Considerations for clinical trial design and conduct in the evaluation of novel advanced therapeutics in neurodegenerative disease.

The recent advances in the development of potentially disease modifying cell and gene therapies for neurodegenerative disease has resulted in the production of a number of promising novel therapies which are now moving forward to clinical evaluation. The robust evaluation of these therapies pose a significant number of challenges when compared to more traditional evaluations of pharmacotherapy, which is the current mainstay of neurodegenerative disease symptom management. Indeed, there is an inherent complexity in the design and conduct of these trials at multiple levels. Here we discuss specific aspects requiring consideration in the context of investigating novel cell and gene therapies for neurodegenerative disease. This extends to overarching trial designs that could be employed and the factors that underpin design choices such outcome assessments, participant selection and methods for delivery of cell and gene therapies. We explore methods of data collection that may improve efficiency in trials of cell and gene therapy to maximize data sharing and collaboration. Lastly, we explore some of the additional context beyond efficacy evaluations that should be considered to ensure implementation across relevant healthcare settings.

Physical activity and exercise outcomes in Huntington's disease (PACE-HD): results of a 12-month trial-within-cohort feasibility study of a physical activity intervention in people with Huntington's disease.

INTRODUCTION: While physical activity (PA) is recognized as important in Huntington's disease (HD) disease management, there has been no long-term evaluation undertaken. We aimed to evaluate the feasibility of a nested (within cohort) randomized controlled trial (RCT) of a physical therapist-led PA intervention. METHODS: Participants were recruited from six HD specialist centers participating in the Enroll-HD cohort study in Germany, Spain and U.S. Assessments were completed at baseline and 12 months and linked to Enroll-HD cohort data. Participants at three sites (cohort) received no contact between baseline and 12 month assessments. Participants at three additional sites (RCT) were randomized to PA intervention or control group. The intervention consisted of 18 sessions delivered over 12 months; control group participants received no intervention, however both groups completed monthly exercise/falls diaries and 6-month assessments. RESULTS: 274 participants were screened, 204 met inclusion criteria and 116 were enrolled (59 in cohort; 57 in RCT). Retention rates at 12-months were 84.7% (cohort) and 79.0% (RCT). Data completeness at baseline ranged from 42.3 to 100% and at 12-months 19.2-85.2%. In the RCT, there was 80.5% adherence, high intervention fidelity, and similar adverse events between groups. There were differences in fitness, walking endurance and self-reported PA at 12 months favoring the intervention group, with data completeness >60%. Participants in the cohort had motor and functional decline at rates comparable to previous studies. CONCLUSION: Predefined progression criteria indicating feasibility were met. PACE-HD lays the groundwork for a future, fully-powered within cohort trial, but approaches to ensure data completeness must be considered. CLINICALTRIALS: GOV: NCT03344601.

Protocol for an open label: phase I trial within a cohort of foetal cell transplants in people with Huntington's disease.

Huntington's disease is a progressive neurodegenerative disorder characterized by motor, cognitive and psychiatric symptoms. Currently, no disease-modifying therapies are available to slow or halt disease progression. Huntington's disease is characterized by relatively focal and specific loss of striatal medium spiny neurons, which makes it suitable for cell-replacement therapy, a process involving the transplantation of donor cells to replace those lost due to disease. TRIal DEsigns for delivery of Novel Therapies in neurodegeneration is a phase I Trial Within a Cohort designed to assess safety and feasibility of transplanting human foetal striatal cells into the striatum of people with Huntington's disease. A minimum of 18 participants will be enrolled in the study cohort, and up to five eligible participants will be randomly selected to undergo transplantation of 12-22 million foetal cells in a dose escalation paradigm. Independent reviewers will assess safety outcomes (lack of significant infection, bleeding or new neurological deficit) 4 weeks after surgery, and ongoing safety will be established before conducting each subsequent surgery. All participants will undergo detailed clinical and functional assessment at baseline (6 and 12 months). Surgery will be performed 1 month after baseline, and transplant participants will undergo regular clinical follow-up for at least 12 months. Evaluation of trial processes will also be undertaken. Transplant participants and their carers will be interviewed ∼1 month before and after surgery. Interviews will also be conducted with non-transplanted participants and healthcare staff delivering the intervention and involved in the clinical care of participants. Evaluation of clinical and functional efficacy outcomes and intervention costs will be carried out to explore plausible trial designs for subsequent randomized controlled trials aimed at evaluating efficacy and cost-effectiveness of cell-replacement therapy. TRIal DEsigns for delivery of Novel Therapies in neurodegeneration will enable the assessment of the safety, feasibility, acceptability and cost of foetal cell transplants in people with Huntington's disease. The data collected will inform trial designs for complex intra-cranial interventions in a range of neurodegenerative conditions and facilitate the development of stable surgical pipelines for delivery of future stem cell trials. Trial Registration: ISRCTN52651778.

