Ring chromosome 20 epilepsy syndrome in children: electroclinical features

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

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

Ring Chromosome 20 Syndrome: Genetics, Clinical Characteristics, and Overlapping Phenotypes

Ring chromosome 20 [r(20)] syndrome is a rare condition characterized by a non-supernumerary ring chromosome 20 replacing a normal chromosome 20. It is commonly seen in a mosaic state and is diagnosed by means of karyotyping. r(20) syndrome is characterized by a recognizable epileptic phenotype with typical EEG pattern, intellectual disability manifesting after seizure onset in otherwise normally developing children, and behavioral changes. Despite the distinctive phenotype, many patients still lack a diagnosis-especially in the genomic era-and the pathomechanisms of ring formation are poorly understood. In this review we address the genetic and clinical aspects of r(20) syndrome, and discuss differential diagnoses and overlapping phenotypes, providing the reader with useful tools for clinical and laboratory practice. We also discuss the current issues in understanding the mechanisms through which ring 20 chromosome causes the typical manifestations, and present unpublished data about methylation studies. Ultimately, we explore future perspectives of r(20) research. Our intended audience is clinical and laboratory geneticists, child and adult neurologists, and genetic counselors.

Ring chromosome 20 syndrome – A rare chromosomal cause of refractory epilepsy in children

Genetic disorders and chromosomal abnormalities have been shown to represent 2–3% of all cases of epilepsy. Ring chromosome 20 syndrome is a rare chromosomal abnormality and a rare cause of intractable epilepsy. Exact prevalence of ring chromosome 20 is not known. We report a case of a 10-year old boy who had had intractable epilepsy since 2 years of age. Birth history was insignificant and there was no obvious dysmorphism. His motor milestones were normal but cognition and speech were delayed. Electroencephalography showed progressive worsening from initial bi-frontal epileptiform activity to generalized discharges. Neuroimaging and metabolic work up was normal. Karyotype study showed ring chromosome 20. Diagnosis of ring chromosome 20 or r(20) syndrome was made. Ring chromosome 20 syndrome is a rare cause of refractory epilepsy A patient who present with intractable epilepsy with frontal epileptiform discharges, mental developmental delay, without dysmorphic features should be suspected of chromosomal abnormalities especially ring chromosome 20.

Specificity of electroclinical features in the diagnosis of ring chromosome 20

BACKGROUND

Ring chromosome 20 (R20) syndrome is a chromosomal disorder characterized mainly by drug-resistant frontal lobe seizures, recurrent nonconvulsive status epilepticus (NCSE), and typical EEG features. The aim of this study was to investigate if this triad is common and specific to all patients with R20.

METHODS

In this cross-sectional study (from 2000 to 2011), we selected patients who fulfilled at least two out of three criteria: drug-resistant frontal lobe seizures, recurrent NCSE, and characteristic electroencephalography (EEG) features. In all patients, diagnosis was based on karyotype analysis of at least 100 metaphases.

RESULTS

We identified 36 patients who met at least two of the selected criteria: six patients (16.7%) with R20 and 30 (83.3%) without R20 (non-R20). All patients with R20 met all three criteria. Eleven (36.7%) patients without R20, however, also displayed the full triad. In 19 patients without R20 (63.3%), one of the three clinical features was missing: frontal lobe seizures were not resistant to antiepileptic drugs (AED) in four (13.3%), recurrent NCSE was missing in six (20%), and nine (30%) patients did not have typical EEG features. Based on this data, specificity was 63.3%, positive predictive value was 35.3%, and sensitivity and negative predictive values were 100%. Additionally, a review of all publications describing the R20 phenotype revealed that 81.98% of patients with R20 display the full electroclinical triad.

CONCLUSIONS

In our study, all patients with R20 displayed the three electroclinical characteristics. This is in line with previous reports (presenting high sensitivity and negative predictive value). However, these features can also be observed in other epilepsies and are not specific to R20. Our findings suggest that in the presence of the full triad of symptoms, karyotype analysis focused on chromosome 20 should be conducted.

Epilepsy in ring chromosome 20 syndrome

OBJECTIVE

Ring chromosome 20 syndrome is characterized by severe, drug resistant childhood onset epilepsy, often accompanied by cognitive impairment. We characterized the electro-clinical phenotype and the long-term course of epilepsy in a large series.

METHODS

We reviewed the electro-clinical phenotype of 25 patients (aged 8-59 years), and assessed the relationship between epilepsy severity and clinical and/or genetic variables. We also searched for reports of patients diagnosed with r(20) syndrome in the literature, included those whose clinical information was sufficiently accurate, and compared their clinical features with the ones of our patients.

