The immunogenetics of neurological disease

Genes encoding antigen‐presenting molecules within the human major histocompatibility complex (MHC) account for the highest component of genetic risk for many neurological diseases, such as multiple sclerosis, neuromyelitis optica, Parkinson's disease, Alzheimer's disease, schizophrenia, myasthenia gravis and amyotrophic lateral sclerosis. Myriad genetic, immunological and environmental factors may contribute to an individual's susceptibility to neurological disease. Here, we review and discuss the decades long research on the influence of genetic variation at the MHC locus and the role of immunogenetic killer cell immunoglobulin‐like receptor (KIR) loci in neurological diseases, including multiple sclerosis, neuromyelitis optica, Parkinson's disease, Alzheimer's disease, schizophrenia, myasthenia gravis and amyotrophic lateral sclerosis. The findings of immunogenetic association studies are consistent with a polygenic model of inheritance in the heterogeneous and multifactorial nature of complex traits in various neurological diseases. Future investigation is highly recommended to evaluate both coding and non‐coding variation in immunogenetic loci using high‐throughput high‐resolution next‐generation sequencing technologies in diverse ethnic groups to fully appreciate their role in neurological diseases.     

The Contribution of Immune Regulatory and Thyroid Specific Genes to the Etiology of Graves' and Hashimoto's Diseases

The autoimmune thyroid diseases (AITD) are complex diseases which are caused by an interaction between susceptibility genes and environmental triggers. Genetic susceptibility in combination with external factors (e.g. dietary iodine) are believed to initiate the autoimmune response to thyroid antigens. Abundant epidemiological data, including family and twin studies, point to a strong genetic influence on the development of AITD. Various techniques have been employed to identify the genes contributing to the etiology of AITD, including candidate gene analysis and whole genome screening. These studies have enabled the identification of several loci (genetic regions) that are linked with AITD, and in some of these loci putative AITD susceptibility genes have been identified. Some of these genes/loci are unique to Graves' disease (GD) and Hashimoto's thyroiditis (HT) and some are common to both diseases, indicating that there is a shared genetic susceptibility to GD and HT. The putative GD and HT susceptibility genes include both immune modifying genes (e.g. HLA, CTLA-4) and thyroid specific genes (e.g. TSHR, Tg). Most likely these loci interact and their interactions may influence disease phenotype and severity.     

Sudden death: ethical and legal problems of post‐mortem forensic genetic testing for hereditary cardiac diseases

Elger BS, Michaud K, Fellmann F, Mangin P. Sudden death: ethical and legal problems of post‐mortem forensic genetic testing for hereditary cardiac diseases. Hereditary non‐structural diseases such as catecholaminergic polymorphic ventricular tachycardia (CPVT), long QT, and the Brugada syndrome as well as structural disease such as hypertrophic cardiomyopathy (HCM) and arrhythmogenic right ventricular cardiomyopathy (ARVC) cause a significant percentage of sudden cardiac deaths in the young. In these cases, genetic testing can be useful and does not require proxy consent if it is carried out at the request of judicial authorities as part of a forensic death investigation. Mutations in several genes are implicated in arrhythmic syndromes, including SCN5A, KCNQ1, KCNH2, RyR2, and genes causing HCM. If the victim's test is positive, this information is important for relatives who might be themselves at risk of carrying the disease‐causing mutation. There is no consensus about how professionals should proceed in this context. This article discusses the ethical and legal arguments in favour of and against three options: genetic testing of the deceased victim only; counselling of relatives before testing the victim; counselling restricted to relatives of victims who tested positive for mutations of serious and preventable diseases. Legal cases are mentioned that pertain to the duty of geneticists and other physicians to warn relatives. Although the claim for a legal duty is tenuous, recent publications and guidelines suggest that geneticists and others involved in the multidisciplinary approach of sudden death (SD) cases may, nevertheless, have an ethical duty to inform relatives of SD victims. Several practical problems remain pertaining to the costs of testing, the counselling and to the need to obtain permission of judicial authorities.     

