Catherine J. McAllister

Disruption of Peripheral Circadian Timekeeping in a Mouse Model of Huntington's Disease and Its Restoration by Temporally Scheduled Feeding

Behavioral circadian rhythms disintegrate progressively in the R6/2 mouse model of Huntingtons disease (HD), recapitulating the sleep–wake disturbance seen in HD patients. Here we show that disturbances in circadian pacemaking are not restricted to the brain, but also encompass peripheral metabolic pathways in R6/2 mice. Notably, circadian rhythms of clock-driven genes that are key metabolic outputs in the liver are abolished in vivo. This deficiency is accompanied by arrhythmic expression of the clock genes Cry1 and Dbp, and a phase-advanced Per2 cycle. Compromised circadian metabolic cycles are not, however, a consequence of deficient pacemaking intrinsic to the liver, because when cultured in vitro, R6/2 liver slices exhibit self-sustained circadian bioluminescence rhythms. We therefore propose that compromised metabolic cycles arise from an internal desynchronization secondary to altered feeding patterns and impaired circadian signaling from the central pacemaker of the suprachiasmatic nucleus (SCN). Importantly, the SCN-independent food-entrainable oscillator remains intact in R6/2 mice and, when invoked, can restore daily behavioral cycles and reverse some of the metabolic abnormalities seen in the liver. Disturbances of metabolism have long been thought to be an important feature of HD. Uncoupling liver metabolism from circadian drives will reduce metabolic efficiency and cause imbalances in metabolites known to be deleterious to brain function. Thus, even subtle imbalances in liver function may exacerbate symptoms of HD, where neurological function is already compromised.

Development of the eating behaviour in Prader–Willi Syndrome: advances in our understanding

Prader–Willi Syndrome (PWS) is a genetically determined neurodevelopmental disorder associated with mild to moderate intellectual disability, growth and sex-hormone deficiencies and a propensity to overeat that leads to severe obesity. The PWS phenotype changes from an early disinterest in food to an increasing pre-occupation with eating and a failure of the normal satiety response to food intake. The prevention of severe obesity is primarily through strict control of access to food and it is this aspect that most limits the independence of those with PWS. This review considers the eating disorder in PWS, specifically how the as yet uncertain genetics of the syndrome and the transition from the early to the later phenotype might account for the later hyperphagia. On the basis of behavioural and imaging studies, a failure of satiety and excessive activation of neural reward pathways have both been suggested. We speculate that the overeating behaviour, consequent upon one or other of the above, could either be due to a direct effect of the PWS genotype on the feeding pathways of the hypothalamus or a consequence of prenatal changes in the regulation of genes responsible for energy balance that sets a high satiation threshold. Understanding the overeating in PWS will lead to more focused and successful management and ultimately, treatment of this life-threatening behaviour.

Responses to Environmental Enrichment Differ with Sex and Genotype in a Transgenic Mouse Model of Huntington's Disease

Background Environmental enrichment (EE) in laboratory animals improves neurological function and motor/cognitive performance, and is proposed as a strategy for treating neurodegenerative diseases. EE has been investigated in the R6/2 mouse model of Huntingtons disease (HD), where increased social interaction, sensory stimulation, exploration, and physical activity improved survival. We have also shown previously that HD patients and R6/2 mice have disrupted circadian rhythms, treatment of which may improve cognition, general health, and survival. Methodology/Principal Findings We examined the effects of EE on the behavioral phenotype and circadian activity of R6/2 mice. Our mice are typically housed in an “enriched” environment, so the EE that the mice received was in addition to these enhanced housing conditions. Mice were either kept in their home cages or exposed daily to the EE (a large playground box containing running wheels and other toys). The “home cage” and “playground” groups were subdivided into “handling” (stimulated throughout the experimental period) and “no-handling” groups. All mice were assessed for survival, body weight, and cognitive performance in the Morris water maze (MWM). Mice in the playground groups were more active throughout the enrichment period than home cage mice. Furthermore, R6/2 mice in the EE/no-handling groups had better survival than those in the home cage/no-handling groups. Sex differences were seen in response to EE. Handling was detrimental to R6/2 female mice, but EE increased the body weight of male R6/2 and WT mice in the handling group. EE combined with handling significantly improved MWM performance in female, but not male, R6/2 mice. Conclusions/Significance We show that even when mice are living in an enriched home cage, further EE had beneficial effects. However, the improvements in cognition and survival vary with sex and genotype. These results indicate that EE may improve the quality of life of HD patients, but we suggest that EE as a therapy should be tailored to individuals.

