Intracranial abnormalities detected by three-dimensional magnetic resonance imaging in Prader-Willi syndrome

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.

The influence of emotional contexts on mental flexibility in Prader-Willi syndrome

BACKGROUND

The present study investigated the influence of emotional contexts on mental flexibility in adults with Prader-Willi syndrome (PWS) using a voluntary task-switching paradigm that was implemented with emotionally valenced pictures. The study aims were to assess whether adults with PWS have impaired switching abilities, whether the deficit is specific to PWS or linked to intellectual disabilities, and the influence of emotional contexts on performance.

METHOD

The task-switching performance of 30 adults with PWS was compared with that of 30 healthy adults matched on chronological age, and to that of 30 adults with intellectual disabilities but without PWS, matched on intellectual quotient level and chronological age. Indicators of switching performance were switching cost and repetition bias. Emotional contexts were operationalised with positive, neutral and negative task-irrelevant pictures.

RESULTS

Adults with PWS showed a large increase in switching costs compared with the two control groups, and this effect did not vary across emotional contexts. More fine-tuned examination revealed subtle performance modulations: negative contexts tended to increase the repetition bias in all three groups while positive contexts slowed down global performance in PWS.

CONCLUSIONS

The results confirmed previous studies, showing impaired switching abilities in PWS over and beyond the influence of intellectual level, but revealed no robust variations in switching deficits across emotional contexts.

The Diagnostic Journey of a Patient with Prader-Willi-Like Syndrome and a Unique Homozygous SNURF-SNRPN Variant; Bio-Molecular Analysis and Review of the Literature

Prader–Willi syndrome (PWS) is a rare genetic condition characterized by hypotonia, intellectual disability, and hypothalamic dysfunction, causing pituitary hormone deficiencies and hyperphagia, ultimately leading to obesity. PWS is most often caused by the loss of expression of a cluster of genes on chromosome 15q11.2-13. Patients with Prader–Willi-like syndrome (PWLS) display features of the PWS phenotype without a classical PWS genetic defect. We describe a 46-year-old patient with PWLS, including hypotonia, intellectual disability, hyperphagia, and pituitary hormone deficiencies. Routine genetic tests for PWS were normal, but a homozygous missense variant NM_003097.3(SNRPN):c.193C>T, p.(Arg65Trp) was identified. Single nucleotide polymorphism array showed several large regions of homozygosity, caused by high-grade consanguinity between the parents. Our functional analysis, the ‘Pipeline for Rapid in silico, in vivo, in vitro Screening of Mutations’ (PRiSM) screen, showed that overexpression of SNRPN-p.Arg65Trp had a dominant negative effect, strongly suggesting pathogenicity. However, it could not be confirmed that the variant was responsible for the phenotype of the patient. In conclusion, we present a unique homozygous missense variant in SNURF-SNRPN in a patient with PWLS. We describe the diagnostic trajectory of this patient and the possible contributors to her phenotype in light of the current literature on the genotype–phenotype relationship in PWS.

Behavioral and neuroanatomical approaches in models of neurodevelopmental disorders: opportunities for translation

PURPOSE OF REVIEW

This review highlights the invaluable contribution of in-vivo rodent models in dissecting the underlying neurobiology for numerous neurodevelopmental disorders. Currently, models are routinely generated with precision genomics and characterized for research on neurodevelopmental disorders. In order to impact translation, outcome measures that are translationally relevant are essential. This review emphasizes the importance of accurate neurobehavioral and anatomical analyses.

RECENT FINDINGS

Numerous well validated assays for testing alterations across behavioral domains with sensitivity and throughput have become important tools for studying the effects of genetic mutations on neurodevelopment. Recent work has highlighted relationships and links between behavioral outcomes and various anatomical metrics from neuroimaging via magnetic resonance. These readouts are biological markers and outcome measures for translational research and will be have important roles for genetic or pharmacologic intervention strategies.

SUMMARY

Combinatorial approaches that leverage translationally relevant behavior and neuroanatomy can be used to develop a platform for assessment of cutting edge preclinical models. Reliable, robust behavioral phenotypes in preclinical model systems, with clustering of brain disease will lead to well informed, precise biochemical mechanistic hypotheses. Ultimately, these steadfast workhorse techniques will accelerate the progress of developing and testing targeted treatments for multiple neurodevelopmental disorders.

Pathogenic variants in USP7 cause a neurodevelopmental disorder with speech delays, altered behavior, and neurologic anomalies

PURPOSE

Haploinsufficiency of USP7, located at chromosome 16p13.2, has recently been reported in seven individuals with neurodevelopmental phenotypes, including developmental delay/intellectual disability (DD/ID), autism spectrum disorder (ASD), seizures, and hypogonadism. Further, USP7 was identified to critically incorporate into the MAGEL2-USP7-TRIM27 (MUST), such that pathogenic variants in USP7 lead to altered endosomal F-actin polymerization and dysregulated protein recycling.

METHODS

We report 16 newly identified individuals with heterozygous USP7 variants, identified by genome or exome sequencing or by chromosome microarray analysis. Clinical features were evaluated by review of medical records. Additional clinical information was obtained on the seven previously reported individuals to fully elucidate the phenotypic expression associated with USP7 haploinsufficiency.

RESULTS

The clinical manifestations of these 23 individuals suggest a syndrome characterized by DD/ID, hypotonia, eye anomalies,feeding difficulties, GERD, behavioral anomalies, and ASD, and more specific phenotypes of speech delays including a nonverbal phenotype and abnormal brain magnetic resonance image findings including white matter changes based on neuroradiologic examination.

CONCLUSION

The consistency of clinical features among all individuals presented regardless of de novo USP7 variant type supports haploinsufficiency as a mechanism for pathogenesis and refines the clinical impact faced by affected individuals and caregivers.

