Mapping of the HLA-linked genes controlling the susceptibility to Takayasu's arteritis

Genetics of vasculitis

Systemic vasculitis encompasses a wide range of conditions characterized by varying degrees of inflammation in blood vessels. Although the etiology of vasculitis remains unclear, accumulated data suggest that it is triggered in genetically predisposed individuals by the concurrence of certain environmental factors. The importance of the genetic component has been consistently supported by evidence of familial aggregation, differential prevalence by ethnicity, and multiple genetic associations with disease susceptibility and severity reported in recent years. The strongest association signals in most vasculitides correspond to genetic variants within the HLA region, suggesting an important role of the immune system in its pathophysiology. However, each type of vasculitis has distinct defining HLA association markers, likely due to disease-specific differences in antigenic drivers. Furthermore, other genetic polymorphisms located outside the HLA region play an important role in susceptibility to different vasculitides. More recent research has assessed the shared genetic susceptibility evident across different vasculitides. Future studies should focus on the identification of genetic markers that can serve as reliable biomarkers for early diagnosis, prognosis, and treatment response in systemic vasculitis.

Multiple occlusions in extracranial arteries in patients with aortic arch syndrome: is minimally invasive treatment still possible? Technical aspects of the treatment based on our own experience and a review of the literature

Takayasu arteritis is a large vessel vasculitis of granulomatous nature and unknown aetiology affecting predominantly the aorta and its major branches, which may lead to ischaemic symptoms of many organs including the central nervous system. To decrease the risk of neurological complications and improve the quality of life, an arterial revascularisation may be necessary. The treatment options include pharmacotherapy as well as both open surgical and endovascular procedures, which has to be carefully chosen to obtain clinical success. There is an ongoing debate on the advantages, possibilities, and indications for implementing endovascular and open surgical methods, especially in high-risk patients. In this article we present our own experience in the treatment of an unusually complex and high-risk patient with multiple occlusion of supra-aortic branches, focusing on the technical aspects of the procedures and the decision-making process, as well as to confront with contemporary medical knowledge.

Review of children with Takayasu's arteritis at a Southern African tertiary care centre

IntroductionTakayasu's arteritis is a rare idiopathic arteritis causing stenosis or aneurysms of the aorta, pulmonary arteries, and their branches. It usually occurs in women, but has been described in children.

OBJECTIVE

The objective of this study was to determine the clinical presentation, demographic profile, vascular involvement, origins, management, and outcome of children diagnosed with Takayasu's arteritis at a Southern African tertiary care centre between 1993 and 2015.

METHODS

This is a retrospective analysis of all children with Takayasu's arteritis captured on a computerised electronic database during the study period.

RESULTS

A total of 55 children were identified. The female:male ratio was 3.2:1, and the mean age was 9.7±3.04 years. Most originated outside the provincial borders of the study centre. The majority presented with hypertension and heart failure. In all, 37 (67%) patients had a cardiomyopathy with a mean fractional shortening of 15±5%. A positive purified protein derivative test was documented in 73%. Abdominal aorta and renal artery stenosis were the predominant angiographic lesions. A total of 23 patients underwent 30 percutaneous interventions of the aorta, pulmonary, and renal arteries: eight stents, 22 balloon angioplasties, and seven had nephrectomies. All patients received empiric tuberculosis treatment, immunosuppressive therapy, and anti-hypertensive agents as required. Overall, there was a significant reduction in systolic blood pressure and improvement in fractional shortening (p<0.05) with all treatments.

CONCLUSION

Takayasu's arteritis is more common in girls and frequently manifests with hypertension and heart failure. The abdominal aorta and renal arteries are mostly affected. Immunosuppressive, anti-hypertensive, and vascular intervention therapies improve blood pressure control and cardiac function.

