Angelman syndrome caused by deletion: a genotype-phenotype correlation determined by breakpoint

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.

Ubiquitin-protein ligase E3A (UBE3A) mediation of viral infection and human diseases

The Ubiquitin-protein ligase E3A, UBE3A, also known as E6-associated protein (E6-AP), is known to play an essential role in regulating the degradation of various proteins by transferring Ub from E2 Ub conjugating enzymes to the substrate proteins. Several studies indicate that UBE3A regulates the stabilities of key viral proteins in the virus-infected cells and, thereby, the infected virus-mediated diseases, even if it were reported that UBE3A participates in non-viral-related human diseases. Furthermore, mutations such as deletions and duplications in the maternally inherited gene in the brain cause human neurodevelopmental disorders such as Angelman syndrome (AS) and autism. It is also known that UBE3A functions as a transcriptional coactivator for the expression of steroid hormone receptors. These reports establish that UBE3A is distinguished by its multitudinous functions that are paramount to viral pathology and human diseases. This review is focused on molecular mechanisms for such intensive participation of UBE3A in disease formation and virus regulation.

Clinical features and magnesium levels: Novel insights in 15q11.2 BP1-BP2 copy number variants

BACKGROUND

Investigating copy number variations (CNVs) such as microdeletions or microduplications can significantly contribute to discover the aetiology of neurodevelopmental disorders. 15q11.2 genomic region, including NIPA1 and NIPA2 genes, contains a recurrent but rare CNV, flanked by the break points BP1 and BP2. Both BP1-BP2 microdeletion and microduplication have been associated with intellectual disability (ID), neuropsychiatric/behavioural disturbances and mild clinical features, even if with incomplete penetrance and variable expressivity. The pathogenic role of this CNV is quite unclear though. Unknown variants in other DNA regions and parent-of-origin effect (POE) are some of the mechanisms that have been proposed as an explanation of the wide phenotypic variability. As NIPA1 and NIPA2 encode for proteins that mediate magnesium (Mg²⁺ ) metabolism, it has been suggested that urinary Mg²⁺ levels could potentially represent informative and affordable biomarkers for a rapid screening of 15q11.2 duplications or deletions. Furthermore, magnesium supplementation has been proposed as possible therapeutic strategy.

METHODS

Thirty one children with ID and/or other neurodevelopmental disorders carrying either a duplication or a deletion in 15q11.2 BP1-BP2 region have been recruited. When available, blood samples from parents have been analysed to identify the CNV origin. All participants underwent family and medical data collection, physical examination and neuropsychiatric assessment. Electroencephalogram (EEG) and brain magnetic resonance imaging (MRI) scan were performed in 15 children. In addition, 11 families agreed to participate to the assessment of blood and urinary Mg²⁺ levels.

RESULTS

We observed a highly variable phenotypic spectrum of developmental issues encompassing ID in most subjects as well as a variety of behavioural disorders such as autism and attention-deficit disorder/attention-deficit hyperactivity disorder. Dysmorphic traits and malformations were detected only in a minority of the participants, and no clear association with growth anomalies was found. Abnormal brain MRI and/or EEG were reported respectively in 64% and 92% of the subjects. Inheritance assessment highlighted an excess of duplication of maternal origin, while cardiac alterations were detected only in children with 15q11.2 CNV inherited from the father. We found great variability in Mg²⁺ urinary values, without correlation with 15q11.2 copy numbers. However, the variance of urinary Mg²⁺ levels largely increases in individuals with 15q11.2 deletion/duplication.

CONCLUSIONS

This study provides further evidence that 15q11.2 BP1-BP2 CNV is associated with a broad spectrum of neurodevelopmental disorders and POE might be an explanation for clinical variability. However, some issues may question the real impact of 15q11.2 CNV on the phenotype in the carriers: DNA sequencing could be useful to exclude other pathogenic gene mutations. Our results do not support the possibility that urinary Mg²⁺ levels can be used as biomarkers to screen children with neurodevelopmental disorders for 15q11.2 duplication/deletion. However, there are evidences of correlations between 15q11.2 BP1-BP2 CNV and Mg²⁺ metabolism and future studies may pave the way to new therapeutic options.

