Long-standing fever and Angelman syndrome: report of two cases

An 8-month-old girl and a 20-month-old boy who presented with motor and developmental delay and long-standing fever are presented. The patients were diagnosed as Angelman syndrome with fluorescence in situ hybridization (FISH) analysis. Despite extensive clinical and laboratory examinations, no inflammatory or infectious origin for the fever was found. It was considered that the long-standing fever observed in these cases was due to hypothalamic dysfunction for thermoregulation.

Bone mineral density in angelman syndrome

Our aim was to evaluate bone mineral densitometry in patients with Angelman syndrome with or without antiepileptic therapy. Eighteen patients (9 females, 9 males), aged 4.0-24.3 years (mean age, 10.1 years), and two control groups consisting of 18 epileptic and 24 healthy patients, underwent dual-energy X-ray absorptiometry at the lumbar spine (L(1)-L(4)), and z score was evaluated for each patient; the t score was considered for patients aged > or = 18 years. Abnormal bone mineral density was present in 8/18 (44.5%) of patients with Angelman syndrome, in 7/18 (38.9%) of the epileptic group, and in none of the healthy controls. Furthermore, a significant difference regarding mean age of patients (6 versus 15 years, P = 0.008, by Fisher exact test), and mean length of drug treatment (3.5 versus 11.1 years, P = 0.005 by Fisher exact test), appeared in the group with Angelman syndrome. Most of these patients (94.4%) were receiving antiepileptic drugs, mainly valproic acid, for many years. In conclusion, our study revealed osteopenia in almost half the children and young patients with Angelman syndrome. Dual-energy X-ray absorptiometry should be performed in all patients with Angelman syndrome, particularly if they are treated with antiepileptic drugs.

Angelman syndrome revisited

OBJECTIVES

Angelman syndrome (AS) is characterized by severe mental retardation, epilepsy, absent speech, dysmorphic facial features, and a characteristic behavioral phenotype. It is caused by deficiency of gene expression from maternally derived chromosome 15q11-q13.

STUDY DESIGN

The authors present the clinical picture of 9 children (median age, 4.9 years; range, 1 to 10 years) with confirmed Angelman syndrome. The patients complied with the international consensus criteria for AS and were consecutively investigated for psychomotor development, epilepsy, and electroencephalogram (EEG) profiles.

RESULTS

The median age at diagnosis was 3.9 years. The motor milestones were delayed. Median developmental quotient level was 26. All patients but 1 experienced predominantly polymorphic seizures. In 4 cases, the epilepsy was refractory to treatment. The EEG of all patients displayed an abnormal sleep pattern and generalized abnormalities, with a maximum over the posterior areas.

CONCLUSIONS

Milder or less typical phenotypes of AS may remain undiagnosed, leading to an overall underdiagnosis of the disease. The EEG shows no clear relation to genotype, clinical picture, or to the presence and severity of epilepsy. AS should be considered in the differential diagnosis of children with severe cryptogenic epilepsy and a characteristic configuration of clinical features.

Sensory Processing Patterns in Persons With Angelman Syndrome

OBJECTIVE

Research examining sensory processing patterns in persons with Angelman syndrome is nonexistent despite anecdotal evidence and clinical diagnostic criteria that may reflect these features. The goal of this study was to better characterize sensory processing patterns in persons with Angelman syndrome.

METHOD

Parents of 340 persons with Angelman syndrome between 3 and 22 years of age completed a standardized measure of sensory processing, the Sensory Experiences Questionnaire.

RESULTS

Results confirmed a high degree and variety of sensory processing abnormalities in persons with Angelman syndrome. These problems were most prominent in the areas of hypo-responsiveness to tactile and vestibular input, consistent with reports of sensory seeking behaviors in this population. Sensory processing deficits were not related to gender, seizure disorder, or genetic subtype. However, some behaviors were correlated with age.

