Abnormal carbohydrate metabolism in cerebrospinal fluid in Rett syndrome

Systemic proteome phenotypes reveal defective metabolic flexibility in Mecp2 mutants

Genes mutated in monogenic neurodevelopmental disorders are broadly expressed. This observation supports the concept that monogenic neurodevelopmental disorders are systemic diseases that profoundly impact neurodevelopment. We tested the systemic disease model focusing on Rett syndrome, which is caused by mutations in MECP2. Transcriptomes and proteomes of organs and brain regions from Mecp2-null mice as well as diverse MECP2-null male and female human cells were assessed. Widespread changes in the steady-state transcriptome and proteome were identified in brain regions and organs of presymptomatic Mecp2-null male mice as well as mutant human cell lines. The extent of these transcriptome and proteome modifications was similar in cortex, liver, kidney, and skeletal muscle and more pronounced than in the hippocampus and striatum. In particular, Mecp2- and MECP2-sensitive proteomes were enriched in synaptic and metabolic annotated gene products, the latter encompassing lipid metabolism and mitochondrial pathways. MECP2 mutations altered pyruvate-dependent mitochondrial respiration while maintaining the capacity to use glutamine as a mitochondrial carbon source. We conclude that mutations in Mecp2/MECP2 perturb lipid and mitochondrial metabolism systemically limiting cellular flexibility to utilize mitochondrial fuels.

Systemic Proteome Phenotypes Reveal Defective Metabolic Flexibility in Mecp2 Mutants

Genes mutated in monogenic neurodevelopmental disorders are broadly expressed. This observation supports the concept that monogenic neurodevelopmental disorders are systemic diseases that profoundly impact neurodevelopment. We tested the systemic disease model focusing on Rett syndrome, which is caused by mutations in MECP2. Transcriptomes and proteomes of organs and brain regions from Mecp2-null mice as well as diverse MECP2-null male and female human cells were assessed. Widespread changes in the steady-state transcriptome and proteome were identified in brain regions and organs of presymptomatic Mecp2-null male mice as well as mutant human cell lines. The extent of these transcriptome and proteome modifications was similar in cortex, liver, kidney, and skeletal muscle and more pronounced than in the hippocampus and striatum. In particular, Mecp2- and MECP2-sensitive proteomes were enriched in synaptic and metabolic annotated gene products, the latter encompassing lipid metabolism and mitochondrial pathways. MECP2 mutations altered pyruvate-dependent mitochondrial respiration while maintaining the capacity to use glutamine as a mitochondrial carbon source. We conclude that mutations in Mecp2/MECP2 perturb lipid and mitochondrial metabolism systemically limiting cellular flexibility to utilize mitochondrial fuels.

MeCP2 Is an Epigenetic Factor That Links DNA Methylation with Brain Metabolism

DNA methylation, one of the most well-studied epigenetic modifications, is involved in a wide spectrum of biological processes. Epigenetic mechanisms control cellular morphology and function. Such regulatory mechanisms involve histone modifications, chromatin remodeling, DNA methylation, non-coding regulatory RNA molecules, and RNA modifications. One of the most well-studied epigenetic modifications is DNA methylation that plays key roles in development, health, and disease. Our brain is probably the most complex part of our body, with a high level of DNA methylation. A key protein that binds to different types of methylated DNA in the brain is the methyl-CpG binding protein 2 (MeCP2). MeCP2 acts in a dose-dependent manner and its abnormally high or low expression level, deregulation, and/or genetic mutations lead to neurodevelopmental disorders and aberrant brain function. Recently, some of MeCP2-associated neurodevelopmental disorders have emerged as neurometabolic disorders, suggesting a role for MeCP2 in brain metabolism. Of note, MECP2 loss-of-function mutation in Rett Syndrome is reported to cause impairment of glucose and cholesterol metabolism in human patients and/or mouse models of disease. The purpose of this review is to outline the metabolic abnormalities in MeCP2-associated neurodevelopmental disorders that currently have no available cure. We aim to provide an updated overview into the role of metabolic defects associated with MeCP2-mediated cellular function for consideration of future therapeutic strategies.

