The common BDNF polymorphism may be a modifier of disease severity in Rett syndrome

Forensically relevant challenging behaviors and the genetics domain

Impulsive and aggressive behaviors along with intellectual disabilities often manifest in the context of genetic disorders and are a persisting challenge to professionals in the forensic psychiatric and psychological setting. The following chapter comprises an overview of relevant factors in the gene-context-behavior interaction such as monoamine oxidase A activity and specific epileptic phenomena. It presents several examples of monogenetic disorders with behaviors from the aggression spectrum and summarizes emerging strategies for treatment and clinical management thereof. The final part focuses on challenges and future developments in this field with relevance for the judicial and forensic systems. It is concluded that the relationship between a genetic syndrome and forensically relevant and/or violent behaviors should typically be addressed within a multidisciplinary framework that also includes the application of modern genetic techniques.

A perspective on molecular signalling dysfunction, its clinical relevance and therapeutics in autism spectrum disorder

Intellectual disability (ID) and autism spectrum disorder (ASD) are neurodevelopmental disorders that have become a primary clinical and social concern, with a prevalence of 2-3% in the population. Neuronal function and behaviour undergo significant malleability during the critical period of development that is found to be impaired in ID/ASD. Human genome sequencing studies have revealed many genetic variations associated with ASD/ID that are further verified by many approaches, including many mouse and other models. These models have facilitated the identification of fundamental mechanisms underlying the pathogenesis of ASD/ID, and several studies have proposed converging molecular pathways in ASD/ID. However, linking the mechanisms of the pathogenic genes and their molecular characteristics that lead to ID/ASD has progressed slowly, hampering the development of potential therapeutic strategies. This review discusses the possibility of recognising the common molecular causes for most ASD/ID based on studies from the available models that may enable a better therapeutic strategy to treat ID/ASD. We also reviewed the potential biomarkers to detect ASD/ID at early stages that may aid in diagnosis and initiating medical treatment, the concerns with drug failure in clinical trials, and developing therapeutic strategies that can be applied beyond a particular mutation associated with ASD/ID.

Variable predicted pathogenic mechanisms for novel MECP2 variants in RTT patients

BACKGROUND

Methyl CpG binding protein 2 (MeCP2) is essential for the normal function of mature neurons. Mutations in the MECP2 gene are the main cause of Rett syndrome (RTT). Gene mutations have been identified throughout the gene and the mutation effect is mainly correlated with its type and location.

METHODS

In this study, a series of in silico algorithms were applied for analyzing the functional consequences of 3 novel gene missense mutations (D121A, S359Y, and P403S) and a rarely reported one with suspicious effect (R133H) on RettBASE. Besides, a ROC curve analysis was performed to investigate the critical factors affecting variant pathogenicity.

RESULTS

(1) The ROC curve analysis for a retrieved set of MeCP2 variants showed that physicochemical characters do not significantly affect variant pathogenicity; (2) PREM PDI tool revealed that both D121A and R133H mainly contribute to disease progression via reducing MeCP2 affinity to DNA; (3) GPS v5.0 software indicated that P403S may correlate with altered protein phosphorylation; however, no defective protein interaction has been already documented. (4) The applied computational algorithms failed to explore any informative pathogenic mechanism for the S359Y variant.

CONCLUSION

The conducted approach might provide an efficient prediction model for the effect of MECP2 variants that are located in MBD and CTD.

Proteomic and transcriptional changes associated with MeCP2 dysfunction reveal nodes for therapeutic intervention in Rett syndrome

Mutations in the methyl-CpG binding protein 2 (MECP2) gene cause Rett syndrome (RTT), an X-linked neurodevelopmental disorder predominantly impacting females. MECP2 is an epigenetic transcriptional regulator acting mainly to repress gene expression, though it plays multiple gene regulatory roles and has distinct molecular targets across different cell types and specific developmental stages. In this review, we summarize MECP2 loss-of-function associated transcriptome and proteome disruptions, delving deeper into the latter which have been comparatively severely understudied. These disruptions converge on multiple biochemical and cellular pathways, including those involved in synaptic function and neurodevelopment, NF-κB signaling and inflammation, and the vitamin D pathway. RTT is a complex neurological disorder characterized by myriad physiological disruptions, in both the central nervous system and peripheral systems. Thus, treating RTT will likely require a combinatorial approach, targeting multiple nodes within the interactomes of these cellular pathways. To this end, we discuss the use of dietary supplements and factors, namely, vitamin D and polyunsaturated fatty acids (PUFAs), as possible partial therapeutic agents given their demonstrated benefit in RTT and their ability to restore homeostasis to multiple disrupted cellular pathways simultaneously. Further unravelling the complex molecular alterations induced by MECP2 loss-of-function, and contextualizing them at the level of proteome homeostasis, will identify new therapeutic avenues for this complex disorder.

Music-Based Intervention Ameliorates Mecp2-Loss-Mediated Sociability Repression in Mice through the Prefrontal Cortex FNDC5/BDNF Pathway

Patients with Rett syndrome (RTT) show severe difficulties with communication, social withdrawl, and learning. Music-based interventions improve social interaction, communication skills, eye contact, and physical skills and reduce seizure frequency in patients with RTT. This study aimed to investigate the mechanism by which music-based interventions compromise sociability impairments in mecp2 ^null/y mice as an experimental RTT model. Male mecp2 ^null/y mice and wild-type mice (24 days old) were randomly divided into control, noise, and music-based intervention groups. Mice were exposed to music or noise for 6 h/day for 3 consecutive weeks. Behavioral patterns, including anxiety, spontaneous exploration, and sociability, were characterized using open-field and three-chamber tests. BDNF, TrkB receptor motif, and FNDC5 expression in the prefrontal cortex (PFC), hippocampus, basal ganglia, and amygdala were probed using RT-PCR or immunoblotting. mecp2 ^null/y mice showed less locomotion in an open field than wild-type mice. The social novelty rather than the sociability of these animals increased following a music-based intervention, suggesting that music influenced the mecp2-deletion-induced social interaction repression rather than motor deficit. Mechanically, the loss of BDNF signaling in the prefrontal cortex and hippocampal regions, but not in the basal ganglia and amygdala, was compromised following the music-based intervention in mecp2 ^null/y mice, whereas TrkB signaling was not significantly changed in either region. FNDC5 expression in the prefrontal cortex region in mecp2 ^null/y mice also increased following the music-based intervention. Collective evidence reveals that music-based interventions improve mecp2-loss-induced social dysfunction. BDNF and FNDC5 signaling in the prefrontal cortex region mediates the music-based-intervention promotion of social interactions. This study gives new insight into the mechanisms underlying the improvement of social behaviors in mice suffering from experimental Rett syndrome following a music-based intervention.

