Magnetic resonance spectroscopy and analysis of MECP2 in Rett syndrome

White Matter Structural and Network Topological Changes Underlying the Behavioral Phenotype of MECP2 Mutant Monkeys

To explore the brain structural basis underlying the behavioral abnormalities associated with Rett syndrome (RTT), we carried out detailed longitudinal noninvasive magnetic resonance imaging analyses of RTT monkey models created by gene-editing, from weaning, through adolescence, till sexual maturation. Here, we report abnormal developmental dynamics of brain white matter (WM) microstructures and network topological organizations via diffusion tensor imaging. Specifically, disrupted WM microstructural integrity was observed at 9 months, but recovered thereafter, whereas WM network topological properties showed persistent abnormal dynamics from 9 to 37 months. Changes in the WM microstructure and WM network topology were correlated well with RTT-associated behavioral abnormalities including sleep latency, environmental exploration, and conflict encounters. Deleterious and protracted early WM myelination process likely lead to abnormal synaptic pruning, resulting in poor functional segregations. Together, this study provides initial evidence for changes in WM microstructure and network topological organization, which may underlie the neuro-patho-etilogy of RTT.

Transcriptome data of temporal and cingulate cortex in the Rett syndrome brain

Rett syndrome is an X-linked neurodevelopmental disorder caused by mutation in the methyl-CpG-binding protein 2 gene (MECP2) in the majority of cases. We describe an RNA sequencing dataset of postmortem brain tissue samples from four females clinically diagnosed with Rett syndrome and four age-matched female donors. The dataset contains 16 transcriptomes, including two brain regions, temporal and cingulate cortex, for each individual. We compared our dataset with published transcriptomic analyses of postmortem brain tissue from Rett syndrome and found consistent gene expression alterations among regions of the cerebral cortex. Our data provide a valuable resource to explore the biology of the human brain in Rett syndrome.

Choline Rescues Behavioural Deficits in a Mouse Model of Rett Syndrome by Modulating Neuronal Plasticity

Rett syndrome (RTT) is a postnatal neurodevelopmental disorder that primarily affects girls, with 95% of RTT cases resulting from mutations in the methyl-CpG-binding protein 2 (MECP2) gene. Choline, a dietary micronutrient found in most foods, has been shown to be important for brain development and function. However, the exact effects and mechanisms are still unknown. We found that 13 mg/day (1.7 × required daily intake) of postnatal choline treatment to Mecp2-conditional knockout mice rescued not only deficits in motor coordination, but also their anxiety-like behaviour and reduced social preference. Cortical neurons in the brains of Mecp2-conditional knockout mice supplemented with choline showed enhanced neuronal morphology and increased density of dendritic spines. Modelling RTT in vitro by knocking down the expression of the MeCP2 protein with shRNA, we found that choline supplementation to MeCP2-knockdown neurons increased their soma sizes and the complexity of their dendritic arbors. Rescue of the morphological defects could lead to enhanced neurotransmission, as suggested by an observed trend of increased expression of synaptic proteins and restored miniature excitatory postsynaptic current frequency in choline-supplemented MeCP2-knockdown neurons. Through the use of specific inhibitors targeting each of the known physiological pathways of choline, synthesis of phosphatidylcholine from choline was found to be essential in bringing about the changes seen in the choline-supplemented MeCP2-knockdown neurons. Taken together, these data reveal a role of choline in modulating neuronal plasticity, possibly leading to behavioural changes, and hence, a potential for using choline to treat RTT.

MeCP2 Deficiency in Neuroglia: New Progress in the Pathogenesis of Rett Syndrome

Rett syndrome (RTT) is an X-linked neurodevelopmental disease predominantly caused by mutations of the methyl-CpG-binding protein 2 (MeCP2) gene. Generally, RTT has been attributed to neuron-centric dysfunction. However, increasing evidence has shown that glial abnormalities are also involved in the pathogenesis of RTT. Mice that are MeCP2-null specifically in glial cells showed similar behavioral and/or neuronal abnormalities as those found in MeCP2-null mice, a mouse model of RTT. MeCP2 deficiency in astrocytes impacts the expression of glial intermediate filament proteins such as fibrillary acidic protein (GFAP) and S100 and induces neuron toxicity by disturbing glutamate metabolism or enhancing microtubule instability. MeCP2 deficiency in oligodendrocytes (OLs) results in down-regulation of myelin gene expression and impacts myelination. While MeCP2-deficient microglia cells fail in response to environmental stimuli, release excessive glutamate, and aggravate impairment of the neuronal circuit. In this review, we mainly focus on the progress in determining the role of MeCP2 in glial cells involved in RTT, which may provide further insight into a therapeutic intervention for RTT.

