Analysis of MHC encoded antigen-processing genes TAP1 and TAP2 polymorphisms in sarcoidosis

Immune mechanisms of granuloma formation in sarcoidosis and tuberculosis

Sarcoidosis is a complex immune-mediated disease characterized by clusters of immune cells called granulomas. Despite major steps in understanding the cause of this disease, many questions remain. In this Review, we perform a mechanistic interrogation of the immune activities that contribute to granuloma formation in sarcoidosis and compare these processes with its closest mimic, tuberculosis, highlighting shared and divergent immune activities. We examine how Mycobacterium tuberculosis is sensed by the immune system; how the granuloma is initiated, formed, and perpetuated in tuberculosis compared with sarcoidosis; and the role of major innate and adaptive immune cells in shaping these processes. Finally, we draw these findings together around several recent high-resolution studies of the granuloma in situ that utilized the latest advances in single-cell technology combined with spatial methods to analyze plausible disease mechanisms. We conclude with an overall view of granuloma formation in sarcoidosis.

A transcriptomics-based meta-analysis identifies a cross-tissue signature for sarcoidosis

Sarcoidosis is a granulomatous disease of unknown etiology, immunologically characterized by a Th1 immune response. Transcriptome-wide expression studies in various types of sarcoid tissues contributed to better understanding of disease mechanisms. We performed a systematic database search on Gene Expression Omnibus (GEO) and utilized transcriptomic data from blood and sarcoidosis-affected tissues in a meta-analysis to identify a cross-tissue, cross-platform signature. Datasets were further separated into training and testing sets for development of a diagnostic classifier for sarcoidosis. A total of 690 differentially expressed genes were identified in the analysis among various tissues. 29 of the genes were robustly associated with sarcoidosis in the meta-analysis both in blood and in lung-associated tissues. Top genes included LINC01278 (P = 3.11 × 10^–13), GBP5 (P = 5.56 × 10^–07), and PSMB9 (P = 1.11 × 10^–06). Pathway enrichment analysis revealed activated IFN-γ, IL-1, and IL-18, autophagy, and viral infection response. IL-17 was observed to be enriched in peripheral blood specific signature genes. A 16-gene classifier achieved excellent performance in the independent validation data (AUC 0.711–0.964). This study provides a cross-tissue meta-analysis for expression profiles of sarcoidosis and identifies a diagnostic classifier that potentially can complement more invasive procedures.

Current Insights in Genetics of Sarcoidosis: Functional and Clinical Impacts

Sarcoidosis is a complex disease that belongs to the vast group of autoinflammatory disorders, but the etiological mechanisms of which are not known. At the crosstalk of environmental, infectious, and genetic factors, sarcoidosis is a multifactorial disease that requires a multidisciplinary approach for which genetic research, in particular, next generation sequencing (NGS) tools, has made it possible to identify new pathways and propose mechanistic hypotheses. Codified treatments for the disease cannot always respond to the most progressive forms and the identification of new genetic and metabolic tracks is a challenge for the future management of the most severe patients. Here, we review the current knowledge regarding the genes identified by both genome wide association studies (GWAS) and whole exome sequencing (WES), as well the connection of these pathways with the current research on sarcoidosis immune-related disorders.

Serum CXCL11 correlates with pulmonary outcomes and disease burden in sarcoidosis

BACKGROUND

Sarcoidosis is a systemic granulomatous disease of unknown etiology that affects the lungs in 90% of patients, but has a wide range of disease manifestations and outcomes including chronic and progressive courses. Noninvasive biomarkers are needed to assess these outcomes and guide decisions for long term monitoring and treatment. Interferon-gamma (IFN-γ)-inducible chemotactic cytokines (chemokines), CXCL9, CXCL10 and CXCL11, show promise in this regard because they have been implicated in the pathogenesis of and reflect the burden of granulomatous inflammation. CXCL11 has been reported to have unique functional properties in modulating adaptive immunity in model systems so our goal was to examine serum levels of CXCL11 in relation to clinical outcomes in a heterogeneous cohort of sarcoidosis subjects.

METHODS

CXCL19, CXCL10, and CXCL11 serum levels were measured in sarcoidosis and healthy subjects using ELISA assay. We determined relationships between CXCL11 and standard clinical inflammatory markers, expression of IFN-γ-related genes in whole blood, organ involvement, dyspnea scores, and measures of pulmonary function.

RESULTS

In a cross-sectional analysis of 104 sarcoidosis subjects, serum CXCL11 was significantly elevated compared to 49 healthy controls (p < 0.001). CXCL11 was positively correlated with CXCL9 and CXCL10 (p < 0.001), sedimentation rate (p < 0.01), and mean expression of three IFN-γ-related genes in whole blood (GBP1, STAT1, and STAT2) (p < 0.001). CXCL11 was inversely correlated with FVC %predicted (%pred) and FEV1 %pred and higher levels were associated with higher patient-reported dyspnea scores. We found positive correlations between CXCL11 and number of organs involved. Using survival analyses, we found that CXCL11 levels were predictive of future pulmonary function test (PFT) decline (log rank <0.001 and HR of log₁₀(CXCL11) = 5.1, 95% CI 1.2-21, p = 0.026).

CONCLUSIONS

The pattern of expression of serum CXCL11 in sarcoidosis patients suggests that this blood measure could be helpful in identifying patients that need longer-term monitoring for progressive thoracic and extra-thoracic sarcoidosis.

