Juvenile-Onset Huntington Disease Pathophysiology and Neurodevelopment: A Review

Prevalence of Juvenile-Onset and Pediatric Huntington's Disease and Their Availability and Ability to Participate in Trials: A Dutch Population and Enroll-HD Observational Study

Background

Juvenile-onset Huntington's disease (JHD) represents 1-5% of Huntington's disease (HD) patients, with onset before the age of 21. Pediatric HD (PHD) relates to a proportion of JHD patients that is still under 18 years of age. So far, both populations have been excluded from interventional trials.

Objective

Describe the prevalence and incidence of JHD and PHD in the Netherlands and explore their ability to participate in interventional trials.

Methods

The prevalence and incidence of PHD and JHD patients in the Netherlands were analyzed. In addition, we explored proportions of JHD patients diagnosed at pediatric versus adult age, their diagnostic delay, and functional and modelled (CAP100) disease stage in JHD and adult-onset HD patients at diagnosis.

Results

The prevalence of JHD and PHD relative to the total manifest HD population in January 2024 was between 0.84-1.25% and 0.09-0.14% respectively. The mean incidence of JHD patients being diagnosed was between 0.85-1.28 per 1000 patient years and of PHD 0.14 per 1.000.000 under-aged person years. 55% of JHD cases received a clinical diagnosis on adult age. At diagnosis, the majority of JHD patients was functionally compromised and adolescent-onset JHD patients were significantly less independent compared to adult-onset HD patients.

Conclusions

In the Netherlands, the epidemiology of JHD and PHD is lower than previously suggested. More than half of JHD cases are not eligible for trials in the PHD population. Furthermore, higher functional dependency in JHD patients influences their ability to participate in trials. Lastly, certain UHDRS functional assessments and the CAP100 score do not seem appropriate for this particular group.

Atypical Presentations of Huntington Disease-like 2 in South African Individuals

BACKGROUND

Huntington disease-like 2 (HDL2) is a neurodegenerative disorder, affecting only individuals of African ancestry. Full penetrance occurs in individuals with 40 repeats or more.

OBJECTIVE

To describe the phenotypic variability of HDL2 in a group of mixed ancestry individuals from South Africa.

METHODS

Eight patients were assessed with analysis of repeat size and magnetic resonance brain imaging. We applied the Unified Huntington's Disease Rating Scale (UHDRS), but in deceased patients (4), this was estimated from video material.

RESULTS

Cognitive domains were more severely affected than motor; UHDRS motor scores were notable for bradykinesia, and to a slightly lesser extent, for rigidity and dystonia; a single patient had marked chorea. Repeat lengths ranged from 45 to 63 (median, 52).

CONCLUSION

This South African group of mixed ancestry HDL2 individuals presented with severe cognitive and behavioral impairments, with lesser degrees or absence of chorea. This presentation is possibly related to large repeat sizes.

Prevalence and burden of pain across the entire spectrum of Huntington's disease

BACKGROUND

Pain is an important symptom in Huntington's disease (HD), however, not systematically studied and understood. The objective of the current study is to assess the prevalence of pain, pain interference in daily activities, painful conditions, analgesic use and the severity of the pain burden across different disease stages and 'Age at symptom Onset' groups. Additionally, the association between pain and disease burden was investigated.

METHODS

A cross-sectional analysis was conducted within two large data sets, which included different types of pain scales. Multivariable logistic regression analyses and analyses of variance were performed to compare the pain levels with those in the general population. The analyses were adjusted for sex and age. Locally Estimated Scatterplot Smoothing was used to test the association between pain and the HD pathology score: a measure of disease burden.

RESULTS

The mean prevalence of pain in the HD population was 40% and for pain interference around 35% in both data sets. Patients in the early, middle and late stage of HD experience more pain burden compared with what is reported in patients with chronic pain (p<0.01). A positive and significant association was demonstrated between pain and disease burden. Patients in late stage HD with pain use significantly less analgesics compared with the general population (5% vs 13%, respectively (p<0.01)).

CONCLUSIONS

Pain is a prevalent and important symptom in HD. Severe pain burden in the HD population is present and positively associated with disease burden. Risk for undertreatment with analgesics is nevertheless present. Awareness of pain in HD needs to be increased, both clinically and scientifically.