Asymptomatic sleep abnormalities are a common early feature in patients with Huntington's disease.

Huntington’s disease (HD) is a fatal neurodegenerative disease characterized by motor, cognitive, and psychiatric disturbance. In this article, we used polysomnography, actigraphy and a variety of validated questionnaires to ascertain the extent to which sleep changes are identifiable and measurable in mild stage HD, and importantly, to see whether patients are negatively impacted by the changes in their sleep. We found significant differences in sleep architecture and sleep efficiency in patients compared with controls using polysomnography. However, patient scores on the Functional Outcomes of Sleep Questionnaire, Medical Outcomes of Sleep Scale, and Epworth Sleepiness Scale were not significantly different to controls. These results suggest that although marked changes in sleep architecture are present in early HD and can be detected using polysomnography, patients do not necessarily recognize or report these abnormalities.

The transition between the phenotypes of Prader-Willi syndrome during infancy and early childhood

Aim  Prader–Willi syndrome (PWS) is a genetic disorder historically characterized by two phenotypic stages. The early phenotype in infants is associated with hypotonia, poor suck, and failure to thrive. In later childhood, PWS is associated with intellectual disability, hyperphagia, as well as growth and sex hormone deficiency. Little is known about the transition between phenotypes. This study investigates the nature of the change in infancy and childhood PWS.

Defective Mitochondrial Function In Vivo in Skeletal Muscle in Adults with Down’s Syndrome: A 31P-MRS Study

Down’s syndrome (DS) is a developmental disorder associated with intellectual disability (ID). We have previously shown that people with DS engage in very low levels of exercise compared to people with ID not due to DS. Many aspects of the DS phenotype, such as dementia, low activity levels and poor muscle tone, are shared with disorders of mitochondrial origin, and mitochondrial dysfunction has been demonstrated in cultured DS tissue. We undertook a phosphorus magnetic resonance spectroscopy (31P-MRS) study in the quadriceps muscle of 14 people with DS and 11 non-DS ID controls to investigate the post-exercise resynthesis kinetics of phosphocreatine (PCr), which relies on mitochondrial respiratory function and yields a measure of muscle mitochondrial function in vivo. We found that the PCr recovery rate constant was significantly decreased in adults with DS compared to non-DS ID controls (1.7±0.1 min−1 vs 2.1±0.1 min−1 respectively) who were matched for physical activity levels, indicating that muscle mitochondrial function in vivo is impaired in DS. This is the first study to investigate mitochondrial function in vivo in DS using 31P-MRS. Our study is consistent with previous in vitro studies, supporting a theory of a global mitochondrial defect in DS.

Novel insights into maladaptive behaviours in Prader–Willi syndrome: serendipitous findings from an open trial of vagus nerve stimulation

Abstract Background We report striking and unanticipated improvements in maladaptive behaviours in Prader–Willi syndrome (PWS) during a trial of vagus nerve stimulation (VNS) initially designed to investigate effects on the overeating behaviour. PWS is a genetically determined neurodevelopmental disorder associated with mild–moderate intellectual disability (ID) and social and behavioural difficulties, alongside a characteristic and severe hyperphagia. Methods Three individuals with PWS underwent surgery to implant the VNS device. VNS was switched on 3 months post‐implantation, with an initial 0.25 mA output current incrementally increased to a maximum of 1.5 mA as tolerated by each individual. Participants were followed up monthly. Results Vagal nerve stimulation in these individuals with PWS, within the stimulation parameters used here, was safe and acceptable. However, changes in eating behaviour were equivocal. Intriguingly, unanticipated, although consistent, beneficial effects were reported by two participants and their carers in maladaptive behaviour, temperament and social functioning. These improvements and associated effects on food‐seeking behaviour, but not weight, indicate that VNS may have potential as a novel treatment for such behaviours. Conclusions We propose that these changes are mediated through afferent and efferent vagal projections and their effects on specific neural networks and functioning of the autonomic nervous system and provide new insights into the mechanisms that underpin what are serious and common problems affecting people with IDs more generally.