Novel HLA class I associations with HIV-1 control in a unique genetically admixed population

Associations between HLA class I alleles and HIV progression in populations exhibiting Amerindian and Caucasian genetic admixture remain understudied. Using univariable and multivariable analyses we evaluated HLA associations with five HIV clinical parameters in 3,213 HIV clade B-infected, ART-naïve individuals from Mexico and Central America (MEX/CAM cohort). A Canadian cohort (HOMER, n = 1622) was used for comparison. As expected, HLA allele frequencies in MEX/CAM and HOMER differed markedly. In MEX/CAM, 13 HLA-A, 24 HLA-B, and 14 HLA-C alleles were significantly associated with at least one clinical parameter. These included previously described protective (e.g. B*27:05, B*57:01/02/03 and B*58:01) and risk (e.g. B*35:02) alleles, as well as novel ones (e.g. A*03:01, B*15:39 and B*39:02 identified as protective, and A*68:03/05, B*15:30, B*35:12/14, B*39:01/06, B*39:05~C*07:02, and B*40:01~C*03:04 identified as risk). Interestingly, both protective (e.g. B*39:02) and risk (e.g. B*39:01/05/06) subtypes were identified within the common and genetically diverse HLA-B*39 allele group, characteristic to Amerindian populations. While HLA-HIV associations identified in MEX and CAM separately were similar overall (Spearman's rho = 0.33, p = 0.03), region-specific associations were also noted. The identification of both canonical and novel HLA/HIV associations provides a first step towards improved understanding of HIV immune control among unique and understudied Mestizo populations.

Takayasu Arteritis

Takayasu arteritis is an idiopathic granulomatous vasculitis of the aorta and its main branches and it constitutes one of the more common vasculitides in children. Inflammation and intimal proliferation lead to wall thickening, stenotic or occlusive lesions, and thrombosis, while destruction of the elastica and muscularis layers originates aneurysms and dissection. Carotid artery tenderness, claudication, ocular disturbances, central nervous system abnormalities, and weakening of pulses are the most frequent clinical features. The diagnosis is usually confirmed by the observation of large vessel wall abnormalities: stenosis, aneurysms, occlusion, and evidence of increased collateral circulation in angiography, MRA or CTA imaging. The purpose of this revision is to address the current knowledge on pathogenesis, investigations, classification, outcome measures and management, and to emphasize the need for timely diagnosis, effective therapeutic intervention, and close monitoring of this severe condition.

The genetics of Takayasu arteritis

Takayasu arteritis (TAK) is a rare systemic vasculitis that is characterized by granulomatous inflammation of the aorta and its major branches. The cellular and biochemical processes involved in the pathogenesis of TAK are beginning to be elucidated, and implicate both cell and antibody-mediated autoimmune mechanisms. In addition, the underlying etiology to TAK may be explained, at least in part, by a complex genetic contribution. The most well-recognized genetic susceptibility locus for the disease is the classical HLA allele, HLA-B*52, which has been confirmed in several ethnicities. The genetic susceptibility with HLA-B*52, as well as additional classical alleles and loci, implicate both HLA class I and class II involvement in TAK. Furthermore, genetic associations with genes encoding immune response regulators, pro-inflammatory cytokines and mediators of humoral immunity may directly relate to disease mechanisms. Non-HLA susceptibility loci that have been recently established for TAK with a genome-wide level of significance include FCGR2A/FCGR3A, IL12B, IL6, RPS9/LILRB3, and a locus on chromosome 21 near PSMG1. In this review, we present the complex genetic predisposition to TAK and discuss how recent findings identified potential targets in the pathogenesis and treatment of the disease.

Single Nucleotide Polymorphism rs10919543 in FCGR2A/FCGR3A Region Confers Susceptibility to Takayasu Arteritis in Chinese Population

Background:

Takayasu arteritis (TA) is a rare inflammatory arteriopathy of unknown etiology. The aim of this study was to investigate the genetic susceptibility to TA in a Chinese population.

Methods:

Four single nucleotide polymorphisms (SNPs) those locate in the IL12B region (rs56167332), the MLX region (rs665268), the FCGR2A/FCGR3A locus (rs10919543), and the HLA-B/MICA locus (rs12524487), associated with TA in different population, were genotyped in 123 Chinese TA patients and 147 healthy controls from January 2013 to August 2014. A Chi-square test was used to test for genotype/allele frequencies variants.

