MHC Class I Chain-related Gene A Alleles Research Articles

Has the Time Come for Widespread MHC Class I MICA Genotyping in Solid Organ Transplantation?

Has the Time Come for Widespread MHC Class I MICA Genotyping in Solid Organ Transplantation?

MICA Polymorphism and Genetic Predisposition to T1D in Jordanian Patients: A Case-Control Study.

Type 1 diabetes (T1D) is an autoimmune disorder whose etiology includes genetic and environmental factors. The non-classical Major Histocompatibility Complex (MHC) class I chain-related gene A (MICA) gene has been associated with increased susceptibility to T1D as the interaction of MICA to the Natural Killer Group 2D (NK2GD) receptors found on the cell surface of natural killer (NK) cells and T cells is responsible for inducing immune responses. MICA polymorphisms were reported in association with T1D among different ethnic groups. However, data from different populations revealed conflicting results, so the association of MICA polymorphisms with predisposition to T1D remains uncertain. The aim of this sequencing-based study was to identify, for the first time, the possible MICA alleles and/or genotypes that could be associated with T1D susceptibility in the Jordanian population. Polymorphisms in exons 2-4 and the short tandem repeats (STR) in exon 5 of the highly polymorphic MICA gene were analyzed. No evidence for association between T1D and MICA alleles/genotypes was found in this study, except for the MICA*011 allele which was found to be negatively associated with T1D (p = 0.023, OR = 0.125). In conclusion, MICA polymorphisms seem not to be associated with increasing T1D susceptibility in Jordanian patients.

MICA*019 Allele and Soluble MICA as Biomarkers for Ankylosing Spondylitis in Taiwanese.

MICA (major histocompatibility complex class I chain-related gene A) interacts with NKG2D on immune cells to regulate host immune responses. We aimed to determine whether MICA alleles are associated with AS susceptibility in Taiwanese. MICA alleles were determined through haplotype analyses of major MICA coding SNP (cSNP) data from 895 AS patients and 896 normal healthy controls in Taiwan. The distributions of MICA alleles were compared between AS patients and normal healthy controls and among AS patients, stratified by clinical characteristics. ELISA was used to determine soluble MICA (sMICA) levels in serum of AS patients and healthy controls. Stable cell lines expressing four major MICA alleles (MICA*002, MICA*008, MICA*010 and MICA*019) in Taiwanese were used for biological analyses. We found that MICA*019 is the only major MICA allele significantly associated with AS susceptibility (PFDR = 2.25 × 10−115; OR, 14.90; 95% CI, 11.83–18.77) in Taiwanese. In addition, the MICA*019 allele is associated with syndesmophyte formation (PFDR = 0.0017; OR, 1.69; 95% CI, 1.29–2.22) and HLA-B27 positivity (PFDR = 1.45 × 10−33; OR, 28.79; 95% CI, 16.83–49.26) in AS patients. Serum sMICA levels were significantly increased in AS patients as compared to healthy controls. Additionally, MICA*019 homozygous subjects produced the highest levels of sMICA, compared to donors with other genotypes. Furthermore, in vitro experiments revealed that cells expressing MICA*019 produced the highest level of sMICA, as compared to other major MICA alleles. In summary, the MICA*019 allele, producing the highest levels of sMICA, is a significant risk factor for AS and syndesmophyte formation in Taiwanese. Our data indicate that a high level of sMICA is a biomarker for AS.

MHC Class I Chain-Related Gene A Polymorphisms and Linkage Disequilibrium with HLA-B and HLA-C Alleles in Ocular Toxoplasmosis.