Modeling Rett Syndrome with Human Pluripotent Stem Cells: Mechanistic Outcomes and Future Clinical Perspectives

Rett syndrome (RTT) is a neurodevelopmental disorder caused by mutations in the gene encoding the methyl-CpG-binding protein 2 (MeCP2). Among many different roles, MeCP2 has a high phenotypic impact during the different stages of brain development. Thus, it is essential to intensively investigate the function of MeCP2, and its regulated targets, to better understand the mechanisms of the disease and inspire the development of possible therapeutic strategies. Several animal models have greatly contributed to these studies, but more recently human pluripotent stem cells (hPSCs) have been providing a promising alternative for the study of RTT. The rapid evolution in the field of hPSC culture allowed first the development of 2D-based neuronal differentiation protocols, and more recently the generation of 3D human brain organoid models, a more complex approach that better recapitulates human neurodevelopment in vitro. Modeling RTT using these culture platforms, either with patient-specific human induced pluripotent stem cells (hiPSCs) or genetically-modified hPSCs, has certainly contributed to a better understanding of the onset of RTT and the disease phenotype, ultimately allowing the development of high throughput drugs screening tests for potential clinical translation. In this review, we first provide a brief summary of the main neurological features of RTT and the impact of MeCP2 mutations in the neuropathophysiology of this disease. Then, we provide a thorough revision of the more recent advances and future prospects of RTT modeling with human neural cells derived from hPSCs, obtained using both 2D and organoids culture systems, and its contribution for the current and future clinical trials for RTT.

Dual Profile of Environmental Enrichment and Autistic-Like Behaviors in the Maternal Separated Model in Rats

BACKGROUND

Environmental Enrichment (EE) has been suggested as a possible therapeutic intervention for neurodevelopmental disorders such as autism. Although the benefits of this therapeutic method have been reported in some animal models and human studies, the unknown pathophysiology of autism as well as number of conflicting results, urge for further examination of the therapeutic potential of EE in autism. Therefore, the aim of this study was to examine the effects of environmental enrichment on autism-related behaviors which were induced in the maternal separation (MS) animal model.

MATERIAL AND METHODS

Maternally separated (post-natal day (PND) 1-14, 3h/day) and control male rats were at weaning (PND21) age equally divided into rats housed in enriched environment and normal environment. At adolescence (PND42-50), the four groups were behaviorally tested for direct social interaction, sociability, repetitive behaviors, anxiety behavior, and locomotion. Following completion of the behavioral tests, the blood and brain tissue samples were harvested in order to assess plasma level of brain derived neurotrophic factor (BDNF) and structural plasticity of brain using ELISA and stereological methods respectively.

RESULTS

We found that environmental enrichment reduced repetitive behaviors but failed to improve the impaired sociability and anxiety behaviors which were induced by maternal separation. Indeed, EE exacerbated anxiety and social behaviors deficits in association with increased plasma BDNF level, larger volume of the hippocampus and infra-limbic region and higher number of neurons in the infra-limbic area (p < 0.05). Conclusion: We conclude that environmental enrichment has a significant improvement effect on the repetitive behavior as one of the core autistic-like behaviors induced by maternal separation but has negative effect on the anxiety and social behaviors which might have been modulated by BDNF.

The emerging role of the BDNF-TrkB signaling pathway in the modulation of pain perception

The brain derived neurotrophic factor (BDNF) is a crucial neuromodulator in pain transmission both in peripheral and central nervous system (CNS). Despite evidence of a pro-nociceptive role of BDNF, recent studies have reported contrasting results, including anti-nociceptive and anti-inflammatory activities. Moreover, BDNF polymorphisms can interfere with BDNF role in pain perception. In Val66Met carriers, the Met allele may have a dual role, with anti-nociceptive actions in normal condition and pro-nociceptive effects during chronic pain. In order to elucidate the main effects of BDNF in nociception, we reviewed the main characteristics of this neurotrophin, focusing on its involvement in pain.

Expansion of the phenotypic spectrum of de novo missense variants in kinesin family member 1A (KIF1A)

Defects in the motor domain of kinesin family member 1A (KIF1A), a neuron-specific ATP-dependent anterograde axonal transporter of synaptic cargo, are well-recognized to cause a spectrum of neurological conditions, commonly known as KIF1A-associated neurological disorders (KAND). Here, we report one mutation-negative female with classic Rett syndrome (RTT) harboring a de novo heterozygous novel variant [NP_001230937.1:p.(Asp248Glu)] in the highly conserved motor domain of KIF1A. In addition, three individuals with severe neurodevelopmental disorder along with clinical features overlapping with KAND are also reported carrying de novo heterozygous novel [NP_001230937.1:p.(Cys92Arg) and p.(Pro305Leu)] or previously reported [NP_001230937.1:p.(Thr99Met)] variants in KIF1A. In silico tools predicted these variants to be likely pathogenic, and 3D molecular modeling predicted defective ATP hydrolysis and/or microtubule binding. Using the neurite tip accumulation assay, we demonstrated that all novel KIF1A variants significantly reduced the ability of the motor domain of KIF1A to accumulate along the neurite lengths of differentiated SH-SY5Y cells. In vitro microtubule gliding assays showed significantly reduced velocities for the variant p.(Asp248Glu) and reduced microtubule binding for the p.(Cys92Arg) and p.(Pro305Leu) variants, suggesting a decreased ability of KIF1A to move along microtubules. Thus, this study further expanded the phenotypic characteristics of KAND individuals with pathogenic variants in the KIF1A motor domain to include clinical features commonly seen in RTT individuals.

Consensus guidelines on managing Rett syndrome across the lifespan

BACKGROUND

Rett syndrome (RTT) is a severe neurodevelopmental disorder with complex medical comorbidities extending beyond the nervous system requiring the attention of health professionals. There is no peer-reviewed, consensus-based therapeutic guidance to care in RTT. The objective was to provide consensus on guidance of best practice for addressing these concerns.

METHODS

Informed by the literature and using a modified Delphi approach, a consensus process was used to develop guidance for care in RTT by health professionals.

RESULTS

Typical RTT presents early in childhood in a clinically recognisable fashion. Multisystem comorbidities evolve throughout the lifespan requiring coordination of care between primary care and often multiple subspecialty providers. To assist health professionals and families in seeking best practice, a checklist and detailed references for guidance were developed by consensus.

CONCLUSIONS

The overall multisystem issues of RTT require primary care providers and other health professionals to manage complex medical comorbidities within the context of the whole individual and family. Given the median life expectancy well into the sixth decade, guidance is provided to health professionals to achieve current best possible outcomes for these special-needs individuals.

