Update on genetic disorders affecting white matter

MV2Net: Multi-Variate Multi-View Brain Network Comparison over Uncertain Data

Visually identifying effective bio-markers from human brain networks poses non-trivial challenges to the field of data visualization and analysis. Existing methods in the literature and neuroscience practice are generally limited to the study of individual connectivity features in the brain (e.g., the strength of neural connection among brain regions). Pairwise comparisons between contrasting subject groups (e.g., the diseased and the healthy controls) are normally performed. The underlying neuroimaging and brain network construction process is assumed to have 100% fidelity. Yet, real-world user requirements on brain network visual comparison lean against these assumptions. In this work, we present MV^2Net, a visual analytics system that tightly integrates multi-variate multi-view visualization for brain network comparison with an interactive wrangling mechanism to deal with data uncertainty. On the analysis side, the system integrates multiple extraction methods on diffusion and geometric connectivity features of brain networks, an anomaly detection algorithm for data quality assessment, single- and multi-connection feature selection methods for bio-marker detection. On the visualization side, novel designs are introduced which optimize network comparisons among contrasting subject groups and related connectivity features. Our design provides level-of-detail comparisons, from juxtaposed and explicit-coding views for subject group comparisons, to high-order composite view for correlation of network comparisons, and to fiber tract detail view for voxel-level comparisons. The proposed techniques are inspired and evaluated in expert studies, as well as through case analyses on diffusion and geometric bio-markers of certain neurology diseases. Results in these experiments demonstrate the effectiveness and superiority of MV^2Net over state-of-the-art approaches.

The protein interaction network of the inherited central nervous system diseases reveals new gene candidates for molecularly unclassified myelin disorders

Mutations in numerous genes cause the inherited disorders of the white matter in the central nervous system. Interestingly, all these mutations ultimately affect myelin, even though the corresponding proteins are involved in dissimilar functions. To address this system-level issue, we assembled the myelin disease network (MDN), in which each node represents a protein (either the mutated protein or one of its interactors), while each edge linking two nodes represents the physical interaction between the two proteins. Compared with control random networks, the MDN contains more pairs of disease proteins, whose members are linked either directly or via one intermediate protein. Then, we surmised that the interactions might not only cluster proteins into functionally homogenous and distinct modules but also link the modules together. This way, even gene mutations arising in functionally distinct modules might propagate their effects to the other modules, thus accounting for a similar pathological outcome. We found, however, that concerning the function the modules are neither homogeneous nor distinct, mostly because many proteins participate in more than one biological process. Rather, our analysis defines a region of the interactome, where different processes intersect. Finally, we propose that many non-disease proteins in the network might be candidates for molecularly unclassified myelin disorders.

Expanded Phenotypic Definition Identifies Hundreds of Potential Causative Genes for Leukodystrophies and Leukoencephalopathies

Background:

The genes responsible for genetic white matter disorders (GWMD; leukodystrophies and leukoencephalopathies) are incompletely known. Our goal was to revise the list of genes considered to cause GWMD. We considered a GWMD to consist of any genetic disease causing T2 signal white matter changes in magnetic resonance images.

Methods and Results:

Using a systematic review of PubMed, Google, published literature reviews, and commercial gene panels, we identified 399 unique genes meeting the GWMD definition. Of this, 87 (22%) genes were hypomyelinating. Only 3 genes had contrast enhancement on magnetic resonance imaging (MRI): ABCD1, GFAP, and UNC13D.

Conclusions:

A significantly greater number of genes than previously recognized, 399, are associated with white matter signal changes on T2 MRI. This expansion of GWMD genes can be useful in analysis and interpretation of next-generation sequencing results for GWMD diagnosis, and for understanding shared pathophysiological mechanisms of GWMDs.

Neurodegeneration in an adolescent with Sjogren-Larsson syndrome: a decade-long follow-up case report

BACKGROUND

Sjogren-Larsson syndrome is a hereditary neurocutaneous syndrome that is non-progressive in nature. Although neuroregression has been reported in seizure-prone preschool children requiring anti-epileptic treatment, teenage-onset dystonia precipitating neurodegeneration without any immediate causal events has yet to be reported.

