Rett Syndrome: A Tale of Altered Genetics, Synaptic Plasticity, and Neurodevelopmental Dynamics

Rett syndrome (RTT) is a neurodevelopmental disorder that is a leading cause of severe cognitive and physical impairment. RTT typically occurs in females, although rare cases of males with the disease exist. Its genetic cause, symptoms, and clinical progression timeline have also become well-documented since its initial discovery. However, a relatively late diagnosis and lack of an available cure signify that our understanding of the disease is incomplete. Innovative research methods and tools are thereby helping to fill gaps in our knowledge of RTT. Specifically, mouse models of RTT, video analysis, and retrospective parental analysis are well-established tools that provide valuable insights into RTT. Moreover, current and anticipated treatment options are improving the quality of life of the RTT patient population. Collectively, these developments are creating optimistic future perspectives for RTT.

Label-free three-photon imaging of intact human cerebral organoids for tracking early events in brain development and deficits in Rett syndrome

Human cerebral organoids are unique in their development of progenitor-rich zones akin to ventricular zones from which neuronal progenitors differentiate and migrate radially. Analyses of cerebral organoids thus far have been performed in sectioned tissue or in superficial layers due to their high scattering properties. Here, we demonstrate label-free three-photon imaging of whole, uncleared intact organoids (~2 mm depth) to assess early events of early human brain development. Optimizing a custom-made three-photon microscope to image intact cerebral organoids generated from Rett Syndrome patients, we show defects in the ventricular zone volumetric structure of mutant organoids compared to isogenic control organoids. Long-term imaging live organoids reveals that shorter migration distances and slower migration speeds of mutant radially migrating neurons are associated with more tortuous trajectories. Our label-free imaging system constitutes a particularly useful platform for tracking normal and abnormal development in individual organoids, as well as for screening therapeutic molecules via intact organoid imaging.

Expanding the MECP2 network using comparative genomics reveals potential therapeutic targets for Rett syndrome

Inactivating mutations in the Methyl-CpG Binding Protein 2 (MECP2) gene are the main cause of Rett syndrome (RTT). Despite extensive research into MECP2 function, no treatments for RTT are currently available. Here, we used an evolutionary genomics approach to construct an unbiased MECP2 gene network, using 1028 eukaryotic genomes to prioritize proteins with strong co-evolutionary signatures with MECP2. Focusing on proteins targeted by FDA-approved drugs led to three promising targets, two of which were previously linked to MECP2 function (IRAK, KEAP1) and one that was not (EPOR). The drugs targeting these three proteins (Pacritinib, DMF, and EPO) were able to rescue different phenotypes of MECP2 inactivation in cultured human neural cell types, and appeared to converge on Nuclear Factor Kappa B (NF-κB) signaling in inflammation. This study highlights the potential of comparative genomics to accelerate drug discovery, and yields potential new avenues for the treatment of RTT.

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.

Metabolic Signatures Differentiate Rett Syndrome From Unaffected Siblings

Rett syndrome (RTT, OMIM 312750), a severe neurodevelopmental disorder characterized by regression with loss of spoken language and hand skills, development of characteristic hand stereotypies, and gait dysfunction, is primarily caused by de novo mutations in the X-linked gene Methyl-CpG-binding protein 2 (MECP2). Currently, treatment options are limited to symptomatic management, however, reversal of disease phenotype is possible in mouse models by restoration of normal MECP2 gene expression. A significant challenge is the lack of biomarkers of disease state, disease severity, or treatment response. Using a non-targeted metabolomic approach we evaluated metabolite profiles in plasma from thirty-four people with RTT compared to thirty-seven unaffected age- and gender-matched siblings. We identified sixty-six significantly altered metabolites that cluster broadly into amino acid, nitrogen handling, and exogenous substance pathways. RTT disease metabolite and metabolic pathways abnormalities point to evidence of oxidative stress, mitochondrial dysfunction, and alterations in gut microflora. These observed changes provide insight into underlying pathological mechanisms and the foundation for biomarker discovery of disease severity biomarkers.

Functional and Structural Impairments in the Perirhinal Cortex of a Mouse Model of CDKL5 Deficiency Disorder Are Rescued by a TrkB Agonist

Cyclin-dependent kinase-like 5 (CDKL5) deficiency disorder (CDD) is a severe X-linked neurodevelopmental encephalopathy caused by mutations in the CDKL5 gene and characterized by early-onset epilepsy and intellectual and motor impairments. No cure is currently available for CDD patients, as limited knowledge of the pathology has hindered the development of therapeutics. Cdkl5 knockout (KO) mouse models, recently created to investigate the role of CDKL5 in the etiology of CDD, recapitulate various features of the disorder. Previous studies have shown alterations in synaptic plasticity and dendritic pattern in the cerebral cortex and in the hippocampus, but the knowledge of the molecular substrates underlying these alterations is still limited. Here, we have examined for the first time synaptic function and plasticity, dendritic morphology, and signal transduction pathways in the perirhinal cortex (PRC) of this mouse model. Being interconnected with a wide range of cortical and subcortical structures and involved in various cognitive processes, PRC provides a very interesting framework for examining how CDKL5 mutation leads to deficits at the synapse, circuit, and behavioral level. We found that long-term potentiation (LTP) was impaired, and that the TrkB/PLCγ1 pathway could be mechanistically involved in this alteration. PRC neurons in mutant mice showed a reduction in dendritic length, dendritic branches, PSD-95-positive puncta, GluA2-AMPA receptor levels, and spine density and maturation. These functional and structural deficits were associated with impairment in visual recognition memory. Interestingly, an in vivo treatment with a TrkB agonist (the 7,8-DHF prodrug R13) to trigger the TrkB/PLCγ1 pathway rescued defective LTP, dendritic pattern, PSD-95 and GluA2-AMPA receptor levels, and restored visual recognition memory in Cdkl5 KO mice. Present findings demonstrate a critical role of TrkB signaling in the synaptic development alterations due to CDKL5 mutation, and suggest the possibility of TrkB-targeted pharmacological interventions.

Development, behaviour and autism in individuals with SMC1A variants

INTRODUCTION

Development and behaviour in Cornelia de Lange Syndrome (CdLS), including autism characteristics, have been described infrequently stratified to genetic cause and only a few studies have considered behavioural characteristics in relation to developmental level. Here, we describe the behavioural phenotype in individuals with CdLS with SMC1A variants.

METHODS

We performed an international, interdisciplinary study on 51 individuals with SMC1A variants. Results of questionnaire studies are compared to those in individuals with Down Syndrome and with Autism Spectrum Disorder. Results on cognition and self-injurious behaviour (SIB) are compared to those in individuals with CdLS caused by NIPBL variants. For Dutch participants with SMC1A variants we performed direct in-person assessments of cognition, autism, and added an interview and questionnaire on adaptive behaviour and sensory processing.

