Angelman syndrome without detectable chromosome 15q11-13 anomaly: Clinical study of familial and isolated cases

Research protocol: The initiation, design and establishment of the Global Angelman Syndrome Registry

BACKGROUND

Angelman syndrome (AS) is a rare neurodevelopmental disorder affecting between 1 in 15 000 and 1 in 24 000 individuals. The condition results in severe developmental and expressive language delays, motor impairments and a unique behavioural phenotype consisting of excessive laughter, smiling and sociability. While many studies have contributed knowledge about the causes and natural history of the syndrome, large scale longitudinal studies are required to advance research and therapeutics for this rare syndrome.

METHOD

This article describes the protocol for the Global Angelman Syndrome Registry, and some initial findings. Due to the rarity of AS and the variability in symptom presentation, the registry team will strive for complete case ascertainment. Parents and caregivers will submit data to the registry via a secure internet connection. The registry consists of 10 modules that cover patient demographics; developmental, diagnostic, medical and surgical history, behaviour and development, epilepsy, medications and interventions and sleep.

RESULTS

Since its launch at https://angelmanregistry.info in September 2016, almost 470 individuals with AS have been signed up to the registry worldwide: 59% are from North and South America, 23% are from Europe, 17% are from the Asia Pacific region and 1% are from the Middle East or Africa. The majority of registrants are children, with only 16% aged over 20 years. Most participants indicated a chromosome deletion (76%), with fewer participants indicating a mutation, uniparental disomy or imprinting defect (20%).

CONCLUSION

Findings indicate a need to consider recruitment strategies that target caregivers of older children and adults, and parents and caregivers from non-English speaking backgrounds.

Strain-dependence of the Angelman Syndrome phenotypes in Ube3a maternal deficiency mice

Angelman syndrome (AS) is a genetic neurodevelopmental disorder, most commonly caused by deletion or mutation of the maternal allele of the UBE3A gene, with behavioral phenotypes and seizures as key features. Currently no treatment is available, and therapeutics are often ineffective in controlling AS-associated seizures. Previous publications using the Ube3a maternal deletion model have shown behavioral and seizure susceptibility phenotypes, however findings have been variable and merit characterization of electroencephalographic (EEG) activity. In this study, we extend previous studies comparing the effect of genetic background on the AS phenotype by investigating the behavioral profile, EEG activity, and seizure threshold. AS C57BL/6J mice displayed robust behavioral impairments, spontaneous EEG polyspikes, and increased cortical and hippocampal power primarily driven by delta and theta frequencies. AS 129 mice performed poorly on wire hang and contextual fear conditioning and exhibited a lower seizure threshold and altered spectral power. AS F1 hybrid mice (C57BL/6J × 129) showed milder behavioral impairments, infrequent EEG polyspikes, and fewer spectral power alterations. These findings indicate the effect of common genetic backgrounds on the Ube3a maternal deletion behavioral, EEG, and seizure threshold phenotypes. Our results will inform future studies on the optimal strain for evaluating therapeutics with different AS-like phenotypes.

Genetic disorders associated with postnatal microcephaly

Several genetic disorders are characterized by normal head size at birth, followed by deceleration in head growth resulting in postnatal microcephaly. Among these are classic disorders such as Angelman syndrome and MECP2-related disorder (formerly Rett syndrome), as well as more recently described clinical entities associated with mutations in CASK, CDKL5, CREBBP, and EP300 (Rubinstein-Taybi syndrome), FOXG1, SLC9A6 (Christianson syndrome), and TCF4 (Pitt-Hopkins syndrome). These disorders can be identified clinically by phenotyping across multiple neurodevelopmental and neurobehavioral realms, and enough data are available to recognize these postnatal microcephaly disorders as separate diagnostic entities in their own right. A second diagnostic grouping, comprised of Warburg MICRO syndrome, Cockayne syndrome, and Cerebral-oculo-facial skeletal syndrome, share similar features of somatic growth failure, ophthalmologic, and dysmorphologic features. Many postnatal microcephaly syndromes are caused by mutations in genes important in the regulation of gene expression in the developing forebrain and hindbrain, although important synaptic structural genes also play a role. This is an emerging group of disorders with a fascinating combination of brain malformations, specific epilepsies, movement disorders, and other complex neurobehavioral abnormalities.

Age related change in social behavior in children with Angelman syndrome

We investigated the relationship between age and laughing and smiling in children with Angelman syndrome. Twenty-four children with Angelman syndrome were exposed to three experimentally manipulated conditions: proximity only, restricted social interaction, and social interaction. Children smiled the most in the social interaction condition and the least in the proximity only condition confirming the effect of social interaction on these behaviors. There was a decline in smiling and laughing in the oldest group (13.4-15.9 years) only in the social interaction condition. This trajectory of a decline in resource soliciting behaviors with age is consistent with predictions based on kinship theory.