A randomised feasibility study of computerised cognitive training as a therapeutic intervention for people with Huntington's disease (CogTrainHD).

BACKGROUND: Huntington's disease (HD) is associated with a range of cognitive deficits including problems with executive function. In the absence of a disease modifying treatment, cognitive training has been proposed as a means of slowing cognitive decline; however, the impact of cognitive training in HD patient populations remains unclear. The CogTrainHD study assessed the feasibility and acceptability of home-based computerised executive function training, for people impacted by HD. METHODS: Thirty HD gene carriers were recruited and randomised to either executive function training or non-intervention control groups. Participants allocated to the intervention group were asked to complete executive function training three times a week for 30 min for 12 weeks in their own homes. Semi-structured interviews were conducted with participants and friends, family or carers, to determine their views on the study. RESULTS: 26 out of 30 participants completed the baseline assessments and were subsequently randomised: 13 to the control group and 13 to the intervention group. 23 of the 30 participants were retained until study completion: 10/13 in the intervention group and 13/13 in the control group. 4/10 participants fully adhered to the executive function training. All participants in the control group 13/13 completed the study as intended. Interview data suggested several key facilitators including participant determination, motivation, incorporation of the intervention into routine and support from friends and family members. Practical limitations, including lack of time, difficulty and frustration in completing the intervention, were identified as barriers to study completion. CONCLUSIONS: The CogTrainHD feasibility study provides important evidence regarding the feasibility and acceptability of a home-based cognitive training intervention for people with HD. Variable adherence to the cognitive training implies that the intervention is not feasible to all participants in its current form. The study has highlighted important aspects in relation to both the study and intervention design that require consideration, and these include the design of games in the executive function training software, logistical considerations such as lack of time, the limited time participants had to complete the intervention and the number of study visits required. Further studies are necessary before computerised executive function training can be recommended routinely for people with HD. TRIAL REGISTRATION: ClinicalTrials.gov, Registry number NCT02990676.

A protocol for a randomised controlled, double-blind feasibility trial investigating fluoxetine treatment in improving memory and learning impairments in patients with mesial temporal lobe epilepsy: Fluoxetine, Learning and Memory in Epilepsy (FLAME trial).

BACKGROUND: People with temporal lobe epilepsy (TLE) report significant problems with learning and memory. There are no effective therapies for combatting these problems in people with TLE, resulting in an unmet therapeutic need. The lack of treatment is, in part, due to a poor understanding of the neurobiology underlying these memory deficits. We know that hippocampal neurogenesis, a process believed to be important in learning and memory formation, is permanently reduced in chronic TLE, and this may go some way to explain the learning and memory impairments seen in people with TLE.The common anti-depressant drug fluoxetine has been shown to stimulate neurogenesis both in the healthy brain and in neurological diseases where neurogenesis is impaired. In an animal model of TLE, administration of fluoxetine was found to restore neurogenesis and improve learning on a complex spatial navigational task. We now want to test this effect in humans by investigating whether administration of fluoxetine to people with TLE can improve learning and memory. METHODS: This is a single-centre randomised controlled, double-blind feasibility trial. We plan to recruit 20 participants with a diagnosis of TLE and uni-lateral hippocampal sclerosis, confirmed by 3T MRI. Eligible participants will undergo baseline assessments of learning and memory prior to being randomised to either 20 mg/day fluoxetine or matching placebo for 60 days. Follow-up assessments will be conducted after 60 days of trial medication and then again at 60 days after cessation of trial medication. Feasibility will be assessed on measures of recruitment, retention and adherence against pre-determined criteria. DISCUSSION: This trial is designed to determine the feasibility of conducting a double-blind randomised controlled trial of fluoxetine for the treatment of learning and memory impairments in people with TLE. Data collected in this trial will inform the design and utility of any future efficacy trial involving fluoxetine for the treatment of learning and memory in people with TLE. TRIAL REGISTRATION: EudraCT 2014-005088-34, registered on May 18, 2015.

