Neurophysiology of Rett syndrome

24-h continuous non-invasive multiparameter home monitoring of vitals in patients with Rett syndrome by an innovative wearable technology: evidence of an overlooked chronic fatigue status

Background

Sleep is disturbed in Rett syndrome (RTT), a rare and progressive neurodevelopmental disorder primarily affecting female patients (prevalence 7.1/100,000 female patients) linked to pathogenic variations in the X-linked methyl-CpG-binding protein 2 (MECP2) gene. Autonomic nervous system dysfunction with a predominance of the sympathetic nervous system (SNS) over the parasympathetic nervous system (PSNS) is reported in RTT, along with exercise fatigue and increased sudden death risk. The aim of the present study was to test the feasibility of a continuous 24 h non-invasive home monitoring of the biological vitals (biovitals) by an innovative wearable sensor device in pediatric and adolescent/adult RTT patients.

Methods

A total of 10 female patients (mean age 18.3 ± 9.4 years, range 4.7-35.5 years) with typical RTT and MECP2 pathogenic variations were enrolled. Clinical severity was assessed by validated scales. Heart rate (HR), respiratory rate (RR), and skin temperature (SkT) were monitored by the YouCare Wearable Medical Device (Accyourate Group SpA, L'Aquila, Italy). The average percentage of maximum HR (HRmax%) was calculated. Heart rate variability (HRV) was expressed by consolidated time-domain and frequency-domain parameters. The HR/LF (low frequency) ratio, indicating SNS activation under dynamic exercise, was calculated. Simultaneous continuous measurement of indoor air quality variables was performed and the patients' contributions to the surrounding water vapor partial pressure [PH2O (pt)] and carbon dioxide [PCO2 (pt)] were indirectly estimated.

Results

Of the 6,559.79 h of biovital recordings, 5051.03 h (77%) were valid for data interpretation. Sleep and wake hours were 9.0 ± 1.1 h and 14.9 ± 1.1 h, respectively. HRmax % [median: 71.86% (interquartile range 61.03-82%)] and HR/LF [median: 3.75 (interquartile range 3.19-5.05)] were elevated, independent from the wake-sleep cycle. The majority of HRV time- and frequency-domain parameters were significantly higher in the pediatric patients (p ≤ 0.031). The HRV HR/LF ratio was associated with phenotype severity, disease progression, clinical sleep disorder, subclinical hypoxia, and electroencephalographic observations of multifocal epileptic activity and general background slowing.

Conclusion

Our findings indicate the feasibility of a continuous 24-h non-invasive home monitoring of biovital parameters in RTT. Moreover, for the first time, HRmax% and the HR/LF ratio were identified as potential objective markers of fatigue, illness severity, and disease progression.

Effect of presentation rate on auditory processing in Rett syndrome: event-related potential study

BACKGROUND

Rett syndrome (RS) is a rare neurodevelopmental disorder characterized by mutations in the MECP2 gene. Patients with RS have severe motor abnormalities and are often unable to walk, use hands and speak. The preservation of perceptual and cognitive functions is hard to assess, while clinicians and care-givers point out that these patients need more time to process information than typically developing peers. Neurophysiological correlates of auditory processing have been also found to be distorted in RS, but sound presentation rates were relatively quick in these studies (stimulus onset asynchrony, SOA < 1000 ms). As auditory event-related potential (ERP) is typically increased with prolongation of SOA we aim to study if SOA prolongation might compensate for observed abnormalities.

METHODS

We presented a repetitive stimulus (1000 Hz) at three different SOAs of 900 ms, 1800 ms, and 3600 ms in children with RS (N = 24, Mean age = 9.0 ± 3.1) and their typical development (TD) peers (N = 27, Mean age = 9.7 ± 3.4) while recording 28-channels electroencephalogram, EEG. Some RS participants (n = 10) did not show clear ERP and were excluded from the analysis.

RESULTS

Major ERP components (here assessed as N1P1 and P2N1 peak-to-peak values) were smaller at SOA 900 than at longer SOAs in both groups, pointing out that the basic mechanism of adaptation in the auditory system is preserved in at least in RS patients with evident ERPs. At the same time the latencies of these components were significantly delayed in the RS than in TD. Moreover, late components (P2N1 and N2P2) were drastically reduced in Rett syndrome irrespective of the SOA, suggesting a largely affected mechanism of integration of upcoming sensory input with memory. Moreover, developmental stagnation of auditory ERP characterized patients with RS: absence of typical P2N1 enlargement and P1 and N1 shortening with age at least for shortest SOA.

LIMITATIONS

We could not figure out the cause for the high percentage of no-evident ERP RS participants and our final sample of the RS group was rather small. Also, our study did not include a control clinical group.

CONCLUSIONS

Thus, auditory ERPs inform us about abnormalities within auditory processing that cannot be fully overcomed by slowing presentation rate.