Electroencephalographic (EEG) Biomarkers in Genetic Neurodevelopmental Disorders

Collectively, neurodevelopmental disorders are highly prevalent, but more than a third of neurodevelopmental disorders have an identifiable genetic etiology, each of which is individually rare. The genes associated with neurodevelopmental disorders are often involved in early brain development, neuronal signaling, or synaptic plasticity. Novel treatments for many genetic neurodevelopmental disorders are being developed, but disease-relevant clinical outcome assessments and biomarkers are limited. Electroencephalography (EEG) is a promising noninvasive potential biomarker of brain function. It has been used extensively in epileptic disorders, but its application in neurodevelopmental disorders needs further investigation. In this review, we explore the use of EEG in 3 of the most prevalent genetic neurodevelopmental disorders-Angelman syndrome, Rett syndrome, and fragile X syndrome. Quantitative analyses of EEGs, such as power spectral analysis or measures of connectivity, can quantify EEG signatures seen on qualitative review and potentially correlate with phenotypes. In both Angelman syndrome and Rett syndrome, increased delta power on spectral analysis has correlated with clinical markers of disease severity including developmental disability and seizure burden, whereas spectral power analysis on EEG in fragile X syndrome tends to demonstrate abnormalities in gamma power. Further studies are needed to establish reliable relationships between quantitative EEG biomarkers and clinical phenotypes in rare genetic neurodevelopmental disorders.

Quantitative EEG Analysis in Angelman Syndrome: Candidate Method for Assessing Therapeutics

The goal of these studies was to use quantitative (q)EEG techniques on data from children with Angelman syndrome (AS) using spectral power analysis, and to evaluate this as a potential biomarker and quantitative method to evaluate therapeutics. Although characteristic patterns are evident in visual inspection, using qEEG techniques has the potential to provide quantitative evidence of treatment efficacy. We first assessed spectral power from baseline EEG recordings collected from children with AS compared to age-matched neurotypical controls, which corroborated the previously reported finding of increased total power driven by elevated delta power in children with AS. We then retrospectively analyzed data collected during a clinical trial evaluating the safety and tolerability of minocycline (3 mg/kg/d) to compare pretreatment recordings from children with AS (4-12 years of age) to EEG activity at the end of treatment and following washout for EEG spectral power and epileptiform events. At baseline and during minocycline treatment, the AS subjects demonstrated increased delta power; however, following washout from minocycline treatment the AS subjects had significantly reduced EEG spectral power and epileptiform activity. Our findings support the use of qEEG analysis in evaluating AS and suggest that this technique may be useful to evaluate therapeutic efficacy in AS. Normalizing EEG power in AS therefore may become an important metric in screening therapeutics to gauge overall efficacy. As therapeutics transition from preclinical to clinical studies, it is vital to establish outcome measures that can quantitatively evaluate putative treatments for AS and neurological disorders with distinctive EEG patterns.

Status Epilepticus in Chromosomal Disorders Associated with Epilepsy: A Systematic Review

Status Epilepticus (SE) is a neurological emergency resulting from the failure of mechanisms of seizure termination or from the initiation of mechanisms that lead to prolonged seizures. The International League Against Epilepsy (ILAE) identified 13 chromosomal disorders associated with epilepsy (CDAE); data regarding SE occurrence in these patients is lacking. A systematic scoping review was conducted to outline current literature evidence about clinical features, treatments, and outcomes of SE in pediatric and adult patients with CDAE. A total of 373 studies were identified with the initial search; 65 of these were selected and regarded as SE in Angelman Syndrome (AS, n = 20), Ring 20 Syndrome (R20, n = 24), and other syndromes (n = 21). Non-convulsive status epilepticus (NCSE) is frequently observed in AS and R20. No specific, targeted therapies for SE in CDAE are available to date; anecdotal reports about SE treatment are described in the text, as well as various brief- and long-term outcomes. Further evidence is needed to precisely portray the clinical features, treatment options, and outcomes of SE in these patients.

The Angelman Syndrome Online Registry - A multilingual approach to support global research

In collaboration with the German Angelman syndrome (AS) community, we developed a web-based AS Online Registry to congregate existing as well as future information and scientifically quantify observations made by parents, families and medical professionals. With its user-friendly design as well as its concise and multilingual questionnaire, the registry aims at families who had so far refrained from being recruited by other, more comprehensive and/or English-only, registries. Data can be entered by both parents/families and medical professionals. The study design allows for re-contacting individuals (e.g. to request additional information) enabling collection of longitudinal data. Since its launch in June 2020, more than 200 individuals with AS age 2 month to 83 years have registered and entered their clinical and genetic data. In addition to the German, Turkish, English, Dutch, Italian, Danish and Finnish versions of the registry, we aim for translation into further languages to enable international and user-friendly recruitment of AS individuals. This novel registry will allow for extensive genotype-phenotype correlations and facilitate sharing of de-identified information among clinicians, researchers as well as the Global AS Registry. Furthermore, the registry will allow for identification of individuals suitable for future clinical or pharmacologic trials according to particular genotypic and/or phenotypic properties.

