Angelman syndrome: correlations between epilepsy phenotypes and genotypes

Autism: a "critical period" disorder?

Cortical circuits in the brain are refined by experience during critical periods early in postnatal life. Critical periods are regulated by the balance of excitatory and inhibitory (E/I) neurotransmission in the brain during development. There is now increasing evidence of E/I imbalance in autism, a complex genetic neurodevelopmental disorder diagnosed by abnormal socialization, impaired communication, and repetitive behaviors or restricted interests. The underlying cause is still largely unknown and there is no fully effective treatment or cure. We propose that alteration of the expression and/or timing of critical period circuit refinement in primary sensory brain areas may significantly contribute to autistic phenotypes, including cognitive and behavioral impairments. Dissection of the cellular and molecular mechanisms governing well-established critical periods represents a powerful tool to identify new potential therapeutic targets to restore normal plasticity and function in affected neuronal circuits.

Altered GABA signaling in early life epilepsies

The incidence of seizures is particularly high in the early ages of life. The immaturity of inhibitory systems, such as GABA, during normal brain development and its further dysregulation under pathological conditions that predispose to seizures have been speculated to play a major role in facilitating seizures. Seizures can further impair or disrupt GABA_A signaling by reshuffling the subunit composition of its receptors or causing aberrant reappearance of depolarizing or hyperpolarizing GABA_A receptor currents. Such effects may not result in epileptogenesis as frequently as they do in adults. Given the central role of GABA_A signaling in brain function and development, perturbation of its physiological role may interfere with neuronal morphology, differentiation, and connectivity, manifesting as cognitive or neurodevelopmental deficits. The current GABAergic antiepileptic drugs, while often effective for adults, are not always capable of stopping seizures and preventing their sequelae in neonates. Recent studies have explored the therapeutic potential of chloride cotransporter inhibitors, such as bumetanide, as adjunctive therapies of neonatal seizures. However, more needs to be known so as to develop therapies capable of stopping seizures while preserving the age- and sex-appropriate development of the brain.

Angelman syndrome: insights into genomic imprinting and neurodevelopmental phenotypes

Angelman syndrome (AS) is a severe genetic disorder caused by mutations or deletions of the maternally inherited UBE3A gene. UBE3A encodes an E3 ubiquitin ligase that is expressed biallelically in most tissues but is maternally expressed in almost all neurons. In this review, we describe recent advances in understanding the expression and function of UBE3A in the brain and the etiology of AS. We highlight current AS model systems, epigenetic mechanisms of UBE3A regulation, and the identification of potential UBE3A substrates in the brain. In the process, we identify major gaps in our knowledge that, if bridged, could move us closer to identifying treatments for this debilitating neurodevelopmental disorder.

Epilepsy in Prader-Willi syndrome: clinical characteristics and correlation to genotype

Prader-Willi syndrome (PWS) is a genomic imprinting disease secondary to the loss of a functional paternal copy of 15q11-q13. Unlike its related imprinting disorder, Angelman syndrome, PWS has not been regarded as a risk factor for epilepsy. A retrospective analysis of 92 patients with PWS identified 24 (26%) with seizures. Twenty-two of these (92%) were affected by focal epilepsy and only two (8%) had generalized epilepsy. The most common seizure type was staring spells (67%). Correlation to genotype analysis showed deletions were more common in patients with epilepsy than in patients without epilepsy. The epilepsy syndromes were easy to control with a single antiepileptic drug in most cases. Three patients (11%) had had febrile seizures. These findings suggest that PWS may be a risk factor for epilepsy, which can manifest with focal features. Patients with PWS with a deletion genotype showed a trend toward developing seizures compared with patients with other genotypes in our series, even though this difference did not achieve statistical significance.

Altered ultrasonic vocalization and impaired learning and memory in Angelman syndrome mouse model with a large maternal deletion from Ube3a to Gabrb3

Angelman syndrome (AS) is a neurobehavioral disorder associated with mental retardation, absence of language development, characteristic electroencephalography (EEG) abnormalities and epilepsy, happy disposition, movement or balance disorders, and autistic behaviors. The molecular defects underlying AS are heterogeneous, including large maternal deletions of chromosome 15q11–q13 (70%), paternal uniparental disomy (UPD) of chromosome 15 (5%), imprinting mutations (rare), and mutations in the E6-AP ubiquitin ligase gene UBE3A (15%). Although patients with UBE3A mutations have a wide spectrum of neurological phenotypes, their features are usually milder than AS patients with deletions of 15q11–q13. Using a chromosomal engineering strategy, we generated mutant mice with a 1.6-Mb chromosomal deletion from Ube3a to Gabrb3, which inactivated the Ube3a and Gabrb3 genes and deleted the Atp10a gene. Homozygous deletion mutant mice died in the perinatal period due to a cleft palate resulting from the null mutation in Gabrb3 gene. Mice with a maternal deletion (m−/p+) were viable and did not have any obvious developmental defects. Expression analysis of the maternal and paternal deletion mice confirmed that the Ube3a gene is maternally expressed in brain, and showed that the Atp10a and Gabrb3 genes are biallelically expressed in all brain sub-regions studied. Maternal (m−/p+), but not paternal (m+/p−), deletion mice had increased spontaneous seizure activity and abnormal EEG. Extensive behavioral analyses revealed significant impairment in motor function, learning and memory tasks, and anxiety-related measures assayed in the light-dark box in maternal deletion but not paternal deletion mice. Ultrasonic vocalization (USV) recording in newborns revealed that maternal deletion pups emitted significantly more USVs than wild-type littermates. The increased USV in maternal deletion mice suggests abnormal signaling behavior between mothers and pups that may reflect abnormal communication behaviors in human AS patients. Thus, mutant mice with a maternal deletion from Ube3a to Gabrb3 provide an AS mouse model that is molecularly more similar to the contiguous gene deletion form of AS in humans than mice with Ube3a mutation alone. These mice will be valuable for future comparative studies to mice with maternal deficiency of Ube3a alone.