Increased brain age in adults with Prader-Willi syndrome

Prader-Willi syndrome (PWS) is the most common genetic obesity syndrome, with associated learning difficulties, neuroendocrine deficits, and behavioural and psychiatric problems. As the life expectancy of individuals with PWS increases, there is concern that alterations in brain structure associated with the syndrome, as a direct result of absent expression of PWS genes, and its metabolic complications and hormonal deficits, might cause early onset of physiological and brain aging. In this study, a machine learning approach was used to predict brain age based on grey matter (GM) and white matter (WM) maps derived from structural neuroimaging data using T1-weighted magnetic resonance imaging (MRI) scans. Brain-predicted age difference (brain-PAD) scores, calculated as the difference between chronological age and brain-predicted age, are designed to reflect deviations from healthy brain aging, with higher brain-PAD scores indicating premature aging. Two separate adult cohorts underwent brain-predicted age calculation. The main cohort consisted of adults with PWS (n = 20; age mean 23.1 years, range 19.8-27.7; 70.0% male; body mass index (BMI) mean 30.1 kg/m2, 21.5-47.7; n = 19 paternal chromosome 15q11-13 deletion) and age- and sex-matched controls (n = 40; age 22.9 years, 19.6-29.0; 65.0% male; BMI 24.1 kg/m2, 19.2-34.2) adults (BMI PWS vs. control P = .002). Brain-PAD was significantly greater in PWS than controls (effect size mean ± SEM +7.24 ± 2.20 years [95% CI 2.83, 11.63], P = .002). Brain-PAD remained significantly greater in PWS than controls when restricting analysis to a sub-cohort matched for BMI consisting of n = 15 with PWS with BMI range 21.5-33.7 kg/m2, and n = 29 controls with BMI 21.7-34.2 kg/m2 (effect size +5.51 ± 2.56 years [95% CI 3.44, 10.38], P = .037). In the PWS group, brain-PAD scores were not associated with intelligence quotient (IQ), use of hormonal and psychotropic medications, nor severity of repetitive or disruptive behaviours. A 24.5 year old man (BMI 36.9 kg/m2) with PWS from a SNORD116 microdeletion also had increased brain PAD of 12.87 years, compared to 0.84 ± 6.52 years in a second control adult cohort (n = 95; age mean 34.0 years, range 19.9-55.5; 38.9% male; BMI 28.7 kg/m2, 19.1-43.1). This increase in brain-PAD in adults with PWS indicates abnormal brain structure that may reflect premature brain aging or abnormal brain development. The similar finding in a rare patient with a SNORD116 microdeletion implicates a potential causative role for this PWS region gene cluster in the structural brain abnormalities associated primarily with the syndrome and/or its complications. Further longitudinal neuroimaging studies are needed to clarify the natural history of this increase in brain age in PWS, its relationship with obesity, and whether similar findings are seen in those with PWS from maternal uniparental disomy.

Oxytocin and Prader-Willi Syndrome

In the chapter, we explore the relationship between the peptide hormone, oxytocin (OT), and behavioral and metabolic disturbances observed in the genetic disorder Prader-Willi Syndrome (PWS). Phenotypic and genotypic characteristics of PWS are described, as are the potential implications of an abnormal OT system with respect to neural development including the possible effects of OT dysfunction on interactions with other regulatory mediators, including neurotransmitters, neuromodulators, and hormones. The major behavioral characteristics are explored in the context of OT dysfunction, including hyperphagia, impulsivity, anxiety and emotion dysregulation, sensory processing and interoception, repetitive and restrictive behaviors, and dysfunctional social cognition. Behavioral overlaps with autistic spectrum disorders are discussed. The implications of OT dysfunction on the mechanisms of reward and satiety and their possible role in informing behavioral characteristics are also discussed. Treatment implications and future directions for investigation are considered.

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.

Loss of the imprinted, non-coding Snord116 gene cluster in the interval deleted in the Prader Willi syndrome results in murine neuronal and endocrine pancreatic developmental phenotypes

Global neurodevelopmental delay is a prominent characteristic of individuals with Prader-Willi syndrome (PWS). The neuromolecular bases for these delays are unknown. We identified neuroanatomical changes in the brains of mice deficient for a gene in the minimal critical deletion region for PWS (Snord116p-/m+). In Snord116p-/m+ mice, reduced primary forebrain neuron cell body size is apparent in embryonic day 15.5 fetuses, and persists until postnatal day 30 in cerebellar Purkinje neurons. Snord116 is a snoRNA gene cluster of unknown function that can localize to the nucleolus. In cerebellar Purkinje neurons from postnatal day 30 Snord116p-/m+ mice the reduction in neuronal cell body size was associated with decreased neuronal nucleolar size. We also identified developmental changes in the endocrine pancreas of Snord116p-/m+ animals that persist into adulthood. Mice lacking Snord116 have smaller pancreatic islets; within the islet the percentage of δ-cells is increased, while the percentage of α-cells is reduced. The α-cell markers, Sst and Hhex, are upregulated in Snord116p-/m+ isolated islets while Ins1, Ins2, Pdx1, Nkx6-1, and Pax6 are downregulated. There is a 3-fold increase in the percentage of polyhormonal cells in the neonatal pancreata of Snord116p-/m+ mice, due primarily to an increase in cells co-positive with somatostatin. Snord116 may play a role in islet cell lineage specification. The Snord116 gene cluster is important for developmental processes in the brain as well as the endocrine pancreas.