RESULTS

Individuals with SMC1A variants show a higher cognitive level and less SIB than individuals with NIPBL variants. Individuals with SMC1A variants without classic CdLS phenotype but with a Rett-like phenotype show more severe intellectual disability and more SIB compared to those with a CdLS phenotype. Autism is less present if outcomes in direct in-person assessments are evaluated taking developmental level into account compared to results based on a questionnaire.

CONCLUSIONS

Behaviour in individuals with CdLS should be evaluated taking genetic cause into account. Detailed interdisciplinary approaches are of clinical importance to inform tailored care and may eventually improve quality of life of patients and families.

Rett Syndrome in Males: A Case Report and Review of Literature

Rett syndrome (RTT) is a neurodevelopmental disorder in which a period of normal development is followed by regression of previously acquired skills. RTT was originally thought to be present exclusively in females. However, advances in genetic testing and phenotypic identification revealed that it is not a female-only disorder as cases of males with similar phenotype were reported. RTT was considered lethal in males as it has an X-linked dominant inheritance. The purpose of this review is to report a case of RTT in young male and elaborate genetics and phenomenology of this disorder in males.

Development of the Tailored Rett Intervention and Assessment Longitudinal (TRIAL) database and the Rett Evaluation of Symptoms and Treatments (REST) Questionnaire

INTRODUCTION

Rett syndrome (RTT) is a pervasive neurodevelopmental disorder that presents with deficits in brain functioning leading to language and learning regression, characteristic hand stereotypies and developmental delay. Different mutations in the gene implicated in RTT-methyl-CpG-binding protein 2 (MECP2) establishes RTT as a disorder with divergent symptomatology ranging from individuals with severe to milder phenotypes. A reliable and single multidimensional questionnaire is needed that can embrace all symptoms, and the relationships between them, and can map clinically meaningful data to symptomatology across the lifespan in patients with RTT. As part of the HealthTracker-based Tailored Rett Intervention and Assessment Longitudinal (TRIAL) database, the Rett Evaluation of Symptoms and Treatments (REST) Questionnaire will be able to marry with the physiological aspects of the disease obtained using wearable sensor technology, along with genetic and psychosocial data to stratify patients. Taken together, the web-based TRIAL database will empower clinicians and researchers with the confidence to delineate between different aspects of disorder symptomatology to streamline care pathways for individuals or for those patients entering clinical trials. This protocol describes the anticipated development of the REST questionnaire and the TRIAL database which links with the outcomes of the wearable sensor technology, and will serve as a barometer for longitudinal patient monitoring in patients with RTT.

METHODS AND ANALYSIS

The US Food and Drug Administration Guidance for Patient-Reported Outcome Measures will be used as a template to inform the methodology of the study. It will follow an iterative framework that will include item/concept identification, item/concept elicitation in parent/carer-mediated focus groups, expert clinician feedback, web-based presentation of questionnaires, initial scale development, instrument refinement and instrument validation.

ETHICS AND DISSEMINATION

The study has received favourable opinion from the National Health Service (NHS) Research Ethics Committee (REC): NHS Research Ethics Committee (REC)-London, Bromley Research Ethics Committee (reference: 15/LO/1772).

Impact of Rett Syndrome Mutations on MeCP2 MBD Stability

Rett syndrome causing missense mutations in the methyl-CpG-binding domain (MBD) of methyl CpG-binding protein 2 (MeCP2) were investigated both in silico and in vitro to reveal their effect on protein stability. It is demonstrated that the vast majority of frequently occurring mutations in the human population indeed alter the MBD folding free energy by a fraction of a kcal/mol up to more than 1 kcal/mol. While the absolute magnitude of the change of the free energy is small, the effect on the MBD functionality may be substantial since the folding free energy of MBD is about 2 kcal/mol only. Thus, it is emphasized that the effect of mutations on protein integrity should be evaluated with respect to the wild-type folding free energy but not with the absolute value of the folding free energy change. Furthermore, it was observed that the magnitude of the effect is correlated neither with the burial of the mutation sites nor with the basic amino acid physicochemical property change. Mutations that strongly perturb the immediate structural features were found to have little effect on folding free energy, while very conservative mutations resulted in large changes of the MBD stability. This observation was attributed to the protein's ability to structurally relax and reorganize to reduce the effect of mutation. Comparison between in silico and in vitro results indicated that some Web servers perform relatively well, while the free energy perturbation approach frequently overpredicts the magnitude of the free energy change especially when a charged amino acid is involved.

Breathing abnormalities in a female mouse model of Rett syndrome

Rett syndrome (RTT) is a female neurodevelopmental disease with breathing abnormalities. To understand whether breathing defects occur in the early lives of a group of female Mecp2(+/-) mice, a mouse model of RTT, and what percentage of mice shows RTT-like breathing abnormality, breathing activity was measured by plethysmography in conscious mice. Breathing frequency variation and central apnea in a group of Mecp2(+/-) females displayed a distribution pattern similar to Mecp2(-/Y) males, while the rest resembled the wild-type mice. Similar results were obtained using the k-mean clustering statistics analysis. With two independent methods, about 20% of female Mecp2(+/-) mice showed RTT-like breathing abnormalities that began as early as 3 weeks of age in the Mecp2(+/-) mice, and were suppressed with 3% CO2. The finding that only a small proportion of Mecp2(+/-) mice develops RTT-like breathing abnormalities suggests incomplete allele inactivation in the RTT-model Mecp2(+/-) mice.

Rett Syndrome: Reaching for Clinical Trials

Rett syndrome (RTT) is a syndromic autism spectrum disorder caused by loss-of-function mutations in MECP2. The methyl CpG binding protein 2 binds methylcytosine and 5-hydroxymethycytosine at CpG sites in promoter regions of target genes, controlling their transcription by recruiting co-repressors and co-activators. Several preclinical studies in mouse models have identified rational molecular targets for drug therapies aimed at correcting the underlying neural dysfunction. These targeted therapies are increasingly translating into human clinical trials. In this review, we present an overview of RTT and describe the current state of preclinical studies in methyl CpG binding protein 2-based mouse models, as well as current clinical trials in individuals with RTT.

