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One of the roadblocks to developing effective therapeutics for Huntington disease (HD) is the lack of animal models that develop progressive clinical traits comparable to those seen in patients. Here we report a longitudinal study that encompasses cognitive and motor assessment, and neuroimaging of a group of transgenic HD and control monkeys from infancy to adulthood. Along with progressive cognitive and motor impairment, neuroimaging revealed a progressive reduction in striatal volume. Magnetic resonance spectroscopy at 48 months of age revealed a decrease of N-acetylaspartate (NAA), further suggesting neuronal damage/loss in the striatum. Postmortem neuropathological analyses revealed significant neuronal loss in the striatum. Our results indicate that HD monkeys share similar disease patterns with HD patients, making them potentially suitable as a preclinical HD animal model.

Background A two-year longitudinal study composed of morphometric MRI measures and cognitive behavioral evaluation was performed on a transgenic Huntington’s disease (HD) monkey. rHD1, a transgenic HD monkey expressing exon 1 of the human gene encoding huntingtin ( HTT ) with 29 CAG repeats regulated by a human polyubiquitin C promoter was used together with four age-matched wild-type control monkeys. This is the first study on a primate model of human HD based on longitudinal clinical measurements. Results Changes in striatal and hippocampal volumes in rHD1 were observed with progressive impairment in motor functions and cognitive decline, including deficits in learning stimulus-reward associations, recognition memory and spatial memory. The results demonstrate a progressive cognitive decline and morphometric changes in the striatum and hippocampus in a transgenic HD monkey. Conclusions This is the first study on a primate model of human HD based on longitudinal clinical measurements. While this study is based a single HD monkey, an ongoing longitudinal study with additional HD monkeys will be important for the confirmation of our findings. A nonhuman primate model of HD could complement other animal models of HD to better understand the pathogenesis of HD and future development of diagnostics and therapeutics through longitudinal assessment.

Purpose of Review Expanding therapeutic targets from proteins to RNAs opens up new possibilities for neurodegenerative disorders therapeutics development. Recently, a disease-modifying antisense oligonucleotide (ASO) agent was approved for spinal muscular atrophy, suggesting ASOs will fulfill their early promise and become a significant new therapeutic category for neurodegenerative disorders. Recent Findings ASOs are in human subjects testing for Huntington disease, monogenic forms of amyotrophic lateral sclerosis, Alzheimer disease, myotonic dystrophy, Leber congenital amaurosis, Usher syndrome, and retinitis pigmentosum, with many more in preclinical development. Current ASO strategies encompass RNA processing modulation, and RNA target breakdown. Broad ASO mechanism categories are protein restoring versus protein lowering. Individual ASO mechanisms of action range from mutation-specific to impacting many proteins. Summary Current ASOs show great promise in neurodegenerative disorders. Specific ASO designs and mechanisms may be more tenable in this disease area. Preclinical development is already leveraging early knowledge from these initial clinical trials to develop novel ASO cocktails, new ASO chemical modifications, and new ASO RNA and protein targets.

Huntington disease (HD) is a progressive neurodegenerative disease that causes psychiatric and neurological symptoms, including involuntary and irregular muscle movements (chorea). Chorea can disrupt activities of daily living, pose safety issues, and may lead to social withdrawal. The vesicular monoamine transporter 2 inhibitors tetrabenazine, deutetrabenazine, and valbenazine are approved treatments that can reduce chorea. This post hoc analysis was conducted to evaluate safety and efficacy among participants who received high-dosage deutetrabenazine treatment (> 48 mg/d) in ARC-HD, an open-label study that assessed long-term safety and efficacy of deutetrabenazine for the treatment of chorea in HD in adults. ARC-HD was a single-arm, two-cohort, open-label study. Participants either successfully completed the First-HD study or switched overnight from tetrabenazine to deutetrabenazine. Participants were dosed with deutetrabenazine in a response-driven manner (maximum 72 mg/d allowed). For the current analysis, exposure-adjusted incidence rates (EAIRs) for adverse events of interest were analyzed according to daily dosage (≤ 48 mg/d versus > 48 mg/d), and total maximal chorea (TMC) scores were analyzed by cohort during the stable-dose period. In total, 116 of the 119 participants enrolled in ARC-HD entered the stable-dose period, where no apparent differences were seen in EAIRs when receiving deutetrabenazine dosages ≤ 48 mg/d (exposure = 177.7 person-years) compared with > 48 mg/d (exposure = 74.1 person-years). Similar results were found among the subset of participants who received deutetrabenazine dosages > 48 mg/d at least once during the study (n = 49, 42%) when their dosage was ≤ 48 mg/d (exposure = 37.9 person-years) versus > 48 mg/d (74.1 person-years). Efficacy analyses were conducted for participants who had TMC scores available (rollover cohort, n = 77; switch cohort, n = 35). For most participants, the lowest deutetrabenazine dosage needed to achieve a TMC response (≥ 30% improvement from baseline) was between 24 and 48 mg/d in both the rollover (n = 57, 74.0%) and switch (n = 16, 46.0%) cohorts. Whereas the dosage needed for a TMC response was independent of baseline TMC score in the rollover cohort, participants with higher baseline TMC scores in the switch cohort required higher dosages to achieve a TMC response during the trial. In this open-label, long-term study, some participants received deutetrabenazine dosing > 48 mg/d to achieve adequate chorea control. There was no new safety concern or incremental change in the safety profile between dosages of ≤ 48 mg/d and > 48 mg/d. These results include dosages that have not been approved for clinical use, however, they increase our understanding of safety and tolerability of deutetrabenazine doses. ARC-HD (ClinicalTrials.gov identifier: NCT01897896); First-HD (ClinicalTrials.gov identifier: NCT01795859).

