Safety and feasibility of research lumbar puncture in Huntington's disease: the HDClarity cohort and bioresource

Background: Biomarkers are needed to monitor disease progression, target engagement and efficacy in Huntington's disease (HD). Cerebrospinal fluid (CSF) is an ideal medium to research such biomarkers due to its proximity to the brain. Objectives: To investigate the safety and feasibility of research lumbar punctures (LP) in HD. Methods: HDClarity (NCT02855476) is an ongoing international biofluid collection initiative built on the Enroll-HD platform, where clinical assessments are recorded. It aims to recruit 1,200 participants. Biosamples are collected following an overnight fast: blood via venipuncture and CSF via LP. Participants are healthy controls and HD gene expansion carriers across the disease spectrum. We report on monitored data from February 2016 to September 2019. Results: Of 448 participants screened, 398 underwent at least 1 sampling visit, of which 98.24% were successful (i.e. CSF was collected), amounting to 10,610mL of CSF and 8,200mL of plasma. In the total 572 sampling visits, adverse events were reported in 24.13%, and headaches of any kind and post-LP headaches in 14.86% and 12.24%, respectively. Frequencies were less in manifest HD; gender, age, body mass index and disease burden score were not associated with the occurrence of the events in gene expansion carriers. Headaches and back pain were the most frequent adverse events. Conclusions: HDClarity is the largest CSF collection initiative to support scientific research into HD and is now established as a leading resource for HD research. Our data confirm that research LP in HD are feasible and acceptable to the community, and have a manageable safety profile.

Mild Cognitive Impairment as an Early Landmark in Huntington's Disease

As one of the clinical triad in Huntington's disease (HD), cognitive impairment has not been widely accepted as a disease stage indicator in HD literature. This work aims to study cognitive impairment thoroughly for prodromal HD individuals with the data from a 12-year observational study to determine whether Mild Cognitive Impairment (MCI) in HD gene-mutation carriers is a defensible indicator of early disease. Prodromal HD gene-mutation carriers evaluated annually at one of 32 worldwide sites from September 2002 to April 2014 were evaluated for MCI in six cognitive domains. Linear mixed-effects models were used to determine age-, education-, and retest-adjusted cut-off values in cognitive assessment for MCI, and then the concurrent and predictive validity of MCI was assessed. Accelerated failure time (AFT) models were used to determine the timing of MCI (single-, two-, and multiple-domain), and dementia, which was defined as MCI plus functional loss. Seven hundred and sixty-eight prodromal HD participants had completed all six cognitive tasks, had MRI, and underwent longitudinal assessments. Over half (i.e., 54%) of the participants had MCI at study entry, and half of these had single-domain MCI. Compared to participants with intact cognitive performances, prodromal HD with MCI had higher genetic burden, worsened motor impairment, greater brain atrophy, and a higher likelihood of estimated HD onset. Prospective longitudinal study of those without MCI at baseline showed that 48% had MCI in subsequent visits and data visualization suggested that single-domain MCI, two-domain MCI, and dementia represent appropriate cognitive impairment staging for HD gene-mutation carriers. Findings suggest that MCI represents an early landmark of HD and may be a sensitive enrichment variable or endpoint for prodromal clinical trials of disease modifying therapeutics.

Timing and Impact of Psychiatric, Cognitive, and Motor Abnormalities in Huntington Disease

ObjectiveTo assess the prevalence, timing and functional impact of psychiatric, cognitive and motor abnormalities in Huntington’s disease (HD) gene carriers, we analysed retrospective clinical data from individuals with manifest HD.MethodsClinical features of HD patients were analysed for 6316 individuals in the European REGISTRY study from 161 sites across 17 countries. Data came from clinical history and the patient-completed Clinical Characteristics Questionnaire that assessed eight symptoms: motor, cognitive, apathy, depression, perseverative/obsessive behavior, irritability, violent/aggressive behavior, and psychosis. Multiple logistic regression was used to analyse relationships between symptoms and functional outcomes.ResultsThe initial manifestation of HD is increasingly likely to be motor, and less likely to be psychiatric, as age at presentation increases, and is independent of pathogenic CAG repeat length. The Clinical Characteristics Questionnaire captures data on non-motor symptom prevalence that correlate specifically with validated clinical measures. Psychiatric and cognitive symptoms are common in HD gene carriers, with earlier onsets associated with longer CAG repeats. 42.4% of HD patients reported at least one psychiatric or cognitive symptom before motor symptoms, with depression most common. Each non-motor symptom was associated with significantly reduced total functional capacity scores.ConclusionsPsychiatric and cognitive symptoms are common and functionally debilitating in HD gene carriers. They require recognition and targeting with clinical outcome measures and treatments. However, as it is impossible to distinguish confidently between non-motor symptoms arising from HD and primary psychiatric disorders, particularly in younger pre-manifest patients, non-motor symptoms should not be used to make a clinical diagnosis of HD.

