Preserved expressive language as a phenotypic determinant of Mosaic Angelman Syndrome

Testing With Intent in Mosaic Conditions: A Case-Based Review

Recent advancements in genetic testing have revealed cases of mosaicism, demonstrating the phenomenon may be more common than once thought. Broadly defined, mosaicism describes the presence of two genotypically different cell lineages within the same organism. This can arise from small mutations or errors in chromosome segregation, as early as in gametes, before or after fertilization. Mosaicism is directly responsible for many conditions that present in a wide range of tissues, with the presence of the mutation or genetic abnormality following a tissue-dependent pattern. This makes it possible for patients to test negative for a condition using a standard tissue sample while harboring the variant in a different tissue. Understanding the timing and mechanisms of mosaic conditions will aid in targeted testing that is more appropriate to identify a pathogenic variant. This targeted testing should reduce the length of a patient's diagnostic odyssey and provide a better understanding of the chances of passing on their variant to their offspring, thereby allowing for more accurate genetic counseling. We illustrate this phenomenon with two cases: one of Pallister-Killian syndrome and the other of tuberous sclerosis complex. Both patients had increased time to diagnosis because of difficulties in identifying genetic variants in tested tissues. Beyond just increased time to diagnosis, we illustrate that mosaic conditions can present as less severe and more variable than the germline condition and how specific germ layers may be affected by the variant. Knowing which germ layers may be affected by the variant can give clinicians a clue as to which tissues may need to be tested to yield the most accurate result.

Typical and atypical neural mechanisms support spoken word processing in Angelman syndrome

Angelman syndrome (AS) is known to affect expressive and receptive communication abilities. This study examined individual differences in neural mechanisms underlying speech processing in children with AS (n = 24, M age = 10.01 years) and typical development (n = 30, M age = 10.82 years) using auditory event-related potentials during passive listening to common English words and novel pseudowords. A group of adults with AS (n = 7, M = 31.78 years) provided data about the upper developmental range. The typically developing group demonstrated the expected more negative amplitudes in response to words than pseudowords within 250-500 ms after stimulus onset at the left temporal scalp region. Children and adults with AS exhibited a similar left-lateralized pattern of word-pseudoword differentiation at temporal and parietal regions, but not the midline parietal memory response for known words observed in the typically developing group, suggesting typical-like word-pseudoword differentiation along with possible alterations in the automatic recall of word meaning. These results have important implications for understanding receptive and expressive communication processes in AS and support the use of auditory neural responses for characterizing individual differences in neurodevelopmental disorders with limited speech.

Atypical presentation of Angelman syndrome with intact expressive language due to low-level mosaicism

BACKGROUND

Angelman syndrome (AS) occurs due to a lack of expression or function of the maternally inherited UBE3A gene. Individuals with AS typically have significant developmental delay, severe speech impairment with absent to minimal verbal language, gait abnormalities including ataxia, and an incongruous happy demeanor. The majority of individuals with AS also have seizures and microcephaly. Some individuals with mosaic AS have been reported to have expressive language and milder levels of developmental delay.

CASE REPORT

We report a male patient presenting with mild to moderate intellectual disability, hyperphagia, obesity, and the ability to communicate verbally. His phenotype was suggestive of Prader-Willi syndrome. However, methylation testing was positive for Angelman syndrome and additional methylation specific multiplex ligation-dependent amplification (MS-MLPA) study revealed low-level mosaicism for AS.

CONCLUSION

A broader phenotypic spectrum should be considered for AS as patients with atypical presentations may otherwise elude diagnosis.

Novel multilocus imprinting disturbances in a child with expressive language delay and intellectual disability

Multilocus imprinting disturbances (MLID) have been associated with up to 12% of patients with Beckwith‐Wiedemann syndrome, Silver‐Russell syndrome, and pseudohypoparathyroidism type 1B (PHP1B). Single‐gene defects affecting components of the subcortical maternal complex (SCMC) have been reported in cases with multilocus hypomethylation defects. We present a patient with speech and language impairment with mild Angelman syndrome (AS) features who demonstrates maternal hypomethylation at 15q11.2 (SNRPN) as well as 11p15.5 (KCNQ1OT1) imprinted loci, but normal methylation at 6q24.2 (PLAGL1), 7p12.1 (GRB10), 7q32.2 (MEST), 11p15.5 (H19), 14q32.2 (MEG3), 19q13.43 (PEG3), and 20q13.32 (GNAS and GNAS‐AS1). The proband also has no copy number nor sequence variants within the AS imprinting center or in UBE3A. Maternal targeted next generation sequencing did not identify any pathogenic variants in ZPF57, NLRP2, NLRP5, NLRP7, KHDC3L, PADI6, TLE6, OOEP, UHRF1 or ZAR1. The presence of very delayed, yet functional speech, behavioral difficulties, EEG abnormalities but without clinical seizures, and normocephaly are consistent with the 15q11.2 hypomethylation defect observed in this patient. To our knowledge, this is the first report of MLID in a patient with mild, likely mosaic, Angelman syndrome.