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.

Differentiating molecular etiologies of Angelman syndrome through facial phenotyping using deep learning

Angelman syndrome (AS) is caused by several genetic mechanisms that impair the expression of maternally-inherited UBE3A through deletions, paternal uniparental disomy (UPD), UBE3A pathogenic variants, or imprinting defects. Current methods of differentiating the etiology require molecular testing, which is sometimes difficult to obtain. Recently, computer-based facial analysis systems have been used to assist in identifying genetic conditions based on facial phenotypes. We sought to understand if the facial-recognition system DeepGestalt could find differences in phenotype between molecular subtypes of AS. Images and molecular data on 261 individuals with AS ranging from 10 months through 32 years were analyzed by DeepGestalt in a cross-validation model with receiver operating characteristic (ROC) curves generated. The area under the curve (AUC) of the ROC for each molecular subtype was compared and ranked from least to greatest differentiable phenotype. We determined that DeepGestalt demonstrated a high degree of discrimination between the deletion subtype and UPD or imprinting defects, and a lower degree of discrimination with the UBE3A pathogenic variants subtype. Our findings suggest that DeepGestalt can recognize subclinical differences in phenotype based on etiology and may provide decision support for testing.

Angelman syndrome: a journey through the brain

Angelman syndrome (AS) is an incurable neurodevelopmental disease caused by loss of function of the maternally inherited UBE3A gene. AS is characterized by a defined set of symptoms, namely severe developmental delay, speech impairment, uncontrolled laughter, and ataxia. Current understanding of the pathophysiology of AS relies mostly on studies using the murine model of the disease, although alternative models based on patient-derived stem cells are now emerging. Here, we summarize the literature of the last decade concerning the three major brain areas that have been the subject of study in the context of AS: hippocampus, cortex, and the cerebellum. Our comprehensive analysis highlights the major phenotypes ascribed to the different brain areas. Moreover, we also discuss the major drawbacks of current models and point out future directions for research in the context of AS, which will hopefully lead us to an effective treatment of this condition in humans.

Angelman Syndrome: From Mouse Models to Therapy

The UBE3A gene is part of the chromosome 15q11-q13 region that is frequently deleted or duplicated, leading to several neurodevelopmental disorders (NDD). Angelman syndrome (AS) is caused by the absence of functional maternally derived UBE3A protein, while the paternal UBE3A gene is present but silenced specifically in neurons. Patients with AS present with severe neurodevelopmental delay, with pronounced motor deficits, absence of speech, intellectual disability, epilepsy, and sleep problems. The pathophysiology of AS is still unclear and a treatment is lacking. Animal models of AS recapitulate the genotypic and phenotypic features observed in AS patients, and have been invaluable for understanding the disease process as well as identifying apropriate drug targets. Using these AS mouse models we have learned that loss of UBE3A probably affects many areas of the brain, leading to increased neuronal excitability and a loss of synaptic spines, along with changes in a number of distinct behaviours. Inducible AS mouse models have helped to identify the critical treatment windows for the behavioral and physiological phenotypes. Additionally, AS mouse models indicate an important role for the predominantly nuclear UBE3A isoform in generating the characteristic AS pathology. Last, but not least, the AS mice have been crucial in guiding Ube3a gene reactivation treatments, which present a very promising therapy to treat AS.

Angelman syndrome in adolescence and adulthood: A retrospective chart review of 53 cases

Angelman syndrome is a neurogenetic disorder with varying clinical presentations and symptoms as the individual ages. The goal of this study was to characterize changes over time in the natural history of this syndrome in a large population. We reviewed the medical records of the 53 patients who were born prior to 2000 and seen at the Angelman Syndrome Clinic at Massachusetts General Hospital to assess neurological, sleep, behavioral, gastrointestinal, orthopedic, and ophthalmologic functioning. The average age of this cohort was 24 years. Active seizures were present in 35%, nonepileptic myoclonus in 42%, and clinically significant tremors in 55%. Anxiety was present in 57%, increasing to 71% in those ages 26-43 years. In terms of sleep, 56% reported 8 hr of sleep or more, although 43% reported frequent nocturnal awakenings. Gastrointestinal issues remain problematic with 81% having constipation and 53% gastroesophageal reflux. The majority lived in a parent's home and remained independently mobile, though scoliosis was reportedly present in 30%, and 20% had reported low bone density/osteoporosis. The results of this study suggest that the prevalence of active seizures may decrease in adulthood but that the prevalence of movement disorders such as tremor and nonepileptic myoclonus may increase. Anxiety increases significantly as individuals age while defiant behaviors appear to decrease. Sleep dysfunction typically improves as compared to childhood but remains a significant issue for many adults. Other areas that require monitoring into adulthood include gastrointestinal dysfunction, and orthopedic/mobility issues, such as reported scoliosis and bone density, and ophthalmologic disorders.