In Vivo NMR Studies of the Brain with Hereditary or Acquired Metabolic Disorders

Metabolic disorders, whether hereditary or acquired, affect the brain, and abnormalities of the brain are related to cellular integrity; particularly in regard to neurons and astrocytes as well as interactions between them. Metabolic disturbances lead to alterations in cellular function as well as microscopic and macroscopic structural changes in the brain with diabetes, the most typical example of metabolic disorders, and a number of hereditary metabolic disorders. Alternatively, cellular dysfunction and degeneration of the brain lead to metabolic disturbances in hereditary neurological disorders with neurodegeneration. Nuclear magnetic resonance (NMR) techniques allow us to assess a range of pathophysiological changes of the brain in vivo. For example, magnetic resonance spectroscopy detects alterations in brain metabolism and energetics. Physiological magnetic resonance imaging (MRI) detects accompanying changes in cerebral blood flow related to neurovascular coupling. Diffusion and T1/T2-weighted MRI detect microscopic and macroscopic changes of the brain structure. This review summarizes current NMR findings of functional, physiological and biochemical alterations within a number of hereditary and acquired metabolic disorders in both animal models and humans. The global view of the impact of these metabolic disorders on the brain may be useful in identifying the unique and/or general patterns of abnormalities in the living brain related to the pathophysiology of the diseases, and identifying future fields of inquiry.

Review of evolution of clinical, training and educational services and research program for autism spectrum disorders in Hong Kong

The evolution of a local fragmented model of services for children with autism in Hong Kong emerged gradually over the past three decades with lack of government funding or support. This had been due to increasing number of children with autism being detected and referred for earlier assessment. With increasing pressure from parents due to long waiting time for assessment and training services and the increasing polarization by mass media there had been a gradual increasing public awareness over the past five years. Though still highly fragmented in the availability of services, there is a growing "business model" available in the community due to increasing need and lack of public funding for support. There is a lack of strategic planning for medical diagnostic and management issues in Hong Kong. Our University of Hong Kong based Autism Research Program was pioneered in 1985 based on the increasing load of autism cases referred for assessment for other developmental problems and diagnosed as Autism in the Duchess of Kent Children's Hospital. As the first author has been the staff of the University of Hong Kong, this program flourished as a research based program. The benefits of early identification and intervention of autism spectrum disorder (ASD) had been increasingly recognized, and with the increased public awareness and increasing trend of earlier diagnosis, there has been a continuously high demand from parents for earlier assessment and training for children suspected to have ASD. This model had not received extra funding for this integrated program for research, teaching and training in autism. We had to apply for various donations and grants to support the development of this pioneer program. The research output and organization of forums for public education and awareness are reviewed. The latter part of the paper reports the summary of clinical profile of autism cases (N=1441) assessed from 1985 to 2010 June under the University of Hong Kong. As the waiting time for initial developmental assessment for any children in Hong Kong is 12-24 months, we also report our preliminary experience with a newly launched triaging service provision for children suspected to be ASD since 2009, including multi-disciplinary assessment and parallel interim training in our university affiliated child assessment centre in Hong (N=89).

One-carbon metabolism in neurodevelopmental disorders: using broad-based nutraceutics to treat cognitive deficits in complex spectrum disorders

Folate and choline, two nutrients involved in the one-carbon metabolic cycle, are intimately involved in regulating DNA integrity, synthesis, biogenic amine synthesis, and methylation. In this review, we discuss evidence that folate and choline play an important role in normal cognitive development, and that altered levels of these nutrients during periods of high neuronal proliferation and synaptogenesis can result in diminished cognitive function. We also discuss the use of these nutrients as therapeutic agents in a spectrum of developmental disorders in which intellectual disability is a prominent feature, such as in Fragile-X, Rett syndrome, Down syndrome, and Autism spectrum disorders. A survey of recent literature suggests that nutritional supplements have mild, but generally consistent, effects on improving cognition. Intervening with supplements earlier rather than later during development is more effective in improving cognitive outcomes. Given the mild improvements seen after treatments using nutrients alone, and the importance of the genetic profile of parents and offspring, we suggest that using nutraceutics early in development and in combination with other therapeutics are likely to have positive impacts on cognitive outcomes in a broad spectrum of complex neurodevelopmental disorders.

Altered carbon dioxide metabolism and creatine abnormalities in rett syndrome

Despite their good appetite, many females with Rett syndrome (RTT) meet the criteria for moderate to severe malnutrition. Although feeding difficulties may play a part in this, other constitutional factors such as altered metabolic processes are suspected. Irregular breathing is a common clinical feature, leading to chronic respiratory alkalosis or acidosis. We assumed that these changes in intracellular pH cause disturbances in the metabolic equilibrium, with important nutritional consequences. The study population consisted of a group of thirteen well-defined RTT girls with extended clinical, molecular and neurophysiological assessments. Despite normal levels of total dietary energy and protein intakes, malnutrition was confirmed based on significantly low fat-free mass index (FFMI) values. Biochemical screening of multiple metabolic pathways showed significantly elevated plasma creatine concentrations and increased urinary creatine/creatinine ratio in five RTT girls. Four girls, 10 years and older, were forceful breathers, one 13-year-old girl had an undetermined cardiorespiratory phenotype. An isolated increase of the urinary creatine/creatinine ratio was seen in two girls, a 9-year old forceful and a 4-year old feeble breather. Given that the young girls are feeble breathers and the older girls are forceful breathers, it is impossible to determine whether the elevated creatine concentrations are due to increasing age or cardiorespiratory phenotype. Furthermore, MeCP2 deficiency may cause epigenetic aberrations affecting the expression of the creatine-transporter gene, which is located at Xq28. Further studies are required to confirm these findings and to provide greater insight into the pathogenesis of the abnormal creatine metabolism in RTT.

