Increased body mass in infancy and early toddlerhood in Angelman syndrome patients with uniparental disomy and imprinting center defects

Stem cell models of Angelman syndrome

Angelman syndrome (AS) is an imprinted neurodevelopmental disorder that lacks a cure, characterized by developmental delay, intellectual impairment, seizures, ataxia, and paroxysmal laughter. The condition arises due to the loss of the maternally inherited copy of the UBE3A gene in neurons. The paternally inherited UBE3A allele is unable to compensate because it is silenced by the expression of an antisense transcript (UBE3A-ATS) on the paternal chromosome. UBE3A, encoding enigmatic E3 ubiquitin ligase variants, regulates target proteins by either modifying their properties/functions or leading them to degradation through the proteasome. Over time, animal models, particularly the Ube3a mat-/pat+ Knock-Out (KO) mice, have significantly contributed to our understanding of the molecular mechanisms underlying AS. However, a shift toward human pluripotent stem cell models (PSCs), such as human embryonic stem cells (ESCs) and induced pluripotent stem cells (iPSCs), has gained momentum. These stem cell models accurately capture human genetic and cellular characteristics, offering an alternative or a complement to animal experimentation. Human stem cells possess the remarkable ability to recapitulate neurogenesis and generate "brain-in-a-dish" models, making them valuable tools for studying neurodevelopmental disorders like AS. In this review, we provide an overview of the current state-of-the-art human stem cell models of AS and explore their potential to become the preclinical models of choice for drug screening and development, thus propelling AS therapeutic advancements and improving the lives of affected individuals.

Hyperphagia, Growth, and Puberty in Children with Angelman Syndrome

Angelman Syndrome (AS) is a rare genetic disorder caused by lack of maternal UBE3A protein due to a deletion of the chromosome 15q11.2-q13 region, uniparental paternal disomy, imprinting center defect, or pathogenic variant in the UBE3A gene. Characteristics are developmental delay, epilepsy, behavioral, and sleep problems. There is some evidence for hyperphagia, shorter stature, and higher BMI compared to neurotypical children, but longitudinal studies on growth are lacking. In this study, we analyzed prospectively collected data of 145 children with AS, who visited the ENCORE Expertise Center between 2010 and 2021, with a total of 853 visits. Children showed an elevated mean score of 25 on the Dykens Hyperphagia questionnaire (range 11-55) without genotype association. Higher scores were significantly associated with higher body mass index (BMI) standard deviation scores (SDS) (p = 0.004). Mean height was -1.2 SDS (SD 1.3), mean BMI-SDS was 0.6 (SD 1.7); 43% had a BMI-SDS > 1 and 20% had a BMI-SDS > 2. Higher BMI-SDS was significantly associated with non-deletion genotype (p = 0.037) and walking independently (p = 0.023). Height SDS decreased significantly with age (p < 0.001) and BMI-SDS increased significantly with age (p < 0.001. Onset of puberty was normal. In conclusion, children with AS showed moderate hyperphagia, lower height SDS, and higher BMI-SDS compared to norm data, with increasing deviation from the norm with age. It is uncertain how loss of maternal UBE3A function may influence growth. Attention to diet, exercise, and hyperphagia from an early age is recommended to prevent obesity and associated health problems.

Drosophila UBE3A regulates satiety signaling through the Piezo mechanosensitive ion channel

Angelman syndrome (AS) is a rare neurogenetic disorder characterized by developmental delays, speech impairments, ataxic movements, and in some cases, hyperphagic feeding behavior. Loss of function mutations, loss of expression from the maternal allele or absence of maternal UBE3A result in AS. Recent studies have established a connection between UBE3A and the mechanosensitive ion channel PIEZO2, suggesting the potential role of UBE3A in the regulation of PIEZO channels. In this study, we investigated the role of Drosophila UBE3A (Dube3a) in Piezo associated hyperphagic feeding behavior. We developed a novel assay using green fluorescent protein (GFP) expressing yeast to quantify gut distention in flies with Piezo and Dube3a mutations. We confirmed that Dube3a15b loss of function flies displayed gut distention to almost identical levels as PiezoKO flies. Further analysis using deficiency (Df) lines encompassing the Dube3a locus provided proof for a role of Dube3a in satiety signaling. We also investigated endogenous Piezo expression across the fly midgut and tracheal system. Piezo protein could be detected in both neurons and trachea of the midgut. Overexpression of Dube3a driven by the Piezo promoter resulted in distinct tracheal remodeling within the midgut. These findings suggest that Dube3a plays a key role in the regulation of Piezo and that subsequent dysregulation of these ion channels may explain the hyperphagic behavior observed in 32% of cases of AS. Further investigation will be needed to identify the intermediate protein(s) interacting between the Dube3a ubiquitin ligase and Piezo channels, as Piezo does not appear to be a direct ubiquitin substrate for UBE3A in mice and humans.