Physical Activity and Exercise Outcomes in Huntington Disease (PACE-HD): Protocol for a 12-Month Trial Within Cohort Evaluation of a Physical Activity Intervention in People With Huntington Disease.

BACKGROUND: Exercise is emerging as an important aspect in the management of disease-related symptoms and functional decline in people with Huntington disease (HD). Long-term evaluation of physical activity and exercise participation in HD has yet to be undertaken. OBJECTIVE: The objective is to investigate the feasibility of a nested randomized controlled trial (RCT) alongside a longitudinal observational study of physical activity and exercise outcomes in people with HD. DESIGN: This will be a 12-month longitudinal observational study (n = 120) with a nested evaluation of a physical activity intervention (n = 30) compared with usual activity (n = 30) using a "trial within a cohort" design. SETTING: The study will take place in HD specialist clinics in Germany, Spain, and the United States, with intervention delivery in community settings. PARTICIPANTS: The participants will have early-mid-stage HD and be participating in the Enroll-HD study. INTERVENTION: This will be a 12-month physical activity behavioral change intervention, delivered by physical therapists in 18 sessions, targeting uptake of aerobic exercise and increased physical activity. MEASUREMENTS: All participants (n = 120) will complete Enroll-HD assessments (motor, cognitive, behavioral, and quality of life) at baseline and at 12 months. Additional Physical ACtivity and Exercise Outcomes in Huntington Disease (PACE-HD) assessments include fitness (predicted maximal oxygen uptake [V o2max]), self-reported and quantitative measures of physical activity, disease-specific symptoms, and walking endurance. RCT participants (n = 60) will complete an additional battery of quantitative motor assessments and a 6-month interim assessment. Enroll-HD data will be linked to PACE-HD physical activity and fitness data. LIMITATIONS: The limitations include that the embedded RCT is open, and assessors at RCT sites are not blinded to participant allocation. CONCLUSION: PACE-HD will enable determination of the feasibility of long-term physical activity interventions in people with HD. The novel "trial within a cohort" design and incorporation of data linkage have potential to reduce participant burden. This design could be applied to other neurological diseases and movement disorders where recruitment and retention are challenging.

Exploring computerised cognitive training as a therapeutic intervention for people with Huntington's disease (CogTrainHD): protocol for a randomised feasibility study.

BACKGROUND: Cognitive impairments, especially deficits of executive function, have been well documented as a core and early feature in Huntington's disease (HD). Cognitive impairments represent considerable burden and can be devastating for people and families affected by HD. Computerised cognitive training interventions that focus on improving executive function present a possible non-pharmacological treatment option. We propose to determine the feasibility, acceptability, and appropriate outcome measures for use in a randomised controlled feasibility study. METHODS/DESIGN: Participants will be randomised into either a computerised cognitive training group or a control group. Those randomised to the training group will be asked to complete a cognitive training intervention based on the HappyNeuron Pro software tasks of executive function, for a minimum of 30 min, three times a week for the 12-week study duration. Participants in the control group will not receive computerised cognitive training but will receive a similar degree of social interaction via equivalent study and home visits. We will explore quantitative outcome measures, including measures of cognitive performance, motor function, questionnaires and semi-structured interviews, as well as magnetic resonance imaging (MRI) measures in a subset of participants. Feasibility will be determined through assessment of recruitment, retention, adherence and acceptability of the intervention. DISCUSSION: The results of this study will provide crucial guidance and information regarding the feasibility of conducting a randomised controlled study into computerised cognitive training in HD. This study is crucial for the development of larger definitive randomised controlled trials which are powered to determine efficacy and for the development of future cognitive training programmes for people affected by HD. TRIAL REGISTRATION: The study is registered on clinicaltrials.gov and has the unique identifier NCT02990676.

