Polymorphism in MICA rather than HLA-B/C genes is associated with psoriatic arthritis in the Jewish population

The aim of this study was to examine whether the association of psoriatic arthritis (PsA) with human leukocyte antigen (HLA) class I genes is secondary to linkage disequilibrium with a nearby gene. We examined a sample of the Jewish population to investigate whether HLA-B/C and DR polymorphism is associated with susceptibility, or whether other closely related class I loci, such as the major histocompatibility complex class I chain-related gene A (MICA) and tumor necrosis factor (TNF), might play a role in disease development. Comparisons of different populations with different HLA profiles would be of value in identifying the candidate genes involved in PSA. Fifty-two patients with PsA and 73 random matched controls from a Jewish population were selected and DNA typed by polymerase chain reaction-single-strand oligonucleotide probe (PCR-SSOP) (HLA-C), PCR sequence-specific primers (PCR-SSP) (HLA-B, -DR), radioactive PCR (MICA-TM polymorphism in the transmembrane region), and PCR-RFLP (TNF). Some findings can be concluded from the study: (1) the frequency of HLA-B*5701, B*3801, B*39, B*27, Cw*0602, Cw*07, DRB1*0402, and DRB1*0701 were not found to be significantly increased in PsA; (2) no significant differences of TNFalpha promoter alleles at positions -308 and -238 were found between PsA and healthy controls; (3) the trinucleotide repeat polymorphism MICA-A9 was present at a higher frequency in PsA patients, (p(c) < 0.009, RR = 3.34, EF = 0.39); and (4) MICA-A9 polymorphism was found in linkage disequilibrium with HLA-B alleles (B*5701, B*3801) described to be associated with PsA in Caucasians. These results suggest that the MICA gene or other nearby gene(s) may be involved in the development of PsA, and it would thus appear that psoriasis vulgaris (PsV) and PsA are associated with different MHC susceptibility genes.     

MICA and MICB microsatellite alleles in HLA extended haplotypes.

The present study is a contribution to the definition of the linkage disequilibrium relationship of MICA and MICB with adjacent loci and to the characterization of extended HLA haplotypes. These issues are of importance for the identification of disease associations and for a better definition of donor-recipient compatibility in bone-marrow grafts through the typing of haplospecific markers. The distribution of the five alleles of MICA and the 13 alleles of MICB microsatellites, located, respectively, in MICA transmembrane exon 5 and in MICB intron 1, was examined in 133 healthy Italian individuals previously typed for HLA class I, class II and complement loci and for the TNFa microsatellite. The MICB microsatellite was also analysed in 49 HTCLs for which MICA typing was already available. Very strong linkage disequilibria with HLA-B and TNFa were detected in the Italian population for both MICA and MICB microsatellite alleles, in spite of the high mutability rate of the larger MICB alleles. Some strong associations were also detected between MICB and DRB1. The strongest associations (P < 0.001, D' > 0.7) were those of MICA-A4 with HLA-B18, B27 and TNFa1, MICA-A5 with HLA-B35, B61 and B62, MICA-A5.1 with HLA-B7, B8, B13, B63 and MICB-CA24, MICA-A6 with HLA-B51, MICA-A9 with HLA-B39, B57 and TNFa2, MICB-CA14 with HLA-B14, B27 and TNFa1, MICB-CA15 with HLA-B52, TNFa4 and TNFa13, MICB-CA17 with HLA-B7 and TNFa11, MICB-CA18 with HLA-B13 and TNFa7, MICB-CA22 with HLA-B57, and MICB-CA24 with HLA-B8 and TNFa2. From pairwise associations in the random panel and results for the homozygous cell lines it was possible to deduce the MICA and MICB microsatellite alleles present in many of the well-known Caucasoid extended haplotypes.     

