The neuroanatomy of genetic subtype differences in Prader-Willi syndrome

14 and 6 Hz like spike wave activity is a common finding in young patients with Prader-Willi syndrome

STUDY OBJECTIVES

Our aim was to characterize the 14 and 6 like spike wave activity seen on electroencephalograms (EEG) in children with Prader-Willi syndrome (PWS) undergoing polysomnograms.

METHODS

We performed a retrospective review of children with PWS and healthy controls who underwent diagnostic polysomnograms between January 1, 2007, and December 31, 2020, at SickKids, Toronto, Canada. EEGs from the polysomnograms were reviewed for the presence of the 14 and 6 like spike wave activity and its characteristics. Clinical correlation of the EEG variant with sleep-disordered breathing indices from the polysomnograms was also evaluated.

RESULTS

A total of 94 children with PWS and 50 healthy controls were included. The median age and interquartile range for the cohort was 1.42 (0.6, 4.2) years. There were 50 (53.2%) males in the PWS cohort. The EEG variant prevalence in this cohort was 51.0% (n = 48) in children with PWS and 0% for the healthy controls. 14 and 6 Hz like spike wave activity was bilateral in 52% (25/48) children with PWS. The waves had a negative deflection in almost all patients, 44/48 (92%), with PWS. It was predominantly located in the frontal leads for children with PWS, 23/48 (47.9%). It most frequently occurred during non-rapid eye movement stage 2 sleep for children with PWS, 25/48 (52.0%). The mean (standard deviation) frequency was 6.8 (0.97) Hz. The median (interquartile range) length of the waves was 1.1 (0.8, 1.4) seconds in children with PWS. There was no correlation between the presence of the EEG variant and sleep-disordered breathing indices in children with PWS.

CONCLUSIONS

The 14 and 6 Hz like spike wave activity EEG variant was present in more than 50% of a pediatric cohort of children with PWS compared with 0% in healthy children. This EEG variant did not appear to be associated with sleep-disordered breathing indices in children with PWS and is of unknown clinical significance.

CITATION

Alzaid M, Sunkonkit K, Massicotte C, Otsubo H, Amin R, Al-Saleh S. 14 and 6 Hz like spike wave activity is a common finding in young patients with Prader-Willi syndrome. J Clin Sleep Med. 2024;20(8):1227-1232.

Neuromodulation for the treatment of Prader-Willi syndrome - A systematic review

Prader-Willi syndrome (PWS) is a complex, genetic disorder characterized by multisystem involvement, including hyperphagia, maladaptive behaviors and endocrinological derangements. Recent developments in advanced neuroimaging have led to a growing understanding of PWS as a neural circuit disorder, as well as subsequent interests in the application of neuromodulatory therapies. Various non-invasive and invasive device-based neuromodulation methods, including vagus nerve stimulation (VNS), transcranial direct current stimulation (tDCS), repetitive transcranial magnetic stimulation (rTMS), and deep brain stimulation (DBS) have all been reported to be potentially promising treatments for addressing the major symptoms of PWS. In this systematic literature review, we summarize the recent literature that investigated these therapies, discuss the underlying circuits which may underpin symptom manifestations, and cover future directions of the field. Through our comprehensive search, there were a total of 47 patients who had undergone device-based neuromodulation therapy for PWS. Two articles described VNS, 4 tDCS, 1 rTMS and 2 DBS, targeting different symptoms of PWS, including aberrant behavior, hyperphagia and weight. Multi-center and multi-country efforts will be required to advance the field given the low prevalence of PWS. Finally, given the potentially vulnerable population, neuroethical considerations and dialogue should guide the field.

Early psychomotor development and growth hormone therapy in children with Prader-Willi syndrome: a review

Prader-Willi syndrome (PWS) is a rare genetic disorder caused by the loss of imprinted gene expression on the paternal chromosome 15q11-q13. PWS is characterized by varying degrees of early psychomotor developmental deficits, primarily in cognition, language, and motor development. This review summarizes the early mental cognitive development, language development, and motor development in patients with PWS, compares the correlation of genotype with phenotype, and provides an update regarding the effects and concerns related to potential main side effects of treatment with recombinant human growth hormone on early psycho-cognitive and motor function development along with the linear growth and body composition of children with PWS.Conclusion: Early psychomotor development is strongly correlated with the prognosis of patients with PWS; moreover, current studies support that the initiation of interventions at an early age can exert significant beneficial effects on enhancing the cognitive and linguistic development of patients with PWS and allow them to "catch up" with motor development.  What is Known: • Prader-Willi syndrome is a rare genetic disorder characterized by multisystem damage, and children with Prader-Willi syndrome are typically characterized by early developmental delays, specifically in the areas of cognitive and motor development. • Recombinant human growth hormone therapy is the only medical treatment approved for Prader-Willi syndrome. What is New: • Extensive presentation of psycho-cognitive and motor development features and genotype-phenotype correlation in children with Prader-Willi syndrome.  • The effects of growth hormone on early psychomotor development in children with Prader-Willi syndrome were thoroughly reviewed, including their short- and long-term outcomes and any associated adverse effects.