Leptin antagonism improves Rett syndrome phenotype in symptomatic male Mecp2-null mice

Rett syndrome (RTT) is a severe neurodevelopmental disorder that arise from de novo mutations in the X-linked gene MECP2 (methyl-CpG-binding protein 2). Circulating levels of the adipocyte hormone leptin are elevated in RTT patients and rodent models of the disease. Leptin targets a large number of brain structures and regulates a wide range of developmental and physiological functions which are altered in RTT. We hypothesized that elevated leptin levels might contribute to RTT pathogenesis. Accordingly, we show that pharmacological antagonism of leptin or genetic reduction of leptin production prevents the degradation of health status, weight loss and the progression of breathing and locomotor deficits. At the neuronal level, the anti-leptin strategies rescue the hippocampal excitatory/inhibitory imbalance and synaptic plasticity impairment. Targeting leptin might therefore represent a new approach for RTT treatment.

Electrophysiological Biomarkers in Genetic Epilepsies

Precision treatments for epilepsy targeting the underlying genetic diagnoses are becoming a reality. Historically, the goal of epilepsy treatments was to reduce seizure frequency. In the era of precision medicine, however, outcomes such as prevention of epilepsy progression or even improvements in cognitive functions are both aspirational targets for any intervention. Developing methods, both in clinical trial design and in novel endpoints, will be necessary for measuring, not only seizures, but also the other neurodevelopmental outcomes that are predicted to be targeted by precision treatments. Biomarkers that quantitatively measure disease progression or network level changes are needed to allow for unbiased measurements of the effects of any gene-level treatments. Here, we discuss some of the promising electrophysiological biomarkers that may be of use in clinical trials of precision therapies, as well as the difficulties in implementing them.

Reviewing Evidence for the Relationship of EEG Abnormalities and RTT Phenotype Paralleled by Insights from Animal Studies

Rett syndrome (RTT) is a rare neurodevelopmental disorder that is usually caused by mutations of the MECP2 gene. Patients with RTT suffer from severe deficits in motor, perceptual and cognitive domains. Electroencephalogram (EEG) has provided useful information to clinicians and scientists, from the very first descriptions of RTT, and yet no reliable neurophysiological biomarkers related to the pathophysiology of the disorder or symptom severity have been identified to date. To identify consistently observed and potentially informative EEG characteristics of RTT pathophysiology, and ascertain areas most worthy of further systematic investigation, here we review the literature for EEG abnormalities reported in patients with RTT and in its disease models. While pointing to some promising potential EEG biomarkers of RTT, our review identify areas of need to realize the potential of EEG including (1) quantitative investigation of promising clinical-EEG observations in RTT, e.g., shift of mu rhythm frequency and EEG during sleep; (2) closer alignment of approaches between patients with RTT and its animal models to strengthen the translational significance of the work (e.g., EEG measurements and behavioral states); (3) establishment of large-scale consortium research, to provide adequate Ns to investigate age and genotype effects.

Evoked Potentials and EEG Analysis in Rett Syndrome and Related Developmental Encephalopathies: Towards a Biomarker for Translational Research

Rett syndrome is a debilitating neurodevelopmental disorder for which no disease-modifying treatment is available. Fortunately, advances in our understanding of the genetics and pathophysiology of Rett syndrome has led to the development of promising new therapeutics for the condition. Several of these therapeutics are currently being tested in clinical trials with others likely to progress to clinical trials in the coming years. The failure of recent clinical trials for Rett syndrome and other neurodevelopmental disorders has highlighted the need for electrophysiological or other objective biological markers of treatment response to support the success of clinical trials moving forward. The purpose of this review is to describe the existing studies of electroencephalography (EEG) and evoked potentials (EPs) in Rett syndrome and discuss the open questions that must be addressed before the field can adopt these measures as surrogate endpoints in clinical trials. In addition to summarizing the human work on Rett syndrome, we also describe relevant studies with animal models and the limited research that has been carried out on Rett-related disorders, particularly methyl-CpG binding protein 2 (MECP2) duplication syndrome, CDKL5 deficiency disorder, and FOXG1 disorder.

Diurnal variation in autonomic regulation among patients with genotyped Rett syndrome

BACKGROUND

Rett syndrome is a severe neurological disorder with a range of disabling autonomic and respiratory symptoms and resulting predominantly from variants in the methyl-CpG binding protein 2 gene on the long arm of the X-chromosome. As basic research begins to suggest potential treatments, sensitive measures of the dynamic phenotype are needed to evaluate the results of these research efforts. Here we test the hypothesis that the physiological fingerprint of Rett syndrome in a naturalistic environment differs from that of controls, and differs among genotypes within Rett syndrome.

METHODS

A comprehensive array of heart rate variability, cardiorespiratory coupling and cardiac repolarisation measures were evaluated from an existing database of overnight and daytime inhome ambulatory recordings in 47 cases and matched controls.

