Child Neurol Research Articles

Neuropathology of Rett Syndrome

Rett syndrome is a sporadic disorder (except for a few familial cases) occurring in 1 in 10,000 to 1 in 23,000 girls worldwide. It is associated with profound mental and motor handicap. About 90% of cases involve a mutation in the methyl-CpG binding protein 2 gene (MECP2). The role of this gene in the pathogenesis of this enigmatic disorder is being extensively investigated in animal models. Rett syndrome is associated with a complex phenotype that is unique in every aspect of its presentation, clinical physiology, chemistry, and pathology. Years of concentrated observations have defined the clinical presentation of classic Rett syndrome and its variants and related features (eg, neurophysiologic, radiologic, chemical, metabolic, and anatomic). This article reviews the neuropathology of Rett syndrome, which involves individual neurons, perhaps selected neurons, of decreased size, dendritic branching, and numbers of spines. This article also summarizes the studies in the human and mouse brain with Rett syndrome that are beginning to reveal the disorder's pathoetiology.

MeCP2 Dysfunction in Humans and Mice

Rett syndrome is a leading cause of postnatal neurodevelopmental regression. Rett syndrome is caused by mutations in MECP2, the gene encoding methyl-CpG binding protein 2. In up to 96% of all classic cases, Rett syndrome cases are caused by mutations or deletions in MECP2. The phenotypic spectrum of MECP2 mutations is broad and includes mental retardation with or without seizures, Angelman syndrome-like phenotype, and autism. Mecp308/Y mice carry a truncating mutation and display many of the features seen in Rett syndrome. Social behavior abnormalities and impaired social interactions in Mecp308/Y mice suggest that MeCP2 plays a role in modulating the activity of genes and neurons important for social interactions. Mice that overexpress MeCP2 at twice the endogenous levels develop a progressive neurologic disorder, demonstrating that MeCP2 levels are tightly regulated and raising the possibility that duplications or gain-of-function mutations of MECP2 might underlie some cases of neurodevelopmental X-linked disorders.

Rett Syndrome and Neuronal Development

The clinical signs of Rett syndrome, as well as neuropathology and brain imaging, suggest that the disorder disrupts neuronal circuits. Studies using receptor autoradiography demonstrate abnormalities in the density of excitatory glutamate and inhibitory gamma-aminobutyric acid (GABA) synaptic receptors in postmortem brain from young female subjects with Rett syndrome. MeCP2, the protein that is abnormal in most female individuals with Rett syndrome, is expressed predominantly in neurons and appears during development at the time of synapse formation. Studies of nasal epithelium from patients with Rett syndrome show that the maturation of olfactory receptor neurons is impeded prior to the time of synapse formation. Recent reports indicate that MeCP2 controls the expression of brain-derived neurotrophic factor and the DNA-binding homeobox protein Dlx5. Brain-derived neurotrophic factor enhances glutamate neurotransmission at excitatory synapses, whereas Dlx5 is expressed in most GABAergic neurons and stimulates the synthesis of GABA. Taken together, this information supports the hypothesis that Rett syndrome is a genetic disorder of synapse development, especially synapses that use glutamate and GABA as neurotransmitters.

Newborn Screening and Prenatal Diagnosis for Rett Syndrome: Implications for Therapy

Most girls with Rett syndrome develop normally prior to the appearance of the typical symptoms. A presymptomatic phase is also observed in many inborn errors of metabolism that are included in newborn screening programs. Diagnostic testing for mutations or large genomic rearrangements involving methyl-CpG binding protein 2 gene (MECP2) is highly sensitive and identifies mutations in up to 95% of female individuals with classic Rett syndrome. This has prompted some to ask whether MECP2 testing should be included in newborn and prenatal screening programs. We review current and evolving practices in these programs, emphasizing their relevance to Rett syndrome. The availability of a reliable test and the characteristic early latent phase, which creates a window of opportunity for early treatment, favor universal newborn screening for Rett syndrome. However, the high cost and the lack of an effective presymptomatic treatment make universal newborn screening for Rett syndrome impractical at present. In contrast, prenatal diagnosis should be offered to the parents of an affected child if the responsible mutation has been identified in the index case.

