MICA A6 and HLA-B51 is the strongest genetic marker for this disease. Homozygous A6 patients seem to develop more severe mucosal gut involvement. This finding sheds light on the role of a receptor for MICA, named NKG2D, presented by natural killer cells, and CD8+, alphabetaT cells and gammadeltaT cells, usually localised in gut mucosa.