Rett syndrome and epilepsy: an update for child neurologists

The ketogenic diet in pharmacoresistant childhood epilepsy

Available pharmacologic treatments for seizures are limited in their efficacy. For a patient with seizures, pharmacologic treatment with available anticonvulsant medications leads to seizure control in <70% of patients. Surgical resection can lead to control in a select subset of patients but still leaves a significant number of patients with uncontrolled seizures. The ketogenic diet and related diets have proven to be useful in pharmacoresistant childhood epilepsy.

Is riluzole a potential therapy for Rett syndrome?

Rett syndrome (RTT) is a severe neurodevelopmental disorder with autistic features and is caused by loss-of-function mutations in the gene encoding methyl-CpG-binding protein 2 (MECP2) in the majority of cases. Besides symptomatic treatment, no therapeutic trials have shown effectiveness for RTT. Some perspectives in the treatment of RTT have been provided by recent works showing a phenotypic reversal by increasing brain-derived neurotrophic factor (BDNF) expression in a RTT mouse model. Glutamate may also play an important role in the primary pathogenesis in Rett syndrome through the excitotoxic neuronal injury in experimental models. Riluzole, an agent currently approved for the treatment of amyotrophic lateral sclerosis, is a glutamatergic modulator and BDNF enhancer with neuroprotective properties. For these reasons, riluzole could potentially play an important role in the treatment of RTT symptoms. Several points regarding the use of riluzole in RTT are discussed. Further evaluation of the therapeutic effects of this agent in RTT animal models is needed before clinical trials can begin.

Reprogramming patient-derived cells to study the epilepsies

The epilepsies and related disorders of brain circuitry present significant challenges associated with the use of human cells to study disease mechanisms and develop new therapies. Some of these obstacles are being overcome through the use of induced pluripotent stem cells to obtain patient-derived neural cells for in vitro studies and as a source of cell-based treatments. The field is evolving rapidly with the addition of genome-editing approaches and expanding protocols for generating different neural cell types and three-dimensional tissues, but the application of these techniques to neurological disorders, and particularly to the epilepsies, is in its infancy. We discuss the progress made and the distinct advantages and limitations of using patient-derived cells to study or treat epilepsy, as well as critical future directions for the field.

Paroxysmal alpha activity in Rett syndrome: a case report

BACKGROUND

Rett syndrome is a severe neurodevelopmental disorder that primarily affects females. Classically the disorder is characterized by early normal development, followed by a period of regression and later recovery or stagnation. Typical features include a loss of purposeful hand skills, development of hand stereotypies, loss of spoken language, gait abnormalities, and acquired microcephaly. Epilepsy affects between 70% and 90% of individuals with Rett syndrome. A number of stereotypical electroencephalography findings have been reported in Rett syndrome.

PATIENT DESCRIPTION

We report a 9-year-old girl with Rett syndrome and epilepsy with a unique electroencephalography finding consisting of intermittent paroxysms of alpha activity in both wakefulness and sleep without clinical signs.

RESULTS

This unique electroencephalography signature has not previously been reported in the English literature.

CONCLUSIONS

Knowledge of this unique electroencephalography pattern of diffuse paroxysmal alpha activity represents an additional distinct feature of the electroencephalogram in Rett syndrome and expands the spectrum of electroencephalography abnormalities in Rett syndrome.

Pinpointing brainstem mechanisms responsible for autonomic dysfunction in Rett syndrome: therapeutic perspectives for 5-HT1A agonists

Rett syndrome is a neurological disorder caused by loss of function of methyl-CpG-binding protein 2 (MeCP2). Reduced function of this ubiquitous transcriptional regulator has a devastating effect on the central nervous system. One of the most severe and life-threatening presentations of this syndrome is brainstem dysfunction, which results in autonomic disturbances such as breathing deficits, typified by episodes of breathing cessation intercalated with episodes of hyperventilation or irregular breathing. Defects in numerous neurotransmitter systems have been observed in Rett syndrome both in animal models and patients. Here we dedicate special attention to serotonin due to its role in promoting regular breathing, increasing vagal tone, regulating mood, alleviating Parkinsonian-like symptoms and potential for therapeutic translation. A promising new symptomatic strategy currently focuses on regulation of serotonergic function using highly selective serotonin type 1A (5-HT_1A) “biased agonists.” We address this newly emerging therapy for respiratory brainstem dysfunction and challenges for translation with a holistic perspective of Rett syndrome, considering potential mood and motor effects.

Genetic disorders associated with postnatal microcephaly

Several genetic disorders are characterized by normal head size at birth, followed by deceleration in head growth resulting in postnatal microcephaly. Among these are classic disorders such as Angelman syndrome and MECP2-related disorder (formerly Rett syndrome), as well as more recently described clinical entities associated with mutations in CASK, CDKL5, CREBBP, and EP300 (Rubinstein-Taybi syndrome), FOXG1, SLC9A6 (Christianson syndrome), and TCF4 (Pitt-Hopkins syndrome). These disorders can be identified clinically by phenotyping across multiple neurodevelopmental and neurobehavioral realms, and enough data are available to recognize these postnatal microcephaly disorders as separate diagnostic entities in their own right. A second diagnostic grouping, comprised of Warburg MICRO syndrome, Cockayne syndrome, and Cerebral-oculo-facial skeletal syndrome, share similar features of somatic growth failure, ophthalmologic, and dysmorphologic features. Many postnatal microcephaly syndromes are caused by mutations in genes important in the regulation of gene expression in the developing forebrain and hindbrain, although important synaptic structural genes also play a role. This is an emerging group of disorders with a fascinating combination of brain malformations, specific epilepsies, movement disorders, and other complex neurobehavioral abnormalities.