Integrating technology into complex intervention trial processes: a case study.

BACKGROUND: Trials of complex interventions are associated with high costs and burdens in terms of paperwork, management, data collection, validation, and intervention fidelity assessment occurring across multiple sites. Traditional data collection methods rely on paper-based forms, where processing can be time-consuming and error rates high. Electronic source data collection can potentially address many of these inefficiencies, but has not routinely been used in complex intervention trials. Here we present the use of an on-line system for managing all aspects of data handling and for the monitoring of trial processes in a multicentre trial of a complex intervention. We custom built a web-accessible software application for the delivery of ENGAGE-HD, a multicentre trial of a complex physical therapy intervention. The software incorporated functionality for participant randomisation, data collection and assessment of intervention fidelity. It was accessible to multiple users with differing levels of access depending on required usage or to maintain blinding. Each site was supplied with a 4G-enabled iPad for accessing the system. The impact of this system was quantified through review of data quality and collation of feedback from site coordinators and assessors through structured process interviews. RESULTS: The custom-built system was an efficient tool for collecting data and managing trial processes. Although the set-up time required was significant, using the system resulted in an overall data completion rate of 98.5% with a data query rate of 0.1%, the majority of which were resolved in under a week. Feedback from research staff indicated that the system was highly acceptable for use in a research environment. This was a reflection of the portability and accessibility of the system when using the iPad and its usefulness in aiding accurate data collection, intervention fidelity and general administration. CONCLUSIONS: A combination of commercially available hardware and a bespoke online database designed to support data collection, intervention fidelity and trial progress provides a viable option for streamlining trial processes in a multicentre complex intervention trial. There is scope to further extend the system to cater for larger trials and add further functionality such as automatic reporting facilities and participant management support. TRIAL REGISTRATION: ISRCTN65378754 , registered on 13 March 2014.

New hyperekplexia mutations provide insight into glycine receptor assembly, trafficking, and activation mechanisms.

Hyperekplexia is a syndrome of readily provoked startle responses, alongside episodic and generalized hypertonia, that presents within the first month of life. Inhibitory glycine receptors are pentameric ligand-gated ion channels with a definitive and clinically well stratified linkage to hyperekplexia. Most hyperekplexia cases are caused by mutations in the α1 subunit of the human glycine receptor (hGlyR) gene (GLRA1). Here we analyzed 68 new unrelated hyperekplexia probands for GLRA1 mutations and identified 19 mutations, of which 9 were novel. Electrophysiological analysis demonstrated that the dominant mutations p.Q226E, p.V280M, and p.R414H induced spontaneous channel activity, indicating that this is a recurring mechanism in hGlyR pathophysiology. p.Q226E, at the top of TM1, most likely induced tonic activation via an enhanced electrostatic attraction to p.R271 at the top of TM2, suggesting a structural mechanism for channel activation. Receptors incorporating p.P230S (which is heterozygous with p.R65W) desensitized much faster than wild type receptors and represent a new TM1 site capable of modulating desensitization. The recessive mutations p.R72C, p.R218W, p.L291P, p.D388A, and p.E375X precluded cell surface expression unless co-expressed with α1 wild type subunits. The recessive p.E375X mutation resulted in subunit truncation upstream of the TM4 domain. Surprisingly, on the basis of three independent assays, we were able to infer that p.E375X truncated subunits are incorporated into functional hGlyRs together with unmutated α1 or α1 plus ß subunits. These aberrant receptors exhibit significantly reduced glycine sensitivity. To our knowledge, this is the first suggestion that subunits lacking TM4 domains might be incorporated into functional pentameric ligand-gated ion channel receptors.