CASE PRESENTATION

We describe a young woman with spastic diplegia and intellectual disability who began to show progressive neurological deterioration from 12 years of age, with the onset of dystonia and tremor. She was initially diagnosed with spastic cerebral palsy and periventricular leukomalacia based on brain magnetic resonance imaging. Follow-up brain imaging from 13 years of age did not reveal apparent changes, though abnormal electroencephalographic findings occurred in parallel with her decline in motor function. By 19 years of age, she had developed dysphagia and became completely dependent on others for most activities of daily living. Ultimately, whole-exome sequencing revealed a heterozygous compound mutation in the ALDH3A2 gene that corresponds to Sjogren-Larsson syndrome: an exon 9 deletion (1291-1292delAA) from the mother and an exon 5 splicing mutation (798 + 1delG) from the father. Neuroregression has been reported in preschool children after seizures requiring treatment, though our patient did not experience any immediate causal events. This report summarizes the clinical, radiologic, and electrophysiological findings observed over a decade concurrent with neurological deterioration after the onset of dystonia and tremor at the age of developmental ceiling in Sjogren-Larsson syndrome.

CONCLUSIONS

In addition to the influence of additive variants or other environmental factors, accumulation of metabolites due to defective fatty aldehyde dehydrogenase is a potential pathomechanism of neurodegeneration in this patient. Neurological deterioration may be a presentation that is unnoticed in Sjogren-Larsson syndrome due to the rarity of the disease. This report highlights a unique clinical feature of Sjogren-Larsson syndrome with progressive neurodegeneration associated with dystonia and tremor.

Canine NAPEPLD-associated models of human myelin disorders

Canine leukoencephalomyelopathy (LEMP) is a juvenile-onset neurodegenerative disorder of the CNS white matter currently described in Rottweiler and Leonberger dogs. Genome-wide association study (GWAS) allowed us to map LEMP in a Leonberger cohort to dog chromosome 18. Subsequent whole genome re-sequencing of a Leonberger case enabled the identification of a single private homozygous non-synonymous missense variant located in the highly conserved metallo-beta-lactamase domain of the N-acyl phosphatidylethanolamine phospholipase D (NAPEPLD) gene, encoding an enzyme of the endocannabinoid system. We then sequenced this gene in LEMP-affected Rottweilers and identified a different frameshift variant, which is predicted to replace the C-terminal metallo-beta-lactamase domain of the wild type protein. Haplotype analysis of SNP array genotypes revealed that the frameshift variant was present in diverse haplotypes in Rottweilers, and also in Great Danes, indicating an old origin of this second NAPEPLD variant. The identification of different NAPEPLD variants in dog breeds affected by leukoencephalopathies with heterogeneous pathological features, implicates the NAPEPLD enzyme as important in myelin homeostasis, and suggests a novel candidate gene for myelination disorders in people.

Clinical, biochemical, and genetic aspects of Sjögren-Larsson syndrome

Sjögren-Larsson syndrome (SLS) is caused by an autosomal recessive mutation in ALDH3A2, which encodes the fatty aldehyde dehydrogenase responsible for the metabolism of long-chain aliphatic aldehydes and alcohols. The pathophysiologic accumulation of aldehydes in various organs, including the skin, brain, and eyes, leads to characteristic features of ichthyosis, intellectual disability, spastic di-/quadriplegia, and low visual acuity with photophobia. The severity of the clinical manifestations thereof can vary greatly, although most patients are bound to a wheelchair due to contractures. To date, correlations between genotype and phenotype have proven difficult to document due to low disease incidence and high heterogenetic variability in mutations. This review summarizes the clinical characteristics of SLS that have been found to contribute to the prognosis thereof, as well as recent updates from genetic and brain imaging studies. In addition, the differential diagnoses of SLS are briefly illustrated, covering cerebral palsy and other genetic or neurocutaneous syndromes mimicking the syndrome.