MICA and MICB microsatellite alleles in HLA extended haplotypes

The present study is a contribution to the definition of the linkage disequilibrium relationship of MICA and MICB with adjacent loci and to the characterization of extended HLA haplotypes. These issues are of importance for the identification of disease associations and for a better definition of donor–recipient compatibility in bone-marrow grafts through the typing of haplospecific markers. The distribution of the five alleles of MICA and the 13 alleles of MICB microsatellites, located, respectively, in MICA transmembrane exon 5 and in MICB intron 1, was examined in 133 healthy Italian individuals previously typed for HLA class I, class II and complement loci and for the TNFa microsatellite. The MICB microsatellite was also analysed in 49 HTCLs for which MICA typing was already available. Very strong linkage disequilibria with HLA-B and TNFa were detected in the Italian population for both MICA and MICB microsatellite alleles, in spite of the high mutability rate of the larger MICB alleles. Some strong associations were also detected between MICB and DRB1. The strongest associations (P < 0.001, D′ > 0.7) were those of MICA-A4 with HLA-B18, B27 and TNFa1, MICA-A5 with HLA-B35, B61 and B62, MICA-A5.1 with HLA-B7, B8, B13, B63 and MICB-CA24, MICA-A6 with HLA-B51, MICA-A9 with HLA-B39, B57 and TNFa2, MICB-CA14 with HLA-B14, B27 and TNFa1, MICB-CA15 with HLA-B52, TNFa4 and TNFa13, MICB-CA17 with HLA-B7 and TNFa11, MICB-CA18 with HLA-B13 and TNFa7, MICB-CA22 with HLA-B57, and MICB-CA24 with HLA-B8 and TNFa2. From pairwise associations in the random panel and results for the homozygous cell lines it was possible to deduce the MICA and MICB microsatellite alleles present in many of the well-known Caucasoid extended haplotypes.     

强直性脊柱炎患者MICA基因第2、3和4外显子的多态性及其与HLA-B抗原的连锁不平衡

目的探讨皖籍汉族人群MICA基因（major histocompatibility complex class Ⅰchain-related gene A，MICA）第2、3、4外显子的多态性，及其与HLA-B抗原的连锁不平衡在强直性脊柱炎（ankylosing spondylitis，AS）发病中的作用。方法采用聚合酶链反应-序列特异性寡核苷酸探针杂交（polymerase chain reactionsequence-specific oligonucleotide probing，PCR-SS0）技术对56例AS患者和112名正常对照人群进行MICA基因第2、3、4外显子的多态性和HLA-B抗原的检测。结果AS患者和正常对照人群的MICA等位基因分布均以MICA＊008占优势，频率分别为32．14％和30．36％。两组人群MICA＊007等位基因的分布差异有统计学意义（X^2=10．18，P〈0．05，RR=2．50）。单倍型分析显示，AS患者和正常对照人群的MICA等位基因均显示出与多个HLA-B位点的连锁不平衡现象，两组间差异有统计学意义的单倍型为MICA＊007-B27（X^2=18．46，P〈0．05，RR=7．47）。分层分析结果显示，HLA-B27阳性与AS的相关性有统计学意义（P〈0．05），但MICA＊007基因与AS的相关性无统计学意义（P〉0．05）。结论AS患者中MICA＊007等位基因频率的显著升高可能源于MICA基因与HLA-B位点间的广泛连锁不平衡。     

Linkage disequilibrium analysis of familial psoriasis: identification of multiple disease-associated MHC haplotypes

Although psoriasis vulgaris (PsV) is strongly associated with certain human leukocyte antigens, the pathogenetic nature of these associations remains elusive. The objectives of this study were: (i) to determine whether HLA loci directly determine susceptibility or merely serve as markers for the susceptibility allele; and (ii) to identify additional disease-associated haplotypes. By applying maximum likelihood linkage disequilibrium analysis (LDA) in cases vs. controls, we found the susceptibility gene to be more strongly associated with specific HLA haplotypes than with their component alleles. Stronger linkage disequilibrium between PsV and HLA alleles was detected at HLA-C and HLA-B than at DRB1 and DQB1. Parametric linkage analysis accounting for marker-trait disequilibrium in psoriasis vulgaris pedigrees yielded most significant results for a locus close to HLA-B and -C. Furthermore, we found that susceptibility is linked to at least three different ancestral HLA haplotypes; among them, HLA-Cw7-B8-DRB1*0301-DQB1*02 is linked to PsV for the first time. These results identify a major PsV susceptibility locus in the immediate vicinity of, but distinct from HLA-B or HLA-C, and suggest that multiple disease alleles have arisen during human evolution.     