Altered GABA(A) receptor subunit expression and pharmacology in human Angelman syndrome cortex

The neurodevelopmental disorder Angelman syndrome is most frequently caused by deletion of the maternally derived chromosome 15q11-q13 region, which includes not only the causative UBE3A gene, but also the beta(3)-alpha(5)-gamma(3) GABA(A) receptor subunit gene cluster. GABAergic dysfunction has been hypothesized to contribute to the occurrence of epilepsy and cognitive and behavioral impairments in this condition. In the present study, analysis of GABA(A) receptor subunit expression and pharmacology was performed in cerebral cortex from four subjects with Angelman syndrome and compared to that from control tissue. The membrane fraction of frozen postmortem neocortical tissue was isolated and subjected to quantitative Western blot analysis. The ratios of beta(3)/beta(2) and alpha(5)/alpha(1) subunit protein expression in Angelman syndrome cortex were significantly decreased when compared with controls. An additional membrane fraction was injected into Xenopus oocytes, resulting in incorporation of the brain membrane vesicles with their associated receptors into the oocyte cellular membrane. Two-electrode voltage-clamp analysis of GABA(A) receptor currents was then performed. Studies of GABA(A) receptor pharmacology in Angelman syndrome cortex revealed increased current enhancement by the alpha(1)-selective benzodiazepine-site agonist zolpidem and by the barbiturate phenobarbital, while sensitivity to current inhibition by zinc was decreased. GABA(A) receptor affinity and modulation by neurosteroids were unchanged. This shift in GABA(A) receptor subunit expression and pharmacology in Angelman syndrome is consistent with impaired extrasynaptic but intact to augmented synaptic cortical GABAergic inhibition, which could contribute to the epileptic, behavioral, and cognitive phenotypes of the disorder.

Epilepsy in patients with Angelman syndrome

Angelman syndrome (AS) is a neuro-behavioural, genetically determined condition, characterized by ataxic jerky movements, happy sociable disposition and unprovoked bouts of laughter in association with seizures, learning disabilities and language impairment. Most of the cases are hardly diagnosed during infancy as jerky movements, the cardinal sign, appear later in childhood. AS is caused by a variety of genetic mechanisms involving the 15q 11-13 chromosome. About 70% of cases are due to a "de novo" interstitial deletion in the long arm region, arising on the maternally inherited chromosome. The diagnosis is confirmed by methylation test or by mutation analysis of UBE3A gene. The deletion phenotype is generally linked to a more severe clinical picture in that 95% of patients manifest more severe seizures, severe mental and motor retardation, dysmorphic features and microcephaly.The pathogenesis of epilepsy in AS is still not fully understood. The presence in the commonly deleted region of a cluster of genes coding for 3 subunits of the GABAa receptor complex has lead to the hypothesis that GABA neurotransmission is involved. Epilepsy, often severe and hard to control, is present in 85% of patients within the first three years of life, although less than 25% develop seizures during the first year. It was observed that febrile seizures often precede the diagnosis. Most frequent types are atypical absences, generalized tonic-clonic, atonic or myoclonic seizures, with multiple seizure types occurring in 50% of deleted patients. There is still some doubt about the association with West syndrome. The EEG abnormalities are not themselves pathognomonic of AS and both background activity and epileptic discharges vary even in the same patient with time. Nevertheless, the existence of some suggestive patterns should facilitate the early diagnosis allowing the correct genetic counselling for the family. Some drugs seems to act better than others, Valproate, ethosuximide and clonazepam giving the best results.

Mutations affecting GABAergic signaling in seizures and epilepsy

The causes of epilepsies and epileptic seizures are multifactorial. Genetic predisposition may contribute in certain types of epilepsies and seizures, whether idiopathic or symptomatic of genetic origin. Although these are not very common, they have offered a unique opportunity to investigate the molecular mechanisms underlying epileptogenesis and ictogenesis. Among the implicated gene mutations, a number of GABAA receptor subunit mutations have been recently identified that contribute to several idiopathic epilepsies, febrile seizures, and rarely to certain types of symptomatic epilepsies, like the severe myoclonic epilepsy of infancy. Deletion of GABAA receptor genes has also been linked to Angelman syndrome. Furthermore, mutations of proteins controlling chloride homeostasis, which indirectly defines the functional consequences of GABAA signaling, have been identified. These include the chloride channel 2 (CLCN2) and the potassium chloride cotransporter KCC3. The pathogenic role of CLCN2 mutations has not been clearly demonstrated and may represent either susceptibility genes or, in certain cases, innocuous polymorphisms. KCC3 mutations have been associated with hereditary motor and sensory polyneuropathy with corpus callosum agenesis (Andermann syndrome) that often manifests with epileptic seizures. This review summarizes the recent progress in the genetic linkages of epilepsies and seizures to the above genes and discusses potential pathogenic mechanisms that contribute to the age, sex, and conditional expression of these seizures in carriers of these mutations.

Angelman syndrome: current understanding and research prospects

Angelman syndrome is a neurogenetic disorder characterized by developmental delay, severe intellectual disability, absent speech, exuberant behavior with happy demeanor, motor impairment, and epilepsy, due to deficient UBE3A gene expression that may be caused by various abnormalities of chromosome 15. Recent findings in animal models demonstrated altered dendritic spine formation as well as both synaptic [including gamma-aminobutyric acid (GABA)(A) and N-methyl-D-aspartate (NMDA) transmission] and nonsynaptic (including gap junction) influences in various brain regions, including hippocampus and cerebellar cortex. Reversal of selected abnormalities in rescue genetically engineered animal models is encouraging, although it should not be misinterpreted as promising "cure" for affected patients. Much research is still required to fully understand the functional links between lack of UBE3A expression and clinical manifestations of Angelman syndrome. Studies of regulation of UBE3A expression, including imprinting-related methylation, may point to possibilities of therapeutic upregulation. Understanding relevant roles of the gene product might lead to targeted intervention. Further documentation of brain network dynamics, with particular emphasis on hippocampus, thalamocortical, and cerebellar networks is needed, including in a developmental perspective. There is also a need for further clinical research for improving management of problems such as epilepsy, behavior, communication, learning, motor impairment, and sleep disturbances.