Amygdala hyperactivation relates to eating behaviour: a potential indicator of food addiction in Prader-Willi syndrome

Prader-Willi syndrome is a rare neurodevelopmental genetic disorder characterized by various endocrine, cognitive and behavioural problems. The symptoms include an obsession for food and reduced satiety, which leads to hyperphagia and morbid obesity. Neuropsychological studies have reported that Prader-Willi patients display altered social interactions with a specific weakness in interpreting social information and responding to them, a symptom close to that observed in autism spectrum disorders. In the present case-control study, we hypothesized that brain regions associated with compulsive eating behaviour would be abnormally activated by food-related odours in Prader-Willi syndrome, as these can stimulate the appetite and induce hunger-related behaviour. We conducted a brain imaging study using the olfactory modality because odours have a high-hedonic valence and can cause stronger emotional reactions than other modalities. Further, the olfactory system is also intimately associated with the endocrine regulation of energy balance and is the most appropriate modality for studies of Prader-Willi syndrome. A total of 16 Prader-Willi participants were recruited for this study, which is a significant achievement given the low incidence rate of this rare disease. The second group of 11 control age-matched subjects also participated in the brain imaging study. In the MRI scanner, using an MRI-compatible olfactometer during 56 block sessions, we randomly presented two odours (tulip and caramel), which have different hedonic valence and a different capacity to arouse hunger-related behaviour. Our results demonstrate that Prader-Willi participants have abnormal activity in the brain reward system that regulates eating behaviour. Indeed, we found that these patients had right amygdala activity up to five times higher in response to a food odour (caramel) compared with the tulip odour. In contrast, age-matched control participants had similar activity levels in response to both odours. The amygdala activity levels were found to be associated with the severity of the hyperphagia in Prader-Willi patients. Our results provide evidence for functional alteration of the right amygdala in Prader-Willi syndrome, which is part of the brain network involved in food addiction modulated by the ghrelin and oxytocin systems, which may drive the hyperphagia. Our study provides important new insights into the functioning of emotion-related brain circuits and pathology, and it is one of the few to explore the dysfunction of the neural circuits involved in emotion and addiction in Prader-Willi syndrome. It suggests new directions for the exploration and remediation of addictive behaviours.

Progress in Brain Magnetic Resonance Imaging of Individuals with Prader-Willi Syndrome

Prader-Willi syndrome (PWS), a rare epigenetic disease mapping the imprinted chromosomal domain of 15q11.2-q13.3, manifests a regular neurodevelopmental trajectory in different phases. The current multimodal magnetic resonance imaging (MRI) approach for PWS focues on morphological MRI (mMRI), diffusion MRI (dMRI) and functional MRI (fMRI) to uncover brain alterations. This technique offers another perspective to understand potential neurodevelopmental and neuropathological processes of PWS, in addition to specific molecular gene expression patterns, various clinical manifestations and metabolic phenotypes. Multimodal MRI studies of PWS patients demonstrated common brain changes in the volume of gray matter, the integrity of the fiber tracts and the activation and connectivity of some networks. These findings mainly showed that brain alterations in the frontal reward circuit and limbic system were related to molecular genetics and clinical manifestations (e.g., overwhelming eating, obsessive compulsive behaviors and skin picking). Further exploration using a large sample size and advanced MRI technologies, combined with artificial intelligence algorithms, will be the main research direction to study the structural and functional changes and potential pathogenesis of PWS.

Clinical Features, Brain-Structure Changes, and Cognitive Impairment in Basal Ganglia Infarcts: A Pilot Study

Introduction

Stroke has been considered to raise the risk of dementia in several studies, but the relationship between brain structural changes and poststroke cognitive impairment (PSCI) is unclear.

Methods

In this study, 23 PSCI patients with basal ganglia infarcts after 2 weeks and 29 age-matched controls underwent magnetic resonance imaging measuring cortical thickness and volume changes, as well as neuropsychological tests. CI was derived from a performance score <1.5 standard deviations for normally distributed scores. We compared Z scores in different cognitive domains and cortical thickness and volumes in two groups. Multiple linear regressions were used to investigate the relationship between cortical thickness and volumes and neuropsychological tests.

Results

A majority of PSCI patients were in their 50s (55.19±8.52 years). PSCI patients exhibited significantly decreased Z scores in multiple domains, such as memory, language, visuomotor speed, and attention/executive function. The volumes of the middle posterior corpus callosum, middle anterior corpus callosum, and hippocampus in PSCI patients were markedly lower than controls. The thickness of the right inferior temporal cortex and insula were significantly smaller than controls. It found that the reduced right hippocampus was related to executive dysfunction. Hippocampus dysfunction may be involved in language impairment (p<0.05) in PSCI patients with basal ganglia infarcts.

Conclusion

These findings demonstrated that brain structure changed after ischemic stroke, and different gray-matter structural changes could lead to specific cognitive decline in PSCI patients with basal ganglia infarcts. Atrophy of the right hippocampus potentially serves as an imaging marker of early executive function of PSCI.

Analysis of SNHG14: A Long Non-Coding RNA Hosting SNORD116, Whose Loss Contributes to Prader-Willi Syndrome Etiology

The Small Nucleolar Host Gene 14 (SNHG14) is a host gene for small non-coding RNAs, including the SNORD116 small nucleolar C/D box RNA encoding locus. Large deletions of the SNHG14 locus, as well as microdeletions of the SNORD116 locus, lead to the neurodevelopmental genetic disorder Prader-Willi syndrome. This review will focus on the SNHG14 gene, its expression patterns, its role in human cancer, and the possibility that single nucleotide variants within the locus contribute to human phenotypes in the general population. This review will also include new in silico data analyses of the SNHG14 locus and new in situ RNA expression patterns of the Snhg14 RNA in mouse midbrain and hindbrain regions.

Alteration of brain nuclei in obese children with and without Prader-Willi syndrome

Introduction: Prader-Willi syndrome (PWS) is a multisystem genetic imprinting disorder mainly characterized by hyperphagia and childhood obesity. Extensive structural alterations are expected in PWS patients, and their influence on brain nuclei should be early and profound. To date, few studies have investigated brain nuclei in children with PWS, although functional and structural alterations of the cortex have been reported widely. Methods: In the current study, we used T1-weighted magnetic resonance imaging to investigate alterations in brain nuclei by three automated analysis methods: shape analysis to evaluate the shape of 14 cerebral nuclei (bilateral thalamus, caudate, putamen, globus pallidus, hippocampus, amygdala, and nucleus accumbens), automated segmentation methods integrated in Freesurfer 7.2.0 to investigate the volume of hypothalamic subregions, and region of interest-based analysis to investigate the volume of deep cerebellar nuclei (DCN). Twelve age- and sex-matched children with PWS, 18 obese children without PWS (OB) and 18 healthy controls participated in this study. Results: Compared with control and OB individuals, the PWS group exhibited significant atrophy in the bilateral thalamus, pallidum, hippocampus, amygdala, nucleus accumbens, right caudate, bilateral hypothalamus (left anterior-inferior, bilateral posterior, and bilateral tubular inferior subunits) and bilateral DCN (dentate, interposed, and fastigial nuclei), whereas no significant difference was found between the OB and control groups. Discussion: Based on our evidence, we suggested that alterations in brain nuclei influenced by imprinted genes were associated with clinical manifestations of PWS, such as eating disorders, cognitive disability and endocrine abnormalities, which were distinct from the neural mechanisms of obese children.