Results:

Among the four SNPs, rs10919543 was found to be significantly associated with TA in the studied population. The GG genotype of rs10919543 at the FCGR2A/FCGR3A locus is a high risk factor (odds ratio [OR] = 6.532, 95% confidence interval [CI] = 2.402 − 17.763, P < 0.001) for TA. Among TA patients, the level of eosinophil granulocytes (Eos) in the peripheral blood was observed to be higher in the GG group of rs10919543 (n = 23, Eos = 0.11 [0.08, 0.17] ×10⁹/L) than the GA + AA group (n = 100, Eos = 0.08 [0.05, 0.13] ×10⁹/L, P = 0.028). No correlation between the genotypes of the other three SNPs and TA patients was observed.

Conclusions:

Our findings revealed unique genetic pattern in Chinese TA patients that may be partly responsible for the higher risk of TA in this population. FCGR2A/FCGR3A-related immune disorder might contribute to the etiology of TA.

Revisited HLA and non-HLA genetics of Takayasu arteritis--where are we?

Takayasu arteritis (TAK) is an immune-mediated vasculitis affecting large arteries first reported in 1908 from Japan. Case reports of familial onset of TAK from Japan and other countries indicated genetic contribution to TAK onset beyond ethnicity. Genetic studies of TAK have been performed mainly addressing the human leukocyte antigen (HLA) locus. HLA genetic studies of TAK that have previously been reported are reviewed in this manuscript. HLA-B*52:01 is associated with TAK beyond population. Many of the associations other than HLA-B*52:01 can be explained by a haplotype with HLA-B*52:01. HLA-B*67:01 is a novel susceptibility HLA-B allele to TAK confirmed in the Japanese population. Further independent associations are suggested in the HLA locus. Involvement of the 171st and 67th amino acid residues with TAK onset has been indicated. The 67th amino acid may explain the difference in susceptibility effects to TAK and Behçet's disease between HLA-B*52:01 and *51:01. HLA-B*52:01 is associated not only with TAK susceptibility but also with clinical phenotypes. Recent genome-wide association studies of TAK revealed multiple non-HLA susceptibility genes. In particular, the IL12B region seems to have a central role in TAK onset and its progression. Whether TAK and giant cell arteritis (GCA), the other vasculitis affecting large arteries, are the same disease is an interesting question to address in spite of different clinical manifestations between the two diseases. GCA is associated with HLA-DR4, which is not associated with TAK. GCA is not associated with HLA-Bw52. These two diseases seem not to share non-HLA susceptibility loci based on the recent genetic studies.

Rheumatoid arthritis-associated aortitis: a case report and literature review

Rheumatoid arthritis (RA) is a systemic autoimmune inflammatory disorder that primarily affects the synovial joints. Rheumatoid vasculitis (RV) is an extra-articular manifestation of RA, and its association with aortitis is rare and not widely recognised. Here, we report the case of a 69-year-old woman with RA-associated aortitis and review the literature on rheumatoid aortitis. The mean oral steroid dose administered to RA-associated aortitis patients was 46.3 mg/day prednisolone (PSL). In our patient, the aortitis was also thought to be due to RV because she had findings of RV, such as cutaneous ulceration and a high rheumatoid factor titre, and because a moderate PSL dose dramatically improved the clinical findings. RA-associated aortitis, if left untreated, can be fatal; therefore, early detection and treatment initiation is very important.

Clinical characteristics, interdisciplinary treatment and follow-up of 14 children with Takayasu arteritis

BACKGROUND

Pediatric patients with Takayasu arteritis were studied by analyzing clinical presentation, diagnostic images, response to multimodal therapy, and long-term outcome.

METHODS

Fourteen consecutive children and adolescents (mean age: 10 years) were diagnosed with Takayasu arteritis at our institution between 1995 and 2007. They were subjected to clinical and diagnostic studies including color ultrasonography, MRI and angiography, and received interdisciplinary treatment.

