Heritability of age at onset and progression in Huntington’s disease: heritability of symptom onset and progression and identification of the most informative subjects for revealing genetic modifiers of Huntington’s disease
In HD both onset and progression are variable: the variability in HD onset can be attributed to HTT CAG length but also other genetic differences between subjects. The influence of CAG length on disease progression unclear and its heritability poorly understood. To inform the search for modifiers of disease onset and progression we wish to establish the correlation of onset ages of multiple symptoms from the Clinical Characteristics Questionnaire, establish the heritability of progression and onset amongst related subjects and examine Registry for discordant subject relatives in which to search for genetic modifiers of onset and progression of HD.
The use of propensity scores to draw inferences about how lifestyle factors might be associated with HD progression and clinical severity
The overarching aim of this study is to develop statistical methods for the analysis of large scale longitudinal data sets for the ENROLL database. The study will use currently available data from the European Huntington Disease Network Registry ("Registry") database to evaluate whether use of causal modeling techniques (namely propensity score weights) might prove helpful for increasing understanding of the potential environmental modifiers of HD. Specific moderating variables of interest include: education, socioeconomic status, smoking, alcohol, drug use, statin use, aspirin use, nutritional supplements, and antidepressant drug use.
Analysis of the Registry Clinical Characteristics Questionnaire data
The Clinical Characteristics Questionnaire (CCQ) records age of onset in a range of HD symptoms. To inform our use of CCQ information in our ongoing genome-wide association study we wish to obtain data from all subjects in the database who have a filled out CCQ. The two main aims of asking for data on all subjects that are available are to:
Model the relationship of each symptom to CAG repeat length;
Explore whether symptoms recorded are an inevitable part of the disease progression in all or most HD subjects, or whether some symptoms can be regarded as dichotomous.
Investigating the significance of novel huntingtin splice variants in Huntington’s disease patients
Screening the HTT gene in HD and control brain revealed many novel splice variants. A pool of HTT RNA species therefore exists with the potential to encode novel HTT protein isoforms. This study aims to determine whether these different protein isoforms exist and whether they associate with HD pathogenesis. The normal and pathogenic roles of HTT are not fully understood. Characterisation of any novel HTT protein isoform could contribute to a better understanding of the function of HTT in the cell. Furthermore, a comprehensive knowledge of alternative HTT RNA species could have implications for the design of RNA silencing therapies in HD.
CAG repeat length polymorphisms as modifiers of clinical phenotype: Huntington’s disease and the general population
Recently it was shown that subjects with intermediate HTT alleles experience significantly more depressive symptoms than controls. As in the general population the frequency of intermediate alleles can be as high as 6%, these findings could have important implications for both Huntington's disease patients and the community at large. Therefore, we aim to systematically evaluate 1) the role of HTT CAG repeat polymorphisms in the normal range as modifiers of mental health, cognition, metabolism and aging in the general population, and 2) the effects of CAG repeat polymorphisms in other polyglutamine disease-associated genes on the clinical features of Huntington's disease patients.
SNP typing of 96 highest value loci of Registry samples identified from the GWA Study effort
The variance in the neurological age of onset in HD can not be explained by CAG repeat size alone. We have previously performed a GWA study and successfully identified significant SNPs that modify neurological age of onset. Many other sites were nominally associated but not significant. We intend to survey 5000 additional samples at 96 top loci as means to cross validate, and new modifier genes arising from this effort should give rise to high value drug targets.
Identification of epigenetic signatures in HD striatum
Transcriptional dysregulation is an early process that is central to HD pathogenesis. Compounds aimed to improve gene expression through chromatin structure modulation are considered as promising. HDAC inhibitors are such compounds. However they lack selectivity and are relatively toxic. The goal of the project is to better characterize HD epigenome using genome-wide and high-resolution technique (e.g. ChIP-seq) and identify epigenetic signatures that may be useful to define new targets for epigenetic therapies. Our data obtained in HD R6/1 mouse striatum reveal a specific epigenetic signature associating with disease. We will determine whether this signature is conserved in HD brain tissues.