In silico analysis of the V66M variant of human BDNF in psychiatric disorders: An approach to precision medicine

Brain-derived neurotrophic factor (BDNF) plays an important role in neurogenesis and synapse formation. The V66M is the most prevalent BDNF mutation in humans and impairs the function and distribution of BDNF. This mutation is related to several psychiatric disorders. The pro-region of BDNF, particularly position 66 and its adjacent residues, are determinant for the intracellular sorting and activity-dependent secretion of BDNF. However, it has not yet been fully elucidated. The present study aims to analyze the effects of the V66M mutation on BDNF structure and function. Here, we applied nine algorithms, including SIFT and PolyPhen-2, for functional and stability prediction of the V66M mutation. The complete theoretical model of BNDF was generated by Rosetta and validated by PROCHECK, RAMPAGE, ProSa, QMEAN and Verify-3D algorithms. Structural alignment was performed using TM-align. Phylogenetic analysis was performed using the ConSurf server. Molecular dynamics (MD) simulations were performed and analyzed using the GROMACS 2018.2 package. The V66M mutation was predicted as deleterious by PolyPhen-2 and SIFT in addition to being predicted as destabilizing by I-Mutant. According to SNPeffect, the V66M mutation does not affect protein aggregation, amyloid propensity, and chaperone binding. The complete theoretical structure of BDNF proved to be a reliable model. Phylogenetic analysis indicated that the V66M mutation of BDNF occurs at a non-conserved position of the protein. MD analyses indicated that the V66M mutation does not affect the BDNF flexibility and surface-to-volume ratio, but affects the BDNF essential motions, hydrogen-bonding and secondary structure particularly at its pre and pro-domain, which are crucial for its activity and distribution. Thus, considering that these parameters are determinant for protein interactions and, consequently, protein function; the alterations observed throughout the MD analyses may be related to the functional impairment of BDNF upon V66M mutation, as well as its involvement in psychiatric disorders.

Rett syndrome: a neurological disorder with metabolic components

Rett syndrome (RTT) is a neurological disorder caused by mutations in the X-linked gene methyl-CpG-binding protein 2 (MECP2), a ubiquitously expressed transcriptional regulator. Despite remarkable scientific progress since its discovery, the mechanism by which MECP2 mutations cause RTT symptoms is largely unknown. Consequently, treatment options for patients are currently limited and centred on symptom relief. Thought to be an entirely neurological disorder, RTT research has focused on the role of MECP2 in the central nervous system. However, the variety of phenotypes identified in Mecp2 mutant mouse models and RTT patients implicate important roles for MeCP2 in peripheral systems. Here, we review the history of RTT, highlighting breakthroughs in the field that have led us to present day. We explore the current evidence supporting metabolic dysfunction as a component of RTT, presenting recent studies that have revealed perturbed lipid metabolism in the brain and peripheral tissues of mouse models and patients. Such findings may have an impact on the quality of life of RTT patients as both dietary and drug intervention can alter lipid metabolism. Ultimately, we conclude that a thorough knowledge of MeCP2's varied functional targets in the brain and body will be required to treat this complex syndrome.

Environmental enrichment intervention for Rett syndrome: an individually randomised stepped wedge trial

Background

Rett syndrome is caused by a pathogenic mutation in the MECP2 gene with major consequences for motor and cognitive development. One of the effects of impaired MECP2 function is reduced production of Brain Derived Neurotrophic Factor (BDNF), a protein required for normal neuronal development. When housed in an enriched environment, MECP2 null mice improved motor abilities and increased levels of BDNF in the brain. We investigated the effects of environmental enrichment on gross motor skills and blood BDNF levels in girls with Rett syndrome.

Methods

A genetically variable group of 12 girls with a MECP2 mutation and younger than 6 years participated in a modified individually randomised stepped wedge design study. Assessments were conducted on five occasions, two during the baseline period and three during the intervention period. Gross motor function was assessed using the Rett Syndrome Gross Motor Scale (maximum score of 45) on five occasions, two during the baseline period and three during the intervention period. Blood levels of BDNF were measured at the two baseline assessments and at the end of the intervention period. The intervention comprised motor learning and exercise supplemented with social, cognitive and other sensory experiences over a six-month period.

Results

At the first assessment, the mean (SD) age of the children was 3 years (1 year 1 month) years ranging from 1 year 6 months to 5 years 2 months. Also at baseline, mean (SD) gross motor scores and blood BDNF levels were 22.7/45 (9.6) and 165.0 (28.8) ng/ml respectively. Adjusting for covariates, the enriched environment was associated with improved gross motor skills (coefficient 8.2, 95%CI 5.1, 11.2) and a 321.4 ng/ml (95%CI 272.0, 370.8) increase in blood BDNF levels after 6 months of treatment. Growth, sleep quality and mood were unaffected.

Conclusions

Behavioural interventions such as environmental enrichment can reduce the functional deficit in Rett syndrome, contributing to the evidence-base for management and further understanding of epigenetic mechanisms. Environmental enrichment will be an important adjunct in the evaluation of new drug therapies that use BDNF pathways because of implications for the strengthening of synapses and improved functioning.

Trial registration

ACTRN12615001286538.

Pathobiological expression of the brain-derived neurotrophic factor (BDNF) in cerebellar cortex of sudden fetal and infant death victims

Brain-derived neurotrophic factor (BDNF), a neurotrophin of the central nervous system, is able to regulate neuronal differentiation and modulate synaptic plasticity, being particularly involved in the development of the cerebellar cortical structure. The main aim of this study was to delineate, by immunohistochemistry, the BDNF expression in human cerebellar cortex of victims of fetal and infant death. The study was performed on a total of 45 cases, aged between 25 gestational weeks and 6 postnatal months, including 29 victims of sudden fetal and infant death and 16 age-matched subjects who died of known causes (Controls). We observed, in sudden death groups compared with Controls, a significantly higher incidence of defective BDNF expression in granule layers of the cerebellar cortex, which was particularly evident in the posterior lobule, a region that participates in respiratory control. These results were related to maternal smoking, allowing to speculate that nicotine, in addition to the well-known damages, can exert adverse effects during cerebellar cortex development, in particular in hindering the BDNF expression in the posterior lobule. This implies modifications of synaptic transmission in the respiratory circuits, with obvious deleterious consequences on survival.

The BDNF val-66-met Polymorphism Affects Neuronal Morphology and Synaptic Transmission in Cultured Hippocampal Neurons from Rett Syndrome Mice

Brain-derived neurotrophic factor (Bdnf) has been implicated in several neurological disorders including Rett syndrome (RTT), an X-linked neurodevelopmental disorder caused by loss-of-function mutations in the transcriptional modulator methyl-CpG-binding protein 2 (MECP2). The human BDNF gene has a single nucleotide polymorphism (SNP)—a methionine (met) substitution for valine (val) at codon 66—that affects BDNF’s trafficking and activity-dependent release and results in cognitive dysfunction. Humans that are carriers of the met-BDNF allele have subclinical memory deficits and reduced hippocampal volume and activation. It is still unclear whether this BDNF SNP affects the clinical outcome of RTT individuals. To evaluate whether this BDNF SNP contributes to RTT pathophysiology, we examined the consequences of expression of either val-BDNF or met-BDNF on dendrite and dendritic spine morphology, and synaptic function in cultured hippocampal neurons from wildtype (WT) and Mecp2 knockout (KO) mice. Our findings revealed that met-BDNF does not increase dendritic growth and branching, dendritic spine density and individual spine volume, and the number of excitatory synapses in WT neurons, as val-BDNF does. Furthermore, met-BDNF reduces dendritic complexity, dendritic spine volume and quantal excitatory synaptic transmission in Mecp2 KO neurons. These results suggest that the val-BDNF variant contributes to RTT pathophysiology, and that BDNF-based therapies should take into consideration the BDNF genotype of the RTT individuals.