Leukodystrophies: a proposed classification system based on pathological changes and pathogenetic mechanisms

Leukodystrophies are genetically determined disorders characterized by the selective involvement of the central nervous system white matter. Onset may be at any age, from prenatal life to senescence. Many leukodystrophies are degenerative in nature, but some only impair white matter function. The clinical course is mostly progressive, but may also be static or even improving with time. Progressive leukodystrophies are often fatal, and no curative treatment is known. The last decade has witnessed a tremendous increase in the number of defined leukodystrophies also owing to a diagnostic approach combining magnetic resonance imaging pattern recognition and next generation sequencing. Knowledge on white matter physiology and pathology has also dramatically built up. This led to the recognition that only few leukodystrophies are due to mutations in myelin- or oligodendrocyte-specific genes, and many are rather caused by defects in other white matter structural components, including astrocytes, microglia, axons and blood vessels. We here propose a novel classification of leukodystrophies that takes into account the primary involvement of any white matter component. Categories in this classification are the myelin disorders due to a primary defect in oligodendrocytes or myelin (hypomyelinating and demyelinating leukodystrophies, leukodystrophies with myelin vacuolization); astrocytopathies; leuko-axonopathies; microgliopathies; and leuko-vasculopathies. Following this classification, we illustrate the neuropathology and disease mechanisms of some leukodystrophies taken as example for each category. Some leukodystrophies fall into more than one category. Given the complex molecular and cellular interplay underlying white matter pathology, recognition of the cellular pathology behind a disease becomes crucial in addressing possible treatment strategies.

The use of targeted genomic capture and massively parallel sequencing in diagnosis of Chinese Leukoencephalopathies

Leukoencephalopathies are diseases with high clinical heterogeneity. In clinical work, it’s difficult for doctors to make a definite etiological diagnosis. Here, we designed a custom probe library which contains the known pathogenic genes reported to be associated with Leukoencephalopathies, and performed targeted gene capture and massively parallel sequencing (MPS) among 49 Chinese patients who has white matter damage as the main imaging changes, and made the validation by Sanger sequencing for the probands’ parents. As result, a total of 40.8% (20/49) of the patients identified pathogenic mutations, including four associated with metachromatic leukodystrophy, three associated with vanishing white matter leukoencephalopathy, three associated with mitochondrial complex I deficiency, one associated with Globoid cell leukodystrophy (or Krabbe diseases), three associated with megalencephalic leukoencephalopathy with subcortical cysts, two associated with Pelizaeus-Merzbacher disease, two associated with X-linked adrenoleukodystrophy, one associated with Zellweger syndrome and one associated with Alexander disease. Targeted capture and MPS enables to identify mutations of all classes causing leukoencephalopathy. Our study combines targeted capture and MPS technology with clinical and genetic diagnosis and highlights its usefulness for rapid and comprehensive genetic testing in the clinical setting. This method will also expand our knowledge of the genetic and clinical spectra of leukoencephalopathy.

The differential diagnosis of spastic diplegia

Spastic diplegia is the most common form of cerebral palsy worldwide. Many disorders mimic spastic diplegia, which can result in misdiagnosis for the child with resultant negative treatment and family counselling implications. In this paper, the authors provide a brief review of spastic diplegia and the various disorders in the differential diagnosis. We also provide a diagnostic algorithm to assist physicians in making the correct diagnosis.

Clinical exome sequencing identifies a novel TUBB4A mutation in a child with static hypomyelinating leukodystrophy

BACKGROUND

Leukodystrophies are a large group of inherited diseases of central nervous system myelin. There are few treatments, and most patients do not receive a final genetic diagnosis.

PATIENT

We report a novel presentation of a female child with hypotonia, global developmental delay, and rotatory nystagmus. Brain MRI demonstrated profound hypomyelination and minimal or no atrophy in the brain stem or cerebellum.

RESULTS

Extensive testing failed to yield a diagnosis until clinical whole-exome sequencing revealed a novel pathogenic mutation in the β-tubulin gene TUBB4A. TUBB4A is a cause of hereditary dystonia type 4 and has recently been reported to cause hypomyelination with atrophy of the basal ganglia and cerebellum.

CONCLUSIONS

This report expands the phenotypic spectrum of TUBB4A-associated neurological diseases to include static hypomyelinating leukodystrophy and supports the clinical relevance of next-generation sequencing diagnosis approaches.