Kari Stefansson and colleagues report association of a variant in LINGO1 with risk of essential tremor, a common progressive neurological disease. Mice lacking Lingo1 have impaired axonal integrity, which may be relevant to the pathophysiology of the human disease. We identified a marker in LINGO1 showing genome-wide significant association ( P = 1.2 × 10 −9 , odds ratio = 1.55) with essential tremor. LINGO1 has potent, negative regulatory influences on neuronal survival and is also important in regulating both central-nervous-system axon regeneration and oligodendrocyte maturation. Increased axon integrity observed in Lingo1 mouse knockout models highlights the potential role of LINGO1 in the pathophysiology of essential tremor.

Chorea is a prominent motor dysfunction in Huntington's disease (HD). Deutetrabenazine, a vesicular monoamine transporter 2 (VMAT2) inhibitor, is FDA-approved for the treatment of chorea in HD. In the pivotal, 12-week First-HD trial, deutetrabenazine treatment reduced the Unified Huntington's Disease Rating Scale (UHDRS) total maximal chorea (TMC) score versus placebo. ARC-HD, an open-label extension study, evaluated long-term safety and efficacy of deutetrabenazine dosed in a response-driven manner for treatment of HD chorea. Patients who completed First-HD (Rollover) and patients who converted overnight from a stable dose of tetrabenazine (Switch) were included. Safety was assessed over the entire treatment period; exposure-adjusted incidence rates (EAIRs; adverse events [AEs] per person-year) were calculated. A stable, post-titration time point of 8 weeks was chosen for efficacy analyses. Of 119 patients enrolled (Rollover, n=82; Switch, n=37), 100 (84%) completed ≥1 year of treatment (mean [SD] follow-up, 119 [48] weeks). End of study EAIRs for patients in the Rollover and Switch cohorts, respectively, were: any AE, 2.6 and 4.3; serious AEs, 0.13 and 0.14; AEs leading to dose suspension, 0.05 and 0.04. Overall, 68% and 73% of patients in Rollover and Switch, respectively, experienced a study drug-related AE. Most common AEs possibly related to study drug were somnolence (17% Rollover; 27% Switch), depression (23%; 19%), anxiety (9%; 11%), insomnia (10%; 8%), and akathisia (9%; 14%). Rates of AEs of interest include suicidality (9%; 3%) and parkinsonism (6%; 11%). In both cohorts, mean UHDRS TMC score and total motor score (TMS) decreased from baseline to Week 8; mean (SD) change in TMC score (units) was -4.4 (3.1) and -2.1 (3.3) and change in TMS was -7.1 (7.3) and -2.4 (8.7) in Rollover and Switch, respectively. While receiving stable dosing from Week 8 to 132 (or end of treatment), patients showed minimal change in TMC score (0.9 [5.0]), but TMS increased compared to Week 8 (9.0 [11.3]). Upon drug withdrawal, there were no remarkable AEs and TMC scores increased 4.4 (3.7) units compared to end of treatment. The type and severity of AEs observed in long-term deutetrabenazine exposure are consistent with the previous study. Efficacy in reducing chorea persisted over time. There was no unexpected worsening of HD or chorea associated with HD upon deutetrabenazine withdrawal. Teva Pharmaceutical Industries Ltd., Petach Tikva, Israel.

BackgroundIn the First-HD pivotal trial, the maximum deutetrabenazine dose evaluated to treat chorea associated with Huntington’s disease (HD chorea) was 48 mg/d, which is the approved maximum dose for this population. In ARC-HD, an open-label extension study evaluating the long-term efficacy and safety of deutetrabenazine to treat HD chorea, dosage ranged from 6 mg/d to 72 mg/d, with doses ≥12 mg/d administered twice daily. Doses in ARC-HD were increased by 6 mg/d per week in a response-driven manner based on efficacy and tolerability until 48 mg/d (Week 8). At the investigator’s discretion, further increases were permitted by 12 mg/d per week to a maximum of 72 mg/d. This post-hoc analysis evaluates the safety and tolerability of deutetrabenazine >48 mg/d compared to ≤48 mg/d to treat HD chorea in ARC-HD.MethodsPatient counts and safety assessments were attributed to patients when they received a dose of either ≤48 mg/d or >48 mg/d. For 9 selected adverse events (AEs), we compared AE rates adjusted for duration of drug exposure (as number of AEs/year) at ≤48 mg/d or >48 mg/d. The AE rates were determined after titration when participants were on stable doses of deutetrabenazine.ResultsAll 113 patients were exposed to doses ≤48 mg/d (177.1 patient-years) and 49 patients were ever exposed to doses >48 mg/d (74.1 patient-years). In patients taking deutetrabenazine >48 mg/d compared to ≤48 mg/d after the titration period, there were no apparent differences in exposure-adjusted AE rates.ConclusionsBased on clinical experience, some patients with HD may benefit from doses higher than 48 mg/d to adequately control chorea. These doses were tolerated without apparent increase in the exposure-adjusted rates of selected AEs after titration. This analysis does not address the occurrence of other AEs or whether adequate efficacy was achieved at lower doses, factors that may have influenced dose increases.FundingTeva Pharmaceutical Industries Ltd., Petach Tikva, Israel