RettBASE: Rett syndrome database update

Rett syndrome (RTT) is an X-linked progressive neurodevelopmental disorder that primarily affects females. Mutations in the MECP2 gene have been attributed as the major genetic cause of RTT. Recently, mutations in CDKL5 and FOXG1 genes have also been suggested to give rise to RTT, although subsequent more extensive studies suggest that diseases resulting from mutations in these two genes should be considered as distinct clinical entities. While the genetic basis for the RTT has been recognized, so far there is no effective cure for the disease and the treatments available are mainly aimed at ameliorating clinical problems associated with the disorder. The swift identification of the mutations in children is crucial for pursuing the best therapeutic care. RettBASE was created in 2002 as a MECP2 variant database and has grown to become a comprehensive variant database for RTT and related clinical phenotypes, containing a curated collection of variants for MECP2, CDKL5, and FOXG1 genes. Here, we describe the development and growth of RettBASE after its inception in 2001. Currently, RettBASE holds a total of 4,668 variants in MECP2, 498 variants in CDKL5, and 64 variants in FOXG1.

A Potential Life-Threatening Reaction to Glatiramer Acetate in Rett Syndrome

BACKGROUND

Rett syndrome is an X-linked dominant neurodevelopmental disorder manifesting with severe intellectual disability in females caused by various mutations in the MECP2 gene. Brain-derived neurotrophic factor (BDNF) is one of the main proteins regulated by the MECP2 protein; its overexpression in the MeCP2 mouse model partially corrects the Rett phenotype. Pharmacologic manipulations that lead to increased BDNF in individuals with Rett syndrome are expected to have a positive effect on the disorder. Glatiramer acetate, a well-known and safe multiple sclerosis immune modulator, increases BDNF levels in multiple sclerosis animal models and patients responding to treatment, as well as in Rett mouse models.

METHODS

Fourteen patients with mutation-proven Rett syndrome were recruited for a clinical trial with glatiramer acetate. Baseline data and follow-up data were collected during the trial, which had to be stopped because of a severe adverse event. Our objective is to describe this unexpected potentially life-threatening event in response to glatiramer in patients with Rett syndrome.

RESULTS

Four of 14 patients with Rett syndrome who were recruited and treated with daily injections of glatiramer acetate as part of an open-label clinical trial developed an exaggerated immediate postinjection response, which was experienced as life threatening in three of the patients, necessitating arrest of the trial.

CONCLUSION

Despite the known safety profile of glatiramer acetate in adult and pediatric patients with multiple sclerosis, its use in Rett syndrome should be cautiously reconsidered. The described severe adverse event can be related to these patients' primary autonomic nervous system dysfunction.

Clinical and biological progress over 50 years in Rett syndrome

In the 50 years since Andreas Rett first described the syndrome that came to bear his name, and is now known to be caused by a mutation in the methyl-CpG-binding protein 2 (MECP2) gene, a compelling blend of astute clinical observations and clinical and laboratory research has substantially enhanced our understanding of this rare disorder. Here, we document the contributions of the early pioneers in Rett syndrome (RTT) research, and describe the evolution of knowledge in terms of diagnostic criteria, clinical variation, and the interplay with other Rett-related disorders. We provide a synthesis of what is known about the neurobiology of MeCP2, considering the lessons learned from both cell and animal models, and how they might inform future clinical trials. With a focus on the core criteria, we examine the relationships between genotype and clinical severity. We review current knowledge about the many comorbidities that occur in RTT, and how genotype may modify their presentation. We also acknowledge the important drivers that are accelerating this research programme, including the roles of research infrastructure, international collaboration and advocacy groups. Finally, we highlight the major milestones since 1966, and what they mean for the day-to-day lives of individuals with RTT and their families.

The Contradictory Effects of Neuronal Hyperexcitation on Adult Hippocampal Neurogenesis

Adult hippocampal neurogenesis is a highly plastic process that responds swiftly to neuronal activity. Adult hippocampal neurogenesis can be regulated at the level of neural stem cell recruitment and activation, progenitor proliferation, as well as newborn cell survival and differentiation. An "excitation-neurogenesis" rule was proposed after the demonstration of the capability of cultured neural stem and progenitor cells to intrinsically sense neuronal excitatory activity. In vivo, this property has remained elusive although recently the direct response of neural stem cells to GABA in the hippocampus via GABAA receptors has evidenced a mechanism for a direct talk between neurons and neural stem cells. As it is pro-neurogenic, the effect of excitatory neuronal activity has been generally considered beneficial. But what happens in situations of neuronal hyperactivity in which neurogenesis can be dramatically boosted? In animal models, electroconvulsive shock markedly increases neurogenesis. On the contrary, in epilepsy rodent models, seizures induce the generation of misplaced neurons with abnormal morphological and electrophysiological properties, namely aberrant neurogenesis. We will herein discuss what is known about the mechanisms of influence of neurons on neural stem cells, as well as the severe effects of neuronal hyperexcitation on hippocampal neurogenesis.

NT-3 protein levels are enhanced in the hippocampus of PRG1-deficient mice but remain unchanged in PRG1/LPA2 double mutants

The plasticity-related gene 1 (PRG1) modulates bioactive lipids at the postsynaptic density and is a novel player in neuronal plasticity and regulation of glutamatergic transmission at principal neurons. PRG1, a neuronal molecule, is highly expressed during development and regeneration processes at the postsynaptic density, modulates synaptic lysophosphatidic acid (LPA) levels and is related to epilepsy and brain injury. In the present study, we analyzed the interaction between the synaptic molecules PRG1 and LPA2R with other plasticity-related molecules the neurotrophins. The protein levels of NGF, BDNF and NT-3 were measured using ELISA in hippocampal tissue of homozygous (PRG(-/-)) and heterozygous (PRG(+/-)) PRG1 deficient mice and compared to their wild type (PRG(+/+)/WT) littermates. In the hippocampus, protein levels of NT-3 were significantly increased in PRG(-/-) mice (compared to WT-litters) while protein levels of NGF and BDNF were not affected. Since PRG1 deficiency leads to increased neuronal excitability and higher hippocampal network activity, which may well influence neurotrophin levels, we further assessed PRG1 deficient mice on an LPA2-receptor (LPA2R) deficient background, reported to normalize hippocampal over-excitability in PRG1(-/-) mice. However, on an LPA2R deficient background, protein levels of NT-3 in PRG1(-/-) mice (PRG1(-/-)/LPA2R(-/-)) were not significantly different when compared to WT animals. Since PRG1 deficient mice showed over-excitability in glutamatergic neurons. This was normalized by additional LPA2R deletion, and we conclude the increased NT3-levels were directly or indirectly attributable to increased hippocampal network activity, possibly exerting a protective effect against over-excitability.