This study investigated whether polymorphisms of the MICA (major histocompatibility complex class I chain-related gene A) gene are associated with eye lesions due to Toxoplasma gondii infection in a group of immunocompetent patients from southeastern Brazil. The study enrolled 297 patients with serological diagnosis of toxoplasmosis. Participants were classified into two distinct groups after conducting fundoscopic exams according to the presence (n = 148) or absence (n = 149) of ocular scars/lesions due to toxoplasmosis. The group of patients with scars/lesions was further subdivided into two groups according to the type of the ocular manifestation observed: primary (n = 120) or recurrent (n = 28). Genotyping of the MICA and HLA alleles was performed by the polymerase chain reaction-sequence specific oligonucleotide technique (PCR-SSO; One Lambda®) and the MICA-129 polymorphism (rs1051792) was identified by nested polymerase chain reaction (PCR-RFLP). Significant associations involving MICA polymorphisms were not found. Although the MICA*002~HLA-B*35 haplotype was associated with increased risk of developing ocular toxoplasmosis (P-value = 0.04; OR = 2.20; 95% CI = 1.05–4.60), and the MICA*008~HLA-C*07 haplotype was associated with protection against the development of manifestations of ocular toxoplasmosis (P-value = 0.009; OR: 0.44; 95% CI: 0.22–0.76), these associations were not statistically significant after adjusting for multiple comparisons. MICA polymorphisms do not appear to influence the development of ocular lesions in patients diagnosed with toxoplasmosis in this study population.

150-P: POLYMORPHISM OF MICA IN HELICOBACTER PYLORI-POSITIVE MEXICAN PATIENTS WITH GASTRODUODENAL LESIONS

MHC class I chain related gene A (MICA) is a highly polymorphic gene expressed in gastrointestinal epithelial cells. MICA activates NK and gamma delta T cells trough the binding of NKG2D receptor under cellular stress situations (infection or transformation). Helicobacter pylori (H. pylori) colonization of the gastric mucosa is a major cause for chronic gastritis and predisposition for peptic ulcer and gastric cancer. We analyze the associations between allelic and microsatellite polymorphism of MICA, and gastroduodenal lesions related to H. pylori infection in Mexican Mestizo patients. We genotyped by RSCA technique 282 H. pylori-positive patient samples diagnosed by endoscopy and histology (non-atrophic gastritis=139, intestinal metaplasia=67, gastric cancer=34 and duodenal ulcer=42), and 96 H. pylori seropositive asymptomatic persons without gastric lesions. The allelic and microsatellital frequencies in the different groups of patients were statistically compared by chi-square and Fisher test (pc < 0.05). We found in the asymptomatic group five microsatellites: A4 (5.8%), A5 (25.2%), A5.1 (10.7%), A6 (18.0%) and A9 (40.3%) and six MICA alleles: ∗001 (5.2%), ∗00201 (40.6%), ∗004 (17.2%), ∗00801 (10.9%), ∗010 (25.0%) and ∗011 (1.1%). In patients we observed a decrease of the 00201/00201 genotype frequency in duodenal ulcer (9.5%) when compared with non-atrophic gastritis (20.0%) and asymptomatics (23.0%), but it was not statistically significant. We did not find any association with gastric cancer. These results strongly suggest that the MICA polymorphism may not be associated with the gastroduodenal diseases provoked by H. pylori infection in Mexican population. (CONACyT 6957, FOFOI 2001/007 and 2002/110).

Microarrays for high‐throughput genotyping ofMICAalleles using allele‐specific primer extension

The role of major histocompatibility complex (MHC) class I chain-related gene A (MICA), a ligand of NKG2D, has been defined in human diseases by its allele associations with various autoimmune diseases, hematopoietic stem cell transplantation (HSCT) and cancer. This study describes a practical system to develop MICA genotyping by allele-specific primer extension (ASPE) on microarrays. From the results of 20 control primers, strict and reliable cut-off values of more than 30,000 mean fluorescence intensity (MFI) as positive and less than 3000 MFI as negative, were applied to select high-quality specific extension primers. Among 55 allele-specific primers, 44 primers could be initially selected as optimal primer. Through adjusting the length, six primers were improved. The other failed five primers were corrected by refractory modification. MICA genotypes by ASPE on microarrays showed the same results as those by nucleotide sequencing. On the basis of these results, ASPE on microarrays may provide high-throughput genotyping for MICA alleles for population studies, disease-gene associations and HSCT.