CONCLUSION

This study provides the first systematic description of sensory processing abnormalities in a large sample of persons with Angelman syndrome. Considerations for enhancing occupational performance and social participation in this population through occupational therapy interventions are discussed.

Pharmacologic evidence for abnormal thalamocortical functioning in GABA receptor beta3 subunit-deficient mice, a model of Angelman syndrome

PURPOSE

gamma-Aminobutyric acid receptor (GABA(A)r) subunit beta3-deficient mice model Angelman syndrome by displaying impaired learning, abnormal EEG with interictal spikes and slowing, myoclonus, and convulsions. The beta3-subunit deficiency causes a failure of intrathalamic reticular nucleus inhibition, leading to abnormally synchronized thalamocortical oscillations. We postulated that this pathophysiology underlies the abnormal cortical EEG and triggers interictal spikes and seizures, but extrathalamic regions also contribute to interictal spikes and seizures, so that the EEG slowing should reveal an absence-like response profile, whereas spikes and seizures have dual responsiveness to absence and partial-seizure drugs.

METHODS

Recording electrodes were implanted over the parietal cortices of wild-type, heterozygotes, and homozygous null mice. In each experiment, EEG was recorded for 45 min, either drug or vehicle administered, and EEG recorded for another 3 h. Each EEG was scored for slow-wave activity, interictal spikes, and seizures by a reader blinded to treatments.

RESULTS

Interictal spiking and percentage of time in EEG slowing in heterozygotes were increased by the proabsence drug baclofen (GABA(B)-receptor agonist), whereas CGP 35348 (GABA(B)-receptor antagonist) had the opposite effect. The antiabsence drug ethosuximide markedly suppressed EEG slowing and interictal spiking in heterozygote and null mice. Broad-spectrum clonazepam and valproate were more effective on interictal spiking than on EEG slowing, and fosphenytoin suppressed only interictal spiking.

CONCLUSIONS

The results suggest that this model of Angelman syndrome, although not expressing typical absence seizures, is characterized by hypersynchronous thalamocortical oscillations that possess absence-like pharmacologic responsiveness and promote EEG slowing, interictal spikes, and convulsive seizures.

Sleep disturbances in Ube3a maternal-deficient mice modeling Angelman syndrome

BACKGROUND

Angelman syndrome (AS) is a severe neurodevelopmental disorder with electroencephalographic (EEG) abnormalities and sleep disturbances. It results from lack of the functional maternal allele of UBE3A, which encodes a ubiquitin-protein ligase. Different mechanisms of UBE3A inactivation correlate with clinical phenotypes of varying severity; the majority of cases of AS are due to a de novo maternal deletion of the 15q11-q13 region.

METHODS

Ube3a maternal-deficient mice (Ube3a m-/p+) were generated in a C57Bl/6J background. This study compares cortical EEG and architecture of the sleep-waking cycle in adult Ube3a m-/p+ mice compared with those of age-matched WT (m+/p+) mice, under baseline conditions or after 4-h sleep deprivation (SD).

RESULTS

Ube3a m-/p+ mice exhibited: reduced slow-wave sleep (SWS) amount with increase waking (W) at the dark/light transitions; increased SWS and W episode numbers; and deterioration of paradoxical sleep (PS) over 24 h [amount: -44%; episode duration: -46%; episode number: -40%; theta peak frequency (TPF) acceleration: 7.6 Hz vs. 7.0 Hz in WT mice]. Characteristic paroxysmal EEG discharges are observed during W and SWS associated with synchronous muscle bursting activity during hypoactive W. During the recovery period following SD, Ube3a m-/p+ mice exhibited no rebound either in slow-wave activity (+89% in WT) or in delta-power spectra but a slight rebound in PS amount (+20%).

CONCLUSIONS

These data validate the mouse model produced by null mutation of the maternal Ube3a gene and provide useful results to investigate and better understand the molecular basis of sleep disturbances in AS patients.

