Schaaf-Yang syndrome overview: Report of 78 individuals

Truncated variants of MAGEL2 are involved in the etiologies of the Schaaf-Yang and Prader-Willi syndromes

The neurodevelopmental disorders Prader-Willi syndrome (PWS) and Schaaf-Yang syndrome (SYS) both arise from genomic alterations within human chromosome 15q11-q13. A deletion of the SNORD116 cluster, encoding small nucleolar RNAs, or frameshift mutations within MAGEL2 result in closely related phenotypes in individuals with PWS or SYS, respectively. By investigation of their subcellular localization, we observed that in contrast to a predominant cytoplasmic localization of wild-type (WT) MAGEL2, a truncated MAGEL2 mutant was evenly distributed between the cytoplasm and the nucleus. To elucidate regulatory pathways that may underlie both diseases, we identified protein interaction partners for WT or mutant MAGEL2, in particular the survival motor neuron protein (SMN), involved in spinal muscular atrophy, and the fragile-X-messenger ribonucleoprotein (FMRP), involved in autism spectrum disorders. The interactome of the non-coding RNA SNORD116 was also investigated by RNA-CoIP. We show that WT and truncated MAGEL2 were both involved in RNA metabolism, while regulation of transcription was mainly observed for WT MAGEL2. Hence, we investigated the influence of MAGEL2 mutations on the expression of genes from the PWS locus, including the SNORD116 cluster. Thereby, we provide evidence for MAGEL2 mutants decreasing the expression of SNORD116, SNORD115, and SNORD109A, as well as protein-coding genes MKRN3 and SNRPN, thus bridging the gap between PWS and SYS.

MAGEL2 (patho-)physiology and Schaaf-Yang syndrome

Schaaf-Yang syndrome (SYS) is a complex neurodevelopmental disorder characterized by autism spectrum disorder, joint contractures, and profound hypothalamic dysfunction. SYS is caused by variants in MAGEL2, a gene within the Prader-Willi syndrome (PWS) locus on chromosome 15. In this review, we consolidate decades of research on MAGEL2 to elucidate its physiological functions. Moreover, we synthesize current knowledge on SYS, suggesting that while MAGEL2 loss-of-function seems to underlie several SYS and PWS phenotypes, additional pathomechanisms probably contribute to the distinct and severe phenotype observed in SYS. In addition, we highlight recent therapeutic advances and identify promising avenues for future investigation.

Hao-Fountain syndrome: 32 novel patients reveal new insights into the clinical spectrum

Hao-Fountain syndrome (HAFOUS, OMIM: #616863) is a neurodevelopmental disorder caused by pathogenic variants in the gene USP7 coding for USP7, a protein involved in several crucial cellular homeostatic mechanisms and the recently described MUST complex. The phenotype of HAFOUS is insufficiently understood, yet there is a great need to better understand the spectrum of disease, genotype-phenotype correlations, and disease trajectories. We now present a larger cohort of 32 additional individuals and provide further clinical information about six previously reported individuals. A questionnaire-based study was performed to characterize the phenotype of Hao-Fountain syndrome more clearly, to highlight new traits, and to better distinguish the disease from related neurodevelopmental disorders. In addition to confirming previously described features, we report hyperphagia and increased body weight in a subset of individuals. HAFOUS patients present an increased rate of birth complications, congenital anomalies, and abnormal pain thresholds. Speech impairment emerges as a potential hallmark of Hao-Fountain syndrome. Cognitive testing reports reveal borderline intellectual functioning on average, although some individuals score in the range of intellectual disability. Finally, we created a syndrome-specific severity score. This score neither indicates a sex- nor age-specific difference of clinical severity, yet highlights a more severe outcome when amino acid changes colocalize to the catalytic domain of the USP7 protein.

AAV-BDNF gene therapy ameliorates a hypothalamic neuroinflammatory signature in the Magel2-null model of Prader-Willi syndrome

Individuals with Prader-Willi syndrome (PWS) exhibit several metabolic and behavioral abnormalities associated with excessive food-seeking activity. PWS is thought to be driven in part by dysfunctional hypothalamic circuitry and blunted responses to peripheral signals of satiety. Previous work described a hypothalamic transcriptomic signature of individuals with PWS. Notably, PWS patients exhibited downregulation of genes involved in neuronal development and an upregulation of neuroinflammatory genes. Deficiencies of brain-derived neurotrophic factor (BDNF) and its receptor were identified as potential drivers of PWS phenotypes. Our group recently applied an adeno-associated viral (AAV)-BDNF gene therapy within a preclinical PWS model, Magel2-null mice, to improve metabolic and behavioral function. While this proof-of-concept project was promising, it remained unclear how AAV-BDNF was influencing the hypothalamic microenvironment and how its therapeutic effect was mediated. To investigate, we hypothalamically injected AAV-BDNF to wild type and Magel2-null mice and performed mRNA sequencing on hypothalamic tissue. Here, we report that (1) Magel2 deficiency is associated with neuroinflammation in the hypothalamus and (2) AAV-BDNF gene therapy reverses this neuroinflammation. These data newly reveal Magel2-null mice as a valid model of PWS-related neuroinflammation and furthermore suggest that AAV-BDNF may modulate obesity-related neuroinflammatory phenotypes through direct or indirect means.

Caregiver-based perception of disease burden in Schaaf-Yang syndrome

BACKGROUND

Schaaf-Yang syndrome (SYS) is a neurodevelopmental disorder caused by truncating variants in the paternally expressed MAGEL2 gene in the Prader-Willi syndrome-region on chromosome 15q. In addition to hypotonia and intellectual disability, individuals with SYS are frequently affected by neonatal contractures and autism spectrum disorder. In this study, we focus on the burden of disease on patients and their families for the first time.

METHODS

Based on the online SYS Patient Voices Survey the perspective of 81 primary caregivers on SYS was assessed.

RESULTS

The perceived severity of muscular and developmental manifestations dominated the evaluation of the phenotype in early childhood, while behavioral issues were considered more impactful later in life. Importantly, an apprehension toward symptoms with a later onset was observed in caregivers of younger children. Available therapeutic options, while mostly effective, did not sufficiently alleviate the total burden of disease. Overall, parents stated that caring for an individual with SYS was very challenging, affecting their daily lives and long-term planning.

CONCLUSION

Our study demonstrates the necessity for treatments that, adapted to age and in accordance with the caregivers' prioritization, improve the patients' medical condition and thus facilitate their and their families' social participation.

Hormonal Imbalances in Prader-Willi and Schaaf-Yang Syndromes Imply the Evolution of Specific Regulation of Hypothalamic Neuroendocrine Function in Mammals

The hypothalamus regulates fundamental aspects of physiological homeostasis and behavior, including stress response, reproduction, growth, sleep, and feeding, several of which are affected in patients with Prader-Willi (PWS) and Schaaf-Yang syndrome (SYS). PWS is caused by paternal deletion, maternal uniparental disomy, or imprinting defects that lead to loss of expression of a maternally imprinted region of chromosome 15 encompassing non-coding RNAs and five protein-coding genes; SYS patients have a mutation in one of them, MAGEL2. Throughout life, PWS and SYS patients suffer from musculoskeletal deficiencies, intellectual disabilities, and hormonal abnormalities, which lead to compulsive behaviors like hyperphagia and temper outbursts. Management of PWS and SYS is mostly symptomatic and cures for these debilitating disorders do not exist, highlighting a clear, unmet medical need. Research over several decades into the molecular and cellular roles of PWS genes has uncovered that several impinge on the neuroendocrine system. In this review, we will discuss the expression and molecular functions of PWS genes, connecting them with hormonal imbalances in patients and animal models. Besides the observed hormonal imbalances, we will describe the recent findings about how the loss of individual genes, particularly MAGEL2, affects the molecular mechanisms of hormone secretion. These results suggest that MAGEL2 evolved as a mammalian-specific regulator of hypothalamic neuroendocrine function.

Report of two cases of Schaaf-Yang syndrome: Same genotype and different phenotype

We report two, genotypically identical but phenotypically distinct cases of Schaaf-Yang syndrome and propose the early use of Genome Sequencing in patients with nonspecific presentations to facilitate the early diagnosis of children with rare genetic diseases and improve overall health care outcomes.