MICA genetic polymorphism and HLA-A,C,B,MICA and DRB1 haplotypic variation in a southern Chinese Han population: Identification of two new MICA alleles, MICA*060 and MICA*062

In this study, 201 healthy, unrelated Han subjects in Hunan province, southern China, were investigated by sequence-based typing (SBT) for the allelic variation of the human major histocompatibility complex (MHC) class I chain-related gene A (MICA). Nineteen MICA alleles were observed, among which MICA*008:01 predominated with gene frequency of 30.35%. There was significant linkage disequilibrium (LD) of MICA*012:01 with HLA-B*54 and HLA-B*55, which was not observed in a northern Chinese Han population. Haplotype HLA-A*11-C*07-B60-MICA*008:01 (9.16%) was highly specific to this southern Chinese Han population. The most common five-locus haplotype in this population was HLA-A*02-C*01-B*46-MICA*010-DRB1*09 (8.73%). A new MICA allele, MICA*060, was identified on an HLA-A*02-C*01-B*55:02-DRB1*14 haplotype through extended family analysis. MICA*060 has probably arisen from MICA*012:01. Another new MICA allele, MICA*062, was identified by screening 1432 subjects using polymerase chain reaction–sequence-specific priming technology. MICA*062 has probably derived from MICA*010. Of particular interest is that MICA*062 was carried on an HLA-C*08-B*48:01-DRB1*14 haplotypic segment, as HLA-B*48 has been consistently shown to be primarily linked to MICA gene deletion in east Asian populations. Our results provide new insight into MICA genetic polymorphism in human populations. The findings reported here are of importance for future studies on the potential role of MICA in allogeneic organ transplantation and disease association in populations of Chinese ancestry.

Sequence‐based typing of major histocompatibility complex class I chain‐related gene A alleles by use of exons 2–5 information

The polymorphic MICA (major histocompatibility complex class I chain-related gene A) (Gene ID: 100507436) gene products are a ligand of the activating natural killer cell receptor, NKG2D. Their clinical importance spans from solid organ transplantation to bone marrow transplantation and disease susceptibility. Typing of MICA genes by sequencing is hampered by an exon 5 short tandem repeat, the definition of which is critical for the final allelic and functional assignment. We present a novel sequencing approach, which uses group-specific (7T/8T) exon 5 polymerase chain reactions (PCRs) and facilitates hemizygous exon 5 MICA-PCR in approximately 70% of the tested individuals. With this method we typed the International Histocompatibility Workshop Group MICA reference panel (40 cell lines) as well as 110 healthy South German blood donors. All ambiguities, with the exception of MICA*008:01/008:04 (synonymous substitution in exon 1) and MICA*009:01/049 (nonsynonymous substitution in exon 6), could be resolved with our method. Analysis of Hardy-Weinberg equilibrium for our cohort showed no significant difference between expected and observed frequencies of MICA alleles (P = 0.6142). The three most frequent alleles in our blood donor cohort were MICA*008:01/008:04 (40.5%), MICA*002:01 (13.2%), and MICA*009:01/049 (8.6%). The 7T polymorphism was observed in 67.7% and the 8T polymorphism in 32.3% of our blood donor cohort. Individuals (24.5%) tested were homozygous. The approach described in this paper is suitable for accurate sequencing of large sample numbers, including direct readout of exon 5 sequences. It is compatible with laboratory automation and commercial human leukocyte antigen analysis software tools. It may therefore be applied in large clinical trials.

MICApolymorphisms and haplotypes withHLA‐BandHLA‐DRB1in Koreans

Major histocompatibility complex (MHC) class I chain-related gene A (MICA) is located within the human MHC, centromeric to HLA-B and telomeric to HLA-DRB1. The location of MICA in the MHC indicates the presence of linkage disequilibrium with human leukocyte antigen (HLA). Like HLA, MICA is highly polymorphic; however, the information available for MICA polymorphisms is not as comprehensive as that for HLA polymorphisms. We estimated the allelic frequencies of MICA and haplotypes with HLA-B and HLA-DRB1 at high-resolution in a population of 139 unrelated Korean individuals by applying the newly developed method of sequence-based typing (SBT). A total of 17 MICA alleles were identified. The most frequent allele was MICA*010 (19.4%), followed by alleles *00201 (17.6%), *00801 (14.7%), *01201 (9.4%), *004 (8.3%) and *049 (7.9%). The most common two- and three-locus haplotypes were HLA-B*1501-MICA*010 (10.4%), MICA*010-HLA-DRB1*0406 (5.8%) and HLA-B*1501-MICA*010-HLA-DRB1*0406 (5.8%). This is the first study to provide such high-resolution information on the distribution of haplotypes comprising MICA, HLA-B and HLA-DRB1 in Korean individuals, a level of resolution made possible by use of the SBT method. The results of this study should help determine the mechanisms underlying diseases associated with MICA polymorphisms in Korean individuals.

