Genetics of sarcoidosis

Ocular sarcoidosis in adults and children: update on clinical manifestation and diagnosis

Sarcoidosis-associated uveitis, is the predominant ocular sarcoidosis presentation, which affects both adults and children. For adults, international ocular sarcoidosis criteria (IWOS) and sarcoidosis-associated uveitis criteria (SUN) are defined. However, for children they are not yet established internationally. Due to the specificity of pediatric manifestations of sarcoidosis, this task is even more challenging. In children, sarcoidosis is subdivided into Blau syndrome and early-onset sarcoidosis (BS/EOS) affecting younger children (< 5 years) and the one affecting older children with clinical presentation resembling adults. Differential diagnosis, clinical work-up as well as diagnostic criteria should be adapted to each age group. In this article, we review the clinical manifestation of sarcoidosis-associated uveitis in adults and children and the sensitivity and specificity of various ocular sarcoidosis diagnostic modalities, including chest X-ray and CT, FDG PET-CT, gallium-67 scintigraphy, bronchoalveolar lavage fluid, genetic testing for NOD2 mutations and serum biomarkers, such as ACE, lysozyme and IL2R.

Fungal central skull-base osteomyelitis: atypical presentation and management issues

Mucormycosis is a very commonly encountered disease in the sinonasal region in patients with diabetes and immunocompromised status specially in the northern part of the Indian continent. Due to its fulminant nature and involvement in the rhino-orbital-cerebral region, prognosis is poor even after extensive debridement and amphotericin-B therapy. We present a case with diagnosis of sarcoidosis being treated with systemic steroids who developed sudden-onset ptosis and left lateral rectus palsy. On radiological evaluation with MRI, a heterogenously peripherally enhancing lesion was seen in the nasopharynx suggestive of nasopharyngeal abscess. The patient was taken up for emergency surgery; a necrotic lesion with destruction of sphenoid bone, pterygoids and clivus was seen originating in the nasopharynx. The lesion on fungal staining came out to be broad aseptate hyphae suggestive of mucormycosis.

Exome Sequencing Identifies Susceptibility Loci for Sarcoidosis Prognosis

Many sarcoidosis-associating immunological genes have been shown to be shared between other immune-mediated diseases. In Finnish sarcoidosis patients, good prognosis subjects more commonly have HLA-DRB1*03:01 and/or HLA-DRB1*04:01-DPB1*04:01 haplotype, but no marker for persistent disease have been found. The objective was to further pinpoint genetic differences between prognosis subgroups in relation to the HLA markers. Whole-exome sequencing was conducted for 72 patients selected based on disease activity (resolved disease, n = 36; persistent disease, n = 36). Both groups were further divided by the HLA markers (one/both markers, n = 18; neither of the markers, n = 18). The Finnish exome data from the Genome Aggregation Database was used as a control population in the WES sample. Statistical analyses included single-variant analysis for common variants and gene level analysis for rare variants. We attempted to replicate associated variants in 181 Finnish sarcoidosis patients and 150 controls. An association was found in chromosome 1p36.21 (AADACL3 and C1orf158), which has recently been associated with sarcoidosis in another WES study. In our study, variations in these genes were associated with resolved disease (AADACL3, p = 0.0001 and p = 0.0003; C1orf158, p = 7.03E-05). Another interesting chromosomal region also peaked, Leucocyte Receptor Complex in 19q13.42, but the association diminished in the replication sample. In conclusion, this WES study supports the previously found association in the region 1p36.21. Furthermore, a novel to sarcoidosis region was found, but additional studies are warranted to verify this association.

Prediction of Disordered Regions and Their Roles in the Anti-Pathogenic and Immunomodulatory Functions of Butyrophilins

Butyrophilins (BTNs) are a group of the moonlighting proteins, some members of which are secreted in milk. They constitute a large family of structurally similar type 1 transmembrane proteins from the immunoglobulin superfamily. Although the founding member of this family is related to lactation, participating in the secretion, formation and stabilization of milk fat globules, it may also have a cell surface receptor function. Generally, the BTN family members are known to modulate co-stimulatory responses, T cell selection, differentiation, and cell fate determination. Polymorphism of these genes was shown to be associated with the pathology of several human diseases. Despite their biological significance, structural information on human butyrophilins is rather limited. Based on their remarkable multifunctionality, butyrophilins seem to belong to the category of moonlighting proteins, which are known to contain intrinsically disordered protein regions (IDPRs). However, the disorder status of human BTNs was not systematically investigated as of yet. The goal of this study is to fill this gap and to evaluate peculiarities of intrinsic disorder predisposition of the members of human BTN family, and to find if they have IDPRs that can be attributed to the multifunctionality of these important proteins.