Zinc Finger-Homeodomain Transcriptional Factors (ZF-HDs) in Wheat (Triticum aestivum L.): Identification, Evolution, Expression Analysis and Response to Abiotic Stresses

Zinc finger-homeodomain transcriptional factors (ZF-HDs), a kind of plant-specific transcription factor, play important roles in plant growth, development and various stress responses. In this study, the genome-wide analysis of the ZF-HD gene family was performed in wheat. A total of 37 TaZF-HD genes were identified in T. aestivum and classified into six groups. The results of a synteny analysis showed that gene replication events contributed to the expansion of the TaZF-HD gene family. The TaZF-HD paralogous gene pairs with similar chromosomal locations in different subgenomes had similar expression patterns. TaZF-HDs were highly induced under PEG (polyethylene glycol), NaCl and cold stress but not induced under heat stress. Gene ontology (GO) annotation and protein-protein interactions suggested that TaZF-HD proteins may participate in various biological processes of plants. These results increase our understanding of ZF-HD genes and provide robust candidate genes for future functional investigations aimed at crop improvement.

Huntington’s Disease Pathogenesis: Two Sequential Components

Historically, Huntington’s disease (HD; OMIM #143100) has played an important role in the enormous advances in human genetics seen over the past four decades. This familial neurodegenerative disorder involves variable onset followed by consistent worsening of characteristic abnormal movements along with cognitive decline and psychiatric disturbances. HD was the first autosomal disease for which the genetic defect was assigned to a position on the human chromosomes using only genetic linkage analysis with common DNA polymorphisms. This discovery set off a multitude of similar studies in other diseases, while the HD gene, later renamed HTT, and its vicinity in chromosome 4p16.3 then acted as a proving ground for development of technologies to clone and sequence genes based upon their genomic location, with the growing momentum of such advances fueling the Human Genome Project. The identification of the HD gene has not yet led to an effective treatment, but continued human genetic analysis of genotype-phenotype relationships in large HD subject populations, first at the HTT locus and subsequently genome-wide, has provided insights into pathogenesis that divide the course of the disease into two sequential, mechanistically distinct components.

The genetics of Huntington’s disease

This chapter describes the nature of the genetic mistake. The genetic code, or DNA molecule, is wound up onto structures called chromosomes. The gene for HD is located on chromosome 4. As we have two copies of our genes the chromosomes are in pairs. Only one copy of the HD has to be abnormal to cause the condition. This results in a pattern of inheritance called autosomal dominant and both males and females can be affected. Genes code for proteins; the protein encoded by the HD gene is called huntingtin. Proteins are made of building blocks called amino acids. The gene for HD has an expansion of the genetic code for glutamine. Therefore, abnormal huntingtin has an expansion of the number of glutamines. The genetic code for glutamine is CAG so the mistake in the gene is sometimes called a CAG repeat expansion disorder or in referring to the protein it is called a polyglutamine repeat expansion. The gene is in one part of the cell and the protein-making machinery is in another part of the cell so a chemical messenger is required which is called RNA. Explaining this is important for understanding some current clinical trials

Gene Expression Profiling in Huntington’s Disease: Does Comorbidity with Depressive Symptoms Matter?