Health Problems in Adults with Prader-Willi Syndrome of Different Genetic Subtypes: Cohort Study, Meta-Analysis and Review of the Literature

Prader−Willi syndrome (PWS) is a complex, rare genetic disorder caused by a loss of expression of paternally expressed genes on chromosome 15q11.2-q13. The most common underlying genotypes are paternal deletion (DEL) and maternal uniparental disomy (mUPD). DELs can be subdivided into type 1 (DEL-1) and (smaller) type 2 deletions (DEL-2). Most research has focused on behavioral, cognitive and psychological differences between the different genotypes. However, little is known about physical health problems in relation to genetic subtypes. In this cross-sectional study, we compare physical health problems and other clinical features among adults with PWS caused by DEL (N = 65, 12 DEL-1, 27 DEL-2) and mUPD (N = 65). A meta-analysis, including our own data, showed that BMI was 2.79 kg/m2 higher in adults with a DEL (p = 0.001). There were no significant differences between DEL-1 and DEL-2. Scoliosis was more prevalent among adults with a DEL (80% vs. 58%; p = 0.04). Psychotic episodes were more prevalent among adults with an mUPD (44% vs. 9%; p < 0.001). In conclusion, there were no significant differences in physical health outcomes between the genetic subtypes, apart from scoliosis and BMI. The differences in health problems, therefore, mainly apply to the psychological domain.

Altered Gesture Imitation and Brain Anatomy in Adult Prader-Willi Syndrome Patients

OBJECTIVE

To explore motor praxis in adults with Prader-Willi syndrome (PWS) in comparison with a control group of people with intellectual disability (ID) and to examine the relationship with brain structural measurements.

METHOD

Thirty adult participants with PWS and 132 with ID of nongenetic etiology (matched by age, sex, and ID level) were assessed using a comprehensive evaluation of the praxis function, which included pantomime of tool use, imitation of meaningful and meaningless gestures, motor sequencing, and constructional praxis.

RESULTS

Results support specific praxis difficulties in PWS, with worse performance in the imitation of motor actions and better performance in constructional praxis than ID peers. Compared with both control groups, PWS showed increased gray matter volume in sensorimotor and subcortical regions. However, we found no obvious association between these alterations and praxis performance. Instead, praxis scores correlated with regional volume measures in distributed apparently normal brain areas.

CONCLUSIONS

Our findings are consistent in showing significant impairment in gesture imitation abilities in PWS and, otherwise, further indicate that the visuospatial praxis domain is relatively preserved. Praxis disability in PWS was not associated with a specific, focal alteration of brain anatomy. Altered imitation gestures could, therefore, be a consequence of widespread brain dysfunction. However, the specific contribution of key brain structures (e.g., areas containing mirror neurons) should be more finely tested in future research.

Lessons Learned From Neuroimaging Studies of Copy Number Variants: A Systematic Review

Pathogenic copy number variants (CNVs) and aneuploidies alter gene dosage and are associated with neurodevelopmental psychiatric disorders such as autism spectrum disorder and schizophrenia. Brain mechanisms mediating genetic risk for neurodevelopmental psychiatric disorders remain largely unknown, but there is a rapid increase in morphometry studies of CNVs using T1-weighted structural magnetic resonance imaging. Studies have been conducted one mutation at a time, leaving the field with a complex catalog of brain alterations linked to different genomic loci. Our aim was to provide a systematic review of neuroimaging phenotypes across CNVs associated with developmental psychiatric disorders including autism and schizophrenia. We included 76 structural magnetic resonance imaging studies on 20 CNVs at the 15q11.2, 22q11.2, 1q21.1 distal, 16p11.2 distal and proximal, 7q11.23, 15q11-q13, and 22q13.33 (SHANK3) genomic loci as well as aneuploidies of chromosomes X, Y, and 21. Moderate to large effect sizes on global and regional brain morphometry are observed across all genomic loci, which is in line with levels of symptom severity reported for these variants. This is in stark contrast with the much milder neuroimaging effects observed in idiopathic psychiatric disorders. Data also suggest that CNVs have independent effects on global versus regional measures as well as on cortical surface versus thickness. Findings highlight a broad diversity of regional morphometry patterns across genomic loci. This heterogeneity of brain patterns provides insight into the weak effects reported in magnetic resonance imaging studies of cognitive dimension and psychiatric conditions. Neuroimaging studies across many more variants will be required to understand links between gene function and brain morphometry.

Cerebellar Dysfunction in Adults with Prader Willi Syndrome

Severe hypotonia during infancy is a hallmark feature of Prader Willi syndrome (PWS). Despite its transient expression, moto development is delayed and deficiencies in motor coordination are present at older ages, with no clear pathophysiological mechanism yet identified. The diverse motor coordination symptoms present in adult PWS patients could be, in part, the result of a common alteration(s) in basic motor control systems. We aimed to examine the motor system in PWS using functional MRI (fMRI) during motor challenge. Twenty-three adults with PWS and 22 matched healthy subjects participated in the study. fMRI testing involved three hand motor tasks of different complexity. Additional behavioral measurements of motor function were obtained by evaluating hand grip strength, functional mobility, and balance. Whole brain activation maps were compared between groups and correlated with behavioral measurements. Performance of the motor tasks in PWS engaged the neural elements typically involved in motor processing. While our data showed no group differences in the simplest task, increasing task demands evoked significantly weaker activation in patients in the cerebellum. Significant interaction between group and correlation pattern with measures of motor function were also observed. Our study provides novel insights into the neural substrates of motor control in PWS by demonstrating reduced cerebellar activation during movement coordination.