Differential major histocompatibility complex class I chain-related A allele associations with skin and joint manifestations of psoriatic disease

About 30% of patients with psoriasis have psoriatic arthritis (PsA), an inflammatory arthritis that can affect both axial and peripheral joints. Major histocompatibility complex class I chain-related A (MICA) alleles have previously been shown to be associated with PsA; however it is unclear whether there is a differential association of MICA alleles with skin and joint manifestations of PsA. Here, we describe a case-control study that aims to validate previously reported MICA allele associations with PsA and determine whether MICA alleles differentiate patients with PsA from those with psoriasis without PsA. Two hundred forty-nine unrelated Caucasian PsA patients, 243 psoriasis patients without arthritis, and 248 healthy controls were genotyped for 55 MICA alleles using PCR-SSP, and for human leucocyte antigen (HLA)-B and HLA-C alleles by PCR-SSO reverse line blot. Allele frequencies were calculated and logistic regressions were performed, adjusting for HLA-B and HLA-C alleles previously shown to be associated with psoriasis and/or PsA. Several MICA alleles were associated with psoriatic disease, PsA, and psoriasis compared with controls, and PsA compared with psoriasis in univariate analyses. Haplotype analysis showed evidence of strong linkage disequilibrium (LD) between PsA and psoriasis risk alleles of HLA-C, HLA-B, and MICA. After adjusting for significant HLA-B and HLA-C alleles in multivariate analyses, MICA*016 remained significantly associated with psoriasis [odds ratio (OR) = 5.5, P = 0.008]. MICA*00801 homozygosity was associated with susceptibility to PsA when compared with patients with psoriasis alone (OR = 2.26, P = 0.009). We conclude that most MICA allele associations with psoriasis and PsA are dependent on LD with HLA-B and HLA-C risk alleles. Independent of HLA, only MICA*016 influences the risk of developing psoriasis without arthritis, and homozygosity for MICA*00801 increases the risk of developing PsA in patients with psoriasis.     

Human leukocyte antigen class I B and C loci contribute to Type 1 Diabetes (T1D) susceptibility and age at T1D onset

Alleles of human leukocyte antigen (HLA) class II genes are well known to affect susceptibility to type 1 diabetes (T1D), but less is known about the contribution of HLA class I alleles to T1D susceptibility. In this study, molecular genotyping was performed at the HLA-B and HLA-C loci for 283 multiplex Caucasian families, previously typed for HLA-A and the class II loci. Allele frequencies were compared between affected siblings and affected family-based controls. Linkage disequilibrium coefficients were calculated for HLA-B-HLA-C haplotypes and for class I-lass II haplotypes. After adjustment for linkage disequilibrium, the following alleles remain associated with T1D: B*1801, B*3906, B*4403, C*0303, C*0802, and C*1601. B and C allele associations were tested for certain T1D-associated DRB1-DQB1 haplotypes, with the following results: B*3801 is protective on DRB1*0401-DQB1*0302 haplotypes, both C*0701 and C*0702 are predisposing on DRB1*0404-DQB1*0302 haplotypes, and B*3906 is predisposing on DRB1*0801-DQB1*0402 haplotypes. As with previous results for HLA-A, HLA-B and HLA-C are associated with age at T1D onset (mean 11.6 +/- 0.3 years). The protective allele B*4403 was associated with older age at onset (15.1 years; p < 0.04), and the predisposing alleles C*0702 and B*3906 were associated with younger age at onset (9.5 years, p < 0.001; and 7.8 years, p < 0.002, respectively). These data support a role for HLA class I alleles in susceptibility to and age at onset of T1D.     

