Kazuro Yabuki

Association analysis between the MIC-A and HLA-B alleles in Japanese patients with Behçet's disease.

OBJECTIVE Behçets disease is known to be strongly associated with HLA-B51 in many different ethnic groups. Recently, by association analysis using refined microsatellite mapping, the critical region for Behçets disease was identified as a 46-kb segment centromeric to the HLA-B gene. No expressed gene has been detected in this segment to date except the MIC-A (major histocompatibility complex class I chain-related gene A) and HLA-B genes. The present study was undertaken to analyze allelic distribution of the MIC-A gene among Japanese patients with Behçets disease. METHODS Ninety-five Japanese patients with Behçets disease and 116 ethnically matched healthy controls were enrolled in this study. MIC-A genotyping was performed by direct sequencing of polymerase chain reaction products from exons 2, 3, and 4 of the MIC-A gene, using an automated DNA sequencer. RESULTS The MIC-A009 allele was significantly more frequent in the patient group (69.5%) compared with the healthy controls (31.0%) (relative risk 5.06, corrected P = 0.00000024). In stratification analysis on the confounding effect of MIC-A009 on HLA-B*51 association and vice versa, Behçets disease was distinctively associated only with HLA-B*51. Further, MIC-A009 was found to be strongly associated not only with HLA-B51, but also with HLA-B52, which was not increased in the patient group to any degree. CONCLUSION These results imply that the real disease susceptibility gene involved in the development of Behçets disease is the HLA-B*51 allele itself and that the significant increase of the MIC-A009 allele in the patient group results secondarily from a strong linkage disequilibrium with HLA-B*51.

MIC-A allele profiles and HLA class I associations in Behçet's disease

Abstract Recently a new family of non-classical MHC molecules, the MHC class I chain-related protein (MIC), encoded by genes located in the major histocompatability complex have been identified. On the basis of the location of MIC genes and the structure and expression of MIC molecules it has been postulated that MIC may be a susceptibility factor in Behçets disease (BD). We investigated the association of the 16 described external domain alleles and the transmembrane triplet repeats of MIC-A with BD in a Middle Eastern population. DNA from ninety-five patients and 102 age- and sex-matched controls were analyzed by polymerase chain reaction using allele specific primers. Our results show an increase of MIC-A*009 in the BD patient group 44/95 (46%) compared with controls 24/102 (24%) (χ2=11.3, OR=2.8, P=0.00078). MIC-A*009 was also found to be strongly associated with HLA-B51 in the patients 39/44 (88%) when compared with controls 10/24 (42%) (χ2=4, P=0.04). MIC-A*009 was also found in linkage disequilibrium with HLA-B52, but only in controls. The A6 form of a MIC-A transmembrane triplet repeat was found to be significantly raised in the patients (80/95; 84%;) compared with controls (58/102, 57%) (χ2=17.5, OR=4, P=0.000028). Although the MIC-A associations described are highly significant, the association with HLA-B51 independently remains the most significant factor (χ2=56.8, P<10–6). The data suggests that as both MIC-A*009 and A6 are in strong linkage disequilibrium with HLA-B51, they are unlikely to be the susceptibility gene for BD but may be markers for additional risk factors.

Association between MICA gene A4 allele and Acute anterior uveitis in white patients with and without HLA-B27

PURPOSE Acute anterior uveitis is strongly associated with the HLA-B27 antigen and triggered by the involvement of some external factors. However, it is uncertain whether HLA-B27 itself or other gene(s) near the HLA-B region in a linkage disequilibrium with HLA-B27 predispose to this uveitis. We therefore investigated microsatellite polymorphism in the transmembrane region of the major histocompatibility complex class I chain-related gene A (MICA), located 47 kilobases (kb) on the centromeric side of the HLA-B gene on the short arm of chromosome 6 within 6p21.3. METHODS We examined the following patients for MICA gene polymorphism by means of polymerase chain reaction and subsequent automated fragment detection by fluorescent-based technology: 64 (37 HLA-B27-positive and 27 HLA-B27-negative) whites with acute anterior uveitis, 74 (67 HLA-B27-negative and 7 HLA-B27-positive) ethnically matched random controls, and 36 HLA-B27-positive healthy controls. RESULTS The microsatellite allele consisting of four repetitions of GCT/AGC (designated A4 allele) was present at the significantly higher phenotype frequency (71.9%) in the patient group than in the ethnically matched random control group (13.5%) (P < .0000001, corrected P < .0000001). The A4 allele was strongly linked to HLA-B27 in a white population. However, the A4 allele was also found at the significantly higher phenotype frequency (37.0%) even in the HLA-B27-negative patient group than in the ethnically matched HLA-B27-negative control group (4.5%) (P = .0086, corrected P = .043). CONCLUSIONS These results suggest that the MICA gene itself or other nearby gene(s) linked to the MICA A4 allele may be involved in the development of acute anterior uveitis in a white population.

Triplet repeat polymorphism in the MICA gene in HLA-B27 positive and negative caucasian patients with ankylosing spondylitis

Previously, we reported a triplet repeat polymorphism in the transmembrane region within the MICA gene closely linked to HLA-B in a limited number of B27-positive Caucasian patients with ankylosing spondylitis (AS) (N = 48). In this study, we enrolled much more patients including some negative for B27, 162 AS subjects consisting of 140 B27-positive, and 22 B27-negative patients. The microsatellite allele consisting of 4 repetitions of (GCT/AGC) (A4 allele) was present at a significantly higher phenotype frequency in the patient group than in the ethnically matched control group (Pc < 0.000001). However, the frequency of the A4 allele was not significantly higher in the B27-positive and B27-negative patient groups, as compared to the B27-positive and B27-negative control groups, respectively. The higher phenotype frequency of the A4 allele in the patient group was supposed to be due to a strong linkage disequilibrium between the MICA and HLA-B genes. Thus, the possibility that the MICA gene is involved in the pathogenesis of AS can be excluded, supporting the hypothesis of a primary association of AS with HLA-B27.