Genotype-phenotype correlations in hyperekplexia: apnoeas, learning difficulties and speech delay.

Congenital hyperekplexia is a rare, potentially treatable neuromotor disorder. Three major genes of effect are known, and all three affect glycinergic neurotransmission. Two genes encode for subunits of the postsynaptic inhibitory glycine receptor, GLRA1 encoding the α1 subunit and GLRB encoding the ß subunit. The third, SLC6A5, encodes the cognate presynaptic glycine transporter 2. Ninety-seven individuals had a clinical diagnosis of hyperekplexia confirmed by genetic testing: 61 cases had mutations in GLRA1, 24 cases in SLC6A5 and 12 in GLRB. Detailed retrospective clinical analysis ascertained that all gene-positive cases present in the neonatal period (occasionally prenatally) and that clonazepam is the treatment of choice (95% found it to be efficacious). We confirm that hyperekplexia is predominantly a recessive condition but dominant cases are seen (16%). We found no genetic evidence for 'major' or 'minor' forms of hyperekplexia on a population basis. Thirty-five gene-negative cases were studied for comparison, their cardinal feature was presentation after the first month of life (P < 0.001). In addition to the characteristic 'stiffness, startles and stumbles' of hyperekplexia, apnoea attacks (50 of 89) and delayed development (47 of 92) were frequently reported. Patients with SLC6A5 mutations were significantly more likely to have had recurrent infantile apnoeas (RR1.9; P < 0.005) than those with GLRA1 mutations. Patients with GLRB and SLC6A5 mutations were more likely to have developmental delay (RR1.5 P < 0.01; RR1.9 P < 0.03) than those with GLRA1 mutations; 92% of GLRB cases reported a mild to severe delay in speech acquisition. Molecular modelling of pathogenic mutations demonstrates specific patterns of protein disruption that can be used to predict phenotype severity. The developmental delay in hyperekplexia, and speech acquisition in particular, may represent failure of developmental neural networks or subtle neurogenic migration defects in the absence of presynaptic glycine release. We recommend early genetic testing for symptomatic neonates and possibly preconception counselling for those at risk for GLRB and SLC6A5 mutations, because of the more challenging phenotype.

GLRB is the third major gene of effect in hyperekplexia.

Glycinergic neurotransmission is a major inhibitory influence in the CNS and its disruption triggers a paediatric and adult startle disorder, hyperekplexia. The postsynaptic α(1)-subunit (GLRA1) of the inhibitory glycine receptor (GlyR) and the cognate presynaptic glycine transporter (SLC6A5/GlyT2) are well-established genes of effect in hyperekplexia. Nevertheless, 52% of cases (117 from 232) remain gene negative and unexplained. Ligand-gated heteropentameric GlyRs form chloride ion channels that contain the α(1) and ß-subunits (GLRB) in a 2α(1):3ß configuration and they form the predominant population of GlyRs in the postnatal and adult human brain, brainstem and spinal cord. We screened GLRB through 117 GLRA1- and SLC6A5-negative hyperekplexia patients using a multiplex-polymerase chain reaction and Sanger sequencing approach. The screening identified recessive and dominant GLRB variants in 12 unrelated hyperekplexia probands. This primarily yielded homozygous null mutations, with nonsense (n = 3), small indel (n = 1), a large 95 kb deletion (n = 1), frameshifts (n = 1) and one recurrent splicing variant found in four cases. A further three cases were found with two homozygous and one dominant GLRB missense mutations. We provide strong evidence for the pathogenicity of GLRB mutations using splicing assays, deletion mapping, cell-surface biotinylation, expression studies and molecular modelling. This study describes the definitive assignment of GLRB as the third major gene for hyperekplexia and impacts on the genetic stratification and biological causation of this neonatal/paediatric disorder. Driven principally by consanguineous homozygosity of GLRB mutations, the study reveals long-term additive phenotypic outcomes for affected cases such as severe apnoea attacks, learning difficulties and developmental delay.

Next generation sequencing in the clinical domain: clinical advantages, practical, and ethical challenges.