Rett Syndrome: Long-Term Clinical Follow-Up Experiences Over Four Decades

Long-term clinical profiles of female patients with classic Rett syndrome are presented and exemplified by three cases, as experienced over four decades. Emphasized is the frequently surprisingly well-preserved eye contact and primitive memory, in contrast to a premature neuromuscular aging and often advanced peripheral atrophy, usually combined with dystonic-rigid signs that are predominantly right sided.

MECP2 Abnormality Phenotypes: Clinicopathologic Area With Broad Variability

Rett syndrome is a neurodevelopmental disorder that occurs worldwide and predominantly affects girls. The MECP2 gene has been put forward as the underlying gene. Interestingly, other clinical presentations in addition to Rett syndrome have been reported to be the results of deviations in MECP2. This prompted us to outline a working hypothesis of how these diverse phenotypes are connected. Our aim was to summarize the clinical picture of deviations in MECP2 at this moment to obtain a comprehensive overview. Thus, we have attempted to create a gradient, starting at the left with the most severely affected MECP2-deviant subgroups, represented by boys who are diseased in the intrauterine phase or as neonates, and at the right, the most mildly affected subgroup, female asymptomatic carriers. In the center, with dominant numbers, we have placed classic Rett syndrome presentations, together with the late-onset Rett syndrome variant and preserved speech variant. In conclusion, we feel that it is important to emphasize that Rett syndrome is a strictly clinical diagnosis that is not identical to the far broader concept of MECP2 deviations.

Neurophysiology of Rett Syndrome

Rett syndrome is a neurodevelopmental disorder that in most cases is consequent to a mutation in the MECP2 gene. The central nervous system is the primary organ system involved in Rett syndrome. Neurophysiologic evaluations provide information concerning the developmental aspects of Rett syndrome and the character and extent of involvement of the central, peripheral, and autonomic nervous system pathways. Evoked potentials typically demonstrate intactness of peripheral auditory and visual pathways and suggest dysfunction of central or "higher" cortical pathways. Somatosensory evoked potentials can be characterized by "giant" responses, suggesting cortical hyperexcitability. Cortical hyperexcitability is further suggested by the findings of the electroencephalogram (EEG), which are primarily characterized by a loss of expected developmental features; the appearance of focal, multifocal, and generalized epileptiform abnormalities; and the occurrence of rhythmic slow (theta) activity, primarily in the frontal-central regions. Epileptic seizures are reported to occur frequently in Rett syndrome. However, many events presumed to be seizures have no EEG correlate during video-EEG monitoring. Impairment of the autonomic nervous system in Rett syndrome is suggested by an increased incidence of long Q-T intervals during electrocardiographic recordings and diminished heart rate variability. Autonomic nervous system dysfunction can contribute to the increased incidence of sudden unexpected death in Rett syndrome.

Does Genotype Predict Phenotype in Rett Syndrome?

Mutations in the X-linked gene encoding the methyl-CpG binding protein MeCP2 are the primary cause of classic and atypical Rett syndrome and have recently been shown to contribute to other neurodevelopmental disorders of varying severity. To determine whether there are molecular correlates to the phenotypic heterogeneity, numerous groups have performed genotype-phenotype correlation studies. These studies have yielded conflicting results, in part because they used different criteria for determining severity and classifying mutations. Evolution of the phenotype with age and variable expressivity arising from individual variability in X-chromosome inactivation patterns are among other reasons the findings varied. Nonetheless, evidence of differences in the phenotypic consequences of specific types of mutations is emerging. This review analyzes the available literature and makes recommendations for future studies.

Natural History of Rett Syndrome

Rett syndrome is a unique neurodevelopmental disorder, with onset of hypotonia, autistic tendency, and abnormalities of fine finger movements and gross movements of the arms in early infancy. Clinical features include specific age-dependent symptoms. Studies of early and late signs correlated locomotive dysfunction to language disability and stereotypy to regression of higher cortical functions. Studies of sleep parameters revealed early hypofunction of brainstem aminergic neurons and late occurrence of hypofunction of dopaminergic neurons, followed by receptor supersensitivity. The syndrome's pathophysiology suggests that early hypofunction of aminergic neurons interferes with the development of higher neuronal systems. Particular symptoms surface at different ages throughout the natural course of Rett syndrome, with regressional and static periods.