HLA-B27 polymorphism and worldwide susceptibility to ankylosing spondylitis

HLA-B27 is strongly associated to ankylosing spondylitis (AS) and represents a family of eleven B27 alleles (B*2701–11). Our aim was to analyze the distribution of B27 subtypes by PCR/SSOP and genomic sequencing in a large group of populations ( n =17). 711 B27-positive samples from Caucasoid, Asian, African, Amerindian and Polynesian populations were selected to ascertain transracial gene mapping of the B27 subtypes. 476 of these were AS patients, chosen to investigate the contribution of B27 alleles to AS susceptibility. Some significant new findings have arisen from this study: 1) B*2705 was the predominant subtype in circumpolar and subarctic areas. B*2702 was found to be practically restricted to Caucasian populations, showing a higher frequency in Middle-East (Jews) and North Africa (Arabs/Berbers) groups. 2) B*2703 appears associated with AS in Western Africans. This is of remarkable interest since it was suggested that B*2703 would be negatively disease-associated. 3) Although B*2706 appears negatively associated with AS in Thais, we identified two patients from northern China carrying it. This may be a reflection of a disease heterogeneity and could indicate that more than one pathogenic agent can be involved in AS. B*2709 has been recently described as negatively associated with AS in Sardinians. The molecular changes His 114Asp (B*2706) and Asp 116His (B*2709) could modify the genetic susceptibility to AS.     

MICA polymorphism in a population from north Morocco, Metalsa Berbers, using sequence-based typing

The MICA gene encodes a family of nonclassical major histocompatibility complex class I molecules. Data on MICA polymorphism in different populations are still limited. In the present study, MICA allele frequencies (af) were assessed in 82 unrelated healthy individuals from a Moroccan Berber population named Metalsa (ME) by means of sequence-based typing of exons 2, 3, 4, and 5. In consideration of the linkage disequilibrium existing between MICA and human leukocyte antigen (HLA) class I alleles, MICA/HLA-B, MICA/HLA-Cw, and MICA/HLA-A haplotype frequencies (hf) were estimated. A wide allelic distribution including 16 different MICA alleles was found in ME. The most common MICA alleles were MICA*00801 (af = 0.268), *004 (0.232), *00902 (0.140), *00901 (0.085), and *00901 (0.073). The most common MICA/HLA-B haplotypes were MICA*004-B*4403 and MICA*009-B*50 (hf = 0.113 for both these haplotypes). Some known MICA and HLA-B associations were confirmed in this population. Noteworthy was the high frequency of MICA*009 (af = 0.226); the high frequency of B*50 found in ME (af = 0.114) permitted us to evidence the associations of MICA*00902 with B*5001 (hf = 0.068) or *5002 (hf = 0.045), whereas MICA*00901 was mainly associated with B*5101 (hf = 0.038), which corresponds to the previously described association MICA*009/A6-HLA-B*51. This study extends the previous knowledge on MICA polymorphism to a North African white population and may have implications for disease associations and transplantation.     

上海汉族人群MICA基因第5外显子微卫星多态性研究

目的 了解上海地区汉族人群ＭＩＣＡ基因第５外显子微卫生多态性分布,以及ＭＩＣＡ基因与其紧密连锁的ＨＬＡ－Ｂ基因位点的关系。方法 用ＰＣＲ－异源双链分析法,对１７５名正常无关个体的ＭＩＣＡ基因第５外显子微卫星多态性的分布进行研究。结果 （１）上海地区汉族人群ＭＩＣＡ基因第５外显子存在５种等位基因,其中ＭＩＣＡ＊Ａ５最为常见（３９．１４％）,其次为＊Ａ５．１（２２．２９％）;（２）ＭＩＣＡ等位基因与Ｈ     

Study on the haplotypes of MICA and MICB microsatellite and HLA-B locus in the Guangzhou Han population