RESULTS

Differences between girls with Rett syndrome and matched controls were apparent in a range of autonomic measures, and suggest a shift towards sympathetic activation and/or parasympathetic inactivation. Daily temporal trends analysed in the context of circadian rhythms reveal alterations in amplitude and phase of diurnal patterns of autonomic balance. Further analysis by genotype class confirms a graded presentation of the Rett syndrome phenotype such that patients with early truncating mutations were most different from controls, while late truncating and missense mutations were least different from controls.

CONCLUSIONS

Comprehensive autonomic measures from extensive inhome physiological measurements can detect subtle variations in the phenotype of girls with Rett syndrome, suggesting these techniques are suitable for guiding novel therapies.

Sensory evoked potentials in patients with Rett syndrome through the lens of animal studies: Systematic review

OBJECTIVE

Systematically review the abnormalities in event related potential (ERP) recorded in Rett Syndrome (RTT) patients and animals in search of translational biomarkers of deficits related to the particular neurophysiological processes of known genetic origin (MECP2 mutations).

METHODS

Pubmed, ISI Web of Knowledge and BIORXIV were searched for the relevant articles according to PRISMA standards.

RESULTS

ERP components are generally delayed across all sensory modalities both in RTT patients and its animal model, while findings on ERPs amplitude strongly depend on stimulus properties and presentation rate. Studies on RTT animal models uncovered the abnormalities in the excitatory and inhibitory transmission as critical mechanisms underlying the ERPs changes, but showed that even similar ERP alterations in auditory and visual domains have a diverse neural basis. A range of novel approaches has been developed in animal studies bringing along the meaningful neurophysiological interpretation of ERP measures in RTT patients.

CONCLUSIONS

While there is a clear evidence for sensory ERPs abnormalities in RTT, to further advance the field there is a need in a large-scale ERP studies with the functionally-relevant experimental paradigms.

SIGNIFICANCE

The review provides insights into domain-specific neural basis of the ERP abnormalities and promotes clinical application of the ERP measures as the non-invasive functional biomarkers of RTT pathophysiology.

Oculomotor Function in Individuals With Rett Syndrome

BACKGROUND

Individuals with Rett syndrome (RTT) are notoriously reliant on the use of eye gaze as a primary means of communication. Underlying an ability to communicate successfully via eye gaze is a complex matrix of requirements, with an intact oculomotor system being just one element. To date, the underlying neural and motor pathways associated with eye gaze are relatively under-researched in RTT.

PURPOSE

This study was undertaken to plug this gap in knowledge and to further the understanding of RTT in one specific area of development and function, namely oculomotor function.

MATERIAL AND METHODS

The eye movements of 18 girls and young women with RTT were assessed by electronystagmography (ENG). This tested their horizontal saccadic and smooth pursuit eye movements as well as optokinetic nystagmus and vestibulo-ocular reflex. Their results were compared with normative data collected from 16 typically developing children and teenagers.

RESULTS

Overall, the individuals with RTT demonstrated a range of eye movements on a par with their typically developing peers. However, there were a number of difficulties in executing the ENG testing with the RTT cohort which made quantitative analysis tricky, such as reduced motivation and attention to test materials and low-quality electrode signals.

CONCLUSIONS

This study suggests that individuals with RTT have an intact oculomotor system. However, modifications should be made to the ENG assessment procedure to combat problems in testing and add strength to the results. Further investigation into these testing difficulties is warranted in order to inform such modifications.

Heightened Delta Power during Slow-Wave-Sleep in Patients with Rett Syndrome Associated with Poor Sleep Efficiency

Sleep problems are commonly reported in Rett syndrome (RTT); however the electroencephalographic (EEG) biomarkers underlying sleep dysfunction are poorly understood. The aim of this study was to analyze the temporal evolution of quantitative EEG (qEEG) biomarkers in overnight EEGs recorded from girls (2-9 yrs. old) diagnosed with RTT using a non-traditional automated protocol. In this study, EEG spectral analysis identified high delta power cycles representing slow wave sleep (SWS) in 8-9h overnight sleep EEGs from the frontal, central and occipital leads (AP axis), comparing age-matched girls with and without RTT. Automated algorithms quantitated the area under the curve (AUC) within identified SWS cycles for each spectral frequency wave form. Both age-matched RTT and control EEGs showed similar increasing trends for recorded delta wave power in the EEG leads along the antero-posterior (AP). RTT EEGs had significantly fewer numbers of SWS sleep cycles; therefore, the overall time spent in SWS was also significantly lower in RTT. In contrast, the AUC for delta power within each SWS cycle was significantly heightened in RTT and remained heightened over consecutive cycles unlike control EEGs that showed an overnight decrement of delta power in consecutive cycles. Gamma wave power associated with these SWS cycles was similar to controls. However, the negative correlation of gamma power with age (r = -.59; p<0.01) detected in controls (2-5 yrs. vs. 6-9 yrs.) was lost in RTT. Poor % SWS (i.e., time spent in SWS overnight) in RTT was also driven by the younger age-group. Incidence of seizures in RTT was associated with significantly lower number of SWS cycles. Therefore, qEEG biomarkers of SWS in RTT evolved temporally and correlated significantly with clinical severity.