Autism spectrum disorder: neuropathology and animal models

Autism spectrum disorder (ASD) has a major impact on the development and social integration of affected individuals and is the most heritable of psychiatric disorders. An increase in the incidence of ASD cases has prompted a surge in research efforts on the underlying neuropathologic processes. We present an overview of current findings in neuropathology studies of ASD using two investigational approaches, postmortem human brains and ASD animal models, and discuss the overlap, limitations, and significance of each. Postmortem examination of ASD brains has revealed global changes including disorganized gray and white matter, increased number of neurons, decreased volume of neuronal soma, and increased neuropil, the last reflecting changes in densities of dendritic spines, cerebral vasculature and glia. Both cortical and non-cortical areas show region-specific abnormalities in neuronal morphology and cytoarchitectural organization, with consistent findings reported from the prefrontal cortex, fusiform gyrus, frontoinsular cortex, cingulate cortex, hippocampus, amygdala, cerebellum and brainstem. The paucity of postmortem human studies linking neuropathology to the underlying etiology has been partly addressed using animal models to explore the impact of genetic and non-genetic factors clinically relevant for the ASD phenotype. Genetically modified models include those based on well-studied monogenic ASD genes (NLGN3, NLGN4, NRXN1, CNTNAP2, SHANK3, MECP2, FMR1, TSC1/2), emerging risk genes (CHD8, SCN2A, SYNGAP1, ARID1B, GRIN2B, DSCAM, TBR1), and copy number variants (15q11-q13 deletion, 15q13.3 microdeletion, 15q11-13 duplication, 16p11.2 deletion and duplication, 22q11.2 deletion). Models of idiopathic ASD include inbred rodent strains that mimic ASD behaviors as well as models developed by environmental interventions such as prenatal exposure to sodium valproate, maternal autoantibodies, and maternal immune activation. In addition to replicating some of the neuropathologic features seen in postmortem studies, a common finding in several animal models of ASD is altered density of dendritic spines, with the direction of the change depending on the specific genetic modification, age and brain region. Overall, postmortem neuropathologic studies with larger sample sizes representative of the various ASD risk genes and diverse clinical phenotypes are warranted to clarify putative etiopathogenic pathways further and to promote the emergence of clinically relevant diagnostic and therapeutic tools. In addition, as genetic alterations may render certain individuals more vulnerable to developing the pathological changes at the synapse underlying the behavioral manifestations of ASD, neuropathologic investigation using genetically modified animal models will help to improve our understanding of the disease mechanisms and enhance the development of targeted treatments.

Neuroimaging Findings in Pediatric Genetic Skeletal Disorders: A Review

Genetic skeletal disorders (GSDs) are a heterogeneous group characterized by an intrinsic abnormality in growth and (re-)modeling of cartilage and bone. A large subgroup of GSDs has additional involvement of other structures/organs beside the skeleton, such as the central nervous system (CNS). CNS abnormalities have an important role in long-term prognosis of children with GSDs and should consequently not be missed. Sensitive and specific identification of CNS lesions while evaluating a child with a GSD requires a detailed knowledge of the possible associated CNS abnormalities. Here, we provide a pattern-recognition approach for neuroimaging findings in GSDs guided by the obvious skeletal manifestations of GSD. In particular, we summarize which CNS findings should be ruled out with each GSD. The diseases (n = 180) are classified based on the skeletal involvement (1. abnormal metaphysis or epiphysis, 2. abnormal size/number of bones, 3. abnormal shape of bones and joints, and 4. abnormal dynamic or structural changes). For each disease, skeletal involvement was defined in accordance with Online Mendelian Inheritance in Man. Morphological CNS involvement has been described based on extensive literature search. Selected examples will be shown based on prevalence of the diseases and significance of the CNS involvement. CNS involvement is common in GSDs. A wide spectrum of morphological abnormalities is associated with GSDs. Early diagnosis of CNS involvement is important in the management of children with GSDs. This pattern-recognition approach aims to assist and guide physicians in the diagnostic work-up of CNS involvement in children with GSDs and their management.

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.

Loss of Magel2 impairs the development of hypothalamic Anorexigenic circuits

Prader-Willi syndrome (PWS) is a genetic disorder characterized by a variety of physiological and behavioral dysregulations, including hyperphagia, a condition that can lead to life-threatening obesity. Feeding behavior is a highly complex process with multiple feedback loops that involve both peripheral and central systems. The arcuate nucleus of the hypothalamus (ARH) is critical for the regulation of homeostatic processes including feeding, and this nucleus develops during neonatal life under of the influence of both environmental and genetic factors. Although much attention has focused on the metabolic and behavioral outcomes of PWS, an understanding of its effects on the development of hypothalamic circuits remains elusive. Here, we show that mice lacking Magel2, one of the genes responsible for the etiology of PWS, display an abnormal development of ARH axonal projections. Notably, the density of anorexigenic α-melanocyte-stimulating hormone axons was reduced in adult Magel2-null mice, while the density of orexigenic agouti-related peptide fibers in the mutant mice appeared identical to that in control mice. On the basis of previous findings showing a pivotal role for metabolic hormones in hypothalamic development, we also measured leptin and ghrelin levels in Magel2-null and control neonates and found that mutant mice have normal leptin and ghrelin levels. In vitro experiments show that Magel2 directly promotes axon growth. Together, these findings suggest that a loss of Magel2 leads to the disruption of hypothalamic feeding circuits, an effect that appears to be independent of the neurodevelopmental effects of leptin and ghrelin and likely involves a direct neurotrophic effect of Magel2.

Deactivation of the left dorsolateral prefrontal cortex in Prader-Willi syndrome after meal consumption

BACKGROUND/OBJECTIVES

Prader-Willi syndrome (PWS) is a type of human genetic obesity that may give us information regarding the physiology of non-syndromic obesity. The objective of this study was to investigate the functional correlates of hunger and satiety in individuals with PWS in comparison with healthy controls with obesity, hypothesizing that we would see significant differences in activation in the left dorsolateral prefrontal cortex (DLPFC) based on prior findings.

SUBJECTS/METHODS

This study compared the central effects of food consumption in nine individuals with PWS (7 men, 2 women; body fat 35.3±10.0%) and seven controls (7 men; body fat 28.8±7.6%), matched for percentage body fat. H2(15)O-PET (positron emission tomography) scans were performed before and after consumption of a standardized liquid meal to obtain quantitative measures of regional cerebral blood flow (rCBF), a marker of neuronal activity.

RESULTS

Compared with obese controls, PWS showed altered (P<0.05 family-wise error cluster-level corrected; voxelwise P<0.001) rCBF before and after meal consumption in multiple brain regions. There was a significant differential rCBF response within the left DLPFC after meal ingestion with decreases in DLPFC rCBF in PWS; in controls, DLPFC rCBF tended to remain unchanged. In more liberal analyses (P<0.05 family-wise error cluster-level corrected; voxelwise P<0.005), rCBF of the right orbitofrontal cortex (OFC) increased in PWS and decreased in controls. In PWS, ΔrCBF of the right OFC was associated with changes in appetite ratings.