Disease marker combination enhances patient characterization in the Finnish sarcoidosis patients

Sarcoidosis is an inflammatory disease of unknown etiology and multiple clinical phenotypes. Clinical manifestations range from asymptomatic disease to severe loss-of-function leading to the hypothesis that sarcoidosis might not be just one disease, but consists of several distinct disease entities each with potentially distinct genetic associations. We have previously demonstrated that in our series HLADRB1* 03:01 and haplotype HLA-DRB1*04:01-DPB1*04:01 are associated with good prognosis sarcoidosis. In our recent work, we found a novel SNP (rs9905945) in the 5'upstream region of the ACE gene to be associated with favorable disease prognosis as well. The main objective of this study was to expand the previous results and analyse combined influence of the found ACE SNP rs9905945 with the protective HLA markers HLADRB1* 03:01 and HLA-DRB1*04:01-DPB1*04:01 in 188 Finnish sarcoidosis patients (resolved disease, n = 90; persistent disease, n = 98). When combining the frequencies of the rs9905945 and of the HLA markers, the strongest association was found for a combination of either/or both HLA markers and rs9905945 for good disease prognosis (37.1% in resolved vs. 11.3% in persistent, p < 0.001, OR = 4.61, (95%CI 2.15-9.86)). In conclusion, we discovered that a combination of the ACE SNP rs9905945 and HLA markers enhance the accuracy for predicting disease course in Finnish sarcoidosis patients further characterizing genetic differences between Finnish sarcoidosis patients with different prognosis.

Genetics of Tinnitus: Still in its Infancy

Tinnitus is the perception of a phantom sound that affects between 10 and 15% of the general population. Despite this considerable prevalence, treatments for tinnitus are presently lacking. Tinnitus exhibits a diverse array of recognized risk factors and extreme clinical heterogeneity. Furthermore, it can involve an unknown number of auditory and non-auditory networks and molecular pathways. This complex combination has hampered advancements in the field. The identification of specific genetic factors has been at the forefront of several research investigations in the past decade. Nine studies have examined genes in a case-control association approach. Recently, a genome-wide association study has highlighted several potentially significant pathways that are implicated in tinnitus. Two twin studies have calculated a moderate heritability for tinnitus and disclosed a greater concordance rate in monozygotic twins compared to dizygotic twins. Despite the more recent data alluding to genetic factors in tinnitus, a strong association with any specific genetic locus is lacking and a genetic study with sufficient statistical power has yet to be designed. Future research endeavors must overcome the many inherent limitations in previous study designs. This review summarizes the previously embarked upon tinnitus genetic investigations and summarizes the hurdles that have been encountered. The identification of candidate genes responsible for tinnitus may afford gene based diagnostic approaches, effective therapy development, and personalized therapeutic intervention.

Immunogenetics of Disease-Causing Inflammation in Sarcoidosis

Sarcoidosis is a systemic inflammatory disorder characterised by tissue infiltration by mononuclear phagocytes and lymphocytes with associated non-caseating granuloma formation. Originally described as a disorder of the skin, sarcoidosis can involve any organ with wide-ranging clinical manifestations and disease course. Recent studies have provided new insights into the mechanisms involved in disease pathobiology, and we now know that sarcoidosis has a clear genetic basis largely involving human leukocyte antigen (HLA) genes. In contrast to Mendelian-monogenic disorders--which are generally due to specific and relatively rare mutations often leading to a single amino acid change in an encoded protein--sarcoidosis results from genetic variations relatively common in the general population and involving multiple genes, each contributing an effect of varying magnitude. However, an individual may have the necessary genetic profile and yet the disease will not develop unless an environmental or infectious factor is encountered. Genetics appears also to contribute to the huge variability in clinical phenotype and disease behaviour. Moreover, it has been established that sarcoidosis granulomatous inflammation is a highly polarized T helper 1 immune response that starts with an antigenic stimulus followed by T cell activation via a classic HLA class II-mediated pathway. A complex network of lymphocytes, macrophages, and cytokines is pivotal in the orchestration and evolution of the granulomatous process. Despite these advances, the aetiology of sarcoidosis remains elusive and its pathogenesis incompletely understood. As such, there is an urgent need for a better understanding of disease pathogenesis, which hopefully will translate into the development of truly effective therapies.