Brain metabolism in Rett syndrome: age, clinical, and genotype correlations

OBJECTIVE

Brain metabolism, as studied by magnetic resonance spectroscopy (MRS), has been previously shown to be abnormal in Rett syndrome (RTT). This study reports the relation of MRS findings to age, disease severity, and genotype.

METHODS

Forty RTT girls (1-14 years old) and 12 age-matched control subjects were examined. Single-voxel proton MRS of left frontal white matter was performed.

RESULTS

NAA/Cr ratios decreased and myoinositol/Cr ratios increased with age in RTT patients (both p < 0.03), whereas these ratios were stable in control. The mean glutamate and glutamine/Cr ratio was 36% greater in RTT patients than in control (p = 0.043). The mean NAA/Cr ratio was 12.6% lower in RTT patients with seizures compared with those without seizures (p = 0.017). NAA/Cr ratios decreased with increasing clinical severity score (p = 0.031). Compared with patients with T158X, R255X, and R294X mutations, and C-terminal deletions, patients with the R168X mutation tended to have the greatest severity score (0.01 < or = p < or = 0.11) and the lowest NAA/Cr ratio (0.029 < or = p < 0.14).

INTERPRETATION

Decreasing NAA/Cr and increasing myoinositol/Cr with age are suggestive of progressive axonal damage and astrocytosis in RTT, respectively, whereas increased glutamate and glutamine/Cr ratio may be secondary to increasing glutamate/glutamine cycling at the synaptic level. The relations between NAA/Cr, presence or absence of seizures, and disease severity suggest that MRS provides a noninvasive measure of cerebral involvement in RTT.

Neurochemical changes in a mouse model of Rett syndrome: changes over time and in response to perinatal choline nutritional supplementation

Rett syndrome (RTT), the second leading cause of mental retardation in girls, is caused by mutations in the X-linked gene for methyl-CpG-binding protein 2 (MeCP2), a transcriptional repressor. In addition to well-documented neuroanatomical and behavioral deficits, RTT is characterized by reduced markers of cholinergic activity and general neuronal health. Previously, we have shown that early postnatal choline (Cho) supplementation improves behavioral and neuroanatomical symptoms in a mouse model of RTT (Mecp2(1lox) mice). In this study, we use NMR spectroscopy to quantify the relative amounts of Cho, Glutamate (Glu), Glutamine (Gln), and N-acetyl aspartate (NAA) in the brains of wild type and mutant mice at 21, 35, and 42 days of age and in mice receiving postnatal Cho supplementation. We find that the mutant mice have reduced levels of Cho, Glu, and NAA, but elevated Gln levels, compared with their wild type littermates. These differences emerge at different developmental ages. Cho supplementation increases NAA levels, a marker of neuronal integrity, but has no effect on Cho, Glu, or Gln. These data suggest that postnatal nutritional supplementation may improve neuronal function and could serve as a therapeutic agent for human RTT patients.

Nutritional factors in a mouse model of Rett syndrome

Environmental factors such as nutrition and housing can influence behavioral and anatomical characteristics of several neurological disorders, including Rett syndrome (RTT). RTT is associated with mutations in the X-linked gene encoding MeCP2, a transcriptional repressor that binds methylated DNA. While direct genetic intervention in humans is impossible at this time, motor and cognitive deficits in RTT may be ameliorated through manipulations of epigenetic/environmental factors. For example, studies in rodents suggest that choline nutrient supplementation during critical periods of brain development enhances cholinergic neurotransmission, alters neuronal size and distribution, and facilitates performance of memory and motoric tasks. Recent work in a mouse model of RTT shows that enhancing maternal nutrition through choline supplementation improves both anatomical and behavioral symptoms in the mutant offspring. We describe here cellular and molecular mechanisms that may underlie this specific enhancement and may provide more general insights into mechanisms underlying gene-environment interactions in neurological disorders.

Imaging of neurogenetic and neurometabolic disorders of childhood

Magnetic resonance imaging (MRI) has emerged as a powerful tool in the study of normal and abnormal brain structure, function, and biochemistry. In particular, functional MRI has come into its own as a tool to study normal and abnormal brain functions such as learning, memory, and motor learning, as well as delineation of neurogenetic cognitive phenotypes. White matter microstructure can be studied using diffusion tensor imaging, which may allow abnormal white matter to be visualized prior to abnormalities on anatomic MRI. Magnetic resonance spectroscopy, a noninvasive method to study brain biochemistry, may allow for the delineation of regional metabolic changes as a result of disease progression and/or therapeutic intervention. With MRI techniques, one can investigate the relationship between structure, function, genes, and behavior. This report discusses the research applications of MRI to the study of neurogenetic disorders of childhood.