CONCLUSIONS

The pathophysiology of eating behavior in PWS is characterized by a paradoxical meal-induced deactivation of the left DLPFC and activation in the right OFC, brain regions implicated in the central regulation of eating behavior.

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.

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.

The usefulness of biliopancreatic diversion/Scopinaro operation in treatment of patients with Prader-Willi syndrome

Prader-Willi syndrome (PWS) is the most common form of obesity with a genetic basis. The short expected survival time due to numerous accompanying diseases and their complications is the reason for research on the maximally efficient method of treatment of obesity in this syndrome. Undertaken attempts of conservative treatment, for example with somatostatin, are ineffective. It seems that the only effective treatment of obesity in this syndrome may be surgical. In this article we present 2 cases of patients with PWS who underwent surgery consisting of biliopancreatic diversion (BPD)/Scopinaro procedure. The BPD/Scopinaro operation in selected cases of disciplined patients with a co-operative family, which we find of key importance, can be considered as one option of treatment of this syndrome in patients with prior neglect of conservative treatment.

Does the brain shrink as the waist expands?

Recent studies suggest that being overweight or obese is related to worse cognitive performance, particularly executive function. Obesity may also increase the risk of Alzheimer's disease. Consequently, there has been increasing interest in whether adiposity is related to gray or white matter (GM, WM) atrophy. In this review, we identified and critically evaluated studies assessing obesity and GM or WM volumes either globally or in specific regions of interest (ROIs). Across all ages, higher adiposity was consistently associated with frontal GM atrophy, particularly in prefrontal cortex. In children and adults <40 years of age, most studies found no relationship between adiposity and occipital or parietal GM volumes, whereas findings for temporal lobe were mixed. In middle-aged and aged adults, a majority of studies found that higher adiposity is associated with parietal and temporal GM atrophy, whereas results for precuneus, posterior cingulate, and hippocampus were mixed. Higher adiposity had no clear association with global or regional WM in any age group. We conclude that higher adiposity may be associated with frontal GM atrophy across all ages and parietal and temporal GM atrophy in middle and old age.

Explorative function in Prader-Willi syndrome analyzed through an ecological spatial task

This study was aimed at evaluating the spatial abilities in individuals with Prader-Willi syndrome (PWS) by using an ecological large-scale task with multiple rewards. To evaluate the extent of spatial deficit in PWS individuals, we compare their performances with those of individuals with Williams Syndrome (WS) in which the spatial deficits have been widely described. Participants had to explore an open space to search nine rewards placed in buckets arranged according to three spatial configurations: a Cross, a 3×3 Matrix and a Cluster composed by three groups of three buckets each. PWS individuals exhibited an explorative deficit in Cluster and Cross configurations, while WS participants in Matrix and Cross configurations. The findings indicate that the structural affordances of the environment influence the explorative strategies and can be related to how spatial information is processed.

Long-term outcome of epilepsy in patients with Prader-Willi syndrome

Prader-Willi syndrome is a multisystemic genetic disorder that can be associated with epilepsy. There is insufficient information concerning the clinical and electroencephalographic characteristics of epilepsy and the long-term outcome of these patients. The aim of this study is to describe seizure types, electroencephalographic patterns and long-term seizure outcome in Prader-Willi syndrome patients suffering from epilepsy. We retrospectively studied 38 patients with Prader-Willi syndrome and seizures. Results of neuroimaging studies were obtained for 35 individuals. We subdivided these patients into two groups: group A, 24 patients, without brain lesions; and group B, 11 patients, with brain abnormalities. All patients were re-evaluated after a period of at least 10 years. Twenty-one patients (55.2 %) were affected by generalized epilepsy and 17 patients (44.8 %) presented focal epilepsy. The most common seizure type was generalized tonic-clonic seizure. The mean age at seizure onset was 4.5 years (ranged from 1 month to 14 years). In the follow-up period, seizure freedom was achieved in 32 patients (84.2 %). Seizure freedom was associated with electroencephalographic normalization, while the six children presenting drug-resistant epilepsy showed persistence of electroencephalographic abnormalities. Group B patients showed a higher prevalence of drug-resistant epilepsy. Patients with Prader-Willi syndrome were frequently affected by generalized seizures. Most of the patients had a favorable evolution, although, patients with brain abnormalities presented a worse outcome, suggesting that the presence of these lesions can influence the response to antiepileptic therapy.

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.

Malformation syndromes associated with disorders of sex development

When embryological development of the internal and/or external genitalia is disrupted, the patient presents with a disorder of sex development (DSD) in the neonatal period or sometime later in life. Some of these patients have other, nongenital malformations, which makes their overall management more complex than if they just had a DSD. This Review summarises these malformation syndromes and discusses the recent research into their aetiology. The genetic causes of these malformation syndromes, when they are known, will also be described. Many specific genetic mutations are now known in malformation syndromes with a defect in hormonal function. By contrast, the genetic causes remain unknown in many nonhormonal morphological anomalies that affect the genitalia.

Epilepsy in Prader-Willi syndrome: clinical, diagnostic and treatment aspects

BACKGROUND

Epilepsy associated with Prader-Willi syndrome (PWS) represents an early and important complication, often not clearly reported and described in the literature. Consequently, there are controversial data about the clinical characteristics of epilepsy and electroencephalographic (EEG) abnormalities found in these patients.

DATA SOURCES

Based on recent original publications, we have reviewed the different types of seizures and EEG findings in PWS patients, the response to antiepileptic treatment, and the prognosis of epilepsy.