Case Report: An Atypical Angelman Syndrome Case With Obesity and Fulfilled Autism Spectrum Disorder Identified by Microarray

Autism spectrum disorder (ASD) is a group of neurodevelopmental disorders which are etiologically heterogeneous. Chromosomal microarray is now recommended as the first-tier clinical diagnostic test for ASD. We performed chromosomal microarray in 16 Thai patients with ASD using an Illumina HumanCytoSNP-12 v2.1 array and found one case with uniparental disomy (UPD) of chromosome 15. Methylation-specific PCR showed abnormal methylation of the maternal SNRPN allele. Haplotype analysis revealed that the patient had received both chromosomes 15 from his father. These results were consistent with Angelman syndrome. However, his clinical features had no clinical significance for classic Angelman syndrome. He had first presented at the pediatric clinic with no speech, poor social interaction skills and repetitive behaviors consistent with ASD based on the DSM-IV criteria at 2 years of age and later confirmed by ADOS at 5 years of age. He was strikingly overweight but had no dysmorphic facies, seizures nor ataxia and was diagnosed as non-syndromic ASD, a diagnosis which was believed until at 10 years of age, his DNA was included for analysis in this current cohort study. Our findings suggest that ASD patients with unknown etiology should be considered for methylation-specific PCR testing for Angelman syndrome where chromosomal microarray is not available. In the study, we also review the clinical features of Angelman syndrome caused by UPD and the frequency of ASD in individuals with Angelman syndrome.

Genotype-Phenotype Correlations in Angelman Syndrome

Angelman syndrome (AS) is a rare neurodevelopmental disease that is caused by the loss of function of the maternal copy of ubiquitin-protein ligase E3A (UBE3A) on the chromosome 15q11-13 region. AS is characterized by global developmental delay, severe intellectual disability, lack of speech, happy disposition, ataxia, epilepsy, and distinct behavioral profile. There are four molecular mechanisms of etiology: maternal deletion of chromosome 15q11-q13, paternal uniparental disomy of chromosome 15q11-q13, imprinting defects, and maternally inherited UBE3A mutations. Different genetic types may show different phenotypes in performance, seizure, behavior, sleep, and other aspects. AS caused by maternal deletion of 15q11-13 appears to have worse development, cognitive skills, albinism, ataxia, and more autistic features than those of other genotypes. Children with a UBE3A mutation have less severe phenotypes and a nearly normal development quotient. In this review, we proposed to review genotype-phenotype correlations based on different genotypes. Understanding the pathophysiology of the different genotypes and the genotype-phenotype correlations will offer an opportunity for individualized treatment and genetic counseling. Genotype-phenotype correlations based on larger data should be carried out for identifying new treatment modalities.

Nutrition Assessment and Intervention in a Pediatric Patient with Angelman Syndrome: A Case Presentation Highlighting Clinical Challenges and Evidence-Based Solutions

BACKGROUND

Angelman syndrome (AS) is a rare disorder of genetic imprinting which results in intellectual and developmental disability. It meets criteria of a disorder of neurologic impairment. A deletion in the long arm of chromosome 15 (del 15q11.2-q13) is responsible for about 70% of cases of AS (deletion genotype).