Effects of Transcranial Direct Current Stimulation (tDCS) on Go/NoGo Performance Using Food and Non-Food Stimuli in Patients with Prader-Willi Syndrome

Prader–Willi syndrome (PWS) is a neurodevelopmental genetic disorder characterized by multiple system involvement with hypotonia, poor suck with feeding difficulties, growth and other hormone deficiencies, intellectual disability, and behavioral problems with childhood onset of hyperphagia resulting in obesity, if not externally controlled. Transcranial direct current stimulation (tDCS) has been increasingly shown to modulate cognitive and behavioral processes in children and adults, including food-intake behaviors in patients with PWS. This study further reports the positive effects of brief tDCS sessions on Go/NoGo task performance involving food and non-food stimuli images, alterations in N2 brain amplitude, and genetic subgroup differences (maternal disomy 15, UPD; 15q11-q13 deletion, DEL) before and after tDCS as assessed by event-related potentials (ERPs) in 10 adults with PWS. The results indicate a group effect on baseline NoGo N2 amplitude in PWS patients with DEL vs UPD (p =0.046) and a decrease in NoGo N2 amplitude following tDCS (p = 0.031). Our tDCS approach also demonstrated a trend towards decreased response time. Collectively, these results replicate and expand prior work highlighting neurophysiological differences in patients with PWS according to genetic subtype and demonstrate the feasibility in examining neuromodulatory effects of tDCS on information processing in this patient population to stimulate additional research and treatment.

Hippocampal deficits in neurodevelopmental disorders

Neurodevelopmental disorders result from impaired development or maturation of the central nervous system. Both genetic and environmental factors can contribute to the pathogenesis of these disorders; however, the exact causes are frequently complex and unclear. Individuals with neurodevelopmental disorders may have deficits with diverse manifestations, including challenges with sensory function, motor function, learning, memory, executive function, emotion, anxiety, and social ability. Although these functions are mediated by multiple brain regions, many of them are dependent on the hippocampus. Extensive research supports important roles of the mammalian hippocampus in learning and cognition. In addition, with its high levels of activity-dependent synaptic plasticity and lifelong neurogenesis, the hippocampus is sensitive to experience and exposure and susceptible to disease and injury. In this review, we first summarize hippocampal deficits seen in several human neurodevelopmental disorders, and then discuss hippocampal impairment including hippocampus-dependent behavioral deficits found in animal models of these neurodevelopmental disorders.

The neural circuitry of restricted repetitive behavior: Magnetic resonance imaging in neurodevelopmental disorders and animal models

Restricted, repetitive behaviors (RRBs) are patterns of behavior that exhibit little variation in form and have no obvious function. RRBs although transdiagonstic are a particularly prominent feature of certain neurodevelopmental disorders, yet relatively little is known about the neural circuitry of RRBs. Past work in this area has focused on isolated brain regions and neurotransmitter systems, but implementing a neural circuit approach has the potential to greatly improve understanding of RRBs. Magnetic resonance imaging (MRI) is well-suited to studying the structural and functional connectivity of the nervous system, and is a highly translational research tool. In this review, we synthesize MRI research from both neurodevelopmental disorders and relevant animal models that informs the neural circuitry of RRB. Together, these studies implicate distributed neural circuits between the cortex, basal ganglia, and cerebellum. Despite progress in neuroimaging of RRB, there are many opportunities for conceptual and methodological improvement. We conclude by suggesting future directions for MRI research in RRB, and how such studies can benefit from complementary approaches in neuroscience.

Incidental memory for faces in children with different genetic subtypes of Prader-Willi syndrome

The present study examined the effects of genetic subtype on social memory in children (7–16 years) with Prader–Willi syndrome (PWS). Visual event-related potentials (ERPs) during a passive viewing task were used to compare incidental memory traces for repeated vs single presentations of previously unfamiliar social (faces) and nonsocial (houses) images in 15 children with the deletion subtype and 13 children with maternal uniparental disomy (mUPD). While all participants perceived faces as different from houses (N170 responses), repeated faces elicited more positive ERP amplitudes (‘old/new’ effect, 250–500ms) only in children with the deletion subtype. Conversely, the mUPD group demonstrated reduced amplitudes suggestive of habituation to the repeated faces. ERP responses to repeated vs single house images did not differ in either group. The results suggest that faces hold different motivational value for individuals with the deletion vs mUPD subtype of PWS and could contribute to the explanation of subtype differences in the psychiatric symptoms, including autism symptomatology.

Neuroanatomical and molecular correlates of cognitive and behavioural outcomes in hypogonadal males

Robust epidemiological, clinical and laboratory evidence supports emerging roles for the sex steroids in such domains as neurodevelopment, behaviour, learning and cognition. Regions of the mammalian brain that are involved in cognitive development and memory do not only express the classical nuclear androgen receptor, but also the non-genomic membrane receptor, which is a G protein-coupled receptor that mediates some rapid effects of the androgens on neurogenesis and synaptic plasticity. Under physiological conditions, hippocampal neurons do express the enzyme aromatase, and therefore actively aromatize testosterone to oestradiol. Although glial expression of the aromatase enzyme is minimal, increased expression following injury suggests a role for sex steroids in neuroprotection. It is therefore plausible to deduce that low levels of circulating androgens in males would perturb neuronal functions in relation to cognition and memory, as well as neural repair following injury. The present review is an overview of some roles of the sex steroids on cognitive function in males, and the neuroanatomical and molecular underpinnings of some behavioural and cognitive deficits characteristic of such genetic disorders noted for low androgen levels, including Klinefelter syndrome, Bardet-Biedl syndrome, Kallman syndrome and Prader-Willi syndrome. Recent literature in relation to some behavioural and cognitive changes secondary to surgical and pharmacological castration are also appraised.