Early onset critically ill infants with Schaaf-Yang syndrome: a retrospective study from the China neonatal genomes project and literature review

Background

Schaaf-Yang syndrome (SYS) is a recently identified rare neurodevelopmental disorder characterized by neonatal hypotonia, feeding difficulty, joint contractures, autism spectrum disorder and development delay/intellectual disability. It is mainly caused by truncating variants in maternally imprinted gene MAGEL2 within the Prader-Willi syndrome critical region 15q11-q13. Clinical diagnosis of SYS is difficult for clinicians due to its rarity and highly variable phenotypes, while unique inheritance patterns also complicate genetic diagnosis. To date, no published papers have analyzed the clinical consequences and molecular changes in Chinese patients.

Methods

In this study, we retrospectively investigated the mutation spectrums and phenotypic features of 12 SYS infants. The data were from a cohort of critically ill infants from the China neonatal genomes project (CNGP), sponsored by Children's Hospital of Fudan University. We also reviewed relevant literature.

Results

Six previously reported mutations and six novel pathogenic variations of MAGEL2 were identified in 12 unrelated infants. Neonatal respiratory problems were the major complaint for hospitalization, which occurred in 91.7% (11/12) cases. All babies displayed feeding difficulties and a poor suck postnatally, and neonatal dystonia was present in 11 of the cases; joint contractures and multiple congenital defects were also observed. Interestingly, we found that 42.5% (57/134) of the reported SYS patients, including ours carried variants in the c.1996 site, particularly the c.1996dupC variant. The mortality rate was 17.2% (23/134), with the median age of death between 24 gestational weeks in fetuses and 1-month-old in infants. Respiratory failure was the leading cause of death in live-born patients (58.8%, 10/17), especially during the neonatal period.

Conclusions

Our findings expanded the genotype and phenotype spectrum of neonatal SYS patients. The results demonstrated that respiratory dysfunction was a typical characteristic among Chinese SYS neonates that should attract physicians' attention. The early identification of such disorders allows early intervention and can further provide genetic counseling as well as reproductive options for the affected families.

Schaaf-Yang Syndrome: Clinical Phenotype and Effects of 4 years of Growth Hormone Treatment

INTRODUCTION

Schaaf-Yang syndrome (SYS) is a rare neurodevelopmental disorder caused by truncating mutations of the MAGEL2 gene, located in the Prader-Willi syndrome (PWS) region. PWS and SYS have phenotypic overlap. Patients with SYS are often treated with growth hormone (GH), but evidence for the effectiveness of the treatment in patients with SYS is limited.

METHODS

This study describes 7 children with SYS. We studied their phenotype, genotype, and the effect of GH treatment on height and body mass index (BMI) during 4 years and on body composition during 1 year.

RESULTS

All patients had a normal birth weight. Most patients had hypotonia and feeding difficulties after birth (86%). Full-scale IQ ranged from <50 to 92. All patients above the age of 2 years had psycho-behavioral problems. There were no apparent correlations between the phenotype and the location of the defect in the MAGEL2 gene. Mean (95% CI) height SDS increased significantly from -1.74 (-3.55; 0.07) at start to -0.05 (-1.87; 1.77) after 4 years of GH treatment. Mean (95% CI) BMI SDS decreased significantly from 2.01 (1.02; 3.00) to 1.22 (0.18; 2.26) after 6 months and remained the same during the rest of the follow-up. Fat mass percentage SDS decreased and lean body mass did not change during 1 year of treatment in 3 patients.

CONCLUSION

Patients presented with a phenotype of hypotonia, respiratory insufficiency, and feeding difficulties after birth, endocrine disorders, intellectual disability, and behavioral problems. Treatment with GH significantly improved height SDS and BMI over the course of 4 years.

Advancing in Schaaf-Yang syndrome pathophysiology: from bedside to subcellular analyses of truncated MAGEL2

BACKGROUND

Schaaf-Yang syndrome (SYS) is caused by truncating mutations in MAGEL2, mapping to the Prader-Willi region (15q11-q13), with an observed phenotype partially overlapping that of Prader-Willi syndrome. MAGEL2 plays a role in retrograde transport and protein recycling regulation. Our aim is to contribute to the characterisation of SYS pathophysiology at clinical, genetic and molecular levels.

METHODS

We performed an extensive phenotypic and mutational revision of previously reported patients with SYS. We analysed the secretion levels of amyloid-β 1-40 peptide (Aβ_1-40) and performed targeted metabolomic and transcriptomic profiles in fibroblasts of patients with SYS (n=7) compared with controls (n=11). We also transfected cell lines with vectors encoding wild-type (WT) or mutated MAGEL2 to assess stability and subcellular localisation of the truncated protein.

RESULTS

Functional studies show significantly decreased levels of secreted Aβ_1-40 and intracellular glutamine in SYS fibroblasts compared with WT. We also identified 132 differentially expressed genes, including non-coding RNAs (ncRNAs) such as HOTAIR, and many of them related to developmental processes and mitotic mechanisms. The truncated form of MAGEL2 displayed a stability similar to the WT but it was significantly switched to the nucleus, compared with a mainly cytoplasmic distribution of the WT MAGEL2. Based on the updated knowledge, we offer guidelines for the clinical management of patients with SYS.

CONCLUSION

A truncated MAGEL2 protein is stable and localises mainly in the nucleus, where it might exert a pathogenic neomorphic effect. Aβ_1-40 secretion levels and HOTAIR mRNA levels might be promising biomarkers for SYS. Our findings may improve SYS understanding and clinical management.

Two new cases with novel pathogenic variants reflecting the clinical diversity of Schaaf-Yang syndrome

Schaaf-Yang syndrome (SHFYNG) is a rare pleiotropic disorder, characterized by hypotonia, joint contractures, autism spectrum disorders (ASD), and developmental delay/intellectual disability. Although it shares some common features with Prader-Willi Syndrome, joint contractures, and ASD were more commonly detected in in this syndrome. Recently, it was shown that truncating variants in the paternal allele of the MAGEL2 gene cause SHFYNG. Here, we present two patients diagnosed with SHFYNG syndrome having two different novel truncating variants in the MAGEL2 gene, one paternally inherited and one de novo. One patient had obesity, brachydactyly and dysmorphic features, and the other patient presented with contractures, severe hypotonia and early death. This is the first report of Turkish SHFYNG syndrome cases presented to emphasize the phenotypic diversity of the syndrome.

Preimplantation Genetic Testing (PGT) and Prenatal Diagnosis of Schaaf-Yang Syndrome: A Report of Three Families and a Research on Genotype-Phenotype Correlations

Schaaf-Yang Syndrome (SYS) is a genetic disorder caused by truncating pathogenic variants in the paternal allele of the maternally imprinted, paternally expressed gene MAGEL2 and is characterized by genital hypoplasia, neonatal hypotonia, developmental delay, intellectual disability, autism spectrum disorder (ASD), and other features. In this study, eleven SYS patients from three families were enrolled and comprehensive clinical features were gathered regarding each family. Whole-exome sequencing (WES) was performed for the definitive molecular diagnosis of the disease. Identified variants were validated using Sanger sequencing. Three couples underwent PGT for monogenic diseases (PGT-M) and/or a prenatal diagnosis. Haplotype analysis was performed to deduce the embryo's genotype by using the short tandem repeats (STRs) identified in each sample. The prenatal diagnosis results showed that the fetus in each case did not carry pathogenic variants, and all the babies of the three families were born at full term and were healthy. We also performed a review of SYS cases. In addition to the 11 patients in our study, a total of 127 SYS patients were included in 11 papers. We summarized all variant sites and clinical symptoms thus far, and conducted a genotype-phenotype correlation analysis. Our results also indicated that the variation in phenotypic severity may depend on the specific location of the truncating variant, suggestive of a genotype-phenotype association.