Ring 14 chromosome presenting as early-onset isolated partial epilepsy

We report four infants (two males, two females) with ring 14 chromosome presenting with early-onset partial epilepsy. The first seizure occurred between 3 and 6 months (3, 3, 4, and 6mo respectively). In all four cases, diagnosis was based on early focal seizures, rather than on psychomotor retardation or morphological features, which were not prominent at seizure onset. Moreover, despite the young age of the patients and the high frequency of seizures, neither epileptic spasms nor progression to 'epileptic encephalopathy', such as hypsarrhythmia, were observed. Epilepsy remained partial in these patients. At the most recent follow-up, all four children had slight or mild psychomotor delay, and two of them had moderate non-specific dysmorphic traits. Data from the literature about epilepsy in ring 14 chromosome syndrome were also reviewed. Ring 14 chromosome syndrome may be revealed by isolated, early-onset focal epilepsy suggestive of focal lesions with only mild mental retardation and morphological features at the time of diagnosis. The characteristics of these observations differ from classic ring 14 syndrome, and may enlarge this clinical spectrum. Many unanswered questions remain concerning phenotype-genotype correlation and identification of the potential genes and molecular mechanisms responsible for epilepsy in patients with ring 14 syndrome.

Benefit of corticosteroid therapy in Angelman syndrome

Angelman syndrome is often associated with an intractable seizure disorder. We describe 4 children who demonstrated an excellent response to corticosteroid therapy. The benefits included not only reduction in clinical seizures but also modification of the "typical'' Angelman electroencephalogram. In addition, there was improvement in the myoclonic jerks, sleep pattern, and developmental progress. Corticosteroids appeared to have a broad benefit on the epileptic encephalopathy. We believe that these cases pose a challenge to the conventional management of intractable epilepsy in Angelman syndrome.

Myoclonic status in nonprogressive encephalopathies: an update

Myoclonic status in nonprogressive encephalopathies (MSNE) is an epileptic syndrome in development, characterized by the early onset of continuous diffuse epileptiform abnormalities, accompanied by positive and/or negative phenomena correlated with transient and recurring motor, cognitive, or behavioral disturbances. Outcome of MSNE is poor and may determine progressive neurologic deterioration. MSNE is not easy to recognize and should be distinguished from progressive myoclonic epilepsies and other rarely reported infantile myoclonic epilepsies. The identification of MSNE may guide the diagnostic work-up, suggesting the presence of a genetic defect, such as Angelman syndrome, hypoxic-ischemic encephalopathy, or brain malformation.

Spectrum of epilepsy and electroencephalogram patterns in Wolf-Hirschhorn syndrome: experience with 87 patients

To define the spectrum of epilepsy in Wolf-Hirschhorn syndrome (WHS) better, we studied 87 patients (54 females, 33 males; median age 5.6 years; age range 1-25.6 years) with confirmed 4p16.3 deletion. On the basis of clinical charts, we retrospectively analyzed the evolution of the electroencephalogram (EEG) findings and seizures. Epilepsy occurred in 81 patients (93%) within the first 3 years of life. Sixty out of 81 (74%) had generalized tonic-clonic seizures, which was the only seizure pattern in 32. Tonic spasms occurred in 15 out of 81 (18%), complex partial seizures in 10 out of 81 (12%), and clonic seizures in 6 out of 81 (7%). Seizures were frequently triggered by fever (59 out of 81; 73%), and occurred in clusters in 36 out of 72 (50%). In the same 36 (50%), unilateral or generalized clonic or tonic-clonic status epilepticus occurred during the first 3 years of life. Twenty-seven out of 81 patients (33%) developed atypical absences between 1 and 6 years, accompanied by a myoclonic component involving the eyelids and the hands. Distinctive EEG abnormalities were observed in 73 out of 81 (90%). Epilepsy was well controlled in 65 out of 81 (81%), mainly with valproate and phenobarbital, and improved with age in all. Thirty-two out of 58 (55%) are currently seizure-free. Seizures stopped at a median age of 4 years 6 months. Epilepsy represents a major clinical challenge in WHS; however, it has a good prognosis. Early diagnosis and treatment of atypical absences, subtle and often misdiagnosed, is mandatory.

Hyperglycosylation and reduced GABA currents of mutated GABRB3 polypeptide in remitting childhood absence epilepsy

Childhood absence epilepsy (CAE) accounts for 10% to 12% of epilepsy in children under 16 years of age. We screened for mutations in the GABA(A) receptor (GABAR) beta 3 subunit gene (GABRB3) in 48 probands and families with remitting CAE. We found that four out of 48 families (8%) had mutations in GABRB3. One heterozygous missense mutation (P11S) in exon 1a segregated with four CAE-affected persons in one multiplex, two-generation Mexican family. P11S was also found in a singleton from Mexico. Another heterozygous missense mutation (S15F) was present in a singleton from Honduras. An exon 2 heterozygous missense mutation (G32R) was present in two CAE-affected persons and two persons affected with EEG-recorded spike and/or sharp wave in a two-generation Honduran family. All mutations were absent in 630 controls. We studied functions and possible pathogenicity by expressing mutations in HeLa cells with the use of Western blots and an in vitro translation and translocation system. Expression levels did not differ from those of controls, but all mutations showed hyperglycosylation in the in vitro translation and translocation system with canine microsomes. Functional analysis of human GABA(A) receptors (alpha 1 beta 3-v2 gamma 2S, alpha 1 beta 3-v2[P11S]gamma 2S, alpha 1 beta 3-v2[S15F]gamma 2S, and alpha 1 beta 3-v2[G32R]gamma 2S) transiently expressed in HEK293T cells with the use of rapid agonist application showed that each amino acid transversion in the beta 3-v2 subunit (P11S, S15F, and G32R) reduced GABA-evoked current density from whole cells. Mutated beta 3 subunit protein could thus cause absence seizures through a gain in glycosylation of mutated exon 1a and exon 2, affecting maturation and trafficking of GABAR from endoplasmic reticulum to cell surface and resulting in reduced GABA-evoked currents.