Brain-stem serotonin transporter availability in maternal uniparental disomy and deletion Prader-Willi syndrome

Prader-Willi syndrome (PWS) is a rare condition because of the deletion of paternal chromosomal material (del PWS), or a maternal uniparental disomy (mUPD PWS), at 15q11-13. Affective psychosis is more prevalent in mUPD PWS. We investigated the relationship between the two PWS genetic variants and brain-stem serotonin transporter (5-HTT) availability in adult humans. Mean brain-stem 5-HTT availability determined by [123I]-beta-CIT single photon emission tomography was lower in eight adults with mUPD PWS compared with nine adults with del PWS (mean difference -0.93, t = -2.85, P = 0.014). Our findings confirm an association between PWS genotype and brain-stem 5-HTT availability, implicating a maternally expressed/paternally imprinted gene, that is likely to account for the difference in psychiatric phenotypes between the PWS variants. Declaration of interest None.

Grey matter volume and cortical structure in Prader-Willi syndrome compared to typically developing young adults

Prader-Willi syndrome (PWS) is a neurodevelopmental disorder of genomic imprinting, presenting with a characteristic overeating disorder, mild to moderate intellectual disability, and a variable range of social and behavioral difficulties. Consequently, widespread alterations in neural structure and developmental and maturational trajectory would be expected. To date, there have been few quantitative and systematic studies of brain morphology in PWS, although alterations of volume and of cortical organisation have been reported. This study aimed to investigate, in detail, the structure of grey matter and cortex in the brain in a sample of young adults with PWS in a well-matched case-controlled analysis. 20 young adults with PWS, aged 19–27 years, underwent multiparameter mapping magnetic resonance imaging sequences, from which measures of grey matter volume, cortical thickness and magnetisation transfer saturation, as a proxy measure of myelination, were examined. These variables were investigated in comparison to a control group of 40 typically developing young adults, matched for age and sex. A voxel-based morphometry analysis identified large and widespread bilateral clusters of both increased and decreased grey matter volume in the brain in PWS. In particular, widespread areas of increased volume encompassed parts of the prefrontal cortex, especially medially, the majority of the cingulate cortices, from anterior to posterior aspects, insula cortices, and areas of the parietal and temporal cortices. Increased volume was also reported in the caudate, putamen and thalamus. The most ventromedial prefrontal areas, in contrast, showed reduced volume, as did the parts of the medial temporal lobe, bilateral temporal poles, and a small cluster in the right lateral prefrontal cortex. Analysis of cortical structure revealed that areas of increased volume in the PWS group were largely driven by greater cortical thickness. Conversely, analysis of myelin content using magnetisation transfer saturation indicated that myelination of the cortex was broadly similar in the PWS and control groups, with the exception of highly localised areas, including the insula. The bilateral nature of these abnormalities suggests a systemic biological cause, with possible developmental and maturational mechanisms discussed, and may offer insight into the contribution of imprinted genes to neural development.

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Twenty young adults with PWS and forty age and sex-matched control participants underwent multiparameter mapping MRI.

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Large and widespread bilateral clusters of both increased and decreased grey matter volume were identified in PWS.

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Volumetric increases in PWS were largely driven by greater cortical thickness.

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Myelination of the cortex in PWS was broadly similar to the typically-developing control group.

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Potential developmental and maturational explanations are considered, including insights into the of the role of imprinted genes.

Brain structural alterations in obese children with and without Prader-Willi Syndrome

Prader-Willi syndrome (PWS) is a genetic imprinting disorder that is mainly characterized by hyperphagia and childhood obesity. Previous neuroimaging studies revealed that there is a significant difference in brain activation patterns between obese children with and without PWS. However, whether there are differences in the brain structure of obese children with and without PWS remains elusive. In the current study, we used T1-weighted and diffusion tensor magnetic resonance imaging to investigate alterations in the brain structure, such as the cortical volume and white matter integrity, in relation to this eating disorder in 12 children with PWS, 18 obese children without PWS (OB) and 18 healthy controls. Compared with the controls, both the PWS and OB groups exhibited alterations in cortical volume, with similar deficit patterns in 10 co-varying brain regions in the bilateral dorsolateral and medial prefrontal cortices, right anterior cingulate cortex, and bilateral temporal lobe. The white matter integrities of the above regions were then examined with an analysis method based on probabilistic tractography. The PWS group exhibited distinct changes in the reduced fractional anisotropy of white matter fibers connected to the co-varying regions, whereas the OB group did not. Our findings indicated that PWS and OB share similar gray matter alterations that are responsible for the development of eating disorders. Additionally, the distinct white matter alterations might explain the symptoms associated with food intake in PWS, including excessive hyperphagia and constant hunger. Hum Brain Mapp 38:4228-4238, 2017. © 2017 Wiley Periodicals, Inc.

[Neuropsychiatric aspects of Prader-Willi syndrome – a review]

Prader-Willi Syndrome (PWS) is caused by the absence of paternal expression of imprinted genes in the region at 15q11–q13. With an estimated birth incidence of 1/15 000 – 1/30 000, PWS is one of the more frequent genetic syndromes among humans. Typical physical features include neonatal hypotonia and feeding problems, hypogonadism, hyperphagia in later childhood with consecutive obesity, and short stature. Most people with PWS show a mild to moderate intellectual disability. Furthermore, lability of mood, temper tantrums, skin-picking, and compulsive behaviors are quite typical for subjects with PWS. Psychotic disorders have also been found to be quite common in adulthood. This manuscript reviews current knowledge about the etiology, physical features, developmental aspects, behavioral phenotype, and psychiatric disorders that occur as well as existing psychopharmacological and psychotherapeutic interventions.

