Longitudinal observation of electroencephalograms in the Rett syndrome

Clinical EEG of Rett Syndrome: Group Analysis Supplemented with Longitudinal Case Report

Rett syndrome (RTT), a severe neurodevelopmental disorder caused by MECP2 gene abnormalities, is characterized by atypical EEG activity, and its detailed examination is lacking. We combined the comparison of one-time eyes open EEG resting state activity from 32 girls with RTT and their 41 typically developing peers (age 2-16 years old) with longitudinal following of one girl with RTT to reveal EEG parameters which correspond to the RTT progression. Traditional measures, such as epileptiform abnormalities, generalized background activity, beta activity and the sensorimotor rhythm, were supplemented by a new frequency rate index measured as the ratio between high- and low-frequency power of sensorimotor rhythm. Almost all studied EEG parameters differentiated the groups; however, only the elevated generalized background slowing and decrease in our newly introduced frequency rate index which reflects attenuation in the proportion of the upper band of sensorimotor rhythm in RTT showed significant relation with RTT progression both in longitudinal case and group analysis. Moreover, only this novel index was linked to the breathing irregularities RTT symptom. The percentage of epileptiform activity was unrelated to RTT severity, confirming previous studies. Thus, resting EEG can provide information about the pathophysiological changes caused by MECP2 abnormalities and disease progression.

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.

Treatment of epilepsy in Rett syndrome

INTRODUCTION

Epilepsy is very frequent in Rett syndrome (RTT) patients and often difficult to treat. Because most cases of RTT are caused by mutations in the MECP2 gene it is reasonable to assume that convulsions are based on common pathogenetic mechanisms and thus should have a similar response to antiepileptic drugs.

PURPOSE

To find the optimal treatment for epilepsy in RTT.

METHODS

We performed a retrospective study on 110 female patients with confirmed MECP2 mutations.

RESULTS

The median age was 10 years, 58% had a history of epilepsy and 55% received antiepileptic drugs (AEDs). Only sulthiame, carbamazepine and valproate were administered in an adequate frequency to allow statistical analysis. The best anticonvulsive results were seen in the RTT group that was treated with carbamazepine. Sulthiame was slightly less effective while valproate was significantly less effective. The rate of side effects was equivalent in all groups. In conclusion, carbamazepine should be recommended as first choice AED in RTT. If carbamazepine is not effective or not well tolerated sulthiame ought to be taken as second choice AED.

Neurophysiology of Rett syndrome

Rett syndrome is a neurodevelopmental disorder that in most cases is consequent to a mutation in the MECP2 gene. The central nervous system is the primary organ system involved in Rett syndrome. Neurophysiologic evaluations provide information concerning the developmental aspects of Rett syndrome and the character and extent of involvement of the central, peripheral, and autonomic nervous system pathways. Evoked potentials typically demonstrate intactness of peripheral auditory and visual pathways and suggest dysfunction of central or "higher" cortical pathways. Somatosensory evoked potentials can be characterized by "giant" responses, suggesting cortical hyperexcitability. Cortical hyperexcitability is further suggested by the findings of the electroencephalogram (EEG), which are primarily characterized by a loss of expected developmental features; the appearance of focal, multifocal, and generalized epileptiform abnormalities; and the occurrence of rhythmic slow (theta) activity, primarily in the frontal-central regions. Epileptic seizures are reported to occur frequently in Rett syndrome. However, many events presumed to be seizures have no EEG correlate during video-EEG monitoring. Impairment of the autonomic nervous system in Rett syndrome is suggested by an increased incidence of long Q-T intervals during electrocardiographic recordings and diminished heart rate variability. Autonomic nervous system dysfunction can contribute to the increased incidence of sudden unexpected death in Rett syndrome.