Sarcoidosis: a Critical Review of History and Milestones

Sarcoidosis is a chronic systemic disease of unknown origin and uncertain prognosis that most commonly affects young adults, and frequently presents with bilateral hilar lymphadenopathy, pulmonary infiltrates and ocular and skin lesions. The diagnosis is established when characteristic clinical-radiological features are supported by compatible histopathology of epithelioid cell granulomas, following exclusion of known causes of granulomatous inflammation. Indeed, sarcoidosis belongs to a large family of disorders that share granuloma formation as common denominator. Since its first description by Jonathan Hutchinson in 1869, sarcoidosis has generated enormous interest and considerable controversy. In Hutchinson's day, it was considered a dermatological condition, which gradually evolved into a multisystem disorder associated in the majority of cases with respiratory abnormalities. With time, it has also become clear that sarcoidosis occurs throughout the world, affecting individuals of both genders and all races, although its prevalence varies widely across ethnic and racial groups. In recent years, advances in different disciplines, particularly biochemistry, genetics, immunology and molecular biology, have improved dramatically our understanding of the disease. Yet, the critical questions regarding who gets sarcoidosis and whether it has an infectious origin remain unanswered. Sarcoidosis has a distinguished medical history that covers the last 150 years. Right from the time of seminal contributions by Hutchinson, Besnier and Boeck medical discussion on sarcoidosis has always been animated and to a certain extent emotional. Such discussions will inevitable continue until the true cause of the disease has been found, hopefully in the near future.

Sarcoidosis: the links between epidemiology and aetiology

Sarcoidosis is a multisystem inflammatory disease, the aetiology of which has still to be resolved. The proposed mechanism is that a susceptible genotype is exposed to one or more potential antigens. A sustained inflammatory response follows, which ultimately results in pathognomonic granuloma formation. Various clinical phenotypes exist with specific genetic associations influencing disease susceptibility, protection, and clinical progression. Occupational and environmental factors, including microbial elements, may then effect the development of this disease. Sarcoidosis is a heterogeneous disease, showing geographic and racial variation in clinical presentation. It demonstrates a familial tendency and clear genotype associations. Additionally, it appears to cluster within closely associated populations (eg, work colleagues) and appears to be related to selected occupations and environmental exposures. Frequently occult, but occasionally fatal, this disease has a very variable prognosis. It is also unusual in having no specific biomarker. The epidemiology and multiple factors that appear to influence the aetiology of sarcoidosis illustrate why this disease state is frequently described as a clinical enigma.

Cardiac sarcoidosis: diagnosis and management

Cardiac sarcoidosis is one of the most serious and unpredictable aspects of this disease state. Heart involvement frequently presents with arrhythmias or conduction disease, although myocardial infiltration resulting in congestive heart failure may also occur. The prognosis in cardiac sarcoidosis is highly variable, which relates to the heterogeneous nature of heart involvement and marked differences between racial groups. Electrocardiography and echocardiography often provide the first clue to the diagnosis, but advanced imaging studies using positron emission tomography and MRI, in combination with nuclear isotope perfusion scanning are now essential to the diagnosis and management of this condition. The identification of clinically occult cardiac sarcoidosis and the management of isolated and/or asymptomatic heart involvement remain both challenging and contentious. Corticosteroids remain the first treatment choice with the later substitution of immunosuppressive and steroid-sparing therapies. Heart transplantation is an unusual outcome, but when performed, the results are comparable or better than heart transplantation for other disease states. We review the epidemiology, developments in diagnostic techniques and the management of cardiac sarcoidosis.