Cognition in people with Prader-Willi syndrome: Insights into genetic influences on cognitive and social development

We present a mini-review of cognition in Prader-Willi syndrome. Studies cited include findings on general ability (IQ), IQ correlates with family members, strengths and weaknesses in cognitive profiles in genetic subtypes, attainment in literacy and numeracy, language, comprehension, modality preferences, executive functions, and social cognition. The latter includes investigations of theory of mind, emotion recognition, face processing and knowledge of social norms. Results from research on mouse models and brain imaging studies relevant to cognition are briefly discussed. The importance of these studies to understanding and managing education and behaviour in PWS and the limitations of the studies in terms of small numbers, non-representativeness, and lack of replication is also touched upon.

Anomalous basal ganglia connectivity and obsessive-compulsive behaviour in patients with Prader Willi syndrome

BACKGROUND

Prader Willi syndrome is a genetic disorder with a behavioural expression characterized by the presence of obsessive-compulsive phenomena ranging from elaborate obsessive eating behaviour to repetitive skin picking. Obsessive-compulsive disorder (OCD) has been recently associated with abnormal functional coupling between the frontal cortex and basal ganglia. We have tested the potential association of functional connectivity anomalies in basal ganglia circuits with obsessive-compulsive behaviour in patients with Prader Willi syndrome.

METHODS

We analyzed resting-state functional MRI in adult patients and healthy controls. Whole-brain functional connectivity maps were generated for the dorsal and ventral aspects of the caudate nucleus and putamen. A selected obsessive-compulsive behaviour assessment included typical OCD compulsions, self picking and obsessive eating behaviour.

RESULTS

We included 24 adults with Prader Willi syndrome and 29 controls in our study. Patients with Prader Willi syndrome showed abnormal functional connectivity between the prefrontal cortex and basal ganglia and within subcortical structures that correlated with the presence and severity of obsessive-compulsive behaviours. In addition, abnormally heightened functional connectivity was identified in the primary sensorimotor cortex-putamen loop, which was strongly associated with self picking. Finally, obsessive eating behaviour correlated with abnormal functional connectivity both within the basal ganglia loops and between the striatum and the hypothalamus and the amygdala.

LIMITATIONS

Limitations of the study include the difficulty in evaluating the nature of content of obsessions in patients with Prader Willi Syndrome and the risk of excessive head motion artifact on brain imaging.

CONCLUSION

Patients with Prader Willi syndrome showed broad functional connectivity anomalies combining prefrontal loop alterations characteristic of OCD with 1) enhanced coupling in the primary sensorimotor loop that correlated with the most impulsive aspects of the behaviour and 2) reduced coupling of the ventral striatum with limbic structures for basic internal homeostasis that correlated with the obsession to eat.

Promotion of mitochondrial biogenesis by necdin protects neurons against mitochondrial insults

Neurons rely heavily on mitochondria for their function and survival. Mitochondrial dysfunction contributes to the pathogenesis of neurodegenerative diseases such as Parkinson's disease. PGC-1α is a master regulator of mitochondrial biogenesis and function. Here we identify necdin as a potent PGC-1α stabilizer that promotes mitochondrial biogenesis via PGC-1α in mammalian neurons. Expression of genes encoding mitochondria-specific proteins decreases significantly in necdin-null cortical neurons, where mitochondrial function and expression of the PGC-1α protein are reduced. Necdin strongly stabilizes PGC-1α by inhibiting its ubiquitin-dependent degradation. Forced expression of necdin enhances mitochondrial function in primary cortical neurons and human SH-SY5Y neuroblastoma cells to prevent mitochondrial respiratory chain inhibitor-induced degeneration. Moreover, overexpression of necdin in the substantia nigra in vivo of adult mice protects dopaminergic neurons against degeneration in experimental Parkinson's disease. These data reveal that necdin promotes mitochondrial biogenesis through stabilization of endogenous PGC-1α to exert neuroprotection against mitochondrial insults.

Transcranial direct current stimulation reduces food-craving and measures of hyperphagia behavior in participants with Prader-Willi syndrome

Prader-Willi syndrome (PWS) is a neurodevelopmental genetic disorder characterized by intellectual disabilities and insatiable appetite with compulsive eating leading to severe obesity with detrimental health consequences. Transcranial direct current stimulation (tDCS) has been shown to modulate decision-making and cue-induced food craving in healthy adults. We conducted a pilot double blind, sham-controlled, multicenter study of tDCS modulation of food drive and craving in 10 adult PWS participants, 11 adult obese (OB) and 11 adult healthy-weight control (HWC) subjects. PWS and OB subjects received five consecutive daily sessions of active or sham tDCS over the right dorsolateral prefrontal cortex (DLPFC), while HWC received a single sham and active tDCS in a crossover design. Standardized psychometric instruments assessed food craving, drive and hyperphagia by self-report and caregiver assessment over 30 days. Robust baseline differences were observed in severity scores for the Three-Factor Eating Questionnaire (TFEQ) and Dykens Hyperphagia Questionnaire (DHQ) for PWS compared to HWC while obese participants were more similar to HWC. Active tDCS stimulation in PWS was associated with a significant change from baseline in TFEQ Disinhibition (Factor II) (Ƶ = 1.9, P < 0.05, 30 days) and Total Scores (Ƶ = 2.3, P < 0.02, 30 days), and participant ratings of the DHQ Severity (Ƶ = 1.8, P < 0.06, 5 days) and Total Scores (Ƶ = 1.9, P < 0.05, 15 days). These findings support sustained neuromodulatory effects and efficacy of tDCS to reduce food drive and behaviors impacting hyperphagia in PWS. Transcranial direct current stimulation may represent a straight-forward, low risk and low cost method to improve care, management and quality of life in PWS.