Correlation between major histocompatibility complex class I-related chain A gene alleles and graft rejection in small intestine, liver and kidney transplantation

To investigate the correlation between major histocompatibility complex (MHC) class I chain-related gene A (MICA) gene alleles matching rates and graft rejection in small intestine, liver and kidney transplantation. Genome DNA were extracted from blood samples or pathological sections collected from donors and recipients of living-related transplantation, included 4 cases of small bowel transplantation, 5 cases of liver transplantation and 6 cases of kidney transplantation. The correlation between MICA alleles matching rates and acute graft rejection was analyzed following 13 MICA alleles determination by polymerase chain reaction based on sequence-specific primers (PCR-SSP). HLA zygosity of all donors and recipients was confirmed to be half-matching. The recipients displaying higher matching rates of MICA alleles with donors showed lighter clinical and pathological rejection and longer survival time. On the contrary, recipients with lower matching rates of MICA alleles with donors showed severer clinical and pathological rejection and shorter survival time relatively. Matching rates of MICA alleles has negative relevance to acute rejection, and positive relevance to survival time of recipients in small bowel, liver, and kidney transplantation.

Donor-Recipient Mismatches in MHC Class I Chain-Related Gene a (MICA) in Unrelated Donor (UD) Transplantation

MICA is a highly polymorphic locus located in the Class III region of the HLA system in the short arm of chromosome 6. The products of MICA can elicit humoral allo-recognition and are the ligands of the NKG2-D receptors of natural killer cells. MICA is involved in chronic and possibly acute graft rejection in kidney transplantation. The impact of mismatches in MICA has not been examined systematically in bone marrow transplantation. We hypothesized that donor-recipient MICA mismatches may influence graft-versus-host disease (GVHD) and relapse rates after UD hematopoietic stem cell transplantation (HSCT), and tested this hypothesis in a cohort comprised of all patients with myeloid leukemias transplanted in our institution from January, 2002 to December, 2007 (n=238).Methods: Typing of each of the classical human leukocyte antigen (HLA) and MICA loci was performed by amplification with locus-specific primers of genomic DNA by PCR followed by nucleotide sequencing. For the assignment of MICA alleles, the polymorphisms in exons 2, 3, 4, and 5 were evaluated. Matching grade is described in the GVH direction. Outcomes were acute (a) GVHD incidence, and aGVHD-free survival (time dependent variable, with development of aGVHD as the event), and relapse-free survival (RFS), both estimated by the Kaplan Meier method. Cox proportional hazards regression model was used to estimate the influence of HLA match degree, patient, disease, and transplant-related characteristics on outcomes. Median age was 50 years (range, 18–74; 24% over age 59). Diagnosis were AML/high-risk MDS in 82% (n=195) and CML in 18% (n=43). 42% (n=100) of the patients were in remission (CR) at HSCT. Preparative regimens were ablative in 59% (n=141), and contained ATG, fludarabine and IV busulfan in respectively 96%, 90% and 70% of the HSCT. GVHD prophylaxis was tacrolimus and mini-methotrexate-based in all HSCT. Stem cell source was bone marrow (BM) in 72% (n=172) and peripheral blood (PB) in 28% (n=66) of HSCT. 78 patients have relapsed (34%) and 133 have died (56%).Results. 169 pairs were matched in HLA A, B, C, DRB1, and DQB1 (10/10; 71%); 69 (29%) were <10/10 matches, of which 60 were 9/10 (78% of the mismatches were in HLA class I). One or two HLA-DPB1 mismatches were present in 48% and 25% of the patients, respectively. MICA one or two mismatches were present in 22 pairs (9%). Grade (gd) II–IV and III–IV aGVHD rates for patients with MICA mismatches were 80% and 30%, respectively, versus 40% and 14% for those with no MICA mismatches. Effect of MICA on aGVHD was similar among 10/10 and <10/10 patients. RFS at 52 weeks post HSCT was 0.58 (95%CI 0.5–0.66) versus 0.77 (95%CI 0.59–1) for patients without and with MICA mismatches (P=0.5). Multivariate models are shown in the table.Conclusion: MICA mismatches independently increased the incidence of grade II–IV aGVHD.Multivariate Models for grade II-IV acute GVHD and relapse-free survival (RFS)VariableIncidenceUnivariate P valueMultivariate P, HR and 95% CIGrade II-IV aGVHDFludarabine-based regimen(yes vs no)39% vs 72%P=0.00090.02; HR 0.51 (0.29–0.9)DPB1 mismatches (0/1 vs 2)38% vs 52%P=0.060.03; HR 0.59 (0.37–0.94)Ablative conditioning (no vs yes)31% vs 48%P=0.0010.05; HR 0.65 (0.43–0.99)MICA mismatches (yes vs no)80% vs 38%P=0.00020.002; HR 2.33 (1.37–3.98)RFSRate at 52 weeks95%CI Univariate PMultivariate P, HR and 95% CIDPB1 (0 vs 1 vs 2)0.54(0.42, 0.68)P=0.090.03; HR 1.65 (1.051–2.6)0.55(0.45, 0.67)0.7(0.58, 0.84)CR at HSCT (yes vs no)0.78(0.69, 0.87)P<0.0001<0.0001; HR 0.308 (0.18–0.52)0.44(0.36, 0.55)(P and HR for aGVHD-free survival) HR: hazard ratio; CI: confidence interval