Immunologic and neurodevelopmental susceptibilities of autism

Symposium 5 focused on research approaches that are aimed at understanding common patterns of immunological and neurological dysfunction contributing to neurodevelopmental disorders such as autism and ADHD. The session focused on genetic, epigenetic, and environmental factors that might act in concert to influence autism risk, severity and co-morbidities, and immunological and neurobiological targets as etiologic contributors. The immune system of children at risk of autism may be therefore especially susceptible to psychological stressors, exposure to chemical triggers, and infectious agents. Identifying early biomarkers of risk provides tangible approaches toward designing studies in animals and humans that yield a better understanding of environmental risk factors, and can help identify rational intervention strategies to mitigate these risks.

Epilepsy in Angelman syndrome

Angelman syndrome is a neurogenetic disorder caused by lack of UBE3A gene expression from the maternally inherited chromosome 15 due to various 15q11-q13 abnormalities. In addition to severe developmental delay, virtual absence of speech, motor impairment, a behavioural phenotype that includes happy demeanor, and distinctive rhythmic electroencephalographic features, over 90% of patients have epilepsy. Many different seizure types may occur, atypical absences and myoclonic seizures being particularly prevalent. Non-convulsive status epilepticus is common, sometimes in the context of the epileptic syndrome referred to as myoclonic status in non-progressive encephalopathies. Epilepsy predominates in childhood, but may persist or reappear in adulthood. Management is difficult in a proportion of patients. It might be improved by better understanding of pathophysiology. Current hypotheses involve abnormal inhibitory transmission due to impaired regulation of GABAA receptors related to functional absence of UBE3A and abnormal hippocampal CaMKII activity.

Lamotrigine therapy of epilepsy with Angelman's syndrome

PURPOSE

Angelman syndrome (AS) is a neurogenetic disorder characterized by developmental delay and a frequently refractory epileptic condition. Valproate, clonazepam and/or phenytoin are said to be the most effective antiepileptic drugs (AEDs) against the seizures in AS. Experience with the newer AEDs is very limited despite their better safety profile and tolerability. Considering its favorable side effect profile and its effectiveness against both partial and generalized seizures, we hypothesized that lamotrigine (LTG) might be more efficacious and better tolerated.

METHODS

Potential patients for this retrospective study were identified from the epilepsy clinics at Notre-Dame, Sainte-Justine, and Yale New Haven hospitals. Patients were included in the study if they had AS along with refractory seizures. The medical record of each patient was reviewed with interest on seizure types, previous AEDs and response to LTG.

RESULTS

Five patients (2M, 3F) were included in this study. Age at LTG ranged from 10 to 33 years old. All had >or=2 seizure types, mainly generalized tonic-clonic, myoclonic seizures, and atypical absences. Previously tried AEDs included valproic acid (5), benzodiazepines (5), phenytoin (4), carbamazepine (3), and topiramate (1). One patient had pancreatitis on phenytoin, one had worsened seizures on carbamazepine, and one developed hepatic encephalopathy on valproic acid. Three patients became seizure-free with LTG (9, 20, and 36 months FU), one was seizure-free for 1 year with subsequent loss of efficacy, and one showed >50% reduction in myoclonic seizures (20 months FU). No side effects were reported.

CONCLUSION

LTG can be efficacious and well tolerated in patients with AS.

Detection of a deletion of exons 8-16 of the UBE3A gene in familial Angelman syndrome using a semi-quantitative dosage PCR based assay

Angelman syndrome (AS) is a neurodevelopmental disorder caused by failure of expression of the maternal copy of the imprinted UBE3A gene through a variety of mechanisms detected by methylation studies, mutation analysis of UBE3A and FISH. In 10-15% of suspected cases of AS these investigations do not reveal a genetic abnormality. We report here the development of a semi-quantitative dosage PCR technique used to identify sub-microscopic deletions involving UBE3A. Using this method we analysed a panel of 26 patients from 24 families, all fulfilling the clinical criteria for AS. We identified a deletion of UBE3A exons 8-16 in a sibling pair. Analysis of parental samples revealed the same deletion in their phenotypically normal mother. This is an inexpensive and valuable method for detecting UBE3A deletions in a small but important proportion of AS cases of unidentifiable cause.

Inv dup (15): Is the electroclinical phenotype helpful for this challenging clinical diagnosis?

OBJECTIVE

To study the electroclinical phenotype in 5 patients with large supernumerary marker chromosome referred as inv dup (15), in an attempt to analyze the electroclinical spectrum in order to determine if the binomial epilepsy-EEG is stereotyped enough to corroborate this challenging diagnosis.

METHODS

Five patients with large inv dup (15) were submitted to EEG and/or V-EEG, with a minimum duration of 2h. Two certified neurophysiologists analyzed all EEG tracings simultaneously, blinded to clinical and molecular data. Epilepsy was characterized by detailed history and a standard questionnaire according to International League Against Epilepsy guidelines and corroborated by V-EEG findings.