The purpose of this study was to investigate the genetic polymorphisms and haplotypes of microsatellite locus in exon 5 of the MICA gene and intron 1 of the MICB gene and human leukocyte antigen-B (HLA-B) gene based on 106 samples of the Guangzhou Han population through means of polymerase chain reaction and the fluorescent technique (6-FAM). The corresponding haplotype frequencies, linkage disequilibrium values and relative linkage disequilibrium values were estimated based on population data. The results show that the genotype distributions of MICA and MICB microsatellite and HLA-B satisfy the Hardy-Weinberg equilibrium. In total, five alleles of MICA microsatellite locus and 14 alleles of MICB microsatellite locus were observed. MICA A5 was the most common allele (0.2877), whereas A4 was the least common (0.1321). MICB CA14 was the most common allele (0.3255), and CA19 and CA28 were the two least common (0.0047). CA27 was not observed at all. Five kinds of MICA-MICB haplotypes, 18 kinds of MICA-HLA-B haplotypes and 12 kinds of MICB-HLA-B haplotypes occurred at frequencies of more than 1%. The common haplotypes of MICA-MICB, MICA-HLA-B and MICB-HLA-B were A5-CA14, A5.1-CA18, A4-CA26, A9-CA15, A5-B*15(62), A5.1-B*1301/1302, A4-B*1301/1302, A6-B*51, A6-B*4403, A9-B*3802, CA14-B*4601, CA18-B*1301/1302 and CA26-B*1301/1302, and these haplotypes showed strong linkage disequilibrium. The polymorphisms and haplotype distributions of MICA and MICB microsatellite and HLA-B locus in the Guangzhou Han population have their own distinct genetic characteristics. The microsatellite locus of exon 5 of the MICA gene and intron 1 of the MICB gene could therefore be used as genetic markers in the studies of anthropology, gene linkage analysis in genetic diseases, individual identification and paternity testing in forensic medicine.     

Association of HLA genes with ankylosing spondylitis in Han population of eastern China

Ankylosing spondylitis (AS) is a chronic inflammatory disorder with a multifactorial genetic basis. HLA-B27 was reported with the greatest susceptibility to AS but did not act alone. The aim of this study was to search for other gene(s) associated with AS independently of HLA-B27 using 13 microsatellite markers spanning 1.5 Mb from locus TAP1 to HLA-Cw and a single-nucleotide polymorphism marker within NFkappaBIL1 gene promoter. Genotyping for microsatellites was performed in 175 AS patients of eastern Chinese and 219 ethnically matched healthy controls using polymerase chain reaction with fluorescence-labelled primers, whereas the SNP marker was genotyped by direct DNA sequencing. Allele as well as haplotype frequencies were compared between cases and controls, and a linkage disequilibrium analysis was performed to estimate the LD relationship between the candidate regions. The frequencies of alleles D6S2811*128, STR_MICA*A5.1 and D6S2672*109, as well as haplotypes D6S2811*128-D6S2927*213-D6S2810*340, D6S2927* 221-D6S2810*350-MICA*A5.1, and D6S2810*350-MICA*A5.1-D6S2800* 136 were significantly increased in B27-positive AS patients when compared with B27-positive controls. The results indicated that there may be other gene(s) within the HLA region, especially around locus HLA-B or HLA-Cw, with susceptibility to AS independently of HLA-B27.     

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.     

Does a central MHC gene in linkage disequilibrium with HLA-DRB1*0401 affect susceptibility to type 1 diabetes?

