Huntington's Disease Status Research Articles

Huntington's disease: Mortality and risk factors in an Australian cohort

IntroductionThere has not been any examination of the risk factors associated with mortality in Huntington's Disease (HD) in an Australian cohort. MethodThis retrospective study included inpatients admitted to a specialist neuropsychiatry service in Melbourne, Australia. HD status was based on genetic testing. Risk factors included age of onset, CAG repeat length and neuroimaging. Mortality data was acquired through the Australian Institute of Health and Welfare National Death Index. ResultsThe cohort included 83 participants, with 44 (53%) deceased. The median age of death was 59 years and median survival was 18.8 years from onset age (median 41.0 years). CAG repeat length (median 44.0, IQR 42.5, 47.0) was inversely correlated with age of onset (r = −0.73) and age at death (r = −0.80) but was not correlated with mortality status. There was no difference in functional and cognitive assessments, nor brain volumes, in the alive group compared to the deceased group. There were more people who were alive who had a positive family history of a psychiatric condition (p = 0.006) or dementia (p = 0.009). Standardised mortality ratios demonstrated a 5.9× increased risk of death for those with HD compared to the general population. ConclusionsThis is the first study to examine risk factors of mortality in HD in an Australian cohort. Median survival in our cohort is consistent with previous studies in HD, and markedly reduced compared to the general Australian population. CAG repeat length was not associated with mortality suggesting that non-genetic factors contribute to mortality status and warrant further investigation.

Predicting Severity of Huntington's Disease With Wearable Sensors.

The Unified Huntington's Disease Rating Scale (UHDRS) is the primary clinical assessment tool for rating motor function in patients with Huntington's disease (HD). However, the UHDRS and similar rating scales (e.g., UPDRS) are both subjective and limited to in-office assessments that must be administered by a trained and experienced rater. An objective, automated method of quantifying disease severity would facilitate superior patient care and could be used to better track severity over time. We conducted the present study to evaluate the feasibility of using wearable sensors, coupled with machine learning algorithms, to rate motor function in patients with HD. Fourteen participants with symptomatic HD and 14 healthy controls participated in the study. Each participant wore five adhesive biometric sensors applied to the trunk and each limb while completing brief walking, sitting, and standing tasks during a single office visit. A two-stage machine learning method was employed to classify participants by HD status and to predict UHDRS motor subscores. Linear discriminant analysis correctly classified all participants' HD status except for one control subject with abnormal gait (96.4% accuracy, 92.9% sensitivity, and 100% specificity in leave-one-out cross-validation). Two regression models accurately predicted individual UHDRS subscores for gait, and dystonia within a 10% margin of error. Our regression models also predicted a composite UHDRS score–a sum of left and right arm rigidity, total chorea, total dystonia, bradykinesia, gait, and tandem gait subscores–with an average error below 15%. Machine learning classifiers trained on brief in-office datasets discriminated between controls and participants with HD, and could accurately predict selected motor UHDRS subscores. Our results could enable the future use of biosensors for objective HD assessment in the clinic or remotely and could inform future studies for the use of this technology as a potential endpoint in clinical trials.

The Prospective Huntington At-Risk Observational Study (PHAROS): The Emotional Well-Being, Safety and Feasibility of Long-Term Research Participation.

There is limited understanding of the feasibility of conducting long-term research among undiagnosed (pre-symptomatic) adults at risk to develop Huntington disease (HD), while protecting their emotional well-being and safety. To assess pre-specified events pertaining to emotional well-being, safety, and feasibility among healthy consenting adults at risk for developing HD who have chosen not to undergo genetic testing. PHAROS research participants prospectively reported the occurrence of events pertaining to psychological distress (psychiatric evaluations, depression, suicidality) and feasibility (maintaining confidentiality, study attrition). PHAROS enrolled 1001 participants. Events pertaining to psychological distress were reported by 35% of participants. The most common events included heightened suicide risk (26%), new onset depression (12%), and new mental health evaluation (9%); all occurred significantly more frequently among participants with expanded trinucleotide CAG repeats (≥37). Five deaths occurred, none related to suicide. Forty-one percent of participants reported self-disclosure of their HD at-risk status, and 15% reported that someone else (usually a family member) had done so. Confidentiality of CAG test results was maintained by investigators. The withdrawal rate was largely uniform over the study period and did not differ significantly by gender or CAG status. The potentially vulnerable research participants in PHAROS showed good emotional tolerability and safety. Individual CAG data were not disclosed, and confidentiality about disclosure of at-risk HD status was well maintained by others (family, friends, etc.). Long-term research participation of adults at risk for HD who choose not to undergo pre-symptomatic DNA testing is well tolerated, safe and feasible.