RESULTS

Epilepsy started during infancy in 4 patients, in 3 with spasms. Spasms were easily controlled in one but not in others. Epilepsy evolved with generalized seizures in two patients and, generalized and focal in one. Currently, 3 patients present refractory epilepsy and two are seizure-free. In one patient, only one isolated episode suggestive of a secondary generalized tonic-clonic event occurred at the age of 12 years without recurrence. Regarding the EEG, patients had distinct features, except for two patients with very high amplitude fast activity, resembling recruiting rhythm. Despite good seizure outcome in 3 patients, EEGs remained remarkably abnormal with frequent epileptiform discharges over poorly organized background.

CONCLUSIONS

Our data showed a heterogeneous electroclinical phenotype with generalized and partial epilepsy, presenting distinct degrees of severity and refractoriness.

SIGNIFICANCE

Our findings suggest that it is not possible to delineate an electroclinical phenotype in this neurogenetic syndrome. Therefore, inv dup (15) remains as a diagnostic challenge and epilepsy and EEG features are valuable only when inserted in the proper clinical context.

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.

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.

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.

L'épilepsie dans les aberrations chromosomiques

Epilepsy is among the most frequent finding in many chromosome aberrations. While most chromosome aberrations can be associated with different seizure types, there are few aberrations which feature specific seizures and EEG patterns. Among the 400 different chromosomal imbalances described with seizures and EEG abnormalities, eight have a high association with epilepsy. These comprise: the monosomy 1p36, Wolf-Hirschhorn syndrome (4p-), Angelman syndrome, Miller-Dieker del 17p13.3, the inversion duplication 15 syndrome, ring 20 and ring 14 syndromes, Down's syndrome. These chromosomal regions where aberrations have an evident association with epilepsy may be useful targets for gene hunters. On the other hand, a better characterisation of epileptic syndrome in these disorders may lead to a better and specific treatment.

Relationship between severity of epilepsy and developmental outcome in Angelman syndrome

To clarify the relationship between the degree of developmental disturbance and the severity of epilepsy in Angelman syndrome, we investigated 11 patients and measured both clinical outcomes and EEG parameters. Seven patients were followed up until after 8 years of age. Eight patients were found to have 15q11-q13 deletions. All patients experienced epileptic seizures and all but one displayed non-convulsive status epilepticus (NCSE) during the period of observation. Epileptic seizures, including NCSE, disappeared by around 8 years of age. In addition, specific epileptic discharges, as measured by EEG, tended to subside with age. Although development seemed almost normal or only slightly delayed during the first 6 months of life, all patients eventually developed severe retardation. Two patients displayed very severe retardation and were unable to comprehend language or walk independently at the last follow-up. Only one patient was able to speak a few meaningful words. In one of the most severely affected patients, who showed the earliest onset of seizures and NCSE, it is possible that the repetitive bouts of NCSE might be responsible for the severe developmental outcome. However, the other patient with particularly severe retardation did not experience NCSE, while the patient with the most favorable outcome had repetitive episodes of NCSE. Therefore, we conclude that the severity of developmental disturbance in Angelman syndrome is not necessarily related to the degree of epilepsy. However, intensive therapy for NCSE might still be justified because there are some patients in whom NCSE results in a transient and sometimes permanent decline in mental and motor functioning.

Multi-institutional study on the correlation between chromosomal abnormalities and epilepsy

While there is an abundance of literature describing the association of chromosome aberrations with epilepsy, only a few refer to the detailed features of epilepsy. It is important to investigate the associations between specific chromosome abnormalities and features of epilepsy to identify genes involved in epilepsy and treat them more effectively. We investigated the correlation between specific chromosome aberrations and epilepsy by sending questionnaires to the members of Kyoto Multi-institutional Study Group of Pediatric Neurology. Seventy-six patients were collected from 10 institutions. Chromosome abnormalities included: Down syndrome (n = 19); Angelman syndrome (n = 8); Prader-Willi syndrome (n = 4); 4p- syndrome (n = 3); 1q- syndrome (n = 2); 5p- syndrome (n = 2); Miller-Dieker syndrome (n = 2); 18q- syndrome; (n = 2); Klinefelter syndrome; (n = 2); and 32 other individual chromosomal aberrations. Overall, the severity of mental retardation correlated with the severity of epilepsy. We could abstract characteristic features of epilepsy in some syndromes. In Angelman and Prader-Willi syndromes, febrile seizures occurred frequently, the onset of epilepsy was in early childhood and seizure phenotype was multiple. Paroxysmal discharge of the occipital region and diffuse high voltage slow wave on electroencephalography were characteristic in Angelman syndrome. In Down syndrome, West syndrome and focal epilepsy were common and the prognosis of epilepsy in West syndrome with Down syndrome was good. In 4p- syndrome, febrile seizures were often seen, and unilateral or generalized clonic or tonic-clonic status epilepticus were characteristic. For the other chromosomal aberrations investigated here, the patient numbers were too small to abstract common features of epilepsy.

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.

Chromosomal phenotypes and submicroscopic abnormalities

The finding, during the last decade, that several common, clinically delineated syndromes are caused by submicroscopic deletions or, more rarely, by duplications, has provided a powerful tool in the annotation of the human genome. Since most microdeletion/microduplication syndromes are defined by a common deleted/duplicated region, abnormal dosage of genes located within these regions can explain the phenotypic similarities among individuals with a specific syndrome. As such, they provide a unique resource towards the genetic dissection of complex phenotypes such as congenital heart defects, mental and growth retardation and abnormal behaviour. In addition, the study of phenotypic differences in individuals with the same microdeletion syndrome may also become a treasury for the identification of modifying factors for complex phenotypes. The molecular analysis of these chromosomal anomalies has led to a growing understanding of their mechanisms of origin. Novel tools to uncover additional submicroscopic chromosomal anomalies at a higher resolution and higher speed, as well as the novel tools at hand for deciphering the modifying factors and epistatic interactors, are 'on the doorstep' and will, besides their obvious diagnostic role, play a pivotal role in the genetic dissection of complex phenotypes.