Atypical cases of Angelman syndrome

Angelman syndrome (AS) is a profound disorder notable for mental retardation and severe language deficits that results from lack of function of the maternally inherited copy of the UBE3A gene. Chromosome deletions of 15q11q13, paternal uniparental disomy (UPD), UBE3A gene mutations, and imprinting center defects are all commonly recognized mechanisms that disrupt the function of the maternal copy of the UBE3A gene. We report here two patients with different atypical etiologies of AS. The first patient is a 3-year-old boy with global developmental delay, severe speech deficits, seizures, and very happy disposition. Southern blot analysis for the maternal and paternal chromosome 15 methylation products showed a mosaic methylation pattern, suggesting an imprinting center defect. The second patient is a 4(1/2)-year-old boy with global developmental delay, no expressive language, microcephaly, seizures, and ataxic gait. Array-based comparative genomic hybridization (CGH) demonstrated a loss in copy number for two overlapping clones encompassing the UBE3A gene, indicating a partial deletion within UBE3A. His mother, who was adopted, had an identical pattern, suggesting that her deletion was probably on her paternally imprinted allele. These patients illustrate the expanding spectrum of molecular findings in AS, reinforce the need to maintain suspicion when clinical features suggest AS but initial testing is normal, and show the power of CGH as a tool to uncover partial UBE3A deletions.

[Medical and behavioural aspects of Angelman syndrome]

INTRODUCTION

Angelman syndrome (AS) is a genetically-based disorder that is characterised by a physical and behavioural phenotype. Additionally, it presents a number of different systemic conditions that must also be taken into account. To evaluate the symptomatic spectrum of AS, we sought the aid of families linked to AS associations by sending them a questionnaire designed to investigate the clinical characteristics of AS.

PATIENTS AND METHODS

The families were sent a questionnaire aimed at determining the medical and behavioural characteristics of AS. Results from 68 patients were analysed.

RESULTS

The mean age at diagnosis was 4.8 years. The first symptoms that called parents' attention were feeding problems, followed by gastroesophageal reflux and hypotonia. The mean age at which patients were capable of maintaining a sitting posture was 18 months, while autonomous walking was not achieved until 43 months. Epilepsy, which was present in 91% of cases, began with febrile seizures in 55% of patients. In this study we found that a high percentage of patients with AS have a high resistance to pain (67%), a very common symptom in Prader-Willi syndrome, but little known in AS.

CONCLUSIONS

This study offers a wide array of information about the clinical spectrum of AS obtained from an extensive populational sample. Some highly prevalent clinical aspects, such as the relative insensitivity to pain, have not been reported in previous publications as a symptom that is typical of AS.

Asystole during outbursts of laughing in a child with Angelman syndrome

A girl with Angelman syndrome had recurrent episodes of ventricular asystole and syncope caused by severe vagal hypertonia during outbursts of laughing. After intravenous administration of atropine, laughing no longer induced asystole or syncope. The vast majority of patients with Angelman syndrome have seizures. Since hypoxia associated with asystole can provoke convulsions, we suggest electrocardiographic evaluation of Angelman patients with symptomatic bradycardia, loss of consciousness, or convulsions related to laughing.

Angelman syndrome: uniparental paternal disomy 15 determines mild epilepsy, but has no influence on EEG patterns

The authors describe the electroclinical phenotype of four patients with Angelman syndrome (AS) determined by its rarest genetic mechanism-uniparental disomy (UPD). The analysis of ours and published patients showed that in UPD, when epilepsy occurred, it was milder compared to patients with deletion, although a suggestive EEG was observed in most patients. We found that UPD patients do not completely fit the scenario delineated for AS, suggesting that patients determined by different mechanisms should be distinctly addressed, for a better understanding of this syndrome.

Sleep breathing and periodic leg movement pattern in Angelman Syndrome: a polysomnographic study

OBJECTIVE

The aim of this study was to evaluate the sleep breathing patterns and to detect the eventual presence of periodic leg movements (PLMs) in patients affected by Angelman syndrome (AS).