Seizures and EEG features in 74 patients with genetic-dysmorphic syndromes

Epilepsy is one of the most common findings in chromosome aberrations. Types of seizures and severity may significantly vary both between different conditions and within the same aberration. Hitherto specific seizures and EEG patterns are identified for only few syndromes. We studied 74 patients with defined genetic-dysmorphic syndromes with and without epilepsy in order to assess clinical and electroencephalographic features, to compare our observation with already described electro-clinical phenotypes, and to identify putative electroencephalographic and/or seizure characteristics useful to address the diagnosis. In our population, 10 patients had chromosomal disorders, 19 microdeletion or microduplication syndromes, and 32 monogenic syndromes. In the remaining 13, syndrome diagnosis was assessed on clinical grounds. Our study confirmed the high incidence of epilepsy in genetic-dysmorphic syndromes. Moreover, febrile seizures and neonatal seizures had a higher incidence compared to general population. In addition, more than one third of epileptic patients had drug-resistant epilepsy. EEG study revealed poor background organization in 42 patients, an excess of diffuse rhythmic activities in beta, alpha or theta frequency bands in 34, and epileptiform patterns in 36. EEG was completely normal only in 20 patients. No specific electro-clinical pattern was identified, except for inv-dup15, Angelman, and Rett syndromes. Nevertheless some specific conditions are described in detail, because of notable differences from what previously reported. Regarding the diagnostic role of EEG, we found that--even without any epileptiform pattern--the generation of excessive rhythmic activities in different frequency bandwidths might support the diagnosis of a genetic syndrome.

Rett Syndrome: Coming to Terms with Treatment

Rett syndrome (RTT) has experienced remarkable progress over the past three decades since emerging as a disorder of worldwide proportions, particularly with discovery of the linkage of RTT to MECP2 mutations. The advances in clinical research and the increasing pace of basic science investigations have accelerated the pattern of discovery and understanding. Clinical trials are ongoing and others are planned. A review of these events and the prospects for continued success are highlighted below. The girls and women encountered today with RTT are, overall, in better general, neurologic, and behavioral health than those encountered earlier. This represents important progress worldwide from the concerted efforts of a broadly based and diverse clinical and basic research consortium as well as the efforts of parents, family, and friends.

Metabolic differences in hippocampal 'Rett' neurons revealed by ATP imaging

Understanding metabolic control of neuronal function requires detailed knowledge of ATP handling in living neurons. We imaged ATP in organotypic hippocampal slices using genetically encoded sensor Ateam 1.03 modified to selectively transduce neurons in the tissue. ATP imaging indicated distinct differences in ATP production and consumption in dentate gyrus and cornu ammonis (CA) areas. Removal of extracellular Mg(2+) from the bath evoked epileptiform-like activity that was accompanied by ATP decline from 2-3 to 1-2mM. The slices fully recovered from treatment and showed persistent spontaneous activity. Neuronal discharges were followed by transient ATP changes and periodic activation of ATP-sensitive K(+) (K-ATP) channels. The biggest ATP decreases during epileptiform-like episodes of activity were observed in CA1 and CA3 neurons. Examination of neurons from the Rett model mice MeCP2(-/y) showed that seizure-like activity had earlier onset and subsequent spontaneous activity demonstrated more frequent discharges. Hippocampal MeCP2(-/y) neurons had higher resting ATP levels and showed bigger ATP decreases during epileptiform-like activity. More intense ATP turnover in MeCP2(-/y) neurons may result from necessity to maintain hippocampal function in Rett syndrome. Elevated ATP may make, in turn, Rett hippocampus more prone to epilepsy due to inadequate activity of K-ATP channels.

The relationship of Rett syndrome and MECP2 disorders to autism

Rett syndrome (RTT, MIM#312750) is a neurodevelopmental disorder that is classified as an autism spectrum disorder. Clinically, RTT is characterized by psychomotor regression with loss of volitional hand use and spoken language, the development of repetitive hand stereotypies, and gait impairment. The majority of people with RTT have mutations in Methyl-CpG-binding Protein 2 (MECP2), a transcriptional regulator. Interestingly, alterations in the function of the protein product produced by MECP2, MeCP2, have been identified in a number of other clinical conditions. The many clinical features found in RTT and the various clinical problems that result from alteration in MeCP2 function have led to the belief that understanding RTT will provide insight into a number of other neurological disorders. Excitingly, RTT is reversible in a mouse model, providing inspiration and hope that such a goal may be achieved for RTT and potentially for many neurodevelopmental disorders.