Convergent cerebrospinal fluid proteomes and metabolic ontologies in humans and animal models of Rett syndrome

MECP2 loss-of-function mutations cause Rett syndrome, a neurodevelopmental disorder resulting from a disrupted brain transcriptome. How these transcriptional defects are decoded into a disease proteome remains unknown. We studied the proteome of Rett cerebrospinal fluid (CSF) to identify consensus Rett proteome and ontologies shared across three species. Rett CSF proteomes enriched proteins annotated to HDL lipoproteins, complement, mitochondria, citrate/pyruvate metabolism, synapse compartments, and the neurosecretory protein VGF. We used shared Rett ontologies to select analytes for orthogonal quantification and functional validation. VGF and ontologically selected CSF proteins had genotypic discriminatory capacity as determined by receiver operating characteristic analysis in Mecp2 ^-/y and Mecp2 ^-/+ . Differentially expressed CSF proteins distinguished Rett from a related neurodevelopmental disorder, CDKL5 deficiency disorder. We propose that Mecp2 mutant CSF proteomes and ontologies inform putative mechanisms and biomarkers of disease. We suggest that Rett syndrome results from synapse and metabolism dysfunction.

Metabolomic Fingerprint of Mecp2-Deficient Mouse Cortex: Evidence for a Pronounced Multi-Facetted Metabolic Component in Rett Syndrome

Using unsupervised metabolomics, we defined the complex metabolic conditions in the cortex of a mouse model of Rett syndrome (RTT). RTT, which represents a cause of mental and cognitive disabilities in females, results in profound cognitive impairment with autistic features, motor disabilities, seizures, gastrointestinal problems, and cardiorespiratory irregularities. Typical RTT originates from mutations in the X-chromosomal methyl-CpG-binding-protein-2 (Mecp2) gene, which encodes a transcriptional modulator. It then causes a deregulation of several target genes and metabolic alterations in the nervous system and peripheral organs. We identified 101 significantly deregulated metabolites in the Mecp2-deficient cortex of adult male mice; 68 were increased and 33 were decreased compared to wildtypes. Pathway analysis identified 31 mostly upregulated metabolic pathways, in particular carbohydrate and amino acid metabolism, key metabolic mitochondrial/extramitochondrial pathways, and lipid metabolism. In contrast, neurotransmitter-signaling is dampened. This metabolic fingerprint of the Mecp2-deficient cortex of severely symptomatic mice provides further mechanistic insights into the complex RTT pathogenesis. The deregulated pathways that were identified—in particular the markedly affected amino acid and carbohydrate metabolism—confirm a complex and multifaceted metabolic component in RTT, which in turn signifies putative therapeutic targets. Furthermore, the deregulated key metabolites provide a choice of potential biomarkers for a more detailed rating of disease severity and disease progression.

Brain protein changes in Mecp2 mouse mutant models: Effects on disease progression of Mecp2 brain specific gene reactivation

Rett syndrome (RTT) is a leading cause of severe intellectual disability in females, caused by de novo loss-of function mutations in the X-linked methyl-CpG binding protein 2 (MECP2). To better investigate RTT disease progression/pathogenesis animal models of Mecp2 deficiency have been developed. Here, Mecp2 mouse models are employed to investigate the role of protein patterns in RTT. A proteome analysis was carried out in brain tissue from i) Mecp2 deficient mice at the pre-symptomatic and symptomatic stages and, ii) mice in which the disease phenotype was reversed by Mecp2 reactivation. Several proteins were shown to be differentially expressed in the pre-symptomatic (n = 18) and symptomatic (n = 20) mice. Mecp2 brain reactivated mice showed wild-type comparable levels of expression for twelve proteins, mainly related to proteostasis (n = 4) and energy metabolic pathways (n = 4). The remaining ones were found to be involved in redox homeostasis (n = 2), nitric oxide regulation (n = 1), neurodevelopment (n = 1). Ten out of twelve proteins were newly linked to Mecp2 deficiency. Our study sheds light on the relevance of the protein-regulation of main physiological process in the complex mechanisms leading from Mecp2 mutation to the RTT clinical phenotype. SIGNIFICANCE: We performed a proteomic study of a Mecp2^stop/y mouse model for Rett syndrome (RTT) at the pre-symptomatic and symptomatic Mecp2 deficient mice stage and for the brain specific reactivated Mecp2 model. Our results reveal major protein expression changes pointing out to defects in proteostasis or energy metabolic pathways other than, to a lesser extent, in redox homeostasis, nitric oxide regulation or neurodevelopment. The Mecp2 mouse rescued model provides the possibility to select target proteins more susceptible to the Mecp2 gene mutation, potential and promising therapeutical targets.