Exploring the Genetic Landscape of Chorea in Infancy and Early Childhood: Implications for Diagnosis and Treatment

Chorea is a hyperkinetic movement disorder frequently observed in the pediatric population, and, due to advancements in genetic techniques, an increasing number of genes have been associated with this disorder. In genetic conditions, chorea may be the primary feature of the disorder, or be part of a more complex phenotype characterized by epileptic encephalopathy or a multisystemic syndrome. Moreover, it can appear as a persistent disorder (chronic chorea) or have an episodic course (paroxysmal chorea). Managing chorea in childhood presents challenges due to its varied clinical presentation, often involving a spectrum of hyperkinetic movement disorders alongside neuropsychiatric and multisystemic manifestations. Furthermore, during infancy and early childhood, transient motor phenomena resembling chorea occurring due to the rapid nervous system development during this period can complicate the diagnosis. This review aims to provide an overview of the main genetic causes of pediatric chorea that may manifest during infancy and early childhood, focusing on peculiarities that can aid in differential diagnosis among different phenotypes and discussing possible treatment options.

Identifying and verifying Huntington's disease subtypes: Clinical features, neuroimaging, and cytokine changes

AIMS

Huntington's disease (HD) is a progressive neurodegenerative disorder with heterogeneous clinical manifestations. Identifying distinct clinical clusters and their relevant biomarkers could elucidate the underlying disease pathophysiology.

METHODS

Following the Enroll-HD program initiated in 2018.09, we have recruited 104 HD patients (including 21 premanifest) and 31 health controls at Beijing Tiantan Hospital. Principal components analysis and k-means cluster analysis were performed to determine HD clusters. Chi-square test, one-way ANOVA, and covariance were used to identify features among these clusters. Furthermore, plasma cytokines levels and brain structural imaging were used as biomarkers to delineate the clinical features of each cluster.

RESULTS

Three clusters were identified. Cluster 1 demonstrated the most severe motor and nonmotor symptoms except for chorea, the lowest whole brain volume, the plasma levels of IL-2 were higher and significantly associated with cluster 1. Cluster 2 was characterized with the most severe chorea and the largest pallidum volume. Cluster 3 had the most benign motor symptoms but moderate psychiatric problems.

CONCLUSION

We have identified three HD clusters via clinical manifestations with distinct biomarkers. Our data shed light on better understanding about the pathophysiology of HD.

The improvement of motor symptoms in Huntington's disease during cariprazine treatment

BACKGROUND

Huntington's disease (HD) is a progressive neurodegenerative disease, characterised by motor disturbances and non-motor (i.e., psychiatric) symptoms. Motor symptoms are the hallmark features of HD and take many forms. Their emergence is related to alterations in striatal dopaminergic neurotransmission: dopamine levels increase in the early stages of the disease, while more advanced stages are characterised by reduced dopamine levels. Such a biphasic change potentially explains the alterations in motor symptoms: increased dopamine-production induces hyperkinetic movements early in the disease course, while depleted dopamine storage leads to hypokinetic symptoms in the advanced phase. Dopamine D2-D3 partial agonists could be a promising treatment option in HD, as they have the potential to either elevate or lower the surrounding dopamine levels if the levels are too low or too high, respectively, potentially offering symptom-relief across the illness-course. Therefore, the present study aimed at exploring the effects of cariprazine, a dopamine D2-D3 partial agonist with high affinity to D3 receptors, on motor symptoms associated with HD.

METHODS

This was a single-centre, retrospective study where sixteen patients received off-label cariprazine treatment for 12 weeks (1.5-3 mg/day). Motor symptoms were evaluated using the Motor Assessment of the Unified Huntington's Disease Rating Scale. Least Square (LS) Mean Changes from Baseline (BL) to Week 8 and Week 12 in the Total Motor Score (TMS) were analysed using the Mixed Model for Repeated Measures method. In addition, improvement from BL to Week 8 and 12 was calculated for all motor items.