Rett syndrome and epilepsy: an update for child neurologists

Rett syndrome, a neurogenetic disorder predominantly affecting females, has many characteristic features including psychomotor retardation, impaired language development, hand stereotypies, gait dysfunction, and acquired microcephaly. Although each of these features undoubtedly contributes to the morbidity of this neurologic disorder, epilepsy is perhaps one of the most well-described and problematic, affecting as many as 50%-90% of patients. Seizures can often be refractory, requiring polytherapy and consideration of nonpharmacologic management (e.g., ketogenic diets and vagus nerve stimulation). In addition, many nonepileptic symptoms of Rett syndrome can occasionally be difficult to differentiate from seizures making clinical management and family counseling challenging. Our goal in this review is to better define the clinical and electrophysiological aspects of the epilepsy associated with Rett syndrome and provide practical guidance regarding management.

Epilepsy in Rett syndrome: association between phenotype and genotype, and implications for practice

PURPOSE

To investigate the association between genotype (methyl-CpG-binding protein 2 (MECP2 gene mutation)) and epileptic seizure phenotype in Rett syndrome.

METHODS

We used the British Isles Rett syndrome survey to identify 137 subjects with one of the nine most frequent MECP2 gene mutations and invited their parents or carers to participate in a postal questionnaire and telephone interview. The questionnaire recorded information about epileptic seizure types, non-epileptic vacant spells and treatments. Two investigators conducted telephone interviews and three epileptologists classified their epileptic seizures.

RESULTS

89 subjects (65%) responded. The epilepsy prevalence was 67%, and 74% had non-epileptic vacant spells. The epilepsy prevalence within specific genotypes ranged from 47% (mutation C-terminal deletion, downstream of the Transcription Repression Domain) to 100% (mutation p.R270X, c.808C>T). The prevalence of non-epileptic vacant spells within genotypes ranged from 50% (mutation p.R306C, c.916C>T) to 100% (mutation p.R106W, c.316C>T). The epileptologists differed considerably in their classification of events, particularly of non-epileptic vacant spells.

CONCLUSIONS

The large majority of people with Rett syndrome have epilepsy. Most have multiple epileptic seizure types, although generalised tonic-clonic seizures are the most common. There were no significant clinical differences between genotypes. The clinical differentiation of non-epileptic vacant spells is difficult. Discordance in epileptic seizure classification between clinicians suggests that caution is needed, since the clinical history alone cannot adequately classify the epileptic seizure type in Rett syndrome.

Network hyperexcitability in hippocampal slices from Mecp2 mutant mice revealed by voltage-sensitive dye imaging

Dysfunctions of neuronal and network excitability have emerged as common features in disorders associated with intellectual disabilities, autism, and seizure activity, all common clinical manifestations of Rett syndrome (RTT), a neurodevelopmental disorder caused by loss-of-function mutations in the transcriptional regulator methyl-CpG-binding protein 2 (MeCP2). Here, we evaluated the consequences of Mecp2 mutation on hippocampal network excitability, as well as synapse structure and function using a combination of imaging and electrophysiological approaches in acute slices. Imaging the amplitude and spatiotemporal spread of neuronal depolarizations with voltage-sensitive dyes (VSD) revealed that the CA1 and CA3 regions of hippocampal slices from symptomatic male Mecp2 mutant mice are highly hyperexcitable. However, only the density of docked synaptic vesicles and the rate of release from the readily releasable pool are impaired in Mecp2 mutant mice, while synapse density and morphology are unaffected. The differences in network excitability were not observed in surgically isolated CA1 minislices, and blockade of GABAergic inhibition enhanced VSD signals to the same extent in Mecp2 mutant and wild-type mice, suggesting that network excitability originates in area CA3. Indeed, extracellular multiunit recordings revealed a higher level of spontaneous firing of CA3 pyramidal neurons in slices from symptomatic Mecp2 mutant mice. The neuromodulator adenosine reduced the amplitude and spatiotemporal spread of VSD signals evoked in CA1 of Mecp2 mutant slices to wild-type levels, suggesting its potential use as an anticonvulsant in RTT individuals. The present results suggest that hyperactive CA3 pyramidal neurons contribute to hippocampal dysfunction and possibly to limbic seizures observed in Mecp2 mutant mice and RTT individuals.