There has been an academic "gold rush" with researchers mining the deep seams of whole-exome and whole-genome sequencing since 2008. Although undoubtedly a major advance initially for identifying new disease-associated genes for rare monogenetic disorders--more recently, common and complex conditions have been successfully studied using these techniques. With great power comes great responsibility, however, and we must not forget that next generation sequencing produces unique ethical conundrums and validation challenges. We review the progression of published papers using whole-exome sequencing from a clinical and technical viewpoint before then reflecting on the key arguments that need to be fully understood before these tools can become a routine part of clinical practice and we ask what may be the role for the biomedical scientists?

Mutations in the GlyT2 gene (SLC6A5) are a second major cause of startle disease.

Hereditary hyperekplexia or startle disease is characterized by an exaggerated startle response, evoked by tactile or auditory stimuli, leading to hypertonia and apnea episodes. Missense, nonsense, frameshift, splice site mutations, and large deletions in the human glycine receptor α1 subunit gene (GLRA1) are the major known cause of this disorder. However, mutations are also found in the genes encoding the glycine receptor ß subunit (GLRB) and the presynaptic Na(+)/Cl(-)-dependent glycine transporter GlyT2 (SLC6A5). In this study, systematic DNA sequencing of SLC6A5 in 93 new unrelated human hyperekplexia patients revealed 20 sequence variants in 17 index cases presenting with homozygous or compound heterozygous recessive inheritance. Five apparently unrelated cases had the truncating mutation R439X. Genotype-phenotype analysis revealed a high rate of neonatal apneas and learning difficulties associated with SLC6A5 mutations. From the 20 SLC6A5 sequence variants, we investigated glycine uptake for 16 novel mutations, confirming that all were defective in glycine transport. Although the most common mechanism of disrupting GlyT2 function is protein truncation, new pathogenic mechanisms included splice site mutations and missense mutations affecting residues implicated in Cl(-) binding, conformational changes mediated by extracellular loop 4, and cation-π interactions. Detailed electrophysiology of mutation A275T revealed that this substitution results in a voltage-sensitive decrease in glycine transport caused by lower Na(+) affinity. This study firmly establishes the combination of missense, nonsense, frameshift, and splice site mutations in the GlyT2 gene as the second major cause of startle disease.

Direct Visualisation of Abnormal Dendritic Spine Morphology in the Hippocampus of the R6/2 Transgenic Mouse Model of Huntington's Disease.

BACKGROUND: Spatial learning deficits are observed in R6/2 mice, a transgenic mouse model of Huntington's Disease (HD). Spatial learning is a hippocampal-dependent process, and impairment of memory is thought to be due, at least in part, to structural changes such as loss of dendritic spines. OBJECTIVE: To analyse dendritic spines in the hippocampus of R6/2 mice to determine if there are changes that correlate with the hippocampal dysfunction observed in these mice. METHODS: A double transgenic cross between R6/2 mice and a reporter line (YFP-H) of mice that express yellow fluorescent protein (YFP) in a subset of their neurons was used. This allowed us to visualise dendritic spines in the brains of R6/2 mice directly. RESULTS: Clear differences were seen in the distribution of YFP in the hippocampal formation of wild-type (WT)-YFP-H and R6/2-YFP-H mice, particularly in the CA1 region. We quantified dendritic spine density and dendritic spine length in the apical dendrites of the CA1 hippocampal neurons. A significant reduction in dendritic spine density, and a concomitant increase in dendritic spine length was observed in R6/2-YFP-H mice compared to WT-YFP-H mice. CONCLUSION: The R6/2-YFP-H mouse is a useful tool for directly visualising dendritic spines in the brain of a Huntington's disease mouse model. The changes we observed in dendritic spine density and length in the hippocampus might contribute to the synaptic plasticity deficits and behavioural alteration of impaired spatial learning seen in R6/2 mice.

Chronic treatment with 13-cis-retinoic acid changes aggressive behaviours in the resident-intruder paradigm in rats.