Experts' opinions on ethical issues of genetic research into Alzheimer's disease: results of a Delphi study in the Netherlands

van der Vorm A, van der Laan AL, Borm G, Vernooij‐Dassen M, Rikkert MO, van Leeuwen E, Dekkers W. Experts' opinions on ethical issues of genetic research into Alzheimer's disease: results of a Delphi study in the Netherlands. Most publications on the ethical aspects of genetic research into Alzheimer's Disease (AD) concentrate on the differences between the opinions of professionals and non‐professionals. Differences in rating of morally relevant issues between groups of professionals have not yet been described. A modified Delphi study in two rounds was held to identify differences between groups of experts (i.e. clinicians, representatives of patient organisations, ethicists and persons with a commercial background). The strongest correlation was found between the opinions of ethicists and representatives of patient organisations (0.67) and between clinicians and ethicists (0.62). Moderate correlation (0.55) was found between the opinions of clinicians and representatives of patient organisations. Persons with a commercial background showed a weak correlation with clinicians (0.41), ethicists (0.35) and representatives of patient organisations (0.30). These differences in rating of morally relevant issues between various professional groups are relevant for clinical practice and dementia care, particularly the different rating of prenatal diagnosis found between clinicians and representatives of patient organisations. Interdisciplinary consultations between various professional groups –including at least researchers, clinicians and ethicists –are recommended to guarantee that all considerations will be incorporated into the debate on ethical issues of genetic research into AD.     

Early‐onset inflammatory bowel disease as a model disease to identify key regulators of immune homeostasis mechanisms

Rare, monogenetic diseases present unique models to dissect gene functions and biological pathways, concomitantly enhancing our understanding of the etiology of complex (and often more common) traits. Although inflammatory bowel disease (IBD) is a generally prototypic complex disease, it can also manifest in an early‐onset, monogenic fashion, often following Mendelian modes of inheritance. Recent advances in genomic technologies have spurred the identification of genetic defects underlying rare, very early‐onset IBD (VEO‐IBD) as a disease subgroup driven by strong genetic influence, pinpointing key players in the delicate homeostasis of the immune system in the gut and illustrating the intimate relationships between bowel inflammation, systemic immune dysregulation, and primary immunodeficiency with increased susceptibility to infections. As for other human diseases, it is likely that adult‐onset diseases may represent complex diseases integrating the effects of host genetic susceptibility and environmental triggers. Comparison of adult‐onset IBD and VEO‐IBD thus provides beautiful models to investigate the relationship between monogenic and multifactorial/polygenic diseases. This review discusses the present and novel findings regarding monogenic IBD as well as key questions and future directions of IBD research.     

Association among genetic predisposition,gut microbiota,and host immune response in the etiopathogenesis of inflammatory bowel disease

Inflammatory bowel disease (IBD), which includes Crohn''s disease (CD) and ulcerative colitis (UC), is a chronic disorder that affects thousands of people around the world. These diseases are characterized by exacerbated uncontrolled intestinal inflammation that leads to poor quality of life in affected patients. Although the exact cause of IBD still remains unknown, compelling evidence suggests that the interplay among immune deregulation, environmental factors, and genetic polymorphisms contributes to the multifactorial nature of the disease. Therefore, in this review we present classical and novel findings regarding IBD etiopathogenesis. Considering the genetic causes of the diseases, alterations in about 100 genes or allelic variants, most of them in components of the immune system, have been related to IBD susceptibility. Dysbiosis of the intestinal microbiota also plays a role in the initiation or perpetuation of gut inflammation, which develops under altered or impaired immune responses. In this context, unbalanced innate and especially adaptive immunity has been considered one of the major contributing factors to IBD development, with the involvement of the Th1, Th2, and Th17 effector population in addition to impaired regulatory responses in CD or UC. Finally, an understanding of the interplay among pathogenic triggers of IBD will improve knowledge about the immunological mechanisms of gut inflammation, thus providing novel tools for IBD control.     

Endophenotypes in normal brain morphology and Alzheimer's disease: a review

Late-onset Alzheimer's disease is a common complex disorder of old age. Though these types of disorders can be highly heritable, they differ from single-gene (Mendelian) diseases in that their causes are often multifactorial with both genetic and environmental components. Genetic risk factors that have been firmly implicated in the cause are mutations in the amyloid precursor protein (APP), presenilin 1 (PSEN1) and presenilin 2 (PSEN2) genes, which are found in large multi-generational families with an autosomal dominant pattern of disease inheritance, the apolipoprotein E (APOE)ε4 allele and the sortilin-related receptor (SORL1) gene. Environmental factors that have been associated with late-onset Alzheimer's disease include depressive illness, various vascular risk factors, level of education, head trauma and estrogen replacement therapy. This complexity may help explain their high prevalence from an evolutionary perspective, but the etiologic complexity makes identification of disease-related genes much more difficult. The “endophenotype” approach is an alternative method for measuring phenotypic variation that may facilitate the identification of susceptibility genes for complexly inherited traits. The usefulness of endophenotypes in genetic analyses of normal brain morphology and, in particular for Alzheimer's disease will be reviewed as will the implications of these findings for models of disease causation. Given that the pathways from genotypes to end-stage phenotypes are circuitous at best, identifying endophenotypes more proximal to the effects of genetic variation may expedite the attempts to link genetic variants to disorders.     