Analysis of genes participating in the dopamine and serotonin neurotransmitter system as potential modifier genes for Huntington disease pathogenesis
The pathogenesis of Huntington disease is provoked by the CAG repeat expansion in the HTT gene, but seems to be determined by a wide spectrum of pathways. To date, different studies showed an involvement of proteins in the dopamine and serotonin system in the pathological process of HD. Alterations in the dopamine and serotonin metabolism have been detected in HD animal models as well as in HD patients. In the present study, we intend to test various components of the dopamine and serotonin system (MAO-A, SLC6A3, SLC6A4, DRD2, DRD3, DRD4, ANKK1, HTR2A) as putative HD genetic modifiers. The identification of phenotype-associated polymorphisms may improve prognosis prediction and evaluation of medical intervention during patient assessment.
Can genetic imprinting be a factor in the pathogenesis of Huntington’s disease?
This study aims at verifying if genetic imprinting may modify the age at onset (AO) in Huntington’s disease (HD). The proportion of variation in the AO explained by the sex of parent affected with HD in a large population of patients, with the dominant impact of (CAG)n repeats included in the analyses, will be determined. Simple linear regression analyses and nested multiple models will be performed. The AO will be treated as the outcome measure while the number of CAG repeats, parental sex and parental age at conception will be included in the analyses as the predictor variables.
The role of SMAD-dependent TGFβ signalling in transcriptional dysregulation in early stage models of HD
SMAD proteins are major regulators of gene expression that act within the transforming growth factor-beta (TGFβ) signalling pathway. Preliminary data has revealed potential differences in this pathway in a cell model of HD. This project aims to characterise the role of SMAD proteins in mouse and human cell models of HD by comparing their expression, localisation and activity, as well as by manipulating the TGFβ pathway in order to determine whether it may contribute to the altered gene expression that is observed in HD.
An investigation into gender influence on anxiety and depression in Huntington's Disease (HD) across disease-stage
The proposed study aims to examine gender differences in depression and anxiety in HD. A consistent finding among the general population is that women are more likely to experience anxiety and depression than men. While there is some evidence of a higher frequency of depression in females with HD when compared to men with HD, the results are inconsistent. Moreover, anxiety remains a relatively neglected area in HD research and little is known about any impact of gender on anxiety symptoms. This study proposes to use REGISTRY data from a UK sample, with the Hospital Anxiety and Depression scale (HADs) as a measure of symptomology. Due to the variable course of anxiety and depression in HD, an analysis of gender by disease-stage will be conducted.
Does the presence of the HD mutation affect the development of the human striatum?
The aim of this project is to set-up a network across six University Hospital sites in the UK for the collection of fetal tissue carrying the HD mutation. Consent will be obtained by a specially trained research nurse and tissue will be collected following both surgical and medical termination of pregnancy. Tissue will be returned to the School of Biosciences at Cardiff University where it will be used to collect preliminary data on the HD mutation, including gene expression profiles, CNS anatomy, and cellular characteristics.
Replication study of non-genetic factors that can influence the age at onset (AO)
It is estimated that 60% of the age at onset of Huntington’s disease variability is due to environmental factors; however, few studies have analysed the influence of that factors. Previously, we have detected some association between two different environmental factors and age at onset, but in a small HD patient’s sample. Therefore, the aim of this work is to carry out a replication study in a larger sample in order to confirm or reject the previously obtained results. The relationship between premorbid factors (such as Diabetes mellitus, arterial hypertension, allergies, etc.), life style habits (such as tobacco smoking, alcohol abuse, drug consume…) and age at onset will be studied.
