Predictive testing: presymptomatic diagnosis in neurogenetic disorders

Presymptomatic testing is available since 15 years for Huntington disease and it is now possible for a number of other neurogenetic disorders, mostly neurodegenerative disorders. The possibility of determining the genetic status of an at-risk person for the disorder which run in his family raises questions because of the absence of preventive and curative treatments in most instances. In addition, being carrier does not tell you when the disease will start and how it will evolve, impairing the possibilities of planning the future. A pluridisciplinary approach to predictive testing with care before, during and after the test taking into account the medical, social and psychological aspects of the disease is good practice. At the present time, only a minority of at-risk individuals request presymptomatic testing and almost 50 % do not pursue until the results. The consequences of the test may be harmful, more frequently after an unfavorable than after a favorable result. Although the motivations and the outcome in terms of request for prenatal testing after a carrier result are different in Huntington's disease and spinocerebellar ataxias, our experience underlines the benefit of pluridisciplinary care and of time for decision taking. For other disorders like familial Alzheimer's disease, or familial Creutzfeldt-Jakob disease, the experience in presymptomatic testing is still limited but the situation seems similar to Huntington's disease because of the presence of dementia. It will be interesting to study the motivations and the outcome of the tests in disorders like autosomal dominant spastic paraplegias which usually do not reduce the life expectancy. Nevertheless, the overall situation might change greatly when efficient treatments will become available in these disorders.     

Blood levels of kynurenines, interleukin-23 and soluble human leucocyte antigen-G at different stages of Huntington's disease

There is substantial evidence that abnormal concentrations of oxidised tryptophan metabolites, produced via the kynurenine pathway, contribute to progressive neurodegeneration in Huntington's disease. We have now examined the blood levels of these metabolites in patients at different stages of Huntington's disease, assessed both in terms of clinical disease severity and numbers of CAG repeats. Close relatives of the patients were included in the study as well as unrelated healthy controls. Levels of lipid peroxidation products, the pro-inflammatory cytokine interleukin (IL)-23 and the soluble human leucocyte antigen-G (sHLA-G) were also measured. There were lower levels of tryptophan and a higher kynurenine : tryptophan ratio, indicating activation of indoleamine-2,3-dioxygenase, in the most severely affected group of patients, with increased levels of IL-23 and sHLA-G. Marked correlations were noted between IL-23 and the patient severity group, anthranilic acid levels and the number of CAG repeats, and between anthranilic acid and IL-23, supporting our previous evidence of a relationship between anthranilic acid and inflammatory status. Tryptophan was negatively correlated with symptom severity and number of CAG repeats, and positively correlated with sHLA-G. The results support the proposal that tryptophan metabolism along the kynurenine pathway in Huntington's disease is related to the degree of genetic abnormality, to clinical disease severity and to aspects of immunopathogenesis.     

Mutant huntingtin activates Nrf2-responsive genes and impairs dopamine synthesis in a PC12 model of Huntington's disease

Background  

Huntington's disease is a progressive autosomal dominant neurodegenerative disorder that is caused by a CAG repeat expansion in the HD or Huntington's disease gene. Although micro array studies on patient and animal tissue provide valuable information, the primary effect of mutant huntingtin will inevitably be masked by secondary processes in advanced stages of the disease. Thus, cell models are instrumental to study early, direct effects of mutant huntingtin. mRNA changes were studied in an inducible PC12 model of Huntington's disease, before and after aggregates became visible, to identify groups of genes that could play a role in the early pathology of Huntington's disease.     

Huntington's disease: modeling the gait disorder and proposing novel treatments

Huntington's disease is a movement disorder originated from malfunctioning of Basal Ganglia (BG). There are some models for this disease, most of them being conceptual. So, it seems that considering all physiological information and structural specifications to develop a holistic model is needed. We introduce a computational model based on experimental and physiological findings. Parts of the brain known to be involved in Huntington's disease are all considered in our model and most features of the movement disorders have been appeared in the model. This mathematical model has considered the involved parts of the brain in a fairly accurate way, explaining the behavior and mechanism of the disease according to the physiological information. Our model has several advantages. It is able to simulate the normal and Huntington's disease stride time intervals. It shows how the present treatment, i.e. diazepam, is able to ameliorate the gait disorder. In this research we assessed the effects of changing some neurotransmitter levels in order to propose new treatments. Although we showed that gamma amino butyric acid (GABA) blockers reduce Huntington's disease movement disorder, but we discussed that it is unfair to use this route for treatment. We evaluated our model response to increment of GABA, alone and observed that the gait disorder was strengthened. Our novel idea in this regard is resuscitation of BG loop in order to maintain its major physiological functions, and at the same time raising the threshold in order to weaken the internal disturbances. Our last idea about BG treatment is to decrease glutamate. Our model was able to show the effectiveness of this treatment on Huntington's disease disturbances. We propose that experimental studies should be designed in which these two novel methods of treatment will be evaluated. This validation would implement a milestone in treatment of such a debilitating disease at Huntington.     