RESULTS

The median time lag between the first onset of symptoms and diagnosis was 7.7 weeks. The majority of patients presented with acute severe clinical symptoms and extensive vascular lesions. Hypertension was the most common finding on first presentation (93%), followed by headache (64%), nausea (64%) and palpitation (50%). Ten patients (71%) had reduced or absent carotid, brachial or femoral pulses in one or more locations. C-reactive protein was elevated in 79% of the patients and erythrocyte sedimentation rate in 64%. Cardiovascular imaging showed extensive vasculitis of both sides of the diaphragm in 86%. Complications included renal artery stenosis (n=7), aortic dissection, thoracic aortic aneurysm and infrarenal aneurysm (all n=1). Conservative drug treatment was effective in 50%. Interventional dilatation of stenosis and surgical therapy, including aortic bypass, resection of aneurysms and nephrectomy, were necessary in the remaining patients. Follow-up for 25 months to 12 years showed that all children are well without disease-related mortality.

CONCLUSIONS

Takayasu arteritis is a rare and potentially life-threatening disease in children, likely with a prolonged subclinical course. Rapid diagnosis and interdisciplinary management help to prevent life-threatening complications.

Takayasu disease on the centenary of its discovery

Takayasu disease was first reported in 1908 by Mikito Takayasu as "a case of peculiar changes in the central retinal vessels." Because in these patients the pulse of the radial artery is impalpable, investigations focusing on the ischemic symptoms of the upper body were conducted. In 1948, Shimizu and Sano named this pathological condition "pulseless disease." Since then, the lesions of Takayasu disease have been detected not only in the aortic arch and its main branches but also in various vessels, including the abdominal aorta and renal arteries. The ocular symptoms of Takayasu disease are considered to be due to ischemia in the retina and choroid. The typical wreath-like arteriovenous anastomosis around the disc reported by Takayasu is observed at a relatively late stage of the disease. The characteristic fundus findings of Takayasu disease include tortuosity and dilatation of the central retinal artery and vein, retinal arteriovenous anastomosis, prominent retinal vasculature, microaneurysms in the capillaries, occlusion of retinal arterioles, soft exudate, choked disc, and optic atrophy. Fluorescein angiography reveals retinal microaneurysms, sludging, slower blood flow, dilatation of retinal vessels, leakage of fluorescence dye due to increased vascular permeability, and arteriovenous anastomosis. Arteriovenous anastomosis initially appears in the periphery at the early stage, and in the arteriovenous crossing at the advanced stage. Systemic administration of corticosteroids is required to prevent vascular stenosis during the early stages of Takayasu disease. Reconstruction of the carotid artery may improve subjective symptoms and fundus findings.

Vasculitis in children

Vasculitis is rare in children, and, apart from HSP and perhaps KD, most practicing pediatricians will never encounter a case. Nonetheless, progress in the diagnosis and treatment of these conditions has afforded most children with vasculitis a reasonably good prognosis. Accordingly, it is important to consider vasculitis as a potential cause of unexplained inflammation, perplexing rashes, or strange combinations of symptoms. Although evaluation and management of suspected vasculitis are difficult in the best of situations, they are impossible if the diagnosis is not considered.

Interleukin (IL)-12, IL-2, and IL-6 gene polymorphisms in Takayasu's arteritis from Turkey

