mHTT Seeding Activity: A Marker of Disease Progression and Neurotoxicity in Models of Huntington's Disease.

Self-propagating, amyloidogenic mutant huntingtin (mHTT) aggregates may drive progression of Huntington's disease (HD). Here, we report the development of a FRET-based mHTT aggregate seeding (FRASE) assay that enables the quantification of mHTT seeding activity (HSA) in complex biosamples from HD patients and disease models. Application of the FRASE assay revealed HSA in brain homogenates of presymptomatic HD transgenic and knockin mice and its progressive increase with phenotypic changes, suggesting that HSA quantitatively tracks disease progression. Biochemical investigations of mouse brain homogenates demonstrated that small, rather than large, mHTT structures are responsible for the HSA measured in FRASE assays. Finally, we assessed the neurotoxicity of mHTT seeds in an inducible Drosophila model transgenic for HTTex1. We found a strong correlation between the HSA measured in adult neurons and the increased mortality of transgenic HD flies, indicating that FRASE assays detect disease-relevant, neurotoxic, mHTT structures with severe phenotypic consequences in vivo.

Effects of mutant huntingtin in oxytocin neurons on non-motor features of Huntington's disease.

BACKGROUND: Early non-motor features including anxiety, depression and altered social cognition are present in Huntington's disease (HD). The underlying neurobiological mechanisms are not known. Oxytocin (OXT) is involved in the regulation of emotion, social cognition and metabolism, and our previous work showed that the OXT system is affected early in HD. The aim of the study was to investigate the potential causal relationship between the selective expression of mutant huntingtin (mHTT) in OXT neurons and the development of non-motor features and neuropathology. METHODS: To express mHTT only in OXT neurons, we used a novel flex-switch adeno-associated viral vector design to selectively express either mHTT or wild-type HTT in the paraventricular nucleus of the hypothalamus using OXT-Cre-recombinase mice. We also performed a mirror experiment to selectively delete mHTT in OXT neurons using the BACHD mouse model. Mice underwent a battery of behavioural tests to assess psychiatric and social behaviours 3 months post-injection or at 2 months of age, respectively. Post-mortem analyses were performed to assess the effects on the OXT system. RESULTS: Our results show that selective expression of mHTT in OXT neurons was associated with the formation of mHTT inclusions and a 26% reduction of OXT-immunopositive neurons as well as increased anxiety-like behaviours compared with uninjected mice. However, selective deletion of mHTT from OXT neurons alone was not sufficient to alter the metabolic and psychiatric phenotype of the BACHD mice at this early time point. CONCLUSIONS: Our results indicate that mHTT expression can exert cell-autonomous toxic effects on OXT neurons without affecting the non-motor phenotype at early time points in mice.

Effects of mutant huntingtin inactivation on Huntington disease-related behaviours in the BACHD mouse model.

AIMS: Huntington disease (HD) is a fatal neurodegenerative disorder with no disease-modifying treatments approved so far. Ongoing clinical trials are attempting to reduce huntingtin (HTT) expression in the central nervous system (CNS) using different strategies. Yet, the distribution and timing of HTT-lowering therapies required for a beneficial clinical effect is less clear. Here, we investigated whether HD-related behaviours could be prevented by inactivating mutant HTT at different disease stages and to varying degrees in an experimental model. METHODS: We generated mutant BACHD mice with either a widespread or circuit-specific inactivation of mutant HTT by using Cre recombinase (Cre) under the nestin promoter or the adenosine A2A receptor promoter respectively. We also simulated a clinical gene therapy scenario with allele-specific HTT targeting by injections of recombinant adeno-associated viral (rAAV) vectors expressing Cre into the striatum of adult BACHD mice. All mice were assessed using behavioural tests to investigate motor, metabolic and psychiatric outcome measures at 4-6 months of age. RESULTS: While motor deficits, body weight changes, anxiety and depressive-like behaviours are present in BACHD mice, early widespread CNS inactivation during development significantly improves rotarod performance, body weight changes and depressive-like behaviour. However, conditional circuit-wide mutant HTT deletion from the indirect striatal pathway during development and focal striatal-specific deletion in adulthood failed to rescue any of the HD-related behaviours. CONCLUSIONS: Our results indicate that widespread targeting and the timing of interventions aimed at reducing mutant HTT are important factors to consider when developing disease-modifying therapies for HD.