Clinical and genetic aspects of the 15q11.2 BP1-BP2 microdeletion disorder

BACKGROUND

The 15q11.2 BP1-BP2 microdeletion (Burnside-Butler susceptibility locus) is an emerging condition with over 200 individuals reported in the literature. TUBGCP5, CFYIP1, NIPA1 and NIPA2 genes are located in this chromosome 15 region and when disturbed individually are known to cause neurological, cognitive or behavioural problems as well as playing a role in both Prader-Willi and Angelman syndromes. These syndromes were the first examples in humans of genomic imprinting and typically caused by a deletion but involving the distal chromosome 15q11-q13 breakpoint BP3 and proximally placed breakpoints BP1 or BP2 of different parental origin. The typical 15q11-q13 deletion involves BP1 and BP3 and the typical type II deletion at BP2 and BP3. Several studies have shown that individuals with the larger type I deletion found in both Prader-Willi and Angelman syndromes are reported with more severe neurodevelopmental symptoms compared to those individuals with the smaller type II deletion.

METHODS

The literature was reviewed and clinical and cytogenetic findings summarised in 200 individuals with this microdeletion along with the role of deleted genes in diagnosis, medical care and counseling of those affected and their family members.

RESULTS

Reported findings in this condition include developmental delays (73% of cases) and language impairment (67%) followed by motor delay (42%), attention deficit disorder/attention deficit hyperactivity disorder (35%) and autism spectrum disorder (27%). The de novo deletion frequency has been estimated at 5 to 22% with low penetrance possibly related to subclinical manifestation or incomplete clinical information on family members. A prevalence of 0.6 to 1.3% has been identified in one study for patients with neurological or behavioural problems presenting for genetic services and chromosomal microarray analysis.

CONCLUSIONS

The summarised results indicate that chromosome 15q11.2 BP1-BP2 microdeletion is emerging as one of the most common cytogenetic abnormalities seen in individuals with intellectual impairment, autism spectrum disorder and other related behavioural or clinical findings, but more research is needed.

Angelman syndrome: Current and emerging therapies in 2016

Angelman syndrome (AS) is a severe neurodevelopmental disorder caused by a loss of the maternally-inherited UBE3A; the paternal UBE3A is silenced in neurons by a mechanism involving an antisense transcript (UBE3A-AS) at the unmethylated paternal locus. We reviewed all published information on the clinical trials that have been completed as well as the publicly available information on ongoing trials of therapies in AS. To date, all clinical trials that strove to improve neurodevelopment in AS have been unsuccessful. Attempts at hypermethylating the maternal locus through dietary compounds were ineffective. The results of an 8-week open-label trial using minocycline as a matrix metalloproteinase-9 inhibitor were inconclusive, while a subsequent randomized placebo-controlled trial suggested that treatment with minocycline for 8 weeks did not result in any neurodevelopmental gains. A 1-year randomized placebo-controlled trial using levodopa to alter the phosphorylation of calcium/calmodulin-dependent kinase II did not lead to any improvement in neurodevelopment. Topoisomerase inhibitors and antisense oligonucleotides are being developed to directly inhibit UBE3A-AS. Artificial transcription factors are being developed to "super activate" UBE3A or inhibit UBE3A-AS. Other strategies targeting specific pathways are briefly discussed. We also reviewed the medications that are currently used to treat seizures and sleep disturbances, which are two of the more common complications of AS. © 2016 Wiley Periodicals, Inc.

Epilepsy and cataplexy in Angelman syndrome. Genotype-phenotype correlations

BACKGROUND

Angelman syndrome (AS) is a neurogenetic disorder characterized by intellectual disability, epilepsy, and low threshold for laughter.

AIMS

We investigated the occurrence and severity of epilepsy and laughter-induced loss of postural muscle tone determined by the different genetic subtypes.