Exploring the possible link between MeCP2 and oxidative stress in Rett syndrome

Rett syndrome (RTT, MIM 312750) is a rare and orphan progressive neurodevelopmental disorder affecting girls almost exclusively, with a frequency of 1/15,000 live births of girls. The disease is characterized by a period of 6 to 18 months of apparently normal neurodevelopment, followed by early neurological regression, with a progressive loss of acquired cognitive, social, and motor skills. RTT is known to be caused in 95% of the cases by sporadic de novo loss-of-function mutations in the X-linked methyl-CpG-binding protein 2 (MECP2) gene encoding methyl-CpG binding protein 2 (MeCP2), a nuclear protein able to regulate gene expression. Despite almost two decades of research into the functions and role of MeCP2, little is known about the mechanisms leading from MECP2 mutation to the disease. Oxidative stress (OS) is involved in the pathogenic mechanisms of several neurodevelopmental and neurodegenerative disorders, although in many cases it is not clear whether OS is a cause or a consequence of the pathology. Fairly recently, the presence of a systemic OS has been demonstrated in RTT patients with a strong correlation with the patients' clinical status. The link between MECP2 mutation and the redox imbalance found in RTT is not clear. Animal studies have suggested a possible direct correlation between Mecp2 mutation and increased OS levels. In addition, the restoration of Mecp2 function in astrocytes significantly improves the developmental outcome of Mecp2-null mice and reexpression of Mecp2 gene in the brain of null mice restored oxidative damage, suggesting that Mecp2 loss of function can be involved in oxidative brain damage. Starting from the evidence that oxidative damage in the brain of Mecp2-null mice precedes the onset of symptoms, we evaluated whether, based on the current literature, the dysfunctions described in RTT could be a consequence or, in contrast, could be caused by OS. We also analyzed whether therapies that at least partially treated some RTT symptoms can play a role in defense against OS. At this stage we can propose that OS could be one of the main causes of the dysfunctions observed in RTT. In addition, the major part of the therapies recommended to alleviate RTT symptoms have been shown to interfere with oxidative homeostasis, suggesting that MeCP2 could somehow be involved in the protection of the brain from OS.

MECP2 disorders: from the clinic to mice and back

Two severe, progressive neurological disorders characterized by intellectual disability, autism, and developmental regression, Rett syndrome and MECP2 duplication syndrome, result from loss and gain of function, respectively, of the same critical gene, methyl-CpG-binding protein 2 (MECP2). Neurons acutely require the appropriate dose of MECP2 to function properly but do not die in its absence or overexpression. Instead, neuronal dysfunction can be reversed in a Rett syndrome mouse model if MeCP2 function is restored. Thus, MECP2 disorders provide a unique window into the delicate balance of neuronal health, the power of mouse models, and the importance of chromatin regulation in mature neurons. In this Review, we will discuss the clinical profiles of MECP2 disorders, the knowledge acquired from mouse models of the syndromes, and how that knowledge is informing current and future clinical studies.

Brain derived neurotrophic factor and serotonin transporter binding as markers of clinical response to fluoxetine therapy in children with autism

Fluoxetine, a selective serotonin reuptake inhibitor (SSRI), has shown favorable effects in some children with autism. There are no previous studies evaluating the connection between clinical outcome and markers of clinical response to fluoxetine treatment. We examined serum brain derived neurotrophic factor (BDNF) concentrations and serotonin transporter (SERT) binding in the medial frontal cortex and midbrain, measured by single photon emission computed tomography (SPECT) scanning, in a group of 13 autistic children and adolescents (12 males, one female; age 5-16 years), who were treated for six months with fluoxetine at a dose range of 10-40 mg/day. Clinical response was evaluated by the Autism Treatment Evaluation Checklist (ATEC). Serum concentrations of BDNF and SERT binding were measured at baseline and two months after termination of fluoxetine treatment. At baseline, before starting fluoxetine treatment, the serum concentration of BDNF had a bimodal distribution in the autism group with either a low concentration (n = 8, mean 1497 pg/mL) or a high concentration (n = 5, mean 14062 pg/mL) with respect to controls (n = 15, mean 9652 pg/mL), and SERT binding was uniformly low in the autistic subjects in medial frontal cortex and midbrain. Fluoxetine treatment led to positive effects in several aspects of communication, socialization and cognitive awareness, with 6 out 13 subjects being particularly good responders. These six also had a significant decrease in BDNF (p = 0.03) and minimal change in SERT binding after therapy. The other 7 subjects showed a trend towards an increase in BDNF and SERT binding. Our results indicate that fluoxetine may improve core autistic symptoms, and that this clinical response is linked to a decrease in serum BDNF.

Brain derived neurotrophic factor (BDNF) and autism spectrum disorders (ASD) in childhood

BACKGROUND

Neurotrophic factors are essential regulators of neuronal maturation including synaptic synthesis. Among those, Brain derived neurotrophic factor (BDNF) has been in particular focus in the understanding of autism spectrum disorders (ASD).

PURPOSE

The aim of our study was to investigate whether BNDF could be used as diagnostic/biological marker for ASD. For this purpose we examined the plasma levels of BDNF and the precursors pro- BDNF in patients with ASD and compared it with non-autistic controls; determined whether there was a correlation between the BDNF and proBDNF levels and clinical severity. We also investigated the coding region of BDNF identify for well-variations which could be associated to ASD.

METHODS

The 65 ASD patients (51 boys) were enrolled from a recent completed epidemiological survey covering two counties (Oppland and Hedmark) in Norway. The mean age of the total number of children who participated in this study was 11,7 years. 30 non-autistic children were included as controls, 14 boys and 16 girls. The mean age was 11.3 years. Exclusion criteria for control group were individuals suffering from either neurological, endocrine, or immune insuffiency.

RESULTS AND CONCLUSIONS

Patients with ASD were characterized by moderately but significantly elevated plasma levels of BDNF compared to matched controls. No differences were observed in the proBDNF level between patients and controls. Within the ASD group, children with intellectual disability demonstrated increased BDNF, but not proBDNF levels, while the presence of ADHD had no impact on circulating proBDNF or BDNF. No further associations between plasma proBDNF or BDNF and other clinical demographics were observed.

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.

BDNF promoter I methylation correlates between post-mortem human peripheral and brain tissues

Several psychiatric disorders have been associated with CpG methylation changes in CG rich promoters of the brain-derived neurotrophic factor (BDNF) mainly by extracting DNA from peripheral blood cells. Whether changes in peripheral DNA methylation can be used as a proxy for brain-specific alterations remains an open question. In this study we aimed to compare DNA methylation levels in BDNF promoter regions in human blood cells, muscle and brain regions using bisulfite-pyrosequencing. We found a significant correlation between the levels of BDNF promoter I methylation measured in quadriceps and vPFC tissues extracted from the same individuals (n = 98, Pearson, r = 0.48, p = 4.5 × 10(-7)). In the hippocampus, BDNF promoter I and IV methylation levels were strongly correlated (Pearson, n = 37, r = 0.74, p = 1.4 × 10(-7)). We found evidence for sex-dependent effect on BDNF promoter methylation levels in the various tissues and blood samples. Taken together, these data indicate a strong intra-individual correlation between peripheral and brain tissue. They also suggest that sex determines methylation patterns in BDNF promoter region across different types of tissue, including muscle, brain, and blood.