Loss of Mevalonate/Cholesterol Homeostasis in the Brain: A Focus on Autism Spectrum Disorder and Rett Syndrome

The mevalonate (MVA)/cholesterol pathway is crucial for central nervous system (CNS) development and function and consequently, any dysfunction of this fundamental metabolic pathway is likely to provoke pathologic changes in the brain. Mutations in genes directly involved in MVA/cholesterol metabolism cause a range of diseases, many of which present neurologic and psychiatric symptoms. This raises the question whether other diseases presenting similar symptoms are related albeit indirectly to the MVA/cholesterol pathway. Here, we summarized the current literature suggesting links between MVA/cholesterol dysregulation and specific diseases, namely autism spectrum disorder and Rett syndrome.

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.

Increased Mitochondrial Mass and Cytosolic Redox Imbalance in Hippocampal Astrocytes of a Mouse Model of Rett Syndrome: Subcellular Changes Revealed by Ratiometric Imaging of JC-1 and roGFP1 Fluorescence

Rett syndrome (RTT) is a neurodevelopmental disorder with mutations in the MECP2 gene. Mostly girls are affected, and an apparently normal development is followed by cognitive impairment, motor dysfunction, epilepsy, and irregular breathing. Various indications suggest mitochondrial dysfunction. In Rett mice, brain ATP levels are reduced, mitochondria are leaking protons, and respiratory complexes are dysregulated. Furthermore, we found in MeCP2-deficient mouse (Mecp2^−/y) hippocampus an intensified mitochondrial metabolism and ROS generation. We now used emission ratiometric 2-photon imaging to assess mitochondrial morphology, mass, and membrane potential (ΔΨm) in Mecp2^−/y hippocampal astrocytes. Cultured astrocytes were labeled with the ΔΨm marker JC-1, and semiautomated analyses yielded the number of mitochondria per cell, their morphology, and ΔΨm. Mecp2^−/y astrocytes contained more mitochondria than wild-type (WT) cells and were more oxidized. Mitochondrial size, ΔΨm, and vulnerability to pharmacological challenge did not differ. The antioxidant Trolox opposed the oxidative burden and decreased the mitochondrial mass, thereby dampening the differences among WT and Mecp2^−/y astrocytes; mitochondrial size and ΔΨm were not markedly affected. In conclusion, mitochondrial alterations and redox imbalance in RTT also involve astrocytes. Mitochondria are more numerous in Mecp2^−/y than in WT astrocytes. As this genotypic difference is abolished by Trolox, it seems linked to the oxidative stress in RTT.

MeCP2 co-ordinates liver lipid metabolism with the NCoR1/HDAC3 corepressor complex

Rett syndrome (RTT; OMIM 312750), a progressive neurological disorder, is caused by mutations in methyl-CpG-binding protein 2 (MECP2; OMIM 300005), a ubiquitously expressed factor. A genetic suppressor screen designed to identify therapeutic targets surprisingly revealed that downregulation of the cholesterol biosynthesis pathway improves neurological phenotypes in Mecp2 mutant mice. Here, we show that MeCP2 plays a direct role in regulating lipid metabolism. Mecp2 deletion in mice results in a host of severe metabolic defects caused by lipid accumulation, including insulin resistance, fatty liver, perturbed energy utilization, and adipose inflammation by macrophage infiltration. We show that MeCP2 regulates lipid homeostasis by anchoring the repressor complex containing NCoR1 and HDAC3 to its lipogenesis targets in hepatocytes. Consistently, we find that liver targeted deletion of Mecp2 causes fatty liver disease and dyslipidemia similar to HDAC3 liver-specific deletion. These findings position MeCP2 as a novel component in metabolic homeostasis. Rett syndrome patients also show signs of peripheral dyslipidemia; thus, together these data suggest that RTT should be classified as a neurological disorder with systemic metabolic components. We previously showed that treatment of Mecp2 mice with statin drugs alleviated motor symptoms and improved health and longevity. Lipid metabolism is a highly treatable target; therefore, our results shed light on new metabolic pathways for treatment of Rett syndrome.