Microsatellite polymorphism within the MICB gene among japanese patients with behçet’s disease

Behçets disease (BD) is known to be associated with HLA-B51. In order to investigate the influence of the MICB gene, located about 120 kb centromeric of the HLA-B gene, on the susceptibility to BD, (CA/TG) dinucleotide repeat microsatellite polymorphism in intron 1 of the MICB gene was investigated among 77 Japanese patients with BD, 60 randomly selected controls and 28 HLA-B51-positive unrelated healthy controls. There was no significant difference in the phenotype frequency of the microsatellite polymorphism between the BD patients and controls. This result suggests that the MICB gene itself is not responsible for the development of BD, and that the candidate gene(s) for BD is located between the MICA and HLA-C genes.

Microsatellite mapping of a susceptible locus within the HLA region for Behçet's disease using Jordanian patients.

Behçets disease (BD) has been established to be associated with HLA-B51. However, it has not been revealed whether the HLA-B51 gene itself or another gene located near the HLA-B gene is directly involved in the pathogenesis of BD. Previously, using Japanese BD patients, our group has narrowed down a BD-causative gene to 46 kb between the MICA and HLA-B genes by means of fine mapping analysis with eight microsatellite markers distributed within a 1100 kb segment around the HLA-B gene. To know whether this mapping result is generally observed in BD of another population we have investigated repeat polymorphisms of the same microsatellite markers in Jordanian BD patients. Furthermore, we have evaluated these data by Mantel-Haenzel stratified analysis to find out a primarily associated locus for BD. As a result, HLA-B51 was found to be the most strongly and primarily associated marker. This result suggests that the pathogenic gene of BD is HLA-B51 itself, but unlikely to be other genes located in the vicinity of HLA-B.

HLA testing in patients with uveitis.

It is well known that some uveitis syndromes are associated with the possession of certain human leukocyte antigen (HLA) types. HLA is the human major histocompatibility complex (MHC) in humans and is located on the short arm of chromosome 6. HLA genes are subdivided into two types—I and II—on the basis of their molecular structure. HLA class I antigens are expressed on almost all somatic cells. Class I molecules bind peptides derived from endogenously synthesized proteins (e.g., viral proteins in virus-infected cells) and present them to CD8 T cells. Class II antigens are found on relatively few cell types, such as macrophages, B lymphocytes, and dendritic cells. Class II molecules bind peptides derived from exogenous proteins that have been internalized by antigenpresenting cells and present them to CD4 T cells. Thus, HLA plays an important role in the immune system to recognize self from non-self, to present foreign antigens, and ultimately to stimulate T cells. In clinical medicine, HLA antigens are the major “transplantation antigens” that determine the compatibility of transplanted tissues and organs. HLA genes are the most polymorphic of all human genes. HLA matching and histocompatibility testing have an enormous influence on organ transplantation practices. On the other hand, it has been shown that there are associations between HLA antigens and some diseases during the past two or three decades. The first reports of an association between an HLA antigen and disease were published in 1967 and showed that Hodgkin’s lymphoma was related to a group of HLA antigens. Subsequently, it has been revealed that there are strong associations with HLA antigens in almost all autoimmune diseases. In the ophthalmological field, the association between some uveitis syndromes and HLA antigens has been known since the 1970s.

Visual performance of the intraindividual implantation of a trifocal intraocular lens in the bag and a +4.0 D bifocal intraocular lens in the sulcus with optic capture created by femtosecond laser-assisted cataract surgery

At present, only one design is available for trifocal intraocular lens (IOL); unfortunately, this particular design is not suitable for implantation in the sulcus with optic capture when posterior capsule rupture (PCR) occurs. Although three-piece bifocal IOLs can be implanted in the sulcus, this form of IOL can be vulnerable to tilt and decentration, thus causing aberration and photopic phenomena, such as halos and glares. However, visual axis centered optic capture using femtosecond laser-assisted cataract surgery (FLACS) is able to manage such complex operations. In the present study, we implanted a three-piece +4.0 D bifocal IOL into the sulcus of a patient who experienced PCR using optic capture and FLACS following the straightforward implantation of a one-piece trifocal IOL in the other eye. Defocus curves showed that the weakness of the trifocal IOL (nearest distances) was compensated for by the strength of the +4.0 D bifocal IOL, whereas the weakness of the +4.0 D bifocal IOL (middle distance) was compensated for by the strength of the trifocal IOL. Therefore, this combination provided the patient with a wider range of depth of focus. The contrast sensitivity in both eyes was within the normal range. Photopic phenomena were comparable with the bilateral implantation of the trifocal IOL. Anterior segment optical coherence tomography showed that tilt and decentration in the trifocal IOL implanted in the bag was significantly higher than the +4.0 D bifocal IOL implanted in the visual axis centered optic capture. This case showed that the intraindividual implantation of a single-piece trifocal IOL in the bag and a three-piece +4.0 D bifocal IOL in the sulcus, using a combination of optic capture and FLACS, is promising particularly in cases of PCR and can provide a wider range of vision without losing visual quality.