Dendritic spine dysgenesis in Rett syndrome

Spines are small cytoplasmic extensions of dendrites that form the postsynaptic compartment of the majority of excitatory synapses in the mammalian brain. Alterations in the numerical density, size, and shape of dendritic spines have been correlated with neuronal dysfunction in several neurological and neurodevelopmental disorders associated with intellectual disability, including Rett syndrome (RTT). RTT is a progressive neurodevelopmental disorder associated with intellectual disability that is caused by loss of function mutations in the transcriptional regulator methyl CpG-binding protein 2 (MECP2). Here, we review the evidence demonstrating that principal neurons in RTT individuals and Mecp2-based experimental models exhibit alterations in the number and morphology of dendritic spines. We also discuss the exciting possibility that signaling pathways downstream of brain-derived neurotrophic factor (BDNF), which is transcriptionally regulated by MeCP2, offer promising therapeutic options for modulating dendritic spine development and plasticity in RTT and other MECP2-associated neurodevelopmental disorders.

The best-laid plans go oft awry: synaptogenic growth factor signaling in neuropsychiatric disease

Growth factors play important roles in synapse formation. Mouse models of neuropsychiatric diseases suggest that defects in synaptogenic growth factors, their receptors, and signaling pathways can lead to disordered neural development and various behavioral phenotypes, including anxiety, memory problems, and social deficits. Genetic association studies in humans have found evidence for similar relationships between growth factor signaling pathways and neuropsychiatric phenotypes. Accumulating data suggest that dysfunction in neuronal circuitry, caused by defects in growth factor-mediated synapse formation, contributes to the susceptibility to multiple neuropsychiatric diseases, including epilepsy, autism, and disorders of thought and mood (e.g., schizophrenia and bipolar disorder, respectively). In this review, we will focus on how specific synaptogenic growth factors and their downstream signaling pathways might be involved in the development of neuropsychiatric diseases.

A selective histone deacetylase-6 inhibitor improves BDNF trafficking in hippocampal neurons from Mecp2 knockout mice: implications for Rett syndrome

Rett syndrome (RTT) is a neurodevelopmental disorder caused by loss-of-function mutations in the transcriptional modulator methyl-CpG-binding protein 2 (MECP2). One of the most prominent gene targets of MeCP2 is brain-derived neurotrophic factor (Bdnf), a potent modulator of activity-dependent synaptic development, function and plasticity. Dysfunctional BDNF signaling has been demonstrated in several pathophysiological mechanisms of RTT disease progression. To evaluate whether the dynamics of BDNF trafficking is affected by Mecp2 deletion, we analyzed movements of BDNF tagged with yellow fluorescent protein (YFP) in cultured hippocampal neurons by time-lapse fluorescence imaging. We found that both anterograde and retrograde vesicular trafficking of BDNF-YFP are significantly impaired in Mecp2 knockout hippocampal neurons. Selective inhibitors of histone deacetylase 6 (HDAC6) show neuroprotective effects in neurodegenerative diseases and stimulate microtubule-dependent vesicular trafficking of BDNF-containing dense core vesicles. Here, we show that the selective HDAC6 inhibitor Tubastatin-A increased the velocity of BDNF-YFP vesicles in Mecp2 knockout neurons in both directions by increasing α–tubulin acetylation. Tubastatin-A also restored activity-dependent BDNF release from Mecp2 knockout neurons to levels comparable to those shown by wildtype neurons. These findings demonstrate that a selective HDAC6 inhibitor is a potential pharmacological strategy to reverse cellular and synaptic impairments in RTT resulting from impaired BDNF signaling.

Genetic diseases: congenital central hypoventilation, Rett, and Prader-Willi syndromes

The present review summarizes current knowledge on three rare genetic disorders of respiratory control, congenital central hypoventilation syndrome (CCHS), Rett syndrome (RTT), and Prader-Willi syndrome (PWS). CCHS is characterized by lack of ventilatory chemosensitivity caused by PHOX2B gene abnormalities consisting mainly of alanine expansions. RTT is associated with episodes of tachypneic and irregular breathing intermixed with breathholds and apneas and is caused by mutations in the X-linked MECP2 gene encoding methyl-CpG-binding protein. PWS manifests as sleep-disordered breathing with apneas and episodes of hypoventilation and is caused by the loss of a group of paternally inherited genes on chromosome 15. CCHS is the most specific disorder of respiratory control, whereas the breathing disorders in RTT and PWS are components of a more general developmental disorder. The main clinical features of these three disorders are reviewed with special emphasis on the associated brain abnormalities. In all three syndromes, disease-causing genetic defects have been identified, allowing the development of genetically engineered mouse models. New directions for future therapies based on these models or, in some cases, on clinical experience are delineated. Studies of CCHS, RTT, and PWS extend our knowledge of the molecular and cellular aspects of respiratory rhythm generation and suggest possible pharmacological approaches to respiratory control disorders. This knowledge is relevant for the clinical management of many respiratory disorders that are far more prevalent than the rare diseases discussed here.

Pubertal trajectory in females with Rett syndrome: a population-based study

BACKGROUND

Rett syndrome is a severe genetic neurodevelopmental disorder mainly affecting females. The aim of this study was to describe pubertal development in a population-based cohort of females with Rett syndrome.

METHODS

To assess pubertal trajectory we used six waves of data provided by parents of girls and women, recruited through the Australian population-based Rett Syndrome Database. The age at which adrenarche, thelarche or menarche occurred was used as the parameter for time to event (survival) analysis. The relationships between BMI, mutation type and the trajectories were investigated, using Cox proportional hazards.

RESULTS

One quarter of girls reached adrenarche by 9.6 years, half by 11 years and three quarters by 12.6 years. Half reached menarche by 14 years (range 8-23). Being underweight was associated with later age at adrenarche, thelarche and menarche, while higher BMI (overweight) was associated with earlier onset. In general, girls with C-terminal deletions and early truncating mutations reached pubertal stages earlier and those with the p.R168X mutation reached them later.

CONCLUSION

The pubertal course in Rett syndrome may be abnormal, sometimes with early adrenarche but delayed menarche. These features may be genotype dependent and may have varying relationships with growth and bone acquisition.