SHOULD CHILDREN AND ADOLESCENTS BE TESTED FOR HUNTINGTON’S DISEASE? ATTITUDES OF FUTURE LAWYERS AND PHYSICIANS IN SWITZERLAND

The objective of the study was to identify future lawyers' and physicians' views on testing children for Huntington's disease (HD) against parents' wishes. After receiving general information about HD, patient autonomy and confidentiality, law students and advanced medical students were shown an interview with a mother suffering from HD who is opposed to informing and testing her two children (aged 10 and 16) for HD. Students then filled out questionnaires concerning their agreement with testing. No significant differences were found between medical and law students or between students from different courses concerning the adolescent son. Three quarters of students thought that he should be told about his mother's disease, and 91% thought the adolescent son should have the opportunity of genetic testing for HD himself. However, significant differences were found concerning the 10-year old son, with 44% of law students and 30% of medical students in favour of testing the child for HD. Students raised some important ethical issues in their elective comments. In conclusion, we found highly positive attitudes towards informing a 16-year old of his mother's HD and offering to test him. These attitudes were not in tune with guidelines. Students did not consider several practical and ethical issues of genetic testing of children and adolescents. Specific education should ensure that attitudes are based on sufficiently detailed knowledge about all aspects of genetic testing of children to discourage pressures on persons at risk of HD.     

Variation within the Huntington's disease gene influences normal brain structure

Genetics of the variability of normal and diseased brain structure largely remains to be elucidated. Expansions of certain trinucleotide repeats cause neurodegenerative disorders of which Huntington's disease constitutes the most common example. Here, we test the hypothesis that variation within the IT15 gene on chromosome 4, whose expansion causes Huntington's disease, influences normal human brain structure. In 278 normal subjects, we determined CAG repeat length within the IT15 gene on chromosome 4 and analyzed high-resolution T1-weighted magnetic resonance images by the use of voxel-based morphometry. We found an increase of GM with increasing long CAG repeat and its interaction with age within the pallidum, which is involved in Huntington's disease. Our study demonstrates that a certain trinucleotide repeat influences normal brain structure in humans. This result may have important implications for the understanding of both the healthy and diseased brain.     

Protein aggregation in Huntington's disease

The presence of an expanded polyglutamine produces a toxic gain of function in huntingtin. Protein aggregation resulting from this gain of function is likely to be the cause of neuronal death. Two main mechanisms of aggregation have been proposed: hydrogen bonding by polar-zipper formation and covalent bonding by transglutaminase-catalyzed cross-linking. In cell culture models of Huntington's disease, aggregates are mostly stabilized by hydrogen bonds, but covalent bonds are also likely to occur. Nothing is known about the nature of the bonds that stabilize the aggregates in the brain of patients with Huntington's disease. It seems that the nature of the bond stabilizing the aggregates is one of the most important questions, as the answer would condition the therapeutic approach to Huntington's disease.     

Disclosure of Huntington's disease to family members: the dilemma of known but unknowing parties

Predictive genetic testing presents unique issues in the legal and ethical debate concerning disclosure of information within the physician-patient relationship. A duty to disclose information to family members has been found when the disclosure is likely to result in the ability to mitigate the damaging effects of the disease. When evaluating the situation where a individual is at risk of Huntington's disease, the analysis must be different, as shown in this paper, and necessitates an ethical and legal examination of the consequences of receipt of the information on family members, those known but unknowing parties who are at risk of inheriting a genetic disease. This paper analyzes the potential legal duty of a physician to disclose or withhold genetic information from the family members of patients. Existing statutes governing genetic information do not directly address the interests of family members. Courts that have ruled on the duty to disclose medical or genetic information have analyzed these issues using traditional concepts of tort law. Yet the situation presented by Huntington's disease is unique and demands a different framework for analysis, given the late onset and lack of curative or ameliorative treatment. This paper also analyzes the ethical standards to be invoked when considering violating the privacy of a patient or a family member. The principles of autonomy and self-determination of family members are considered, versus the risk of harm and the privacy interest in not knowing potentially devastating information.     