RESULTS

Epilepsy exhibited an age dependent course. When seizure onset occurred in childhood (21 patients), terrifying hallucinations associated with focal motor seizures, often sleep-related (8 patients), or dyscognitive seizures (13 patients), were prominent features, often evolving into epileptic encephalopathy associated with non-convulsive status epilepticus (11 patients). In the long-term, progressive stabilization of drug resistant epilepsy associated with non-convulsive status epilepticus, focal seizures with motor and autonomic features, and eyelid myoclonia were noticed. Epilepsy onset in adolescence (3 patients) was accompanied by a milder developmental course, dyscognitive seizures and non-convulsive status epilepticus, and no cognitive decline. Only three older patients became seizure free (>5 years) We found statistically significant correlations between age at epilepsy onset and cognitive level. Although in the study cohort the relationship between r(20) ratio, age at epilepsy onset and cognitive level was non-statistically significant, it reached significance evaluating the larger cohort of patients previously published.

SIGNIFICANCE

In ring(20) syndrome, epilepsy has an age dependent course and a worse outcome when age at seizure onset is earlier. The r(20) ratio and severity of cognitive impairment appear to be directly related to each other and inversely correlated with the age at epilepsy onset.

A practical, simple, and useful method of categorizing interictal EEG features in children

We introduce a simple scheme of categorizing interictal EEG in patients with pediatric epilepsy. Five patterns of EEG can be determined by using 2 interictal EEG domains: organization of the background activity and a morphology/topography of epileptiform discharges. These patterns relate to commonly recognized categories of pediatric epilepsy: familial epilepsies, genetic generalized epilepsies, self-limited epilepsies, epilepsies with encephalopathy, and focal structural epilepsies. Each group has distinguishable clinical presentations, inheritance patterns, and outcomes. This categorization may be a useful educational tool; it may also guide decisions about further testing and management.

Emerging neuroimaging contribution to the diagnosis and management of the ring chromosome 20 syndrome

Ring chromosome 20 [r(20)] syndrome is an underdiagnosed chromosomal anomaly characterized by severe epilepsy, behavioral problems, and mild-to-moderate cognitive deficits. Since the cognitive and behavioral decline follows seizure onset, this syndrome has been proposed as an epileptic encephalopathy (EE). The recent overwhelming development of advanced neuroimaging techniques has opened a new era in the investigation of the brain networks subserving the EEs. In particular, functional neuroimaging tools are well suited to show alterations related to epileptiform discharges at the network level and to build hypotheses about the mechanisms underlying the cognitive disruption observed in these conditions. This paper reviews the brain circuits and their disruption as revealed by functional neuroimaging studies in patients with [r(20)] syndrome. It discusses the clinical consequences of the neuroimaging findings on the management of patients with [r(20)] syndrome, including their impact to an earlier diagnosis of this disorder. Based on the available lines of evidences, [r(20)] syndrome is characterized by interictal and ictal dysfunctions within basal ganglia-prefrontal lobe networks and by long-lasting effects of the peculiar theta-delta rhythm, which represents an EEG marker of the syndrome on integrated brain networks that subserve cognitive functions.

Epilepsy-related brain networks in ring chromosome 20 syndrome: an EEG-fMRI study

OBJECTIVE

To identify the brain networks that are involved in the different electroencephalography (EEG) abnormalities in patients with ring chromosome 20 [r(20)] syndrome. We hypothesize the existence of both distinctive and common brain circuits for the paroxysmal high voltage sharp waves (hSWs), the seizures, and the slow-wave 3-7 Hz rhythm that characterize this condition.

METHODS

Thirteen patients with [r(20)] syndrome were studied by means of EEG simultaneously recorded with functional magnetic resonance imaging (EEG-fMRI). EEG traces were reviewed in order to detect the pathologic interictal (hSWs) and ictal activities; the 3-7 Hz theta-delta power was derived using a fast Fourier transform. A group-level analysis was performed for each type of EEG abnormality separately using a fixed-effect model and a conjunction analysis. Finally, a second-level random-effect model was applied considering together the different EEG abnormalities, without distinction between hSW, seizures, or theta-delta rhythms.