Sarcoidosis and cancer risk: systematic review and meta-analysis of observational studies

BACKGROUND

An increased cancer risk in patients with sarcoidosis has been suggested, although results are conflicting in a number of case-control and cohort studies. We conducted a systematic review of all available data and performed a meta-analysis to better define and quantify the association between sarcoidosis and cancer.

METHODS

We searched Medline and Embase for all original articles on cancer and sarcoidosis published up to January 2013. Two independent authors reviewed all titles/abstracts to identify studies according to predefined selection criteria. We derived summary estimates using a random-effects model and reported them as relative risk (RR). Publication bias was evaluated using a funnel plot and was quantified by the Egger test.

RESULTS

Sixteen original studies, involving > 25,000 patients, were included in the present review. The summary RR to develop all invasive cancers was 1.19 (95% CI, 1.07-1.32). The results for selected cancer sites indicated a significantly increased risk of skin (RR, 2.00; 95% CI, 1.69-2.36), hematopoietic (RR, 1.92; 95% CI, 1.41-2.62), upper digestive tract (RR, 1.73; 95% CI, 1.07-2.79), kidney (RR, 1.55; 95% CI, 1.21-1.99), liver (RR, 1.79; 95% CI, 1.03-3.11), and colorectal cancers (RR, 1.33; 95% CI, 1.07-1.67). There was no evidence of publication bias for all cancers (P = .9), nor for any specific cancer site.

CONCLUSIONS

The present meta-analysis suggests a significant, though moderate, association between sarcoidosis and malignancy.

Genetic testing in diffuse parenchymal lung disease

Diffuse parenchymal lung diseases (DPLD) represent a diverse group of disorders affecting the distal lung parenchyma, specifically the tissue and spaces surrounding the alveoli, which may be filled with inflammatory cells, proliferating fibroblasts or established fibrosis, often leading to architectural distortion and impaired gas exchange. While the underlying pathogenetic mechanisms are known or inferred for some DPLD (such as sarcoidosis, silicosis, drug reactions and collagen vascular diseases), the pathogenesis of the majority of these entities - particularly those characterized by progressive fibrosis - is poorly understood.

Several lines of evidence indicate that the development of pulmonary fibrosis is genetically determined. They include: 1. familial clustering; 2. the occurrence of pulmonary fibrosis in the context of rare inherited disorders; 3. substantial variability in the development of pulmonary fibrosis amongst individuals exposed to organic or inorganic dusts; 4. difference in susceptibility to fibrogenic stimuli amongst inbred strains of mice.

This review focuses on idiopathic pulmonary fibrosis (IPF) and sarcoidosis, the two most common DPLD and the two entities for which there is stronger evidence of a genetic predisposition, although how aberrant genes interact with each other and with environmental factors, such as smoking in IPF and infectious agents in sarcoidosis, in determining disease susceptibility and clinical phenotypes is largely unknown. Finally, we discuss practical issues and implications for both patients and physicians of recent advances in the genetics of sarcoidosis and IPF.

Sarcoidosis and molecular mimicry--important etiopathogenetic aspects: current state and future directions

Sarcoidosis is a disease of uncertainty in terms of its cause, presentation, and clinical course. The disease has a worldwide distribution and affects all ages, races, and both sex. Sarcoidosis of the skin may have an extremely heterogeneous clinical presentation, so that the definitions of 'great imitator' and 'clinical chameleon' have long been used. The factors that influence clinical picture and severity of the disease are probably linked to the etiopathogenesis of sarcoidosis, which continues to be shrouded in mystery. The current state of the art on the pathogenesis of sarcoidosis is that it is an immunological response in a genetically susceptible individual to an as-yet undefined antigenic stimulus. How exposure occurs in genetically predisposed patients is not completely clear, but the most likely explanation is that these agents or antigens are either inhaled into the lungs or enter through contact with the skin, as these are the common target organs that are constantly in contact with the environment. An autoimmune etiology of sarcoidosis could possibly occur through a process of molecular mimicry of infectious or other environmental antigens to host antigens. This could lead to a cross-mediated immune response and induction of autoimmune disease. This molecular mimicry may probably be responsible for the heterogeneous clinical presentations of the disease. Several investigations and studies have provided valuable evidence on the etiopathogenesis of sarcoidosis, which may lead to the future development of targeted and innovative treatment strategies. Nevertheless, we are still a long way from unravelling the underlying cause of this mysterious disease.