Error processing in normal aging and in basal ganglia disorders

Recently it has been shown that effects of aging and pathologically induced changes of basal ganglia structures may have quite similar effects on cognitive functions mediated by the medial prefrontal cortex. The question appears, if this pattern may be assignable to other cognitive functions that are mediated via the basal ganglia and medial prefrontal brain areas. Error processing is a component of executive functions that also depends on these areas and especially on the anterior cingulate cortex (ACC). Hence we ask, if error processing functions are differentially modulated by normal aging and basal ganglia diseases. Error processing mechanisms in these groups were investigated using a cognitive event-related potential (ERP), the error negativity. Enrolling an extended sample of young and elderly controls, as well as patients with Parkinson's and Huntington's disease, we show that modulations of error processing differ between aging, different basal ganglia diseases. Despite that the examined basal ganglia disorder groups (Parkinson's and Huntington's disease) differ in their age they show similar modulations in error processing, suggesting that aging effects are overridden by pathogenic effects. The study shows that it may be valuable to compare aging not only to different forms of basal ganglia disorders in order to gain knowledge about age- and disease-related mechanisms and the effects of these on cognitive functions. Diseases of the basal ganglia may impact error processing above and beyond the effects of normal aging. Although many aging, Parkinson's disease and Huntington's disease studies on error processing functions have already been published, this study ties together several related observations across all of these groups in one experiment.     

Jehovah's Witnesses and transfusion: where do we stand in Europe?

Transfusion refusal expressed by Jehovah's Witnesses has always been questioning for medical community. However, abundant literature exists treating about how to manage difficult medical bleeding situations in Jehovah's witnesses, there is a few information available on the legal and ethical aspects of transfusion refusal. Since 1994, Europe has putted a spotlight on patient's right. The question of patient's autonomy and consent have taken a predominant place in care. In order to summarize the actual situation in Europe, this work intends to draw a global view on legal, ethical and medical aspects of transfusion refusal expressed by Jehovah witnesses.     

Autoimmune thyroid diseases: genetic susceptibility of thyroid‐specific genes and thyroid autoantigens contributions

Autoimmune thyroid diseases are common polygenic multifactorial disorders with the environment contributing importantly to the emergence of the disease phenotype. Some of the disease manifestations, such as severe thyroid‐associated ophthalmopathy, pretibial myxedema and thyroid antigen/antibody immune complex nephritis are unusual to rare. The spectrum of autoimmune thyroid diseases includes: Graves’ disease (GD), Hashimoto's thyroiditis (HT), atrophic autoimmune thyroiditis, postpartum thyroiditis, painless thyroiditis unrelated to pregnancy and thyroid‐associated ophthalmopathy. This spectrum present contrasts in terms of thyroid function, disease duration and spread to other anatomic location. The genetic basis of autoimmune thyroid disease (AITD) is complex and likely to be due to genes of both large and small effects. In GD the autoimmune process results in the production of thyroid‐stimulating antibodies and lead to hyperthyroidism, whereas in HT the end result is destruction of thyroid cells and hypothyroidism. Recent studies in the field of autoimmune thyroid diseases have largely focused on (i) the genes involved in immune response and/or thyroid physiology with could influence susceptibility to disease, (ii) the delineation of B‐cell autoepitopes recognized by the main autoantigens, thyroglobulin, thyroperoxidase and TSH receptor, to improve our understanding of how these molecules are seen by the immune system and (iii) the regulatory network controlling the synthesis of thyroid hormones and its dysfunction in AITD. The aim of the present review is to summarize the current knowledge regarding the relation existing between some susceptibility genes, autoantigens and dysfunction of thyroid function during AITD.     

How Far Are We from Understanding the Genetic Basis of Hashimoto's Thyroiditis?

Hashimoto's thyroiditis (HT), an autoimmune thyroid disease (AITD), is becoming more and more prevalent in the recent years. Data on family and twin studies carry evidence for strong genetic influence on AITD susceptibility and development. The most common approaches to unravel the background of those diseases are whole genome screening and candidate gene analysis. Common Hashimoto's thyroiditis and Graves’ disease (GD) genes have been identified, as well as genes that are characteristic for only one of those diseases. Because of the complex nature of AITD, caused by their polygenic nature and a complex mode of inheritance, there are still more questions to be answered than answers that can be given, especially about the nature of Hashimoto's thyroiditis. There are plenty of papers concerning the pathogenesis of AITD. However, not seldom do they end up in conclusions about GD, because the results for this disease are far clearer and more unambiguous than those obtained for HT. Similarly, meta-analyses and especially reviews most often concentrate on AITD in general or on GD alone. In this review, Hashimoto's thyroiditis is the main player. It aims to review the state of the art about the background of the development of this disease.     