Pathophysiology and pharmacology of GABA(A) receptors

By controlling spike timing and sculpting neuronal rhythms, inhibitory interneurons play a key role in brain function. GABAergic interneurons are highly diverse. The respective GABA(A) receptor subtypes, therefore, provide new opportunities not only for understanding GABA-dependent pathophysiologies but also for targeting of selective neuronal circuits by drugs. The pharmacological relevance of GABA(A) receptor subtypes is increasingly being recognized. A new central nervous system pharmacology is on the horizon. The development of anxiolytic drugs devoid of sedation and of agents that enhance hippocampus-dependent learning and memory has become a novel and highly selective therapeutic opportunity.

Angelman syndrome: etiology, clinical features, diagnosis, and management of symptoms

It is estimated that Angelman syndrome (AS) accounts for up to 6% of all children presenting with severe mental retardation and epilepsy. The main clinical features of AS may not be apparent early in life. Clinical findings present in all patients include developmental delay, which becomes apparent by 6-12 months of age, severely impaired expressive language, ataxic gait, tremulousness of limbs, and a typical behavioral profile, including a happy demeanor, hypermotoric behavior, and low attention span. Seizures, abnormal electroencephalography, microcephaly, and scoliosis are observed in >80% of patients. Approximately 70% of patients show a deletion involving the maternally inherited chromosome 15q11-q13, encompassing a cluster of gamma-aminobutyric acid receptor subunit genes, 3% show chromosome 15 paternal uniparental disomy (UPD), 1% harbor a mutation in the imprinting center (a transcriptional regulatory element), and 6% harbor intragenic mutations of the ubiquitin-protein ligase E3A (UBE3A) gene. Twenty percent of patients have no detectable genetic abnormality. Rare cases of familial recurrence of AS show either imprinting center (IC) or UBE3A mutations. Approximately 75% of cases are detected through the methylation test, which allows the detection of AS due to deletions, UPD and IC mutations. Mutation analysis of the UBE3A gene should be performed when the methylation test is negative. Individuals with chromosome 15q11-q13 deletions have a more severe clinical picture and are more prone to develop severe epilepsy. Epilepsy has typical features, including absence and myoclonic seizures, and insidious episodes of nonconvulsive or subtle myoclonic status which are easily overlooked as children appear apathetic or in a state of neurologic regression. Tremulousness, present in all patients even when seizures are well controlled or absent, is related to distal cortical myoclonus. Valproic acid (sodium valproate), benzodiazepines, and ethosuximide, in various combinations, are quite effective in treating the typical seizure types. Piracetam may help in reducing distal myoclonus. Carbamazepine and vigabatrin may seriously aggravate absence and myoclonic seizures and should be avoided. Cognitive, language, and orthopedic problems must be addressed with vigorous rehabilitation programs, including early physical therapy, which may help to develop communicative skills and prevent severe scoliosis and subsequent immobility. Where these treatment strategies are applied, individuals with AS may reach an appreciable level of integration, self care, and have a normal life span.

Electroclinical patterns and evolution of epilepsy in the 4p- syndrome

BACKGROUND

Wolf-Hirschhorn syndrome (WHS) is a well-known clinical entity caused by partial deletion of the short arm of one chromosome 4 (4p- syndrome). Seizures occur in almost all the cases, but studies on the electroclinical disorder and its evolution are still scarce. We present a longitudinal study of the electroclinical features in 10 children with WHS.

METHODS

Ten patients (five boys and five girls) underwent a detailed clinical assessment and a prolonged EEG study. Six of the 10 also had video-polygraphy.

RESULTS

Nine of the 10 patients had seizures; they were generalized or unilateral clonic and tonic-clonic, and atypical absences associated with myoclonic jerks. Age at onset of seizures varied from 1 day to 2.5 years. In all the patients, including the only one without seizures, two stereotyped EEG patterns were observed, consisting of (a) bursts of rhythmic (3-5 Hz), high-voltage slow waves located in the posterior regions and increased by sleep, or bursts of rapid spike-wave complexes in the centroparietal and parietooccipital regions; and (b) repetitive rapid posterior spikes. Sleep organization was constantly absent or very poor. The evolution of epilepsy was frequently good, with four seizure-free cases at the end of follow-up, two of them weaned from antiepileptic drugs (AEDs).

CONCLUSIONS

Seizure onset in WHS also can occur at neonatal age. At least two electrical stereotyped patterns of the epileptic disorder are associated with a relevant disorganization of the sleep states. Prognosis of epilepsy is generally good both for the seizure control and for its evolution.

Angelman syndrome: difficulties in EEG pattern recognition and possible misinterpretations

PURPOSE

This study aimed to evaluate the sensitivity of the EEG in Angelman syndrome (AS), to verify the age at onset of suggestive EEGs and to study EEG patterns, analyzing variations and comparing our findings with nomenclature previously used.

METHODS

Seventy EEG and 15 V-EEGs of 26 patients were analyzed. Suggestive EEG patterns of AS were classified in delta pattern (DP), theta pattern (TP), and posterior discharges (PDs). Generic terms were used to simplify the analysis.

RESULTS

Suggestive EEGs were observed in 25 (96.2%) patients. DP occurred in 22 patients with four variants-hypsarrhythmic-like: irregular, high-amplitude, generalized delta activity (DA) with multifocal epileptiform discharges (EDs); slow variant: regular, high-amplitude, generalized DA with rare EDs; ill-defined slow spike-and-wave: regular, high-amplitude, generalized DA with superimposed EDs characterizing a slow wave, with notched appearance; triphasic-like: rhythmic, moderate-amplitude DA over anterior regions with superimposed EDs. TP was observed in eight patients, as generalized or over the posterior regions. PDs were seen in 19 patients as runs of sharp waves or runs of high-amplitude slow waves with superimposed EDs. TP was the only age-related pattern (younger than 8 years) and observed only in patients with deletion. In 15 patients who had an EEG before the clinical diagnosis, 60% had a suggestive tracing.