RESULTS

Subcontinuous theta-delta rhythm was recorded in seven patients, seizures in two, and hSWs in three patients. The main results are the following: (1) the slow-wave rhythm was related to blood oxygen level-dependent (BOLD) increases in the premotor, sensory-motor, and temporoparietal cortex, and to BOLD decrements involving the default mode (DMN) and the dorsal attention networks (DANs); (2) the ictal-related BOLD changes showed an early involvement of the prefrontal lobe; (3) increases in BOLD signal over the basal ganglia, either for interictal and ictal activities, were observed; (4) a common pattern of positive BOLD changes in the bilateral perisylvian regions was found across the different EEG abnormalities.

SIGNIFICANCE

The BOLD increment in the perisylvian network and the decrease of the DMN and DAN could be the expression of the [r(20)] syndrome-related cognitive and behavioral deficits. The observed BOLD patterns are similar to the ones detected in other epileptic encephalopathies, suggesting that different epileptic disorders characterized by neurobehavioral regression are associated with dysfunction in similar brain networks. A PowerPoint slide summarizing this article is available for download in the Supporting Information section here.

Low frequency mu-like activity characterizes cortical rhythms in epilepsy due to ring chromosome 20

OBJECTIVES

To evaluate the spectral and spatial features of the cortical rhythms in patients affected by ring chromosome 20 - [r(20)]-syndrome.

METHODS

Twelve patients with [r(20)] syndrome were studied. As controls we enrolled 12 patients with idiopathic generalized epilepsy (IGE) and 12 healthy volunteers (HV). Blind source separation, spectral analyses and source reconstruction were applied in all cases in order to identify reliable spatio-temporal patterns of cortical activity.

RESULTS

A theta-delta EEG rhythm was identified in [r(20)] patients, with spectral peak ranging between 3 and 7Hz and whose generators mapped over the sensory-motor cortices. A second peak laying at a frequency about double with respect to the first one was present in 6 cases. Analogue methodological approach in HV and IGE groups failed to show similar findings.

CONCLUSIONS

EEG of [r(20)] patients reveals the existence of a highly reproducible EEG pattern arising from the sensory-motor system.

SIGNIFICANCE

The recognition of this peculiar EEG pattern could help the diagnostic work-up. Additionally, our findings supports the existence of a parallelism between this EEG trait and the physiological "mu" rhythm which is generate by the sensory-motor system. Such link suggests a sensory-motor system dysfunction in [r(20)] patients.

Chromosome disorders associated with epilepsy

Epilepsy is a feature of several hundred chromosome abnormalities. However, there are relatively few conditions in which epilepsy is a consistent feature and even fewer in which the electroclinical phenotype is recognizable. Advances in cytogenetics and molecular genetics are leading to the detection of more complex and smaller chromosomal re-arrangements, duplications, and deletions using techniques such as comparative genome hybridization (CGH). This will provide new challenges for the epilepsy specialist who, in partnership with the geneticist, will have to judge the clinical relevance of these abnormalities. Most chromosome anomalies associated with epilepsy are individually rare therefore clinicians must continue to collaborate to describe novel electroclinical phenotypes. Cytogenetic studies should be requested in all individuals with refractory epilepsy and no clear underlying cause even in cases with no dysmorphic features, no learning disability, and an EEG suggestive of genetic generalized epilepsy. In syndromes where epilepsy is a consistent feature the seizure semiology and EEG features can suggest a specific diagnosis and guide the clinician to the appropriate cytogenetic investigation. An early correct diagnosis can save unnecessary investigations and guide prognosis. Children with chromosomal disorders frequently have learning disability, which can be further compromised by an epileptic encephalopathy. Medications should be targeted to specific seizure types.

Ictal involvement of the nigrostriatal system in subtle seizures of ring chromosome 20 epilepsy

Studies in animal models and patients with epilepsy have suggested that basal ganglia circuits may control epileptic seizures and that striatal dopaminergic transmission may play a role in seizure modulation and interruption. Chromosome 20 [r(20)] syndrome is a well-defined chromosomal disorder characterized by epilepsy, mild-to-moderate mental retardation, and lack of recognizable dysmorphic features. Epilepsy is often the most important clinical manifestation of the syndrome, with prolonged episodes of nonconvulsive status epilepticus suggesting dysfunction in the seizure control system. We present the ictal blood oxygen level-dependent (BOLD) changes in brief seizures recorded by means of electroencephalography-functional magnetic resonance imaging (EEG-fMRI) coregistration in a patient with [r(20)] syndrome. We observed ictal BOLD increments in a cortical-subcortical network involving substantia nigrastriatum and frontal cortex. At present, this is the first functional neuroimaging evidence of the involvement of the nigrostriatal system during ictal EEG discharges in [r(20)] syndrome supporting a role of the basal ganglia circuits in human epileptic seizures.