Rett Syndrome: Model of Neurodevelopmental Disorders

Rett syndrome is a neurodevelopmental disorder that primarily affects girls, most of whom have mutations in the transcription regulatory gene MECP2. However, mutations in MECP2 also have been identified in normal carrier female individuals, female individuals with mild learning disabilities and features of Angelman syndrome, and male individuals with Klinefelter syndrome or Rett syndrome-like features, fatal neonatal encephalopathy, and familial X-linked mental retardation with or without motor abnormalities. Therefore, molecular testing should be considered for a wide spectrum of individuals. As such, Rett syndrome remains a clinical diagnosis. In this article, we also discuss three recent developments: (1) the recognition of significant gallbladder dysfunction, especially in those 20 years of age or younger; (2) a clinical trial of folate and betaine, which produced no objective improvement but did yield a subjective increase in attention and interaction; and (3) measurement of cerebrospinal fluid folate levels in a large cohort, which yielded normal values, indicating no need for supplementation.

Focal Status Epilepticus as Atypical Presentation of Pyridoxine-Dependent Epilepsy

Pyridoxine-dependent epilepsy usually presents in the neonatal period or even in utero, is refractory to antiepileptic medications, and is treatable with lifelong administration of pyridoxine. The seizures are typically generalized tonic-clonic, although myoclonic seizures or infantile spasms have been described. We report an infant who presented at 5 months of age with a right-sided clonic seizure with fever. Subsequently, she had recurrent right focal or generalized seizures despite sequential treatment with various antiepileptic medications. At 7 months, she was hospitalized with status epilepticus, which was finally controlled with pyridoxine. After she became seizure free, she continued to have a strong left arm preference with mild weakness of the right arm and delayed language skill. Eventually, she outgrew these symptoms. This case illustrates that pyridoxine-dependent epilepsy, although rare, must be included in the differential diagnosis of focal seizures, especially when the seizures are refractory to traditional antiepileptic drugs.

Relationship Between Brain Glucose Metabolism Positron Emission Tomography (PET) and Electroencephalography (EEG) in Children With Continuous Spike-and-Wave Activity During Slow-Wave Sleep

We studied the relationship between brain glucose metabolism patterns and objectively measured interictal epileptiform abnormalities in six children with intractable epilepsy and continuous spike-and-wave activity during slow-wave sleep. Five of the six patients showed lateralized positron emission tomographic (PET) findings, with the hemisphere showing a relative increase in glucose metabolism concordant with the presumed origin of the generalized interictal spike activity delineated by quantitative electroencephalographic (EEG) analysis. One of these five patients achieved seizure freedom following cortical resection involving the areas of unilateral multifocal hypermetabolism, and another patient has been approved for cortical resection. The results in the present study add further support to the hypothesis that the generalized spike-waves in most cases of continuous spike-and-wave activity during slow-wave sleep are the result of secondary bilateral synchrony. Resective surgery can be effective in selected patients with uncontrolled seizures associated with continuous spike-and-wave activity during slow-wave sleep provided that there is concordance between focal abnormalities on PET and EEG.

Efficacy and Tolerability of Topiramate in Children Younger Than 2 Years Old

To evaluate the efficacy and tolerability of topiramate in children with epilepsy younger than 2 years of age, we retrospectively reviewed the records of patients treated at our institution between 2001 and 2003. Thirteen children ages 5 to 23 months, five boys and eight girls, were identified. Seizure types were partial (five), generalized tonic-clonic (three), myoclonic (one), and infantile spasms (four). The mean age at seizure onset was 9.7 months. Topiramate was started at a mean age of 11.4 months (4-23 months). The number of antiepileptic drugs prior to topiramate therapy ranged from zero to four. One patient had been on the ketogenic diet. Topiramate was used as monotherapy in seven children and as polytherapy in six children. Mean follow-up was 14 months. The mean dose of topiramate was 8.8 mg/kg/day (2.5-18 mg/kg/day). The degree of seizure reduction was as follows: > 75% in five (38.5%) children, 50% to 75% in three (23%) children, and 0 to 25% in five (38.5%) children. Three of four (75%) patients with infantile spasms had a > 75% reduction in seizures. Adverse effects occurred in two children, including lethargy, hyperthermia, and anorexia. In children younger than 2 years of age, for whom the antiepileptic drug armamentarium is limited, topiramate appears to be an efficacious and safe therapeutic alternative for a variety of seizure types.