Rescue of Methyl-CpG Binding Protein 2 Dysfunction-induced Defects in Newborn Neurons by Pentobarbital

Rett syndrome is a neurodevelopmental disorder that usually arises from mutations or deletions in methyl-CpG binding protein 2 (MeCP2), a transcriptional regulator that affects neuronal development and maturation without causing cell loss. Here, we show that silencing of MeCP2 decreased neurite arborization and synaptogenesis in cultured hippocampal neurons from rat fetal brains. These structural defects were associated with alterations in synaptic transmission and neural network activity. Similar retardation of dendritic growth was also observed in MeCP2-deficient newborn granule cells in the dentate gyrus of adult mouse brains in vivo, demonstrating direct and cell-autonomous effects on individual neurons. These defects, caused by MeCP2 deficiency, were reversed by treatment with the US Food and Drug Administration-approved drug, pentobarbital, in vitro and in vivo, possibly caused by modulation of γ-aminobutyric acid signaling. The results indicate that drugs modulating γ-aminobutyric acid signaling are potential therapeutics for Rett syndrome.

Abnormalities of the DNA methylation mark and its machinery: an emerging cause of neurologic dysfunction

Recently, Mendelian disorders of the DNA methylation machinery have been described which demonstrate the complex roles of epigenetics in neurodevelopment and disease. For example, defects of DNMT1, the maintenance methyltransferase, lead to adult-onset progressive neurologic disorders, whereas defects of the de novo methyltransferases DNMT3A and DNMT3B lead to nonprogressive neurodevelopmental conditions. Furthermore, patients with DNMT3A deficiency demonstrate overgrowth, a feature common to disorders of histone machinery and imprinting disorders, highlighting the interconnectedness of the many epigenetic layers. Disorders of the DNA methylation machinery include both the aforementioned "writers" and also the "readers" of the methyl mark, such as MeCP2, the cause of Rett syndrome. Any dosage disruption, either haploinsufficiency or overexpression of DNA methylation machinery leads to widespread gene expression changes in trans, disrupting expression of a subset of target genes that contribute to individual disease phenotypes. In contrast, classical imprinting disorders such as Angelman syndrome have been thought generally to cause epigenetic dysregulation in cis. However, the recent description of multilocus methylation disorders challenges this generalization. Here, in addition to summarizing recent developments in identifying the pathogenesis of these diseases, we highlight clinical considerations and some unexpected therapeutic opportunities, such as topoisomerase inhibitors for classical imprinting disorders.

Three different profiles: early socio-communicative capacities in typical Rett syndrome, the preserved speech variant and normal development

BACKGROUND AND AIMS

This is the first study aiming to compare pre-diagnostic socio-communicative development of a female with typical Rett syndrome (RTT), a female with the preserved speech variant of RTT (PSV) and a control toddler.

METHODS

We analysed 1275 min of family videos at the participants' age between 9 and 24 months and used the Inventory of Potential Communicative Acts (IPCA) to delineate their repertoires of communicative forms and functions.

RESULTS

The results revealed different profiles for the three different conditions. The repertoire of communicative gestures and (pre)linguistic vocalizations was most comprehensive in the control toddler, followed by the female with PSV and the female with RTT.

CONCLUSION

These findings contribute to the growing knowledge about early developmental abnormalities in RTT. In order to define distinctive profiles for typical and atypical RTT and evaluate their specificity, a larger body of evidence is needed.

Assessment and management of nutrition and growth in Rett syndrome

OBJECTIVES

We developed recommendations for the clinical management of poor growth and weight gain in Rett syndrome through evidence review and the consensus of an expert panel of clinicians.

METHODS

Initial draft recommendations were created based upon literature review and 34 open-ended questions in which the literature was lacking. Statements and questions were made available to an international, multidisciplinary panel of clinicians in an online format and a Microsoft Word-formatted version of the draft via e-mail. Input was sought using a 2-stage modified Delphi process to reach consensus. Items included clinical assessment of growth, anthropometry, feeding difficulties and management to increase energy intake, decrease feeding difficulties, and consideration of gastrostomy.

RESULTS

Agreement was achieved on 101 of 112 statements. A comprehensive approach to the management of poor growth in Rett syndrome is recommended that takes into account factors such as feeding difficulties and nutritional needs. A body mass index of approximately the 25th centile can be considered as a reasonable target in clinical practice. Gastrostomy is indicated for extremely poor growth, if there is risk of aspiration and if feeding times are prolonged.

CONCLUSIONS

These evidence- and consensus-based recommendations have the potential to improve care of nutrition and growth in a rare condition and stimulate research to improve the present limited evidence base.

Changing the perspective on early development of Rett syndrome

We delineated the achievement of early speech-language milestones in 15 young children with Rett syndrome (MECP2 positive) in the first two years of life using retrospective video analysis. By contrast to the commonly accepted concept that these children are normal in the pre-regression period, we found markedly atypical development of speech-language capacities, suggesting a paradigm shift in the pathogenesis of Rett syndrome and a possible approach to its early detection.

The impact of MeCP2 loss- or gain-of-function on synaptic plasticity

Methyl-CpG-binding protein 2 (MeCP2) is a transcriptional regulator of gene expression that is an important epigenetic factor in the maintenance and development of the central nervous system. The neurodevelopmental disorders Rett syndrome and MECP2 duplication syndrome arise from loss-of-function and gain-of-function alterations in MeCP2 expression, respectively. Several animal models have been developed to recapitulate the symptoms of Rett syndrome and MECP2 duplication syndrome. Cell morphology, neurotransmission, and cellular processes that support learning and memory are compromised as a result of MeCP2 loss- or gain-of-function. Interestingly, loss-of-MeCP2 function and MeCP2 overexpression trigger diametrically opposite changes in synaptic transmission. These findings indicate that the precise regulation of MeCP2 expression is a key requirement for the maintenance of synaptic and neuronal homeostasis and underscore its importance in central nervous system function. This review highlights the functional role of MeCP2 in the brain as a regulator of synaptic and neuronal plasticity as well as its etiological role in the development of Rett syndrome and MECP2 duplication syndrome.

Profiling early socio-communicative development in five young girls with the preserved speech variant of Rett syndrome

Rett syndrome (RTT) is a developmental disorder characterized by regression of purposeful hand skills and spoken language, although some affected children retain some ability to speech. We assessed the communicative abilities of five young girls, who were later diagnosed with the preserved speech variant of RTT, during the pre-regression period (aged 12-24 months). Videotapes, obtained by parents during routine family situations and celebrations, were analyzed to identify communicative forms and functions used by these toddlers. Non-verbal communicative forms dominated over verbal-communicative forms for six of the eight identified communication functions. Although the girls used various non-verbal forms to make requests, for example, none of the individuals were observed to make choices or request information. Early peculiarities in the speech-language domain during the first year of life became more prominent and evident during the second year of life as general differences between typical development and atypical development become more obvious in RTT. These findings highlight the importance of assessing socio-communicative forms and functions at early age in children with RTT. The results suggest that speech-language functions did not appear to play a major role in the children's communicative attempts. We conclude that, even among children with the preserved speech variant, socio-communicative deficits are present before regression and persist after this period.