Exploring the dynamic changes between pulmonary and cutaneous sarcoidosis based on gene expression

Sarcoidosis is a disease involving the growth of abnormal inflammatory granulomas and affecting multisystems. It has an unknown etiology. The lung and the skin are the most commonly involved organs. Although large amounts of research have focused on the pathogenesis of sarcoidosis, little is known about the link between cutaneous sarcoidosis and pulmonary sarcoidosis. Moreover, the gene expression profiles provide a novel way to find diagnostic or prognostic biomarkers. Therefore, the aim of this study was to analyze the differentially expressed genes (DEGs) in pulmonary sarcoidosis and cutaneous sarcoidosis patients and to compare them to healthy individuals. DEGs and their biological functions are dynamically dysregulated, and several common disease-related genes and mutual disease progression-related genes were identified which linked pulmonary sarcoidosis and cutaneous sarcoidosis together. The biological functional pathways regulated by these DEGs may allow to define the common mechanism shared by different type of sarcoidosis, providing novel insight into the common pathogenesis of sarcoidosis and opening the way to the development of new therapeutic strategies.

Sarcoidosis Related Novel Candidate Genes Identified by Multi-Omics Integrative Analyses

Sarcoidosis is a multifactorial systemic disease characterized by granulomatous inflammation and greatly impacting on global public health. The etiology and mechanisms of sarcoidosis are not fully understood. Recent high-throughput biological research has generated vast amounts of multi-omics big data on sarcoidosis, but their significance remains to be determined. We sought to identify novel candidate regions, and genes consistently altered in heterogeneous omics studies so as to reveal the underlying molecular mechanisms. We conducted a comprehensive integrative literature analysis on global data on sarcoidosis, including genomic, transcriptomic, proteomic, and phenomic studies. We performed positional integration analysis of 38 eligible datasets originating from 17 different biological layers. Using the integration interval length of 50 kb, we identified 54 regions reaching significance value p ≤ 0.0001 and 15 regions with significance value p ≤ 0.00001, when applying more stringent criteria. Secondary literature analysis of the top 20 regions, with the most significant accumulation of signals, revealed several novel candidate genes for which associations with sarcoidosis have not yet been established, but have considerable support for their involvement based on omic data. These new plausible candidate genes include NELFE, CFB, EGFL7, AGPAT2, FKBPL, NRC3, and NEU1. Furthermore, annotated data were prepared to enable custom visualization and browsing of these sarcoidosis related omics evidence in the University of California Santa Cruz (UCSC) Genome Browser. Further multi-omics approaches are called for sarcoidosis biomarkers and diagnostic and therapeutic innovation. Our approach for harnessing multi-omics data and the findings presented herein reflect important steps toward understanding the etiology and underlying pathological mechanisms of sarcoidosis.

The impact of ACE gene polymorphism on the incidence and phenotype of sarcoidosis in rural and urban settings

INTRODUCTION

Sarcoidosis is a multisystem granulomatous disease of unknown etiology. Current theory on the etiology of this disease involves participation of genetic factors and unknown antigens present in the patients' environment. The aim of the study was to evaluate the prevalence of different polymorphic forms of the ACE gene in healthy individuals and sarcoidosis patients, and to estimate the risk of sarcoidosis in carriers of different ACE genotypes living in rural and urban settings.

MATERIAL AND METHODS

The study group included 180 patients with pulmonary sarcoidosis. Assessment of the disease was based on clinical features, laboratory and imaging examinations, as well as bronchoscopy with bronchoalveolar lavage (BAL). ACE gene polymorphism was examined in DNA isolated from peripheral blood or BAL fluid (BALF) leukocytes.

RESULTS

Incidence of sarcoidosis was not influenced by gender, age or place of residence of the patients. There were no differences in the frequency of particular genotypes in patients with sarcoidosis and in healthy individuals. The risk of disease did not depend on the ACE gene polymorphism. There were no differences in the frequencies of the different genotypes and alleles of the ACE gene in patients with sarcoidosis divided by gender, age and place of residence or by clinical manifestation of sarcoidosis.

CONCLUSIONS

Our results do not support the previous concept which suggested a higher incidence of sarcoidosis in individuals living in rural areas and in carriers of selected ACE genotypes. It is possible that this is related to the changing environment of rural areas, increasing urbanization and pollution.

Genetic susceptibility to beryllium: a case-referent study of men and women of working age with sarcoidosis or other chronic lung disease

OBJECTIVE

The study was designed to investigate whether beryllium exposure was related to illness diagnosed as sarcoidosis. Chronic beryllium disease (CBD) and sarcoidosis are clinically and pathologically indistinguishable, with only the presence of beryllium-specific T-lymphocytes identifying CBD. Testing for such cells is not feasible in community studies of sarcoidosis but a second characteristic of CBD, its much greater incidence in those with a glutamic acid residue at position 69 of the HLA-DPB1 gene (Glu69), provides an alternative approach to answering this question.

METHODS

Cases of sarcoidosis aged 18-60 years diagnosed in Alberta, Canada, from 1999 to 2005 were approached through their specialist physician, together with age-matched and sex-matched referents with other chronic lung disease. Referents were grouped into chronic obstructive pulmonary disease (COPD), asthma and other lung disease. Participants completed a telephone questionnaire, including industry-specific questionnaires. DNA was extracted from mailed-in mouthwash samples and genotyped for Glu69. Duration of employment in types of work with independently documented beryllium exposure was calculated.