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.

Impaired CO2 sensitivity of astrocytes in a mouse model of Rett syndrome

Rett syndrome, a prototypical neurological disorder caused by loss of function of the transcriptional regulator methyl-CpG-binding protein 2 (MeCP2) gene, is associated with a severely disordered breathing pattern and reduced ventilatory CO2 sensitivity. In a mouse model of Rett syndrome (MeCP2 knockout), re-introduction of the MeCP2 gene selectively in astrocytes rescues normal respiratory phenotype. In the present study we determined whether the metabolic and/or signalling functions of astrocytes are affected by testing the hypotheses that in conditions of MeCP2 deficiency, medullary astrocytes are unable to produce/release appropriate amounts of lactate or detect changes in PCO2/[H(+) ], or both. No differences in tonic or hypoxia-induced release of lactate from the ventral surface of the medulla oblongata or cerebral cortex in brain slices of MeCP2-knockout and wild-type mice were found. In brainstem slices of wild-type mice, respiratory acidosis triggered robust elevations in [Ca(2+) ]i in astrocytes residing near the ventral surface of the medulla oblongata. The magnitude of CO2 -induced [Ca(2+) ]i responses in medullary astrocytes was markedly reduced in conditions of MeCP2 deficiency, whereas [Ca(2+) ]i responses to ATP were unaffected. These data suggest that (i) metabolic function of astrocytes in releasing lactate into the extracellular space is not affected by MeCP2 deficiency, and (ii) MeCP2 deficiency impairs the ability of medullary astrocytes to sense changes in PCO2/[H(+) ]. Taken together with the evidence of severely blunted ventilatory sensitivity to CO2 in mice with conditional MeCP2 deletion in astroglia, these data support the hypothesis of an important role played by astrocytes in central respiratory CO2 /pH chemosensitivity.

Aberrant redox homoeostasis and mitochondrial dysfunction in Rett syndrome

RTT (Rett syndrome) is a severe progressive neurodevelopmental disorder with a monogenetic cause, but complex and multifaceted clinical appearance. Compelling evidence suggests that mitochondrial alterations and aberrant redox homoeostasis result in oxidative challenge. Yet, compared with other severe neuropathologies, RTT is not associated with marked neurodegeneration, but rather a chemical imbalance and miscommunication of neuronal elements. Different pharmacotherapies mediate partial improvement of conditions in RTT, and also antioxidants or compounds improving mitochondrial function may be of potential merit. In the present paper, we summarize findings from patients and transgenic mice that point towards the nature of RTT as a mitochondrial disease. Also, open questions are addressed that require clarification to fully understand and successfully target the associated cellular redox imbalance.

Metabolic differences in hippocampal 'Rett' neurons revealed by ATP imaging

Understanding metabolic control of neuronal function requires detailed knowledge of ATP handling in living neurons. We imaged ATP in organotypic hippocampal slices using genetically encoded sensor Ateam 1.03 modified to selectively transduce neurons in the tissue. ATP imaging indicated distinct differences in ATP production and consumption in dentate gyrus and cornu ammonis (CA) areas. Removal of extracellular Mg(2+) from the bath evoked epileptiform-like activity that was accompanied by ATP decline from 2-3 to 1-2mM. The slices fully recovered from treatment and showed persistent spontaneous activity. Neuronal discharges were followed by transient ATP changes and periodic activation of ATP-sensitive K(+) (K-ATP) channels. The biggest ATP decreases during epileptiform-like episodes of activity were observed in CA1 and CA3 neurons. Examination of neurons from the Rett model mice MeCP2(-/y) showed that seizure-like activity had earlier onset and subsequent spontaneous activity demonstrated more frequent discharges. Hippocampal MeCP2(-/y) neurons had higher resting ATP levels and showed bigger ATP decreases during epileptiform-like activity. More intense ATP turnover in MeCP2(-/y) neurons may result from necessity to maintain hippocampal function in Rett syndrome. Elevated ATP may make, in turn, Rett hippocampus more prone to epilepsy due to inadequate activity of K-ATP channels.