Huntington disease (HD) is a progressive neurodegenerative disorder. Presymptomatic genetic testing allows at-risk individuals to clarify their risk status. Understanding the characteristics and motivations of individuals seeking HD presymptomatic genetic testing better equips genetic counselors and other healthcare professionals to provide comprehensive and personalized care. The aims of this study were to (1) determine whether the average age when individuals seek presymptomatic HD genetic testing has decreased over time, (2) assess motivations for seeking testing, (3) explore whether there is a relationship between age and motivations, and (4) explore genetic counselors’ perceptions of the shift in age. Data from the US HD testing centers ( N  = 4) were analyzed. A small but statistically significant decrease in age of individuals seeking presymptomatic testing was observed ( p  = 0.045). HD community members ( N  = 77) were surveyed regarding presymptomatic testing motivations. Younger individuals were more likely than older individuals to cite “To learn whether or not you would develop HD” and “To make choices about further education or a career” compared to older individuals ( p  < 0.05). Conversely, older individuals more frequently cited “To give children a better idea of their risk” ( p  < 0.002). Sixteen percent of genetic counselors surveyed (6/37) perceived a change in age of testing. All of these respondents had provided HD testing for ten or more years and anecdotally believed the age at testing has decreased over time. Study results help providers personalize counseling based on patient’s age and serve as a starting point for more research into the relationship between age at testing and motivations for testing.

Genetic variation in the leucine-rich repeat and Ig domain containing 1 gene ( LINGO1 ) was recently associated with an increased risk of developing essential tremor (ET) and Parkinson disease (PD). Herein, we performed a comprehensive study of LINGO1 and its paralog LINGO2 in ET and PD by sequencing both genes in patients (ET, n  = 95; PD, n  = 96) and by examining haplotype-tagging single-nucleotide polymorphisms (tSNPs) in a multicenter North American series of patients (ET, n  = 1,247; PD, n  = 633) and controls ( n  = 642). The sequencing study identified six novel coding variants in LINGO1 (p.S4C, p.V107M, p.A277T, p.R423R, p.G537A, p.D610D) and three in LINGO2 (p.D135D, p.P217P, p.V565V), however segregation analysis did not support pathogenicity. The association study employed 16 tSNPs at the LINGO1 locus and 21 at the LINGO2 locus. One variant in LINGO1 (rs9652490) displayed evidence of an association with ET (odds ratio (OR) = 0.63; P  = 0.026) and PD (OR = 0.54; P  = 0.016). Additionally, four other tSNPs in LINGO1 and one in LINGO2 were associated with ET and one tSNP in LINGO2 associated with PD ( P  < 0.05). Further analysis identified one tSNP in LINGO1 and two in LINGO2 which influenced age at onset of ET and two tSNPs in LINGO1 which altered age at onset of PD ( P  < 0.05). Our results support a role for LINGO1 and LINGO2 in determining risk for and perhaps age at onset of ET and PD. Further studies are warranted to confirm these findings and to determine the pathogenic mechanisms involved.

Genetics research is an avenue towards understanding essential tremor (ET). Advances have been made in genetic linkage and association: there are three reported ET susceptibility loci, and mixed but growing data on risk associations. However, causal mutations have not been forthcoming. This disappointing lack of progress has opened productive discussions on challenges in ET and specifically ET genetics research, including fundamental assumptions in the field. This article reviews the ET genetics literature, results to date, the open questions in ET genetics and the current challenges in addressing them. SEVERAL INHERENT ET FEATURES COMPLICATE GENETIC LINKAGE AND ASSOCIATION STUDIES: high potential phenocopy rates, inaccurate tremor self-reporting, and ET misdiagnoses are examples. Increasing use of direct examination data for subjects, family members, and controls is one current response. Smaller moves towards expanding ET phenotype research concepts into non-tremor features, clinically disputed ET subsets, and testing phenotype features instead of clinical diagnosis against genetic data are gradually occurring. The field has already moved to considering complex trait mechanisms requiring detection of combinations of rare genetic variants. Hypotheses may move further to consider novel mechanisms of inheritance, such as epigenetics. It is an exciting time in ET genetics as investigators start moving past assumptions underlying both phenotype and genetics experimental contributions, overcoming challenges to collaboration, and engaging the ET community. Multicenter collaborative efforts comprising rich longitudinal prospective phenotype data and neuropathologic analysis combined with the latest in genetics experimental design and technology will be the next wave in the field.