RESULTS

DNA was extracted for 655 cases (270 Glu69 positive) and 1382 referents (561 positive). No increase in sarcoidosis was seen with either Glu69 or beryllium exposure (none, <10, ≥10 years) as main effects: longer duration in possible beryllium jobs was related to COPD. In Glu69 positive men with exposure ≥10 years, the trend towards increasing rate of COPD was reversed, and a significant interaction of duration of exposure and Glu69 was detected (OR=4.51 95% CI 1.17 to 17.48).

CONCLUSIONS

The gene-environment interaction supports the hypothesis that some cases diagnosed as sarcoidosis result from occupational beryllium exposure.

Esophageal sarcoidosis: a review of cases and an update

Sarcoidosis is a chronic disorder that can virtually affect any organ system in the body. Histologically, it is characterized by the presence of T lymphocytes, mononuclear phagocytes, and noncaseating granulomas. Most commonly affected are the intrathoracic structures, with 90% of the reported cases involving the lungs. Esophageal involvement in sarcoidosis is extremely rare. Dysphagia is the most common presentation in these patients and can be attributed to various mechanisms such as direct esophageal wall infiltration, extrinsic compression, cranial neuropathy, and brainstem involvement. A thorough online literature review revealed only 23 reported cases of esophageal involvement in sarcoidosis. This paper reviews these reported cases in detail along with newer diagnostic and treatment options, including direction of future therapy.

Genetic evidence of TAP1 gene variant as a susceptibility factor in Indian leprosy patients

The heterodimeric transporter associated with antigen processing (TAP) gene loci is known to play a vital role in immune surveillance. We investigated a possible association of gene polymorphisms both in TAP1 and TAP2 in a cohort of clinically classified leprosy patients (n=222) and in ethnically matched controls (n=223). The TAP1 and TAP2 genes were genotyped for four single nucleotide polymorphisms TAP1 (rs1057141 Iso333Val and rs1135216 Asp637Gly) and TAP2 (rs2228396 Ala565Thr and rs241447 Ala665Thr) by direct sequencing and ARMS-PCR. The minor allele of TAP1 637G contributes to an increased risk to leprosy compared to controls (OR: 1.68, 95% CI 1.2-2.36, P=0.0057). An increased risk for the variant minor allele of the TAP1 637G to multibacillary (BL+LL) or paucibacillary (BT+TT) infections was also observed [multibacillary vs. controls (OR: 1.56, 95% CI 1.07-2.28, P=0.054); paucibacillary vs. controls (OR: 1.92, 95% CI 1.21-3.01, P=0.013)]. In the dominant model, the genotypes of the TAP1 rs1135216AG+GG additionally contributed to an increased risk. Overall our findings demonstrate that the TAP1 gene variant (rs1135216 Asp637Gly) influences the susceptibility to clinically classified leprosy patients in Indian population.

Testicular Sarcoidosis: Sonographic Findings

Testicular sarcoidosis is a rare but benign entity. It is often mistaken for testicular neoplasm, leading to orchiectomy. It is, therefore, extremely important to identify and correctly diagnose testicular sarcoidosis on sonography to avoid unnecessary orchiectomy. This case study reports a young patient who had a prior history of unilateral orchiectomy for cryporchidism and presented with testicular lesions on the contralateral testis. He was later found to have skin lesions and chest symptoms that led to a diagnosis of sarcoidosis.

[Sarcoidosis and genetics]

Familial features of sarcoidosis and observations in monozygotic twins affected by the condition suggest the presence of a genetic predisposition. Various genetic associations have been described with genes coding for proteins involved in immune regulation in particular at the level of interaction between T-lymphocyte and antigen presenting cell. We review the various genetic targets described with techniques ranging from classic human lymphocyte antigen genotype to genome wide linkage scans. The 6p21 region has been highlighted, which includes relevant genes such as MHC class II, BTNL2 and TNFα. These studies show that the genetics of sarcoidosis are complex, that patient sub-groups exist, which may explain some of the heterogeneity in the results of genetic studies and that the interactions between genetic and environmental factors remains to be elucidated.

Transporter associated with antigen processing (TAP) 1 gene polymorphisms in patients with hypersensitivity pneumonitis

Hypersensitivity pneumonitis (HP) is a lung inflammatory disease caused by the inhalation of a variety of antigens. Previous studies support the role of the major histocompatibility complex (MHC) class II genes in the susceptibility to develop HP. However, the putative role of other MHC loci has not been elucidated. Transporters associated with antigen processing (TAP) genes are located within the MHC class II region and play an important role transporting peptides across the endoplasmic reticulum membrane for MHC class I molecules assembly. The distribution of single nucleotide polymorphisms (SNPs) in TAP1 genes was analyzed in 73 hypersensitivity pneumonitis (HP) patients and 58 normal subjects. We found a significant association of the allele Gly-637 (GGC) (p=0.00004, OR=27.30, CI=3.87-548.04) and the genotypes Asp-637/Gly-637 (p=0.01, OR=16.0, CI=2.19-631.21), Pro-661/Pro-661 (p=0.006, OR=11.30, CI=2.28-75.77) with HP. A significant decrease in the frequency of the allele Pro-661 (CCA) (p=0.008, OR=0.06, CI=0-0.45), the genotype Asp-637/Asp-637 (p=0.01, OR=0.17, 95% CI=0.05-0.58) and the haplotype [Val-333 (GTC), Val-458 (GTG), Gly-637 (GGC), Pro-661 (CCA)] was detected in HP patients compared with controls (p=0.002, OR=0.07, CI=0.0-0.57). These findings suggest that TAP1 gene polymorphisms are related to HP risk, and highlight the importance of the MHC in the development of this disease.