Loss of the metabolism and sleep regulating neuronal populations expressing orexin and oxytocin in the hypothalamus in amyotrophic lateral sclerosis.

AIMS: To determine the underlying cellular changes and clinical correlates associated with pathology of the hypothalamus in amyotrophic lateral sclerosis (ALS), as hypothalamic atrophy occurs in the preclinical phase of the disease. METHODS: The hypothalamus was pathologically examined in nine patients with amyotrophic lateral sclerosis in comparison to eight healthy control subjects. The severity of regional atrophy (paraventricular nucleus: PVN, fornix and total hypothalamus) and peptidergic neuronal loss (oxytocin, vasopressin, cocaine- and amphetamine-regulating transcript: CART, and orexin) was correlated with changes in eating behaviour, sleep function, cognition, behaviour and disease progression. RESULTS: Tar DNA-binding protein 43 (TDP-43) inclusions were present in the hypothalamus of all patients with amyotrophic lateral sclerosis. When compared to controls, there was atrophy of the hypothalamus (average 21% atrophy, p = 0.004), PVN (average 30% atrophy p = 0.014) and a loss of paraventricular oxytocin-producing neurons (average 49% loss p = 0.02) and lateral hypothalamic orexin-producing neurons (average 37% loss, significance p = 0.02). Factor analysis identified strong relationships between abnormal eating behaviour, hypothalamic atrophy and loss of orexin-producing neurons. With increasing disease progression, abnormal sleep behaviour and cognition associated with atrophy of the fornix. CONCLUSIONS: Substantial loss of hypothalamic oxytocin-producing neurons occurs in ALS, with regional atrophy and the loss of orexin neurons relating to abnormal eating behaviour in ALS. Oxytocin- and orexin neurons display TDP43 inclusions. Our study points to significant pathology in the hypothalamus that may play a key role in metabolic and pathogenic changes in ALS.

Brain white matter lesions are associated with reduced hypothalamic volume and cranial radiotherapy in childhood-onset craniopharyngioma.

CONTEXT: White matter lesions (WML) are caused by obstruction of small cerebral vessels associated with stroke risk. Craniopharyngioma (CP) patients suffer from increased cerebrovascular mortality. OBJECTIVE: To investigate the effect of reduced HT volume and cranial radiotherapy (CRT) on WML in childhood-onset CP patients. DESIGN: A cross-sectional study of 41 patients (24 women) surgically treated childhood-onset CP in comparison to controls. SETTING: The South Medical Region of Sweden (2.5 million inhabitants). METHODS: With magnetic resonance imaging (MRI), we analysed qualitative measurement of WML based on the visual rating scale of Fazekas and quantitative automated segmentation of WML lesion. Also, measurement HT volume and of cardiovascular risk factors were analysed. RESULTS: Patients had a significant increase in WML volume (mL) (P = .001) compared to controls. Treatment with cranial radiotherapy (CRT) vs no CRT was associated with increased WML volume (P = .02) as well as higher Fazekas score (P = .001). WML volume increased with years after CRT (r = 0.39; P = .02), even after adjustment for fat mass and age. A reduced HT volume was associated with increased WML volume (r = -0.61, P < .001) and explained 26% of the variation (r2  = 0.26). Altogether, 47% of the WML volume was explained by age at investigation, HT volume and CRT. Patients with more WML also had higher cardiovascular risk. CONCLUSIONS: CRT may be associated directly with increased WML volume or indirectly with reduced HT volume associated with higher cardiovascular risk. Risk factors should be carefully monitored in these patients.

Early white matter pathology in the fornix of the limbic system in Huntington disease.