Developmental and Functional Outcomes at School Age of Preschool Children With Global Developmental Delay

The later developmental trajectory of young children diagnosed early with global developmental delay was determined. Using a prospective study, preschool children diagnosed with global developmental delay were systematically reassessed during the early school years with standardized developmental and functional outcome measures (Battelle Developmental Inventory and Vineland Adaptive Behavior Scale). Of an original cohort of 99 children assessed and diagnosed at a mean age of 3.4 +/- 1.1 years, 48 were reassessed at a mean age of 7.3 +/- 0.9 years. Group performance on the Battelle Developmental Inventory overall was 66.4 +/- 4.3 (mean 100 +/- 15). Between 75% and 100% of the cohort performed at least 1.5 SD below the normative mean on the individual domains of the Battelle Developmental Inventory. Similarly, the group mean on the Vineland Adaptive Behavior Scale overall was 63.5 +/- 20.8 (mean 100 +/- 15), with between 61% and 76% of the cohort scoring more than 1.5 SD below the mean on each of the domains. Univariate and multivariate analyses on potential predictor variables identified a lack of an underlying etiology as predictive of poorer performance on the Battelle Developmental Inventory fine motor and motor domains and increasing severity of initial delay as predictive of poorer performance on the Vineland Adaptive Behavior Scale communication domain and overall score. Similarly, maternal employment and paternal postsecondary education improved Vineland Adaptive Behavior Scale communication scores, whereas paternal postsecondary education alone predicted better socialization and total scores on the Vineland Adaptive Behavior Scale. Children with early global developmental delay demonstrate persistent and consistently poor performance across all developmental and functional domains. Few variables are apparent at intake to predict later performance.

Hallermann-Streiff Syndrome Associated With Complete Agenesis of the Corpus Callosum

Hallermann-Streiff syndrome is a rare clinical entity with unknown etiology characterized by a birdlike face, microphthalmia, a beaked nose, hypotrichosis, and proportional small stature. We present a 4-year-old boy in whom magnetic resonance imaging showed complete agenesis of the corpus callosum, which has not been presented in the literature.

Embryology of the Neural Crest: Its Inductive Role in the Neurocutaneous Syndromes

Neural crest cells are first recognized at the lateral margin of the neural placode shortly after gastrulation, although they are not committed to their diverse fates until later. After dorsal closure of the neural tube, neural crest cells separate and migrate throughout the embryo to form many structures of ectodermal origin (eg, dorsal root and autonomic ganglia, peripheral nerve sheaths) and mesodermal origin (eg, blood vessels, melanocytes, adipose tissue, membranous bone, connective tissue, most of the ocular globe). Terminal differentiation occurs after migration is complete. Three regions of the neural tube generate neural crest: rhombencephalon, mesencephalon, and prosencephalon, each with a different migratory pattern. The most important genes promoting neural crest differentiation and migration are those with a dorsalizing influence in the vertical axis of the neural tube (eg, PAX3, BMP4, ZIC2), some segmentation genes (eg, WNT1), genes that inhibit neural crest (eg, EGR2), and neural crest-specific differentiating genes (eg, SLUG, SOX10). In the neurocutaneous syndromes, diverse features result from abnormal neural crest differentiation, providing a more encompassing embryologic basis for these disorders than the traditional view that these syndromes are somehow related to skin and brain because both are ectodermal derivatives. Abnormal angiogenesis, areas of abnormal pigmentation that sometimes follow the lines of Blashko, nerve sheath proliferations, disorders of chromaffin tissue, lipomes and benign and malignant tumors are frequent features. Many defective genes in neurocutaneous syndromes have an additional function as tumor suppressors. Interactions between genes associated with these disorders and others essential to neural crest formation, migration, and differentiation, are a likely molecular genetic basis for these diseases. The craniofacial abnormalities associated with many cerebral malformations and cutaneous lesions in some neurocutaneous syndromes emphasize an important inductive role of the neural tube in the development of non-neural tissues, mediated through neural crest.