Magel2 truncation alters select behavioral and physiological outcomes in a rat model of Schaaf-Yang syndrome

Previous studies in mice have utilized Magel2 gene deletion models to examine the consequences of its absence. We report the generation, molecular validation and phenotypic characterization of a novel rat model with a truncating Magel2 mutation modeling variants associated with Schaaf-Yang syndrome-causing mutations. Within the hypothalamus, a brain region in which human MAGEL2 is paternally expressed, we demonstrated, at the level of transcript and peptide detection, that rat Magel2 exhibits a paternal, parent-of-origin effect. In evaluations of behavioral features across several domains, juvenile Magel2 mutant rats displayed alterations in anxiety-like behavior and sociability measures. Moreover, the analysis of peripheral organ systems detected alterations in body composition, cardiac structure and function, and breathing irregularities in Magel2 mutant rats. Several of these findings are concordant with reported mouse phenotypes, indicating the conservation of MAGEL2 function across rodent species. Our comprehensive analysis revealing impairments across multiple domains demonstrates the tractability of this model system for the study of truncating MAGEL2 mutations.

Modulation of the thermosensory system by oxytocin

Oxytocin (OT) is a neurohormone involved early in neurodevelopment and is implicated in multiple functions, including sensory modulation. Evidence of such modulation has been observed for different sensory modalities in both healthy and pathological conditions. This review summarizes the pleiotropic modulation that OT can exercise on an often overlooked sensory system: thermosensation. This system allows us to sense temperature variations and compensate for the variation to maintain a stable core body temperature. Oxytocin modulates autonomic and behavioral mechanisms underlying thermoregulation at both central and peripheral levels. Hyposensitivity or hypersensitivity for different sensory modalities, including thermosensitivity, is a common feature in autism spectrum disorder (ASD), recapitulated in several ASD mouse models. These sensory dysregulations occur early in post-natal development and are correlated with dysregulation of the oxytocinergic system. In this study, we discussed the potential link between thermosensory atypia and the dysregulation of the oxytocinergic system in ASD.

Hypothalamic AAV-BDNF gene therapy improves metabolic function and behavior in the Magel2-null mouse model of Prader-Willi syndrome

Individuals with Prader-Willi syndrome (PWS) display developmental delays, cognitive impairment, excessive hunger, obesity, and various behavioral abnormalities. Current PWS treatments are limited to strict supervision of food intake and growth hormone therapy, highlighting the need for new therapeutic strategies. Brain-derived neurotrophic factor (BDNF) functions downstream of hypothalamic feeding circuitry and has roles in energy homeostasis and behavior. In this preclinical study, we assessed the translational potential of hypothalamic adeno-associated virus (AAV)-BDNF gene therapy as a therapeutic for metabolic dysfunction in the Magel2-null mouse model of PWS. To facilitate clinical translation, our BDNF vector included an autoregulatory element allowing for transgene titration in response to the host's physiological needs. Hypothalamic BDNF gene transfer prevented weight gain, decreased fat mass, increased lean mass, and increased relative energy expenditure in female Magel2-null mice. Moreover, BDNF gene therapy improved glucose metabolism, insulin sensitivity, and circulating adipokine levels. Metabolic improvements were maintained through 23 weeks with no adverse behavioral effects, indicating high levels of efficacy and safety. Male Magel2-null mice also responded positively to BDNF gene therapy, displaying improved body composition, insulin sensitivity, and glucose metabolism. Together, these data suggest that regulating hypothalamic BDNF could be effective in the treatment of PWS-related metabolic abnormalities.

A nationwide survey of Schaaf-Yang syndrome in Japan

Schaaf-Yang syndrome (SYS) is a congenital disorder characterized by developmental delay, autism spectrum disorder and congenital joint contractures. In this study, a nationwide epidemiological questionnaire-based survey of SYS in the Japanese population was conducted to establish patient numbers, clinical features and genetic information. In the primary survey, we investigated the number of SYS patients. In the secondary survey, we obtained and analyzed detailed clinical and genetic information of SYS patients. This survey collected information on 25 genetically-confirmed patients. The major clinical symptoms included neonatal hypotonia (96% of the patients), poor suck in infancy (82%), developmental delay (100%) and joint contractures (83%). Other main symptoms and findings included characteristic facial features (100%), small hands (92%), eye abnormalities (92%) and short stature (79%). Based on the information collected on activities of daily living, 71% of patients were unable to walk, while 67%, 71%, and 81% of patients required full assistance with eating, toileting and bathing, respectively. Regarding inheritability, the genetic analysis of 21 patients revealed that 14 (67%) carried de novo truncating variants in the melanoma antigen L2 (MAGEL2) gene and seven (33%) had inherited truncating variants from their fathers who were carriers. This survey revealed the clinical and genetic features in Japanese SYS patients. The majority of SYS patients required assistance in many aspects of daily living, and there were a certain number of carriers of the imprinting disorder.

Early life oxytocin treatment improves thermo-sensory reactivity and maternal behavior in neonates lacking the autism-associated gene Magel2

Atypical responses to sensory stimuli are considered as a core aspect and early life marker of autism spectrum disorders (ASD). Although recent findings performed in mouse ASD genetic models report sensory deficits, these were explored exclusively during juvenile or adult period. Whether sensory dysfunctions might be present at the early life stage and rescued by therapeutic strategy are fairly uninvestigated. Here we found that under cool environment neonatal mice lacking the autism-associated gene Magel2 present pup calls hypo-reactivity and are retrieved with delay by their wild-type dam. This neonatal atypical sensory reactivity to cool stimuli was not associated with autonomic thermoregulatory alteration but with a deficit of the oxytocinergic system. Indeed, we show in control neonates that pharmacogenetic inactivation of hypothalamic oxytocin neurons mimicked atypical thermosensory reactivity found in Magel2 mutants. Furthermore, pharmacological intranasal administration of oxytocin to Magel2 neonates was able to rescue both the atypical thermosensory response and the maternal pup retrieval. This preclinical study establishes for the first-time early life impairments in thermosensory integration and suggest a therapeutic potential benefit of intranasal oxytocin treatment on neonatal atypical sensory reactivity for autism.

A Korean Child with Schaaf-Yang Syndrome Presented with Hearing Impairment: A Case Report

Schaaf-Yang syndrome (SYS) is a rare genomic imprinting disorder caused by truncating mutations in the paternally derived MAGE family member L2 (<i>MAGEL2</i>) allele. It is also responsible for Prader-Willi syndrome, characterized by neonatal hypotonia, developmental delay, intellectual disability, respiratory distress in early infancy, and arthrogryposis. More than 250 individuals with approximately 57 different molecular variants have been reported since 2013, but the phenotype-genotype association in SYS is not yet fully understood. Here, we describe the case of a Korean patient diagnosed with SYS harboring a mutation in the paternal allele of <i>MAGEL2</i>: c.2895G>A, resulting in a protein change of p.Trp965*. The patient’s phenotype included respiratory distress, arthrogryposis, hypotonia, and feeding difficulty in the early neonatal period. Mild renal dysfunction and hearing impairment were observed during infancy.

Oxytocin-based therapies for treatment of Prader-Willi and Schaaf-Yang syndromes: evidence, disappointments, and future research strategies

The prosocial neuropeptide oxytocin is being developed as a potential treatment for various neuropsychiatric disorders including autism spectrum disorder (ASD). Early studies using intranasal oxytocin in patients with ASD yielded encouraging results and for some time, scientists and affected families placed high hopes on the use of intranasal oxytocin for behavioral therapy in ASD. However, a recent Phase III trial obtained negative results using intranasal oxytocin for the treatment of behavioral symptoms in children with ASD. Given the frequently observed autism-like behavioral phenotypes in Prader-Willi and Schaaf-Yang syndromes, it is unclear whether oxytocin treatment represents a viable option to treat behavioral symptoms in these diseases. Here we review the latest findings on intranasal OT treatment, Prader-Willi and Schaaf-Yang syndromes, and propose novel research strategies for tailored oxytocin-based therapies for affected individuals. Finally, we propose the critical period theory, which could explain why oxytocin-based treatment seems to be most efficient in infants, but not adolescents.