Prader-Willi Syndrome: A spectrum of anatomical and clinical features

Prader-Willi Syndrome (PWS) is estimated to affect 400,000 people worldwide. First described clinically in 1956, PWS is now known to be a result of a genetic mutation, involving Chromosome 15. The phenotypical appearance of individuals with the syndrome follows a similar developmental course. During infancy, universal hypotonia accompanied by feeding problems, hypogonadism, and dolichocephaly are evident. Characteristic facial features such as narrow bifrontal diameter, almond-shaped eyes, and small mouth (with downturned corners and thin upper lip) may also be evident at this stage. In early childhood, the craniofacial features become more obvious and a global developmental delay is observed. Simultaneously, individuals develop hyperphagia that leads to excessive or rapid weight gain, which, if untreated, exists throughout their lifespan and may predispose them to numerous, serious health issues. The standard tool for differential diagnosis of PWS is genetic screening; however, clinicians also need to be aware of the characteristic features of this disorder, including differences between the genetic subtypes. As the clinical manifestations of the syndrome vary between individuals and become evident at different developmental time points, early assessment is hindered. This article focuses on the clinical and anatomical manifestations of the syndrome and highlights the areas of discrepancy and limitations within the existing literature. Clin. Anat. 29:590-605, 2016. © 2016 Wiley Periodicals, Inc.

Puzzle Pieces: Neural Structure and Function in Prader-Willi Syndrome

Prader-Willi syndrome (PWS) is a neurodevelopmental disorder of genomic imprinting, presenting with a behavioural phenotype encompassing hyperphagia, intellectual disability, social and behavioural difficulties, and propensity to psychiatric illness. Research has tended to focus on the cognitive and behavioural investigation of these features, and, with the exception of eating behaviour, the neural physiology is currently less well understood. A systematic review was undertaken to explore findings relating to neural structure and function in PWS, using search terms designed to encompass all published articles concerning both in vivo and post-mortem studies of neural structure and function in PWS. This supported the general paucity of research in this area, with many articles reporting case studies and qualitative descriptions or focusing solely on the overeating behaviour, although a number of systematic investigations were also identified. Research to date implicates a combination of subcortical and higher order structures in PWS, including those involved in processing reward, motivation, affect and higher order cognitive functions, with both anatomical and functional investigations indicating abnormalities. It appears likely that PWS involves aberrant activity across distributed neural networks. The characterisation of neural structure and function warrants both replication and further systematic study.

From Prader-Willi syndrome to psychosis: translating parent-of-origin effects into schizophrenia research

Prader-Willi syndrome (PWS) is a relatively rare disorder that originates from paternally inherited deletions and maternal disomy (mUPD) within the 15q11-q13 region or alterations in the PWS imprinting center. Evidence is accumulating that mUPD underlies high prevalence of psychosis among PWS patients. Several genes involved in differentiation and survival of neurons as well as neurotransmission known to act in the development of PWS have been also implicated in schizophrenia. In this article, we provide an overview of genetic and epigenetic underpinnings of psychosis in PWS indicating overlapping points in the molecular background of PWS and schizophrenia. Simultaneously, we highlight the need for studies investigating genetic and epigenetic makeup of the 15q11-q13 in schizophrenia indicating promising candidate genes.

Reduced cortical complexity in children with Prader-Willi Syndrome and its association with cognitive impairment and developmental delay

Background

Prader-Willi Syndrome (PWS) is a complex neurogenetic disorder with symptoms involving not only hypothalamic, but also a global, central nervous system dysfunction. Previously, qualitative studies reported polymicrogyria in adults with PWS. However, there have been no quantitative neuroimaging studies of cortical morphology in PWS and no studies to date in children with PWS. Thus, our aim was to investigate and quantify cortical complexity in children with PWS compared to healthy controls. In addition, we investigated differences between genetic subtypes of PWS and the relationship between cortical complexity and intelligence within the PWS group.

Methods

High-resolution structural magnetic resonance images were acquired in 24 children with genetically confirmed PWS (12 carrying a deletion (DEL), 12 with maternal uniparental disomy (mUPD)) and 11 age- and sex-matched typically developing siblings as healthy controls. Local gyrification index (lGI) was obtained using the FreeSurfer software suite.

Results

Four large clusters, two in each hemisphere, comprising frontal, parietal and temporal lobes, had lower lGI in children with PWS, compared to healthy controls. Clusters with lower lGI also had significantly lower cortical surface area in children with PWS. No differences in cortical thickness of the clusters were found between the PWS and healthy controls. lGI correlated significantly with cortical surface area, but not with cortical thickness. Within the PWS group, lGI in both hemispheres correlated with Total IQ and Verbal IQ, but not with Performance IQ. Children with mUPD, compared to children with DEL, had two small clusters with lower lGI in the right hemisphere. lGI of these clusters correlated with cortical surface area, but not with cortical thickness or IQ.

Conclusions

These results suggest that lower cortical complexity in children with PWS partially underlies cognitive impairment and developmental delay, probably due to alterations in gene networks that play a prominent role in early brain development.

Divergent structural brain abnormalities between different genetic subtypes of children with Prader-Willi syndrome

Background

Prader–Willi syndrome (PWS) is a complex neurogenetic disorder with symptoms that indicate not only hypothalamic, but also a global, central nervous system (CNS) dysfunction. However, little is known about developmental differences in brain structure in children with PWS. Thus, our aim was to investigate global brain morphology in children with PWS, including the comparison between different genetic subtypes of PWS. In addition, we performed exploratory cortical and subcortical focal analyses.

Methods

High resolution structural magnetic resonance images were acquired in 20 children with genetically confirmed PWS (11 children carrying a deletion (DEL), 9 children with maternal uniparental disomy (mUPD)), and compared with 11 age- and gender-matched typically developing siblings as controls. Brain morphology measures were obtained using the FreeSurfer software suite.