Huntington disease (HD) is a fatal neurodegenerative disorder caused by an expanded CAG repeat in the huntingtin (HTT) gene. The typical motor symptoms have been associated with basal ganglia pathology. However, psychiatric and cognitive symptoms often precede the motor component and may be due to changes in the limbic system. Recent work has indicated pathology in the hypothalamus in HD but other parts of the limbic system have not been extensively studied. Emerging evidence suggests that changes in HD also include white matter pathology. Here we investigated if the main white matter tract of the limbic system, the fornix, is affected in HD. We demonstrate that the fornix is 34% smaller already in prodromal HD and 41% smaller in manifest HD compared to controls using volumetric analyses of MRI of the IMAGE-HD study. In post-mortem fornix tissue from HD cases, we confirm the smaller fornix volume in HD which is accompanied by signs of myelin breakdown and reduced levels of the transcription factor myelin regulating factor but detect no loss of oligodendrocytes. Further analyses using RNA-sequencing demonstrate downregulation of oligodendrocyte identity markers in the fornix of HD cases. Analysis of differentially expressed genes based on transcription-factor/target-gene interactions also revealed enrichment for binding sites of SUZ12 and EZH2, components of the Polycomb Repressive Complex 2, as well as RE1 Regulation Transcription Factor. Taken together, our data show that there is early white matter pathology of the fornix in the limbic system in HD likely due to a combination of reduction in oligodendrocyte genes and myelin break down.

Early postnatal behavioral, cellular, and molecular changes in models of Huntington disease are reversible by HDAC inhibition.

Huntington disease (HD) is an autosomal dominant neurodegenerative disorder caused by expanded CAG repeats in the huntingtin gene (HTT). Although mutant HTT is expressed during embryonic development and throughout life, clinical HD usually manifests later in adulthood. A number of studies document neurodevelopmental changes associated with mutant HTT, but whether these are reversible under therapy remains unclear. Here, we identify very early behavioral, molecular, and cellular changes in preweaning transgenic HD rats and mice. Reduced ultrasonic vocalization, loss of prepulse inhibition, and increased risk taking are accompanied by disturbances of dopaminergic regulation in vivo, reduced neuronal differentiation capacity in subventricular zone stem/progenitor cells, and impaired neuronal and oligodendrocyte differentiation of mouse embryo-derived neural stem cells in vitro. Interventional treatment of this early phenotype with the histone deacetylase inhibitor (HDACi) LBH589 led to significant improvement in behavioral changes and markers of dopaminergic neurotransmission and complete reversal of aberrant neuronal differentiation in vitro and in vivo. Our data support the notion that neurodevelopmental changes contribute to the prodromal phase of HD and that early, presymptomatic intervention using HDACi may represent a promising novel treatment approach for HD.

Gene therapy for Parkinson's disease: Disease modification by GDNF family of ligands.

Gene transfer is a promising drug delivery method of advanced therapeutic entities for Parkinson's disease. One advantage over conventional therapies, such as peripheral delivery of the dopamine pre-cursor l-DOPA, is site-specific expression of proteins with regenerative, disease-modifying and potentially neuroprotective capacity. Several clinical trials have been performed to test the capacity of glial-cell line derived neurotrophic factor and neurturin to rescue degenerating dopaminergic neurons in the substantia nigra and their axon terminals in the striatum by delivery of these neurotrophic factors either as purified protein or by means of viral vector mediated gene delivery to the brain. Although gene therapy approaches tested so far have been shown to be safe, none met their primary endpoints in phase II clinical trials designed and powered to test the efficacy of the intervention. Within the scope of this review we aim to describe the state-of-the-art in the field, how different technical parameters were translated from pre-clinical studies in non-human primates to clinical trials, and what these trials taught us regarding important factors that may pave the way to the success of gene therapy for the treatment of Parkinson's disease.

Low dietary protein content alleviates motor symptoms in mice with mutant dynactin/dynein-mediated neurodegeneration.

Mutations in components of the molecular motor dynein/dynactin lead to neurodegenerative diseases of the motor system or atypical parkinsonism. These mutations are associated with prominent accumulation of vesicles involved in autophagy and lysosomal pathways, and with protein inclusions. Whether alleviating these defects would affect motor symptoms remain unknown. Here, we show that a mouse model expressing low levels of disease linked-G59S mutant dynactin p150(Glued) develops motor dysfunction >8 months before loss of motor neurons or dopaminergic degeneration is observed. Abnormal accumulation of autophagosomes and protein inclusions were efficiently corrected by lowering dietary protein content, and this was associated with transcriptional upregulations of key players in autophagy. Most importantly this dietary modification partially rescued overall neurological symptoms in these mice after onset. Similar observations were made in another mouse strain carrying a point mutation in the dynein heavy chain gene. Collectively, our data suggest that stimulating the autophagy/lysosomal system through appropriate nutritional intervention has significant beneficial effects on motor symptoms of dynein/dynactin diseases even after symptom onset.