Preventable Infections in Children with Leukodystrophy

Children with inherited leukodystrophies have high hospitalization rates, often associated with infection. We studied whether potentially modifiable risk factors (pre-existing in-dwelling central intravenous access, urinary catheter, hardware, or mechanical ventilation; and influenza vaccine) were associated with infection-related hospitalization in children with leukodystrophy. Central intravenous access was associated with sepsis (odds ratio (OR) 9.8); urinary catheter was associated with urinary tract infections (OR 9.0); lack of seasonal vaccination was associated with influenza (OR 6.4); and mechanical ventilation was associated with pneumonia (OR 2.7). We conclude that potentially modifiable risk factors are significantly associated with infection and hospitalization in children with leukodystrophies.

Merosin-deficient congenital muscular dystrophy with cerebral white matter changes: a clue to its diagnosis beyond infancy

A 6-year-old boy born by a third-degree consanguineous marriage presented with progressive muscle weakness and delayed motor milestones noticed in early infancy with preserved language and social milestones. Examination revealed generalised hypotonia and hyporeflexia. Baseline haematological and biochemical investigations were normal except for mildly elevated creatine kinase. Provisional diagnosis of congenital myopathy was entertained. We performed brain imaging to look for abnormalities associated with congenital muscular dystrophy even though there were only features of myopathy with normal mentation. An MRI of the brain revealed periventricular and subcortical white matter hyperintensities suggestive of leucoencephalopathy. Muscle biopsy findings were consistent with degenerative muscle changes and immunohistochemical staining for merosin was negative, thus confirming the diagnosis of merosin-deficient congenital muscular dystrophy. Supportive care in the form of physiotherapy was initiated. The family was offered genetic counselling in their second pregnancy and immunohistochemistry at 12 weeks confirmed the fetus to be affected, which was then terminated.

[Globoid cell leukodystrophy of adult. A first case in Poland]

Krabbe disease (globoid cell leukodystrophy) is a progressive, autosomal recessive disorder affecting peripheral and central nervous system. This disease is associated with mutation in GALC gene and its locus has been mapped to chromosome 14q31. GALC gene codes lysosomal hydrolytic enzyme: galactocerebroside β-galactosidase (galactosylceramidase) which is crucial for degradation of galactolipids, mostly galactosylceramide and galactosylsphingosine (psychosine). The disease may be subdivided into four types: infantile form with onset within the first six months, child form presenting between 6 months and 3 years, juvenile form presenting between 3 and 10 years and the rarest adult form with onset after 10 years. The diagnosis of Krabbe disease is based on clinical findings and confirmed with galactocerebroside β-galactosidase deficiency. We have found family with adult-onset disease. To our knowledge, this is the first observation of patient with adult form of Krabbe disease in Poland.

Determinants of health care use in a population-based leukodystrophy cohort

OBJECTIVES

To determine the costs for children with leukodystrophies and whether high costs are associated with characteristic clinical features or resources use.

STUDY DESIGN

We determined health care costs in a population cohort of 122 patients with leukodystrophies, including inpatient, outpatient, and emergency department use, during a 9-year period. We analyzed differences in patients with high costs (>85th percentile) and their health care use.

RESULTS

Patients with leukodystrophy had significant variability in resource use, with the top 15th percentile of patients accounting for 73% of costs ($9.6 million). The majority of costs, 81% ($10.8 million), arose from inpatient hospitalization. High-cost patients had more and longer hospitalizations, increased requirements for intensive unit care and mechanical ventilation, and significantly more infections. Importantly, bone marrow transplantation did not solely account for the difference between high-cost and low-cost groups.

CONCLUSION

Inpatient hospitalization is the greatest source of health care resource use in patients with leukodystrophies. A minority of patients account for the majority of costs, primarily attributable to an increased volume of hospitalization. Strategies to improve care and reduce costs will need to reduce inpatient stays and target modifiable reasons for hospitalization.