Incontinence in Individuals with Rett Syndrome: A Comparative Study

Frequency and type of incontinence and its association with other variables were assessed in females with Rett Syndrome (RS) (n = 63), using an adapted Dutch version of the 'Parental Questionnaire: Enuresis/Urinary Incontinence' (Beetz et al. 1994). Also, incontinence in RS was compared to a control group consisting of females with non-specific (mixed) intellectual disability (n = 26). Urinary incontinence (UI) (i.e., daytime incontinence and nocturnal enuresis) and faecal incontinence (FI) were found to be common problems among females with RS that occur in a high frequency of days/nights. UI and FI were mostly primary in nature and occur independent of participants' age and level of adaptive functioning. Solid stool, lower urinary tract symptoms and urinary tract infections (UTI's) were also common problems in females with RS. No differences in incontinence between RS and the control group were found, except for solid stool that was more common in RS than in the control group. It is concluded that incontinence is not part of the behavioural phenotype of RS, but that there is an increased risk for solid stool in females with RS.

Genetic and epileptic features in Rett syndrome

PURPOSE

Rett syndrome is a severe neurodevelopmental disorder in females. Most have mutations in the methyl-CpG-binding protein 2 (MECP2) gene (80-90%). Epilepsy is a significant commonly accompanied feature in Rett syndrome. Our study was aimed at comprehensive analysis of genetic and clinical features in Rett syndrome patients, especially in regards to epileptic features.

MATERIALS AND METHODS

We retrospectively reviewed 20 patients who were diagnosed with MECP2 mutations at Severance Children's Hospital between January 1995 and July 2010. All patients met clinical criteria for Rett syndrome. Evaluations included clinical features, epilepsy classification, electroencephalography analysis, and treatment of seizures.

RESULTS

Ages ranged from 3.6 to 14.3 years (7.7±2.6). Fourteen different types of MECP2 mutations were found, including a novel in-frame mutation (1153-1188 del36). Fourteen of these patients (70.0%) had epilepsy, and the average age of seizure onset was 3.0±1.8 years. Epilepsy was diverse, including partial seizure in four patients (28.5%), secondarily generalized seizure in six (42.8%), generalized tonic seizure in two (14.3%), Lennox-Gastaut syndrome in one (7.1%), and myoclonic status in non-progressive encephalopathy in one (7.1%). Motor functions were delayed so that only 10 patients (50.0%) were able to walk independently: five (35.8%) in the epilepsy group and five (83.3%) in the non-epilepsy group. Average developmental scale was 33.5±32.8 in the epilepsy group and 44.4±21.2 in the non-epilepsy group. A clear genotype-phenotype correlation was not found.

CONCLUSION

There is a tendency for more serious motor impairment and cognitive deterioration in Rett syndrome patients with epilepsy.

Self-injurious behaviour in intellectual disability syndromes: evidence for aberrant pain signalling as a contributing factor

BACKGROUND

In most individuals, injury results in activation of peripheral nociceptors (pain-sensing neurons of the peripheral nervous system) and amplification of central nervous system (CNS) pain pathways that serve as a disincentive to continue harmful behaviour; however, this may not be the case in some developmental disorders that cause intellectual disability (ID). Moreover, individuals affected by ID disorders may initiate self-injurious behaviour to address irritating or painful sensations. In normal individuals, a negative feedback loop decreases sensation of pain, which involves descending inhibitory neurons in the CNS that attenuate spinal nociceptive processing. If spinal nociceptive signalling is impaired in these developmental disorders, an exaggerated painful stimulus may be required in order to engage descending anti-nociceptive signals.

METHODS

Using electronic databases, we conducted a review of publications regarding the incidence of chronic pain or altered pain sensation in ID patients or corresponding preclinical models.

RESULTS

There is a body of evidence indicating that individuals with fragile X mental retardation and/or Rett syndrome have altered pain sensation. These findings in humans are supported by mechanistic studies using genetically modified mice harbouring mutations consistent with the human disease. Thus, once self-injurious behaviour is initiated, the signal to stop may be missing. Several developmental disorders that cause ID are associated with increased incidence of gastroesophageal reflux disease (GERD), which can cause severe visceral pain. Individuals affected by these disorders who also have GERD may self-injure as a mechanism to engage descending inhibitory circuits to quell visceral pain. In keeping with this hypothesis, pharmacological treatment of GERD has been shown to be effective for reducing self-injurious behaviour in some patients. Hence, multiple lines of evidence suggest aberrant nociceptive processing in developmental disorders that cause ID.

CONCLUSIONS

There is evidence that pain pathways and pain amplification mechanisms are altered in several preclinical models of developmental disorders that cause ID. We present hypotheses regarding how impaired pain pathways or chronic pain might contribute to self-injurious behaviour. Studies evaluating the relationship between pain and self-injurious behaviour will provide better understanding of the mechanisms underlying self-injurious behaviour in the ID population and may lead to more effective treatments.

MicroRNAs in neuronal function and dysfunction

MicroRNAs (miRNAs) are small noncoding RNA transcripts expressed throughout the brain that can regulate neuronal gene expression at the post-transcriptional level. Here, we provide an overview of the role for miRNAs in brain development and function, and review evidence suggesting that dysfunction in miRNA signaling contributes to neurodevelopment disorders such as Rett and fragile X syndromes, as well as complex behavioral disorders including schizophrenia, depression and drug addiction. A better understanding of how miRNAs influence the development of neuropsychiatric disorders may reveal fundamental insights into the causes of these devastating illnesses and offer novel targets for therapeutic development.

Contributing to the early detection of Rett syndrome: the potential role of auditory Gestalt perception

To assess whether there are qualitatively deviant characteristics in the early vocalizations of children with Rett syndrome, we had 400 native Austrian-German speakers listen to audio recordings of vocalizations from typically developing girls and girls with Rett syndrome. The audio recordings were rated as (a) inconspicuous, (b) conspicuous or (c) not able to decide between (a) and (b). The results showed that participants were accurate in differentiating the vocalizations of typically developing children compared to children with Rett syndrome. However, the accuracy for rating verbal behaviors was dependent on the type of vocalization with greater accuracy for canonical babbling compared to cooing vocalizations. The results suggest a potential role for the use of rating child vocalizations for early detection of Rett syndrome. This is important because clinical criteria related to speech and language development remain important for early identification of Rett syndrome.