Takayasu's arteritis (TA) is a chronic arterial inflammation of unknown etiology involving mainly the aorta and its major branches. Genetic polymorphisms of cytokines are screened as susceptibility factors for TA in Turkey. A total of 94 patients with TA were investigated for the genetic polymorphisms of the interleukin genes IL12, IL2,and IL6 and were compared with 108 healthy control subjects using polymerase chain reaction-sequence-specific primer method. The frequencies of IL12B 1188 C allele (p = 0.03, OR = 1.7) and CC genotype (p = 0.007, OR = 3.7) were both higher in TA patients than in control subjects. TT genotype at IL2-330 (p = 0.006, OR = 2.4) and GG genotype at IL6-174 (p = 0.04, OR = 1.9) were more frequent in TA patients. Lower prevalence of GT genotype at IL2-330 (p = 0.005, OR = 0.4), CG genotype at IL6-174 (p = 0.001, OR = 0.4), and AG genotypes at IL6-598 (p = 0.01, OR = 0.4) were also detected. The polymorphism of IL-12 as well as IL-6 and IL-2 genes may contribute to susceptibility and pathogenesis of TA by altering cytokine production and inducing inflammation.

Direct Determination of Single Nucleotide Polymorphism Haplotype of NFKBIL1 Promoter Polymorphism by DNA Conformation Analysis and Its Application to Association Study of Chronic Inflammatory Diseases

We previously revealed that one of the human leukocyte antigen-linked susceptibility genes for Takayasu's arteritis (TA) was mapped between TNFA and MICB loci and that -63T allele of NFKBIL1, which is between TNFA and MICB loci, was associated with rheumatoid arthritis (RA) in the Japanese population. We have developed a novel typing method based on reference strand-mediated conformation analysis for the upstream sequence of the NFKBIL1 gene, where -422 (T)8/(T)9, -325 C/G, -263 A/G, and -63 T/A polymorphisms were found. Upon the analysis of the patients with TA (n = 84), those with RA (n = 120), and healthy control subjects (n = 217), five common haplotypes named IKBLp*01 through IKBLp*05 were found in the Japanese population. The frequency of IKBLp*03 was significantly increased in the patient with TA (57.1% vs 35.0%, giving an odds ratio of 2.47). In addition, the frequency of IKBLp*01, but not that of other -63T-bearing alleles, was increased in the patients with RA (73.3% vs 58.1%, giving an odds ratio of 1.99), suggesting that the susceptibility to RA was conferred not by -63T alone but by combination of single nucleotide polymorphisms in the NFKBIL1 promoter. A higher promoter activity associated with IKBLp*03 and a lower activity associated with IKBLp*01 may contribute to the susceptibility to TA and RA, respectively.

Takayasu's arteritis: a review of the literature

Takayasu's arteritis is a rare, idiopathic, chronic inflammatory disease with cell-mediated inflammation, involving mainly the aorta and its major branches. It leads to stenosis, occlusion or aneurysmal degeneration of large arteries. The clinical presentation is characterised by an acute phase with constitutional symptoms, followed, months or years later, by a chronic phase in which symptoms relate to fibrosis or occlusion of vessels. Angiography is the gold standard for diagnosis and for topographical classification and it correlates with symptoms and prognosis. Here we focus on the pathophysiology, clinical and angiographical classification, diagnostic assessment and therapeutic approach of Takayasu's arteritis.

Vasculitis in children

This article provides a general overview of vasculitis, situations in which the diagnosis should be considered, diagnostic methods, and therapeutic considerations. Details and treatments unique to specific vasculitides are also reviewed.

Takayasu's disease

Takayasu's arteritis (TA) is a chronic inflammatory disease of unknown etiology that can produce stenosis, occlusion, or aneurysmal degeneration of large arteries. TA occurs worldwide but disproportionately affects young females of Asian descent. A variable acute phase of largely constitutional symptoms is followed by a chronic phase in which symptoms related to arterial compromise predominate. Diagnosis is made using a combination of clinical and angiographic criteria. Initial therapy involves the use of corticosteroids to induce remission of acute phase activity, with the addition of cytotoxic medications for nonresponders. Angioplasty and stenting can be used in the treatment of shorter stenoses such as those encountered in the renal arteries. Surgical bypass is the preferred treatment of longer segment stenoses and occlusions. Bypass grafts should originate from unaffected arteries to ensure durable inflow. Endovascular therapy is effective initially but long-term durability data are lacking.