Genes related to mitochondrial functions, protein degradation, and chromatin folding are differentially expressed in lymphomonocytes of Rett syndrome patients

Rett syndrome (RTT) is mainly caused by mutations in the X-linked methyl-CpG binding protein (MeCP2) gene. By binding to methylated promoters on CpG islands, MeCP2 protein is able to modulate several genes and important cellular pathways. Therefore, mutations in MeCP2 can seriously affect the cellular phenotype. Today, the pathways that MeCP2 mutations are able to affect in RTT are not clear yet. The aim of our study was to investigate the gene expression profiles in peripheral blood lymphomonocytes (PBMC) isolated from RTT patients to try to evidence new genes and new pathways that are involved in RTT pathophysiology. LIMMA (Linear Models for MicroArray) and SAM (Significance Analysis of Microarrays) analyses on microarray data from 12 RTT patients and 7 control subjects identified 482 genes modulated in RTT, of which 430 were upregulated and 52 were downregulated. Functional clustering of a total of 146 genes in RTT identified key biological pathways related to mitochondrial function and organization, cellular ubiquitination and proteosome degradation, RNA processing, and chromatin folding. Our microarray data reveal an overexpression of genes involved in ATP synthesis suggesting altered energy requirement that parallels with increased activities of protein degradation. In conclusion, these findings suggest that mitochondrial-ATP-proteasome functions are likely to be involved in RTT clinical features.

Rett syndrome: the state of clinical and basic research, and future perspectives

To clarify the pathophysiology of brain and spinal cord impairment in Rett syndrome (RTT), we report on the current status of research on Rett syndrome and review the abnormalities reported in neurotransmitters, neuromodulators and other biological markers in patients with RTT. We have previously investigated the levels of various factors in the blood, plasma, and cerebrospinal fluid (CSF) of RTT patients, including biogenic amines, lactate, melatonin, pyruvate and other citric acid cycle intermediates, substance P, β-endorphin and other neuropeptides, and a neuromodulator of β-phenylethylamine. In addition, we have performed near-infrared spectroscopy of the cerebral cortices in patients with RTT and genetic studies of the methyl-CpG-binding protein 2 (MECP2) in these patients. Taken together, the multiple abnormalities we and other authors have revealed in the various neurotransmitters/neuromodulator systems explain the pervasive effects of Rett syndrome. We also discuss the possible role of plasma ghrelin and present the results of our mouse study of the MECP2-null mutation using ES cells. Finally, we consider the potential for future analyses using our recently developed iPS cell system and discuss the future perspectives for the treatment and management of this disease.

Brain glucose metabolism in Rett Syndrome

Rett syndrome is a progressive neurologic disorder affecting girls in early childhood with loss of achieved psychomotor abilities and mental retardation. Six sedated female patients (4 to 15 years of age) with a diagnosis of Rett syndrome were studied with [(18)F]fluorodeoxyglucose (FDG) and underwent positron emission tomography scanning of the brain. Relative tracer concentrations between different areas of the brain were assessed, and results were compared with 18 age-matched control subjects. Patients were divided into two age groups: 3 to 8 years of age and 9 to 15 years of age. A relative decrease in [(18)F]FDG uptake in the lateral occipital areas in relation with the whole brain and a relative increase in the cerebellum was evident in both age groups (P < 0.001, unpaired Student t test). A relative increase in frontal tracer uptake was observed in the younger group. Sensorimotor areas and relations between cortical and subcortical structures were preserved in all patients. Changes in glucose cerebral metabolism resemble the regional distribution of normal children less than 1 year of age, likely reflecting a maturational arrest. Changes in frontal areas parallel those in postmortem N-methyl-D-aspartate receptor densities and could correlate with different clinical stages of the disease. This pattern differs from those described in Down syndrome, autism, and Alzheimer's disease.