Astrocytes in Huntington's chorea: accomplice or guilty of the neuronal death?

Huntington's disease is an hereditary dominant neurodegenerative disorder clinically characterised by progressive motor deficits, personality changes, decreased mental capacity and death after about 15-20 years. Most studies are based on the research of intrinsic mechanisms that could be responsible for dysfunction and later degeneration of neuronal subsets. It is only in the last five years that more interest has been focused on another brain cell type : the astrocytes. This review presents evidence that astroglial function is also affected in Huntington's disease. Among the possible mechanisms, Huntington's disease mutation may alter the EGF receptor signaling pathway, that regulates the astrocytic response to neuronal injuries.     

Protein-misfolding diseases and chaperone-based therapeutic approaches

A large number of neurodegenerative diseases in humans result from protein misfolding and aggregation. Protein misfolding is believed to be the primary cause of Alzheimer's disease, Parkinson's disease, Huntington's disease, Creutzfeldt-Jakob disease, cystic fibrosis, Gaucher's disease and many other degenerative and neurodegenerative disorders. Cellular molecular chaperones, which are ubiquitous, stress-induced proteins, and newly found chemical and pharmacological chaperones have been found to be effective in preventing misfolding of different disease-causing proteins, essentially reducing the severity of several neurodegenerative disorders and many other protein-misfolding diseases. In this review, we discuss the probable mechanisms of several protein-misfolding diseases in humans, as well as therapeutic approaches for countering them. The role of molecular, chemical and pharmacological chaperones in suppressing the effect of protein misfolding-induced consequences in humans is explained in detail. Functional aspects of the different types of chaperones suggest their uses as potential therapeutic agents against different types of degenerative diseases, including neurodegenerative disorders.     

Electron spin resonance, hematological, and deformability studies of erythrocytes from patients with Huntington's disease.

Electron spin resonance, hematologic, and deformability studies of erythrocytes from patients with Huntington's disease have been performed A decreased deformability of Huntington's disease erythrocytes compared to normal controls was demonstrated. No difference in erythrocyte hematologic indices, osmotic fragility, reticulocyte counts, or intracellular Na+ concentration was found. Huntington's disease serum had no demonstrable effect on electron spin resonance parameters of a protein-specific spin label attached to membrane proteins in control erythrocytes compared to the effect of control serum. This finding suggests that under the conditions employed no serum component or circulating factor is responsible for the changes in the physical state of membrane proteins in Huntington's disease erythrocytes (Butterfield, D.A., Oeswein, J.Q. and Markesbery, W.R. (1977) Nature 267, 453--455). No alteration in lipid fluidity of Huntington's disease erythrocyte membranes could be discerned suggesting that the underlying molecular defect in Huntington's disease involves a membrane protein. The results of the present studies on erythrocytes strongly support the concept that Huntington's disease is associated with a generalized membrane abnormality.     

Population-demographic and clinico-genetic characteristics of Huntington chorea in one region of Azerbaijan

The data are presented on prevalence and clinical patterns of Huntington disease in Shamkhor region of Azerbaijan, where about 126.8 thousand inhabitants live. Population, demographic and genealogical data show that high prevalence of Huntington disease in that region is determined by the founder effects, reinforced later by extended reproduction of the population. Linkage analysis using the affected sib-pair method failed to reveal a linkage between Huntington's chorea locus and HLA, AB0, MN systems. Significant probability of linkage to Huntington's chorea locus was calculated for Gc marker.     

Calculating risk changes after negative mutation test outcomes for autosomal dominant hereditary late-onset disorders

We demonstrate, in a specific scenario, the effect of negative test results from relatives in families at risk for an autosomal dominant hereditary late-onset disorder. A hypothetical pedigree, of a family at risk of Huntington's disease, was used to demonstrate the consequences for the risk status of various family members in the case where relatives have been tested, and found to be mutation negative. We argue that accurate assessment of conditional probabilities in clinical genetics is important for individuals at risk for hereditary disorders with Mendelian transmission patterns; our formulae offer the opportunity -- when simplifying assumptions are met -- to determine the changed risk status of individuals in such cases.     