RESULTS

The frequency of epilepsy in PWS patients ranges from 4% to 26%. The types of seizure include generalized tonic-clonic seizures, complex partial seizures, atypical absence, staring spells, and myoclonic, tonic and hemiclonic seizures, but the most frequent type is focal epilepsy. Status epilepticus has never been reported. EEG abnormalities are not typical but variable in different patients. However, generalized and focal discharges are the most frequently reported findings. There is no evidence of relationship between the course of epilepsy and frequency, morphology and spread of EEG discharges. However, epilepsy in PWS patients is usually responsive to antiepileptic monotherapy with rapid seizure control and a good outcome.

CONCLUSIONS

The frequency of epilepsy is higher in PWS patients than in general populations and this complication can be a challenge for the clinicians of these patients. Prospective studies are needed to confirm the good long-term prognosis.

Genetic diseases: congenital central hypoventilation, Rett, and Prader-Willi syndromes

The present review summarizes current knowledge on three rare genetic disorders of respiratory control, congenital central hypoventilation syndrome (CCHS), Rett syndrome (RTT), and Prader-Willi syndrome (PWS). CCHS is characterized by lack of ventilatory chemosensitivity caused by PHOX2B gene abnormalities consisting mainly of alanine expansions. RTT is associated with episodes of tachypneic and irregular breathing intermixed with breathholds and apneas and is caused by mutations in the X-linked MECP2 gene encoding methyl-CpG-binding protein. PWS manifests as sleep-disordered breathing with apneas and episodes of hypoventilation and is caused by the loss of a group of paternally inherited genes on chromosome 15. CCHS is the most specific disorder of respiratory control, whereas the breathing disorders in RTT and PWS are components of a more general developmental disorder. The main clinical features of these three disorders are reviewed with special emphasis on the associated brain abnormalities. In all three syndromes, disease-causing genetic defects have been identified, allowing the development of genetically engineered mouse models. New directions for future therapies based on these models or, in some cases, on clinical experience are delineated. Studies of CCHS, RTT, and PWS extend our knowledge of the molecular and cellular aspects of respiratory rhythm generation and suggest possible pharmacological approaches to respiratory control disorders. This knowledge is relevant for the clinical management of many respiratory disorders that are far more prevalent than the rare diseases discussed here.

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.

Epilepsy in Prader-Willi syndrome: experience of a national referral centre

AIM

The aim of the study was to characterize epilepsy, febrile seizures, electrographic features, and brain abnormalities in a large, national cohort of individuals with Prader-Willi syndrome (PWS).

METHOD

This was an observational cohort study. Clinic charts of 126 individuals (63 males, 63 females) with genetically confirmed PWS (due to a deletion in 72 cases, to uniparental disomy [UPD] in 51 cases, and to an imprinting centre defect in two cases), aged from 1 month to 48 years (mean age 13y), were reviewed and 119 interviews conducted. Information regarding seizures, medication, imaging studies, and family history of seizures was collected. Ninety-five individuals (aged 1mo-48y) underwent electroencephalography (EEG).

RESULTS

Five individuals had epilepsy (4.0%), three of whom had major cerebral findings on imaging, and eight others had febrile seizures (6.4%). Of the three genetic abnormalities, deletion was associated with seizures. Focal epileptiform abnormalities were found in 12 out of 94 individuals, and five out of these 12 had a frank electrographic seizure pattern. Epileptogenic EEG abnormalities were associated with young age.

INTERPRETATION

The risk of epilepsy and febrile seizures in PWS is significantly lower than in Angelman syndrome and is associated with brain abnormalities. Electrographic seizures and focal epileptiform activity were present in 5% of individuals and were associated with young age. The underpinnings of epileptiform abnormalities in PWS and how they differ from those of the Angelman syndrome should be studied further.

Deconvolution-based assessment of pituitary GH secretion stimulated with GHRH+arginine in Prader-Willi adults and obese controls

OBJECTIVE

The assessment of GH deficiency in adult patients with Prader-Willi syndrome (PWS) has been previously assessed through the evaluation of quantitative parameters, such as the peak value of GH response to exogenous stimuli. A comprehensive description of the pattern of secretory response obtainable by deconvolution analysis is still lacking. The aim of our study was to characterize the time evolution of responses of PWS subjects compared with obese controls.

DESIGN AND SUBJECTS

GH responsiveness was measured following the combined administration of GHRH+arginine to 65 PWS adults (24 males, 41 females) aged 18-41·2 years, and 17 age-, gender- and body mass index-matched obese controls. PWS subjects were analysed considering the stratification on different genotypes.

MEASUREMENTS

GH response to GHRH+arginine was analysed in terms of peak values, standard area under the curves (AUCs), AUCs due to the stimulus, AUCs of the Instantaneous Secretion Rate signal and Secretion Response Analysis.

RESULTS

In terms of both peak values and AUC, GH responses were statistically different between PWS UPD15 and PWS DEL15 subjects as well as between PWS UPD15 and obese controls. PWS subjects showed a lower and a more delayed GH response compared with obese controls. Moreover, PWS UPD15 subjects had the most delayed GH response.

CONCLUSIONS

Our findings demonstrate that impaired GH secretion in PWS subjects compared with obese controls regards not only amplitude parameters such as peak value and AUC, but also the shape of the secretory response, which is more delayed, especially for UPD15 subjects.

Altered functional brain networks in Prader-Willi syndrome

Prader-Willi syndrome (PWS) is a genetic imprinting disorder characterized mainly by hyperphagia and early childhood obesity. Previous functional neuroimaging studies used visual stimuli to examine abnormal activities in the eating-related neural circuitry of patients with PWS. It was found that patients with PWS exhibited both excessive hunger and hyperphagia consistently, even in situations without any food stimulation. In the present study, we employed resting-state functional MRI techniques to investigate abnormal brain networks related to eating disorders in children with PWS. First, we applied amplitude of low-frequency fluctuation analysis to define the regions of interest that showed significant alterations in resting-state brain activity levels in patients compared with their sibling control group. We then applied a functional connectivity (FC) analysis to these regions of interest in order to characterize interactions among the brain regions. Our results demonstrated that patients with PWS showed decreased FC strength in the medial prefrontal cortex (MPFC)/inferior parietal lobe (IPL), MPFC/precuneus, IPL/precuneus and IPL/hippocampus in the default mode network; decreased FC strength in the pre-/postcentral gyri and dorsolateral prefrontal cortex (DLPFC)/orbitofrontal cortex (OFC) in the motor sensory network and prefrontal cortex network, respectively; and increased FC strength in the anterior cingulate cortex/insula, ventrolateral prefrontal cortex (VLPFC)/OFC and DLPFC/VLPFC in the core network and prefrontal cortex network, respectively. These findings indicate that there are FC alterations among the brain regions implicated in eating as well as rewarding, even during the resting state, which may provide further evidence supporting the use of PWS as a model to study obesity and to provide information on potential neural targets for the medical treatment of overeating.