The evolving electroclinical syndrome of "epilepsy with ring chromosome 20"

PURPOSE

Ring chromosome 20 {r(20)}--manifests as a refractory epilepsy syndrome with complex partial seizures (CPS), nocturnal frontal lobe seizures and non-convulsive status epilepticus (NCSE) in the majority of cases. r20 lacks a specific phenotypic expression or dysmorphic features. Psychomotor development may be normal, making the diagnosis difficult unless there is a high index of suspicion. This description of further cases is intended to improve recognition of this syndrome.

METHODS

Karyotyping for r20 was done in patients presenting with cryptogenic refractory epilepsy suggestive of r20 from August 2008 to September 2010. We identified three patients with r20 associated with refractory epilepsy. All were investigated with long-term video EEG. Their unique electro clinical features; epilepsy syndrome and outcome are discussed and compared to the available literature.

RESULTS

Karyotyping revealed ring 20 in 6-40% of lymphocytes. All manifested with seizures beginning at 2-10years of age. All had CPS; two had NCSE and one a seizure disorder resembling Lennox-Gastaut syndrome. The interictal EEG showed epileptiform abnormalities predominantly over the frontotemporal regions. Two patients had NCSE with generalized, frontally dominant theta and spike and wave discharges. None had facial dysmorphism or imaging abnormalities. They remained resistant to antiepileptic drugs.

CONCLUSIONS

The use of routine karyotyping can easily pick up r(20); this information is especially useful in resource-poor countries. We have evolved an algorithm stating the indications to attempt r(20) karyotyping in a given patient in the light of the results of the present study and the existing literature.

Genetic investigations on 8 patients affected by ring 20 chromosome syndrome

Background

Mosaic Chromosome 20 ring [r(20)] is a chromosomal disorder associated with a rare syndrome characterized by a typical seizure phenotype, a particular electroclinical pattern, cognitive impairment, behavioural problems and absence of a consistent pattern of dysmorphology. The pathogenic mechanism underlying seizures disorders in r(20) syndrome is still unknown. We performed a detailed clinical and genetic study on 8 patients with r(20) chromosome, aimed at detecting the genetic mechanism underlying r(20) syndrome.

Methods

We submitted 8 subjects with a previous diagnosis of ring 20 chromosome mosaicism to a clinical re-evaluation, followed by cytogenetic, FISH, array-CGH and molecular analyses. The genetic study was also extended to their available parents.

Results

FISH and array-CGH experiments indicate that cryptic deletions on chromosome 20 are not the cause of the r(20) chromosome associated disease. Moreover, no evidence of chromosome 20 uniparental disomy was found. Analysis of FISH signals given by variant in size alphoid tandem repeats probes on the normal chromosome 20 and the r(20) chromosome in the mosaic carriers suggests that the r(20) chromosome is the same chromosome not circularized in the "normal" cell line.

Conclusions

Higher percentages of r(20) chromosome cells were observed to be related with precocious age at seizure onset and with resistance to antiepileptic drug treatment. Behavioural problems also seem to be associated with higher percentages of r(20) chromosome cells. Our results suggest that an epigenetic mechanism perturbing the expression of genes close to the telomeric regions, rather than deletion of genes located at the distal 20p and/or 20q regions, may underlie the manifestation of r(20) syndrome.

Ring chromosome 20 syndrome: a link between epilepsy onset and neuropsychological impairment in three children

PURPOSE

Ring chromosome 20 [r(20)] syndrome is a well-defined chromosomal disorder characterized by epilepsy, mild-to-moderate mental retardation, and lack of recognizable dysmorphic features. Epilepsy is often the most important clinical manifestation of the syndrome, even if its appearance is not constantly precocious. Seizures are frequently drug resistant.

METHODS

We describe three children with [r(20)] syndrome in whom the onset of epilepsy (age at onset range: 4 years and 6 months to 9 years and 4 months) determined a kind of epileptic status (age at onset range: 6 years and 10 months to 9 years and 8 months) with dramatic neuropsychological deterioration. This epileptic status lasted for several months because of refractoriness to most antiepileptic drugs (AEDs), but it was treated successfully with a combination of valproate and lamotrigine in two children.

RESULTS

As soon as seizures stopped, the children showed prompt recovery with partial restoration of the neuropsychological impairment.

CONCLUSION

This clinical picture can be described as abrupt epileptic encephalopathy.