Congenital CNS hypomyelination in the Fig4 null mouse is rescued by neuronal expression of the PI(3,5)P(2) phosphatase Fig4

The plt (pale tremor) mouse carries a null mutation in the Fig4(Sac3) gene that results in tremor, hypopigmentation, spongiform degeneration of the brain, and juvenile lethality. FIG4 is a ubiquitously expressed phosphatidylinositol 3,5-bisphosphate phosphatase that regulates intracellular vesicle trafficking along the endosomal-lysosomal pathway. In humans, the missense mutation FIG4(I41T) combined with a FIG4 null allele causes Charcot-Marie-Tooth 4J disease, a severe form of peripheral neuropathy. Here we show that Fig4 null mice exhibit a dramatic reduction of myelin in the brain and spinal cord. In the optic nerve, smaller-caliber axons lack myelin sheaths entirely, whereas many large- and intermediate-caliber axons are myelinated but show structural defects at nodes of Ranvier, leading to delayed propagation of action potentials. In the Fig4 null brain and optic nerve, oligodendrocyte (OL) progenitor cells are present at normal abundance and distribution, but the number of myelinating OLs is greatly compromised. The total number of axons in the Fig4 null optic nerve is not reduced. Developmental studies reveal incomplete myelination rather than elevated cell death in the OL linage. Strikingly, there is rescue of CNS myelination and tremor in transgenic mice with neuron-specific expression of Fig4, demonstrating a non-cell-autonomous function of Fig4 in OL maturation and myelin development. In transgenic mice with global overexpression of the human pathogenic FIG4 variant I41T, there is rescue of the myelination defect, suggesting that the CNS of CMT4J patients may be protected from myelin deficiency by expression of the FIG4(I41T) mutant protein.

Genetic influence on the working memory circuitry: behavior, structure, function and extensions to illness

Working memory is a highly heritable complex cognitive trait that is critical for a number of higher-level functions. However, the neural substrates of this behavioral phenotype are intricate and it is unknown through what precise biological mechanism variation in working memory is transmitted. In this review we explore different functional and structural components of the working memory circuitry, and the degree to which each of them is contributed to by genetic factors. Specifically, we consider dopaminergic function, glutamatergic function, white matter integrity and gray matter structure all of which provide potential mechanisms for the inheritance of working memory deficits. In addition to discussing the overall heritability of these measures we also address specific genes that may play a role. Each of these heritable components has the potential to uniquely contribute to the working memory deficits observed in genetic disorders, including 22q deletion syndrome, fragile X syndrome, phenylketonuria (PKU), and schizophrenia. By observing the individual contributions of disruptions in different components of the working memory circuitry to behavioral performance, we highlight the concept that there may be many routes to a working memory deficit; even though the same cognitive measure may be a valid endophenotype across different disorders, the underlying cause of, and treatment for, the deficit may differ. This has implications for our understanding of the transmission of working memory deficits in both healthy and disordered populations.

Pediatric multiple sclerosis

In the past 5 years, there has been an exponential growth in the knowledge about multiple sclerosis (MS) in children and adolescents. Recent publications have shed light on its diagnosis, pathogenesis, clinical course, and treatment. However, there remain several key areas that require further exploration. This article summarizes the current state of knowledge on pediatric MS and discusses future avenues of investigation.

The burden of inherited leukodystrophies in children

OBJECTIVES

Leukodystrophies are diseases of the white matter for which data concerning clinical characteristics, incidence, disease burden, and description of outcomes are sparse. The purpose of our study was to determine the incidence and most common types of inherited leukodystrophies in a population, the mortality and time course of deaths, common neurologic features in patients, and health care costs associated with leukodystrophies.

METHODS

We conducted a retrospective, hospital- and clinic-based surveillance of inherited leukodystrophies among children younger than 18 years presenting to a regional children's hospital. We enrolled children evaluated from January 1, 1999, through December 31, 2007; clinical information was obtained from medical records. We calculated incidence based on state birth rates.

RESULTS

A total of 122 children with an inherited leukodystrophy were identified; 542 patients were excluded. A total of 49% had epilepsy, 43% required a gastrostomy tube, and 32% had a history of developmental regression. Mortality was 34%; average age at death was 8.2 years. No final diagnosis was reported in 51% of patients. The most common diagnoses were metachromatic leukodystrophy (8.2%), Pelizaeus-Merzbacher disease (7.4%), mitochondrial diseases (4.9%), and adrenoleukodystrophy (4.1%). Endocrine abnormalities and hypoplastic cerebellum were noted in significant portions of patients (15% and 14%). Average yearly per-patient medical costs were $22,579. Population incidence was 1 in 7,663 live births.