Genetic controls balancing excitatory and inhibitory synaptogenesis in neurodevelopmental disorder models

Proper brain function requires stringent balance of excitatory and inhibitory synapse formation during neural circuit assembly. Mutation of genes that normally sculpt and maintain this balance results in severe dysfunction, causing neurodevelopmental disorders including autism, epilepsy and Rett syndrome. Such mutations may result in defective architectural structuring of synaptic connections, molecular assembly of synapses and/or functional synaptogenesis. The affected genes often encode synaptic components directly, but also include regulators that secondarily mediate the synthesis or assembly of synaptic proteins. The prime example is Fragile X syndrome (FXS), the leading heritable cause of both intellectual disability and autism spectrum disorders. FXS results from loss of mRNA-binding FMRP, which regulates synaptic transcript trafficking, stability and translation in activity-dependent synaptogenesis and plasticity mechanisms. Genetic models of FXS exhibit striking excitatory and inhibitory synapse imbalance, associated with impaired cognitive and social interaction behaviors. Downstream of translation control, a number of specific synaptic proteins regulate excitatory versus inhibitory synaptogenesis, independently or combinatorially, and loss of these proteins is also linked to disrupted neurodevelopment. The current effort is to define the cascade of events linking transcription, translation and the role of specific synaptic proteins in the maintenance of excitatory versus inhibitory synapses during neural circuit formation. This focus includes mechanisms that fine-tune excitation and inhibition during the refinement of functional synaptic circuits, and later modulate this balance throughout life. The use of powerful new genetic models has begun to shed light on the mechanistic bases of excitation/inhibition imbalance for a range of neurodevelopmental disease states.

Correlations between neurophysiological, behavioral, and cognitive function in Rett syndrome

Rett syndrome, a neurodevelopmental disorder affecting mainly females, is caused by a mutation of the MeCP2 gene. Girls with Rett syndrome manifest diverse behavioral and cognitive phenotypes, and the reasons for this variability remain unknown. In addition, girls with Rett syndrome often have epileptic seizures and abnormal EEGs, the characteristics of which differ with the patient. The aim of the study was to verify if neurophysiological and epileptological characteristics could be correlated with cognitive measures, obtained using eye tracker technology, and behavioral scores (Vineland Adaptive Behavior Scales and Rett Assessment Rating Scale) in 18 patients with Rett syndrome (mean age 13.7 years) at clinical stages III and IV. Age at epilepsy onset and seizure frequency were strictly correlated with neuropsychological outcome, as were EEG stage and distribution of paroxysmal abnormalities. Our findings demonstrate that neurophysiological features should be considered prognostic of cognitive and behavioral outcome in the clinical management of Rett syndrome.

Drug-resistant epilepsy and epileptic phenotype-EEG association in MECP2 mutated Rett syndrome

OBJECTIVE

To determine in MECP2-mutated Rett syndrome (RTT [MIM 312750]): (1) the prevalence of drug-resistant epilepsy (DRE); (2) whether the presence of DRE is related to the abnormal EEG patterns or to the particular MECP2 mutant genotype.

METHODS

Retrospective survey of a large population of patients (n=154) evaluated between 1978 to 2007 (May) at the Child Psychiatry and Neurology Unit of Siena (Italy) with both clinical and genetic (i.e. MECP2 mutated) diagnoses of RTT. Some subjects were followed for up to 20 years. Among those, cases with epilepsy were first selected for study; within that group, cases with DRE were identified and studied. The association between clinical severity of their epilepsy and quantitative or qualitative scores of EEG severity was tested using rank coefficients (Spearman's rho values). The relationship between DRE and RTT genotype category (i.e. gene deletion, gene duplication, early truncating mutation, late truncating mutation, and missense mutation) or a specific MECP2 genotype was tested using the chi-square test. A p-value <0.05 (two sided) was considered to indicate statistical significance.

RESULTS

Prevalence of DRE was 16% (i.e. 16 DRE out of 100 MECP2-mutated RTT epileptic patients). No significant relationship was found between clinical severity of DRE and quantitative (p=0.9190) or qualitative EEG scores (p=0.1511). In addition, no significant relationship was found between the DRE and the RTT genotype category (chi-square=1.147, DF=4, p=0.8867), or a specific MECP2 genotype (chi-square=30.958, DF=39, p=0.8173).

CONCLUSIONS

Although RTT MECP2-mutated patients suffer from a serious and progressive encephalopathy, it is "epileptogenic" but not "DREgenic" as they have a decreased risk (16%) for DRE compared to the general epileptic population (DRE: 20-40%). The presence of DRE is not related to abnormal EEG findings or a particular MECP2 mutant genotype.

SIGNIFICANCE

These observations could be of help in the practical management and family counseling.

A methyl-CpG-binding protein 2-enhanced green fluorescent protein reporter mouse model provides a new tool for studying the neuronal basis of Rett syndrome

Rett syndrome, a pervasive X-linked neurodevelopmental disorder in young girls, is caused by loss-of-function mutations in the gene that encodes the transcriptional repressor methyl-CpG-binding protein 2 (MeCP2). Mecp2-knockout mice phenocopy the major symptoms found in human patients and have advanced our understanding of the function of MeCP2 and mechanism of Rett syndrome. To study the behavior of the MeCP2 protein in vivo, we have generated a knock-in reporter mouse model that expresses MeCP2-enhanced green fluorescent protein (EGFP) fusion protein instead of endogenous MeCP2. Here we show that expression of the fusion protein in the brain remarkably mirrors endogenous MeCP2 expression in all temporal and spatial aspects. This mouse model may be a valuable tool for studying Rett syndrome and for developing therapies.