Genetic analysis on HLA loci in Japanese patients with abdominal aortic aneurysm

PURPOSE

autoimmunity has been proposed as one of the pathogenesis of abdominal aortic aneurysm (AAA). There is also a likelihood that when aorto-iliac occlusive disease (AIOD) coexists with AAA, some other occlusive atherosclerotic diseases, such as ischemic heart disease and cerebrovascular disease, may develop, leading to a very poor long-term prognosis. Previous studies using serological HLA typing showed that HLA-DR15 was a risk factor for AAA. In this study, we performed HLA-DNA typing by PCR to clarify the relationship between AAA and HLA genotypes in Japanese patients with AAA. In addition, we analyzed whether HLA genotypes are involved in the pathogenesis of AIOD.

RESULTS

we examined 78 HLA genotypes of class I (HLA-A and -B) and class II (HLA-DR) and found that 60.4 and 30.4% of 49 AAA patients had HLA-A2 and HLA-B61, respectively. These frequencies were significantly higher than those in control individuals (HLA-A2, p < 0.05; HLA-B61, p < 0.005). We also found that 55.6% of nine AAA patients with AIOD had both HLA-B52 and HLA-DR B1*1502. In contrast, only 10.0% each of 40 AAA patients without AIOD showed HLA-B53 or HLA-DR B1*1502.

CONCLUSIONS

this study showed that HLA A-2 and HLA B-61, but not HLA DR-15, were important genetic risk factors for the development of AAA among the Japanese population. We also found high frequencies of HLA-B52 and HLA-DR B1*1502 in the AAA patients with AIOD than in those without, although this must be confirmed using a larger number of AAA patients with AIOD.

Association of the HLA-DRB1 gene with susceptibility to aortoarteritis in a Chinese Han population

Aortoarteritis is a chronic inflammatory disease mainly affecting the aorta and its major branches. Recent immunogenetic studies indicate that certain human leucocyte antigen (HLA) alleles are significantly associated with aortoarteritis in several populations. The purpose of the present study was to investigate the relationship between the HLA-DRB1 alleles and aortoarteritis in a Chinese Han population. HLA-DRB1 genotypes were identified by PCR-SSP and PCR-RFLP in 84 Chinese patients with aortoarteritis and 102 healthy Chinese controls. It was found that the HLA-DRB1*04 allele (38.1% in patients vs. 15.7% in controls, p<0.001, relative risk (RR)=2.43) and the HLA-DRB1*07 allele (47.6% vs. 10.8%, p<0.001, RR = 4.42) were significantly associated with aortoarteritis. Furthermore, there was no significant difference in the frequency of the DRB1*0405 subtype between the patient and control groups. Thus the susceptibility to aortoarteritis in this Chinese Han population was closely related with the HLA-DRB1*04 and DRB1*07 alleles. Thus individuals with the HLA-DRB1*04 and DRB1*07 alleles may be at higher risk for developing aortoarteritis.

Susceptibility locus for non-obstructive azoospermia is localized within the HLA-DR/DQ subregion: primary role of DQB1*0604

Non-obstructive azoospermia is a male infertility characterized by no or little sperm in semen as a result of a congenital dysfunction in spermatogenesis. Previous studies have reported a higher prevalence of particular human leukocyte antigen (HLA) antigens in non-obstructive azoospermia. As the expression of the RING3 gene located in the HLA class II region was predominant in the testis, mainly around spermatids and pachytene spermatocytes, it is tempting to speculate that RING3 is one of the strong candidate genes responsible for the pathogenesis of the disease. In this study, the genetic polymorphism in the RING3 gene was investigated by the direct sequencing technique. As a result, a total of 14 single nucleotide polymorphisms were identified. Among them, six were localized in the coding region but none of them was accompanied by an amino-acid substitution. No significant difference in the allelic distribution at these 14 polymorphic sites was observed between the patients and healthy controls, suggesting that the susceptible gene for non-obstructive azoospermia is not the RING3 gene. Then, in order to map the susceptibility locus for non-obstructive azoospermia precisely within the HLA region, 11 polymorphic microsatellite markers distributed from the SACM2L gene just outside the HLA class II region (187 kb telomeric of the DPB1 gene) to the OTF3 gene in the HLA class I region were subjected to association analysis in the patients. Statistical analysis of distribution in the allelic frequency at each microsatellite locus demonstrated that the pathogenic gene for non-obstructive azoospermia is located within the HLA-DR/DQ subregion. In fact, DRB1*1302 and DQB1*0604 were found to be strongly associated with non-obstructive azoospermia by polymerase chain reaction-based DNA typing. Further, haplotype analysis suggested that the DQB1*0604 allele may play a decisive role in the pathogenesis of non-obstructive azoospermia.