The role of phosphorylation pathways in the oligomerization and toxicity of mutant huntingtin
Aggregation of the huntingtin protein is a central event in Huntington's disease. While mutations in huntingtin affect its aggregation, it is becoming evident that post-translational modifications, such as phosphorylation, may also influence the aggregation propensity and toxicity of the protein. In order to understand how phosphorylation modulates huntingtin aggregation and toxicity we will search for genetic and pharmacological modifiers of the initial steps of aggregation and toxicity using an assay we recently developed, known as bimolecular fluorescence complementation. Ultimately, our findings may enable the development of novel strategies for therapeutic intervention by modulating huntingtin phosphorylation.
Investigation of polymorphisms affecting the dopaminergic system on age of onset and disease progression in human Huntington's disease
The abnormal gene in HD contains a large repeat that codes for an
abnormal form of the huntingtin protein and the size of this repeat governs
to some extent when people get the disease. However, there are other
influences on this and we are investigating whether changes in a specific
transmitter system in the brain could be involved. In order to do this we
are testing small variations in the genes coding for dopamine receptors and
analysing whether it affects when people get HD. If this does prove to be
the case then it may open up new treatment strategies.
Progression patterns of HD
We will analyze REGISTRY data using a new method that looks for similarities among data from different patients over time. This will let us answer questions such as the following. Which measures (singly or in combination) are the best predictors of progression? Which measures are redundant? Do people progress at the same rate in all measures, or do they progress more slowly in some symptom domains than others? Is rate of progression consistent over time? Does progression vary smoothly from premanifest to manifest HD, and from early stage to late stage, or are there long plateaus connected by sudden jumps?
Disease Progression Modeling in HD
This is a collaborative effort between CHDI, FDA and the HD research community to develop a disease progression model, using REGISTRY data and data from other observational studies (COHORT, PREDICT, TRACK and ENROLL) and selected clinical trials. The model will be used in the planning of future clinical trials. We model the age at first appearance and rate of progression of various signs and symptoms of HD, search for genetic, environmental, and life-style related variables that explain variability in disease progression and attempt to characterize the diverse patterns of disease progression that appear in the study population.
Unbiased prioritarization of neuroprotective targets for HD
A project developed by the Biological Modifiers Working Group at EHDN
The aim of this project is to develop data integration and network analysis to prioritize neuroprotective targets in HD. Huntington’s disease is extensively studied thanks to models that were developed in several species and that recapitulate complementary components of HD pathogenesis. Genome-wide analyses in these models have generated a large amount of data with high potential for target selection. The comprehensive and unbiased integration of ‘omics data’ on HD will allow better decisions in candidate target selection to be reached. Selecting for gene networks, modules and strings that are consistently highlighted by different model systems as ‘targets’ and/or ‘modifiers’ of mutant huntingtin activity may provide a strong basis to develop neuroprotective strategies that may be efficient against several stages and/or key features of HD. This concerted action involves the laboratories of Juan Botas, Bob Hughes, Lesley Jones, Ruth Luthi-Carter, Christian Neri and Shen Zhang.
Are there specific lifestyle factors that could be associated with the HD clinical characteristics and progression thereof: a retrospective data mining study?
This data mining study aims to use currently available data from Registry to evaluate whether there are any specific environmental factors that could be associated with progression of symptoms in the first instance and ultimately with onset of symptoms. This will not prove causal links but may identify a starting point to aid further understanding of environmental modifiers. We will investigate any associations between a) education and occupation, b) concomitant disorders c) smoking, d) alcohol e) drug use and HD clinical characteristics using multiple regression analysis. Classification and regression tree (CART) analysis will also be utilised.
Analysis of potential modifier genes involved in intracellular trafficking and mitochondrial function
The expanded CAG repeat in the HTT gene causes Huntington disease (HD), but other genetic factors additionally influence the course of the disease. We identified HAP1 as one of these genes modifying the age-at-onset.
So, we aim at verifying this effect of HAP1 in an additionally patient cohort and examining the association between HAP1 and the body mass index of these patients.
Additionally, we intend to search for further modifier genes participating in intracellular transport and mitochondrial function. As both aspects seem to be closely related to the pathogenesis of HD, modifying effects of these genes may influence the disease.