METHODS

Ten children with AS were recruited to participate in the study; the clinical diagnosis was confirmed by the genetic analysis (maternal 15q deletion, uniparental paternal disomy, or mutation of the UBE3A gene). All patients but two had presented epileptic seizures. Two age-matched groups of patients with mental retardation (MR) associated (MRE+) or not (MRE-) to epilepsy were used as control groups. All subjects underwent one polysomnographic recording, after one adaptation night. Sleep stages were scored according to standard criteria slightly modified in order to take into account the specific EEG patterns of AS, also the apnea/hypopnea index (AHI) was quantified; PLMs were identified and the PLM index (PLMI) was computed. The statistical analysis was carried out by means of the one-way ANOVA, followed by the Fisher LSD post-hoc test, when appropriate, and by means of the linear correlation coefficient between AHI and PLMI.

RESULTS

Sleep macrostructure showed only few significant differences between children with AS and the other two groups of subjects: AS patients showed higher percentage of wakefulness after sleep onset and sleep onset latency; moreover, the percentage of REM sleep was reduced in AS and in MRE+ subjects. A tendency for AS subjects to present a higher PLMI than the other two groups was also found. AHI >5 was found in 30% of AS subjects, in 30.8% of MRE+, and only in 20% of MRE- patients (chi(2) = 2.359, NS); 70% of AS patients, 38.5% of MRE+, and 46.7% of MRE- subjects had PLMI >5 (chi(2) = 3.088, NS).

CONCLUSIONS

These results confirm our previous questionnaire-based findings of a high prevalence of sleep breathing disorder and important PLMs in AS and allow us to hypothesize that epilepsy, rather than mental retardation, might exacerbate these sleep disorders.

SIGNIFICANCE

Sleep breathing disorder and PLMs might contribute to the cognitive impairment and to the worsening of life quality of subjects with AS and with MR (mostly those with epilepsy). Therefore, our findings suggest the need to explore these sleep disorders in children affected by MR and to set up a correct treatment.

Notched Delta, Phenotype, and Angelman Syndrome

The notched delta pattern is one of the characteristic EEG features found in Angelman syndrome patients. The purpose of this study was to evaluate the possibility of using the notched delta pattern as a detection tool for Angelman syndrome patients by analyzing its frequency in a tertiary care pediatric center, its specificity for Angelman syndrome, and the age at which it was observed. The authors performed a retrospective review of the video-EEG recordings of all the patients who had either the notched delta pattern or a phenotype consistent with Angelman syndrome. The notched delta was observed in 1.1% of all the EEGs performed. Its specificity for Angelman syndrome was evaluated at 38%. The youngest age at which it was noted was 14 months. The results indicate that the notched delta pattern is relatively rare, but more frequent than expected, and is easily recognizable. The pattern was observed not only in Angelman syndrome patients, but also in children with a spectrum of conditions wider than reported. It is a powerful detection tool for Angelman syndrome when correlated to a suggestive phenotype, and the association of these features should raise suspicion for Angelman syndrome in both infants and adults.

Evolution of seizures and electroencephalographical findings in 23 cases of deletion type Angelman syndrome