Microstructure alterations in the hypothalamus in cranially radiated childhood leukaemia survivors but not in craniopharyngioma patients unaffected by hypothalamic damage.

OBJECTIVE: Metabolic complications are frequent in childhood leukaemia (ALL) survivors treated with cranial radiotherapy (CRT). These complications are potentially mediated by damage to the hypothalamus (HT), as childhood onset (CO) craniopharyngioma (CP) survivors without HT involvement are spared overt obesity. Diffusion tensor imaging (DTI) shows brain tissue microstructure alterations, by fractional anisotrophy (FA), mean diffusivity (MD), axial diffusivity (AD) and radial diffusivity (RD). We used DTI to determine the integrity of the microstructure of the HT in ALL survivors. DESIGN: Case-control study. PATIENTS: Three groups were included: (i) 27 CRT treated ALL survivors on hormone supplementation, (ii) 17 CO-CP survivors on hormone supplementation but without HT involvement and (iii) 27 matched controls. MEASUREMENTS: DTI parameters of the HT were measured and body composition. RESULTS: Microstructural alterations in the HT were more severe in ALL survivors with a BMI ≥25 than with BMI <25. Compared to controls, ALL survivors had reduced FA (P=.04), increased MD (P<.001), AD (P<.001) and RD (P<.001) in the right and left HT. In the right HT, ALL survivors with a BMI ≥25 showed elevated MD (P=.03) and AD (P=.02) compared to ALL survivors with BMI <25. In contrast, DTI parameters did not differ between CP survivors and controls. CONCLUSIONS: Long-term follow-up after CRT for ALL DTI measures were affected in the HT despite complete hormone replacement. The present data suggest that ALL survivors have demyelination and axonal loss in the HT.

Hypothalamic atrophy is related to body mass index and age at onset in amyotrophic lateral sclerosis.

OBJECTIVE: Our objective was to study the hypothalamic volume in a cohort of patients with amyotrophic lateral sclerosis (ALS) including symptomatic and presymptomatic ALS mutation carriers. METHODS: High-resolution three-dimensional T1-weighted MRI datasets from 251 patients with sporadic ALS, 19 symptomatic and 32 presymptomatic ALS mutation carriers and 112 healthy controls (HC) were retrospectivally registered for manual delineation of the hypothalamus. The volume of the hypothalamus, in total or subdivided, was normalised to the intracranial volume and adjusted to age. Correlation analyses were performed with clinical and metabolic outcomes. Pathologically defined ALS stages were determined in vivo by diffusion tensor imaging (DTI). RESULTS: We observed a severe atrophy of the hypothalamus both in patients with sporadic ALS (-21.8%, p<0.0001) and symptomatic ALS mutation carriers (-13.4%, p<0.001). The atrophy in patients with sporadic ALS was observed in both the anterior (-27.6% p<0.0001) and the posterior parts of the hypothalamus (-17.7%, p<0.0001). Notably, this atrophy was also observed in presymptomatic ALS mutation carriers (-15.5%, p<0.001) and was unrelated to whole brain volume atrophy or disease stage as assessed using DTI or functional status. Hypothalamic volume was correlated with body mass index (BMI) in patients with sporadic ALS (p=0.0434, ρ=+0.1579), and this correlation was much stronger in patients with familial ALS (fALS) (p=0.0060, ρ=+0.6053). Anterior hypothalamic volume was correlated with age at onset, but not with survival after MRI. CONCLUSIONS: Hypothalamus is atrophied in ALS, even in premorbid stages, and correlates with BMI, especially in fALS. Decreased anterior hypothalamic volume is associated with earlier onset of disease.

Neuropeptide Y (NPY) in cerebrospinal fluid from patients with Huntington's Disease: increased NPY levels and differential degradation of the NPY1-30 fragment.