Diagnosis and management of nonconvulsive status epilepticus in children

Nonconvulsive status epilepticus (NCSE) encompasses a wide range of diagnoses with variable outcomes and treatment recommendations. In children, NCSE can be observed in various conditions, including acute neurological injuries, specific childhood epilepsy syndromes and other neurological conditions, and can also be observed in individuals with learning difficulties. NCSE in children is thought to be under-recognized, and further studies examining the electrographic characteristics of very young children in NCSE would aid the prompt recognition of additional patients. Some subtypes of NCSE are probably more harmful than others, and long-term prospective studies are needed to evaluate the damaging potential of NCSE itself as opposed to that of the underlying circumstances in which it occurs. Specific data in childhood are clearly lacking, but extrapolation from adult studies indicates that aggressive treatment is most warranted in comatose patients. By contrast, a cautious approach seems to be indicated for absence status epilepticus, complex partial status epilepticus and electrical status epilepticus during sleep.

The epidemiology of convulsive status epilepticus in children: a critical review

There is ongoing debate regarding the most appropriate definition of status epilepticus. This depends upon the research question being asked. Based on the most widely used "30 min definition," the incidence of childhood convulsive status epilepticus (CSE) in developed countries is approximately 20/100,000/year, but will vary depending, among others, on socioeconomic and ethnic characteristics of the population. Age is a main determinant of the epidemiology of CSE and, even within the pediatric population there are substantial differences between older and younger children in terms of incidence, etiology, and frequency of prior neurological abnormalities or prior seizures. Overall, incidence is highest during the first year of life, febrile CSE is the single most common cause, around 40% of children will have previous neurological abnormalities and less than 15% will have a prior history of epilepsy. Outcome is mainly a function of etiology. However, the causative role of CSE itself on mesial temporal sclerosis and subsequent epilepsy or the influence of age, duration, or treatment on outcome of CSE remains largely unknown. Future studies should aim at clarifying these issues and identifying specific ethnic, genetic, or socioeconomic factors associated with CSE to pinpoint potential targets for its primary and secondary prevention.

More severe epilepsy and cognitive impairment in the offspring of a mother with mosaicism for the ring 20 chromosome

PURPOSE

Ring chromosome 20 [r(20)] syndrome is a rare chromosomal disorder. Cases tend to be sporadic. We elucidate the characteristics of an inherited r(20) mosaicism by describing the clinical features of three family members: a mother and her two children.

RESULTS

The mosaicism rate of the mother was 10% and that of the children 40%. The mother experienced her first epileptic seizures at 24 years of age. Epilepsy was diagnosed two years later. After an unstable period lasting 3 years, she has been seizure-free for 13 years on a combination of valproate and lamotrigine. She has normal intelligence with full working capacity. The daughter exhibited her first epileptic seizures at the age of 7 years and she continues to have seizures weekly. The first epileptic seizures in the son were observed at 5 years of age. The son's epilepsy has been drug resistant from the onset, and a vagal nerve stimulator (VNS) has been ineffective. Psychomotor development was normal in both children up to the onset of epilepsy. Learning difficulties increased throughout school age and both children needed special educational programs. Neuropsychological evaluations have shown deterioration of cognitive levels. Both children had behavioural problems during school age but no longer in adolescence. All three subjects are nondysmophic, normocephalic and of normal growth.

CONCLUSION

In this family the phenotype of r(20) mosaicism seems to be more severe in the successive generation along with a greater level of mosaicism. The aggravated clinical picture in inherited r(20) mosaicism concerned the onset of epilepsy, drug responsiveness, the cognitive level and behavioural features.

Electroclinical evolution in ring chromosome 20 epilepsy syndrome: a case with severe phenotypic features followed for 25 years

Intractable epilepsy and peculiar EEG patterns characterize ring chromosome 20 syndrome [r(20)], while dysmorphic features, mental retardation and behavioural disturbances are widely variable. The clinical evolution of r(20) over time is not well defined as relatively few cases have been reported. Here we describe a patient with severe clinical features followed for a 25-year period. The patient was subjected to clinical, psychometric and EEG evaluation twice a year from the age of 21 years. Cytogenetic studies, using chromosome analysis and fluorescence in situ hybridization (FISH) and several immunological investigations were performed. Ring chromosome 20 was found in 50% of examined metaphases with the deletion of subtelomeric regions 20p and 20q. Our patient presented with marked dysmorphic features, severe mental retardation, tetraparesis, dysarthria and intractable epilepsy with onset during the first year of life. During follow up, EEG findings and clinical features progressively worsened: a progressive disorganization of background EEG activity occurred and mental and motor impairment evolved. The severity of clinical expression depended on the extent of chromosomal deletion and on the haploinsufficiency of other important related genetic loci due to ring instability. The progressive worsening of both clinical and EEG features over a long period, which has also been reported by other authors, further characterized this syndrome.