Subtypes of HLA-DR4 are associated with susceptibility or protection against type 1 diabetes (T1DM). We addressed whether this reflects linkage disequilibrium with the true susceptibility locus by studying broader MHC haplotypes marked by alleles of HLA-B, IKBL (adjacent to TNFA) and complement C4. The study used a largely Caucasian cohort from Western Australia. HLA-DRB1*0401 and HLA-DRB1*0405 marked susceptibility to T1DM. In Caucasians, DRB1*0401 occurs predominantly in the 44.1 ancestral haplotype (AH; HLA-A2,B44, DRB1*0401,DQB1*0301) and the 62.1AH (HLA-A2,B15(62),DRB1*0401,DQB1*0302). HLA-B15 marked susceptibility and HLA-B44 marked with resistance to T1DM in patients and controls preselected for HLA-DRB1*0401. A gene between TNFA and HLA-B on the 8.1AH (HLA-A1,B8,;DR3,DQ2) modifies the effects of the class II alleles. Here, alleles characteristic of the 62.1AH (C4B3, IKBL+446*T and HLA-A2,B15) were screened in donors preselected for HLA-DRB1*0401. C4B3 was associated with diabetes, consistent with a diabetes gene telomeric of MHC class II. However, increases in carriage of IKBL+446*T and HLA-A2,B15 were marginal, as too few control subjects were available with the diabetogenic alleles. However, with these tools, selection of HLA-DRB1*0401, DQB1*0302 donors who are positive and negative for C4B3 will allow bidirectional mapping of diabetes genes in the central MHC.     

HLA-A*2402 and a microsatellite (D6S248) are secondary independent susceptibility markers to ankylosing spondylitis in Basque patients

Ankylosing spondylitis (AS) is universally associated with human leukocyte antigen B27 (HLA-B27), although other genes could determine the development and clinical expression of the disease. HLA-A9 (A*2402) allele was previously found to be associated in Basque patients. The objective of this study is to perform a more precise analysis of microsatellite polymorphisms in HLA-A*2402 and B27 haplotypes to elucidate the significance of this association. A group of 50 unrelated AS patients and 113 controls of Basque origin were studied. Eight microsatellites in the class I major histocompatibility complex region with vicinity to HLA-A and -B were analyzed and the strength of allelic associations to AS and linkage disequilibrium (LD) between alleles were evaluated. Allele 15 at the microsatellite locus D6S248, 1000 Kb telomeric to HLA-A showed a strong positive association with the disease (OR:6; pc=4.7x10(-4)) and it could not be explained by LD to HLA-B27, HLA-A*2402 or any other loci. We found that D6S248-15 allele together with HLA-A*2402 could be B27-independent markers of additional susceptibility gene/s localised in the region telomeric to HLA-A in Basque AS patients.     

HLA-B*07 allele frequencies and haplotypic associations in Koreans

We have investigated the frequencies of HLA-B*07 alleles and their haplotypic associations with HLA-A, -C and -DRB1 loci in 489 healthy unrelated Koreans, including 214 parents from 107 families. All of the 45 samples (9.2%) typed as B7 by serology were analyzed for B*07 alleles using polymerase chain reaction (PCR)-single strand conformation polymorphism (SSCP) method. Two different B*07 alleles were detected: B*0702 (allele frequency 0.041) and B*0705 (0.005). Two characteristic haplotypes showing strong linkage disequilibrium in Koreans were A*2402-Cw*07-B*0702-DRB1*0101 (haplotype frequency 0.028) and A*2901-B*0705-DRB1*0803 (0.005). The characteristic haplotype A*2901-B*0705-DRB1*0803, found in 100% (5/5) of B*0705-positive individuals, has not been previously described in other ethnic groups. HLA-B7 alleles comprise distinctive extended haplotypes in the Korean population. The probability of HLA-B7 allele mismatches among ABDR-matched unrelated donor-recipient pairs is expected to be low in Koreans.     

Allelic diversity of MICA gene and MICA/HLA-B haplotypic variation in a population of the Murcia region in southeastern Spain