Rett syndrome and epilepsy: an update for child neurologists

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

BDNF deregulation in Rett syndrome

BDNF is the best-characterized neurotrophin in terms of its gene structure and modulation, secretion processing, and signaling cascades following its release. In addition to diverse features at the genetic and molecular levels, the abundant expression in several regions of the central nervous system has implicated BDNF as a potent modulator in many aspects of neuronal development, as well as synaptic transmission and plasticity. Impairments in any of these critical functions likely contribute to a wide array of neurodevelopmental, neurodegenerative, and neuropsychiatric diseases. In this review, we focus on a prevalent neurodevelopmental disorder, Rett syndrome (RTT), which afflicts 1:15,000 women world-wide. We describe the consequences of loss-of-function mutations in the gene encoding the transcription factor methyl-CpG binding protein 2 (MeCP2) in RTT, and then elaborate on the current understanding of how MeCP2 controls BDNF expression. Finally, we discuss the literature regarding alterations in BDNF levels in RTT individuals and MeCP2-based mouse models, as well as recent progress in searching for rational therapeutic interventions. This article is part of the Special Issue entitled 'BDNF Regulation of Synaptic Structure, Function, and Plasticity'.

Peripheral administration of brain-derived neurotrophic factor to Rett syndrome animal model: a possible approach for the treatment of Rett syndrome

Rett syndrome (RTT) is a postnatal, severe, disabling neurodevelopmental disorder occurring almost exclusively in females and is the second most common cause for genetic mental retardation in girls. In the majority of cases it is caused by mutations in gene (MECP2) encoding methyl-CpG-binding protein 2. Brain-derived neurotrophic factor (BDNF) is a neurotrophic factor playing a major role in neuronal survival, neurogenesis and plasticity. Animal studies suggested that abnormalities in BDNF homeostasis may contribute to the pathogenesis in Mecp2 null mice, and BDNF administration in the Mecp2 mutant brain led to later onset/slower disease progression, suggesting that increased BDNF in the brain could be therapeutic for this disease. Mature BDNF is a 14 kDa protein that may have poor blood-brain barrier penetrability. However, recent animal studies demonstrated that peripheral administration of BDNF, either by intravenous injection or intranasal delivery, could increase BDNF levels in the brain. Thus it is proposed that peripheral administration of BDNF in the early stage could have therapeutic potential for RTT subjects. Furthermore, the combination use of mannitol may temporarily open the blood-brain barrier and facilitate the entry of BDNF into brain. The potential therapeutic effect of peripheral BDNF administration could be tested in RTT animal models such as Mecp2 KO mice, which may provide a new intervention for this devastating disease.

The neurotrophins and their role in Alzheimer's disease

Besides being essential for correct development of the vertebrate nervous system the neurotrophins also play a vital role in adult neuron survival, maintenance and regeneration. In addition they are implicated in the pathogenesis of certain neurodegenerative diseases, and may even provide a therapeutic solution for some. In particular there have been a number of studies on the involvement of nerve growth factor (NGF) and brain derived neurotrophic factor (BDNF) in the development of Alzheimer’s disease. This disease is of growing concern as longevity increases worldwide, with little treatment available at the moment to alleviate the condition. Memory loss is one of the earliest symptoms associated with Alzheimer’s disease. The brain regions first affected by pathology include the hippocampus, and also the entorhinal cortex and basal cholinergic nuclei which project to the hippocampus; importantly, all these areas are required for memory formation. Both NGF and BDNF are affected early in the disease and this is thought to initiate a cascade of events which exacerbates pathology and leads to the symptoms of dementia. This review briefly describes the pathology, symptoms and molecular processes associated with Alzheimer’s disease; it discusses the involvement of the neurotrophins, particularly NGF and BDNF, and their receptors, with changes in BDNF considered particularly in the light of its importance in synaptic plasticity. In addition, the possibilities of neurotrophin-based therapeutics are evaluated.

Multiple approaches to investigate the transport and activity-dependent release of BDNF and their application in neurogenetic disorders

Studies utilizing genetic and pharmacological manipulations in rodent models and neuronal cultures have revealed myriad roles of brain-derived neurotrophic factor (BDNF). Currently, this knowledge of BDNF function is being translated into improvement strategies for several debilitating neurological disorders in which BDNF abnormalities play a prominent role. Common among the BDNF-related disorders are irregular trafficking and release of mature BDNF (mBDNF) and/or its prodomain predecessor, proBDNF. Thus, investigating the conditions required for proper trafficking and release of BDNF is an essential step toward understanding and potentially improving these neurological disorders. This paper will provide examples of disorders related to BDNF release and serve as a review of the techniques being used to study the trafficking and release of BDNF.

The phenotype associated with a large deletion on MECP2

Multiplex ligation-dependent Probe Amplification (MLPA) has become available for the detection of a large deletion on the MECP2 gene allowing genetic confirmation of previously unconfirmed cases of clinical Rett syndrome. This study describes the phenotype of those with a large deletion and compares with those with other pathogenic MECP2 mutations. Individuals were ascertained from the Australian Rett Syndrome and InterRett databases with data sourced from family and clinician questionnaires, and two case studies were constructed from the longitudinal Australian data. Regression and survival analysis were used to compare severity and age of onset of symptoms in those with and without a large deletion. Data were available for 974 individuals including 51 with a large deletion and ages ranged from 1 year 4 months to 49 years (median 9 years). Those with a large deletion were more severely affected than those with other mutation types. Specifically, individuals with large deletions were less likely to have learned to walk (OR 0.42, 95% CI: 0.22-0.79, P=0.007) and to be currently walking (OR 0.53, 95% CI: 0.26-1.10, P=0.089), and were at higher odds of being in the most severe category of gross motor function (OR 1.84, 95% CI: 0.98-3.48, P=0.057) and epilepsy (OR 2.72, 95% CI: 1.38-5.37, P=0.004). They also developed epilepsy, scoliosis, hand stereotypies and abnormal breathing patterns at an earlier age. We have described the disorder profile associated with a large deletion from the largest sample to date and have found that the phenotype is severe with motor skills particularly affected.

Predisposition to epilepsy in fragile X syndrome: does the Val66Met polymorphism in the BDNF gene play a role?

Epilepsy is detected in about 23% of patients with fragile X syndrome (FXS). Absence or reduced levels of the fragile X mental retardation protein (FMRP), a global regulator of translation in neurons and an important factor in synaptic plasticity, produce the observed epileptic patterns. The brain-derived neurotrophic factor (BDNF) gene is a specific regulator of synaptic plasticity, and disturbances in its function cause dendrite abnormalities similar to those observed in FXS. A putative reciprocal regulation of FMRP and BDNF has been hypothesized. The Val66Met polymorphism in the BDNF gene may be involved in the alteration of normal secretion of the mature peptide and may modulate the epileptic phenotype observed in some patients with FXS. We investigated the relationship of this Met66 allele to the prevalence of epilepsy in 77 patients with FXS. No association was observed between this polymorphism and epilepsy in our group of patients. Therefore, it should not be considered a biomarker for developing epilepsy in patients with FXS.