Association of TNF polymorphisms with sarcoidosis, its prognosis and tumour necrosis factor (TNF)-alpha levels in Asian Indians

Tumour necrosis factor (TNF)-alpha, an important proinflammatory cytokine, has been implicated in the pathogenesis of sarcoidosis, a multi-systemic granulomatous disorder of unknown aetiology. Here, we report for the first time the association of TNF haplotypes and genotypes with sarcoidosis and its prognosis in the Indian population. Five potentially functional promoter polymorphisms in the TNFA gene and a LTA_NcoI polymorphism (+252 position) of the LTA gene were genotyped in a clinically well-defined cohort of North-Indian patients with sarcoidosis (n = 96) and their regional controls (n = 155). Serum TNF-alpha (sTNF-alpha) and serum angiotensin converting enzyme (SACE) levels were measured and correlated with genotypes and haplotypes. The TNFA_-1031 and TNFA_-863 polymorphisms were identified as markers for disease onset (FET P = 0.006 and 0.042 for TNFA_-1031 and TNFA_-863, respectively). Additionally, the allele A of LTA_NcoI polymorphism was shown to be prevalent in the 'no treatment' group (FET P = 0.005), while the G allele was associated with frequent relapses on drug withdrawal (P = 0.057). Furthermore, the TNFA-308G>A and the TNFA-238G>A polymorphisms were found to influence sTNF-alpha (P = 0.054 and 0.0005, respectively) and SACE levels (P = 0.0017 and 0.056, respectively). The haplotype frequencies were significantly different in the patients and the controls (P = 0.0067). The haplotype GTCCGG was identified as the major risk/susceptibility haplotype (P = 0.003) and was associated with increased SACE levels in the patient population. In conclusion, our study suggests an association of TNF polymorphisms with sarcoidosis.

HLA class II amino acid epitopes as susceptibility markers of sarcoidosis

Sarcoidosis is a multisystemic disorder of unknown etiology, affecting primarily the lung and characterized by epithelioid granulomas. Disease association studies showed human leukocyte antigen (HLA) class II to be related to sarcoidosis. Initially, we studied the association of sarcoidosis with DQB1, and in the present study, we evaluated all amino acid variants of the HLA-DPB1, -DQB1, -DRB1, -DRB3, -DRB4 and -DRB5 genes to identify possible polymorphisms associated with the disease. Patients and controls were typed for class II genes to the allele level by sequence-based typing. Multiple logistic regression models showed DRAla71 and DQPhe9 to be independently associated with the disease. Subdivision of patients according to their radiographic stage resulted in identification of DRArg74 as independent associated residue in the RS I group, whereas DRAla71 and DQTyr30 were associated with RS II-IV groups. Polymorphic residues specifically associated with sarcoidosis shed new light on the characteristics of sarcoidosis-triggered peptides. Overall, pocket 9 of DQ and pocket 4 of DR seem to be the most important areas involved in the association with sarcoidosis.

Genetics of sarcoidosis

The predisposition to sarcoidosis is genetically determined, and genetics appears also to account for the variability in clinical phenotype and behaviour. Many genetic loci have been investigated to date, mainly in case-control association studies. However, only a small number of human leukocyte antigen (HLA) alleles have been consistently associated with sarcoidosis susceptibility/phenotype. In this regard, the association between Löfgren's syndrome and the extended HLA-DRB1*0301/DQB1*0201 haplotype is probably the most extensively reproduced. Several, generally less convincing, associations have been also reported. Of these, the chemokine receptor and butyrophilin-like 2 (BTNL2) associations are most promising. However, two major limitations of genetic studies are that the understanding of the biological relevance of gene variations in the genome is still incomplete and that the reported associations need to be verified in populations of different ethnicities. Despite a number of intriguing hypotheses, what causes sarcoidosis remains obscure. Genetic studies and, importantly, functional analysis of candidate genes will provide insight into pathogenesis and disease risk. However, if, as many believe, sarcoidosis is a heterogeneous collection of disorders, a critical step will be to carefully refine the clinical phenotype, as genetic studies of complex diseases are more rewording if a very specific disease subset is addressed.

Role of genetic polymorphisms in ACE and TNF-alpha gene in sarcoidosis: a meta-analysis

A great number of association studies have been performed to identify the genes involved in the etiology and prognosis of sarcoidosis. We performed a systematic review of case-control studies through the PubMed database and evaluated them for a possible inclusion into a meta-analysis in order to assess whether the reported genetic polymorphisms are the risk factors of sarcoidosis. Case-control studies with clear diagnostic criteria and interventions were included. Only investigations of a single polymorphism/gene involvement in sarcoidosis reported more than five times were selected. Aggregating data from 12 studies on ID/ACE polymorphisms, the odds ratio (OR) for sarcoidosis, if the polymorphism was considered under the dominant genetic model, was not significantly increased: 1.19 (95% CI 0.98-1.43); OR under the recessive model was 1.20 (95% CI 0.98-1.46). In seven case-control studies on -308/TNF-alpha polymorphism, the OR for sarcoidosis if the polymorphism considered under the dominant genetic model was significantly increased at 1.47 (95% CI 1.03-2.08); the OR under the recessive model was 1.39 (95% CI 0.67-2.90). In conclusion, the results showed that the TNF-alpha genotype could be a significant risk factor for sarcoidosis, whereas the risk of sarcoidosis due to the ACE genotype was not substantially elevated.