Angelman syndrome (AS) is a genetic disorder with characteristic clinical and EEG findings. We report here the results of long-term follow-up studies on the epileptic seizures and EEG findings of 23 cases of deletion type AS confirmed by FISH analysis, including seven cases previously reported by Matsumoto et al. in 1992. The age at last follow-up in 23 patients was from 1 to 37 years of age (average: 18.0 years), with 10 patients (43.5%) in their 20s, and five over 30. Epileptic seizures were seen in all patients, and the age at seizure onset ranged from 3 to 50 months (average: 21.7 months). Status epilepticus was seen in 11 patients (47.8%). The percentages of cases seizure-free for more than 3 years were 25% (4/16) at 10 years of age, 70% (7/10) at 20, and 80% (4/5) at 30. The EEG findings were classified into six patterns according to the previous report: N (no spike, including focal slow waves), HVS (diffuse high-voltage slow bursts with or without spikes), F (focal spikes or multifocal spikes), S (diffuse spike and waves), C (continuous diffuse spike and waves), Hy (hypsarrythmia or hypsarrhythmia like waves). Hy was noted at ages 0-2 years in two cases. C was observed from the ages 2 to 15 years, being most frequently noted at 3-6 years of age, and it was never seen after 16 years of age. S was observed from ages 1 to 21 years. F was seen from 2 to 21 years of age, and most frequently during the ages of 2-7 years. HVS was seen from 0 years, and still remained after the age of 20. After 22 years of age, all patients showed N pattern including focal slow waves. One of the two patients who had bilateral frontal dominant delta slow waves in their 30s, had a recent seizure. Even if the spikes disappear with age, when bi-frontal focal slow waves remain, seizures may occur even in patients over 30.

Uniparental disomy and imprinting defects in Japanese patients with Angelman syndrome

We examined 54 patients with deletion-negative Angelman syndrome (AS) using DNA methylation testing and microsatellite polymorphism analysis, and identified three patients with paternal uniparental disomy (UPD) and seven patients with imprinting defects (ID). The three patients with UPD were shown to have paternal isodisomy 15, which we hypothesized to have arisen from duplication of chromosome 15. Two of the patients with ID were siblings and carried microdeletions of the imprinting center (IC), while the remaining five patients had no evidence of deletions and represented sporadic cases. Two of the three patients with UPD and two of the seven patients with ID had not developed seizures. The only patients displaying microcephaly were those with ID who had microdeletions at the IC. These data support the previous findings that indicate that patients with UPD and ID may have a milder phenotype of AS.

GABAA receptor beta3 subunit gene-deficient heterozygous mice show parent-of-origin and gender-related differences in beta3 subunit levels, EEG, and behavior

The homozygous knockout mouse for the beta3 subunit of the GABAA receptor has been proposed as a model for the neurodevelopmental disorder, Angelman syndrome, based on phenotypic similarities of craniofacial abnormalities, cognitive defects, hyperactivity, motor incoordination, disturbed rest-activity cycles, and epilepsy. Since most children with Angelman syndrome are autosomal heterozygotes of maternal origin, apparently through genomic imprinting, we used gabrb3-deficient heterozygote mice of defined parental origin to investigate whether this phenotype is also maternally imprinted in mouse. Whole brain extracts showed greatly reduced beta3 subunit levels in male mice of maternal origin but not in male mice of paternal origin. Females of both parental origin showed greatly reduced beta3 subunit levels. Heterozygotes did not exhibit hyperactive circling behavior, convulsions, or electrographically recorded seizures. EEGs showed qualitative differences among heterozygotes, with male mice of maternal origin demonstrating more abnormalities including increased theta activity. Ethosuximide inhibited theta bursts, suggesting an alteration in the thalamocortical relay. Carbamazepine induced EEG slowing in males and EEG acceleration in females, with a larger effect in paternal-origin heterozygotes. Evidence thus suggests both parent-of-origin and gender-related components in developmental regulation of beta3 expression, in particular, that the maternally-derived male heterozygote may carry a developmental modification resulting in less beta3 protein, which may reflect partial genomic imprinting of the gabrb3 gene in mice.

Another patient with MECP2 mutation without classic Rett syndrome phenotype

Rett syndrome and Angelman syndrome are two neurodevelopmental disorders characterized by partial overlapping features. Rett syndrome is frequently caused by a mutation in methyl-CpG-binding protein (MECP2) gene, localized on chromosome Xq28, whereas Angelman syndrome is frequently caused by different genetic anomalies at chromosome 15q11-q13 (deletions, uniparental disomy, imprinting center mutations, ubiquitin E3 ligase [UBE3A] gene mutations). Recently, some patients with a clinical diagnosis of Angelman syndrome were found to have a mutation in MECP2 gene. This report describes another patient with an Angelman-like phenotype and with an MECP2 mutation.