Epilepsy in children

10.5 million children worldwide are estimated to have active epilepsy. Over the past 15 years, syndrome-oriented clinical and EEG diagnosis, and better aetiological diagnosis, especially supported by neuroimaging, has helped to clarify the diversity of epilepsy in children, and has improved management. Perinatal and postinfective encephalopathy, cortical dysplasia, and hippocampal sclerosis account for the most severe symptomatic epilepsies. Ion channel defects can underlie both benign age-related disorders and severe epileptic encephalopathies with a progressive disturbance in cerebral function. However, the reasons for age-related expression in children are not understood. Neither are the mechanisms whereby an epileptic encephalopathy originates. Several new drugs have been recently introduced but have provided limited therapeutic benefits. However, treatment and quality of life have improved because the syndrome-specific efficacy profile of drugs is better known, and there is heightened awareness that compounds with severe cognitive side-effects and heavy polytherapies should be avoided. Epilepsy surgery is an important option for a few well-selected individuals, but should be considered with great caution when there is no apparent underlying brain lesion.

Ring chromosome 20 with nonconvulsive status epilepticus: electroclinical correlation of a rare epileptic syndrome

The electroclinical features of two Thai women with ring chromosome 20 and nonconvulsive status epilepticus (NCSE) were studied. Both have also had generalized tonic-clonic seizures and complex partial seizures of varying frequencies since adolescence. Their intellectual functions were normal. Twenty-four-hour video/EEG telemetry recorded during the NCSE showed fluctuating consciousness between overt unresponsiveness and normal awareness. The EEG consisted of long-lasting generalized rhythmic 3-5 Hz sharp or slow waves with a few spikes, lasting several days. Despite the continuous discharges, the patients had relatively subtle clinical episodes of seizures, during which they were sometimes responsive to verbal stimuli. Intravenous antiepileptic drugs (AED) had little effect on the rhythmic EEG. No lesion in their MRIs contributed to NCSE. Ring chromosome 20 was found in 20% of female karyotype in both patients [46,XX,r(20) (p13 q13)/46,XX] but were negative in four healthy siblings. Oral AEDs decreased more than 75% of the overt CPS episodes in both patients at 22 and 26 months of follow-up but had no effect on the natural history of electrical NCSE. The patients' daily activities were minimally affected by the ongoing electrical discharges. These are the first two cases reported of ring chromosome 20 with NCSE in Thailand. Our patients present a rather benign and pharmacologically responsive course probably because of the low percentage of r(20) mosaicism. The electroclinical correlations in our cases raise the possibility that the mechanism of continuous rhythmic waves in this syndrome may be unrelated to epilepsy. Assessing the severity of this syndrome using both clinical seizures and EEG is crucial.

Mosaicism and phenotype in ring chromosome 20 syndrome

Ring chromosome 20 [r(20)] syndrome is a rare chromosomal disorder characterized by epilepsy, mild to moderate mental impairment, and malformation. Patients generally show mosaicism in 1-100% of lymphocytes with r(20). We report here a patient with r(20) syndrome who exhibited mild phenotype with the small ratio of mosaicism (13%) with r(20). Although previous small-scale studies concluded that the mosaicism ratio was unrelated to clinical phenotype, our reassessment of all 57 reported cases has revealed that the ratio is significantly associated with age at seizure onset, intelligence quotient, and malformation, but not with the response of epilepsy to drug treatment. Our results provide important clinical information and prediction for r(20) syndrome.

Malignant Refractory Epilepsy in Identical Twins Mosaic for a Supernumerary Ring Chromosome 19

We report identical twins with supernumerary ring chromosome 19 mosaicism, who had severe refractory epilepsy at an early age. The epilepsy was dominated largely by severe life-threatening tonic seizures. Both twins died, likely as a consequence of their severe epilepsy. They displayed no dysmorphic features. Eight cases of ring chromosome 19 have been reported in the literature, all to our knowledge without epilepsy. The clinical picture of these twins emphasizes the importance of carrying out a karyotype study on patients with early-onset epilepsy even in the absence of dysmorphic features.