The overlapping spectrum of rett and angelman syndromes: a clinical review

Rett and Angelman syndromes comprise part of the spectrum of neurologic disorders associated with autism. Their clinical presentations overlap, with both presenting in later infancy with global developmental delays, severe speech and communication impairments, progressive microcephaly, seizures, autistic behaviors, and characteristic albeit different movement disorders and stereotypic hand movements. Although other features can help differentiate these disorders, significant phenotypic overlap and variation in severity sometimes cloud the underlying diagnosis. Rett syndrome is caused by a mutation in the MECP2 gene located on Xq28, whereas Angelman syndrome results from the loss of UBE3A function on chromosomal region 15q11-q13 related to a variety of molecular genetic mechanisms. Recent advances have uncovered interactions between these and other genes that affect the function and structure of neurons in the brain. The reversal of symptoms of Rett syndrome in a mature mouse model suggests the possibility for treatment of these and perhaps other autism-related disorders in the future.

Rett syndrome: clinical and electrophysiologic aspects

Rett syndrome is a neurodevelopmental disorder that almost exclusively affects females. The clinical course as well as the electroencephalogram pattern are characteristic and have been correlated to the clinical stages of the disease. Sixty to 70 percent of the patients develop epilepsy. The aim of this retrospective study was to investigate the correlation between clinical stages and electroencephalogram stages and to more specifically correlate epileptic activity in electroencephalograms with the clinical symptoms of patients. The clinical development and electroencephalogram results of 11 patients diagnosed with Rett syndrome between 1 and 33 years old are compared. In 8 of 11 patients, a correlation was found between electroencephalogram stage and clinical stage. In three of them, epileptic activity in the electroencephalogram was not associated with clinical seizures. Some typical symptoms of Rett patients (hand stereotypies, vacant spells) can be difficult to differentiate from seizures. Therefore application of antiepileptic treatment should be well evaluated, as the clinical course is decisive.

Predictors of seizure onset in Rett syndrome

OBJECTIVES

To investigate risk factors for seizure onset in Rett syndrome.

STUDY DESIGN

Information on presence and age at onset of seizures, perinatal and developmental history, and genetic status was abstracted on 275 cases in the Australian Rett Syndrome Database. Cox and Weibull regression were used to investigate and provide a model for predicting the effects of genetic and developmental factors on age at seizure onset.

RESULTS

Seizures were reported in 81% of 275 cases; the median age of onset was 48 months. Not having gained the ability to walk (P = .003) and developmental problems in the first 10 months of age (P = .04) were associated with an almost 2-fold increased risk of seizures. Cases without a detectable MECP2 mutation had a higher risk of seizure onset up to 4 years of age (P < .001) but a lower risk after 4 years (P = .08).

CONCLUSIONS

Seizure onset in Rett syndrome is associated with early developmental factors and with genotype. Information on these factors can be used to predict age at seizure onset after diagnosis.

Forensic issues and possible mechanisms of sudden death in Rett syndrome

A 20-year-old female with an established diagnosis of Rett syndrome was found dead in bed. There had been no history of recent deterioration in health and at autopsy no acute lesions were found. There was no evidence of trauma. Toxicological analysis of blood revealed therapeutic levels of carbamazepine and clonazepam. Death was attributed to the complications of Rett syndrome, an uncommon developmental disorder characterized by autistic type behaviour, hypotonia, stereotyped movements, seizures and growth failure, caused by mutations in the MECP2 gene on the X chromosome. Establishing the precise cause of sudden death in individuals with Rett syndrome may be difficult as epilepsy, defective autonomic nervous system control and cardiac arrhythmias may relate more to functional problems rather than to defects that can be demonstrated at autopsy. Thus, although there are a variety of well-documented underlying mechanisms that may cause sudden death in this condition, determining the exact sequence of events in an unwitnessed death may be more by inference and elimination, given the absence of pathognomonic and acute lethal lesions that are able to be found histopathologically. 'Complications of Rett syndrome' may, therefore, be the most accurate designation when individuals with this condition are found unexpectedly dead and no anatomical cause of death can be identified at autopsy.

Dissecting MECP2 function in the central nervous system

Rett syndrome is a neurodevelopmental disorder and an important cause of mental retardation and autistic behavior in girls and in a small group of boys. In 1999, mutation of the methyl-CpG binding protein 2 (MECP2) gene encoding a transcriptional repressor on the X chromosome was found to cause Rett syndrome. Since this discovery, significant research has focused on the elucidation of its specific role in the central nervous system. Recent studies revealed that MECP2 is expressed in more differentiated neurons rather than in less differentiated neuroblasts and that MECP2 is involved in the maturation and maintenance of neurons, including dendritic arborization and axonal projections, rather than in early cell fate decisions in the mammalian brain. In this review, we summarize recent findings regarding regional, temporal, and cell type-specific MECP2 expression in the central nervous system; neurobiologic abnormalities in MECP2 -mutant mice; and MECP2 target genes in the central nervous system.