Genetics of Nickel Allergic Contact Dermatitis

Nickel sulfate is the most frequently detected cause of allergic contact dermatitis in the world; the prevalence of nickel allergic contact dermatitis is between 8 and 11% in the general female population. Although it is well recognized that environmental factors are important in the pathogenesis of this dermatitis, some investigators have hypothesized that genetic factors are important as well. This review summarizes animal and human studies evaluating genetic factors in the development of allergic contact dermatitis from nickel.

[Epidemiology of sarcoidosis]

La sarcoidosis es una enfermedad multisistémica que afecta frecuentemente al pulmón. Su incidencia y prevalencia han sido ampliamente estudiadas, pero la falta de estandarización del diagnóstico, los diferentes métodos de detección de casos y la escasa sensibilidad y especificidad de las pruebas diagnósticas explican los datos discordantes. El pronóstico es generalmente favorable. Gran parte de las personas afectadas no manifestarán nunca síntomas y muchas tienen remisión espontánea. El curso es crónico en el 10-30% de los casos, con un deterioro permanente de la función pulmonar. La enfermedad es el resultado de la acción de un agente externo que desencadena la respuesta inmunitaria característica en individuos genéticamente susceptibles. Se han implicado factores ambientales, ocupacionales y genéticos, pero las investigaciones están todavía en los inicios. Estudios de casos y controles, así como los avances en biología molecular, ayudarán a definir los factores de susceptibilidad genética y a entender los distintos fenotipos de la sarcoidosis.

The role of TAP1 and TAP2 gene polymorphism in idiopathic bronchiectasis in children

Bronchiectasis is characterized by permanent changes in the structure and function of the airways. Its cause cannot be identified in some cases. A genetic disease can predispose to bronchiectasis in our country, where consanguinity of parents is common. Transporter associated with antigen presentation (TAP) deficiency syndrome is characterized by recurrent bacterial lower respiratory tract infections, which cause bronchiectasis. Our aim was to document the relationship between idiopathic bronchiectasis and TAP gene polymorphisms. Forty-four patients with idiopathic bronchiectasis and 100 healthy individuals as the control group were included. DNA was extracted and gene polymorphisms for TAP1 and TAP2 were studied. When compared to healthy controls, in the patient group, Ile/Ile genotype was decreased and Ile/Val genotype was increased in TAP1-333 polymorphism analysis; Asp/Asp and Gly/Gly genotypes were decreased and Asp/Gly frequency was increased in TAP1-637 polymorphism analysis; Ile/Val genotype was increased and Ile/Ile genotype was decreased in TAP2-379 polymorphism analysis; and Thr/Thr genotype frequency was decreased and Thr/Ala and Ala/Ala genotypes were increased in TAP2-665 polymorphism analysis. No statistically significant difference between patient and control groups was noted only in TAP2-565 polymorphism analysis. These results indicate that TAP gene polymorphisms may have had a role in the development of bronchiectasis in our patient group. Therefore, TAP deficiency syndrome should be considered in children with idiopathic diagnosis, since early diagnosis of the disease will improve life quality and survival.

Racial and ethnic disparities in sarcoidosis: from genetics to socioeconomics

Sarcoidosis is a multisystem granulomatous disease of unknown cause that occurs worldwide. The clinical expression of sarcoidosis varies by race. These racial differences may be the result of genetic and socioeconomic factors. Many of these genetic associations are race-specific in that they are found in either African Americans or whites but not both. Socioeconomic differences may also explain the racial disparities between African American and white patients with sarcoidosis. Finally, the phenotypic differences be-tween races may relate to an interaction between genetics and socioeconomic factors. The influences of genetics and socioeconomic status on the development and phenotypic expression of sarcoidosis will be better understood as the mechanisms of disease development are uncovered.

Genome-wide search for sarcoidosis susceptibility genes in African Americans

Sarcoidosis, a systemic granulomatous disease of unknown etiology, likely results from an environmental insult in a genetically susceptible host. In the US, African Americans are more commonly affected with sarcoidosis and suffer greater morbidity than Caucasians. We searched for sarcoidosis susceptibility loci by conducting a genome-wide, sib pair multipoint linkage analysis in 229 African-American families ascertained through two or more sibs with a history of sarcoidosis. Using the Haseman-Elston regression technique, linkage peaks with P-values less than 0.05 were identified on chromosomes 1p22, 2p25, 5p15-13, 5q11, 5q35, 9q34, 11p15 and 20q13 with the most prominent peak at D5S2500 on chromosome 5q11 (P=0.0005). We found agreement for linkage with the previously reported genome scan of a German population at chromosomes 1p and 9q. Based on the multiple suggestive regions for linkage found in our study population, it is likely that more than one gene influences sarcoidosis susceptibility in African Americans. Fine mapping of the linked regions, particularly on chromosome 5q, should help to refine linkage signals and guide further sarcoidosis candidate gene investigation.