Multivoxel Magnetic Resonance Spectroscopy in a Rhizomelic Chondrodysplasia Punctata Case

A case of a 5-day-old newborn with rhizomelic chondrodysplasia punctata was investigated with multivoxel magnetic resonance spectroscopy, including chemical shift imaging maps, which disclosed a decrease in the choline peak and the choline signal intensity, respectively, in the right cerebral hemisphere. This is the second report of multivoxel magnetic resonance spectroscopy examination of the brain associated with rhizomelic chondrodysplasia punctata in the literature. Multivoxel magnetic resonance spectroscopy with chemical shift imaging maps has the advantage of obtaining more information in a short period of time, which shortens the duration of anesthesia and its associated risks and complications. We suggest that future efforts be directed to evaluating such patients with multivoxel magnetic resonance spectroscopy instead of single-voxel magnetic resonance spectroscopy.

Comorbidity of Epilepsy and Headache in Patients With Sturge-Weber Syndrome

Sturge-Weber syndrome is associated with leptomeningeal angioma, trigeminal port-wine stain, epilepsy, and glaucoma. Clinically, many patients with Sturge-Weber syndrome are observed to have both seizures and headaches, but this has never been described in the literature. A questionnaire was mailed to 190 patients with reported comorbid epilepsy and headache as identified by the Sturge-Weber Foundation. Sixty-eight surveys were returned anonymously; 55 reported both seizures and headaches. The median age at headache onset was 8 years, with a median of three headaches per month. Fifty-eight percent felt that headaches were an equal or greater problem. Ibuprofen and acetaminophen were the most frequently tried abortive medications; 22% had tried sumatriptan. Only 22% reported a neurologist suggesting the use of an anticonvulsant as a preventive agent. Subjects with a family history of headaches had an earlier age at headache onset (7.5 vs 11 years; P = .02), and those with a family history of seizures were more likely to report behavior problems (69% vs 33%; P = .02). Subjects reporting learning problems or hemiparesis had an earlier age at seizure onset. Migraine-like headaches can be as significant a problem as epilepsy for patients with Sturge-Weber syndrome. Despite this, triptans and prophylactic medications (including anticonvulsants) were used in less than half of the patients. Correlations of family history with both age at symptom onset and behavior problems suggest that genetic substrate could be one factor determining the variable neurologic manifestations seen in Sturge-Weber syndrome.

Unusual Clinical Presentations in Four Cases of Leigh Disease, Cytochrome C Oxidase Deficiency, and SURF1 Gene Mutations

Mutations in the SURF1 gene are the most frequent causes of Leigh disease with cytochrome c oxidase deficiency. We describe four children with novel SURF1 mutations and unusual features: three had prominent renal symptoms and one had ragged red fibers in the muscle biopsy. We identified five pathogenic mutations in SURF1: two mutations were novel, an in-frame nonsense mutation (834G-->A) and an out-of-frame duplication (820-824dupTACAT). Although renal manifestations have not been described in association with SURF1 mutations, they can be part of the clinical presentation. Likewise, mitochondrial proliferation in muscle (with ragged red fibers) is most unusual in Leigh disease but might be part of an emerging phenotype.

Factors Predicting the Efficacy of Botulinum Toxin-A Treatment of the Lower Limb in Children With Cerebral Palsy

Botulinum toxin A is widely used for spasticity management in children with cerebral palsy, although outcomes are unpredictable. The aim of this study was to identify criteria for selecting patients most likely to benefit from botulinum toxin A treatment. Fifty-five subjects, aged 2.5 to 18 years, were recruited. The assessment covered measures of spasticity (Modified Ashworth Scale), function (using the Gross Motor Function Measure and the Physician's Rating Scale), selective motor control, static range of motion at the ankle with knee extended and flexed, range of motion of the knee flexors, central and peripheral vision, and cognitive ability. Outcomes at 3 months were compared with baseline values. All of the scales showed significant differences between pre- and postinjection values. Significantly increased Gross Motor Function Measure scores were found in children aged 48 months or under and in those able to walk with support. Greater improvements in selective motor control and Physician's Rating Scale were seen in those with a less severe pattern of paralysis, lower levels of impairment, the ability to walk (with or without support), normal visual acuity, and normal or borderline cognition. We identified factors that mark out patients as most likely to achieve functional gains: young age, hemiplegia or diplegia, slight to moderate disability, walking with support, normal or borderline cognition, and normal or borderline visual acuity.