Rett syndrome: review of biological abnormalities

The Rett syndrome (RS) is a peculiar, sporadic, atrophic disorder, almost entirely confined to females. After the first six months of life there is developmental slowing with reduced communication and head growth for about one year. This is followed by a rapid destructive stage with severe dementia and loss of hand skills (with frequent hand wringing), apraxia and ataxia, autistic features and irregular breathing with hyperventilation. Seizures often supervene. Subsequently there is some stabilization in a pseudo-stationary stage during the preschool to school years, associated with more emotional contact but also abnormalities of the autonomic and skeletal systems. After the age of 15-20 years, a late motor deterioration occurs with dystonia and frequent spasticity but seizures become milder. RS has generally been considered an X-linked disorder in which affected females represent a new mutation, with male lethality. Linkage studies suggested a critical region at Xq28. In 1999, mutations in the gene MECP2 encoding X-linked methyl cytosine-binding protein 2 (MeCP2) were found in a proportion of Rett girls. This protein can bind methylated DNA. Analyses are leading to much further investigation of mutants and their effects on genes. Neuropathological and electrophysiological studies of RS are described. Description of neurometabolic factors includes reduced levels of dopamine, serotonin, noradrenaline and choline acetyltransferase (ChAT) in brain, also estimation of nerve growth factors, endorphin, substance P, glutamate and other amino acids and their receptor levels. The results of neuroimaging are surveyed, including volumetric magnetic resonance imaging (MRI) and positron emission tomography (PET).

Rett syndrome

Rett syndrome is a progressive neurodegenerative disease of unknown etiology. Reported here are three children who presented with all clinical features of Rett syndrome. The aim of this presentation is to alert physicians to the existence of this progressive brain disease which only affects girls and so far no specific treatment has been suggested.

Cerebral oxygenation and hemodynamics during hyperventilation and sleep in patients with Rett syndrome

We continuously monitored changes in cerebral oxygenation and hemodynamics in the frontal lobes of six patients with Rett syndrome during the awake state, which is associated with hyperventilation (HV) and breath-holding (BH), and during sleep by near-infrared spectroscopy. We also monitored three adult volunteers during simulated episodes of HV and BH. In patients with Rett syndrome, the oxygenated hemoglobin (HbO2) and total hemoglobin (HbT) decreased significantly during HV and BH in the awake state compared with the sleep state. The HbO2 and HbT decreased gradually in adult volunteers in response to prolonged episodes of HV and BH. Further studies are required to investigate the relationship, if any, between the discovered continuous decreases in HbO2 and HbT during the awake state and the brain damage seen in patients with Rett syndrome.

Mutational analysis of mitochondrial DNA of children with Rett syndrome

The present study was undertaken to identify whether mitochondrial DNA (mtDNA) mutations were involved in the pathogenesis of Rett syndrome (RS). Mitochondrial DNA from 15 children with RS and 14 of their mothers was analyzed. No large deletions in mtDNA were found using Southern blot with a full-length mtDNA as a probe. Polymerase chain reaction amplification and single strand conformation polymorphism analysis showed mutations in region 2650-3000 encoding 16S rRNA of mtDNA in 13 cases of RS and 11 of their mothers. DNA sequence analysis and mismatch polymerase chain reaction results revealed a point mutation (C --> T) at position 2835 in 7 cases of RS and 6 of their mothers. The same mutation was not found in a total of 30 normal controls. These data indicate that mtDNA may play an important role in the pathogenesis of RS.