Huntington's disease (HD) is an inherited and fatal polyglutamine neurodegenerative disorder caused by an expansion of the CAG triplet repeat coding region within the HD gene. Progressive dysfunction and loss of striatal GABAergic medium spiny neurons (MSNs) may account for some of the characteristic symptoms in HD patients. Interestingly, in HD, MSNs expressing neuropeptide Y (NPY) are spared and their numbers is even up-regulated in HD patients. Consistent with this, we report here on increased immuno-linked NPY (IL-NPY) levels in human cerebrospinal fluid (hCSF) from HD patients (Control n = 10; early HD n = 9; mid HD n = 11). As this antibody-based detection of NPY may provide false positive differences as a result of the antibody-based detections of only fragments of NPY, the initial finding was validated by investigating the proteolytic stability of NPY in hCSF using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS) and selective inhibitors. A comparison between resulting NPY-fragments and detailed epitope analysis verified significant differences in IL-NPY1-36/3-36 and NPY1-30 levels between HD patients and control subjects with no significant differences between early vs mid HD cases. Ex vivo degradomics analysis demonstrated that NPY is initially degraded to NPY1-30 by cathepsin D in both HD patients and control subjects. Yet, NPY1-30 is then further differentially hydrolyzed by thimet oligopeptidase (TOP) in HD patients and by neprilysin (NEP) in control subjects. Furthermore, altered hCSF TOP-inhibitor Dynorphin A1-13 (Dyn-A1-13 ) and TOP-substrate Dyn-A1-8 levels indicate an impaired Dyn-A-TOP network in HD patients. Thus, we conclude that elevated IL-NPY-levels in conjunction with TOP-/NEP-activity/protein as well as Dyn-A1-13 -peptide levels may serve as a potential biomarker in human CSF of HD. Huntington's disease (HD) patients' cerebrospinal fluid (CSF) exhibits higher neuropeptide Y (NPY) levels. Further degradomics studies show that CSF-NPY is initially degraded to NPY1-30 by Cathepsin D. The NPY1-30 fragment is then differentially degraded in HD vs control involving Neprilysin (NEP), Thimet Oligopeptidase (TOP), and TOP-Dynorphin-A network. Together, these findings may help in search for HD biomarkers.

Ubiquitin-specific protease-14 reduces cellular aggregates and protects against mutant huntingtin-induced cell degeneration: involvement of the proteasome and ER stress-activated kinase IRE1α.

Huntington's disease (HD) is an autosomal inherited neurological disease caused by a CAG-repeat expansion in the first exon of huntingtin gene encoding for the huntingtin protein (Htt). In HD, there is an accumulation of intracellular aggregates of mutant Htt that negatively influence cellular functions. The aggregates contain ubiquitin, and part of the HD pathophysiology could result from an imbalance in cellular ubiquitin levels. Deubiquitinating enzymes are important for replenishing the ubiquitin pool, but less is known about their roles in brain diseases. We show here that overexpression of the ubiquitin-specific protease-14 (Usp14) reduces cellular aggregates in mutant Htt-expressing cells mainly via the ubiquitin proteasome system. We also observed that the serine-threonine kinase IRE1 involved in endoplasmic reticulum (ER) stress responses is activated in mutant Htt-expressing cells in culture as well as in the striatum of mutant Htt transgenic (BACHD) mice. Usp14 interacted with IRE1 in control cells but less in mutant Htt-expressing cells. Overexpression of Usp14 in turn was able to inhibit phosphorylation of IRE1α in mutant Htt-overexpressing cells and to protect against cell degeneration and caspase-3 activation. These results show that ER stress-mediated IRE1 activation is part of mutant Htt toxicity and that this is counteracted by Usp14 expression. Usp14 effectively reduced cellular aggregates and counteracted cell degeneration indicating an important role of this protein in mutant Htt-induced cell toxicity.

Ethical aspects of a predictive test for Huntington's Disease: A long term perspective.

BACKGROUND: A predictive genetic test for Huntington's disease can be used before any symptoms are apparent, but there is only sparse knowledge about the long-term consequences of a positive test result. Such knowledge is important in order to gain a deeper understanding of families' experiences. OBJECTIVES: The aim of the study was to describe a young couple's long-term experiences and the consequences of a predictive test for Huntington's disease. RESEARCH DESIGN: A descriptive case study design was used with a longitudinal narrative life history approach. PARTICIPANTS AND RESEARCH CONTEXT: The study was based on 18 interviews with a young couple, covering a period of 2.5 years; starting 6 months after the disclosure of the test results showing the woman to be a carrier of the gene causing Huntington's disease. ETHICAL CONSIDERATIONS: Even though the study was extremely sensitive, where potential harm constantly had to be balanced against the benefits, the couple had a strong wish to contribute to increased knowledge about people in their situation. The study was approved by the ethics committee. FINDINGS: The results show that the long-term consequences were devastating for the family. This 3-year period was characterized by anxiety, repeated suicide attempts, financial difficulties and eventually divorce. DISCUSSION: By offering a predictive test, the healthcare system has an ethical and moral responsibility. Once the test result is disclosed, the individual and the family cannot live without the knowledge it brings. Support is needed in a long-term perspective and should involve counselling concerning the families' everyday life involving important decision-making, reorientation towards a new outlook of the future and the meaning of life. CONCLUSION: As health professionals, our ethical and moral responsibility thus embraces not only the phase in direct connection to the actual genetic test but also a commitment to provide support to help the family deal with the long-term consequences of the test.