CONCLUSIONS

Inherited leukodystrophies are associated with substantial morbidity and mortality in children. Overall population incidence is higher than generally appreciated (1 in 7,663 live births). Most leukodystrophies remain undiagnosed, but a logical algorithm based on prevalence could aid testing.

Stem cells in genetic myelin disorders

The genetic myelin disorders are a range of diseases that manifest with severe neurological problems, often from infancy. It has been postulated for some time that stem cells might be an effective treatment for these disorders, primarily as agents to restore dysfunctional or lost myelin. Stem cells, however, may offer a wider range of therapeutic potential, for instance as vehicles to replace abnormal enzymes or genes, or to provide trophic support for residual CNS tissue. This article will review several of the more common genetic myelin disorders and currently available therapies, including bone marrow transplantation for adrenoleukodystrophy. Specific stem cell subtypes and their relevance to potential therapeutic use will be discussed and stem cell transplantation in animal model studies will also be reviewed.

The contributions of myelin and axonal caliber to transverse relaxation time in shiverer and neurofilament-deficient mouse models

White matter disorders can involve injury to myelin or axons but the respective contribution of each to clinical course is difficult to evaluate non-invasively. Here, to develop a paradigm for further investigations of axonal pathology by MRI, we compared two genetic mouse models exhibiting relatively selective axonal or myelin deficits using quantitative MRI relaxography of the transverse relaxation times (T2) in vivo and ultrastructural morphometry. In HM-DKO mice, which lack genes encoding the heavy (NF-H) and medium (NF-M) subunits of neurofilaments, neurofilament content of large myelinated axons of the central nervous system (CNS) is markedly reduced in the absence of changes in myelin thickness and volume. In shiverer mutant mice, which lack functional myelin basic protein, CNS myelin sheath formation is markedly reduced but neurofilament content is normal. We observed increases in T2 in nearly all white matter in shiverer mice compared to their wild type, while more subtle increases in T2 were observed in HM-DKO in the corpus callosum. White matter T2 was generally greater in shiverer mice than HM-DKO mice. Ultrastructural morphometry of the corpus callosum, which exhibited the greatest T2 differences, confirmed that total cross-sectional area occupied by axons was similar in the two mouse models and that the major ultrastructural differences, determined by morphometry, were an absence of myelin and larger unmyelinated axons in shiverer mice and absence of neurofilaments in HM-DKO mice. Our findings indicate that T2 is strongly influenced by myelination state and axonal volume, while neurofilament structure within the intra-axonal compartment has a lesser effect upon single compartment T2 estimates.

Familial leukoencephalopathy with slowly progressive dystonia and ataxia

We describe two siblings with childhood onset, slowly progressive generalized dystonia and cerebellar signs. Brain neuroimaging revealed white matter abnormalities compatible with a neuronal degenerative disorder. An extensive evaluation for mitochondrial, metabolic, autoimmune or other known neurodegenerative disorders did not reveal the etiology of the disease. During a three-year follow-up other neurological signs appeared, but progression was very slow. We believe that our patients have a new type of a leukoencephalopathy with slowly progressive dystonia and cerebellar signs.

Prospects of cell therapy for disorders of myelin

Recent advances in stem cell biology have raised expectations that both diseases of, and injuries to, the central nervous system may be ameliorated by cell transplantation. In particular, cell therapy has been studied for inducing efficient remyelination in disorders of myelin, including both the largely pediatric disorders of myelin formation and maintenance and the acquired demyelinations of both children and adults. Potential cell-based treatments of two major groups of disorders include both delivery of myelinogenic replacements and mobilization of residual oligodendrocyte progenitor cells as a means of stimulating endogenous repair; the choice of modality is then predicated upon the disease target. In this review we consider the potential application of cell-based therapeutic strategies to disorders of myelin, highlighting the promises as well as the problems and potential perils of this treatment approach.