Growth hormone, gender and face shape in Prader-Willi syndrome.

Prader–Willi syndrome is a neurodevelopmental disorder resulting from the absence of expression of paternally expressed gene(s) in a highly imprinted region of chromosome 15q11‐13. The physical phenotype includes evidence of growth retardation due to relative growth hormone deficiency, small hands and feet, a failure of normal secondary sexual development, and a facial appearance including narrow bifrontal diameter, almond‐shaped palpebral fissures, narrow nasal root, and thin upper vermilion with downturned corners of the mouth. Anecdotally, the face of individuals with PWS receiving hGH treatment is said to “normalize.” We used dense surface modelling and shape signature techniques to analyze 3D photogrammetric images of the faces of 72 affected and 388 unaffected individuals. We confirmed that adults with Prader–Willi syndrome who had never received human growth supplementation displayed known characteristic facial features. Facial growth was significantly reduced in these adults, especially in males. We demonstrated that following human growth hormone (hGH) supplementation, vertical facial growth of affected individuals falls within the normal range. However, lateral and periorbital face shape and nose shape differences in affected children who have received hGH therapy remain sufficiently strong to be significantly discriminating in comparisons with age–sex matched, unaffected individuals. Finally, we produced evidence that age at initiation and length of treatment with hGH do not appear to play a role in normalization or in consistent alteration of the face shape of affected individuals. This is the first study to provide objective shape analysis of craniofacial effects of hGH therapy in Prader–Willi syndrome.

Adaptation to Experimental Jet-Lag in R6/2 Mice despite Circadian Dysrhythmia

The R6/2 transgenic mouse model of Huntington’s disease (HD) shows a disintegration of circadian rhythms that can be delayed by pharmacological and non-pharmacological means. Since the molecular machinery underlying the circadian clocks is intact, albeit progressively dysfunctional, we wondered if light phase shifts could modulate the deterioration in daily rhythms in R6/2 mice. Mice were subjected to four x 4 hour advances in light onset. R6/2 mice adapted to phase advances, although angles of entrainment increased with age. A second cohort was subjected to a jet-lag paradigm (6 hour delay or advance in light onset, then reversal after 2 weeks). R6/2 mice adapted to the original shift, but could not adjust accurately to the reversal. Interestingly, phase shifts ameliorated the circadian rhythm breakdown seen in R6/2 mice under normal LD conditions. Our previous finding that the circadian period (tau) of 16 week old R6/2 mice shortens to approximately 23 hours may explain how they adapt to phase advances and maintain regular circadian rhythms. We tested this using a 23 hour period light/dark cycle. R6/2 mice entrained to this cycle, but onsets of activity continued to advance, and circadian rhythms still disintegrated. Therefore, the beneficial effects of phase-shifting are not due solely to the light cycle being closer to the tau of the mice. Our data show that R6/2 mice can adapt to changes in the LD schedule, even beyond the age when their circadian rhythms would normally disintegrate. Nevertheless, they show abnormal responses to changes in light cycles. These might be caused by a shortened tau, impaired photic re-synchronization, impaired light detection and/or reduced masking by evening light. If similar abnormalities are present in HD patients, they may suffer exaggerated jet-lag. Since the underlying molecular clock mechanism remains intact, light may be a useful treatment for circadian dysfunction in HD.

A short clinical overview of Prader-Willi syndrome.

Prader–Willi syndrome (PWS) is a multifaceted developmental disorder most commonly associated with extreme hyperphagia and life‐threatening obesity. PWS is a genetic disorder of imprinting with almost all cases occurring spontaneously. Behavioural and imaging studies have shown that obesity in PWS arises from overeating driven by a faulty satiety mechanism which manifests as an almost permanent state similar to starvation. With no available treatments, management of the eating behaviour is the only option and has two main strategies: restrict access to food and distract thoughts from food. In this mini review, which we have aimed at clinicians, we outline the main aspects of PWS including genetics, development of the eating behaviour and best practice approaches to management.