Rett syndrome: neurobiological changes underlying specific symptoms

Rett syndrome (RS) is a progressive disorder that is predominant in females. It is associated with cortical atrophy, stereotyped hand movements mimicking hand-washing, severe mental deficiency, and cortical and extrapyramidal dysfunction. The cause of RS is unknown; no consistent genetic abnormalities, at either the cellular or mitochondrial levels, have been identified. The diagnosis still depends solely upon clinical evidence. The clinical progression of RS is consistent with an arrested neuronal development that may be due to either impaired cellular differentiation or the lack of appropriate trophic factors. Neuropathological studies have confirmed (1) a generalized brain atrophy involving the cerebrum and cerebellum; (2) a decrease in neuronal cell size and increased cell packing density throughout the brain; (3) a reduction in the number of basal forebrain cholinergic neurons; (4) a reduction in the concentration of melanin-containing neurons in the substantia nigra. Biochemical studies have identified (1) a decrease in cholinergic markers in the neocortex, hippocampus, thalamus and basal ganglia; (2) inconsistent and variable changes in biogenic amine biomarkers in post-mortem tissues and cerebrospinal fluid (CSF); (3) an elevation of beta-endorphin levels in the thalamus and glutamate levels in the CSF; (4) no evidence for mitochondrial dysfunction. These data suggest that there is a primary deficit in cholinergic function that might underlie some of the higher cognitive impairments and extrapyramidal dysfunction. Overall, the clinical, biochemical and neuropathological data suggest that RS is a neurodevelopmental disorder that has its greatest effects upon a limited number of neural systems during the first few years of postnatal life.

Rett syndrome

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Choline acetyltransferase activity and vesamicol binding in Rett syndrome and in rats with nucleus basalis lesions

The decline in choline acetyltransferase activity has been identified previously within the brains of patients with Rett syndrome and Alzheimer's disease. The level of [3H]vesamicol binding to a terminal vesicular acetylcholine transporter is inversely related to the decline in cortical choline acetyltransferase activity in Alzheimer's disease, which may be due to compensatory processes within surviving cholinergic terminals. In order to investigate whether similar cholinergic compensatory processes are present in the Rett syndrome brain and are altered by normal aging, we investigated the density of cholinergic vesicular transporters in (i) the brains of Rett syndrome patients, and (ii) young and old rats with experimentally-induced cholinergic cell loss. In Rett syndrome, a significant decline in choline acetyltransferase activity within the putamen and thalamus was directly correlated with a decline in [3H]vesamicol binding. In both young and old rats, basal forebrain lesions decreased cortical choline acetyltransferase activity significantly, while [3H]vesamicol binding was unchanged. In contrast to young and old lesioned rats and patients with Alzheimer's disease, cholinergic cells in the brains of patients with Rett syndrome do not compensate for the loss of cholinergic cells by increasing acetylcholine vesicular storage.

Elevated cerebrospinal fluid lactate/pyruvate ratio in Machado-Joseph disease

To identify the metabolic alterations related to mitochondrial functions in Machado-Joseph disease (MJD), we analyzed the cerebrospinal fluid (CSF) levels of lactate, pyruvate, and citric acid cycle intermediates by high performance liquid chromatography (HPLC) in 7 Japanese patients with that disease and then measured some mitochondrial enzymes. Their mean age was 46 years. Diseased controls were matched by age to the patients studied. The CSF level of lactate was significantly elevated, pyruvate was significantly decreased, and the lactate/pyruvate (L/P) ratio was significantly elevated in the patients with MJD. There were no significant differences of citric acid cycle intermediates of the CSF between the patients and the controls. We measured the native and dichloroacetate (DCA)-activated pyruvate dehydrogenase complex (PDHC) activities, and mitochondrial electron transport activities in 3 patients with MJD, and found these activities to be normal. Therefore, the increased CSF lactate, increased lactate/pyruvate ratio, and decreased pyruvate may reflect the decreased regional cerebral blood flow rather than metabolic derangement of the mitochondria.

Polysomnographic recordings of respiratory disturbances in Rett syndrome

Polygraphic recordings in the awake state and during sleep were performed in two girls with Rett syndrome, aged 9 y and 17 y, in order to characterize the clinically manifest breathing disorder of these patients. Primary hyperventilation was detected, leading to hypocapnia and compensatory apnoea. Hypoxaemia occurred as the consequence of prolonged apnoea. In the younger patient these disturbances were observed only in the awake state, whereas in the older patient they were found in the awake state and during sleep.