Results

Both children with DEL and mUPD showed smaller brainstem volume, and a trend towards smaller cortical surface area and white matter volume. Children with mUPD had enlarged lateral ventricles and larger cortical cerebrospinal fluid (CSF) volume. Further, a trend towards increased cortical thickness was found in children with mUPD. Children with DEL had a smaller cerebellum, and smaller cortical and subcortical grey matter volumes. Focal analyses revealed smaller white matter volumes in left superior and bilateral inferior frontal gyri, right cingulate cortex, and bilateral precuneus areas associated with the default mode network (DMN) in children with mUPD.

Conclusions

Children with PWS show signs of impaired brain growth. Those with mUPD show signs of early brain atrophy. In contrast, children with DEL show signs of fundamentally arrested, although not deviant brain development and presented few signs of cortical atrophy. Our results of global brain measurements suggest divergent neurodevelopmental patterns in children with DEL and mUPD.

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.

Social and emotional processing in Prader-Willi syndrome: genetic subtype differences

Background

People with Prader-Willi syndrome (PWS) demonstrate social dysfunction and increased risk of autism spectrum disorder, especially those with the maternal uniparental disomy (mUPD) versus paternal deletion genetic subtype. This study compared the neural processing of social (faces) and nonsocial stimuli, varying in emotional valence, across genetic subtypes in 24 adolescents and adults with PWS.

Methods

Upright and inverted faces, and nonsocial objects with positive and negative emotional valence were presented to participants with PWS in an oddball paradigm with smiling faces serving as targets. Behavioral and event-related potential (ERP) data were recorded.

Results

There were no genetic subtype group differences in accuracy, and all participants performed above chance level. ERP responses revealed genetic subtype differences in face versus object processing. In those with deletions, the face-specific posterior N170 response varied in size for face stimuli versus inverted faces versus nonsocial objects. Persons with mUPD generated N170 of smaller amplitude and showed no stimulus differentiation. Brain responses to emotional content did not vary by subtype. All participants elicited larger posterior and anterior late positive potential responses to positive objects than to negative objects. Emotion-related differences in response to faces were limited to inverted faces only in the form of larger anterior late positive potential amplitudes to negative emotions over the right hemisphere. Detection of the target smiling faces was evident in the increased amplitude of the frontal and central P3 responses but only for inverted smiling faces.

Conclusion

Persons with the mUPD subtype of PWS may show atypical face versus object processes, yet both subtypes demonstrated potentially altered processing, attention to and/or recognition of faces and their expressions.

Expressive and receptive language in Prader-Willi syndrome: report on genetic subtype differences

Prader-Willi syndrome (PWS), most recognized for the hallmark hyperphagia and food preoccupations, is caused by the absence of expression of the paternally active genes in the q11-13 region of chromosome 15. Since the recognition of PWS as a genetic disorder, most research has focused primarily on the medical, genetic, and behavioral aspects of the syndrome. Extensive research has not been conducted on the cognitive, speech, and language abilities in PWS. In addition, language differences with regard to genetic mechanism of PWS have not been well investigated. To date, research indicates overall language ability is markedly below chronological age with expressive language more impaired than receptive language in people with PWS. Thus, the aim of the present study was to further characterize expressive and receptive language ability in 35 participants with PWS and compare functioning by genetic subtype using the Clinical Evaluation of Language Fundamentals-4 (CELF-IV). Results indicate that core language ability is significantly impaired in PWS and both expressive and receptive abilities are significantly lower than verbal intelligence. In addition, participants with the maternal uniparental disomy (mUPD) genetic subtype exhibit discrepant language functioning with higher expressive vs. receptive language abilities. Future research is needed to further examine language functioning in larger genetic subtype participant samples using additional descriptive measures. Further work should also delineate findings with respect to size of the paternal deletion (Type 1 and Type 2 deletions) and explore how overexpression of maternally expressed genes in the 15q11-13 region may relate to verbal ability.

LEARNING OUTCOMES

After reading this article, the reader will be able to: (1) summarize primary characteristics of Prader-Willi syndrome (PWS), (2) describe differentiating characteristics for the PWS genetic subtypes, (3) recall limited research regarding language functioning in PWS to date, (4) summarize potential genetic variations of language ability in Prader-Willi syndrome, and (5) summarize language ability in PWS with respect to adaptive functioning.

Brain structural correlates of reward sensitivity and impulsivity in adolescents with normal and excess weight

Introduction

Neuroscience evidence suggests that adolescent obesity is linked to brain dysfunctions associated with enhanced reward and somatosensory processing and reduced impulse control during food processing. Comparatively less is known about the role of more stable brain structural measures and their link to personality traits and neuropsychological factors on the presentation of adolescent obesity. Here we aimed to investigate regional brain anatomy in adolescents with excess weight vs. lean controls. We also aimed to contrast the associations between brain structure and personality and cognitive measures in both groups.

Methods

Fifty-two adolescents (16 with normal weight and 36 with excess weight) were scanned using magnetic resonance imaging and completed the Sensitivity to Punishment and Sensitivity to Reward Questionnaire (SPSRQ), the UPPS-P scale, and the Stroop task. Voxel-based morphometry (VBM) was used to assess possible between-group differences in regional gray matter (GM) and to measure the putative differences in the way reward and punishment sensitivity, impulsivity and inhibitory control relate to regional GM volumes, which were analyzed using both region of interest (ROI) and whole brain analyses. The ROIs included areas involved in reward/somatosensory processing (striatum, somatosensory cortices) and motivation/impulse control (hippocampus, prefrontal cortex).

Results

Excess weight adolescents showed increased GM volume in the right hippocampus. Voxel-wise volumes of the second somatosensory cortex (SII) were correlated with reward sensitivity and positive urgency in lean controls, but this association was missed in excess weight adolescents. Moreover, Stroop performance correlated with dorsolateral prefrontal cortex volumes in controls but not in excess weight adolescents.

Conclusion

Adolescents with excess weight have structural abnormalities in brain regions associated with somatosensory processing and motivation.