Change in prevalence of congenital defects in children with Prader-Willi syndrome

OBJECTIVE

The aim of this study was to assess the prevalence of congenital defects observed in patients with Prader-Willi syndrome (PWS) and to compare this prevalence with that described in the general population. In addition, these findings were correlated with the different etiologic subtypes.

METHODS

A total of 180 children with PWS followed for 13 years were included in this study. Diagnosis was confirmed by the methylation test, and genetic subtypes were established by using fluorescence in situ hybridization or multiplex ligation-dependent probe amplification and microsatellite analyses. The prevalence of congenital defects was compared with national and international registries of congenital defects in the general population (Estudio Colaborativo Latinoamericano de Malformaciones Congénitas, European Surveillance of Congenital Anomalies, and the New York Registry).

RESULTS

Twenty-two percent of the patients presented congenital defects with a risk of 5.4 to 18.7 times higher than that of the general population. The most frequent congenital defects were heart defects, renoureteral malformations, vertebral anomalies, hip dysplasia, clubfoot, and agenesis/hypoplasia of the corpus callosum. Each of these congenital defects was significantly more frequent in the children with PWS than in the general population. The congenital heart defects were more frequent in girls than in boys with PWS. No significant differences were found when the defects were correlated with the different etiologic subtypes.

CONCLUSIONS

An increased prevalence of congenital defects was found in our PWS patients. This finding suggests the need for further studies in PWS children that allow physicians to detect the congenital defects found in this series and, thus, to anticipate complications, with the ultimate aim of enhancing the management of PWS patients.

The neuroanatomy of genetic subtype differences in Prader-Willi syndrome

Despite behavioral differences between genetic subtypes of Prader-Willi syndrome (PWS), no studies have been published characterizing brain structure in these subgroups. Our goal was to examine differences in the brain structure phenotype of common subtypes of PWS [chromosome 15q deletions and maternal uniparental disomy 15 (UPD)]. Fifteen individuals with PWS due to a typical deletion [(DEL) type I; n = 5, type II; n = 10], eight with PWS due to UPD, and 25 age-matched healthy-weight individuals (HWC) participated in structural magnetic resonance imaging (MRI) scans. A custom voxel-based morphometry processing stream was used to examine regional differences in gray and white matter volume (WMV) between groups, covarying for age, sex, and body mass index (BMI). Overall, compared to HWC, PWS individuals had lower gray matter volumes (GMV) that encompassed the prefrontal, orbitofrontal and temporal cortices, hippocampus and parahippocampal gyrus, and lower WMVs in the brain stem, cerebellum, medial temporal, and frontal cortex. Compared to UPD, the DEL subtypes had lower GMV primarily in the prefrontal and temporal cortices, and lower white matter in the parietal cortex. The UPD subtype had more extensive lower gray and WMVs in the orbitofrontal and limbic cortices compared to HWC. These preliminary findings are the first structural neuroimaging findings to support potentially separate neural mechanisms mediating the behavioral differences seen in these genetic subtypes.

Appetite hormones and the transition to hyperphagia in children with Prader-Willi syndrome

OBJECTIVE

Prader-Willi syndrome (PWS) is a genetic neurodevelopmental disorder with several nutritional phases during childhood proceeding from poor feeding, through normal eating without and with obesity, to hyperphagia and life-threatening obesity, with variable ages of onset. We investigated whether differences in appetite hormones may explain the development of abnormal eating behaviour in young children with PWS.

SUBJECTS

In this cross-sectional study, children with PWS (n=42) and controls (n=9) aged 7 months-5 years were recruited. Mothers were interviewed regarding eating behaviour, and body mass index (BMI) was calculated. Fasting plasma samples were assayed for insulin, leptin, glucose, peptide YY (PYY), ghrelin and pancreatic polypeptide (PP).

RESULTS

There was no significant relationship between eating behaviour in PWS subjects and the levels of any hormones or insulin resistance, independent of age. Fasting plasma leptin levels were significantly higher (mean ± s.d.: 22.6 ± 12.5 vs 1.97 ± 0.79 ng ml(-1), P=0.005), and PP levels were significantly lower (22.6 ± 12.5 vs 69.8 ± 43.8 pmol l(-1), P<0.001) in the PWS group compared with the controls, and this was independent of age, BMI, insulin resistance or IGF-1 levels. However, there was no significant difference in plasma insulin, insulin resistance or ghrelin levels between groups, though PYY declined more rapidly with age but not BMI in PWS subjects.

CONCLUSION

Even under the age of 5 years, PWS is associated with low levels of anorexigenic PP, as in older children and adults. Hyperghrelinaemia or hypoinsulinaemia was not seen in these young children with PWS. Change in these appetite hormones was not associated with the timing of the transition to the characteristic hyperphagic phase. However, abnormal and/or delayed development or sensitivity of the effector pathways of these appetitive hormones (for example, parasympathetic and central nervous system) may interact with low PP levels, and later hyperghrelinaemia or hypoinsulinaemia, to contribute to hyperphagia in PWS.