CONCLUSIONS

Although some EEG descriptions are not very detailed, and every author describes findings in a slightly different manner, obviously a common denominator must exist. In this context, EEG seems to be a very sensitive method for the diagnosis of AS, offering an opportunity to corroborate this etiologic diagnosis. Conversely, we do not believe that these patterns may be accounted as specific, except for the delta pattern, which seems to be extremely unusual in other syndromes. Other EEG patterns observed in AS, such as theta activity and PDs, occur in a wide variety of disorders. Nonetheless, their importance for the EEG diagnosis of AS is supported by the fact that they are associated with other features and may be helpful in a proper clinical setting.

Reserpine responsive myoclonus and hyperpyrexia in a patient with Angelman syndrome

A case of an older patient with the Angelman syndrome due to a deletion at the 15q11-q13 region is presented. The patient demonstrated generalized prolonged myoclonus severe enough to produce temperatures of 41.4 degrees C and CPK elevations to 7281 U/l. This myoclonus was unresponsive to benztropine, clonazepam and worsened with bromocriptine. It resolved with sleep induced by either lorazepam or diphenhydramine and during treatment with reserpine. Once discharged from the hospital and treated with reserpine, there were much less frequent recurrences of the myoclonus that responded well to concomitant treatment with clonazepam. Later attempts to reduce the reserpine resulted in worsening of the myoclonus. Older patients with Angelman syndrome may display a wide variety of neurologic syndromes. This severe myoclonus in this patient worsened with dopamine agonist treatment and initially improved with dopamine depletion therapy while in the long-term responding best to a combination of clonazepam and reserpine.

A study of EEG and epilepsy profile in Wolf-Hirschhorn syndrome and considerations regarding its correlation with other chromosomal disorders

Wolf-Hirschhorn syndrome (WHS) is a genetic disorder caused by a deletion of the short arm of chromosome 4. Sgrò et al. described an electroclinical profile for WHS, but data regarding this issue are scarce. We report an 8-year-old girl presenting the classic phenotype for WHS, confirmed by FISH test. Epilepsy started during infancy with myoclonic seizures. Later, she presented atypical absences, which gradually increased in frequency, and at the age of 2.5 years, she presented a non-convulsive status epilepticus. Epilepsy was controlled with valproate at the age of 6 years. Serial EEGs were performed and showed unusual bursts of generalized, high amplitude delta waves with superimposed low-moderate amplitude sharp waves. A literature review was performed and our case was compared to others, where EEG and/or epilepsy were addressed. Our case and previously published data show that WHS presents a stereotyped epilepsy profile and EEG patterns. A discussion concerning similarities between these findings and those observed in Angelman syndrome has been performed, since in both syndromes, GABA genes are involved and may play a role in the pathogenesis. Although fascinating, this theory is simplistic, since patients with Angelman syndrome without GABA deletion may present epilepsy and EEG abnormalities. Another issue is the striking overlap regarding these features, between WHS and Pitt-Rogers-Danks syndrome, which may be a key in showing that these disorders could be a spectral variation of the same entity.

Angelman syndrome: a review of the clinical and genetic aspects

Angelman syndrome (AS) is a neurodevelopmental disorder characterised by severe learning difficulties, ataxia, a seizure disorder with a characteristic EEG, subtle dysmorphic facial features, and a happy, sociable disposition. Most children present with delay in developmental milestones and slowing of head growth during the first year of life. In the majority of cases speech does not develop. Patients with AS have a characteristic behavioural phenotype with jerky movements, frequent and sometimes inappropriate laughter, a love of water, and sleep disorder. The facial features are subtle and include a wide, smiling mouth, prominent chin, and deep set eyes. It is caused by a variety of genetic abnormalities involving the chromosome 15q11-13 region, which is subject to genomic imprinting. These include maternal deletion, paternal uniparental disomy, imprinting defects, and point mutations or small deletions within the UBE3A gene, which lies within this region. UBE3A shows tissue specific imprinting, being expressed exclusively from the maternal allele in brain. The genetic mechanisms identified so far in AS are found in 85-90% of those with the clinical phenotype and all interfere with UBE3A expression.

Peripheral markers of the gamma-aminobutyric acid (GABA)ergic system in Angelman's syndrome

It has recently been demonstrated that patients with Angelman's syndrome who exhibited a deletion on cytogenetic tests show more severe clinical pictures with drug-resistant epilepsy than patients with Angelman's syndrome not carrying the deletion. To verify if this difference in clinical severity can be attributed to genes for the three gamma-aminobutyric acid (GABA)A receptor subunits (GABRB3, GABRA5, GABRG3) located in the deleted region, a possible modification of peripheral markers of the GABAergic system was investigated in 12 subjects with Angelman's syndrome and 20 age-matched subjects (8 with idiopathic epilepsy and 12 not affected by neurologic diseases). The results confirmed a more severe clinical picture, and epilepsy syndrome in particular, in Angelman's syndrome patients with deletions versus patients without deletions. In contrast, biochemical study (based on dosage of plasma levels of GABA and diazepam binding inhibitor, an endogenous ligand of GABAA and peripheral benzodiazepine receptors, showed contradictory results: patients with Angelman's syndrome showed significantly higher levels of GABA and diazepam binding inhibitor than patients without neurologic impairment but significantly lower levels than epileptic controls.

