MICA Polymorphism Is Associated With Type 1 Diabetes in the Korean Population

YONGSOO PARK 0 HONGKYU LEE 0 CARANI B. SANJEEVI 0 GEORGE S. EISENBARTH 0 PHD 0 0 From the Department of Internal Medicine (Y.P., H.L.), Hanyang and Seoul National University, School of Medicine , Seoul , Korea; the Department of Molecular Medicine (C.B.S.), Karolinska Hospital , Stockholm , Sweden; and the Barbara Davis Center for Childhood Diabetes (G.S.E.), University of Colorado Health Sci- ences Center , Denver , Colorado. Hanyang University Hospital , 249-1 Kyomun-dong, Kuri, Kyunggi-do, 471-020 , Korea E p i d e m i o l o g y / H e a l t h S e r v i c e s / P s y c h o s o c i a l R e s e a r c h OBJECTIVE - Recent studies have demonstrated that MICA (major histocompatibility complex class I chain-related genes) on the short arm of the chromosome 6 are associated with susceptibility to various autoimmune diseases in Caucasians. The aim of our study was to investigate the role of MICA in type 1 diabetes susceptibility independent of the HLA DR-DQ polymorphism in genetically distinct Koreans. RESEARCH DESIGN AND METHODS - A total of 119 patients selected from Korean Seoul type 1 diabetes registry and 134 nondiabetic unrelated control subjects were typed for exon 5 polymorphism of MICA in addition to HLA DR-DQ typing. A total of 52 simplex families of type 1 diabetes were also studied. RESULTS - The MICA microsatellite allele consisting of six repetitions of GCT/AGC (A6) was present at a significantly lower frequency in the diabetic patient group (Pc 0.01; Pc = P value after Bonferroni correction) than in the control population. The MICA microsatellite allele consisting of four repetitions (A4) was present at a higher frequency in diabetic patients (P 0.05). This deviated distribution was not changed even after controlling for the HLA DRB1-DQB1 haplotype. Transmission/disequilibrium test revealed significant deviation of transmission for alleles at the A6 polymorphism within the MICA gene (P 0.05). CONCLUSIONS - We could assess that the MICA gene might be associated with type 1 diabetes transracially independent of the HLA gene. - Acies among studies on the genes assolthough there were major discrepanciated with type 1 diabetes transracially, highly significant linkage for HLA was revealed in all reports (1,2). It is known that more than one genetic locus, even within HLA, is important for disease risk. A primary role of some antigen-presenting HLA DR and DQ molecules has been established (14); however, the relative importance of HLA class II genes remains to be determined in each population by experimental data. The contribution of HLA class II genes to type 1 diabetes in some Asian populations is less important because a significant portion of the diabetic patients do not have the high-risk HLA genotype (5,6). The HLA DR3/4 (DQB1*0302) heterozygous genotype occurs in 0.9% of children born in Seoul, Korea, and is present in 9.3% of children developing type 1 diabetes. There is a larger probability for the role of genes other than HLA class II genes in Asians. Nevertheless, the population frequency of DR3/4 genotype is still 1020 times higher than the prevalence of type 1 diabetes associated with this genotype (1,7). DRB1 subtyping might change the risk of type 1 diabetes in the DQ high-risk population, even though it is assumed to be accounted for only 10% (7,8). This implies that additional protective genes and/or environmental factors influence susceptibility to the disease. Studies both in animals and in humans have also indicated that other major histocompatibility complex (MHC)linked genes are participating in the susceptibility of HLA complex (9,10). These other MHC-linked genes have not been mapped. The HLA complex encompasses 3.5 Mb of DNA from the centromeric HLADPB2 locus to the telomeric HLA-F locus on chromosome 6p21, and the strong linkage disequilibrium (LD) between genes in the complex makes this a difficult task. One Japanese group reported that HLA class I molecule A and B were associated with early-onset type 1 diabetes (10). Furthermore, a novel family of the human MHC class I genes termed MICA (MHC class I chain-related genes) has been recently identified near the HLA-B gene on the short arm of human chromosome 6 (11,12). This gene has been known to carry numerous nonsynonymous polymorphisms, and when these are overlaid onto a three-dimensional structure, most lie along the edge of the peptide-binding groove in the 2 extracellular domain (13,14). The polymorphism of the MICA gene (11,12) and its location in the HLA region warrant studies aimed at identifying an association with the risk for autoimmune diseases. However, the contribution of this HLA locus to type 1 diabetes susceptibility might be unclear because of the strong LD around this area. In this study, we investigated whether the MICA gene as well as HLA class II polymorphism influenced the genetic predisposition to type 1 diabetes in Korea. RESEARCH DESIGN AND METHODS Subjects The samples used in this study included three groups. First, for the case-control association study, 119 type 1 diabetic patients were selected randomly from the Korean Seoul Registry (5,6,15). All patients MICA alleles and genotypes Patients (n = 119) 56 (23.5) 58 (24.4) 53 (22.3) 30 (12.6) 41 (17.2) 0 (0) 30 (25.2) 89 (74.8) Healthy subjects (n = 134) 41 (15.3) 78 (29.1) 43 (16.0) 66 (24.6) 40 (14.9) 6 (4.5) 54 (40.3) 74 (55.2) NS Data are n (%) unless otherwise indicated. Pc, corrected P value (correction factor was 5 for MICA alleles and 15 for MICA genotypes). were on insulin therapy upon hospital discharge, 15 years of age, and residents of Seoul at the time of disease onset. Their mean age was 13 years (range 322). The second group consisted of 134 nondiabetic control subjects with no family history of diabetes who were selected from the same geographical area. Their mean age was 34 years (1446). In addition, a third group of 52 simplex families with type 1 diabetes was recruited from the Seoul Registry in Korea. All individuals or their parents gave appropriate informed consent to participate in the study. HLA genotyping Peripheral blood lymphocytes from all donors were used for the molecular typing of the low-resolution typing of HLA-DRB1 and most common HLA-DQA and -B chain gene allelic forms (5,6,16). HLA DRB1/DQA1/DQB1 was genotyped using p o l y m e r a s e c h a i n re a c t i o n ( P C R ) sequence-specific oligonucleotide techniques according to previous reports (5,16). The nomenclature used to define the HLA-DR and -DQ alleles was that of the official nomenclature for factors of the HLA System (17). MICA genotyping For analysis of microsatellite repeat polymorphism in the transmembrane (TM) region of the MICA gene, PCR primers flanking the TM region (MICA5F: 5 -CCTT TTTTTCAGGGAAAGTGC-3 ; MICA5R: 5-CCTTACCATCTCCAGAAACTGC-3 ) were designed (18,19). Genotypes were determined using a fluorescent-based method as reported previously (18,19). Briefly, reverse PCR primer was labeled with (...truncated)