Genetic influence of the nonclassical major histocompatibility complex class I molecule MICB in multiple sclerosis susceptibility

It has been widely reported that the major histocompatibility complex (MHC) class II region provides the main genetic contribution to multiple sclerosis (MS) susceptibility. However, recent studies have suggested that the MHC class I region may also contribute to the development of MS. In this study, we investigated the possible association of the human leukocyte antigen (HLA)-B, MHC class I chain-related gene B (MICB) and MHC class I chain-related gene A (MICA) genes, located in the MHC class I region, with MS susceptibility. For this purpose, we analyzed the distribution of HLA-DR, HLA-B, MICB and MICA alleles in 121 MS patients and 156 healthy controls. Neither HLA-B nor MICA alleles were found to be associated with MS susceptibility, and only the frequency of HLA-DRB1*01 allele was found to be increased in controls (31% vs 14%, P(c) = 0.011). However, MICB*004 allele frequency was significantly increased in MS patients (46.3% vs 23.3%, P(c) < 0.001, odds ratio = 2.82, 95% confidence interval = 1.68-4.73). Although, MICB*004 and HLA-DRB1*15 belong to the AH 7.1 ancestral haplotype, the association of MICB*004 to MS susceptibility was found to be independent of HLA-DRB1*15 in our population. This and previous studies clearly suggest that the MHC class I, in addition to class II, could be involved in MS susceptibility.

Early onset of polyglandular failure is associated with HLA-DRB1*03.