The disruption of central CO2 chemosensitivity in a mouse model of Rett syndrome

People with Rett syndrome (RTT) have breathing instability in addition to other neuropathological manifestations. The breathing disturbances contribute to the high incidence of unexplained death and abnormal brain development. However, the cellular mechanisms underlying the breathing abnormalities remain unclear. To test the hypothesis that the central CO(2) chemoreception in these people is disrupted, we studied the CO(2) chemosensitivity in a mouse model of RTT. The Mecp2-null mice showed a selective loss of their respiratory response to 1-3% CO(2) (mild hypercapnia), whereas they displayed more regular breathing in response to 6-9% CO(2) (severe hypercapnia). The defect was alleviated with the NE uptake blocker desipramine (10 mg·kg(-1)·day(-1) ip, for 5-7 days). Consistent with the in vivo observations, in vitro studies in brain slices indicated that CO(2) chemosensitivity of locus coeruleus (LC) neurons was impaired in Mecp2-null mice. Two major neuronal pH-sensitive Kir currents that resembled homomeric Kir4.1 and heteromeric Ki4.1/Kir5.1 channels were identified in the LC neurons. The screening of Kir channels with real-time PCR indicated the overexpression of Kir4.1 in the LC region of Mecp2-null mice. In a heterologous expression system, an overexpression of Kir4.1 resulted in a reduction in the pH sensitivity of the heteromeric Kir4.1-Kir5.1 channels. Given that Kir4.1 and Kir5.1 subunits are also expressed in brain stem respiration-related areas, the Kir4.1 overexpression may not allow CO(2) to be detected until hypercapnia becomes severe, leading to periodical hyper- and hypoventilation in Mecp2-null mice and, perhaps, in people with RTT as well.

Above genetics: lessons from cerebral development in autism

While a distinct minicolumnar phenotype seems to be an underlying factor in a significant portion of cases of autism, great attention is being paid not only to genetics but to epigenetic factors which may lead to development of the conditions. Here we discuss the indivisible role the molecular environment plays in cellular function, particularly the pivotal position which the transcription factor and adhesion molecule, β-catenin, occupies in cellular growth. In addition, the learning environment is not only integral to postnatal plasticity, but the prenatal environment plays a vital role during corticogenesis, neuritogenesis, and synaptogenesis as well. To illustrate these points in the case of autism, we review important findings in genetics studies (e.g., PTEN, TSC1/2, FMRP, MeCP2, Neurexin-Neuroligin) and known epigenetic factors (e.g., valproic acid, estrogen, immune system, ultrasound) which may predispose towards the minicolumnar and connectivity patterns seen in the conditions, showing how one-gene mutational syndromes and exposure to certain CNS teratogens may ultimately lead to comparable phenotypes. This in turn may shed greater light on how environment and complex genetics combinatorially give rise to a heterogenetic group of conditions such as autism.

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.

The role of MeCP2 in CNS development and function

Rett syndrome is a neurodevelopmental disorder that is a direct consequence of functional mutations in the methyl-CpG-binding protein-2 (MeCP2) gene, which has focused attention on epigenetic mechanisms in neurons. MeCP2 is widely believed to be a transcriptional repressor although it may have additional functions in the CNS. Genetic mouse models that compromise MeCP2 function demonstrate that homeostatic regulation of MeCP2 is necessary for normal CNS functioning. Recent work has also demonstrated that MeCP2 plays an important role in mediating synaptic transmission in the CNS in particular, spontaneous neurotransmission and short-term synaptic plasticity. This review will discuss the role of MeCP2 in CNS development and function, as well as a potential important role for MeCP2 and epigenetic processes involved in mediating transcriptional repression in Rett syndrome.

Animal models of intellectual disability: towards a translational approach

Intellectual disability is a prevalent form of cognitive impairment, affecting 2-3% of the general population. It is a daunting societal problem characterized by significant limitations both in intellectual functioning and in adaptive behavior as expressed in conceptual, social and practical adaptive skills. Intellectual disability is a clinically important disorder for which the etiology and pathogenesis are still poorly understood. Moreover, although tremendous progress has been made, pharmacological intervention is still currently non-existent and therapeutic strategies remain limited. Studies in humans have a very limited capacity to explain basic mechanisms of this condition. In this sense, animal models have been invaluable in intellectual disability investigation. Certainly, a great deal of the knowledge that has improved our understanding of several pathologies has derived from appropriate animal models. Moreover, to improve human health, scientific discoveries must be translated into practical applications. Translational research specifically aims at taking basic scientific discoveries and best practices to benefit the lives of people in our communities. In this context, the challenge that basic science research needs to meet is to make use of a comparative approach to benefit the most from what each animal model can tell us. Intellectual disability results from many different genetic and environmental insults. Taken together, the present review will describe several animal models of potential intellectual disability risk factors.

Emerging pharmacotherapies for neurodevelopmental disorders

A growing and interdisciplinary translational neuroscience research effort for neurodevelopmental disorders (NDDs) is investigating the mechanisms of dysfunction and testing effective treatment strategies in animal models and, when possible, in the clinic. NDDs with a genetic basis have received particular attention. Transgenic animals that mimic genetic insults responsible for disease in man have provided insight about mechanisms of dysfunction, and, surprisingly, have shown that cognitive deficits can be addressed in adult animals. This review will present recent translational research based on animal models of genetic NDDs, as well as pharmacotherapeutic strategies under development to address deficits of brain function for Down syndrome, fragile X syndrome, Rett syndrome, neurofibromatosis-1, tuberous sclerosis, and autism. Although these disorders vary in underlying causes and clinical presentation, common pathways and mechanisms for dysfunction have been observed. These include abnormal gene dosage, imbalance among neurotransmitter systems, and deficits in the development, maintenance and plasticity of neuronal circuits. NDDs affect multiple brain systems and behaviors that may be amenable to drug therapies that target distinct deficits. A primary goal of translational research is to replace symptomatic and supportive drug therapies with pharmacotherapies based on a principled understanding of the causes of dysfunction. Based on this principle, several recently developed therapeutic strategies offer clear promise for clinical development in man.

Novel variants identified in methyl-CpG-binding domain genes in autistic individuals

Misregulation of the methyl-CpG-binding protein 2 (MECP2) gene has been found to cause a myriad of neurological disorders including autism, mental retardation, seizures, learning disabilities, and Rett syndrome. We hypothesized that mutations in other members of the methyl-CpG-binding domain (MBD) family may also cause autistic features in individuals. We evaluated 226 autistic individuals for alterations in the four genes most homologous to MECP2: MBD1, MBD2, MBD3, and MBD4. A total of 46 alterations were identified in the four genes, including ten missense changes and two deletions that alter coding sequence. Several are either unique to our autistic population or cosegregate with affected individuals within a family, suggesting a possible relation of these variations to disease etiology. Variants include a R23M alteration in two affected half brothers which falls within the MBD domain of the MBD3 protein, as well as a frameshift in MBD4 that is predicted to truncate almost half of the protein. These results suggest that rare cases of autism may be influenced by mutations in members of the dynamic MBD protein family.