Sarcoidosis: challenging diagnostic aspects of an old disease

Over the past few years, there have been substantial advances in our understanding of sarcoidosis immunopathogenesis. Conversely, the etiology of the disease remains obscure for a number of reasons, including heterogeneity of clinical manifestations, often overlapping with other disorders, and insensitive and nonspecific diagnostic tests. While no cause has been definitely confirmed, there is increasing evidence that one or more infectious agents may cause the disease, although the organism may no longer be viable. Here we present 2 cases, in which sarcoidosis preceded tuberculosis and non-Hodgkin lymphoma. Development of new lesions in a patient with chronic/remitting sarcoidosis should be looked at with suspicion and promptly investigated in order to rule out an alternative/concomitant diagnosis. In such cases, tissue confirmation from the most accessible site, and bone marrow biopsy-if lymphoma is in the differential diagnosis-should be performed. In conclusion, we strongly advise that physicians be ready to reconsider the diagnosis of sarcoidosis in the presence of atypical manifestations or persistent/progressive disease despite conventional therapy.

Major histocompatibility complex class II transactivator gene polymorphism: associations with Löfgren's syndrome

The major histocompatibility complex (MHC) class II transactivator (MHC2TA) is known as a master regulator for expression of MHC class II molecules. In the present study, we investigated the influence on the risk for sarcoidosis of two variants of the MHC2TA gene, selected from previous association studies of inflammatory diseases. Seven hundred and twenty-eight sarcoidosis patients and 873 controls matched by ethnicity were included in the study. Patients were classified as with Löfgren's syndrome (or not) as subphenotypes. Individuals were genotyped for two single nucleotide polymorphisms (SNPs) of the MHC2TA gene, rs3087456 A/G and rs11074932 C/T, and were human leukocyte antigen (HLA)-DRB1-typed. After correction for multiple testing, our data showed a significant association with Löfgren's syndrome in allelic model for the rs3087456 SNP, which was not detected in non-Löfgren's patients. A similar trend was noted for the rs11074932 SNP. These risk factors were independent of HLA-DRB1*03, which is known to be associated with Löfgren's syndrome. The finding of a new genetic association between Löfgren's syndrome and MHC2TA gene polymorphisms, which seems independent of HLA-DRB1*03 and relates to the expression of MHC class II molecules, strongly supports the idea that Löfgren's syndrome is a separate disease entity.

Hypothesis: sarcoidosis is a STAT1-mediated disease

Immunologic pathways involved in sarcoidosis pathogenesis are largely unknown. We hypothesized that patients with sarcoidosis have characteristic mRNA profiles. Microarray analysis of gene expression was done on peripheral blood (12 patients, 12 controls), lung (6 patients, 6 controls) and lymph node (8 patients, 5 controls). Comparing peripheral blood from patients with sarcoidosis to controls, 872 transcripts were upregulated and 1039 were downregulated at >1.5-fold change and a significant q value. Several transcripts associated with interferon and STAT1 were upregulated. Lung and lymph node analyses also showed dramatic increases in STAT1 and STAT1-regulated chemokines. Granulomas in lymph nodes of patients with sarcoidosis expressed abundant STAT1 and phosphorylated STAT1. STAT1 might play an important role in sarcoidosis. This novel hypothesis unites seemingly disparate observations with regard to sarcoidosis including implication of a casual role for interferons, a suspected infectious trigger, T(H)1 predominating lymphocytes in bronchoalveolar lavage, and the association with hypercalcemia.

Löfgren's syndrome: human leukocyte antigen strongly influences the disease course

RATIONALE

Sarcoidosis may consist of a number of distinct disease entities, one of which could be Löfgren's syndrome. Patients with Löfgren's syndrome have an acute onset of erythema nodosum (EN) and/or periarticular inflammation or arthritis of the ankles, with bilateral hilar lymphadenopathy (and in some cases parenchymal infiltrates) and usually fever. There is a known association between HLA-DRB1*03 and Löfgren's syndrome.