A multidisciplinary approach and consensus statement to establish standards of care for Angelman syndrome

BACKGROUND

Angelman syndrome (AS) is a rare neurogenetic disorder present in approximately 1/12,000 individuals and characterized by developmental delay, cognitive impairment, motor dysfunction, seizures, gastrointestinal concerns, and abnormal electroencephalographic background. AS is caused by absent expression of the paternally imprinted gene UBE3A in the central nervous system. Disparities in the management of AS are a major problem in preparing for precision therapies and occur even in patients with access to experts and recognized clinics. AS patients receive care based on collective provider experience due to limited evidence-based literature. We present a consensus statement and comprehensive literature review that proposes a standard of care practices for the management of AS at a critical time when therapeutics to alter the natural history of the disease are on the horizon.

METHODS

We compiled the key recognized clinical features of AS based on consensus from a team of specialists managing patients with AS. Working groups were established to address each focus area with committees comprised of providers who manage >5 individuals. Committees developed management guidelines for their area of expertise. These were compiled into a final document to provide a framework for standardizing management. Evidence from the medical literature was also comprehensively reviewed.

RESULTS

Areas covered by working groups in the consensus document include genetics, developmental medicine, psychology, general health concerns, neurology (including movement disorders), sleep, psychiatry, orthopedics, ophthalmology, communication, early intervention and therapies, and caregiver health. Working groups created frameworks, including flowcharts and tables, to help with quick access for providers. Data from the literature were incorporated to ensure providers had review of experiential versus evidence-based care guidelines.

CONCLUSION

Standards of care in the management of AS are keys to ensure optimal care at a critical time when new disease-modifying therapies are emerging. This document is a framework for providers of all familiarity levels.

Epilepsy and Molecular Phenotype Affect the Neurodevelopment of Pediatric Angelman Syndrome Patients in China

OBJECTIVE

This study investigated the mental development of children with Angelman syndrome (AS) in China and evaluated the relationship between neurodevelopment and molecular subtype, age, epilepsy, and sex using the Chinese version of the Griffith Mental Development Scale (GMDS-C) to provide detailed baseline data regarding neurodevelopment with AS in China.

METHODS

Participants were recruited from the AS Natural History Study. The GMDS-C was used to evaluate all participants' mental age and developmental quotients. The general quotient (GQ) and quotients of five subscales (sports, personal-social, auditory language, eye-hand coordination, and comprehensive performance) were calculated.

RESULTS

A total of 119 children (average age: 42.12 months; range, 7.5-95.5 months) with a genetic diagnosis of AS were enrolled. The median GQ score of the GMDS was 29.6 points (95% confidence interval, 28.6-33.25). The children had relatively good locomotor and personal-social skills but poor language skills. Overall, 89% (106/119) had mental ages younger than 24 months for all five subscales. The non-deletion group (i.e., without deletion in chromosome 15q11-13) had higher GQs and locomotor, personal-social, and performance subscale quotients. The GQ was significantly different among the three age subgroups and significantly correlated with age. Compared with the non-epilepsy group, the epilepsy group had lower GQs and lower quotients for the locomotor, personal-social, speech, language, and eye-hand coordination subscales.

CONCLUSION

Children with AS in China experience severe neurodevelopmental deterioration. In addition to age, molecular subtypes and the onset of seizures may also correlate with these patients' intellectual development. The GMDS-C is an accurate tool that can assess the clinical characteristics of AS. The data of this study can be used as baseline data for clinical trials performed to evaluate drug development or other AS treatment development.