Val/Val genotype of brain-derived neurotrophic factor (BDNF) Val⁶⁶Met polymorphism is associated with a better response to OROS-MPH in Korean ADHD children

Research on psychostimulants, analysis of animal models and genetic association studies all suggest that the brain-derived neurotrophic factor gene (BDNF) may be a good candidate for pharmacogenetic studies of attention deficit hyperactivity disorder (ADHD). Yet to date there have been no pharmacogenetic studies of BDNF in ADHD. A total of 102 drug-naive ADHD children (8.7±2.1 yr) were treated with osmotic release oral system-methylphenidate (OROS-MPH) for 12 wk, and four kinds of response criteria were applied, based first, on a combined threshold of the ADHD Rating Scale - IV (ARS) and the Clinical Global Impression - Improvement scale (CGI-I); second, on scores of 1 or 2 vs. 3-7 on the CGI - Severity scale; third, on a >50% reduction in ARS scores; and fourth, on satisfaction of all of the aforementioned criteria. The Val⁶⁶Met polymorphism of BDNF and six single nucleotide polymorphisms from the SLC6A2, ADRA2A and NTF-3 genes were tested for association with each criterion. Relative to other genotypes, homozygosity for the Val allele of the BDNF Val⁶⁶Met polymorphism was associated with a greater relative frequency of good response under all four response criteria (after controlling for baseline ARS score, age, gender, final dose (mg/kg) of OROS-MPH at 12 wk, and level of academic functioning). This association was significant at the uncorrected level for the first and third response criteria (p=0.013 and p=0.018, respectively) and significant at a Bonferroni-corrected level for the second and fourth response criteria (p=0.0002, p=0.0003, respectively). Our findings support an association between homozygosity for the Val allele of BDNF and better response to OROS-MPH in Korean ADHD children as assessed by four different response criteria.

Change in gross motor abilities of girls and women with rett syndrome over a 3- to 4-year period

Rett syndrome is a rare but severe neurological disorder typically associated with a mutation in the MECP2 gene. We describe change in gross motor function over 3 to 4 years for 70 subjects participating in the Australian Rett Syndrome Database. Linear regression was used to assess relationships with age, genotype, and general and complex gross motor skills scores measured on the Gross Motor Scale for Rett syndrome. Skills were slightly better or maintained in approximately 40% of subjects and slightly decreased in approximately 60%. Teenagers and women who walked in 2004 were less likely to lose complex skills than those younger. Girls with a p.R294X mutation were more likely to lose complex motor skills, otherwise skill changes were spread across the mutation categories. In conclusion, small changes were observed over this period with greater stability of skills in teenagers and women with the ability to walk.

Modulation of dendritic spine development and plasticity by BDNF and vesicular trafficking: fundamental roles in neurodevelopmental disorders associated with mental retardation and autism

The process of axonal and dendritic development establishes the synaptic circuitry of the central nervous system (CNS) and is the result of interactions between intrinsic molecular factors and the external environment. One growth factor that has a compelling function in neuronal development is the neurotrophin brain-derived neurotrophic factor (BDNF). BDNF participates in axonal and dendritic differentiation during embryonic stages of neuronal development, as well as in the formation and maturation of dendritic spines during postnatal development. Recent studies have also implicated vesicular trafficking of BDNF via secretory vesicles, and both secretory and endosomal trafficking of vesicles containing synaptic proteins, such as neurotransmitter and neurotrophin receptors, in the regulation of axonal and dendritic differentiation, and in dendritic spine morphogenesis. Several genes that are either mutated or deregulated in neurodevelopmental disorders associated with mental retardation have now been identified, and several mouse models of these disorders have been generated and characterized. Interestingly, abnormalities in dendritic and synaptic structure are consistently observed in human neurodevelopmental disorders associated with mental retardation, and in mouse models of these disorders as well. Abnormalities in dendritic and synaptic differentiation are thought to underlie altered synaptic function and network connectivity, thus contributing to the clinical outcome. Here, we review the roles of BDNF and vesicular trafficking in axonal and dendritic differentiation in the context of dendritic and axonal morphological impairments commonly observed in neurodevelopmental disorders associated with mental retardation.

Investigation of modifier genes within copy number variations in Rett syndrome

MECP2 mutations are responsible for two different phenotypes in females, classical Rett syndrome and the milder Zappella variant (Z-RTT). We investigated whether Copy Number Variants (CNVs) may modulate the phenotype by comparison of array-CGH data from two discordant pairs of sisters and four additional discordant pairs of unrelated girls matched by mutation type. We also searched for potential MeCP2 targets within CNVs by ChIP-chip analysis. We did not identify one major common gene/region, suggesting that modifiers may be complex and variable between cases. However, we detected CNVs correlating with disease severity that contain candidate modifiers. CROCC (1p36.13) is a potential MeCP2 target in which a duplication in a Z-RTT and a deletion in a classic patient were observed. CROCC encodes a structural component of ciliary motility that is required for correct brain development. CFHR1 and CFHR3, on 1q31.3, may be involved in the regulation of complement during synapse elimination and were found to be deleted in a Z-RTT but duplicated in two classic patients. The duplication of 10q11.22, present in two Z-RTT patients, includes GPRIN2, a regulator of neurite outgrowth and PPYR1, involved in energy homeostasis. Functional analyses are necessary to confirm candidates and to define targets for future therapies.

Longitudinal hand function in Rett syndrome

Loss of hand function is a core feature of Rett syndrome. This article describes longitudinal hand function at 3 time points for 72 subjects participating in the Australian Rett Syndrome Database. Approximately 40% of subjects with some grasping abilities lost skill over the 3- to 4-year period between video assessments. In these subjects, a decrease in hand function was seen less frequently in girls 13 to 19 years old than in those younger than 8 years, in subjects with some mobility compared with those who were wheelchair bound, and in those who had previously been able to finger feed. Relationships with the magnitude of change reflected these findings. Change in hand function did not vary with clinical severity. The results for all subjects were similar to results obtained when analysis was restricted to those with a pathogenic mutation. Variability in the longitudinal course of hand function in Rett syndrome was observed.

Epilepsy in Rett syndrome: clinical and genetic features

Epilepsy often occurs in Rett syndrome and is considered a major problem. The aim of this study was to define the clinical features of epilepsy and the correlation between seizures and both genotype and clinical phenotype in the Rett population. One hundred sixty-five patients with Rett syndrome referred to four Italian centers were recruited. All patients underwent video/EEG monitoring and molecular analysis of the MECP2 gene or, in negative cases, of the CDKL5 and FOXG1 genes. The frequency of epilepsy was 79%. Drug-resistant epilepsy occurred in 30% of all our patients with Rett syndrome and in 38% of those with epilepsy. Our findings demonstrate that epilepsy differs among the various phenotypes and genotypes with respect to age at onset, drug responsiveness, and seizure semiology. The Hanefeld and preserved speech variants represent the extremes of the range of severity of epilepsy: the preserved speech variant is characterized by the mildest epileptic phenotype as epilepsy is much less frequent, starts later, and is less drug resistant than what is observed in the other phenotypes. Another important finding is that seizure onset before 1 year of age and daily frequency are risk factors for drug resistance. Thus, this study should help clinicians provide better clinical counseling to the families of patients with Rett syndrome.