Neurophysiology of Rett syndrome

Neurophysiological evaluations have been widely applied in the study of Rett syndrome (RS) to provide information concerning the developmental aspects of RS; the character and extent of involvement of the central, peripheral, and autonomic nervous system pathways; and evaluation of the clinical symptomatology of RS. The electroencephalogram (EEG) is invariably abnormal and shows characteristic, though not diagnostic, changes: loss of expected developmental features; the appearance of focal, multifocal, and generalized epileptiform abnormalities; and the occurrence of rhythmic slow (theta) activity primarily in the frontal-central regions. Epileptic seizures are reported to occur frequently in RS, and partial and generalized seizures may be experienced by RS girls. However, many events presumed to be seizures have no EEG correlate during video-EEG monitoring, suggesting the possibility of a nonepileptic mechanism. Such monitoring may be necessary to determine appropriate use of antiepileptic drugs. Evoked potentials typically demonstrate intact peripheral auditory and visual pathways and suggest dysfunction of central or "higher" cortical pathways. Somatosensory-evoked potentials may be characterized by "giant" responses, suggesting cortical hyperexcitability. An increased incidence of long QT intervals during electrocardiographic recordings and diminished heart-rate variability, suggesting impairment of the autonomic nervous system, are described in RS. With the discovery of the genetic basis of RS, neurophysiological studies will provide parameters for phenotype-genotype correlations and characterization of animal models.

Neurophysiology of Rett syndrome

Neurophysiological studies on Rett syndrome (RTT) are reviewed, and pathophysiology of RTT is discussed. The electroencephalography (EEG), sensory evoked potentials (SEP), sleep-wake rhythm study and polysomnography (PSG) study showed age-dependent characteristics. PSG revealed the brainstem and midbrain monoaminergic systems are deranged from early developmental stage, that is serotonin and noradrenaline systems seem to be hypoactive and dopaminergic system is also hypoactive associated with receptor supersensitivity. These monoaminergic systems are known to influence the maturation of the higher neuronal systems at specific areas and at specific ages. Particularly the synaptogenesis of the cerebral cortex is modulated by region or layer specifically from an early stage of the development. The observations made in EEG and SEP studies also suggested specific subcortical and cortical involvements taking place during the development. The age-dependent appearance of characteristic clinical features of RTT, and the variation of the clinical severities, e.g. classical, variant, form fruste, etc., can also be explained by the specific features of these monoaminergic systems. Furthermore, analysis of the components of rapid eye movement sleep suggested the onset of RTT lies between 36 gestational weeks to 3-4 months postnatally. The discovery of the mutations of methyl-CpG-binding protein 2 (MECP2) gene as the causative gene of RTT is an epoch helping not only to understand the pathophysiology of RTT but also various neurodevelopmental disorders.

Cerebrolysin therapy in Rett syndrome: clinical and EEG mapping study

Based on the suggestion that nerve growth factor plays a core role in the brain maturation process, which is altered in Rett syndrome, we investigate the influence of Cerebrolysin--the brain-derived peptidergic drug - on motor and higher cortical functions in Rett syndrome girls. The open pilot study was performed on nine Rett syndrome girls (aged from 2 years and 2 months to 7 years and 6 months) at stage 3 of the illness, and included both clinical and quantitative EEG evaluations before and after Cerebrolysin treatment. After Cerebrolysin treatment, increases in the behavioral activity, attention level, motor functions, and non-verbal social communication have been shown in Rett syndrome patients. EEG parameters after Cerebrolysin treatment also changed towards normal values, indicating an improvement of the brain functional state. EEG changes included: decrease of theta activity over all cortical regions, increase of beta activity in the frequency band 13-15 Hz, and some restoration of the occipital alpha rhythm (in the narrow 8-9 Hz band). The data obtained suggested possible perspectives of Cerebrolysin in complex therapy of Rett syndrome.

Rett syndrome: critical examination of clinical features, serial EEG and video-monitoring in understanding and management

We studied data on seizures, vacant spells and breathing dysrhythmia from the British Rett Survey and 150 electroencephalographic records from 78 classic cases, including 23 with prolonged synchronous recordings of EEG, respiration and movement. The proportion of abnormal records increased from 6 of 18 (33%) during the first 6 months of the regression period to 44 of 59 (75%) in the later period to 6 years, the increase in abnormality following rather than preceding the onset of regression. In young girls the EEG abnormality increased in sleep but decreased during episodic hyperventilation and breath-holding. Epileptogenic activity was commonly present without clinical seizures. Eleven vacant spells were monitored and were not epileptic but related to the breathing abnormality. Full monitoring is essential when supposed seizures are intractable. The intermittent EEG abnormality and behavioural changes indicate abnormal fluctuating arousal possibly of midbrain or brainstem origin.