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.

Electroclinical characteristics of seizures-comparing Prader--Willi syndrome with Angelman syndrome

Prader-Willi syndrome (PWS) and Angelman syndrome (AS) are two clinically distinct neurobehavioral syndromes that are caused by deficiency of gene expression from paternally or maternally derived homologues on chromosome 15q11-q13, respectively. Clinical and genetic heterogeneities are common in both syndromes and they are now regarded as 'sister genetic imprinting syndromes'. This study aimed to describe and compare the electroclinical characteristics of seizures between PWS and AS, and to try to explore the possible mechanisms of epileptogenesis in these two syndromes. Fifty patients with genetically documented PWS and 18 patients with a putative diagnosis of AS were included in this study. These patients were diagnosed on the basis of characteristic physical findings and their neurobehavioral phenotype, as well as cytogenetic and molecular studies. Epileptic seizures were present in 16 of 18 patients with AS, but in only eight of 50 patients with PWS. Using electroencephalography (EEG), the most characteristic findings for AS were rhythmic 2-3 Hz delta waves of high-amplitude that were maximal over the frontal regions, and 3-4 Hz spikes and sharp wave runs posteriorly. These were never seen in PWS. Patients with AS had a much higher incidence of seizures with characteristic EEG findings, similar to those seen in mice that are deficient in a single gene (UBE3A) that displays regional brain-specific imprinting in humans and mice. In this series, cases with no detectable cytogenetic or molecular defect at the AS locus displayed similar AS phenotype, seizure severity and EEG abnormalities compared to those with such a defect. Thus, the UBE3A gene is presumed to be potentially involved in the epileptogenesis of AS. It is also possible that UBE3A and another gene located nearby, gamma-aminobutyric receptorbeta3 subunit, may interact in some way, and result in the severe epilepsy seen with AS. Some patients with PWS and AS share the common EEG features of persistent high-amplitude 4-6 Hz activity in recordings during sleep, and while awake. The significance of such EEG findings needs further experience to clarity.

Fast cerebellar oscillation associated with ataxia in a mouse model of angelman syndrome

Ataxia may result from various cerebellar cortex dysfunctions. It is included in the diagnostic criteria of Angelman syndrome, a human neurogenetic condition. In order to better understand the cerebellar dysfunction in this condition, we recorded in vivo cerebellar activity in a mouse model of Angelman syndrome produced by null mutation of the maternal Ube3a gene. We found fast oscillation (approximately 160 Hz) in the cerebellar cortex sustained by abnormally increased Purkinje cell firing rate and rhythmicity. This oscillation is inhibited by sensory stimulation and gap junction or GABA(A) receptor blockers. A physiologically similar oscillation was previously found in mice lacking calcium-binding proteins that also present ataxia, but never in wild-type mice. We propose that fast oscillation in the cerebellar cortex is implicated in the cerebellar symptomatology of Angelman syndrome.

From Electrophysiology to Chromatin: A Bottom-Up Approach to Angelman Syndrome

Angelman syndrome is one of the most studied human diseases related to a gene that is expressed on the maternal chromosome only in at least some brain cells. It is caused by inactivation of the UBE3A gene in the brain due to various abnormalities of the 15q11-q13 chromosome inherited from the mother. It is characterized by severe developmental delay, seizures, virtual absence of speech, motor impairment, and a particular behavioral phenotype. Studies of cortical, electromyographic and cerebellar electrophysiology in patients with Angelman syndrome and a mouse model revealed unique rhythmic neurophysiological activities in the cerebral cortex, cerebellar cortex, and muscles. The oscillatory patterns may be linked to molecular pathophysiology of the syndrome involving dysregulation of synaptic neurotransmission through UBE3A-related modulation of functional GABAA receptor complexes.