Rett syndrome: of girls and mice--lessons for regression in autism

Rett syndrome (RTT) is a neurodevelopmental disorder occurring almost exclusively in females. Regression is a defining feature of RTT. During the regression stage, RTT girls display many autistic features, such as loss of communication and social skills, poor eye contact, and lack of interest, and initially may be given the diagnosis of autism. The discovery of the genetic cause of RTT, mutations in the MECP2 gene, a transcriptional repressor, has promoted the early diagnosis of RTT and development of mouse models. The phenotype of one mouse model includes features such as regression and abnormal behavioral and social interactions. The timing of the period of regression in RTT--during ages 1 to 2 years--parallels the period of intense synaptic development. The effects of the MECP2 mutation also increases concomitantly with peak synaptogenesis. Neuropathological findings in Rett include the selective reduction of dendritric spines in the pyramidal cells of RTT brains; this feature has also been reported in autism. Studies have observed that MECP influences the expression of brain-derived neurotrophic factor and thus may influence synaptic plasticity. Abnormalities in synapse maintenance and modulation may contribute to regression in RTT and autism. Studies of the clinical aspects of the regression period and of the mouse model may be useful in understanding the pathophysiology of RTT and other neurodevelopmental disorders such as autism. A recent study observed abnormal expression of MeCP2 in RTT and other neurodevelopmental disorders such as autism. Although the genetic background and certain clinical features differ in RTT and autism, a similar mechanism involving MeCP2 regulation and expression may contribute to regression.

MECP2 is progressively expressed in post-migratory neurons and is involved in neuronal maturation rather than cell fate decisions

Rett syndrome is a neurodevelopmental disorder and one of the causes of mental retardation and autistic behavior in girls, as well as in a small group of boys. It was recently discovered that mutation of the methyl-CpG-binding protein 2 (MECP2) gene encoding a transcriptional repressor on the X chromosome causes Rett syndrome. Although it is evident that phenotypes of MECP2 mutant mice that resemble those of Rett syndrome are attributable to lack of the MECP2 gene in the central nervous system (CNS), there is little understanding of the neuropathological abnormalities in the CNS of MECP2-null mice. Here, we investigated the developmental regulation and specific cellular expression of MECP2 during neural development both in vitro and in vivo. MECP2 is expressed in mature neurons, but not in astroglia or oligodendroglia, and is increasingly expressed during development of the mouse neocortex. In addition, in vitro culture studies suggest that MECP2 is expressed in more differentiated neurons rather than in less differentiated neuroblasts. Under in vitro conditions using neural precursor cultures, we find that MECP2 mutant neural precursors differentiate into morphologically mature neurons and glia, and no significant differences in differentiation are detected between cells from wild-type and MECP2 mutant mice, suggesting that MECP2 may play a different role in mice than it does in Xenopus embryos. In agreement with this hypothesis, neocortical projection layers in MECP2 -/y mice are thinner than those in wild-type mice, and pyramidal neurons in layer II/III in MECP2 -/y mice are smaller and less complex than those in wild-type mice. Taken together, our results indicate that MECP2 is involved in the maturation and maintenance of neurons, including dendritic arborization, rather than in cell fate decisions.

DNA methylation and Rett syndrome

Methylation of cytosine in human DNA has been studied for over 60 years, but has only recently been confirmed as an important player in human disease. Rett syndrome is a neurological disorder caused by mutations in the MeCP2 protein, which has been shown to bind methylated DNA and repress transcription. This review will focus on experiments addressing the basic properties of MeCP2 and on mouse models of Rett syndrome that are starting to yield insights into this condition.

[Rett syndrome: individual differences in developmental and behavioral markers and psychosocial stress]

OBJECTIVES

Rett Syndrome is a severe neurological developmental disorder caused by a genetic mutation on the long arm of the X chromosome (Xq28). This disorder is characterized by a loss of purposeful hand use, verbal language, and specific behaviors.

METHODS

Data were obtained from a survey of the parents of 83 girls on pre-verbal skills (Pre-verbal Communication Schedule), behavioral characteristics and emotional expression (Rett Syndrome Behaviour Questionnaire) and on maternal psychosocial stress (Handicap-related Problems for Parents Inventory).

RESULTS

There is considerable individual variability in the developmental and behavioral characteristics which is not explained as a function of age. Maternal stress correlates with the daughters' mood, anxious reactions and night-time behaviors.

CONCLUSIONS

Some implications for diagnosis and family counseling are discussed.