Clinical and immunologic components of sarcoidosis

Sarcoidosis is a multisystem granulomatous disease of unknown etiology that affects the lungs and the lymphatic system. It is seen by specialists in allergy, rheumatology, and pulmonary disease. Although there are no clues to etiology, an environmental basis has been implicated primarily on the basis of epidemiologic and anecdotal data. The majority of patients are very readily diagnosed and should not be confused with other pulmonary disorders. Sarcoidosis can become an issue if it occurs in the presence of other significant pulmonary disease, such as patients with asthma or hypersensitivity pneumonitis. Most patients remain asymptomatic and many are diagnosed when picked up on a routine screening exam. Steroids can be used to manage some patients but caution should be exercised to choose the appropriate dose and to treat patients for a limited period of time to avoid the complications of steroids. A minority of patients do progress to significant disease, including morbidity and mortality, and further research is needed to determine more appropriate and specific therapy for such situations.

HLA-DRB1*1101: a significant risk factor for sarcoidosis in blacks and whites

Sarcoidosis is a granulomatous disorder of unknown etiology, associated with an accumulation of CD4+ T cells and a TH1 immune response. Since previous studies of HLA associations with sarcoidosis were limited by serologic or low-resolution molecular identification, we performed high-resolution typing for the HLA-DPB1, HLA-DQB1, HLA-DRB1, and HLA-DRB3 loci and the presence of the DRB4 or DRB5 locus, to define HLA class II associations with sarcoidosis. A Case Control Etiologic Study of Sarcoidosis (ACCESS) enrolled biopsy-confirmed cases (736 total) from 10 centers in the United States. Seven hundred six (706) controls were case matched for age, race, sex, and geographic area. We studied the first 474 ACCESS patients and case-matched controls. The HLA-DRB1 alleles were differentially distributed between cases and controls (P<.0001). The HLA-DRB1*1101 allele was associated (P<.01) with sarcoidosis in blacks and whites and had a population attributable risk of 16% in blacks and 9% in whites. HLA-DRB1-F(47) was the amino acid residue most associated with sarcoidosis and independently associated with sarcoidosis in whites. The HLA-DPB1 locus also contributed to susceptibility for sarcoidosis and, in contrast to chronic beryllium disease, a non-E(69)-containing allele, HLA-DPB1*0101, conveyed most of the risk. Although significant differences were observed in the distribution of HLA class II alleles between blacks and whites, only HLA-DRB1*1501 was differentially associated with sarcoidosis (P<.003). In addition to being susceptibility markers, HLA class II alleles may be markers for different phenotypes of sarcoidosis (DRB1*0401 for eye in blacks and whites, DRB3 for bone marrow in blacks, and DPB1*0101 for hypercalcemia in whites). These studies confirm a genetic predisposition for sarcoidosis and present evidence for the allelic variation at the HLA-DRB1 locus as a major contributor.

Sarcoidosis susceptibility and resistance HLA-DQB1 alleles in African Americans

Sarcoidosis, in the United States, more commonly and severely affects African Americans. HLA associations with sarcoidosis have been reported, but most studies used case-control designs, which may produce biased results because of population stratification. We examined transmission of HLA-DQB1 alleles in 225 African American families with at least one offspring with sarcoidosis. Of five low-resolution HLA-DQB1 alleles, *02 and *06 showed significant deviation in transmission patterns to affected offspring. High-resolution typing of these allelic subsets revealed that HLA-DQB1*0201 was transmitted to affected offspring half as often as expected (p = 0.001), whereas DQB1*0602 was transmitted to affected offspring about 20% more often than expected (p = 0.029). Examining interactions between *0201 and *0602 alleles and environmental exposures showed that *0602 varied little with respect to exposure, but sarcoidosis risk associated with *0201 often depended on exposure status. Alternatively, the *0602 allele in affected probands was associated with radiographic disease progression, but the *0201 allele showed no significant correlation with phenotype. Major differences in the amino acid sequences encoded by *0201 and *0602 alleles exist, which may explain the differential effects these alleles have on sarcoidosis susceptibility and progression in African Americans.

Sarcoidosis

There have been several new insights into the cause and treatment of sarcoidosis. Studies of genetic variation have shown that specific genetic polymorphisms are associated with increased risk of disease or affect disease presentation. These polymorphisms include variation of MHC and cytokines such as tumour necrosis factor (TNF). Not all investigators have come to the same conclusion, suggesting an interaction of various factors, including the patient's ethnic origin. Treatment of sarcoidosis varies considerably. Patients with symptomatic disease for more than 2-5 years have been of particular interest. Corticosteroids remain the standard of care in such cases, but immunosuppressive drugs have proved steroid-sparing in many patients. New agents, including pentoxifylline, thalidomide, and infliximab have proved useful in selected cases. The effectiveness of these agents seems to lie in their ability to block TNF, especially in the treatment of chronic disease.