Phenotypic variability in Angelman syndrome: comparison among different deletion classes and between deletion and UPD subjects

Angelman syndrome (AS) can result from either a 15q11-q13 deletion (del), paternal uniparental disomy (UPD), imprinting, or UBE3A mutations. Here, we describe the phenotypic and behavioral variability detected in 49 patients with different classes of deletions and nine patients with UPD. Diagnosis was made by methylation pattern analysis of exon 1 of the SNRPN-SNURF gene and by microsatellite profiling of loci within and outside the 15q11-q13 region. There were no major phenotypic differences between the two main classes (BP1-BP3; BP2-BP3) of AS deletion patients, except for the absence of vocalization, more prevalent in patients with BP1-BP3 deletions, and for the age of sitting without support, which was lower in patients with BP2-BP3 deletions. Our data suggest that gene deletions (NIPA1, NIPA2, CYF1P1, GCP5) mapped to the region between breakpoints BP1 and BP2 may be involved in the severity of speech impairment, since all BP1-BP3 deletion patients showed complete absence of vocalization, while 38.1% of the BP2-BP3 deletion patients were able to pronounce syllabic sounds, with doubtful meaning. Compared to UPD patients, deletion patients presented a higher incidence of swallowing disorders (73.9% del x 22.2% UPD) and hypotonia (73.3% del x 28.57% UPD). In addition, children with UPD showed better physical growth, fewer or no seizures, a lower incidence of microcephaly, less ataxia and higher cognitive skills. As a consequence of their milder or less typical phenotype, AS may remain undiagnosed, leading to an overall underdiagnosis of the disease.

Somatic mosaicism in patients with Angelman syndrome and an imprinting defect

Angelman syndrome is a neurogenetic disorder caused by the loss of function of the imprinted UBE3A gene in 15q11-q13. In a small group of patients, the disease is due to an imprinting defect (ID) that silences the maternal UBE3A allele. The presence of a faint maternal band detected by methylation-specific PCR analysis of the SNURF-SNRPN locus in approximately one-third of patients who have an ID but no imprinting center deletion suggested that these patients are mosaics of ID cells and normal cells. In two patients studied, somatic mosaicism was proven by molecular and cellular cloning, respectively. X inactivation studies of cloned fibroblasts from one patient suggest that ID occurred before the blastocyst stage. To quantify the degree of mosaicism, we developed a novel quantitative methylation assay based on real-time PCR. In 24 patients tested, the percentage of normal cells ranged from <1% to 40%. Regression analysis suggests that patients with a higher percentage of normally methylated cells tend to have milder clinical symptoms than patients with a lower percentage. In conclusion, we suggest that the role of mosaic imprinting defects in mental retardation is underestimated.

Postural rhythmic muscle bursting activity in Angelman syndrome

Postural impairment is one of the most consistent features of Angelman syndrome. Using multiple-channel electromyography, we studied a lower limb and an upper limb isometric postural task in 14 patients with Angelman syndrome and 18 unimpaired control subjects. Both tasks were associated with synchronous bursts of activity at frequencies of 6-8 s(-1) in all recorded muscles in all patients with Angelman syndrome and none of the control subjects. This pattern was not altered by extra-loading. Electroencephalogram recorded during the upper limb task showed no change in relation to the task. Burst-locked back-averaging of the electroencephalogram showed no spiking before or during the bursts. Various physiological and pathological rhythmic muscle activities have been proposed to be a manifestation of oscillations in the central nervous system and it has been suggested that such oscillations may have a role in the processing of motor commands. The mechanism of the rhythmic muscle bursting activity associated with maintaining posture in patients with Angelman syndrome is not clear, although it could be consistent with cerebellar Purkinje cell dysfunction, either as a pathological feature or as an adaptive process to overcome deficits in motor coordination.