Polyglandular failure or autoimmunity (PGA) involves at least two endocrine diseases. Several genes may play a role in its etiology. This study analyzed 1) whether HLA-DRB1, HLA-DQB1, and MHC class I chain-related gene A (MICA) polymorphisms are associated in PGA and 2) whether PGA patients display stronger associations with these immune genes than patients with monoglandular autoimmunity (MGA). Association study. HLA-DRB1, HLA-DQB1, and MICA alleles were analyzed in 73 patients with PGA, 283 with MGA, and 206 healthy controls. The HLA-DRB1 and HLA-DQB1 polymorphisms were determined with PCR-amplified DNA being hybridized with PCR-sequence-specific oligonucleotide probes. MICA microsatellites were typed by PCR amplification and fragment size analysis on a DNA sequencer. HLA-DRB1*03 was strongly increased in patients with PGA (50.7%) versus both controls (21.8%, P(c)<0.0001; RR=2.32, 95% CI=1.62-3.33) and MGA (11.4%, P(c)<0.0001). HLA-DRB1*03 was highly prevalent in PGA patients with early versus late disease onset (P<0.05, logistic regression analysis). HLA-DRB1*04 allele carriers were more present in PGA versus controls (53.4% vs 22.4%, P(c)<0.0001, RR=2.38, 95% CI=1.68-3.38). Further, HLA-DQB1*02 was increased in PGA versus controls (P(c)<0.01), whereas HLA-DQB1*06 was decreased (P(c)<0.001). Patients with PGA showed more MIC A5.1 and less MIC A6 allele carriers than controls (NS). Presence of the MIC A5.1 allele was not associated with the HLA-DRB1*03 or HLA-DQB1 alleles. HLA-DRB1*03 is a stronger genetic marker in PGA than in MGA, foremost in those with early disease onset.

MHC class I chain-related antigen A in mono- and polyglandular autoimmunity

We have evaluated whether the MHC-class-I-chain-related gene A (MICA), being closely located to HLA-B, predisposes for endocrine autoimmunity. It encodes a cell surface protein. The gene shows in its transmembrane segment a GCT repeat encoding 4, 5, 6, or 9 alanine residues (alleles A4, A5, A6, A9), and A5.1 has an additional 1-bp-insertion (GGCT, A5.1). We determined the polymorphism in 48 patients with Graves' disease (GD), 59 with Hashimoto's thyroiditis (HT) and 206 healthy unrelated controls. 43 patients had one endocrinopathy (monoglandular autoimmunity, MGA) and 64 at least two endocrinopathies (polyglandular autoimmunity, PGA). After extraction of genomic DNA from whole blood, the MICA microsatellites were amplified by PCR, and fragment sizes were determined with an automatic DNA sequencer (ABI PRISM 310). The exact test of Fisher and Odds ratios (OR) were applied for group comparisons. We identified the MICA alleles A4, A5, A5.1, A6, and A9 in either homozygous or heterozygous form in 21.5%, 25.2%, 70.1%, 21.5%, 22.4% of patients versus 24.8%, 27.2%, 62.1%, 36.9%, 23.8% of controls, respectively. Patients with GD (14.6%, 33.3%, 70.8%, 18.8%, 22.9%) and HT (27.1%, 18.6%, 69.5%, 23.7%, 22.0%) did not differ in their frequencies. Allele A6 was less frequent in patients (21.5%) than controls (36.9%; OR=0.468, 95%CI=0.273–0.805); this was more pronounced in patients with PGA (18.8%; OR=0.395, 0.198–0.786 vs. controls) than MGA (25.6%; OR=0.671, 0.265–1.700 vs. controls). Allele A5.1 was more frequent in patients with PGA (78.1%) than MGA (58%; OR=2.571, 1.102–6.001) or controls (62.1%; OR=2.176, 1.129–4.195). No significant relationships were observed between thyroid antibodies against TPO and TSH receptor and MICA frequencies. Allele A5.1 creates a frameshift resulting in a premature termination codon in the transmembrane region of the MICA protein, lacking for its cytoplasmatic domain. This truncated protein is regarded as a soluble, secreted form of MICA. These results indicate that the MICA gene influences susceptibility to endocrine autoimmunity.

Frequency of MICA in All Babies in Southeast Sweden (ABIS) Positive for High‐Risk HLA‐DQ Associated with Type 1 Diabetes