Retinoids, vitamin A related compounds, have an established role in the development of the nervous system and are increasingly recognized to play a role in adult brain function. The synthetic retinoid, 13-cis-retinoic acid (13-cis-RA, Roaccutane) is widely used to treat severe acne but has been linked to an increased risk of neuropsychiatric side effects, including depression. Here we report that chronic administration with 13-cis-RA (1 mg/kg i.p. daily, 7-14 days) in adult rats reduced aggression- and increased flight-related behaviours in the resident-intruder paradigm. However, in the forced swim, sucrose consumption and open field tests treatment for up to 6 weeks with 13-cis-RA did not modify behaviour in adult or juvenile animals. The behavioural change observed in the resident-intruder paradigm is directly opposite to that observed with chronic antidepressant administration. These findings indicate that when a suitably sensitive behavioural test is employed then chronic administration of 13-cis-RA in adult rats induces behavioural changes consistent with a pro-depressant action.

The detection and measurement of locomotor deficits in a transgenic mouse model of Huntington's disease are task- and protocol-dependent: influence of non-motor factors on locomotor function.

Locomotor performance of transgenic R6/2 mice carrying the Huntington's disease (HD) mutation was assessed using four different tasks, fixed speed rotarod, accelerating rotarod, Digigait and footprint test. The tasks were compared directly in age- and CAG repeat-matched R6/2 mice. Accelerating rotarod was more sensitive than fixed speed rotarod for detecting early motor deficits in R6/2 mice. The sensitivity of accelerating rotarod increased with the acceleration rate and/or the start speed from which the rod accelerated. Differences between tasks were not due to inability of R6/2 mice to maintain balance at high speeds or increased fatigue on accelerating rotarod, but to difficulties in coordinating gait changes required by the constant change in speed on accelerating rotarod. The footprint test was sensitive to gait disturbances. However, surprisingly, R6/2 mice did not show major gait abnormalities on an automated treadmill task (Digigait), even though they showed overt gait deficits in the home cage. The fact that the sensitivity for detecting motor deficits depended strongly on the individual task, and on the protocol used, suggests that non-motor factors were differentially engaged in the different paradigms. We thus recommend that more than one task should be used for detecting and tracking different aspects of motor decay in animal models of HD. Since deficits in non-motor factors such as executive function and motivation may differentially influence motor outcome in each task, our results call for a more thorough investigation of the importance of higher level control of locomotion in animal models of HD.

Complexin 1 knockout mice exhibit marked deficits in social behaviours but appear to be cognitively normal.

Complexins are presynaptic proteins that modulate neurotransmitter release. Abnormal expression of complexin 1 (Cplx1) is seen in several neurodegenerative and psychiatric disorders in which disturbed social behaviour is commonplace. These include Parkinsons's disease, Alzheimer's disease, schizophrenia, major depressive illness and bipolar disorder. We wondered whether changes in Cplx1 expression contribute to the psychiatric components of the diseases in which Cplx1 is dysregulated. To investigate this, we examined the cognitive and social behaviours of complexin 1 knockout mice (Cplx1(-/-)) mice. Cplx1(-/-) mice have a profound ataxia that limits their ability to perform co-ordinated motor tasks. Nevertheless, when we taught juvenile Cplx1(-/-) mice to swim, they showed no evidence of cognitive impairment in the two-choice swim tank. In contrast, although olfactory discrimination in Cplx1(-/-) mice was normal, Cplx1(-/-) mice failed in the social transmission of food preference task, another cognitive paradigm. This was due to abnormal social interactions rather than cognitive impairments, increased anxiety or neophobia. When we tested social behaviour directly, Cplx1(-/-) mice failed to demonstrate a preference for social novelty. Further, in a resident-intruder paradigm, male Cplx1(-/-) mice failed to show the aggressive behaviour that is typical of wild-type males towards an intruder mouse. Together our results show that in addition to the severe motor and exploratory deficits already described, Cplx1(-/-) mice have pronounced deficits in social behaviours. Abnormalities in complexin 1 levels in the brain may therefore contribute to the psycho-social aspects of human diseases in which this protein is dysregulated.