The major histocompatibility complex gene region and sarcoidosis susceptibility in African Americans

Investigators have intensively evaluated the major histocompatibility (MHC) complex for sarcoidosis susceptibility genes with the majority of reports implicating the human leukocyte antigen (HLA)-DRB1 gene. Because most studies have been performed in white and Asian populations, we sought to determine which MHC genes might be risk factors for sarcoidosis in African Americans. We genotyped six microsatellite markers spanning 11.6 megabases that overlapped the MHC region on chromosome 6p21-22 in 225 nuclear families ascertained by African American probands with a history of sarcoidosis. Using a family-based association methods approach, we performed multiallelic tests of association between each marker and sarcoidosis. A statistically significant association was detected between sarcoidosis and the DQCAR marker (p = 0.002) less than two kilobases telomeric from the HLA-DQB1 gene. Typing two additional markers in this region revealed that DQCAR-G51152 haplotypes, spanning a 38-kilobase region across the HLA-DQB1 gene, were associated with sarcoidosis on a global level (p = 0.022). Analysis of individual DQCAR and G51152 alleles showed that the DQCAR 178 (expected = 21.0; observed = 10; p = 0.0005) and G51152 217 (expected = 25.6; observed = 14; p = 0.0009) alleles were transmitted to affected offspring less often than expected; whereas the DQCAR 182 allele was transmitted more often than expected (expected = 52.6; observed = 66; p = 0.002). Our results indicate that HLA-DQB1 and not HLA-DRB1 plays an important role in sarcoidosis susceptibility in African Americans. Identification of the specific HLA-DQB1 alleles that influence sarcoidosis susceptibility in African Americans and the study of their antigenic-binding properties may reveal why African Americans suffer disproportionately from this disease.

Genotyping in the MHC locus: potential for defining predictive markers in sarcoidosis

In sarcoidosis, host genetic factors are discussed as contributing to disease susceptibility and course. Since tumor necrosis factor (TNF)-alpha is a central mediator of granuloma formation and since elevated TNF-alpha levels are found during active phases of sarcoidosis, genetic polymorphisms correlating with influences on TNF-alpha levels are of special interest. The complete sequencing of the MHC region and the increase in the number of identified gene polymorphisms in this locus associated with TNF-alpha production offer the opportunity of detecting new genes associated with sarcoidosis and perhaps of defining disease-associated haplotypes that bear the potential of serving as predictive markers for this disease.

Surfactant gene polymorphisms and interstitial lung diseases

Pulmonary surfactant is a complex mixture of phospholipids and proteins, which is present in the alveolar lining fluid and is essential for normal lung function. Alterations in surfactant composition have been reported in several interstitial lung diseases (ILDs). Furthermore, a mutation in the surfactant protein C gene that results in complete absence of the protein has been shown to be associated with familial ILD. The role of surfactant in lung disease is therefore drawing increasing attention following the elucidation of the genetic basis underlying its surface expression and the proof of surfactant abnormalities in ILD.

Histocompatibility leucocyte antigens and closely linked immunomodulatory genes in autoimmune thyroid disease

OBJECTIVES

Associations between autoimmune thyroid disease and antigens of the major histocompatibility complex (MHC) have long been recognized. Graves' disease (GD) is associated with the histocompatibility leucocyte antigen (HLA) haplotype A*01-B*0801-DRB1*0301-DQA1*0501-DQB1*0201 (or B8/DR3) whereas autoimmune hypothyroidism (AIH) has been weakly associated with HLA DRB1*03, *04 and *11/*12 alleles (or DR3, DR4 and DR5). However, the presence of important immunoregulatory genes within the HLA Class II and III regions raises the possibility that these genes harbour the primary susceptibility locus. This study examines genetic variation across the MHC in UK Caucasoid subjects with autoimmune thyroid disease.

PATIENTS AND METHODS

DNA extracted from venous blood samples from 215 patients with autoimmune thyroid disease (GD 135, AIH 77) and 267 control subjects was analysed. Genotyping was performed using polymerase chain reaction and sequence specific primers for HLA Class I and II alleles and polymorphisms within the TAP1, TAP2, tumour necrosis factor (TNF), lymphotoxin alpha (LTalpha), heat shock protein (HSP)70-1, HSP70-2 and HSP70-Hom genes.

RESULTS

For GD, the strongest association was with DRB1*03 [56% patients positive vs. 24% controls, P = 2 x 10(-10), odds ratio (OR) 4.0]. Positive associations were also seen for DRB1*03 linked alleles, B*0801, DRB3*01/02, DQA1*05, DQB1*02 and DPB1*0101 (OR 2.3-3.4). Specific TNF and LTalpha alleles were strongly associated with GD (Pc = 3 x 10(-5) and 0.001) and weak associations were seen for HSP70-1 + 190C and HSP70-2 + 1267G polymorphisms (Pc = 0.05 and 0.01). These associations were not significant when DRB1*03 status was considered. Patients with AIH showed only a weak association with DQB1*03 (P = 0.02).

CONCLUSIONS

These results show that, of the polymorphisms tested within the MHC, GD is most strongly associated with DRB1*03, and associations with other immunoregulatory genes previously described in Caucasian subjects most likely reflect linkage disequilibrium. AIH differs from GD, being less influenced by the MHC region.