LSD1 Neurospecific Alternative Splicing Controls Neuronal Excitability in Mouse Models of Epilepsy

Alternative splicing in the brain is dynamic and instrumental to adaptive changes in response to stimuli. Lysine-specific demethylase 1 (LSD1/KDM1A) is a ubiquitously expressed histone H3Lys4 demethylase that acts as a transcriptional co-repressor in complex with its molecular partners CoREST and HDAC1/2. In mammalian brain, alternative splicing of LSD1 mini-exon E8a gives rise to neuroLSD1, a neurospecific isoform that, upon phosphorylation, acts as a dominant-negative causing disassembly of the co-repressor complex and de-repression of target genes. Here we show that the LSD1/neuroLSD1 ratio changes in response to neuronal activation and such effect is mediated by neurospecific splicing factors NOVA1 and nSR100/SRRM4 together with a novel cis-silencer. Indeed, we found that, in response to epileptogenic stimuli, downregulation of NOVA1 reduces exon E8a splicing and expression of neuroLSD1. Using behavioral and EEG analyses we observed that neuroLSD1-specific null mice are hypoexcitable and display decreased seizure susceptibility. Conversely, in a mouse model of Rett syndrome characterized by hyperexcitability, we measured higher levels of NOVA1 protein and upregulation of neuroLSD1. In conclusion, we propose that, in the brain, correct ratio between LSD1 and neuroLSD1 contributes to excitability and, when altered, could represent a pathogenic event associated with neurological disorders involving altered E/I.

Temporal- and Location-Specific Alterations of the GABA Recycling System in Mecp2 KO Mouse Brains

Rett syndrome (RTT), associated with mutations in methyl-CpG-binding protein 2 (Mecp2), is linked to diverse neurological symptoms such as seizures, motor disabilities, and cognitive impairments. An altered GABAergic system has been proposed as one of many underlying pathologies of progressive neurodegeneration in several RTT studies. This study for the first time investigated the temporal- and location-specific alterations in the expression of γ-amino butyric acid (GABA) transporter 1 (GAT-1), vesicular GABA transporter (vGAT), and glutamic acid decarboxylase 67kD (GAD67) in wild type (WT) and knockout (KO) mice in the Mecp2^tm1.1Bird/y mouse model of RTT. Immunohistochemistry (IHC) co-labeling of GAT-1 with vGAT identified GABAergic synapses that were quantitated for mid-sagittal sections in the frontal cortex (FC), hippocampal dentate gyrus (DG), and striatum (Str). An age-dependent increase in the expression of synaptic GABA transporters, GAT-1, and vGAT, was observed in the FC and DG in WT brains. Mecp2 KO mice showed a significant alteration in this temporal profile that was location-specific, only in the FC. GAD67-positive cell densities also showed an age-dependent increase in the FC, but a decrease in the DG in WT mice. However, these densities were not significantly altered in the KO mice in the regions examined in this study. Therefore, the significant location-specific downregulation of synaptic GABA transporters in Mecp2 KO brains with unaltered densities of GAD67-positive interneurons may highlight the location-specific synaptic pathophysiology in this model of RTT.

Quantification of functional abilities in Rett syndrome: a comparison between stages III and IV

We aimed to evaluate the functional abilities of persons with Rett syndrome (RTT) in stages III and IV. The group consisted of 60 females who had been diagnosed with RTT: 38 in stage III, mean age (years) of 9.14, with a standard deviation of 5.84 (minimum 2.2/maximum 26.4); and 22 in stage IV, mean age of 12.45, with a standard deviation of 6.17 (minimum 5.3/maximum 26.9). The evaluation was made using the Pediatric Evaluation of Disability Inventory, which has 197 items in the areas of self-care, mobility, and social function. The results showed that in the area of self-care, stage III and stage IV RTT persons had a level of 24.12 and 18.36 (P=0.002), respectively. In the area of mobility, stage III had 37.22 and stage IV had 14.64 (P<0.001), while in the area of social function, stage III had 17.72 and stage IV had 12.14 (P=0.016). In conclusion, although persons with stage III RTT have better functional abilities when compared with stage IV, the areas of mobility, self-care, and social function are quite affected, which shows a great functional dependency and need for help in basic activities of daily life.

Mouse models of neurodevelopmental disease of the basal ganglia and associated circuits

This chapter focuses on neurodevelopmental diseases that are tightly linked to abnormal function of the striatum and connected structures. We begin with an overview of three representative diseases in which striatal dysfunction plays a key role--Tourette syndrome and obsessive-compulsive disorder, Rett's syndrome, and primary dystonia. These diseases highlight distinct etiologies that disrupt striatal integrity and function during development, and showcase the varied clinical manifestations of striatal dysfunction. We then review striatal organization and function, including evidence for striatal roles in online motor control/action selection, reinforcement learning, habit formation, and action sequencing. A key barrier to progress has been the relative lack of animal models of these diseases, though recently there has been considerable progress. We review these efforts, including their relative merits providing insight into disease pathogenesis, disease symptomatology, and basal ganglia function.