Linking MECP2 and pain sensitivity: the example of Rett syndrome

Recent animal studies suggest links between MeCP2 function and sensitivity to pain. This study investigated the nature and prevalence of atypical pain responses in Rett syndrome and their relationships with specific MECP2 mutations. Families enrolled in the Australian Rett Syndrome Database (ARSD) and InterRett database participated in this study. Cases with a known MECP2 pathogenic mutation, whose families had completed a questionnaire on registration and had answered questions on pain sensitivity were included (n = 646). Logistic regression was used to analyze relationships between the atypical pain responses and genotype. Descriptions of decreased pain sensitivity were content analyzed. The prevalence estimate of reporting an abnormal pain response was 75.2% and a decreased sensitivity to pain was 65.0% in the population-based ARSD. Families of ARSD and InterRett subjects with a C-terminal (OR 2.6; 95% CI 0.8-8.0), p.R168X (OR 2.1; 95% CI 0.7-6.1), or p.R306C (OR 2.7; 95% CI 0.8-9.6) mutation were more likely to report decreased sensitivity to pain. Parents and carers described decreased and delayed responses in situations judged likely to cause pain such as injections, falls, trauma, and burns. This study has provided the first precise estimate of the prevalence of abnormal sensitivity to pain in Rett syndrome but specific relationships with genotype are not yet clear. Clinical practice should include a low threshold for the clinical assessment of potential injuries in Rett syndrome.

Communication in Individuals with Rett Syndrome: an Assessment of Forms and Functions

In the present study we assessed the forms and functions of prelinguistic communicative behaviors for 120 children and adults with Rett syndrome using the Inventory of Potential Communicative Acts (IPCA) (Sigafoos et al. Communication Disorders Quarterly 21:77-86, 2000a). Informants completed the IPCA and the results were analysed to provide a systematic inventory and objective description of the communicative forms and functions present in each individual's repertoire. Results show that respondents reported a wide variety of communicative forms and functions. By far most girls used prelinguistic communicative behaviors of which eye contact/gazing was the most common form. The most often endorsed communicative functions were social convention, commenting, answering, requesting and choice-making. Problematic topographies (e.g., self-injury, screaming, non-compliance) were being used for communicative purposes in 10 to 41% of the sample. Exploratory analyses revealed that several communicative forms and functions were related to living environment, presence/absence of epilepsy, and age. That is, higher percentages of girls who showed some forms/functions were found in those who lived at home, who had no epilepsy and who were relatively young.

Rett syndrome and other autism spectrum disorders--brain diseases of immune malfunction?

Neuroimmunology was once referred to in terms of its pathological connotation only and was generally understood as covering the deleterious involvement of the immune system in various diseases and disorders of the central nervous system (CNS). However, our conception of the function of the immune system in the structure, function, and plasticity of the CNS has undergone a sea change after relevant discoveries over the past two decades, and continues to be challenged by more recent studies of neurodevelopment and cognition. This review summarizes the recent advances in understanding of immune-system participation in the development and functioning of the CNS under physiological conditions. Considering as an example Rett syndrome a devastating neurodevelopmental disease, we offer a hypothesis that might help to explain the part played by immune cells in its etiology, and hence suggests that the immune system might be a feasible therapeutic target for alleviation of some of the symptoms of this and other autism spectrum disorders.

The role of MeCP2 in brain development and neurodevelopmental disorders

Methyl CpG binding protein-2 (MeCP2) is an essential epigenetic regulator in human brain development. Rett syndrome, the primary disorder caused by mutations in the X-linked MECP2 gene, is characterized by a period of cognitive decline and development of hand stereotypies and seizures following an apparently normal early infancy. In addition, MECP2 mutations and duplications are observed in a spectrum of neurodevelopmental disorders, including severe neonatal encephalopathy, X-linked mental retardation, and autism, implicating MeCP2 as an essential regulator of postnatal brain development. In this review, we compare the mutation types and inheritance patterns of the human disorders associated with MECP2. In addition, we summarize the current understanding of MeCP2 as a central epigenetic regulator of activity-dependent synaptic maturation. As MeCP2 occupies a central role in the pathogenesis of multiple neurodevelopmental disorders, continued investigation into MeCP2 function and regulatory pathways may show promise for developing broad-spectrum therapies.

Dendritic spine pathologies in hippocampal pyramidal neurons from Rett syndrome brain and after expression of Rett-associated MECP2 mutations

Rett syndrome (RTT) is an X chromosome-linked neurodevelopmental disorder associated with the characteristic neuropathology of dendritic spines common in diseases presenting with mental retardation (MR). Here, we present the first quantitative analyses of dendritic spine density in postmortem brain tissue from female RTT individuals, which revealed that hippocampal CA1 pyramidal neurons have lower spine density than age-matched non-MR female control individuals. The majority of RTT individuals carry mutations in MECP2, the gene coding for a methylated DNA-binding transcriptional regulator. While altered synaptic transmission and plasticity has been demonstrated in Mecp2-deficient mouse models of RTT, observations regarding dendritic spine density and morphology have produced varied results. We investigated the consequences of MeCP2 dysfunction on dendritic spine structure by overexpressing ( approximately twofold) MeCP2-GFP constructs encoding either the wildtype (WT) protein, or missense mutations commonly found in RTT individuals. Pyramidal neurons within hippocampal slice cultures transfected with either WT or mutant MECP2 (either R106W or T158M) showed a significant reduction in total spine density after 48 h of expression. Interestingly, spine density in neurons expressing WT MECP2 for 96 h was comparable to that in control neurons, while neurons expressing mutant MECP2 continued to have lower spine density than controls after 96 h of expression. Knockdown of endogenous Mecp2 with a specific small hairpin interference RNA (shRNA) also reduced dendritic spine density, but only after 96 h of expression. On the other hand, the consequences of manipulating MeCP2 levels for dendritic complexity in CA3 pyramidal neurons were only minor. Together, these results demonstrate reduced dendritic spine density in hippocampal pyramidal neurons from RTT patients, a distinct dendritic phenotype also found in neurons expressing RTT-associated MECP2 mutations or after shRNA-mediated endogenous Mecp2 knockdown, suggesting that this phenotype represent a cell-autonomous consequence of MeCP2 dysfunction.