OBJECTIVES

To investigate whether human leukocyte antigen type influences clinical manifestations, including the disease course in Löfgren's syndrome.

METHODS

We clinically characterized and HLA-DRB1 typed 301 patients with Löfgren's syndrome. A total of 275 of the patients were followed for more than 2 years and classified as having a nonresolving or a resolving disease.

MEASUREMENTS AND MAIN RESULTS

Almost every DRB1*03-positive patient had a resolving disease within 2 years, and 49% of the DRB1*03-negative patients developed a nonresolving disease. Mucosal granulomas were identified significantly more often in DRB1*03-negative patients. Among DRB1*03-negative patients who were treated with oral steroids at disease onset, 80% developed a nonresolving disease.

CONCLUSIONS

Patients with Löfgren's syndrome have a different disease course depending on whether they are DRB1*03 positive or not. This observation has clinical implications, and by comparing DRB1*03-positive and DRB1*03-negative patients with Löfgren's syndrome, we can search for additional markers of importance for developing a resolving or a nonresolving disease, respectively.

Genetics of sarcoidosis

PURPOSE OF REVIEW

Increased familial occurrences as well as different disease modes in different ethnic groups suggest a genetic influence in sarcoidosis. Also, genetic analyses have revealed a number of chromosomal regions and specific genes associated with sarcoidosis. This review brings up some recent discoveries on the genetic contribution to sarcoidosis.

RECENT FINDINGS

As a more detailed clinical classification of patients is performed, stronger genetic associations between distinct clinical phenotypes and specific gene variants have been revealed. The strong association between human leucocyte antigen DRB10301/DQB10201 and good prognosis in patients with Löfgren's syndrome is one such recent example. Linkage studies have revealed certain chromosomal regions of interest and furthermore pointed out specific genes of interest, for example, a variant of the butyrophilin-like 2 gene.

SUMMARY

Sarcoidosis is a complex disease which is influenced by a multitude of genes and environmental factors. The strongest genetic associations are found within the human leucocyte antigen region, in which several specific human leucocyte antigen alleles clearly associate with disease risk and phenotype, but additional genes in the same region may turn out to be important as well. Future studies on large, clinically well defined patient cohorts will help to elucidate the genetic impact on sarcoidosis.

The immunology of sarcoidosis

Sarcoidosis continues to be a disease of research interest because of its complicated immune mechanisms and elusive etiology. So far, it has been established that granulomatous inflammation in sarcoidosis is predominantly a T-helper 1 immune response mediated by a complex network of lymphocytes, macrophages, and cytokines. The cause of progression to a chronic and potentially fibrotic form is unclear but may involve loss of apoptotic mechanisms, loss of regulatory response, or a persistent antigen that cannot be cleared. Recent genomic and proteomic technology has emphasized the importance of host susceptibility and gene-environment interaction in the expression of the disease.

Gene-environment interactions in sarcoidosis: challenge and opportunity

Susceptibility to most human diseases is polygenic, with complex interactions between functional polymorphisms of single genes governing disease incidence, phenotype, or both. In this context, the contribution of any discrete gene is generally modest for a single individual, but may confer substantial attributable risk on a population level. Environmental exposure can modify the effects of a polymorphism, either by providing a necessary substrate for development of human disease or because the effects of a given exposure modulate the effects of the gene. In several diseases, genetic polymorphisms have been shown to be context dependent, ie, the effects of a genetic variant are realized only in the setting of a relevant exposure. Because sarcoidosis susceptibility is dependent on both genetic and environmental modifiers, the study of gene-environment interactions may yield important pathogenetic information and will likely be crucial for uncovering the range of genetic susceptibility loci. The complexity of these relationships implies, however, that investigations of gene-environment interactions will require the study of large cohorts with carefully defined exposures and similar clinical phenotypes. A general principle is that the study of gene-environment interactions requires a sample size at least severalfold greater than for either factor alone. To date, the presence of environmental modifiers has been demonstrated for one sarcoidosis susceptibility locus, HLA-DQB1, in African-American families. This article reviews general considerations obtaining for the study of gene-environment interactions in sarcoidosis. It also describes the limited current understanding of the role of environmental influences on sarcoidosis susceptibility genes.