Accelerating the genetic diagnosis of neurological disorders presenting with episodic apnoea in infancy

Unexplained episodic apnoea in infants (aged ≤1 year), including recurrent brief (<1 min) resolved unexplained events (known as BRUE), can be a diagnostic challenge. Recurrent unexplained apnoea might suggest a persistent, debilitating, and potentially fatal disorder. Genetic diseases are prevalent among this group, particularly in those who present with paroxysmal or episodic neurological symptoms. These disorders are individually rare and challenging for a general paediatrician to recognise, and there is often a delayed or even posthumous diagnosis (sometimes only made in retrospect when a second sibling becomes unwell). The disorders can be debilitating if untreated but pharmacotherapies are available for the vast majority. That any child should suffer from unnecessary morbidity or die from one of these disorders without a diagnosis or treatment having been offered is a tragedy; therefore, there is an urgent need to simplify and expedite the diagnostic journey. We propose an apnoea gene panel for hospital specialists caring for any infant who has recurrent apnoea without an obvious cause. This approach could remove the need to identify individual rare conditions, speed up diagnosis, and improve access to therapy, with the ultimate aim of reducing morbidity and mortality.

Recommendations for the diagnosis and management of childhood Prader-Willi syndrome in China

Prader-Willi syndrome (PWS) is a complex and multisystem neurobehavioral disease, which is caused by the lack of expression of paternally inherited imprinted genes on chromosome15q11.2-q13.1. The clinical manifestations of PWS vary with age. It is characterized by severe hypotonia with poor suck and feeding difficulties in the early infancy, followed by overeating in late infancy or early childhood and progressive development of morbid obesity unless the diet is externally controlled. Compared to Western PWS patients, Chinese patients have a higher ratio of deletion type. Although some rare disease networks, including PWS Cooperation Group of Rare Diseases Branch of Chinese Pediatric Society, Zhejiang Expert Group for PWS, were established recently, misdiagnosis, missed diagnosis and inappropriate intervention were usually noted in China. Therefore, there is an urgent need for an integrated multidisciplinary approach to facilitate early diagnosis and optimize management to improve quality of life, prevent complications, and prolong life expectancy. Our purpose is to evaluate the current literature and evidences on diagnosis and management of PWS in order to provide evidence-based guidelines for this disease, specially from China.

Longitudinal analysis of electroencephalography pattern changes in an infant with Schaaf-Yang syndrome and a novel mutation in melanoma antigen L2 (MAGEL2)

Background

Schaaf‐Yang syndrome (SYS) is a rare hereditary disease caused by truncating point mutations of the paternal allele of melanoma antigen L2 (MAGEL2), one of five protein‐coding genes within the Prader‐Willi syndrome (PWS) critical domain. SYS shares many clinical and molecular characteristics with PWS but has some distinct features, such as joint contractures and autism. Patients with PWS show abnormal electroencephalography (EEG) patterns. However, there are very few reports on EEG findings in patients with SYS.

Methods

A SYS patient was included in this study. Detailed neurological examinations and EEG were performed from neonate to infant ages. Sanger sequencing was performed.

Results

Our patient presented abnormal EEG findings and had diffuse brain dysfunction symptoms including a reduced level of consciousness, diminished spontaneous movements, hypotonia, feeding difficulties, and hypoventilation from early after birth. As she grew older and her background activity of EEG normalized, her neurodevelopmental symptoms remained but improved. Sanger sequencing of this patient revealed a novel, heterozygous c.2005C > T, truncating mutation in the MEGAL2 gene.

Conclusions

We described an SYS‐associated, time‐dependent, EEG pattern in a patient with SYS. Our findings of longitudinal EEG changes in a patient with SYS revealed a specific pattern of how affected individuals develop brain function.

The contribution of imprinted genes to neurodevelopmental and neuropsychiatric disorders

Imprinted genes are a subset of mammalian genes that are subject to germline parent-specific epigenetic modifications leading monoallelic expression. Imprinted gene expression is particularly prevalent in the brain and it is unsurprising that mutations affecting their expression can lead to neurodevelopmental and/or neuropsychiatric disorders in humans. Here I review the evidence for this, detailing key neurodevelopmental disorders linked to imprinted gene clusters on human chromosomes 15q11-q13 and 14q32, highlighting genes and possible regulatory links between these different syndromes. Similarly, rare copy number variant mutations at imprinted clusters also provide strong links between abnormal imprinted gene expression and the predisposition to severe psychiatric illness. In addition to direct links between brain-expressed imprinted genes and neurodevelopmental and/or neuropsychiatric disorders, I outline how imprinted genes that are expressed in another tissue hotspot, the placenta, contribute indirectly to abnormal brain and behaviour. Specifically, altered nutrient provisioning or endocrine signalling by the placenta caused by abnormal expression of imprinted genes may lead to increased prevalence of neurodevelopmental and/or neuropsychiatric problems in both the offspring and the mother.

Schaaf-Yang Syndrome: A Real Challenge for Prenatal Diagnosis

Schaaf-Yang syndrome (SYS) is a rare neurodevelopmental disorder caused by pathogenic variants in the MAGEL2 gene. It is usually a postnatal diagnosis in infants with muscular hypotonia and feeding difficulties. There are no cases diagnosed antenatally. During pregnancy, the most common findings reported are polyhydramnios and decreased fetal movements, which are relatively common and unspecific.We present one case of fetal clubfoot and clinodactyly in a fetus postnatally diagnosed with SYS, as well as a brief review of the prenatal findings associated with this syndrome.

The Spectrum of the Prader-Willi-like Pheno- and Genotype: A Review of the Literature

Prader-Willi syndrome (PWS) is a rare genetic syndrome, caused by the loss of expression of the paternal chromosome 15q11-q13 region. Over the past years, many cases of patients with characteristics similar to PWS, but without a typical genetic aberration of the 15q11-q13 region, have been described. These patients are often labelled as Prader-Willi-like (PWL). PWL is an as-yet poorly defined syndrome, potentially affecting a significant number of children and adults. In the current clinical practice, patients labelled as PWL are mostly left without treatment options. Considering the similarities with PWS, children with PWL might benefit from the same care and treatment as children with PWS. This review gives more insight into the pheno- and genotype of PWL and includes 86 papers, containing 368 cases of patients with a PWL phenotype. We describe mutations and aberrations for consideration when suspicion of PWS remains after negative testing. The most common genetic diagnoses were Temple syndrome (formerly known as maternal uniparental disomy 14), Schaaf-Yang syndrome (truncating mutation in the MAGEL2 gene), 1p36 deletion, 2p deletion, 6q deletion, 6q duplication, 15q deletion, 15q duplication, 19p deletion, fragile X syndrome, and Xq duplication. We found that the most prevalent symptoms in the entire group were developmental delay/intellectual disability (76%), speech problems (64%), overweight/obesity (57%), hypotonia (56%), and psychobehavioral problems (53%). In addition, we propose a diagnostic approach to patients with a PWL phenotype for (pediatric) endocrinologists. PWL comprises a complex and diverse group of patients, which calls for multidisciplinary care with an individualized approach.

Colon Transit Scintigraphy in Schaaf-Yang Syndrome

ABSTRACT

Schaaf-Yang syndrome is a genetic disorder characterized by delayed psychomotor development, hypotonia, intellectual disability, feeding difficulties, and variable dysmorphic facial features. It is an extremely rare disorder with over 250 cases reported in the medical literature. This condition has been determined to be inherited by an autosomal dominant pattern. We present colon transit scintigraphy of a 6-year-old boy with history of chronic constipation with poor response to medical treatment, clinical characteristics, and gene mutations consistent with this syndrome. After oral administration of 111In-DTPA, planar and SPECT/CT images showed rapid proximal colonic transit and anorectal retention.