RESULTS

Data of 16 patients were collected, but data of only 15 patients were analysed as one patient dropped out due to non-compliance. Significant changes were observed from BL to Week 8 (LS Mean Change: -9.4, p < 0.0001) and to Week 12 (LS Mean Change: -12.8, p < 0.0001) in the TMS. The improvement was captured in the majority of motor functions, excluding bradykinesia and gait. Mild akathisia was the most commonly reported side-effect, affecting 3 patients.

CONCLUSION

This is the first study investigating the effectiveness of a D2-D3 partial agonist, cariprazine, in the treatment of HD. The findings of this study revealed that cariprazine was effective in the treatment of a wide range of motor symptoms associated with HD.

Mutant huntingtin confers cell-autonomous phenotypes on Huntington's disease iPSC-derived microglia

Huntington's disease (HD) is a neurodegenerative disorder caused by a dominantly inherited CAG repeat expansion in the huntingtin gene (HTT). Neuroinflammation and microglia have been implicated in HD pathology, however it has been unclear if mutant HTT (mHTT) expression has an adverse cell-autonomous effect on microglial function, or if they are only activated in response to the neurodegenerative brain environment in HD. To establish a human cell model of HD microglia function, we generated isogenic controls for HD patient-derived induced pluripotent stem cells (iPSC) with 109 CAG repeats (Q109). Q109 and isogenic Q22 iPSC, as well as non-isogenic Q60 and Q33 iPSC lines, were differentiated to iPSC-microglia. Our study supports a model of basal microglia dysfunction in HD leading to elevated pro-inflammatory cytokine production together with impaired phagocytosis and endocytosis capacity, in the absence of immune stimulation. These findings are consistent with early microglia activation observed in pre-manifest patients and indicate that mHTT gene expression affects microglia function in a cell-autonomous way.

HD and SCA1: Tales from two 30-year journeys since gene discovery

One of the more transformative findings in human genetics was the discovery that the expansion of unstable nucleotide repeats underlies a group of inherited neurological diseases. A subset of these unstable repeat neurodegenerative diseases is due to the expansion of a CAG trinucleotide repeat encoding a stretch of glutamines, i.e., the polyglutamine (polyQ) repeat neurodegenerative diseases. Among the CAG/polyQ repeat diseases are Huntington's disease (HD) and spinocerebellar ataxia type 1 (SCA1), in which the expansions are within widely expressed proteins. Although both HD and SCA1 are autosomal dominantly inherited, and both typically cause mid- to late-life-onset movement disorders with cognitive decline, they each are characterized by distinct clinical characteristics and predominant sites of neuropathology. Importantly, the respective affected proteins, Huntingtin (HTT, HD) and Ataxin 1 (ATXN1, SCA1), have unique functions and biological properties. Here, we review HD and SCA1 with a focus on how their disease-specific and shared features may provide informative insights.

Huntington's Disease: Understanding Its Novel Drugs and Treatments

An inherited neurodegenerative ailment called Huntington's disease (HD) of gradual physical impairment, cognitive decline, and psychiatric symptoms. It is brought on by a mutation of the HTT gene, which causes aberrant huntingtin protein buildup in neurons. This predominantly affects the striatum and cerebral cortex, where neuronal malfunction and eventual cell death follow. The quality index of life for both patients and their families is significantly impacted when symptoms first appear in mid-adulthood. An overview of the available therapies for HD is given in this article. Although HD has no known treatment options, there are several that try to lessen symptoms and reduce the disease's development. By lowering involuntary movements, pharmaceutical treatments like tetrabenazine and deutetrabenazine focus on motor symptoms. Antidepressants and antipsychotic medicines are also used to manage the mental and cognitive symptoms of HD. The investigation of prospective gene-based medicines is a result of research into disease-modifying medications. Reduced synthesis of mutant huntingtin protein is the goal of RNA interference (RNAi) strategies, which may halt the course of illness. Additionally, continuing research into Clustered Regularly Interspaced Short Palindromic Repeats and CRISPR-associated protein 9 (CRISPR-Cas9) and other gene editing methods shows promise for reversing the genetic mutation that causes HD. Individuals with HD can benefit from non-pharmacological therapies such as physical therapy, speech therapy, and occupational therapy to increase their functional abilities and general well-being. Supportive treatment, psychiatric therapy, and caregiver support groups are also essential in addressing the difficult problems the illness presents. In conclusion, tremendous progress is being made in the domain of HD treatment, with an emphasis on symptom control, disease modification, and prospective gene-based therapeutics. Even though there has been significant improvement, more study is still required to provide better therapies and ultimately discover a solution for this debilitating condition.