Deterioration of mitochondrial bioenergetics and ultrastructure impairment in skeletal muscle of a transgenic minipig model in the early stages of Huntington's disease.

ABSTRACTSkeletal muscle wasting and atrophy is one of the more severe clinical impairments resulting from the progression of Huntington's disease (HD). Mitochondrial dysfunction may play a significant role in the etiology of HD, but the specific condition of mitochondria in muscle has not been widely studied during the development of HD. To determine the role of mitochondria in skeletal muscle during the early stages of HD, we analyzed quadriceps femoris muscle from 24-, 36-, 48- and 66-month-old transgenic minipigs that expressed the N-terminal portion of mutated human huntingtin protein (TgHD) and age-matched wild-type (WT) siblings. We found altered ultrastructure of TgHD muscle tissue and mitochondria. There was also significant reduction of activity of citrate synthase and respiratory chain complexes (RCCs) I, II and IV, decreased quantity of oligomycin-sensitivity conferring protein (OSCP) and the E2 subunit of pyruvate dehydrogenase (PDHE2), and differential expression of optic atrophy 1 protein (OPA1) and dynamin-related protein 1 (DRP1) in the skeletal muscle of TgHD minipigs. Statistical analysis identified several parameters that were dependent only on HD status and could therefore be used as potential biomarkers of disease progression. In particular, the reduction of biomarker RCCII subunit SDH30 quantity suggests that similar pathogenic mechanisms underlie disease progression in TgHD minipigs and HD patients. The perturbed biochemical phenotype was detectable in TgHD minipigs prior to the development of ultrastructural changes and locomotor impairment, which become evident at the age of 48 months. Mitochondrial disturbances may contribute to energetic depression in skeletal muscle in HD, which is in concordance with the mobility problems observed in this model.This article has an associated First Person interview with the first author of the paper.

Natural biological variation of white matter microstructure is accentuated in Huntington's disease.

Huntington's disease (HD) is a monogenic neurodegenerative disorder caused by a CAG‐repeat expansion in the Huntingtin gene. Presence of this expansion signifies certainty of disease onset, but only partly explains age at which onset occurs. Genome‐wide association studies have shown that naturally occurring genetic variability influences HD pathogenesis and disease onset. Investigating the influence of biological traits in the normal population, such as variability in white matter properties, on HD pathogenesis could provide a complementary approach to understanding disease modification. We have previously shown that while white matter diffusivity patterns in the left sensorimotor network were similar in controls and HD gene‐carriers, they were more extreme in the HD group. We hypothesized that the influence of natural variation in diffusivity on effects of HD pathogenesis on white matter is not limited to the sensorimotor network but extends to cognitive, limbic, and visual networks. Using tractography, we investigated 32 bilateral pathways within HD‐related networks, including motor, cognitive, and limbic, and examined diffusivity metrics using principal components analysis. We identified three independent patterns of diffusivity common to controls and HD gene‐carriers that predicted HD status. The first pattern involved almost all tracts, the second was limited to sensorimotor tracts, and the third encompassed cognitive network tracts. Each diffusivity pattern was associated with network specific performance. The consistency in diffusivity patterns across both groups coupled with their association with disease status and task performance indicates that naturally‐occurring patterns of diffusivity can become accentuated in the presence of the HD gene mutation to influence clinical brain function.

Huntington's disease accelerates epigenetic aging of human brain and disrupts DNA methylation levels.

Age of Huntington's disease (HD) motoric onset is strongly related to the number of CAG trinucleotide repeats in the huntingtin gene, suggesting that biological tissue age plays an important role in disease etiology. Recently, a DNA methylation based biomarker of tissue age has been advanced as an epigenetic aging clock. We sought to inquire if HD is associated with an accelerated epigenetic age. DNA methylation data was generated for 475 brain samples from various brain regions of 26 HD cases and 39 controls. Overall, brain regions from HD cases exhibit a significant epigenetic age acceleration effect (p=0.0012). A multivariate model analysis suggests that HD status increases biological age by 3.2 years. Accelerated epigenetic age can be observed in specific brain regions (frontal lobe, parietal lobe, and cingulate gyrus). After excluding controls, we observe a negative correlation (r=−0.41, p=5.5×10−8) between HD gene CAG repeat length and the epigenetic age of HD brain samples. Using correlation network analysis, we identify 11 co-methylation modules with a significant association with HD status across 3 broad cortical regions. In conclusion, HD is associated with an accelerated epigenetic age of specific brain regions and more broadly with substantial changes in brain methylation levels.