Autophagy deficiency in neurodevelopmental disorders

Autophagy is a cell self-digestion pathway through lysosome and plays a critical role in maintaining cellular homeostasis and cytoprotection. Characterization of autophagy related genes in cell and animal models reveals diverse physiological functions of autophagy in various cell types and tissues. In central nervous system, by recycling injured organelles and misfolded protein complexes or aggregates, autophagy is integrated into synaptic functions of neurons and subjected to distinct regulation in presynaptic and postsynaptic neuronal compartments. A plethora of studies have shown the neuroprotective function of autophagy in major neurodegenerative diseases, such as Alzheimer’s disease (AD), Parkinson’s disease (PD), Huntington’s disease (HD) and amyotrophic lateral sclerosis (ALS). Recent human genetic and genomic evidence has demonstrated an emerging, significant role of autophagy in human brain development and prevention of spectrum of neurodevelopmental disorders. Here we will review the evidence demonstrating the causal link of autophagy deficiency to congenital brain diseases, the mechanism whereby autophagy functions in neurodevelopment, and therapeutic potential of autophagy.

Oxytocin administration in neonates shapes hippocampal circuitry and restores social behavior in a mouse model of autism

Oxytocin is an important regulator of the social brain. In some animal models of autism, notably in Magel2^tm1.1Mus-deficient mice, peripheral administration of oxytocin in infancy improves social behaviors until adulthood. However, neither the mechanisms responsible for social deficits nor the mechanisms by which such oxytocin administration has long-term effects are known. Here, we aimed to clarify these oxytocin-dependent mechanisms, focusing on social memory performance. Using in situ hybridization (RNAscope), we have established that Magel2 and oxytocin receptor are co-expressed in the dentate gyrus and CA2/CA3 hippocampal regions involved in the circuitry underlying social memory. Then, we have shown that Magel2^tm1.1Mus-deficient mice, evaluated in a three-chamber test, present a deficit in social memory. Next, in hippocampus, we conducted neuroanatomical and functional studies using immunostaining, oxytocin-binding experiments, ex vivo electrophysiological recordings, calcium imaging and biochemical studies. We demonstrated: an increase of the GABAergic activity of CA3-pyramidal cells associated with an increase in the quantity of oxytocin receptors and of somatostatin interneurons in both DG and CA2/CA3 regions. We also revealed a delay in the GABAergic development sequence in Magel2^tm1.1Mus-deficient pups, linked to phosphorylation modifications of KCC2. Above all, we demonstrated the positive effects of subcutaneous administration of oxytocin in the mutant neonates, restoring hippocampal alterations and social memory at adulthood. Although clinical trials are debated, this study highlights the mechanisms by which peripheral oxytocin administration in neonates impacts the brain and demonstrates the therapeutic value of oxytocin to treat infants with autism spectrum disorders.

Correction of vasopressin deficit in the lateral septum ameliorates social deficits of mouse autism model

Intellectual and social disabilities are common comorbidities in adolescents and adults with MAGE family member L2 (MAGEL2) gene deficiency characterizing the Prader-Willi and Schaaf-Yang neurodevelopmental syndromes. The cellular and molecular mechanisms underlying the risk for autism in these syndromes are not understood. We asked whether vasopressin functions are altered by MAGEL2 deficiency and whether a treatment with vasopressin could alleviate the disabilities of social behavior. We used Magel2-knockout mice (adult males) combined with optogenetic or pharmacological tools to characterize disease modifications in the vasopressinergic brain system and monitor its impact on neurophysiological and behavioral functions. We found that the activation of vasopressin neurons and projections in the lateral septum were inappropriate for performing a social habituation/discrimination task. Mechanistically, the lack of vasopressin impeded the deactivation of somatostatin neurons in the lateral septum, which predicted social discrimination deficits. Correction of vasopressin septal content by administration or optogenetic stimulation of projecting axons suppressed the activity of somatostatin neurons and ameliorated social behavior. This preclinical study identified vasopressin in the lateral septum as a key factor in the pathophysiology of Magel2-related neurodevelopmental syndromes.

The N-terminal domain of the Schaaf-Yang syndrome protein MAGEL2 likely has a role in RNA metabolism

MAGEL2 encodes the L2 member of the melanoma-associated antigen gene (MAGE) protein family, truncating mutations of which can cause Schaaf-Yang syndrome, an autism spectrum disorder. MAGEL2 is also inactivated in Prader-Willi syndrome, which overlaps clinically and mechanistically with Schaaf-Yang syndrome. Studies to date have only investigated the C-terminal portion of the MAGEL2 protein, containing the MAGE homology domain that interacts with RING-E3 ubiquitin ligases and deubiquitinases to form protein complexes that modify protein ubiquitination. In contrast, the N-terminal portion of the MAGEL2 protein has never been studied. Here, we find that MAGEL2 has a low-complexity intrinsically disordered N-terminus rich in Pro-Xn-Gly motifs that is predicted to mediate liquid-liquid phase separation to form biomolecular condensates. We used proximity-dependent biotin identification (BioID) and liquid chromatography-tandem mass spectrometry to identify MAGEL2-proximal proteins, then clustered these proteins into functional networks. We determined that coding mutations analogous to disruptive mutations in other MAGE proteins alter these networks in biologically relevant ways. Proteins identified as proximal to the N-terminal portion of MAGEL2 are primarily involved in mRNA metabolic processes and include three mRNA N 6-methyladenosine (m6A)-binding YTHDF proteins and two RNA interference-mediating TNRC6 proteins. We found that YTHDF2 coimmunoprecipitates with MAGEL2, and coexpression of MAGEL2 reduces the nuclear accumulation of YTHDF2 after heat shock. We suggest that the N-terminal region of MAGEL2 may have a role in RNA metabolism and in particular the regulation of mRNAs modified by m6A methylation. These results provide mechanistic insight into pathogenic MAGEL2 mutations associated with Schaaf-Yang syndrome and related disorders.

Phenotypic spectrum and mechanism analysis of Schaff Yang syndrome: A case report on new mutation of MAGEL2 gene

RATIONALE

The Schaaf-Yang syndrome (SYS) is an autosomal dominant multi-system genetic disease caused by melanoma antigen L2 (MAGEL2) gene mutations imprinted by mothers and expressed by fathers on the 15q11-15q13 chromosomes in the critical region of Prader-Willi. MAGEL2 is a single exon gene and one of the protein-coding genes of the Prader-Willi domain. MAGEL2 is a matrilineal imprinted gene (i.e., the maternal chromosome is methylated). It is only expressed by unmethylated paternal alleles, and the individual is affected only when the variation occurs on the paternal allele.

PATIENT CONCERNS

We reported a patient with MAGEL2 gene new site mutation who had mild intellectual disability, social fear, small hands and feet, obesity issues, dyskinesia, growth retardation, language lag and sexual development disorder.

DIAGNOSIS

Whole-exome sequencing showed a heterozygous variation in the MAGEL2 gene, NM_019066.4:c.1687C > T (p.Q563X) and diagnosed as Schaaf-Yang syndrome.

INTERVENTIONS

Patient was advised to reduce weight, control blood lipids, blood glucose through appropriate strengthening of exercise and diet control in the future. At the same time, the family members were advised to provide mental training to the patient to strengthen the contact and communication with the outside world and improve the autistic symptoms. Because of the patient's bilateral cryptorchidism, it is recommended that the patient should be treated with bilateral cryptorchidism reduction fixation.

OUTCOMES

After a follow-up of the patient for 2 months, the patient is still walking unsteadily and requires an auxiliary reference material to walk normally. There is no significant change in height compared to before, and the weight has dropped by about 2 kg in the past 2 months. The symptoms of autism have improved slightly. The patient is willing to communicate with outsiders; his intelligence has not improved significantly, and his academic performance in school is still at the middle and lower levels.

LESSONS

The pathogenesis of SYS is complex, involving multiple pathways such as Leptin-POMC, MAGEL2-USP7-TRIM27 complex and oxytocin. Our study has also found that certain fatal phenotypes such as respiratory distress have a high incidence at individual sites, and early detection and timely intervention may prolong the life span of patients. Therefore, for patients in whom SYS is highly suspected, gene detection should be carried out as soon as possible.

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.