Major histocompatibility complex class I-related chain A (MICA) is located at 46 kb centromeric of HLA-B. It is highly polymorphic and interacts with NKG2D, its receptor on the surface of NK, Tgammadelta and T CD8 lymphocytes. Data on MICA polymorphism in different populations are still limited. Our aim was to establish allelic diversity of MICA gene and linkage disequilibrium with HLA-B in our population. DNA was obtained from 154 unrelated healthy individuals from the Murcia region in southeastern Spain. HLA-B genotyping was performed using polymerase chain reaction (PCR)-sequence-specific oligonucleotide probes and allele-specific PCR-sequence-specific primers, and MICA genotyping by using PCR-sequence-specific oligonucleotide probes. A total of 19 MICA alleles were detected on this study. MICA*008 was the most frequent allele (25.3%), followed by MICA*002 (16.1%), MICA*004 (14.9%), MICA*001 (7.8%), MICA*009 and MICA*016 (7.1%), and MICA*010 (4.6%). Eleven alleles had frequencies of <1%. In the haplotype analysis, MICA*008-B*0702 was found to be the most common, followed by MICA*004-B*4403 and MICA*001-B*1801, MICA*002-B*3501, MICA*008-B*4402, MICA*004-B*4901, MICA*008-B*0801, and MICA*002-B*3801. The frequency of MICA*010-B*1501, MICA*008-B*1302, MICA*015-B*4501, and MICA*008-B*4001 was remarkable inasmuch as these two last haplotypes have not been reported in Spanish population. Indeed, MICA*016 linked to B*1402 has also not been reported in the literature. In conclusion, the allelic diversity in our population is similar to other Caucasian populations; however we found a series of less frequent alleles, in addition to as-yet-undescribed haplotypic associations in other populations of Caucasian origin.     

Associations of major histocompatibility complex class I chain-related molecule polymorphisms with Behcet's disease in Caucasian patients

HLA-B*51 is known to be associated with Behcet's disease (BD) in many ethnic groups. The pathogenic gene, however, may lie close to the HLA-B locus and therefore be in linkage disequilibrium with HLA-B*51. On the basis of the proximity of MIC genes to HLA-B, their expression pattern and their affinity for the activating NKG2D receptor on natural killer (NK) cells and gammadelta T cells, these molecules have been postulated as susceptibility factors in BD. DNA from 56 western European Caucasians with BD and 90 Caucasian controls were analysed by polymerase chain reaction using allele-specific primers for MICA and MICB alleles. An increased allele frequency of MICA*009 was found in the BD patient group (25.0%) when compared with the controls (7.2%). This was associated with a corresponding decrease in MICA*008 in the BD patients (36.6%) compared with the controls (46.7%), which was not significant. MICA*009 was strongly associated with the presence of HLA-B*51 in patients and controls. No significant difference in frequency of MICB alleles was found between patients and controls. Both HLA-B*51 and MICA*009 are strongly associated with BD in a pure Caucasian BD patient group, and the two alleles are in linkage disequilibrium. No MICB allele was found to associate significantly with the disease, an unexpected finding considering the close proximity of the MICA and MICB loci. Our results suggest that while MICB does not influence the development of BD, polymorphisms in MICA may be pathogenic, perhaps through the interaction with NK and gammadelta T cells.     

MICA polymorphisms and haplotypes with HLA-B and HLA-DRB1 in Koreans

Abstract
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.     

HLA-B27 in the Greek Cypriot population: distribution of subtypes in patients with ankylosing spondylitis and other HLA-B27-related diseases. The possible protective role of B*2707

The major purpose of the present study was to investigate the frequency of human leukocyte antigen (HLA)-B27 alleles in healthy controls and in patients with ankylosing spondylitis (AS) and other HLA-B27–related diseases in the Greek Cypriot population. We selected 102 HLA-B27–positive individuals (60 controls and 42 patients). Typing of the HLA-B27 alleles was performed by polymerase chain reaction amplification with sequence-specific primers. Only two alleles were detected in the patient group: B*2702 (n = 31, 73.8%) and B*2705 (n = 11, 26.2%). The HLA-B*2707 allele was detected (n = 10, 16.7%) only in the healthy controls in addition to the B*2702 (n = 31, 51.7%) and B*2705 (n = 19, 31.7%) alleles. Our results show a restricted number of HLA-B27 subtypes associated with AS and other B27-related diseases and an elevated frequency of the B*2702 allele in the AS patients. The allele B*2707 seems to have a protective role in the population studied because it was found only in the healthy controls.