Nutritional Formulation for Patients with Angelman Syndrome: A Randomized, Double-Blind, Placebo-Controlled Study of Exogenous Ketones

BACKGROUND

Angelman syndrome (AS) patients often respond to low glycemic index therapy to manage refractory seizures. These diets significantly affect quality of life and are challenging to implement. These formulations may have benefits in AS even in the absence of biomarkers suggesting ketosis.

OBJECTIVES

We aimed to compare an exogenous medical food ketone formulation (KF) with placebo for the dietary management of AS.

METHODS

This randomized, double-blind, placebo-controlled, crossover clinical trial was conducted in an academic center from 15 November, 2018 to 6 January, 2020. Thirteen participants with molecularly confirmed AS aged 4-11 y met the criteria and completed the 16-wk study. The study consisted of four 4-wk phases: a baseline phase, a blinded KF or placebo phase, a washout phase, and the crossover phase with alternate blinded KF or placebo. Primary outcomes were safety and tolerability rated by retention in the study and adherence to the formulation. Additional secondary outcomes of safety in this nonverbal population included blood chemistry, gastrointestinal health, seizure burden, cortical irritability, cognition, mobility, sleep, and developmental staging.

RESULTS

Data were compared between the baseline, KF, and placebo epochs. One participant exited the trial owing to difficulty consuming the formulation. Adverse events included an increase in cholesterol in 1 subject when consuming KF and a decrease in albumin in 1 subject when consuming placebo. Stool consistency improved with KF consumption, from 6.04 ± 1.61 at baseline and 6.35 ± 1.55 during placebo to 4.54 ± 1.19 during KF (P = 0.0027). Electroencephalograph trends showed a decrease in Δ frequency power during the KF arm and event-related potentials suggested a change in the frontal memory response. Vineland-3 showed improved fine motor skills in the KF arm.

CONCLUSIONS

The exogenous KF appears safe. More data are needed to determine the utility of exogenous ketones as a nutritional approach in children with AS.This trial was registered at clinicaltrials.gov as NCT03644693.

Communication-related assessments in an Angelman syndrome mouse model

INTRODUCTION

Angelman syndrome (AS) is a neurodevelopmental disorder characterized by motor deficits, seizures, some autistic-like behaviors, and severe impairment of speech. A dysfunction of the maternally imprinted UBE3A gene, coupled with a functional yet silenced paternal copy, results in AS. Although studies of transgenic mouse models have revealed a great deal about neural populations and rescue timeframes for specific features of AS, these studies have largely failed to examine intermediate phenotypes that contribute to the profound communicative disabilities associated with AS.

METHODS

Here, we use a variety of tasks, including assessments of rapid auditory processing and social communication. Expressive vocalizations were directly assessed and correlated against other core behavioral measures (motor, social, acoustic perception) to model putative influences on communication.

RESULTS

AS mice displayed the characteristic phenotypes associated with Angelman syndrome (i.e., social and motor deficits), as well as marginal enhancements in rapid auditory processing ability. Our characterization of adult ultrasonic vocalizations further showed that AS mice produce fewer vocalizations and vocalized for a shorter amount of time when compared to controls. Additionally, a strong correlation between motor indices and ultrasonic vocalization output was shown, suggesting that the motor impairments in AS may contribute heavily to communication impairments.

CONCLUSION

In summary, the combination of motor deficits, social impairment, marginal rapid auditory enhancements, and altered ultrasonic vocalizations reported in a mouse model of AS clearly parallel the human symptoms of the disorder. This mouse model offers a novel route to interrogate the underlying genetic, physiologic, and behavioral influences on the under-studied topic of impaired communication in AS.

Imprinting disorders in humans: a review

PURPOSE OF REVIEW

Mammals have two complete sets of chromosomes, one from each parent with equal autosomal gene expression. Less than one percentage of human genes are imprinted or show expression from only one parent without changing gene structure, usually by DNA methylation, but reversible in gametogenesis. Many imprinted genes affect fetal growth and development accounting for several human disorders reviewed in this report.

RECENT FINDINGS

Disorders include Prader-Willi and Angelman syndromes, the first examples of imprinting errors in humans, chromosome 15q11.2-q13.3 duplication, Silver-Russell syndrome, Beckwith-Weidemann syndrome, GNAS gene-related inactivation disorders (e.g. Albright hereditary osteodystrophy), uniparental chromosome 14 disomy, chromosome 6q24-related transient neonatal diabetes mellitus, parent of origin effects in 15q11.2 BP1-BP2 deletion (Burnside-Butler) syndrome and 15q11-q13 single gene imprinted disorders.