METHODS

This study included 39 children with AS. Deletion breakpoints were determined by high resolution CGH microarray (1×1M Agilent). Clinical data were based on a parent interview and medical record review.

RESULTS

All patients with AS based on a deletion had epilepsy. Epilepsy was present in 3/4 children with UBE3A mutation, and 4/5 with pUPD. Onset of epilepsy occurred earlier in deletion cases compared to pUPD or UBE3A mutations cases. Laughter-induced postural muscle tone loss occurred only among deletion cases. We found no differences in severity of epilepsy between children with a larger Class I or a smaller Class II deletions, or between the total group with a deletion compared to children with pUPD or a UBE3A mutation. The drugs most frequently prescribed were benzodiazepines in monotherapy, or a combination of benzodiazepines and valproic acid.

CONCLUSION

Epilepsy is very common in patients with AS, especially in patients with a deletion. Postural muscle tone loss and collapsing during outbursts of laughter were seen in patients with a deletion only.

Pharmacological therapies for Angelman syndrome

Angelman syndrome (AS) is a severe neurodevelopmental disorder caused by a loss of the maternally inherited UBE3A; the paternal UBE3A is silenced in neurons by a mechanism involving an antisense transcript (UBE3A-AS). We reviewed the published information on clinical trials that have been completed as well as the publicly available information on ongoing trials of therapies for AS. Attempts at hypermethylating the maternal locus through dietary compounds were ineffective. The results of a clinical trial using minocycline as a matrix metalloproteinase-9 inhibitor were inconclusive; another clinical trial is underway. Findings from a clinical trial using L-dopa to alter phosphorylation of calcium/calmodulin-dependent kinase II are awaited. Topoisomerase inhibitors and antisense oligonucleotides are being developed to directly inhibit UBE3A-AS. Other strategies targeting specific pathways are briefly discussed. We also reviewed the medications that are currently used to treat seizures and sleep disturbances, which are two of the more debilitating manifestations of AS.

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.

Myoclonic status and central fever in Angelman syndrome due to paternal uniparental disomy

Myoclonic status in nonprogressive encephalopathy (MSNE) is an early-onset, drug-resistant epileptic syndrome characterized by occurrence of continuous diffuse epileptiform abnormalities, associated with positive and/or negative phenomena and accompanied by transient and recurring motor, cognitive, and behavioral impairment. MSNE has been reported in Angelman syndrome (AS) secondary to 15q11-13 deletions or UBE3A mutations but not to paternal uniparental disomy (UPD). We describe the case of a male patient with AS caused by UPD who developed a myoclonic status (MS) associated with long-lasting fever of central origin, both promptly regressed with introduction of levetiracetam. Only three descriptions of thermal dysregulation in AS exist, and none of the previously reported cases were associated with MS or with UPD. Association of MS and central fever expands the spectrum of epileptic and non-epileptic features in UPD-related AS and provides a further evidence of hypothalamus involvement in the pathogenesis of this neurodevelopmental disorder.

From UBE3A to Angelman syndrome: a substrate perspective

Angelman syndrome (AS) is a debilitating neurodevelopmental disorder that is characterized by motor dysfunction, intellectual disability, speech impairment, seizures and common features of autism spectrum disorders (ASDs). Some of these AS related phenotypes can be seen in other neurodevelopmental disorders (Williams, 2011; Tan et al., 2014). AS patients commonly carry mutations that render the maternally inherited UBE3A gene non-functional. Duplication of the chromosomal region containing the UBE3A gene is associated with ASDs. Although the causative role for UBE3A gene mutations in AS is well established, a long-standing challenge in AS research has been to identify neural substrates of UBE3A, an E3 ubiquitin ligase. A prevailing hypothesis is that changes in UBE3A protein levels would alter the levels of a collection of protein substrates, giving rise to the unique phenotypic aspects of AS and possibly UBE3A associated ASDs. Interestingly, proteins altered in AS are linked to additional ASDs that are not previously associated with changes in UBE3A, indicating a possible molecular overlap underlying the broad-spectrum phenotypes of these neurogenetic disorders. This idea raises the possibility that there may exist a “one-size-fits-all” approach to the treatment of neurogenetic disorders with phenotypes overlapping AS. Furthermore, while a comprehensive list of UBE3A substrates and downstream affected pathways should be developed, this is only part of the story. The timing of when UBE3A protein functions, through either changes in UBE3A or possibly substrate expression patterns, appears to be critical for AS phenotype development. These data call for further investigation of UBE3A substrates and their timing of action relevant to AS phenotypes.