Type 1 diabetes mellitus (T1DM) is an autoimmune disease known to occur in genetically susceptible individuals after exposure to certain unknown environmental factors. HLA-DR3-DQ2 or DR4-DQ8 are established genetic markers for the disease. MHC class I chain-related gene-A (MICA) gene polymorphism has been proposed to be associated with T1DM. To identify the environmental factors and for implementing intervention trials to prevent T1DM, it is important to screen subjects at genetically increased risk for developing T1DM. The All Babies in Southeast Sweden (ABIS) study aims to assess the risk of future progression to T1DM in the general child population. In the present report, we studied the frequency of MICA alleles among newborn babies carrying high-risk HLA DQ2 or DQ8. Of 2821 newborns, we found 563 subjects positive for DQ2, 583 subjects positive for DQ8, 133 subjects positive for DQ2-DQ8 (heterozygous), and 1013 subjects positive for either DQ2 or DQ8. Of these 1013 babies, we typed 499 babies for MICA. Frequency of MICA5 was 38% among DQ8+, 35% among for DQ2-DQ8 (heterozygous) positives, and 22.5% among DQ2+ babies. Frequency of MICA5.1 was 81% among DQ+, 62% among DQ8+, and 71% among DQ2-DQ8 (heterozygous) positives. Frequency of MICA6 was between 20% and 22% among the three groups. Frequency of MICA5/5.1 was 19% among DQ2-DQ8 (heterozygous) positives and between 12% and 13% among those positive for DQ2, DQ8, DQ2, or DQ8. The results from genetic typing in this study would be useful, in conjunction with results from autoantibody analysis that are prospectively being followed-up in all the babies, to develop an approach for identifying children at risk for developing T1DM. Inclusion of MICA typing in addition to HLA could be useful for screening of genetic markers associated with T1DM.

Major histocompatibility complex class I chain-related gene A in Thai psoriasis patients: MICA association as a part of human leukocyte antigen-B-Cw haplotypes.

Psoriasis is a chronic inflammatory skin disorder. Although the aetiology and pathogenesis of psoriasis are unproven, it is hypothesised that the major histocompatibility complex (MHC) gene/haplotype contributes to the susceptibility of psoriasis in many populations. MHC class I chain-related gene A (MICA), located 46-kb centromeric of HLA-B, is expressed on keratinocytes and fibroblasts. MICA is in linkage disequilibrium with HLA-B and is involved in natural killer-cell functions. To investigate the relative contribution of the MICA gene in the pathogenesis of psoriasis, extracellular polymorphisms of MICA were studied by polymerase chain reaction-sequence specific primers in 128 Thai psoriasis patients (87 and 41 were Types I and II, respectively) from Srinagarind Hospital, Faculty of Medicine, Khon Kaen University. The control group included 255 healthy, unrelated Northeast Thais. We observed 11 MICA alleles (or groups of alleles) in the patients. A comparison of the psoriasis patients and the control group revealed that MICA*010 and MICA*017 were associated with Type I psoriasis whereas only MICA*010 was associated with Type II. The haplotype analysis revealed that MICA*008-HLA-B*13-Cw*0602 and MICA*010-HLA-B*4601-Cw*01 were significantly increased in both Types I and II, whereas MICA*002-HLA-B*38-Cw*07 (01-03) and MICA*017-HLA-B*57-Cw*0602 were elevated only in Type I. MICA*010 was in strong linkage with Cw*01. Analysis of independent association of MICA*010 in individuals lacking Cw*01 failed to maintain an association. Our results suggest that a significant increase of the MICA alleles in the patient group is a part of HLA-B-Cw haplotypes. It is conceivable that an unknown susceptibility gene, on certain HLA-B-Cw haplotypes, is responsible for the development of psoriasis.

MIC‐A Genotypes 4/5.1 and 9/9 Are Positively Associated with Type 1 Diabetes Mellitus in Brazilian Population

The aim of our study was to evaluate the frequencies of MIC-A alleles and genotypes in Brazilian patients with type 1 diabetes mellitus (T1DM) and healthy controls. MHC class I chain-related gene-A (MIC-A) has been shown to be associated with susceptibility to T1DM in different populations. We analyzed the DNA samples from 86 patients and 201 healthy controls for MIC-A by PCR amplification, and fragment sizes were determined in an ABI prism DNA sequencer. We found increased frequencies of two genotypes, MIC-A 4/5.1 (pc = 0.006; OR, 6.1) and 9/9 (pc = 0.045; OR, 5.75), in our patients (mean diagnosis age, 11.70 years; SD, 8.86; mean age, 20.44 years; SD, 12.17) compared with the controls (median age, 26.41 years; SD, 8.87).