Takayasu's arteritis and Crohn's disease: an unusual association. Report on two cases

Two cases of Takayasu's arteritis associated with Crohn's disease of the colon are described, both of which occurring in young female patients. In the first case, the vasculitic process was widespread, involving the aortic arch, the abdominal aorta, the renal arteries and the left iliac artery, similar to the angiographic "Indian" pattern. The second case presented a typical "Japanese" aortic arch involvement. In the first patient, Crohn's disease appeared to have been present prior to Takayasu's arteritis, vice versa in the second case; steroid treatment, assigned for both diseases might, however, have modified their natural evolution. The association is rare. Moreover, the coexistence of two immune-mediated diseases in the same subject is unusual as they are generally considered to be independent. Hypotheses concerning their possible inter-relationship are advanced.

Pathogenesis: immunogenetic factors

The occurrence, albeit infrequent, of systemic vasculitis in closely related family members suggests that both environmental and genetic factors may play a role in the pathogenesis of these diseases. Malfunction of immune regulation in the systemic vasculitides may indicate a role for genes that encode molecules critical to the immune responses. The extremely polymorphic sequences of MHC molecules may provide a structural basis for associations of MHC genes and systemic vasculitis. This review summarizes recent reports of MHC associations, mechanisms by which MHC may play a role in certain vasculitides, and also examines the role for genes encoding non-MHC molecules, such as Fcgamma receptors, cytokines and T cell co-stimulators. Data suggest that the pathogenesis of systemic vasculitides such as giant-cell arteritis, Takayasu's arteritis and Wegener's granulomatosis might be governed by multiple genes encoding host defence molecules, in conjunction with environmental factors.

Mapping MHC-encoded susceptibility and resistance in primary sclerosing cholangitis: the role of MICA polymorphism

BACKGROUND & AIMS

Recent studies suggest that major histocompatibility complex-encoded susceptibility to primary sclerosing cholangitis (PSC) maps to the HLA B-TNFA region on chromosome 6p21.3.

METHODS

The present study uses a standard polymerase chain reaction protocol to investigate the 16 common alleles of the MICA locus as candidates in 2 patient populations (King's College Hospital, London, and John Radcliffe Hospital, Oxford).

RESULTS

The MICA*002 allele was found in 4 of 62 (6.4%) patients and none of 50 patients vs. 41 of 118 (35%) controls (pc = 0.00018, odds ratio [OR] = 0.12, and P = 0.0000016, OR = 0.0, respectively). Overall, the MICA*008 allele was more common in PSC (gene frequency 66% vs. 48% of controls, P = 0.0023, OR = 2.11). However, unlike MICA*002 in which the difference was a result of the absence of MICA*002 heterozygotes, the MICA*008 association may be caused by an increased frequency of MICA*008 homozygosity in patients (58% vs. 22%, pc = 0.000015, OR = 5.01 and 58% vs. 22%, P = 0.0000056, OR = 4.51, respectively). Though MICA*008 is found on the ancestral 8.1 haplotype, stratification analysis indicates that this association is independent of B8 and other HLA haplotypes associated with PSC.

CONCLUSIONS

The MICA*002 allele has a strong dominant effect in reducing the risk of PSC, whereas the increased risk of disease associated with MICA*008 may be a recessive effect requiring 2 copies of the MICA*008 allele.