SUMMARY

Periconceptional and intrauterine life can be influenced by environmental factors and nutrition impacting DNA methylation. This process not only alters development of the fetus, but pregnancy complications may result from large fetal size. Epigenetic processes control imprinted gene functions and regulation with susceptibility to diseases as described. A better understanding of these processes will impact on care and treatment of affected individuals.

Chromosome 15 Imprinting Disorders: Genetic Laboratory Methodology and Approaches

Chromosome 15 imprinting disorders include Prader-Willi (PWS) and Angelman (AS) syndromes, which are caused by absent expression from the paternal and maternal alleles in the chromosome 15q11. 2-q13 region, respectively. In addition, chromosome 15q duplication caused by the presence of at least one additional maternally derived copy of the 15q11.2-q13 region can lead to seizures, cognitive and behavioral problems. We focus on PWS and AS in the report, and expand the discussion of clinical care and description with genetic testing to include high-resolution studies to more specifically characterize the molecular mechanisms of disease. The importance of early diagnosis with the necessity for accurate molecular characterization through a step-wise algorithm is emphasized in an era of targeted therapeutic interventions. We present a flowchart to aid in ordering specialized genetic testing as several methods are available for patients presenting with features of PWS and/or AS.

Prenatal treatment path for angelman syndrome and other neurodevelopmental disorders

Angelman syndrome (AS) is a rare neurodevelopmental disorder caused by mutation or deletion of the maternally inherited UBE3A allele. These pathogenic mutations lead to loss of maternal UBE3A expression in neurons. Antisense oligonucleotides and gene therapies are in development, which activate the intact but epigenetically silenced paternal UBE3A allele. Preclinical studies indicate that treating during the prenatal period could greatly reduce the severity of symptoms or prevent AS from developing. Genetic tests can detect the chromosome 15q11-q13 deletion that is the most common cause of AS. New, highly sensitive noninvasive prenatal tests that take advantage of single-cell genome sequencing technologies are expected to enter the clinic in the coming years and make early genetic diagnosis of AS more common. Efforts are needed to identify fetuses and newborns with maternal 15q11-q13 deletions and to phenotype these babies relative to neurotypical controls. Clinical and parent observations suggest AS symptoms are detectable in infants, including reports of problems with feeding and motor function. Quantitative phenotypes in the 0- to 1-year age range will permit a more rapid assessment of efficacy when future treatments are administered prenatally or shortly after birth. Although prenatal therapies are currently not available for AS, prenatal testing combined with prenatal treatment has the potential to revolutionize how clinicians detect and treat babies before they are symptomatic. This pioneering prenatal treatment path for AS will lay the foundation for treating other syndromic neurodevelopmental disorders. Autism Res 2020, 13: 11-17. © 2019 International Society for Autism Research, Wiley Periodicals, Inc. LAY SUMMARY: Prenatal treatment could benefit expectant parents whose babies test positive for the chromosome microdeletion that causes Angelman syndrome (AS). Prenatal treatment is predicted to have better outcomes than treating after symptoms develop and may even prevent AS altogether. This approach could generally be applied to the treatment of other syndromic neurodevelopmental disorders.

Preserved expressive language as a phenotypic determinant of Mosaic Angelman Syndrome

Background

Angelman Syndrome (AS) is a neurodevelopmental disorder with core features of intellectual disability, speech impairment, movement disorders, and a unique behavioral profile. Typically, AS results from absent maternal expression of UBE3A, but some individuals have imprinting defects in a portion of their cells. These individuals are mosaic for normal and defective UBE3A expression, resulting in mosaic AS (mAS) with a partial loss of gene expression.

Methods

This study aims to contrast the mAS phenotype to that of AS. Clinical characteristics of mAS were obtained from a parental survey of 22 mAS patients and from the Angelman Natural History study. These were contrasted with those of AS using historical data.

Results

Developmental delay was present in nearly all mAS patients, whereas the core features of AS were reported in less than 40%. While language and ability to manage activities of daily living were markedly improved over that expected in AS, mAS patients demonstrated a high incidence of behavioral challenges.

Conclusion

Clinical work‐up of an individual with developmental delay, hyperactivity, anxiety, and an uncharacteristically happy demeanor should prompt methylation studies to rule out mAS. We expand the phenotypic spectrum of AS to include features that overlap with Prader‐Willi such as hyperphagia.