Prader-Willi syndrome

Prader-Willi syndrome is characterized by severe infantile hypotonia with poor suck and failure to thrive; hypogonadism causing genital hypoplasia and pubertal insufficiency; characteristic facial features; early-childhood onset obesity and hyperphagia; developmental delay/mild intellectual disability; short stature; and a distinctive behavioral phenotype. Sleep abnormalities and scoliosis are common. Growth hormone insufficiency is frequent, and replacement therapy provides improvement in growth, body composition, and physical attributes. Management is otherwise largely supportive. Consensus clinical diagnostic criteria exist, but diagnosis should be confirmed through genetic testing. Prader-Willi syndrome is due to absence of paternally expressed imprinted genes at 15q11.2-q13 through paternal deletion of this region (65-75% of individuals), maternal uniparental disomy 15 (20-30%), or an imprinting defect (1-3%). Parent-specific DNA methylation analysis will detect >99% of individuals. However, additional genetic studies are necessary to identify the molecular class. There are multiple imprinted genes in this region, the loss of which contribute to the complete phenotype of Prader-Willi syndrome. However, absence of a small nucleolar organizing RNA gene, SNORD116, seems to reproduce many of the clinical features. Sibling recurrence risk is typically <1%, but higher risks may pertain in certain cases. Prenatal diagnosis is available.

Top-down or bottom-up: Contrasting perspectives on psychiatric diagnoses

Clinical psychiatry is confronted with the expanding knowledge of medical genetics. Most of the research into the genetic underpinnings of major mental disorders as described in the categorical taxonomies, however, did reveal linkage with a variety of chromosomes. This heterogeneity of results is most probably due to the assumption that the nosological categories as used in these studies are disease entities with clear boundaries. If the reverse way of looking, the so-called bottom-up approach, is applied, it becomes clear that genetic abnormalities are in most cases not associated with a single psychiatric disorder but with a certain probability to develop a variety of aspecific psychiatric symptoms. The adequacy of the categorical taxonomy, the so-called top-down approach, seems to be inversely related to the amount of empirical etiological data. This is illustrated by four rather prevalent genetic syndromes, fragile X syndrome, Prader-Willi syndrome, 22q11 deletion syndrome, and Noonan syndrome, as well as by some cases with rare chromosomal abnormalities. From these examples, it becomes clear that psychotic symptoms as well as mood, anxiety, and autistic features can be found in a great variety of different genetic syndromes. A psychiatric phenotype exists, but comprises, apart from the chance to present several psychiatric symptoms, all elements from developmental, neurocognitive, and physical characteristics.

Impaired hypothalamic regulation of endocrine function and delayed counterregulatory response to hypoglycemia in Magel2-null mice

Hypothalamic dysfunction may underlie endocrine abnormalities in Prader-Willi syndrome (PWS), a genetic disorder that features GH deficiency, obesity, and infertility. One of the genes typically inactivated in PWS, MAGEL2, is highly expressed in the hypothalamus. Mice deficient for Magel2 are obese with increased fat mass and decreased lean mass and have blunted circadian rhythm. Here, we demonstrate that Magel2-null mice have abnormalities of hypothalamic endocrine axes that recapitulate phenotypes in PWS. Magel2-null mice had elevated basal corticosterone levels, and although male Magel2-null mice had an intact corticosterone response to restraint and to insulin-induced hypoglycemia, female Magel2-null mice failed to respond to hypoglycemia with increased corticosterone. After insulin-induced hypoglycemia, Magel2-null mice of both sexes became more profoundly hypoglycemic, and female mice were slower to recover euglycemia, suggesting an impaired hypothalamic counterregulatory response. GH insufficiency can produce abnormal body composition, such as that seen in PWS and in Magel2-null mice. Male Magel2-null mice had Igf-I levels similar to control littermates. Female Magel2-null mice had low Igf-I levels and reduced GH release in response to stimulation with ghrelin. Female Magel2-null mice did respond to GHRH, suggesting that their GH deficiency has a hypothalamic rather than pituitary origin. Female Magel2-null mice also had higher serum adiponectin than expected, considering their increased fat mass, and thyroid (T(4)) levels were low. Together, these findings strongly suggest that loss of MAGEL2 contributes to endocrine dysfunction of hypothalamic origin in individuals with PWS.

Neural correlates of task switching in paternal 15q11-q13 deletion Prader-Willi syndrome

We report a first study of brain activity linked to task switching in individuals with Prader-Willi syndrome (PWS). PWS individuals show a specific cognitive deficit in task switching which may be associated with the display of temper outbursts and repetitive questioning. The performance of participants with PWS and typically developing controls was matched in a cued task switching procedure, and brain activity was contrasted on switching and non-switching blocks using fMRI. Individuals with PWS did not show the typical frontal-parietal pattern of neural activity associated with switching blocks, with significantly reduced activation in regions of the posterior parietal and ventromedial prefrontal cortices. We suggest that this is linked to a difficulty in PWS in setting appropriate attentional weights to enable task-set reconfiguration. In addition to this, PWS individuals did not show the typical pattern of deactivation, with significantly less deactivation in an anterior region of the ventromedial prefrontal cortex. One plausible explanation for this is that individuals with PWS show dysfunction within the default mode network, which has been linked to attentional control. The data point to functional changes in the neural circuitry supporting task switching in PWS even when behavioural performance is matched to controls and thus highlight neural mechanisms that may be involved in a specific pathway between genes, cognition and behaviour.

Food addiction and obesity: evidence from bench to bedside

Obesity has become a major health problem and epidemic. However, much of the current debate has been fractious and etiologies of obesity have been attributed to eating behavior or fast food, personality issues, depression, addiction, or genetics. One of the interesting new hypotheses for epidemic obesity is food addiction, which is associated with both substance-related disorder and eating disorder. Accumulating evidences have shown that there are many shared neural and hormonal pathways as well as distinct differences that may help researchers find why certain individuals overeat and become obese. Functional neuroimaging studies have further revealed that good or great smelling, looking, tasting, and reinforcing food has characteristics similar to that of drugs of abuse. Many of the brain changes reported for hedonic eating and obesity are also seen in various forms of addictions. Most importantly, overeating and obesity may have an acquired drive like drug addiction with respect to motivation and incentive; craving, wanting, and liking occur after early and repeated exposures to stimuli. The acquired drive for great food and relative weakness of the satiety signal would cause an imbalance between the drive and hunger/reward centers in the brain and their regulation.