Huntington Disease: Molecular Diagnostics Approach.

Huntington disease (HD) is caused by expansion of a CAG trinucleotide repeat in the first exon of the Huntingtin (HTT) gene. Molecular testing of Huntington disease for diagnostic confirmation and disease prediction requires detection of the CAG repeat expansion. There are three main types of HD genetic testing: (1) diagnostic testing to confirm or rule out disease, (2) presymptomatic testing to determine whether an at-risk individual inherited the expanded allele, and (3) prenatal testing to determine whether the fetus has inherited the expanded allele. This unit includes protocols that describe the complementary use of polymerase chain reactions (PCR) and Southern blot hybridization to accurately measure the CAG trinucleotide repeat size and interpret the test results. In addition, an indirect linkage analysis that does not reveal the unwanted parental HD status in a prenatal testing will also be discussed.

The use of quantitative oculometry in the assessment of Huntington’s disease

Huntington's disease (HD) is a neurodegenerative disorder characterised by progressive motor, cognitive and psychiatric symptoms. Objective measurement of disease severity is of increasing importance for detecting symptomatic disease, as well as monitoring disease progression and the response to novel therapeutic interventions. Using a newly-developed infra-red scleral oculometer, we measured saccadic latencies and durations in HD patients exhibiting a broad range of symptoms (n=24) and control subjects of comparable ages (n=20) to see whether these parameters might reflect the presence or severity of HD. Latency distributions were characterised by creating reciprobit plots for each subject, whilst parametric statistics were applied to durations. Compared with the control group, we found the HD group had a significantly increased median latency, and early saccades were more prominent. In addition, HD patients exhibited an increased saccadic duration and variability of duration. Using Bayesian (likelihood) analysis, we obtained saccadic support values for the presence of clinical HD, which correlated with the motor Unified Huntington's Disease Rating Scale (UHDRS) score in these patients. A sensitivity/specificity analysis of all 44 participants showed that the use of this multivariate support measure was highly successful in predicting HD status, correctly diagnosing 75% of the HD patients, and (95%) of the controls; with a different criterion, these figures were 96 and 15%. Furthermore, we correctly predicted absence of disease in two additional subjects subsequently confirmed to be genetically unaffected. This strongly suggests that multivariate support values derived from saccadic parameters may provide an objective, quantitative biomarker of HD, especially the degree of motor impairment. However, larger longitudinal studies are required to determine whether they can reliably detect the earliest presymptomatic disease, or faithfully reflect disease progression.

Clinical and counselling implications of preimplantation genetic diagnosis for Huntington's disease in the UK

Huntington's disease is an autosomal dominant neurodegenerative disorder that usually occurs in adult life. Individuals at risk can have a gene test before the onset of symptoms, and prenatal diagnosis is available. Preimplantation genetic diagnosis (PGD) for Huntington's disease is now available for couples in whom one partner has the gene for Huntington's disease. A licence to practise PGD is required from the Human Fertilisation and Embryology Authority, and there are several complex issues relating to PGD for Huntington's disease that require consideration. The partner of the Huntington's disease gene carrier should have a presymptomatic test to ensure accuracy in a PGD cycle. There should be a delay between blood sampling and testing for Huntington's disease to allow time for reflection and withdrawal from testing. All PGD treatment has an associated risk of misdiagnosis. If confirmatory prenatal testing is not undertaken after a successful PGD cycle, no confirmation of diagnosis will be obtained at birth. Guidelines indicate that individuals who are at risk cannot be tested before 18 years. There is concern over the ability of a child or adolescent to make an informed choice about testing before this age. Confirmatory testing at birth after PGD would be in direct contravention of these guidelines. In the UK, the law requires consideration of the welfare of children born after assisted conception treatment. Presenting symptoms of Huntington's disease may affect the parenting abilities of an affected individual. There is a need for an assessment of a patient's current Huntington's disease status and their planned provision of care of children if Huntington's disease affects parenting. It has been necessary to create a detailed working protocol for the management of PGD for Huntington's disease to address these issues.

Prenatal diagnosis for huntington's disease: A molecular and psychological study

Two linked probes were used to determine the Huntington's disease status of the fetus conceived by a woman affected with the condition. The fetus was found to be unaffected with a certainty of 97 per cent. The ethical issues associated with presymptomatic testing were avoided since the mother presented with initial symptoms of Huntington's disease, but other psychological and ethical issues arose. The concerns of an affected woman planning a pregnancy, and the dilemmas involved in decision-making regarding prenatal diagnosis and possible selective abortion were exposed and explored with the patient and her husband.