Neuroinflammation in Synucleinopathies

The causes of most neurodegenerative diseases are attributed to multiple genetic and environmental factors interacting with one another. Above all, inflammation in the nervous system has been implicated in many neurodegenerative diseases. Still, the roles of neuroinflammation in disease mechanisms and the triggers of inflammatory responses in disease‐inflicted brain tissues seem to remain unclear. This review will examine previous studies that had been done from genetic, pathological and epidemiological perspectives. These studies assess the involvement of neuroinflammation in synucleinopathies, a group of neurodegenerative diseases that are characterized by deposition of α‐synuclein aggregates such as Parkinson's disease, dementia with Lewy bodies and multiple system atrophy. The review will also discuss the role of α‐synuclein aggregates in triggering inflammatory responses from glial cells. It is expected that a precise assessment of the roles and mechanisms of neuroinflammation in neurodegenerative diseases will pave the way for the development of disease‐modifying drugs.     

Lay Attitudes toward Genetic Testing for Susceptibility to Inherited Diseases

One of the most important issues facing legal and medical policy makers in the coming years will be whether to employ populationbased testing for genetic markers of inherited diseases. Two hundred and twenty-six randomly selected individuals from Easton, Pennsylvania completed a mail questionnaire that was designed to assess the general public's attitudes toward many of the personal and societal issues surrounding genetic testing for disease susceptibility. Respondents were generally optimistic about the potential benefits of genetic testing, and their attitudes about genetic testing were associated with their personal interest in getting a genetic test. Respondents were more likely to be interested in undergoing genetic testing for disease susceptibility if they might have some control over the targeted disease (i.e. there was a cure) and if the test was highly predictive of their chances of developing the disease. Respondents were wary of granting access to genetic testing results to anyone other than doctors and family members, and they did not want the government, religious leaders, or the courts involved in regulating genetic testing. These results have important implications for psychologists, genetic scientists, bioethicists, and legal scholars who are grappling with the many issues related to population-based genetic testing for inherited diseases.     

Immuno- and genetic therapy in autoimmune diseases

Animal models of autoimmune disease have been developed that mimic some aspects of the pathophysiology of human disease. These models have increased our understanding of possible mechanisms of pathogenesis at the molecular and cellular level and have been important in the testing, development and validation of new immunotherapies. The susceptibility to develop disease in the majority of these models is polygenic as is the case in humans. The exceptions to this rule are gene knock outs and transgenic models of particular genes which, in particular genetic backgrounds, have also contributed to the understanding of single gene function and their possible contribution to pathogenesis. Gene therapy approaches that target immune functions are being developed with encouraging results, despite the polygenic nature of these diseases. Basically this novel immuno-genetic therapy harnesses the knowledge of immunology with the myriad of biotechnological breakthroughs in vector design and delivery. Autoimmune disease is the result of genetic dysregulation which could be controlled by gene therapy. Here we summarize the genetic basis of these human diseases as well as some of the best characterized murine models. We discuss the strategies for their treatment using immuno- and gene therapy.     

Metabolomic profiling in children with inflammatory bowel disease

Ulcerative colitis (UC) and Crohn's disease (CD) represent inflammatory bowel diseases (IBD) with multifactorial pathogenesis, involving genetic, environmental and microbial factors. Interactions between gut microbiota and immune system result in changes in metabolic pathways. Metabolomics is a comprehensive and quantitative (or semi-quantitative) analysis of metabolites synthetized in human's biological system. It has been shown that metabolic profiling might be used to identify disease biomarkers. Recent findings confirmed alterations in the number of metabolites in patients with IBD. However, most of the studies included adult individuals with ongoing treatment which might have affected the metabolite profiling. Therefore, the aim of our study was to collect the knowledge about metabolomics in paediatric patients with CD or UC based on the currently published literature.     