Endophytic fungi: a potential source for drugs against central nervous system disorders

Neuroprotection is one of the important protection methods against neuronal cells and tissue damage caused by neurodegenerative diseases such as Alzheimer's, Parkinson's, Huntington's, and multiple sclerosis. Various bioactive compounds produced by medicinal plants can potentially treat central nervous system (CNS) disorders. Apart from these resources, endophytes also produce diverse secondary metabolites capable of protecting the CNS. The bioactive compounds produced by endophytes play essential roles in enhancing the growth factors, antioxidant defence functions, diminishing neuroinflammatory, and apoptotic pathways. The efficacy of compounds produced by endophytic fungi was also evaluated by enzymes, cell lines, and in vivo models. Acetylcholine esterase (AChE) inhibition is frequently used to assess in vitro neuroprotective activity along with cytotoxicity-induced neuronal cell lines. Some of drugs, such as tacrine, donepezil, rivastigmine, galantamine, and other compounds, are generally used as reference standards. Furthermore, clinical trials are required to confirm the role of these natural compounds in neuroprotection efficacy and evaluate their safety profile. This review illustrates the production of various bioactive compounds produced by endophytic fungi and their role in preventing neurodegeneration.

Aiming for [18F]FDG-PET acquisition time reduction in clinical practice for neurological patients

PURPOSE

Positron emission tomography (PET) imaging with [18F]FDG provides valuable information regarding the underlying pathological processes in neurodegenerative disorders. PET imaging for these populations should be as short as possible to limit head movements and improve comfort. This study aimed to validate an optimized [18F]FDG-PET image reconstruction protocol aiming to reduce acquisition time while maintaining adequate quantification accuracy and image quality.

METHODS

A time-reduced reconstruction protocol (5 min) was evaluated in [18F]FDG-PET retrospective data from healthy individuals and Alzheimer's disease (AD) patients. Standard (8 min) and time-reduced protocols were compared by means of image quality and quantification accuracy metrics, as well as standardized uptake value ratio (SUVR) and Z-scores (pons was used as reference). Images were randomly and blindly presented to experienced physicians and scored in terms of image quality.

RESULTS

No differences between protocols were identified during the visual assessment. Small differences (p < 0.01) in the pons SUVR were observed between the standard and time-reduced protocols for healthy individuals (-0.002 ± 0.011) and AD patients (-0.007 ± 0.013). Likewise, incorporating the PSF correction in the reconstruction algorithm resulted in small differences (p < 0.01) in SUVR between protocols (healthy individuals: -0.003 ± 0.011; AD patients: -0.007 ± 0.014).

CONCLUSION

Quality metrics were similar between time-reduced and standard protocols. In the visual assessment of the images, the physicians did not consider the use of PSF adequate, as it degraded the quality image. Shortening the acquisition time is possible by optimizing the image reconstruction parameters while maintaining adequate quantification accuracy and image quality.

Telomerase reverse transcriptase and neurodegenerative diseases

Neurodegenerative diseases (NDs) are chronic conditions that result in progressive damage to the nervous system, including Alzheimer’s disease (AD), Parkinson’s disease (PD), Huntington’s disease (HD), and Amyotrophic lateral sclerosis (ALS). Age is a major risk factor for NDs. Telomere shortening is a biological marker of cellular aging, and telomerase reverse transcriptase (TERT) has been shown to slow down this process by maintaining telomere length. The blood-brain barrier (BBB) makes the brain a unique immune organ, and while the number of T cells present in the central nervous system is limited, they play an important role in NDs. Research suggests that NDs can be influenced by modulating peripheral T cell immune responses, and that TERT may play a significant role in T cell senescence and NDs. This review focuses on the current state of research on TERT in NDs and explores the potential connections between TERT, T cells, and NDs. Further studies on aging and telomeres may provide valuable insights for developing therapeutic strategies for age-related diseases.