Proteolytic degradation of neuropeptide Y (NPY) from head to toe: Identification of novel NPY-cleaving peptidases and potential drug interactions in CNS and Periphery.

The bioactivity of neuropeptide Y (NPY) is either N-terminally modulated with respect to receptor selectivity by dipeptidyl peptidase 4 (DP4)-like enzymes or proteolytic degraded by neprilysin or meprins, thereby abrogating signal transduction. However, neither the subcellular nor the compartmental differentiation of these regulatory mechanisms is fully understood. Using mass spectrometry, selective inhibitors and histochemistry, studies across various cell types, body fluids, and tissues revealed that most frequently DP4-like enzymes, aminopeptidases P, secreted meprin-A (Mep-A), and cathepsin D (CTSD) rapidly hydrolyze NPY, depending on the cell type and tissue under study. Novel degradation of NPY by cathepsins B, D, L, G, S, and tissue kallikrein could also be identified. The expression of DP4, CTSD, and Mep-A at the median eminence indicates that the bioactivity of NPY is regulated by peptidases at the interphase between the periphery and the CNS. Detailed ex vivo studies on human sera and CSF samples recognized CTSD as the major NPY-cleaving enzyme in the CSF, whereas an additional C-terminal truncation by angiotensin-converting enzyme could be detected in serum. The latter finding hints to potential drug interaction between antidiabetic DP4 inhibitors and anti-hypertensive angiotensin-converting enzyme inhibitors, while it ablates suspected hypertensive side effects of only antidiabetic DP4-inhibitors application. The bioactivity of neuropeptide Y (NPY) is either N-terminally modulated with respect to receptor selectivity by dipeptidyl peptidase 4 (DP4)-like enzymes or proteolytic degraded by neprilysin or meprins, thereby abrogating signal transduction. However, neither the subcellular nor the compartmental differentiation of these regulatory mechanisms is fully understood. Using mass spectrometry, selective inhibitors and histochemistry, studies across various cell types, body fluids, and tissues revealed that most frequently DP4-like enzymes, aminopeptidases P, secreted meprin-A (Mep-A), and cathepsin D (CTSD) rapidly hydrolyze NPY, depending on the cell type and tissue under study. Novel degradation of NPY by cathepsins B, D, L, G, S, and tissue kallikrein could also be identified. The expression of DP4, CTSD, and Mep-A at the median eminence indicates that the bioactivity of NPY is regulated by peptidases at the interphase between the periphery and the CNS. Detailed ex vivo studies on human sera and CSF samples recognized CTSD as the major NPY-cleaving enzyme in the CSF, whereas an additional C-terminal truncation by angiotensin-converting enzyme could be detected in serum. The latter finding hints to potential drug interaction between antidiabetic DP4 inhibitors and anti-hypertensive angiotensin-converting enzyme inhibitors, while it ablates suspected hypertensive side effects of only antidiabetic DP4-inhibitors application.

Hypothalamic expression of mutant huntingtin contributes to the development of depressive-like behavior in the BAC transgenic mouse model of Huntington's disease.