Identification of genetic modifiers of age of onset in HD. Candidate
gene study of CR1, CLU, PICAM, PRNP and APOE
We aim to identify potential genetic modifiers of HD age at onset.
There are many parallels between different neurodegenerative diseases; the processes
which occur in Alzheimers disease and HD may, for example, involve
similar pathways. For that reason we will search for polymorphisms in
several genes/proteins of HD patients that are knownto play a role in
the pathogenesis of Alzheimers Disease. We will investigate 1 SNP
(punctual variabilities in the DNA) in each of the following genes:
CLU, CR1, PICALM and PRNP and 2 SNPs in APOE.
An assessment of CAG repeat length and age at onset on rate of disease progression in Huntington´s disease
While CAG repeat length influences onset age, studies have been insufficiently powered to evaluate the effect on rate of disease progression. We propose to study individuals followed longitudinally for at least three years, and with at least three neurological examinations, to evaluate whether the CAG repeat length and age at onset are independent predictors of rate of progression or if one or the other singly accounts for association to rate of disease progression. These studies may be relevant to clinical trials, to control for the effects of factors that influence rate of disease progression.
Understanding prescribing habits of existing potential neuroprotective substances in HD
It is unknown how many patients receive antioxidants and potentially neuroprotective substances in what dosages and to what effect. Understanding existing prescription habits, and their differences, is important to develop effective clinical trials of both existing and emerging potential neuroprotective substances. We propose a two step analysis. First we would like to analyse prescribing habits in the various countries contributing to REGISTRY. Second, because the use of over-the-counter medications may be underreported, we would like to involve investigators in a subset of Centres to take part in a more systematic survey of the use of over-the-counter medications.
Tau haplotype and its relationship to age of onset and disease progression in Huntington's disease (HD)
Factors influencing the age of onset of HD are largely unknown
outside of CAG repeat length. What affects speed of disease
progression is also unclear. This project will investigate whether
tau haplotype has an influence on either of these aspects of HD, as
we have shown that the H1 tau haplotype is associated with the early
onset of dementia in Parkinsons disease. We will compare tau
haplotype against CAG repeat length, age of disease onset and
evidence of disease progression over a two year period using Total
Functional Capacity measures.
Search for candidate genes implicated in Huntington’s disease (HD) age of onset (AOO)
The aim of this work is the identification of Huntington´s disease AOO genetic modifiers, different from the CAG repeat length in the HD gene. For this purpose we will carry out an association analysis with 115 SNPs from 20 candidate genes in 250 samples collected by the REGISTRY project. The chosen candidate genes are located in several chromosomes and have been selected for being genes which encode proteins that interact directly with huntingtin or because they take part in the pathogenesis of the disease. The selected SNPs are located in coding, intron and 5´ and 3´ regions of the selected genes.
Copy number variation of potential genetic modifiers of Huntington's Disease
Genetic modifiers of Huntington's disease (HD) influence when and how
HD manifests and how HD progresses. We have identified several
potential modifier genes that show copy number variation (CNV).
Various gene mutations can lead to CNV from the standard gene dose of
two copies (one from each parent). CNV of candidate genes influences
resistance or susceptibility e.g. for psoriasis and HIV-1 infection.
This project will investigate the association of CNV of potential
genetic modifiers of HD with age-of-onset and progression. If CNV in a
given candidate modifier gene were associated with e.g. a delay of
age-of-onset or progression, this may help elucidate further the
pathogenesis of HD, as well as offer new therapeutic targets for HD.
Genome-Wide Genotyping of EHDN Samples
The variance of the age at onset (AAO) of first signs of HD cannot be
by CAG repeat size alone. A substantial proportion of the residual
variability is highly heritable indicating that other genes also
influence AAO. In order to identify such genetic variants we will
undertake genome-wide genotyping in REGISTRY participants where the
appropriate clinical information is available. This will employ
powerful analysis tools with the aim of genotyping millions of gene
loci in thousands of REGISTRY participants. The identification of
genetic variants that modify AAO of HD may open new avenues for
developing novel therapeutics.