A retrospective analysis of growth hormone therapy in children with Schaaf-Yang syndrome

Short stature is a common phenotype in children with Schaaf-Yang syndrome (SYS). Prader-Willi syndrome (PWS) and SYS share several phenotypic features including short stature, muscular hypotonia and developmental delay/intellectual disability. Evidence exists that similar to PWS, growth hormone (GH) deficiency may also be a feature of SYS. Recombinant human GH (rhGH) therapy has been approved for PWS, but the effects of rhGH therapy in individuals with SYS have not yet been documented. This retrospective, questionnaire-based study analyzes the prevalence of rhGH therapy in children with SYS, the effects of rhGH therapy on anthropometric measures, and parental perception of the treatment. Twenty-six individuals with SYS were sent a clinical questionnaire and a request for growth charts. We found a significant increase in height z-score (p* = 0.04) as well as a significant decrease in body mass index 6 months after rhGH therapy initiation (p* = 0.04). Furthermore, height z-scores of the treated group (mean z-score = -1.00) were significantly higher than those of the untreated group (mean z-score = -3.36, p = 0.01) at time of enrollment. All parents reported an increase in muscle strength and endurance, and several families noted beneficial effects such as improved cognition and motor development.

Expanding the spectrum of endocrinopathies identified in Schaaf-Yang syndrome - A case report and review of the literature

Schaaf-Yang syndrome is a genetic disorder caused by mutations in the paternal allele of the MAGEL2 gene. Developmental delay, feeding difficulties, joint contractures and a high prevalence of autism spectrum disorders are characteristic of the syndrome. Endocrine abnormalities include mostly various pituitary hormonal deficiencies, presenting as hypoglycemia in 48% of reported cases. Persistent hyperinsulinism was only described in two siblings and responded to diazoxide treatment. We describe a unique case of an infant with Schaaf-Yang syndrome that presented with persistent hyperinsulinism unresponsive to diazoxide. Furthermore, we conducted a literature review of the endocrine abnormalities described in MAGEL2 related disorders. The case presented expands the clinical phenotype of Schaaf-Yang syndrome and emphasizes the importance of endocrine follow-up in these patients. Further investigation into the role of MAGEL2 in the regulation of pancreatic beta-cell insulin secretion, will improve our understanding of the abnormalities in glucose regulation in this syndrome.

Endocrine disorders in Prader-Willi syndrome: a model to understand and treat hypothalamic dysfunction

Prader-Willi syndrome is a rare genetic neurodevelopmental disorder resulting from the loss of expression of maternally imprinted genes located in the paternal chromosomal region, 15q11-13. Impaired hypothalamic development and function is the cause of most of the phenotypes comprising the developmental trajectory of Prader-Willi syndrome: from anorexia at birth to excessive weight gain preceding hyperphagia, and early severe obesity with hormonal deficiencies, behavioural problems, and dysautonomia. Growth hormone deficiency, hypogonadism, hypothyroidism, premature adrenarche, corticotropin deficiency, precocious puberty, and glucose metabolism disorders are the main endocrine dysfunctions observed. Additionally, as a result of hypothalamic dysfunction, oxytocin and ghrelin systems are impaired in most patients. Standard pituitary and gonadal hormone replacement therapies are required. In this Review, we discuss Prader-Willi syndrome as a model of hypothalamic dysfunction, and provide a comprehensive description of the accumulated knowledge on genetics, pathophysiology, and treatment approaches of this rare disorder.

A Comprehensive Review of Genetically Engineered Mouse Models for Prader-Willi Syndrome Research

Prader-Willi syndrome (PWS) is a neurogenetic multifactorial disorder caused by the deletion or inactivation of paternally imprinted genes on human chromosome 15q11-q13. The affected homologous locus is on mouse chromosome 7C. The positional conservation and organization of genes including the imprinting pattern between mice and men implies similar physiological functions of this locus. Therefore, considerable efforts to recreate the pathogenesis of PWS have been accomplished in mouse models. We provide a summary of different mouse models that were generated for the analysis of PWS and discuss their impact on our current understanding of corresponding genes, their putative functions and the pathogenesis of PWS. Murine models of PWS unveiled the contribution of each affected gene to this multi-facetted disease, and also enabled the establishment of the minimal critical genomic region (PWScr) responsible for core symptoms, highlighting the importance of non-protein coding genes in the PWS locus. Although the underlying disease-causing mechanisms of PWS remain widely unresolved and existing mouse models do not fully capture the entire spectrum of the human PWS disorder, continuous improvements of genetically engineered mouse models have proven to be very powerful and valuable tools in PWS research.

Diagnosis of Schaaf-Yang syndrome in Korean children with developmental delay and hypotonia

Schaaf-Yang syndrome (SYS) is a recently identified disorder caused by a loss-of-function mutation in a maternally imprinted gene, MAGEL2, at 15q11.2q13. Due to its extreme rarity and wide range of clinical severity, clinical suspicion is difficult for a physician. In the current study, its frequency among the Korean pediatric patients with developmental delay (DD) or intellectual disability (ID) was assessed. As the first report of Korean patients with SYS, our study aims to increase the awareness of this condition among the physicians taking care of the pediatric patients with DD/ID and hypotonia.The patients diagnosed with SYS by whole-exome sequencing (WES) among the 460 Korean pediatric patients with DD/ID were included, and their clinical and molecular features were reviewed.Four patients (0.9%) were diagnosed with SYS. Profound DD (4 patients), multiple anomalies including joint contractures and facial dysmorphism (4 patients), generalized hypotonia (3 patients), and severe respiratory difficulty requiring mechanical ventilation (3 patients) were noted in most cases, similar to those in previous reports. Sleep apnea (2 patients), autistic features (2 patients), a high grade of gastroesophageal reflux (1 patient), and seizures (1 patient) were found as well. A total of 3 different truncating MAGEL2 mutations were identified. A previously-reported mutation, to be the most common one, c.1996dupC, was found in 2 patients. The other 2 mutations, c.2217delC and c.3449_3450delTT were novel mutations. As MAGEL2 is maternally imprinted, 2 patients had inherited the MAGEL2 mutation from their respective healthy fathers.SYS is an extremely rare cause of DD/ID. However, hypotonia, joint contractures, profound DD/ID and facial dysmorphism are the suggestive clinical features for SYS. As a maternally imprinted disorder, it should be reminded that SYS may be inherited in form of a mutation from a healthy father.

Clinical spectrum and management of imprinting disorders

Imprinting disorders are exceptional within the group of monogenic syndromes. They are associated with molecular changes affecting imprinted regions and usually do not follow the rules of Mendelian inheritance. They account for a relevant proportion of congenital disorders, especially within the syndromal growth entities with endocrine, neurological, and skeletal characteristics. In patients with imprinting disorders and accelerated growth, significant tumor risks have to be considered. The number of known imprinting disorders increases with the identification of new regions in which parentally imprinted genes are located. Imprinting disorders are caused by genomic pathogenic variants affecting imprinted genes, as well as by aberrant imprinting marks (epimutations) in the patients themselves. Additionally, maternal effect mutations have recently been identified that trigger secondary epimutations in the offspring. These maternal effect mutations explain not only imprinting disorders in their children, but also recurrent reproductive failure in the families. This review aims to provide an overview of the recent findings in 13 well-known imprinting disorders relating to clinical diagnosis, management and counseling.

Emerging roles of the MAGE protein family in stress response pathways

The melanoma antigen (MAGE) proteins all contain a MAGE homology domain. MAGE genes are conserved in all eukaryotes and have expanded from a single gene in lower eukaryotes to ∼40 genes in humans and mice. Whereas some MAGEs are ubiquitously expressed in tissues, others are expressed in only germ cells with aberrant reactivation in multiple cancers. Much of the initial research on MAGEs focused on exploiting their antigenicity and restricted expression pattern to target them with cancer immunotherapy. Beyond their potential clinical application and role in tumorigenesis, recent studies have shown that MAGE proteins regulate diverse cellular and developmental pathways, implicating them in many diseases besides cancer, including lung, renal, and neurodevelopmental disorders. At the molecular level, many MAGEs bind to E3 RING ubiquitin ligases and, thus, regulate their substrate specificity, ligase activity, and subcellular localization. On a broader scale, the MAGE genes likely expanded in eutherian mammals to protect the germline from environmental stress and aid in stress adaptation, and this stress tolerance may explain why many cancers aberrantly express MAGEs Here, we present an updated, comprehensive review on the MAGE family that highlights general characteristics, emphasizes recent comparative studies in mice, and describes the diverse functions exerted by individual MAGEs.