Psychiatric symptoms such as depression and anxiety are important clinical features of Huntington's disease (HD). However, the underlying neurobiological substrate for the psychiatric features is not fully understood. In order to explore the biological origin of depression and anxiety in HD, we used a mouse model that expresses the human full-length mutant huntingtin, the BACHD mouse. We found that the BACHD mice displayed depressive- and anxiety-like features as early as at 2 months of age as assessed using the Porsolt forced swim test (FST), the sucrose preference test and the elevated plus maze (EPM). BACHD mice subjected to chronic treatment with the anti-depressant sertraline were not different to vehicle-treated BACHD mice in the FST and EPM. The behavioral manifestations occurred in the absence of reduced hippocampal cell proliferation/neurogenesis or upregulation of the hypothalamic-pituitary-adrenal axis. However, alterations in anxiety- and depression-regulating genes were present in the hypothalamus of BACHD mice including reduced mRNA expression of neuropeptide Y, tachykinin receptor 3 and vesicular monoamine transporter type 2 as well as increased expression of cocaine and amphetamine regulated transcript. Interestingly, the orexin neuronal population in the hypothalamus was increased and showed cellular atrophy in old BACHD mice. Furthermore, inactivation of mutant huntingtin in a subset of the hypothalamic neurons prevented the development of the depressive features. Taken together, our data demonstrate that the BACHD mouse recapitulates clinical HD with early psychiatric aspects and point to the role of hypothalamic dysfunction in the development of depression and anxiety in the disease.

Attenuated huntingtin gene CAG nucleotide repeat size in individuals with Lynch syndrome.

DNA mismatch repair (MMR) is thought to contribute to the onset and progression of Huntington disease (HD) by promoting somatic expansion of the pathogenic CAG nucleotide repeat in the huntingtin gene (HTT). Here we have studied constitutional HTT CAG repeat size in two cohorts of individuals with Lynch syndrome (LS) carrying heterozygous loss-of-function variants in the MMR genes MLH1 (n = 12/60; Lund cohort/Bochum cohort, respectively), MSH2 (n = 15/88), MSH6 (n = 21/23), and controls (n = 19/559). The sum of CAG repeats for both HTT alleles in each individual was calculated due to unknown segregation with the LS allele. In the larger Bochum cohort, the sum of CAG repeats was lower in the MLH1 subgroup compared to controls (MLH1 35.40 CAG repeats ± 3.6 vs. controls 36.89 CAG repeats ± 4.5; p = 0.014). All LS genetic subgroups in the Bochum cohort displayed lower frequencies of unstable HTT intermediate alleles and lower HTT somatic CAG repeat expansion index values compared to controls. Collectively, our results indicate that MMR gene haploinsufficiency could have a restraining impact on constitutional HTT CAG repeat size and support the notion that the MMR pathway is a driver of nucleotide repeat expansion diseases.

Ethical aspects of undergoing a predictive genetic testing for Huntington's disease.

The aim of this study was to describe the experiences of undergoing a presymptomatic genetic test for the hereditary and fatal Huntington's disease, using a case study approach. The study was based on 18 interviews with a young woman and her husband from the decision to undergo the test, to receiving the results and trying to adapt to them, which were analysed using a life history approach. The findings show that the process of undergoing a presymptomatic test involves several closely connected ethical and medical questions, such as the reason for the test, the consequences of the test results and how health-care services can be developed to support people in this situation.

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.

A point mutation in the dynein heavy chain gene leads to striatal atrophy and compromises neurite outgrowth of striatal neurons.

The molecular motor dynein and its associated regulatory subunit dynactin have been implicated in several neurodegenerative conditions of the basal ganglia, such as Huntington's disease (HD) and Perry syndrome, an atypical Parkinson-like disease. This pathogenic role has been largely postulated from the existence of mutations in the dynactin subunit p150(Glued). However, dynactin is also able to act independently of dynein, and there is currently no direct evidence linking dynein to basal ganglia degeneration. To provide such evidence, we used here a mouse strain carrying a point mutation in the dynein heavy chain gene that impairs retrograde axonal transport. These mice exhibited motor and behavioural abnormalities including hindlimb clasping, early muscle weakness, incoordination and hyperactivity. In vivo brain imaging using magnetic resonance imaging showed striatal atrophy and lateral ventricle enlargement. In the striatum, altered dopamine signalling, decreased dopamine D1 and D2 receptor binding in positron emission tomography SCAN and prominent astrocytosis were observed, although there was no neuronal loss either in the striatum or substantia nigra. In vitro, dynein mutant striatal neurons displayed strongly impaired neuritic morphology. Altogether, these findings provide a direct genetic evidence for the requirement of dynein for the morphology and function of striatal neurons. Our study supports a role for dynein dysfunction in the pathogenesis of neurodegenerative disorders of the basal ganglia, such as Perry syndrome and HD.