SUMMARY

There is a paucity of evidence to allow algorithmic nutrition assessment and intervention in pediatric patients with AS. Therefore, our objective is to use a case presentation to provide an example of nutrition assessment and intervention in a pediatric patient with the deletion genotype of AS and then highlight common challenges to providing evidenced-based nutrition care. For the highlighted challenges, we suggest evidence-based solutions to provide a resource for clinicians who may encounter similar challenges in clinical practice. Key Messages: There are genotype-phenotype correlations in AS that can help guide clinicians regarding nutritionally relevant clinical characteristics and corresponding interventions that are patient specific. The deletion genotype in AS is associated with multiple characteristics that are relevant to nutrition care and may also be different and/or more severe than characteristics seen in other AS genetic mechanisms. There is also overlap in certain nutritionally relevant clinical characteristics between AS and other conditions, including Prader-Willi syndrome, autism spectrum disorders, and disorders of neurological impairment like cerebral palsy. Clinicians can utilize nutrition resources related to these conditions to expand the scope of relevant resources available.

An overview of health issues and development in a large clinical cohort of children with Angelman syndrome

This study presents a broad overview of health issues and psychomotor development of 100 children with Angelman syndrome (AS), seen at the ENCORE Expertise Center for AS in Rotterdam, the Netherlands. We aimed to further delineate the phenotype of AS, to evaluate the association of the phenotype with genotype and other determinants such as epilepsy and to get insight in possible targets for intervention. We confirmed the presence of a more severe phenotype in the 15q11.2‐q13 deletion subtype. Novel findings were an association of (early onset of) epilepsy with a negative effect on development, a high occurrence of nonconvulsive status epilepticus, a high rate of crouch gait in the older children with risk of deterioration of mobility, a relatively low occurrence of microcephaly, a higher mean weight for height in all genetic subtypes with a significant higher mean in the nondeletion children, and a high occurrence of hyperphagia across all genetic subtypes. Natural history data are needed to design future trials. With this large clinical cohort with structured prospective and multidisciplinary follow‐up, we provide unbiased data on AS to support further intervention studies to optimize outcome and quality of life of children with AS and their family.

A mouse model of Angelman syndrome imprinting defects

Angelman syndrome, Prader-Will syndrome and Dup15q syndrome map to a cluster of imprinted genes located at 15q11-q13. Imprinting at this domain is regulated by an imprinting control region consisting of two distinct elements, the Angelman syndrome imprinting center (AS-IC) and the Prader-Willi syndrome imprinting center (PWS-IC). Individuals inheriting deletions of the AS-IC exhibit reduced expression of the maternally expressed UBE3A gene and biallelic expression of paternal-only genes. We have previously demonstrated that AS-IC activity partly consists of providing transcription across the PWS-IC in oocytes, and that these transcripts are necessary for maternal imprinting of Snrpn. Here we report a novel mouse mutation that truncates transcripts prior to transiting the PWS-IC and results in a domain-wide imprinting defect. These results confirm a transcription-based model for imprint setting at this domain. The imprinting defect can be preempted by removal of the transcriptional block in oocytes, but not by its removal in early embryos. Imprinting defect mice exhibit several traits often found in individuals with Angelman syndrome imprinting defects.

UBE3A Suppresses Overnutrition-Induced Expression of the Steatosis Target Genes of MLL4 by Degrading MLL4

Regulation of the protein stability of epigenetic regulators remains ill-defined despite its potential applicability in epigenetic therapies. The histone H3-lysine 4-methyltransferase MLL4 is an epigenetic transcriptional coactivator that directs overnutrition-induced obesity and fatty liver formation, and Mll4+/- mice are resistant to both. Here we show that the E3 ubiquitin ligase UBE3A targets MLL4 for degradation, thereby suppressing high-fat diet (HFD)-induced expression of the hepatic steatosis target genes of MLL4. In contrast to Mll4+/- mice, Ube3a+/- mice are hypersensitive to HFD-induced obesity and fatty liver development. Ube3a+/-;Mll4+/- mice lose this hypersensitivity, supporting roles of increased MLL4 levels in both phenotypes of Ube3a+/- mice. Correspondingly, our comparative studies with wild-type, Ube3a+/- and Ube3a-/- and UBE3A-overexpressing transgenic mouse livers demonstrate an inverse correlation of UBE3A protein levels with MLL4 protein levels, expression of the steatosis target genes of MLL4, and their decoration by H3-lysine 4-monomethylation, a surrogate marker for the epigenetic action of MLL4. Conclusion: UBE3A indirectly exerts an epigenetic regulation of obesity and steatosis by degrading MLL4. This UBE3A-MLL4 regulatory axis provides a potential therapeutic venue for treating various MLL4-directed pathogeneses, including obesity and hepatic steatosis.