Influence of gender on progression of HD
Several factors other than the CAG repeat length very likely influence when Huntington’s disease manifests and how it progresses. One such factor may be gender. We will assess in a cross-sectional CAG repeat matched sample whether there is any difference between men and women in the rater estimates of age at onset. In the second part of the study we will look at longitudinal data (at least 3 REGISTRY visits) to test for any gender related differences in the progression of HD signs (motor, behaviour, TFC, cognition). Any difference between the sexes may point to gender specific modifying factors.
PGC-1a as a potential modifier gene of age of onset of HD
The Huntington’s disease (HD) gene determines to some extent when HD signs appear. However, other genes, so called modifier genes, also influence the age of onset. Recent studies implicate PGC-1a, an important regulator of the cell’s main energy generator, the mitochondrion, as a potential modifier gene. We have already found an association of PGC-1a gene variants with age of onset of motor symptoms in an Italian HD population. These findings we intend to replicate in a larger sample of data collected in REGISTRY. If confirmed, it may be worthwhile to explore the potential of PGC-1a as a therapeutic target.
Search for genetic modifiers in HD: exploring the Foxo network
In Huntington’s disease (HD) the CAG repeat length explains much, but not all, of the variance in the age at onset (AO). Other as yet unknown genes also contribute. In mouse and worm models we identified potential modifiers of mutant huntingtin cytotoxicity in the Foxo network. FOXO transcription factors are important regulators of cell survival in response to a variety of stress stimuli such as oxidative stress, DNA damage, and nutrient deprivation. To look at the relevance of our findings in HD model systems for HD patients using REGISTRY data we will investigate the relationship of gene alterations within several FOXO members with the age at onset of HD signs, and progression of HD.
Hunt for Huntington modifiers with systems biology approaches
Genes other than the Huntington’s disease (HD) gene influence when HD signs appear. These genes are called modifier genes. We previously identified potential modifier genes, and mutations within these genes. In this project, we intend to associate the mutations with the variation in age at onset. To this end we will study genotypes of 1000 HD patients and correlate genetic findings with clinical characteristics. Once the potential modifier genes and its mutations have been determined, they could serve as important targets for therapy development to delay the onset of HD.
Sex-specific differences in AO
The CAG repeat length accounts for about half of the variance in the age of onset (AO) in Huntington’s disease (HD). Genes other than the HD gene (Modifier genes) may account for an additional 40% of the variation. N-Methyl-d-aspartate (NMDA) receptor-mediated excitotoxicity has been proposed to play a role in the pathogenesis of HD. We previously found substantial differences of the C2664T SNP in GRIN2B (glutamate receptor; ionotropic NMDA) between men and women, in particular in pre-menopausal patients. If confirmed in a larger sample of data collected in REGISTRY hormonal factors might prove a possible therapeutic target.
Genome Wide Association Scan to Identify Modifiers of HD Onset
The length of the HD CAG trinucleotide repeat plays the major role in determining age at neurologic onset but does not explain all of the variation observed. In an extensive collaborative effort, we are searching the entire human genome for genetic variants that modify age at neurologic onset in HD to identify genes capable of altering HD pathogenesis. A first phase of 1200 HD samples has been genotyped using a high density microarray (Affymetrix GeneChip v6.0) and a second phase of genotyping of 1600-2,000 independent HD samples, is gearing up, to confirm or refute results from phase 1 and to add additional power to detect genetic modifiers that could provide therapeutic targets.
Impact of education on age at onset and progression of HD
Genetic and environmental factors other than the Huntington’s disease (HD) gene influence when HD signs appear and how HD progresses. Education protects from Alzheimer´s disease, and development in an enriched environment slows the disease in mouse models of HD. We aim to investigate the impact of education on 1) the age at onset and 2) the progression of HD. For the first aim we use a cross-sectional sample and for the second longitudinal data from patients with 3 or more REGISTRY visits. If education modified HD onset or progression paying attention to education could improve the prognosis.