New approaches to investigating heterogeneity in complex traits

Great advances in the field of genetics have been made in the last few years. However, resolving the complexity that underlies the susceptibility to many polygenic human diseases remains a major challenge to researchers. The fast increase in availability of genetic data and the better understanding of the clinical and pathological heterogeneity of many autoimmune diseases such as multiple sclerosis, but also Parkinson's disease, Alzheimer's disease, and many more, have changed our views on their pathogenesis and diagnosis, and begins to influence clinical management. At the same time, more powerful methods that allow the analysis of large numbers of genes and proteins simultaneously open opportunities to examine their complex interactions. Using multiple sclerosis as a prototype, we review here how new methodologies such as gene expression profiling can be exploited to gain insight into complex trait diseases.     

Psychological costs and benefits of predictive testing for Huntington's disease

The impact of predictive genetic testing for Huntington's disease (HD) was assessed in 68 persons at high (n = 17) or low risk (n = 51) for the disease at one to six years following disclosure of test results. There was consensus in both groups that knowledge of HD genetic status was beneficial. A majority of persons felt relief from wondering and uncertainty. High-risk persons identified greater family closeness and financial security. For low-risk persons, the knowledge that their children were spared offered great consolation. Negative effects in high-risk persons were psychological burden (worry, guilt). Even for low-risk subjects, there was a period of adjustment and, in some, disappointment that low risk had not alleviated problems unrelated to HD. Although the majority of marriages were unaffected by testing, some persons in both groups reported that their marriages sustained positive or negative impact. Despite mixed consequences, most did not regret being tested. The benefits of testing appear to outweigh its drawbacks, at least among this self-selected group of research participants. We also must conclude, however, that predictive genetic testing will result in negative as well as positive consequences, regardless of test outcome. © 1994 Wiley-Liss, Inc.     

Diagnosis and classification of Goodpasture's disease (anti-GBM)

Goodpasture's disease or anti-glomerular basement membrane disease (anti-GBM-disease) is included among immune complex small vessel vasculitides. The definition of anti-GBM disease is a vasculitis affecting glomerular capillaries, pulmonary capillaries, or both, with GBM deposition of anti-GBM autoantibodies. The disease is a prototype of autoimmune disease, where the patients develop autoantibodies that bind to the basement membranes and activate the classical pathway of the complement system, which start a neutrophil dependent inflammation. The diagnosis of anti-GBM disease relies on the detection of anti-GBM antibodies in conjunction with glomerulonephritis and/or alveolitis. Overt clinical symptoms are most prominent in the glomeruli where the inflammation usually results in a severe rapidly progressive glomerulonephritis. Despite modern treatment less than one third of the patients survive with a preserved kidney function after 6 months follow-up. Frequencies vary from 0.5 to 1 cases per million inhabitants per year and there is a strong genetic linkage to HLA-DRB1¹1501 and DRB1¹1502. Essentially, anti-GBM disease is now a preferred term for what was earlier called Goodpasture's syndrome or Goodpasture's disease; anti-GBM disease is now classified as small vessel vasculitis caused by in situ immune complex formation; the diagnosis relies on the detection of anti-GBM in tissues or circulation in conjunction with alveolar or glomerular disease; therapy is effective only when detected at an early stage, making a high degree of awareness necessary to find these rare cases; 20–35% have anti-GBM and MPO-ANCA simultaneously, which necessitates testing for anti-GBM whenever acute test for ANCA is ordered in patients with renal disease.     

Investigating the role of rare coding variability in Mendelian dementia genes (APP,PSEN1, PSEN2, GRN,MAPT, and PRNP) in late-onset Alzheimer's disease

The overlapping clinical and neuropathologic features between late-onset apparently sporadic Alzheimer's disease (LOAD), familial Alzheimer's disease (FAD), and other neurodegenerative dementias (frontotemporal dementia, corticobasal degeneration, progressive supranuclear palsy, and Creutzfeldt-Jakob disease) raise the question of whether shared genetic risk factors may explain the similar phenotype among these disparate disorders. To investigate this intriguing hypothesis, we analyzed rare coding variability in 6 Mendelian dementia genes (APP, PSEN1, PSEN2, GRN, MAPT, and PRNP), in 141 LOAD patients and 179 elderly controls, neuropathologically proven, from the UK. In our cohort, 14 LOAD cases (10%) and 11 controls (6%) carry at least 1 rare variant in the genes studied. We report a novel variant in PSEN1 (p.I168T) and a rare variant in PSEN2 (p.A237V), absent in controls and both likely pathogenic. Our findings support previous studies, suggesting that (1) rare coding variability in PSEN1 and PSEN2 may influence the susceptibility for LOAD and (2) GRN, MAPT, and PRNP are not major contributors to LOAD. Thus, genetic screening is pivotal for the clinical differential diagnosis of these neurodegenerative dementias.