Cellular biology of epileptogenesis

The ionic currents that underlie the mechanisms of epileptogenesis have been systematically characterised in different experimental preparations. The recent elucidation of the molecular structures of most membrane channels and receptors has enabled structure-function analyses in both physiological and pathophysiological conditions. The neurophysiological and biomolecular features of epileptogenic mechanisms that putatively account for human epilepsies are summarised in this review. Particular emphasis is given to epilepsies that are associated with genetically determined alterations of ligand-gated and voltage-gated ion channels. Changes in ionic currents that flow through sodium, potassium, and calcium channels can lead to different types of epilepsies. Inherited or acquired changes that alter the function of receptors for acetylcholine, glutamate, and gamma-aminobutryic acid are also involved. better understanding of the role of these epileptogenic mechanisms will promote new advances in the development of selective and targeted antiepileptic drugs.

Split-cord malformation in a girl with Angelman syndrome: a mere coincidence?

We present a case of a girl with both Angelman syndrome and split-cord malformation. The child was initially referred at the age of 2.5 years, for developmental delay and a possible diagnosis of spina bifida occulta, based on the presence of a hair tuft located on the midline of the lumbar area. Magnetic resonance imaging of the spine showed split-cord malformation below L1, whereas a cytogenetically detected deletion of chromosome bands 15q11-q13 (SNRPN) confirmed the clinical diagnosis of Angelman syndrome. Split-cord malformation or diastematomyelia is a rare form of spina bifida occulta that occurs sporadically and is not particularly related to specific syndromes. Hair patches or other distinctive cutaneous stigmata such as those seen in the present case have not, to our knowledge, been reported in other patients with Angelman syndrome; therefore, the association of Angelman syndrome and split-cord malformation in this child is probably coincidental. Spinal cord abnormalities have not been consistently reported in patients with Angelman syndrome; only one adult patient with Angelman syndrome and spina bifida occulta has been reported, and this association was probably considered fortuitous. However, some relatively uncommon clinical features such as deterioration of gait, lower limb malformations, and bladder dysfunction, particularly as the patients age, although nonspecific, are reminiscent of such a cause. We therefore urge clinicians to look for cutaneous stigmata along the spine and consider the evaluation of the spinal cord in children with apparent paraparesis, out of proportion to that usually seen in Angelman syndrome, should our case report not just be a coincidental observation.

Modeling human epilepsies in mice

Two categories of mouse models of human epilepsy are now contributing to the experimental analysis of inherited seizure disorders. The first type includes homologous genetic models arrived at in the classic way; the genes from human inherited epilepsy syndromes are cloned, and mice are recreated with functionally identical mutations. The second category involves the reverse strategy: mutating single genes in mice and determining whether the newly created nervous system develops epilepsy. These "gene-forward" models define specific candidate genes that can then be tested for possible involvement in human epilepsies. Spontaneous mutation of genes in mice and other species is also a source for candidate genes. As each of these genes and their physiologic functions is defined, the focus can shift to (a) fully characterizing the clinical epilepsy phenotype, (b) tracing the steps in the molecular pathogenesis of the disorder, and (c) pinpointing molecular targets for early intervention. Along with providing a unique opportunity to understand the mechanisms of inherited epileptogenesis, the mouse models serve as ideal biological test systems to search for novel therapeutic strategies.

Neurobehavioral and electroencephalographic abnormalities in Ube3a maternal-deficient mice

Angelman syndrome (AS), characterized by motor dysfunction, mental retardation, and seizures, is caused by several genetic etiologies involving chromosome 15q11-q13, including mutations of the UBE3A gene. UBE3A encodes UBE3A/E6-AP, a ubiquitin-protein ligase, and shows brain-specific imprinting, with brain expression predominantly from the maternal allele. Lack of a functional maternal allele of UBE3A causes AS. In order to understand the causal relationship between maternal UBE3A mutations and AS, we have constructed a mouse model with targeted inactivation of Ube3a. The inactive allele contains a lacZ reporter gene for analysis of brain-specific imprinting. Maternal, but not paternal, transmission of the targeted allele leads to beta-galactosidase activity in hippocampal and cerebellar neurons. Maternal inheritance of the Ube3a mutant allele also causes impaired performance in tests of motor function and spatial learning, as well as abnormal hippocampal EEG recordings. As predicted from the dependence of UBE3A-mediated ubiquitination of p53 on HPV E6 protein, our maternal-deficient mice show normal brain p53 levels.

Chromosomal abnormalities and epilepsy: a review for clinicians and gene hunters

PURPOSE

We analyzed databases on chromosomal anomalies and epilepsy to identify chromosomal regions where abnormalities are associated with clinically recognizable epilepsy syndromes. The expectation was that these regions could then be offered as targets in the search for epilepsy genes.

METHODS

The cytogenetic program of the Oxford Medical Database, and the PubMed database were used to identify chromosomal aberrations associated with seizures and/or EEG abnormalities. The literature on selected small anomalies thus identified was reviewed from a clinical and electroencephalographic viewpoint, to classify the seizures and syndromes according to the current International League Against Epilepsy (ILAE) classification.

RESULTS

There were 400 different chromosomal imbalances described with seizures or EEG abnormalities. Eight chromosomal disorders had a high association with epilepsy. These comprised: the Wolf-Hirschhorn (4p-) syndrome, Miller-Dieker syndrome (del 17p13.3), Angelman syndrome (del 15q11-q13), the inversion duplication 15 syndrome, terminal deletions of chromosome 1q and 1p, and ring chromosomes 14 and 20. Many other segments had a weaker association with seizures. The poor quality of description of the epileptology in many reports thwarted an attempt to make precise karyotype-phenotype correlations.

CONCLUSIONS

We identified certain chromosomal regions where aberrations had an evident association with seizures, and these regions may be useful targets for gene hunters. New correlations with specific epilepsy syndromes were not revealed. Clinicians should continue to search for small chromosomal abnormalities associated with specific epilepsy syndromes that could provide important clues for finding epilepsy genes, and the epileptology should be rigorously characterized.