Experimental functional analysis of aggression in children with Angelman syndrome

BACKGROUND

Kinship theory suggests that genomic imprinting could account for phenotypic behaviors that increase (in the case of Angelman syndrome) or decrease (for Prader-Willi syndrome) the drive to access social resources (adult contact) depending on the imprinting parent-of-origin. Difficult to manage behaviors, such as aggression that is common in Angelman syndrome, could serve the function of increasing social interaction. We hypothesise that the commonly reported aggressive behavior in children with Angelman syndrome will be attention maintained.

METHODS

Experimental functional analysis was carried out with twelve children with Angelman syndrome caused by either a deletion (n=10) or uniparental disomy (n=2). The relative increase and decrease of aggressive behaviors was observed in response to experimentally manipulated levels of adult attention and demand. Laughing and smiling, crying and frowning, and physical initiation with an adult were also measured.

RESULTS

Aggression was seen in ten of the twelve children. One child evidenced a pattern of aggression across conditions consistent with maintenance by attention, three children showed higher levels of aggression during social interaction and two children showed escape motivated aggression.

DISCUSSION

With the exception of one child the results did not confirm the hypothesis. However, the pattern of increased aggression in the high social contact condition combined with evidence of positive affect during this condition suggests aggression may serve to both maintain and initiate social contact and this interpretation is consistent with previous research. The negative results may also have been influenced by the age of the children and the low levels of observed aggression.

The behavioural phenotype of Angelman syndrome

BACKGROUND

The purpose of this review is to examine the notion of a behavioural phenotype for Angelman syndrome and identify methodological and conceptual influences on the accepted presentation.

METHODS

Studies examining the behavioural characteristics associated with Angelman syndrome are reviewed and methodology is described.

RESULTS

Potential bias in the description of the phenotype emerges with the use of case and cohort studies with the absence of comparison groups. A trend in the literature from a direct gene effect to a socially mediated effect on laughter is evident.

CONCLUSION

Evidence for a behavioural phenotype of Angelman syndrome has begun to emerge. However, by adopting the concept of a 'behavioural phenotype', attention may become biased towards the underlying biological basis of the syndrome, with developmental and environmental factors being overlooked.

Behavioral aspects of Angelman syndrome: a case control study

Angelman syndrome (AS) is a rare congenital disorder characterized by impairments in intellectual, neurological and motor functioning and a postulated behavioral profile. This study compared behavioral characteristics of 62 individuals with genetically confirmed AS and 29 individuals with presumed AS from clinical features, with a control group of young persons with intellectual disability (ID) derived from an Australian epidemiological register. Twelve behavioral items from the developmental behavior checklist (DBC) were used for this comparison. The groups were matched for chronological age, gender, and level of ID. In the AS group, significant differences were found for 10 behaviors, with poor attention span and impulsivity being less common, and overactivity/restlessness, chewing or mouthing objects, eating non-food items, gorging food, food fads, fascination for water, hand flapping and sleep disturbance being more common. Interestingly, there was no difference in prevalence of unprovoked laughter. Comparison of the results of the genetically confirmed with the genetically unconfirmed AS cases showed no significant differences between individual behavior prevalence. These findings show that a "behavioral phenotype" of AS can be distinguished from others of similar level of ID, but it is different from that hitherto published. Abnormal food related behaviors, hyperactivity, fascination for water, hand flapping, and sleep disturbance should be included in a "behavioral phenotype" for AS. Apart from hyperactivity, "ADHD-type" behaviors are not more characteristic of AS than in ID generally. Therefore, the Consensus Criteria for the diagnosis of AS need to be reviewed.

Angelman syndrome: is there a characteristic EEG?

Angelman syndrome (AS) is a genetic disorder characterised by severe mental retardation, subtle dysmorphic facial features, a characteristic behavioural phenotype, epileptic seizures and EEG abnormalities. AS can be caused by various genetic mechanisms involving the chromosome 15q11-13 region. Neurophysiological studies report a variety of EEG abnormalities seen in AS patients. The objective of this article was to analyse whether there are characteristic EEG changes in AS, whether this varies with age and what the differential diagnosis is. Most of the authors agree about the existence of three main EEG patterns in AS which may appear in isolation or in various combinations in the same patient. The pattern most frequently observed both in children and in adults has prolonged runs of high amplitude rhythmic 2-3 Hz activity predominantly over the frontal regions with superimposed interictal epileptiform discharges. High amplitude rhythmic 4-6 Hz activity, prominent in the occipital regions, with spikes, which can be facilitated by eye closure, is often seen in children under the age of 12 years. There is no difference in EEG findings in AS patients with or without epileptic seizures. AS patients with a deletion of chromosome 15q11-13 have more prominent EEG abnormalities than patients with other genetic disturbances of the chromosome 15 region. The EEG findings are characteristic of AS when seen in the appropriate clinical context and can help to identify AS patients at an early age when genetic counselling may be particularly important.

Angelman syndrome: a review of clinical and genetic aspects

This paper reviews Angelman syndrome (AS) with regard to the clinical features in childhood and adulthood, epileptic seizures and EEG findings, neuroimaging studies and the present knowledge on the genetic mechanisms underlying this syndrome. Different clinical phenotypes and genotypes of AS are described, including chromosome 15q11-13 deletion, uniparental disomy, methylation imprinting abnormalities and mutations in the UBE3A gene.