A study of the treatment of Rett syndrome with folate and betaine

We tested the hypothesis that increasing methyl-group pools might promote transcriptional repression by other methyl-binding proteins or by mutant methyl-CpG-binding protein 2 with altered affinity, ameliorating the clinical features of Rett syndrome. A 12-month, double-blind, placebo-controlled folate-betaine trial enrolled 73 methylCpG-binding protein 2 mutation positive female participants meeting consensus criteria for Rett syndrome. Participants were randomized as young (< age 5 years) or old (>or= age 5 years). Structured clinical assessments occurred at baseline, 3, 6, and 12 months. Primary outcome measures included quantitative evaluation of breathing and hand movements during wakefulness, growth, anthropometry, motor/behavioral function, and qualitative evaluations from electroencephalograms and parent questionnaires. In all, 68 participants completed the study. Objective evidence of improvement was not found. Subjective improvement from parent questionnaires was noted for the <5 years group. This study should inform future treatment trials regarding balancing participants with specific mutations and comparable severity to minimize selection bias.

Noncoding RNAs in mental retardation

Recent genome-wide interrogations of transcribed RNA have yielded compelling evidence for pervasive and complex transcription throughout a large majority of the human genome. Tens of thousands of noncoding RNA transcripts have been identified, most of which have yet to be functionally characterized. Along with the revelation that noncoding RNAs in the human genome are surprisingly abundant, there has been a surge in molecular and genetic data showing important and diverse regulatory roles for noncoding RNA. In this report, we summarize the potential roles that noncoding RNAs may play in the molecular pathogenesis of different mental retardation disorders. We suspect that these findings are just the tip of the iceberg, with noncoding RNAs possibly being involved in disease pathogenesis at different levels and through multiple distinct mechanisms.

Plasticity and injury in the developing brain

The child's brain is more malleable or plastic than that of adults and this accounts for the ability of children to learn new skills quickly or recovery from brain injuries. Several mechanisms contribute to this ability including overproduction and deletion of neurons and synapses, and activity-dependent stabilization of synapses. The molecular mechanisms for activity-dependent synaptic plasticity are being discovered and this is leading to a better understanding of the pathogenesis of several disorders including neurofibromatosis, tuberous sclerosis, Fragile X syndrome and Rett syndrome. Many of the same pathways involved in synaptic plasticity, such as glutamate-mediated excitation, can also mediate brain injury when the brain is exposed to stress or energy failure such as hypoxia-ischemia. Recent evidence indicates that cell death pathways activated by injury differ between males and females. This new information about the molecular pathways involved in brain plasticity and injury are leading to insights that will provide better therapies for pediatric neurological disorders.

Childhood developmental disorders: an academic and clinical convergence point for psychiatry, neurology, psychology and pediatrics

BACKGROUND

Significant advances in understanding brain development and behavior have not been accompanied by revisions of traditional academic structure. Disciplinary isolation and a lack of meaningful interdisciplinary opportunities are persistent barriers in academic medicine. To enhance clinical practice, research, and training for the next generation, academic centers will need to take bold steps that challenge traditional departmental boundaries. Such change is not only desirable but, in fact, necessary to bring about a truly innovative and more effective approach to treating disorders of the developing brain.

METHODS

I focus on developmental disorders as a convergence point for transcending traditional academic boundaries. First, the current taxonomy of developmental disorders is described with emphasis on how current diagnostic systems inadvertently hinder research progress. Second, I describe the clinical features of autism, a phenomenologically defined condition, and Rett and fragile X syndromes, neurogenetic diseases that are risk factors for autism. Finally, I describe how the fields of psychiatry, psychology, neurology, and pediatrics now have an unprecedented opportunity to promote an interdisciplinary approach to training, research, and clinical practice and, thus, advance a deeper understanding of developmental disorders.

RESULTS

Research focused on autism is increasingly demonstrating the heterogeneity of individuals diagnosed by DSM criteria. This heterogeneity hinders the ability of investigators to replicate research results as well as progress towards more effective, etiology-specific interventions. In contrast, fragile X and Rett syndromes are 'real' diseases for which advances in research are rapidly accelerating towards more disease-specific human treatment trials.

CONCLUSIONS

A major paradigm shift is required to improve our ability to diagnose and treat individuals with developmental disorders. This paradigm shift must take place at all levels - training, research and clinical activity. As clinicians and scientists who are currently constrained by disciplinary-specific history and training, we must move towards redefining ourselves as clinical neuroscientists with shared interests and expertise that permit a more cohesive and effective approach to improving the lives of patients.

Gross motor profile in rett syndrome as determined by video analysis

Movement impairment is a fundamental but variable component of the Rett syndrome phenotype. This study used video supplemented by parent report data to describe the gross motor profile in females with Rett syndrome (n=99) and to investigate the impact of age, genotype, scoliosis and hand stereotypies. Factor analysis enabled the calculation of general and complex gross motor skills scores. Most subjects were able to sit, slightly less than half were able to walk and a minority were able to transfer without assistance. General gross motor skills declined with age and were poorer in those who had surgically treated scoliosis but not conservatively managed scoliosis. Complex gross motor skills did not decline with age and were better in those without scoliosis. Those with a p.R133C, p.R294X, or a p.R255X mutation appear to have better motor skills overall than those with a p.R270X or large deletion mutation. Motor scores were not related to the frequency of hand stereotypies. This information is useful for the clinician and family when planning support strategies and interventions.

Ube3a mRNA and protein expression are not decreased in Mecp2R168X mutant mice

Mutations in the transcriptional repressor methyl CpG binding protein 2 (MeCP2) are responsible for most cases of Rett Syndrome (RS), a severe neurodevelopmental disorder characterized by developmental regression, minimal speech, seizures, postnatal microcephaly and hand stereotypies. Absence of the maternal copy of ubiquitin protein ligase 3A (UBE3A) results in Angelman syndrome, also a severe developmental disorder that shares some clinical features with RS. As MeCP2 regulates gene expression, this has led to the hypothesis that MeCP2 may regulate UBE3A expression; however, there are conflicting reports regarding the expression of Ube3a in MeCP2 null mutant mice. We have generated a novel MeCP2 mutant knock-in mouse with the mutation R168X, one of the most common mutations in patients with RS. These mice show features similar to RS, including hypoactivity, forelimb stereotypies, breathing irregularities, weight changes, hind limb atrophy, and scoliosis. The male mice experience early death. Analysis of Ube3a mRNA and protein levels in the Mecp2(R168X) male mice showed no significant difference in expression compared to their wild type littermates.