Distribution of MICA alleles and haplotypes associated with HLA in the Korean population

The MICA (MHC class I chain-related gene A) is a polymorphic gene located 46 kb centromeric of the HLA-B gene, and is preferentially expressed in epithelial cells and intestinal mucosa. The MICA gene, similar to human leukocyte antigen (HLA) class I, displays a high degree of genetic polymorphism in exons 2, 3, 4, and 5, amounting to 54 alleles. In this study, we investigated the polymorphisms at exons coding for extracellular domains (exons 2, 3, and 4), and the GCT repeat polymorphism at the transmembrane (exon 5) of MICA in 199 unrelated healthy Koreans. Eight alleles were observed in the Korean population, with allele frequencies for MICA*010, MICA*00201, MICA*027, MICA*004, MICA*012, MICA*00801, MICA*00901, and MICA*00701 being 18.3%, 17.8%, 13.6%, 12.3%, 11.1%, 10.8%, 10.6%, and 3.3%, respectively. Strong linkage disequilibria were also observed between the MICA and HLA-B gene—MICA*00201-B58, MICA*004-B44, MICA*00701-B27, MICA*00801-B60, MICA*00901-B51, MICA*010-B62, MICA*012-B54, and MICA*027-B61. In the analysis of the haplotypes of HLA class I genes (HLA-A, B, and C) and the MICA, the most common haplotype was MICA*004-A33-B44-Cw*07, followed by MICA*00201-A2-B58-Cw*0302 and MICA*012-A2-B54-Cw*0102. The MICA null haplotype might be identified in the HLA-B48 homozygous individual. These results will provide an understanding of the role of MICA in transplantation, disease association, and population analyses in Koreans.

Polymorphism in transmembrane region of MICA gene and cholelithiasis.

To study the significance of polymorphism of MHC class I chain-related gene A (MICA) gene in patients with cholelithiasis. Subjects included 170 unrelated adults (83 males) with cholelithiasis and 245 randomly selected unrelated adults (130 males) as controls. DNA was extracted from peripheral leukocytes and analyzed for polymorphism of 5 alleles (A4, A5, A5.1, A6 and A9) of the MICA gene. There was no significant difference in phenotype, allele, and genotype frequencies of any of the 5 alleles between cholelithiasis patients and controls. This study demonstrates that MICA alleles studied bear no relation to cholelithiasis.

MICA genetic polymorphism and linkage disequilibrium with HLA-B in 29 African-American families.

The human major histocompatibility complex (MHC) class I chain-related gene A ( MICA) is located 46 kb upstream of HLA-B and encodes a stress-inducible protein which displays a restricted pattern of tissue expression. MICA molecules interact with NKG2D, augmenting the activation of natural killer cells, CD8(+) alpha beta T cells, and gamma delta T cells. MICA allelic variation is thought to be associated with disease susceptibility and immune response to transplants. We investigated MICA allelic variations and linkage disequilibrium with HLA-A, B, and DRB1 loci on 110 parental haplotypes from 29 African-American families. PCR/sequence-specific oligonucleotide probing (SSOP) was used to define MICA polymorphisms in exons 2, 3, and 4. Ambiguous allelic combinations were resolved by sequencing exons 2, 3, and 4. Exon 5 polymorphisms were analyzed by size sequencing. For HLA-A, B and DRB1 typing, low-resolution PCR/SSOP and allelic PCR/sequence-specific priming techniques were used. Twelve MICA alleles were observed, the most frequent of which were MICA*008, MICA*004, and MICA*002, with gene frequencies of 28.2, 26.4, and 25.5%, respectively. Thirty-eight HLA-B- MICA haplotypic combinations were uncovered, 22 of which have not been reported in the HLA homozygous typing cell lines from the 10th International Histocompatibility Workshop. Significant positive linkage disequilibria were found in 8 HLA-B- MICA haplotypes. Furthermore, haplotypes bearing HLA-B*1503, *1801, *4901, *5201, *5301, and *5703 were found to segregate with at least two different MICA alleles. Our results provide new data about MICA genetic polymorphisms in African-Americans, which will form the basis for future studies of MICA alleles in allogeneic stem cell transplantation outcome.