Huntington’s disease (HD) is an inherited neurodegenerative disease. Besides the well-characterized motor symptoms, HD is marked by cognitive impairment and behavioral changes. In this study, we analyzed the blood of HD gene carries using RNA-sequencing techniques. We evaluated samples from HD gene carriers with (n = 8) and without clinically meaningful depressive symptoms (n = 8) compared with healthy controls (n = 8). Groups were age- and sex-matched. Preprocessing of data and between-group comparisons were calculated using DESeq2. The Wald test was used to generate p-values and log2 fold changes. We found 60 genes differently expressed in HD and healthy controls, of which 21 were upregulated and 39 downregulated. Within HD group, nineteen genes were differently expressed between patients with and without depression, being 6 upregulated and 13 downregulated. Several of the top differentially expressed genes are involved in nervous system development. Although preliminary, our findings corroborate the emerging view that in addition to neurodegenerative mechanisms, HD has a neurodevelopmental component. Importantly, the emergence of depression in HD might be related to these mechanisms.

9 Aberrant striatal value representation in Huntington’s disease gene carriers 25 years before onset

AimsHuntington’s disease (HD) is a devastating genetic neurodegenerative condition typically manifesting clinically in the fourth or fifth decade. With the advent of genetic therapies there is increased need to identify the earliest changes associated with carrying the HD gene. In this study we sought to determine the earliest functional imaging differences between HD gene carriers and matched controls. Based on previous work, we hypothesised that as compared to controls, HD gene carriers decades from onset would show a neural ‘reward bias’ – an exaggerated striatal response to gains as compared to losses.MethodsWe recruited 35 HD gene carriers, estimated to be on average 26 years from motor onset, and 35 controls. Groups were well matched for age, gender and education level.Participants completed a reinforcement learning task in a fMRI scanner using a sequence optimised for orbitofrontal and striatal signal. In this task participants were required to learn to choose between stimuli with the aim of maximise rewards and avoiding losses. Task behaviour was modelled using a computational model and computational variables from the best fitting model was used to probe fMRI data.ResultsAs hypothesised, we found that, in comparison to matched controls, gene carriers over 25 years from motor onset showed exaggerated striatal responses to gain as compared to loss predicting stimuli (p=0.003) in a reinforcement learning task. Using computational analysis, we also found group differences in striatal representation of stimulus value (p=0.0007).ConclusionThese represent the earliest functional imaging differences between HD gene carriers and controls. Behaviourally gene carriers, 9 years from predicted onset, have shown enhanced learning from gains as compared to losses. Importantly, we found no group differences in behaviour, or caudate volumes. Our data suggests a therapeutic window exists whereby HD- related functional neural changes are detectable 25 years before predicted onset.

Hypomorphic mutation of the mouse Huntington’s disease gene orthologue

Rare individuals with hypomorphic inactivating mutations in the Huntington’s Disease (HD) gene (HTT), identified by CAG repeat expansion in the eponymous neurodegenerative disorder, exhibit variable abnormalities that implyHTTessential roles during organ development. Here we report phenotypes produced when increasingly severe hypomorphic mutations inHtt, the murineHTTorthologue (inHdhneoQ20,HdhneoQ50,HdhneoQ111mice), were placed over a null allele (Hdhex4/5). The most severe hypomorphic allele failed to rescue null lethality at gastrulation, while the intermediate alleles yielded perinatal lethality and a variety of fetal abnormalities affecting body size, skin, skeletal and ear formation, and transient defects in hematopoiesis. Comparative molecular analysis of wild-type andHtt-null retinoic acid-differentiated cells revealed gene network dysregulation associated with organ development and proposed polycomb repressive complexes and miRNAs as molecular mediators. Together these findings demonstrate that the HD gene acts both pre- and post-gastrulation and possibly suggest pleiotropic consequences ofHTT-lowering therapeutic strategies.Author SummaryTheHTTgene product mutated in Huntington’s Disease (HD) has essential roles during normal organism development, however, still not fully predictable are the functional consequences of its partial inactivation. Our genetic study provides a comprehensive effects’ description of progressively stronger suppression ofHttgene, the murineHTTcounterpart. The most severeHttreduction leads to embryo lethality, while intermediateHttdosages yield a variety of developmental abnormalities affecting body size, skin, skeletal and ear formation, and hematopoiesis. Complementing molecular analysis in differentiating cells depleted of a functionalHttgene further elucidates genes’ networks dysregulated during organ development and proposes chromatin regulators and short non-coding RNAs as key molecular mediators. Together these findings demonstrate that the HD gene acts both at early and later stages of development, thus possibly suggesting long-term consequences associated to the newest HD therapeutic strategies aimed at lowering theHTTgene product.