Polysomnographic characteristics and sleep-disordered breathing in Schaaf-Yang syndrome

INTRODUCTION

Schaaf-Yang syndrome (SYS) is a genetic disorder caused by truncating variants in the MAGEL2 gene located in the maternally imprinted Prader-Willi syndrome (PWS) region at 15q11-13. The SYS phenotype shares features with PWS, a syndrome with known high incidence of sleep disorders. However, the spectrum of sleep-disorders in SYS has not been described.

METHODS

We performed a retrospective analysis of polysomnograms from 22 patients in an international SYS cohort. Sleep characteristics for individuals with the common c.1996dupC variant (n = 10) were compared to other truncating variants (n = 11).

RESULTS

We collected 33 sleep study reports from 22 patients, ages 2 months - 18.5 years (mean 6.5 years). Mean sleep efficiency was 70.5% (range 45%-93%) with arousal index 14.1/h (1.2-45/h). The mean apnea-hypopnea index (AHI) was 19.1/h (0.9-49/h) with mean obstructive AHI (oAHI) of 16.3/h (0.6-49/h). Mean central apnea index was 2.8/h (0-14/h). Mean oxygen desaturation index was 20.8/h (range 0-85/hr). Obstructive sleep apnea (OSA) was diagnosed in 81%, and 62% had moderate or severe OSA. Elevated central apnea index occurred in 9.5%. Comparison by genotype groups and age did not reveal any difference in OSA findings. Periodic limb movement index (PLMI) was elevated in 4/15 (26%).

CONCLUSION

OSA is frequently identified on polysomnography in patients with SYS. The mean PLMI is elevated compared to normative data. Patients with SYS should have routine polysomnography screening due to high risk of sleep disorders.

The adult phenotype of Schaaf-Yang syndrome

Background

MAGEL2-associated Schaaf-Yang syndrome (SHFYNG, OMIM #615547, ORPHA: 398069), which was identified in 2013, is a rare disorder caused by truncating variants of the paternal copy of MAGEL2, which is localized in the imprinted region on 15q11.2q13. The phenotype of SHFYNG in childhood partially overlaps with that of the well-established Prader–Willi syndrome (PWS, OMIM #176270). While larger numbers of younger individuals with SHFYNG have been recently published, the phenotype in adulthood is not well established. We recruited 7 adult individuals (aged 18 to 36) with molecularly confirmed SHFYNG and collected data regarding the clinical profile including eating habits, sleep, behavior, personal autonomy, psychiatric abnormalities and other medical conditions, as well as information about the respective phenotypes in childhood.

Results

Within our small cohort, we identified a range of common features, such as disturbed sleep, hypoactivity, social withdrawal and anxiety, but also noted considerable differences at the level of personal autonomy and skills. Behavioral problems were frequent, and a majority of individuals displayed weight gain and food-seeking behavior, along with mild intellectual disability or borderline intellectual function. Classical symptoms of SHFYNG in childhood were reported for most individuals.

Conclusion

Our findings indicate a high variability of the functional abilities and social participation of adults with SHFYNG. A high prevalence of obesity within our cohort was notable, and uncontrollable food intake was a major concern for some caregivers. The phenotypes of PWS and SHFYNG in adulthood might be more difficult to discern than the phenotypes in childhood. Molecular genetic testing for SHFYNG should therefore be considered in adults with the suspected diagnosis of PWS, if testing for PWS has been negative.

Loss of MAGEL2 in Prader-Willi syndrome leads to decreased secretory granule and neuropeptide production

Prader-Willi syndrome (PWS) is a developmental disorder caused by loss of maternally imprinted genes on 15q11-q13, including melanoma antigen gene family member L2 (MAGEL2). The clinical phenotypes of PWS suggest impaired hypothalamic neuroendocrine function; however, the exact cellular defects are unknown. Here, we report deficits in secretory granule (SG) abundance and bioactive neuropeptide production upon loss of MAGEL2 in humans and mice. Unbiased proteomic analysis of Magel2pΔ/m+ mice revealed a reduction in components of SG in the hypothalamus that was confirmed in 2 PWS patient-derived neuronal cell models. Mechanistically, we show that proper endosomal trafficking by the MAGEL2-regulated WASH complex is required to prevent aberrant lysosomal degradation of SG proteins and reduction of mature SG abundance. Importantly, loss of MAGEL2 in mice, NGN2-induced neurons, and human patients led to reduced neuropeptide production. Thus, MAGEL2 plays an important role in hypothalamic neuroendocrine function, and cellular defects in this pathway may contribute to PWS disease etiology. Moreover, these findings suggest unanticipated approaches for therapeutic intervention.

Two mouse models carrying truncating mutations in Magel2 show distinct phenotypes

Schaaf-Yang syndrome (SYS) is a neurodevelopmental disorder caused by truncating variants in the paternal allele of MAGEL2, located in the Prader-Willi critical region, 15q11-q13. Although the phenotypes of SYS overlap those of Prader-Willi syndrome (PWS), including neonatal hypotonia, feeding problems, and developmental delay/intellectual disability, SYS patients show autism spectrum disorder and joint contractures, which are atypical phenotypes for PWS. Therefore, we hypothesized that the truncated Magel2 protein could potentially produce gain-of-function toxic effects. To test the hypothesis, we generated two engineered mouse models; one, an overexpression model that expressed the N-terminal region of Magel2 that was FLAG tagged with a strong ubiquitous promoter, and another, a genome-edited model that carried a truncating variant in Magel2 generated using the CRISPR/Cas9 system. In the overexpression model, all transgenic mice died in the fetal or neonatal period indicating embryonic or neonatal lethality of the transgene. Therefore, overexpression of the truncated Magel2 could show toxic effects. In the genome-edited model, we generated a mouse model carrying a frameshift variant (c.1690_1924del; p(Glu564Serfs*130)) in Magel2. Model mice carrying the frameshift variant in the paternal or maternal allele of Magel2 were termed Magel2^P:fs and Magel2^M:fs, respectively. The imprinted expression and spatial distribution of truncating Magel2 transcripts in the brain were maintained. Although neonatal Magel2^P:fs mice were lighter than wildtype littermates, Magel2^P:fs males and females weighed the same as their wildtype littermates by eight and four weeks of age, respectively. Collectively, the overexpression mouse model may recapitulate fetal or neonatal death, which are the severest phenotypes for SYS. In contrast, the genome-edited mouse model maintains genomic imprinting and distribution of truncated Magel2 transcripts in the brain, but only partially recapitulates SYS phenotypes. Therefore, our results imply that simple gain-of-function toxic effects may not explain the patho-mechanism of SYS, but rather suggest a range of effects due to Magel2 variants as in human SYS patients.

Phenotypic spectrum and genetic analysis in the fatal cases of Schaaf-Yang syndrome: Two case reports and literature review

RATIONALE

Schaaf-Yang syndrome, a rare imprinted hereditary disease caused by MAGEL2 variants, manifests as developmental delay/intellectual disability, neonatal hypotonia, feeding difficulties, contractures, and autism spectrum disorder.

PATIENT CONCERNS

Patient 1 and 2 were infant girls presenting facial dysmorphisms, contractures of interphalangeal joints, neonatal hypotonia, feeding difficulties, congenital heart diseases, and respiratory complications. Besides, Patient 2 presented with delayed psychomotor development.

DIAGNOSIS

Whole-exome sequencing was performed and heterozygous mutations of the MAGEL2 gene were detected in the patients. They were diagnosed as Schaaf-Yang syndrome.

INTERVENTIONS

The patients received supportive treatment including mechanical ventilation, parenteral nutrition and gastric tube feeding.

OUTCOMES

Whole-exome sequencing revealed de novo heterozygous c.1996dupC pathogenic mutations in the MAGEL2 gene in the 2 patients. They died due to respiratory failure at the age of 20 days and 98 days, respectively.