Small gray matter volume in orbitofrontal cortex in Prader-Willi syndrome: a voxel-based MRI study

Prader-Willi syndrome (PWS) is a genetically determined neurodevelopmental disorder presenting with behavioral symptoms including hyperphagia, disinhibition, and compulsive behavior. The behavioral problems in individuals with PWS are strikingly similar to those in patients with frontal pathologies, particularly those affecting the orbitofrontal cortex (OFC). However, neuroanatomical abnormalities in the frontal lobe have not been established in PWS. The aim of this study was to look, using volumetric analysis, for morphological changes in the frontal lobe, especially the OFC, of the brains of individuals with PWS. Twelve adults with PWS and 13 age- and gender-matched control subjects participated in structural magnetic resonance imaging (MRI) scans. The whole-brain images were segmented and normalized to a standard stereotactic space. Regional gray matter volumes were compared between the PWS group and the control group using voxel-based morphometry. The PWS subjects showed small gray-matter volume in several regions, including the OFC, caudate nucleus, inferior temporal gyrus, precentral gyrus, supplementary motor area, postcentral gyrus, and cerebellum. The small gray-matter volume in the OFC remained significant in a separate analysis that included total gray matter volume as a covariate. These preliminary findings suggest that the neurobehavioral symptoms in individuals with PWS are related to structural brain abnormalities in these areas.

Perisylvian polymicrogyria, infantile spasms and arthrogryposis: the severe end of the spectrum of congenital bilateral perisylvian polymicrogyria

Congenital bilateral perisylvian polymicrogyria (CBPP) is the most frequent type of polymicrogyria in children. A 3-month-old male patient is described here with the combination of CBPP, infantile spasms and arthrogryposis. Only four patients have been reported earlier in the literature with this combination. Three of them had epilepsy. These patients represent the more severe phenotype of CBPP, characterized by early onset of symptoms, epilepsy, mental retardation, pseudobulbar palsy and arthrogryposis.

Cognitive profile in a large French cohort of adults with Prader-Willi syndrome: differences between genotypes

BACKGROUND

Prader-Willi syndrome (PWS) is a rare genetic disorder characterised by developmental abnormalities leading to somatic and psychological symptoms. These include dysmorphic features, impaired growth and sexual maturation, hyperphagia, intellectual delay, learning disabilities and maladaptive behaviours. PWS is caused by a lack of expression of maternally imprinted genes situated in the 15q11-13 chromosome region. The origin is a 'de novo' deletion in the paternal chromosome in 70% of the cases and a maternal uniparental disomy in 25%. The two main genotypes show differences, notably regarding cognitive and behavioural features, but the mechanisms are not clear. This study assessed cognitive impairment in a cohort of adults with genetically confirmed PWS, analysed their profiles of cognitive strengths and weaknesses, and compared the profiles in terms of genotype.

METHODS

Ninety-nine male and female adults participated, all inpatients on a specialised unit for the multidisciplinary care of PWS. The Wechsler Adult Intelligence Scale (WAIS-III) was administered to all patients in identical conditions by the same psychologist. Eighty-five patients were able to cope with the test situation. Their scores were analysed with non-parametric statistical tools. The correlations with sex, age and body mass index were explored. Two genotype groups were compared: deletion (n = 57) and non-deletion (n = 27).

RESULTS

The distribution of intelligence quotients in the total cohort was non-normal, with the following values (medians): Full Scale Intelligence Quotient (FSIQ): 52.0 (Q1:46.0; Q3:60.0), Verbal Intellectual Quotient (VIQ): 53.0 (Q1:48; Q3:62) and Performance Intellectual Quotient (PIQ): 52.5 (Q1:48; Q3:61). No correlation was found with sex, age or body mass index. Comparison between groups showed no significant difference in FSIQ or VIQ. PIQ scores were significantly better in the deletion group. The total cohort and the deletion group showed the VIQ = PIQ profile, whereas VIQ > PIQ was observed in the non-deletion group. The subtest scores in the two groups showed significant differences, with the deletion group scoring better in three subtests: object assembly, picture arrangement and digit symbol coding. Some relative strengths and weaknesses concerned the total cohort, but others concerned only one genotype.

DISCUSSION

We documented a global impairment in the intellectual abilities of a large sample of French PWS patients. The scores were slightly lower than those reported in most other studies. Our data confirmed the previously published differences in the cognitive profiles of the two main PWS genotypes and offer new evidence to support this hypothesis. These results could guide future neuropsychological studies to determine the cognitive processing in PWS. This knowledge is essential to improve our understanding of gene-brain-behaviour relationships and to open new perspectives on therapeutic and educational programmes.

Regionally reduced brain volume, altered serotonin neurochemistry, and abnormal behavior in mice null for the circadian rhythm output gene Magel2

Magel2 belongs to the MAGE/necdin family of proteins, which have roles in cell cycle, differentiation, and apoptosis. The Magel2 gene is expressed in various brain regions, most notably the hypothalamus. Mice with a targeted deletion of Magel2 display hypoactivity, blunted circadian rhythm, decreased fertility, and increased adiposity. The human ortholog, MAGEL2, is one of a set of paternally expressed, imprinted genes inactivated in most cases of Prader-Willi syndrome, a complex neurodevelopmental disorder. To explore the role of Magel2, brain morphology, brain neurochemistry, and behavior were measured in Magel2-null mice. Brain volume was reduced in specific regions, particularly in the parieto-temporal lobe of the cerebral cortex, the amygdala, the hippocampus, and the nucleus accumbens, as measured by quantitative magnetic resonance imaging. Abnormal neurochemistry was detected in brain samples from adult mice, consisting of decreased serotonin and 5-hydroxyindoleacetic acid in the cortex and the hypothalamus, and decreased dopamine in the hypothalamus. Magel2-null mice displayed relatively normal motor and learning abilities, but exhibited abnormal behavior in novel environments. This study lends support to the important role of the circadian rhythm output gene Magel2 in brain structure and behavior.