Human leukocyte antigen-DRB1 position 11 residues are a common protective marker for sarcoidosis

Genetic factors, in particular human leukocyte antigens (HLAs) are important determinants of susceptibility to sarcoidosis, a chronic granulomatous disease of undetermined etiology. To clarify the role of HLA in sarcoidosis we determined HLA-DR and -DQ alleles in case-control samples from three European populations (United Kingdom, Czech, and Polish) and compared these results with those published for three additional populations (Italian, Japanese, and Scandinavian) to determine whether the HLA-DR and/or -DQ alleles act as ethnic-dependent, or ethnic-independent modifiers of disease risk. Although variations were apparent in the alleles associated with susceptibility, reductions in the frequency of alleles associated with protection were remarkably consistent in the six populations. Previously detected associations between single-nucleotide polymorphisms at the TAP2 locus and sarcoidosis were shown to be due to linkage disequilibrium with the HLA-DR locus. The protective HLA-DR alleles, which encode the DR1 and DR4 antigens, were found to share characteristic small hydrophobic residues at position 11, which were replaced by small hydrophilic residues in the remaining, nonprotective, HLA-DR alleles. This residue position is within a pocket of the HLA-DR complex antigen binding groove (designated P6), where it is the only variable amino acid and therefore determines the peptide binding preferences of this pocket. A highly significant reduction in the frequency of individuals carrying HLA-DR alleles with a hydrophobic residue at position 11 was observed in the sarcoidosis cases in the three populations we examined. This suggests this HLA-DR residue is an important protective marker in sarcoidosis.

Human leukocyte antigen genes may outweigh racial background when generating a specific immune response in sarcoidosis

Presented is a sarcoidosis patient of African origin, who was adopted at an early age and grew up in Sweden. This patient displayed an immune response identical to that previously reported in human leukocyte antigen (HLA)-DR17 positive Caucasian sarcoidosis patients in Scandinavia, with T-cell receptor AV2S3+ T-cells accumulating in the lungs. HLA typing also established that she was DR17 positive, which is a rare HLA type for individuals of African origin. To the authors' knowledge, this specific immune response has not previously been reported in patients of African origin. Moreover, the clinical manifestations of sarcoidosis were similar to those known to be strongly linked to HLA-DR17 in Scandinavians, i.e. with Löfgren's syndrome. The case presented here suggests certain human leukocyte antigen genes to be strongly linked to specific immune responses that are identical irrespective of the racial background. If such an immune response were important for the subsequent clinical manifestations, this case would argue for the importance of human leukocyte antigen genes in the genetic predisposition to sarcoidosis.

Familial sarcoidosis is linked to the major histocompatibility complex region

Sarcoidosis is a systemic granulomatous disorder associated with high CD4+ cell activity, but no pathogen is detectable. Clustering in families occurs, and the existence of a genetic predisposition to sarcoidosis is widely accepted. The major histocompatibility complex (MHC) is believed to contribute to this susceptibility. Many studies testing this hypothesis have produced conflicting results. We have genotyped 122 affected siblings from 55 families for seven DNA polymorphisms that flank and cover the MHC region on chromosome 6, and for HLA-DPB1, a candidate gene for granulomatous disorders. Multipoint nonparametric linkage (NPL) analysis showed linkage (NPL score > 2.5; p < 0.006) for the entire MHC region with a maximum NPL score of 3.2 (p = 0.0008) at marker locus D6S1666 in the Class III gene cluster. There was a significant excess of marker haplotype sharing among affected siblings. However, the frequency of HLA-DPB1 alleles on 104 shared chromosomes did not differ from that of a control group of founders from the family panel. Transmission disequilibrium was found for allele DPB1*0201, but only nine families contributed to this result. We conclude that genes of the MHC are involved in the genetic predisposition to sarcoidosis, but HLA-DPB1 alone does not sufficiently explain this fact.

Epidemiology of familial sarcoidosis in the UK

BACKGROUND

The last comprehensive epidemiological studies on familial sarcoidosis in the UK were more than 25 years ago, reporting another affected family member in 1.7% of index cases. A significant proportion of like-sex over unlike-sex pairs, an excess of mother-child over father-child associations, and a preponderance of monozygous over dizygous twins was noted. Another study reported ethnic heterogeneity in familial disease. This study was undertaken to identify the risk ratio (lambda(S)) for siblings of familial sarcoidosis in the UK, to determine if the previous epidemiological findings have persisted, and to reassess whether ethnic heterogeneity prevails in familial disease.

METHOD

Questionnaires were sent to 406 index patients.

RESULTS

Two hundred and sixty eight replies (66%) were received. Twenty four of the original 406 index patients (5.91%) were found to have at least one other relative (first, second or third degree) with biopsy proven sarcoidosis. A lambda(S) value of 36-73 was calculated indicating significant familial clustering of the disease. Ethnically the families comprised 62.5% Caucasian, 29.2% Afro-Caribbean, and 8.3% Asian. Mean age at diagnosis was 39.8 years for women and 40.9 years for men with a male to female ratio of 1:1.7. This differed for the Asian families in which all the affected members were male. Three sets of female twins (two monozygous and one dizygous) were included. There was an equal distribution of like-sex (primarily female) and unlike-sex families as well as mother-child and father-child pairs. Pulmonary involvement was predominant irrespective of ethnicity, as was the need for corticosteroid treatment.

CONCLUSIONS

These results support the theory that a shared determinant (either genetic or environmental) is operating in familial sarcoidosis and suggest that this determinant is similar for all ethnic groups.

Neurosarcoidosis

Although there continues to be sporadic reporting of small numbers of patients with neurosarcoidosis, relatively little progress is being made in defining this condition in more detail, making it difficult for clinicians to be confident in their diagnoses and treatments. Although groups continue to use retrospective data to extrapolate diagnostic criteria, there is a need for a multinational collaboration to produce a prospective data set that would more adequately inform the diagnostic and therapeutic process for individual clinicians.