LESSONS

Our results indicate that MAGEL2 variants can cause congenital heart disease and fatal respiratory complications, broadening the phenotypic spectrum and adding to the fatal cases of Schaaf-Yang syndrome. We highly suggest that the MAGEL2 gene should be added to gene-panels or gene-filters in next-generation sequencing-based diagnostics, which is of great significance for early diagnosis and early intervention of Schaaf-Yang syndrome patients.

The necdin interactome: evaluating the effects of amino acid substitutions and cell stress using proximity-dependent biotinylation (BioID) and mass spectrometry

Prader-Willi syndrome (PWS) is a neurodevelopmental disorder caused by the loss of function of a set of imprinted genes on chromosome 15q11-15q13. One of these genes, NDN, encodes necdin, a protein that is important for neuronal differentiation and survival. Loss of Ndn in mice causes defects in the formation and function of the nervous system. Necdin is a member of the melanoma-associated antigen gene (MAGE) protein family. The functions of MAGE proteins depend highly on their interactions with other proteins, and in particular MAGE proteins interact with E3 ubiquitin ligases and deubiquitinases to form MAGE-RING E3 ligase-deubiquitinase complexes. Here, we used proximity-dependent biotin identification (BioID) and mass spectrometry (MS) to determine the network of protein-protein interactions (interactome) of the necdin protein. This process yielded novel as well as known necdin-proximate proteins that cluster into a protein network. Next, we used BioID-MS to define the interactomes of necdin proteins carrying coding variants. Variant necdin proteins had interactomes that were distinct from wildtype necdin. BioID-MS is not only a useful tool to identify protein-protein interactions, but also to analyze the effects of variants of unknown significance on the interactomes of proteins involved in genetic disease.

Disturbed genomic imprinting and its relevance for human reproduction: causes and clinical consequences

BACKGROUND

Human reproductive issues affecting fetal and maternal health are caused by numerous exogenous and endogenous factors, of which the latter undoubtedly include genetic changes. Pathogenic variants in either maternal or offspring DNA are associated with effects on the offspring including clinical disorders and nonviable outcomes. Conversely, both fetal and maternal factors can affect maternal health during pregnancy. Recently, it has become evident that mammalian reproduction is influenced by genomic imprinting, an epigenetic phenomenon that regulates the expression of genes according to their parent from whom they are inherited. About 1% of human genes are normally expressed from only the maternally or paternally inherited gene copy. Since numerous imprinted genes are involved in (embryonic) growth and development, disturbance of their balanced expression can adversely affect these processes.

OBJECTIVE AND RATIONALE

This review summarises current our understanding of genomic imprinting in relation to human ontogenesis and pregnancy and its relevance for reproductive medicine.

SEARCH METHODS

Literature databases (Pubmed, Medline) were thoroughly searched for the role of imprinting in human reproductive failure. In particular, the terms ‘multilocus imprinting disturbances, SCMC, NLRP/NALP, imprinting and reproduction’ were used in various combinations.

OUTCOMES

A range of molecular changes to specific groups of imprinted genes are associated with imprinting disorders, i.e. syndromes with recognisable clinical features including distinctive prenatal features. Whereas the majority of affected individuals exhibit alterations at single imprinted loci, some have multi-locus imprinting disturbances (MLID) with less predictable clinical features. Imprinting disturbances are also seen in some nonviable pregnancy outcomes, such as (recurrent) hydatidiform moles, which can therefore be regarded as a severe form of imprinting disorders. There is growing evidence that MLID can be caused by variants in the maternal genome altering the imprinting status of the oocyte and the embryo, i.e. maternal effect mutations. Pregnancies of women carrying maternal affect mutations can have different courses, ranging from miscarriages to birth of children with clinical features of various imprinting disorders.

WIDER IMPLICATIONS

Increasing understanding of imprinting disturbances and their clinical consequences have significant impacts on diagnostics, counselling and management in the context of human reproduction. Defining criteria for identifying pregnancies complicated by imprinting disorders facilitates early diagnosis and personalised management of both the mother and offspring. Identifying the molecular lesions underlying imprinting disturbances (e.g. maternal effect mutations) allows targeted counselling of the family and focused medical care in further pregnancies.

Schaaf-Yang syndrome shows a Prader-Willi syndrome-like phenotype during infancy

Background

Schaaf-Yang syndrome (SYS) is a newly recognized imprinting related syndrome, which is caused by a truncating variant in maternally imprinted MAGEL2 located in 15q11-q13. Yet, precise pathomechanism remains to be solved. We sequenced MAGEL2 in patients suspected Prader-Willi syndrome (PWS) to delineate clinical presentation of SYS. We examined 105 patients with clinically suspected PWS but without a specific PWS genetic alteration. Sanger sequencing of the entire MAGEL2 gene and methylation-specific restriction enzyme treatment to detect the parent of origin were performed. Clinical presentation was retrospectively assessed in detail.

Results

Truncating variants in MAGEL2 were detected in six patients (5.7%), including a pair of siblings. All truncating variants in affected patients were on the paternally derived chromosome, while the healthy father of the affected siblings inherited the variant from his mother. Patients with MAGEL2 variants shared several features with PWS, such as neonatal hypotonia, poor suck, and obesity; however, there were also unique features, including arthrogryposis and a failure to acquire meaningful words. Additionally, an episode of neurological deterioration following febrile illness was confirmed in four of the six patients, which caused severe neurological sequalae.

Conclusions

SYS can be present in infants suspected with PWS but some unique features, such as arthrogryposis, can help discriminate between the two syndromes. An episode of neurological deterioration following febrile illness should be recognized as an important complication.

MAGEL2-related disorders: A study and case series

Pathogenic MAGEL2 variants result in the phenotypes of Chitayat-Hall syndrome (CHS), Schaaf-Yang syndrome (SYS) and Prader-Willi syndrome (PWS). We present five patients with mutations in MAGEL2, including the first patient reported with a missense variant, adding to the limited literature. Further, we performed a systematic review of the CHS and SYS literature, assess the overlap between CHS, SYS and PWS, and analyze genotype-phenotype correlations among them. We conclude that there is neither a clinical nor etiological difference between CHS and SYS, and propose that the two syndromes simply be referred to as MAGEL2-related disorders.

Mutations in MAGEL2 and L1CAM Are Associated With Congenital Hypopituitarism and Arthrogryposis

CONTEXT

Congenital hypopituitarism (CH) is rarely observed in combination with severe joint contractures (arthrogryposis). Schaaf-Yang syndrome (SHFYNG) phenotypically overlaps with Prader-Willi syndrome, with patients also manifesting arthrogryposis. L1 syndrome, a group of X-linked disorders that include hydrocephalus and lower limb spasticity, also rarely presents with arthrogryposis.

OBJECTIVE

We investigated the molecular basis underlying the combination of CH and arthrogryposis in five patients.

PATIENTS

The heterozygous p.Q666fs*47 mutation in the maternally imprinted MAGEL2 gene, previously described in multiple patients with SHFYNG, was identified in patients 1 to 4, all of whom manifested growth hormone deficiency and variable SHFYNG features, including dysmorphism, developmental delay, sleep apnea, and visual problems. Nonidentical twins (patients 2 and 3) had diabetes insipidus and macrocephaly, and patient 4 presented with ACTH insufficiency. The hemizygous L1CAM variant p.G452R, previously implicated in patients with L1 syndrome, was identified in patient 5, who presented with antenatal hydrocephalus.

RESULTS

Human embryonic expression analysis revealed MAGEL2 transcripts in the developing hypothalamus and ventral diencephalon at Carnegie stages (CSs) 19, 20, and 23 and in the Rathke pouch at CS20 and CS23. L1CAM was expressed in the developing hypothalamus, ventral diencephalon, and hindbrain (CS19, CS20, CS23), but not in the Rathke pouch.

CONCLUSION

We report MAGEL2 and L1CAM mutations in four pedigrees with variable CH and arthrogryposis. Patients presenting early in life with this combined phenotype should be examined for features of SHFYNG and/or L1 syndrome. This study highlights the association of hypothalamo-pituitary disease with MAGEL2 and L1CAM mutations.