The complex genetics in autism spectrum disorders

Autism spectrum disorders (ASD) are a pervasive neurodevelopmental disease characterized by deficits in social interaction and nonverbal communication, as well as restricted interests and stereotypical behavior. Genetic changes/heritability is one of the major contributing factors, and hundreds to thousands of causative and susceptible genes, copy number variants (CNVs), linkage regions, and microRNAs have been associated with ASD which clearly indicates that ASD is a complex genetic disorder. Here, we will briefly summarize some of the high-confidence genetic changes in ASD and their possible roles in their pathogenesis.

Angelman Syndrome

In this review we summarize the clinical and genetic aspects of Angelman syndrome (AS), its molecular and cellular underpinnings, and current treatment strategies. AS is a neurodevelopmental disorder characterized by severe cognitive disability, motor dysfunction, speech impairment, hyperactivity, and frequent seizures. AS is caused by disruption of the maternally expressed and paternally imprinted UBE3A, which encodes an E3 ubiquitin ligase. Four mechanisms that render the maternally inherited UBE3A nonfunctional are recognized, the most common of which is deletion of the maternal chromosomal region 15q11-q13. Remarkably, duplication of the same chromosomal region is one of the few characterized persistent genetic abnormalities associated with autistic spectrum disorder, occurring in >1-2% of all cases of autism spectrum disorder. While the overall morphology of the brain and connectivity of neural projections appear largely normal in AS mouse models, major functional defects are detected at the level of context-dependent learning, as well as impaired maturation of hippocampal and neocortical circuits. While these findings demonstrate a crucial role for ubiquitin protein ligase E3A in synaptic development, the mechanisms by which deficiency of ubiquitin protein ligase E3A leads to AS pathophysiology in humans remain poorly understood. However, recent efforts have shown promise in restoring functions disrupted in AS mice, renewing hope that an effective treatment strategy can be found.

The 15q11.2 BP1-BP2 microdeletion syndrome: a review

Patients with the 15q11.2 BP1–BP2 microdeletion can present with developmental and language delay, neurobehavioral disturbances and psychiatric problems. Autism, seizures, schizophrenia and mild dysmorphic features are less commonly seen. The 15q11.2 BP1–BP2 microdeletion involving four genes (i.e., TUBGCP5, CYFIP1, NIPA1, NIPA2) is emerging as a recognized syndrome with a prevalence ranging from 0.57%–1.27% of patients presenting for microarray analysis which is a two to four fold increase compared with controls. Review of clinical features from about 200 individuals were grouped into five categories and included developmental (73%) and speech (67%) delays; dysmorphic ears (46%) and palatal anomalies (46%); writing (60%) and reading (57%) difficulties, memory problems (60%) and verbal IQ scores ≤75 (50%); general behavioral problems, unspecified (55%) and abnormal brain imaging (43%). Other clinical features noted but not considered as common were seizures/epilepsy (26%), autism spectrum disorder (27%), attention deficit disorder (ADD)/attention deficit hyperactivity disorder (ADHD) (35%), schizophrenia/paranoid psychosis (20%) and motor delay (42%). Not all individuals with the deletion are clinically affected, yet the collection of findings appear to share biological pathways and presumed genetic mechanisms. Neuropsychiatric and behavior disturbances and mild dysmorphic features are associated with genomic imbalances of the 15q11.2 BP1–BP2 region, including microdeletions, but with an apparent incomplete penetrance and variable expressivity.

Angelman syndrome: review of clinical and molecular aspects

"Angelman syndrome" (AS) is a neurodevelopmental disorder whose main features are intellectual disability, lack of speech, seizures, and a characteristic behavioral profile. The behavioral features of AS include a happy demeanor, easily provoked laughter, short attention span, hypermotoric behavior, mouthing of objects, sleep disturbance, and an affinity for water. Microcephaly and subtle dysmorphic features, as well as ataxia and other movement disturbances, are additional features seen in most affected individuals. AS is due to deficient expression of the ubiquitin protein ligase E3A (UBE3A) gene, which displays paternal imprinting. There are four molecular classes of AS, and some genotype-phenotype correlations have emerged. Much remains to be understood regarding how insufficiency of E6-AP, the protein product of UBE3A, results in the observed neurodevelopmental deficits. Studies of mouse models of AS have implicated UBE3A in experience-dependent synaptic remodeling.