Baby food and bedtime: Evidence for opposite phenotypes from different genetic and epigenetic alterations in Prader-Willi and Angelman syndromes

Prader–Willi and Angelman syndromes are often referred to as a sister pair of neurodevelopmental disorders, resulting from different genetic and epigenetic alterations to the same chromosomal region, 15q11-q13. Some of the primary phenotypes of the two syndromes have been suggested to be opposite to one another, but this hypothesis has yet to be tested comprehensively, and it remains unclear how opposite effects could be produced by changes to different genes in one syndrome compared to the other. We evaluated the evidence for opposite effects on sleep and eating phenotypes in Prader–Willi syndrome and Angelman syndrome, and developed physiological–genetic models that represent hypothesized causes of these differences. Sleep latency shows opposite deviations from controls in Prader–Willi and Angelman syndromes, with shorter latency in Prader–Willi syndrome by meta-analysis and longer latency in Angelman syndrome from previous studies. These differences can be accounted for by the effects of variable gene dosages of UBE3A and MAGEL2, interacting with clock genes, and leading to acceleration (in Prader–Willi syndrome) or deceleration (in Angelman syndrome) of circadian rhythms. Prader–Willi and Angelman syndromes also show evidence of opposite alterations in hyperphagic food selectivity, with more paternally biased subtypes of Angelman syndrome apparently involving increased preference for complementary foods (“baby foods”); hedonic reward from eating may also be increased in Angelman syndrome and decreased in Prader–Willi syndrome. These differences can be explained in part under a model whereby hyperphagia and food selectivity are mediated by the effects of the genes SNORD-116, UBE3A and MAGEL2, with outcomes depending upon the genotypic cause of Angelman syndrome. The diametric variation observed in sleep and eating phenotypes in Prader–Willi and Angelman syndromes is consistent with predictions from the kinship theory of imprinting, reflecting extremes of higher resource demand in Angelman syndrome and lower demand in Prader–Willi syndrome, with a special emphasis on social–attentional demands and attachment associated with bedtime, and feeding demands associated with mother-provided complementary foods compared to offspring-foraged family-type foods.

Epigenetic regulation of UBE3A and roles in human neurodevelopmental disorders

The E3 ubiquitin ligase UBE3A, also known as E6-AP, has a multitude of ascribed functions and targets relevant to human health and disease. Epigenetic regulation of the UBE3A gene by parentally imprinted noncoding transcription within human chromosome 15q11.2-q13.3 is responsible for the maternal-specific effects of 15q11.2-q13.3 deletion or duplication disorders. Here, we review the evidence for diverse and emerging roles for UBE3A in the proteasome, synapse and nucleus in regulating protein stability and transcription as well as the current mechanistic understanding of UBE3A imprinting in neurons. Angelman and Dup15q syndromes as well as experimental models of these neurodevelopmental disorders are highlighted as improving understanding of UBE3A and its complex regulation for improving therapeutic strategies.

Model mice for 15q11-13 duplication syndrome exhibit late-onset obesity and altered lipid metabolism

Copy number variations on human chromosome 15q11-q13 have been implicated in several neurodevelopmental disorders. A paternal loss or duplication of the Prader-Willi syndrome/Angelman syndrome (PWS/AS) region confers a risk of obesity, although the mechanism remains a mystery due to a lack of an animal model that accurately recreates the obesity phenotype. We performed detailed analyses of mice with duplication of PWS/AS locus (6 Mb) generated by chromosome engineering and found that animals with a paternal duplication of this region (patDp/+) show late-onset obesity, high sensitivity for high-fat diet, high levels of blood leptin and insulin without an increase in food intake. We show that prior to becoming obese, young patDp/+ mice already had enlarged white adipocytes. Transcriptome analysis of adipose tissue revealed an up-regulation of Secreted frizzled-related protein 5 (Sfrp5), known to promote adipogenesis. We additionally generated a new mouse model of paternal duplication focusing on a 3 Mb region (3 Mb patDp/+) within the PWS/AS locus. These mice recapitulate the obese phenotypes including expansion of visceral adipose tissue. Our results suggest paternally expressed genes in PWS/AS locus play a significant role for the obesity and identify new potential targets for future research and treatment of obesity.