Risk reduction and health promotion behaviors following genetic testing for adult-onset disorders

Although clinical genetic testing is available for over 1,000 inherited disorders, consequences of predictive genetic testing have been most extensively examined for hereditary breast and ovarian cancer (HBOC), hereditary colon cancer, and Huntington disease (HD). These focus primarily on psychological, ethical, legal, and social aspects of genetic testing. Genetic testing may also provide information that can lead to behaviors that promote health and reduce risk for disease, reflecting options available for the disorder for which the person is at risk. However, regardless of condition, people completing a genetic test may inform relatives about the results of the test and implications for their risk to develop the condition. Literature on risk reduction behaviors and communication focuses on families with HBOC or colorectal cancer. Few reports document behaviors for other conditions. This paper presents a systematic review of the research literature on risk reduction and health promotion behaviors following clinical genetic testing for adult onset conditions, primarily HBOC, familial colon cancers, and HD. Insights gleaned from this review are discussed as a basis for planning monitoring of health promotion and risk-reduction behaviors for genetic testing for present and future use.     

PET imaging of the basal ganglia

The present chapter reviews PET imaging in basal ganglia disorders; Parkinson's disease is used as a model of these disorders because the neurochemical pathobiology of this disease is well known and great advances in the imaging area have been achieved. Other basal ganglia disorders including Tourette's syndrome, dystonia, Huntington's chorea and Wilson's disease are also dealt with. With PET and SPECT techniques, the whole integrative dopaminergic network of neurons can be studied, which plays an important role in differential diagnostics. Furthermore, pharmacological effects of medication can be visualized and the role of stereotaxic neurosurgery can be evaluated. Finally, functional imaging gives clues about the prognosis and rehabilitation aspects of the basal ganglia disorders.     

Humanin binds MPP8: mapping interaction sites of the peptide and protein

Humanin (HN), a 24‐amino acid peptide encoded by the mitochondrial 16S rRNA gene, was discovered by screening a cDNA library from the occipital cortex of a patient with Alzheimer's disease (AD) for a protection factor against AD‐relevant insults. Earlier, using the yeast two‐hybrid system, we have identified the M‐phase phosphoprotein 8 (MPP8) as a binding partner for HN. In the present work, we further confirmed interaction of HN with MPP8 in co‐immunoprecipitation experiments and localized an MPP8‐binding site in the region between 5 and 12 aa. of HN. We have also shown that an MPP8 fragment (residues 431–560) is sufficient to bind HN. Further studies on functional consequences of the interaction between the potential oncopetide and the oncoprotein may elucidate some aspects of the molecular mechanisms of carcinogenesis. Copyright © 2013 European Peptide Society and John Wiley & Sons, Ltd.     

Reciprocity and communication of partner quality

In a cooperative exchange, the size of a partner''s contribution is likely to depend both on the partner''s ability to supply help and on the partner''s need for help in return. Referring to such needs and abilities as aspects of partner quality, it follows that variation in the amount of help offered in a relationship could transmit information about partner quality. A plausible behaviour might then be to vary the investment in a partner according to available information about partner quality and to invest little in a partner who offers little in return. Thus, regulation of a relationship through communication of partner quality would tend to follow the principle of reciprocity. In an analysis of an iterated game where players have private information about their needs and abilities, I verify this possibility by describing an evolutionarily stable state space strategy, referred to as ''state-dependent reciprocity'', entailing communication of partner quality. Although the evolution of cooperation has been studied in great detail, there has been no previous analysis of communication of needs and abilities in a relationship. It may well be that such communication is of major importance for the evolution of cooperative behaviour in nature.     

Paradoxical effects of coupling infectious livestock populations and imposing transport restrictions

Spatial heterogeneity of a host population of mobile agents has been shown to be a crucial determinant of many aspects of disease dynamics, ranging from the proliferation of diseases to their persistence and to vaccination strategies. In addition, the importance of regional and structural differences grows in our modern world. Little is known, though, about the consequences when traits of a disease vary regionally. In this paper, we study the effect of a spatially varying per capita infection rate on the behaviour of livestock diseases. We show that the prevalence of an infectious livestock disease in a community of animals can paradoxically decrease owing to transport connections to other communities in which the risk of infection is higher. We study the consequences for the design of livestock transportation restriction measures and establish exact criteria to discriminate those connections that increase the level of infection in the community from those that decrease it.