EEG and evoked potentials in infantile neuronal ceroid-lipofuscinosis

Sixteen children with infantile neuronal ceroid-lipofuscinosis (INCL), age range 0.5 to 5.4 years, were studied using EEG, electroretinograms (ERG), visual evoked potentials (VEP) and somatosensory evoked potentials (SEP). Electroencephalography was the first of these examinations to reveal abnormalities, however the EEG may be normal at the preclinical stage. The first abnormality to appear was an attenuated reaction to passive eye opening and closing which was followed by disturbances in background activity and diminution in amplitude, and by disappearance of sleep spindles. The gradual disappearance of posterior rhythm reactivity and of sleep spindles suggests that thalamic dysfunction progresses with time. EEG inactivity appeared by the age of 3 years. Evoked potentials were normal in the early stages of the disease. SEP showed abnormalities at Stage 2 (1.7 years), while ERG and VEP abnormalities appeared at Stage 3 (by the age of 2.5 years). All neurophysiological reactions examined were abolished by the age of 4 years. Follow-up EEG gives important hints as to the early diagnosis of INCL. Progression of the disease can be followed by evoked potentials which may also be helpful in the differential diagnostics.

Brain perfusion SPECT and EEG findings in Rett syndrome

Thirteen patients (mean age 8.4 + 5.3 years) with Rett syndrome (RS) were studied with EEG and 99mTc-HMPAO SPECT. Eleven patients had background abnormalities and 10 patients paroxysmal activity in EEG. Hypoperfusion of varying severity was detected in 11 patients, 7 patients having multiple lesions. Bifrontal hypoperfusion, observed in 6 patients, was the most distinctive finding. Hypoperfusion was observed also in other cortical regions, except for the occipital lobes. There was no correlation between severity of the background abnormality or presence of paroxysmal activity in EEG and grade of hypoperfusion. There was, however, an association between the severity of hypoperfusion and early manifestation of symptoms in patients with RS. Whether this early-onset group of patients represents a different disease entity or only reflects disease variability the basic pathology being the same, is a possibility that deserves further clarification.

Brainstem frequency-following responses in Rett syndrome

The brainstem frequency-following response (FFR) is a short-latency evoked response that reflects waveform properties of periodic auditory stimuli. Unlike neural activity evoked by transient stimuli, the FFR originates in phase-locked neurons that provide unique information concerning the early processing of auditory inputs. FFRs elicited by a pure tone were recorded from 9 Rett syndrome patients (age 26-55 years, mean = 34.4 years) and compared with those of 18 normal infants (age 2-10 months, mean = 5.0 months), and 113 young adult (age 18-30 years, mean = 22.2 years) controls. The Rett syndrome pattern indicated considerable intersubject latency variability and poor intrasubject repeat reliability except for brief FFR components which were consistently synchronized. The pattern observed in Rett syndrome was similar in certain respects to that observed in infants, but both patterns differed from those of adults, who showed larger amplitudes and consistent waveform synchrony. Clinical and neuropathologic data indicate developmental arrest rather than a neurodegenerative process in Rett syndrome. The present results are consistent with this interpretation. Neurophysiologic studies may identify markers that are distinctive in Rett syndrome and make it possible to monitor changes with age and disease process.

The Rett syndrome: the first case report from Pakistan

We report an 11-yr-old girl who visited the outpatient department of Islamabad Children's Hospital with uncontrolled seizures, psychomotor retardation and hand washing movements since early childhood. She had an uneventful peri- and neonatal history with a normal head size at birth and fulfilled the criteria of classic Rett syndrome. This is the first report of the Rett syndrome in Pakistan.

Giant somatosensory evoked potentials in the Rett syndrome

Somatosensory evoked potentials (SEP) were recorded in ten patients with the Rett syndrome. Seven cases showed abnormal SEP, and five of these cases showed giant SEP. The five cases with giant SEP were relatively young girls with epilepsy and parieto-central spikes on the electro-encephalogram (EEG). Older patients did not show giant SEP. These giant SEP may be the reflection of cortical hyperexcitability and they may subside as the disease progresses.