Sleep problems in Rett syndrome

Rett syndrome (RTT) is a severe neurological disorder, affecting mainly females. It is generally caused by mutations in the MECP2 gene. Sleep problems are thought to occur commonly in Rett syndrome, but there has been little research on prevalence or natural history. An Australian population-based registry of cases born since 1976 has been operating since 1993, with current ascertainment at 300. The Australian Rett Syndrome Database (ARSD) consists of information about Rett syndrome cases including their functional ability, behaviour, sleep patterns, medical conditions and genotype. The cases range in age from 2 to 29 years. The aim of this study was to investigate the type and frequency of sleep problems, relationships with age and MECP2 mutation type and to evaluate changes over time. Parents or carers of the subjects with Rett syndrome were asked to complete a questionnaire about sleep problems on three separate occasions (2000, 2002 and 2004). Regression modelling was used to investigate the relationships between sleep problems, age and mutation type. Sleep problems were identified in over 80% of cases. The prevalence of night-time laughter decreased with age and the prevalence of reported night-time seizures and daytime napping increased with age. The prevalence of sleep problems was highest in cases with a large deletion of the MECP2 gene and in those with the p.R294X or p.R306C mutations. Sleep problems are common in Rett syndrome and there is some variation with age and mutation type.

Seizures in Rett syndrome: an overview from a one-year calendar study

BACKGROUND

Rett syndrome is a neurodevelopmental disorder mainly affecting females. It is principally caused by mutations in the MECP2 gene. Seizures occur in about 80% of subjects but there has been little research into the factors contributing to their frequency.

AIMS

To investigate seizure frequency in Rett syndrome and its relationship with other factors, including genetic characteristics and the use of anti-epileptic drugs.

METHODS

Information on daily seizure occurrence and health service utilization and monthly anti-epileptic drug use was provided on 162 Rett syndrome cases for a calendar year. Age at onset of seizures, developmental history and other clinical and genetic characteristics were obtained from a contemporaneously completed questionnaire and from the Australian Rett Syndrome Database. Negative binomial regression was used to investigate factors associated with seizure rates.

RESULTS

Seizure rates were highest in the 7-12 year age group. They were lower in those with p.R294X, p.R255X mutations and C terminal mutations. Those who had early developmental problems and poorer mobility had higher seizure rates as did those with greater clinical severity and poorer functional ability. Many different combinations of medications were being used with carbamazepine, sodium valproate and lamotrigine either singly or in combination with another being the most common.

CONCLUSIONS

Seizure frequency in Rett syndrome is age-dependent, more common in those with more severe early developmental problems and influenced by mutation type.

Epigenetics and Neural developmental disorders: Washington DC, September 18 and 19, 2006

Neural developmental disorders, such as autism, Rett Syndrome, Fragile X syndrome, and Angelman syndrome manifest during early postnatal neural development. Although the genes responsible for some of these disorders have been identified, how the mutations of these genes affect neural development is currently unclear. Emerging evidence suggest that these disorders share common underlying defects in neuronal morphology, synaptic connectivity and brain plasticity. In particular, alterations in dendritic branching and spine morphology play a central role in the pathophysiology of most mental retardation disorders, suggesting that common pathways regulating neuronal function may be affected. Epigenetic modulations, mediated by DNA methylation, RNA-associated silencing, and histone modification, can serve as an intermediate process that imprints dynamic environmental experiences on the "fixed" genome, resulting in stable alterations in phenotypes. Disturbance in epigenetic regulations can lead to inappropriate expression or silencing of genes, causing an array of multi-system disorders and neoplasias. Rett syndrome, the most common form of mental retardation in young girls, is due to l mutation of MECP2, encoding a methylated DNA binding protein that translates DNA methylation into gene repression. Angelman syndrome is due to faulty genomic imprinting or maternal mutations in UBE3A. Fragile X Syndrome, in most cases, results from the hypermethylation of FMR1 promoter, hence the loss of expression of functional FMRP protein. Autism, with its complex etiology, may have strong epigenetic link. Together, these observations strongly suggest that epigenetic mechanisms may play a critical role in brain development and etiology of related disorders. This report summarizes the scientific discussions and major conclusions from a recent conference that aimed to gain insight into the common molecular pathways affected among these disorders and discover potential therapeutic targets that have been missed by looking at one disorder at a time.

Transient receptor potential channels as novel effectors of brain-derived neurotrophic factor signaling: potential implications for Rett syndrome

In addition to their prominent role as survival signals for neurons in the developing nervous system, neurotrophins have established their significance in the adult brain as well, where their modulation of synaptic transmission and plasticity may participate in associative learning and memory. These crucial activities are primarily the result of neurotrophin regulation of intracellular Ca(2+) homeostasis and, ultimately, changes in gene expression. Outlined in the following review is a synopsis of neurotrophin signaling with a particular focus upon brain-derived neurotrophic factor (BDNF) and its role in hippocampal synaptic plasticity and neuronal Ca(2+) homeostasis. Neurotrophin signaling through tropomyosin-related kinase (Trk) and pan-neurotrophin receptor 75 kD (p75(NTR)) receptors are also discussed, reviewing recent results that indicate signaling through these two receptor modalities leads to opposing cellular outcomes. We also provide an intriguing look into the transient receptor potential channel (TRPC) family of ion channels as distinctive targets of BDNF signaling; these channels are critical for capacitative Ca(2+) entry, which, in due course, mediates changes in neuronal structure including dendritic spine density. Finally, we expand these topics into an exploration of mental retardation (MR), in particular Rett Syndrome (RTT), where dendritic spine abnormalities may underlie cognitive impairments. We propose that understanding the role of neurotrophins in synapse formation, plasticity, and maintenance will make fundamental contributions to the development of therapeutic strategies to improve cognitive function in developmental disorders associated with MR.

Cardiac disease and Rett syndrome

Rett syndrome (RS) is a neurodevelopmental disease,1 affecting approximately 1 in 10 000-15 000 females. Clinical severity of RS may vary with increasing age, following a four stage model.

DNA methylation and histone deacetylation in the control of gene expression: basic biochemistry to human development and disease

DNA methylation is a major determinant in the epigenetic silencing of genes. The mechanisms underlying the targeting of DNA methylation and the subsequent repression of transcription are relevant to human development and disease, as well as for attempts at somatic gene therapy. The success of transgenic technologies in plants and animals is also compromised by DNA methylation-dependent silencing pathways. Recent biochemical experiments provide a mechanistic foundation for understanding the influence of DNA methylation on transcription. The DNA methyltransferase Dnmt1, and several methyl-CpG binding proteins, MeCP2, MBD2, and MBD3, all associate with histone deacetylase. These observations firmly connect DNA methylation with chromatin modifications. They also provide new pathways for the potential targeting of DNA methylation to repressive chromatin as well as the assembly of repressive chromatin on methylated DNA. Here we discuss the implications of the methylation-acetylation connection for human cancers and the developmental syndromes Fragile X and Rett, which involve a mistargeting of DNA methylation-dependent repression.