Diagnostic Uncertainties: Chorea

Chorea is a hyperkinetic movement disorder with a multitude of potential etiologies, both acquired and inherited. Although the differential diagnosis for new-onset chorea is extensive, there are often clues in the history, exam, and basic testing that can help to narrow the options. Evaluation for treatable or reversible causes should take priority, as rapid diagnosis can lead to more favorable outcomes. While Huntington's disease is most common genetic cause of chorea, multiple phenocopies also exist and should be considered if Huntington gene testing is negative. The decision of what additional genetic testing to pursue should be based on both clinical and epidemiological factors. The following review provides an overview of the many possible etiologies as well as a practical approach for a patient presenting with new-onset chorea.

Comorbidities and clinical outcomes in adult- and juvenile-onset Huntington's disease: a study of linked Swedish National Registries (2002-2019)

BACKGROUND

Huntington's disease (HD) is a rare, neurodegenerative disease and its complex motor, cognitive and psychiatric symptoms exert a lifelong clinical burden on both patients and their families.

OBJECTIVE

To describe the clinical burden and natural history of HD.

METHODS

This longitudinal cohort study used data from the linked Swedish national registries to describe the occurrence of comorbidities (acute and chronic), symptomatic treatments and mortality in an incident cohort of individuals who either received the first diagnosis of HD above (adult onset HD; AoHD) or below (juvenile-onset HD; JoHD) 20 years of age, compared with a matched cohort without HD from the general population. Disease burden of all individuals alive in Sweden was described during a single calendar year (2018), including the occurrence of key symptoms, treatments and hospitalizations.

RESULTS

The prevalence of HD in 2018 was approximately 10.2 per 100,000. Of 1492 individuals with a diagnosis of HD during 2002 and 2018, 1447 had AoHD and 45 had JoHD. Individuals with AoHD suffered a higher incidence of obsessive-compulsive disorder, acute psychotic episodes, pneumonia, constipation and fractures compared with matched controls. Individuals with JoHD had higher incidence rates of epilepsy, constipation and acute respiratory symptoms. Median time to all-cause mortality in AoHD was 12.1 years from diagnosis. Patients alive with HD in Sweden in 2018 displayed a pattern of increased clinical burden for a number of years since diagnosis.

CONCLUSIONS

This study demonstrates the significant and progressive clinical burden in individuals with HD and presents novel insights into the natural history of JoHD.

Dysregulation of Human Juvenile Huntington's Disease Brain Proteomes in Cortex and Putamen Involves Mitochondrial and Neuropeptide Systems

BACKGROUND

Huntington's disease (HD) is a genetic neurodegenerative disease caused by trinucleotide repeat CAG expansions in the human HTT gene. Early onset juvenile HD (JHD) in children is the most severe form of the disease caused by high CAG repeat numbers of the HTT gene.

OBJECTIVE

To gain understanding of human HD mechanisms hypothesized to involve dysregulated proteomes of brain regions that regulate motor and cognitive functions, this study analyzed the proteomes of human JHD cortex and putamen brain regions compared to age-matched controls.

METHODS

JHD and age-matched control brain tissues were assessed for CAG repeat numbers of HTT by PCR. Human brain JHD brain cortex regions of BA4 and BA6 with the putamen region (n = 5) were analyzed by global proteomics, compared to age-matched controls (n = 7). Protein interaction pathways were assessed by gene ontology (GO), STRING-db, and KEGG bioinformatics.

RESULTS

JHD brain tissues were heterozygous for one mutant HTT allele containing 60 to 120 CAG repeats, and one normal HTT allele with 10 to 19 CAG repeats. Proteomics data for JHD brain regions showed dysregulated mitochondrial energy pathways and changes in synaptic systems including peptide neurotransmitters. JHD compared to control proteomes of cortex and putamen displayed (a) proteins present only in JHD, (b) proteins absent in JHD, and (c) proteins that were downregulated or upregulated.

CONCLUSIONS

Human JHD brain cortex and putamen regions display significant dysregulation of proteomes representing deficits in mitochondrial and synaptic neurotransmission functions. These findings advance understanding of JHD brain molecular mechanisms associated with HD disabilities.

Recent approaches on Huntington's disease (Review)

Huntington's disease (HD) is a neurodegenerative disorder characterized by severe motor, cognitive and psychiatric symptoms. Patients of all ages can present with a dysfunction of the nervous system, which leads to the progressive loss of movement control and disabilities in speech, swallowing, communications, etc. The molecular basis of the disease is well-known, as HD is related to a mutated gene, a trinucleotide expansion, which encodes to the huntingtin protein. This protein is linked to neurogenesis and the loss of its function leads to neurodegenerative disorders. Although the genetic cause of the disorder has been known for decades, no effective treatment is yet available to prevent onset or to eliminate the progression of symptoms. Thus, the present review focused on the development of novel methods for the timely and accurate diagnosis of HD in an aim to aid the development of therapies which may reduce the severity of the symptoms and control their progression. The majority of the therapies include gene-silencing mechanisms of the mutated huntingtin gene aiming to suppress its expression, and the use of various substances as drugs with highly promising results. In the present review, the latest approaches on the diagnosis of HD are discussed along with the need for genetic counseling and an up-to-date presentation of the applied treatments.

Quinolinic Acid Impairs Redox Homeostasis, Bioenergetic, and Cell Signaling in Rat Striatum Slices: Prevention by Coenzyme Q10

Quinolinic acid (QUIN) is an important agonist of NMDA receptors that are found at high levels in cases of brain injury and neuroinflammation. Therefore, it is necessary to investigate neuroprotection strategies capable of neutralizing the effects of the QUIN on the brain. Coenzyme Q10 (CoQ10) is a provitamin that has an important antioxidant and anti-inflammatory action. This work aims to evaluate the possible neuroprotective effect of CoQ10 against the toxicity caused by QUIN. Striatal slices from 30-day-old Wistar rats were preincubated with CoQ10 25-100 μM for 15 min; then, QUIN 100 μM was added to the incubation medium for 30 min. A dose-response curve was used to select the CoQ10 concentration to be used in the study. Results showed that QUIN caused changes in the production of ROS, nitrite levels, activities of antioxidant enzymes, glutathione content, and damage to proteins and lipids. CoQ10 was able to prevent the effects caused by QUIN, totally or partially, except for damage to proteins. QUIN also altered the activities of electron transport chain complexes and ATP levels, and CoQ10 prevented totally and partially these effects, respectively. CoQ10 prevented the increase in acetylcholinesterase activity, but not the decrease in the activity of Na+,K+-ATPase caused by QUIN. We also observed that QUIN caused changes in the total ERK and phospho-Akt content, and these effects were partially prevented by CoQ10. These findings suggest that CoQ10 may be a promising therapeutic alternative for neuroprotection against QUIN neurotoxicity.

“Spazio Huntington”: Tracing the Early Motor, Cognitive and Behavioral Profiles of Kids with Proven Pediatric Huntington Disease and Expanded Mutations > 80 CAG Repeats

The “Spazio Huntington—A Place for Children” program was launched in 2019. The aim was to contact at risk kids within Huntington disease (HD) families, to provide counseling to their parents and to start a prospective follow-up of kids suspicious to manifest pediatric HD (PHD). We met 25 at risk kids in two years, four of whom with PHD and highly expanded (HE) mutations beyond 80 CAG repeats. We rated motor, neuropsychological and behavioral changes in all PHD kids by the Unified HD Rating Scale (UHDRS)-total motor score (TMS) and additional measures of (1) cognitive level (Leiter International Performance Scale), (2) adaptive functioning (Adaptive Behavior Assessment Systems), (3) receptive language (Peabody Picture Vocabulary Test) and (4) behavioral abnormalities (Child Behavior Check List and Children’s Yale–Brown Obsessive Compulsive Scale). All PHD kids showed a severe progression of neurological and psychiatric manifestations including motor, cognitive and behavioral changes. The magnetic resonance imaging contributed to confirm the suspicious clinical observation by highlighting very initial striatum abnormalities in PHD. Spazio Huntington is a program to prospectively study PHD, the most atypical face of HD, and may represent the basis to recruit PHD patients in future clinical trials.