Stem cell-based strategies for treating pediatric disorders of myelin

The pediatric leukodystrophies comprise a category of disease manifested by neonatal or childhood deficiencies in myelin production or maintenance; these may be due to hereditary defects in one or more genes critical to the initiation of myelination, as in Pelizaeus-Merzbacher Disease, or to enzymatic deficiencies with aberrant substrate accumulation-related dysfunction, as in the lysosomal storage disorders. Despite differences in both phenotype and natural history, these disorders are all essentially manifested by a profound deterioration in neurological function with age. A congenital deficit in forebrain myelination is also noted in children with the periventricular leukomalacia of cerebral palsy, another major source of neurological morbidity. In light of the wide range of disorders to which congenital hypomyelination and/or postnatal demyelination may contribute, and the relative homogeneity of central oligodendrocytes and their progenitors, the pediatric leukodystrophies may be especially attractive targets for cell-based therapeutic strategies. As a result, glial progenitor cells (GPCs), which can give rise to new myelinogenic oligodendrocytes, have become of great interest as potential therapeutic vectors for the restoration of myelin to the hypomyelinated or dysmyelinated childhood CNS. In addition, by distributing themselves throughout the deficient host neuraxis after perinatal allograft, and giving rise to astrocytes as well as oligodendrocytes, glial progenitors appear to be of potential great utility in rectifying enzymatic deficiencies. In this review, we focus on current efforts to develop the use of isolated human GPCs as transplantable agents both for mediating enzymatic restoration to the enzyme-deficient brain and for therapeutic myelination in the disorders of congenital hypomyelination.

Neuroimaging of neonatal encephalopathies

Neonatal brain disorders consist of a wide chapter including brain malformations, hypoxic-ischemic encephalopathy (HIE), intracranial infections, perinatal trauma and metabolic encephalopathy. We will focus here on HIE, intracranial infections (especially materno-fetal infection with or without prolonged and/or premature rupture of membranes) and metabolic encephalopathy, those three conditions being the most frequent so far in our experience. Neonatal stroke is also analyzed. Moreover minor perinatal events might be superimposed on an already damaged (infective, edematous, metabolically abnormal or maldeveloped) brain, highlighting the main role and potential benefits of neuroimaging during the neonatal period. The different methods of brain imaging are thus reported with their advantages and disadvantages.

Cognitive visual impairment with good visual acuity in children with posterior periventricular white matter injury: a series of 7 cases

BACKGROUND

We describe a series of term and preterm children with occipito-parietal periventricular white matter abnormalities on magnetic resonance imaging (MRI) who manifest common clinical features of cognitive visual dysfunction. We also describe a strategy for taking clinical history that highlights the symptom complex and assists with management.

PATIENTS AND METHODS

A retrospective observational case series study of seven children with cognitive visual difficulties despite good (20/32 or better) visual acuities and MRI findings of periventricular white matter pathology in the territory subserving visual function. Structured history taking was used to identify and characterize the visual difficulties. Objective clinical findings (visual acuity, color vision, stereoacuity, visual fields, ocular motility, refraction, and fundoscopy) were recorded.

RESULTS

Seven children with visual acuities of 20/32 (0.200 logMAR) or better had symptoms of cognitive visual difficulties consistent with dorsal stream dysfunction. Four had strabismus of different types and were identified on the basis of parental concern expressed at the ocular motility clinic. The other three children presented to the general ophthalmology clinic. All seven children had various degrees of focal periventricular white matter pathology in a similar distribution on neuroimaging.

CONCLUSIONS

Children born prematurely are susceptible to periventricular white matter pathology. Such pathology can also occur in children born at term. This case series demonstrates that cognitive visual impairment due to periventricular white matter injury can occur despite good central visual function. A range of strategies to help affected children is described.

The earliest MR imaging and proton MR spectroscopy abnormalities in adult-onset Krabbe disease

BACKGROUND

Adult-onset Krabbe disease is an uncommon form of leukodystrophy. Its magnetic resonance imaging (MRI) and magnetic resonance spectroscopy (MRS) manifestations are not well documented.

AIM OF THE STUDY

To describe early MR findings in adult-onset Krabbe disease.

MATERIALS AND METHODS

A 28-year-old woman who had spastic paraparesis and a 5-year history of gait problems underwent MRI of the brain and cervical spine. Proton MRS was performed at 1.5 T using a short echo time. Metabolites were analyzed in the areas of MR signal abnormalities and normal-appearing brain. Six healthy volunteers were examined as controls.

RESULTS

MRI revealed changes in the upper corticospinal tracts, splenium and, minimally, adjacent to the atria of the lateral ventricles. MRS showed decreased creatine, choline, N-acetylaspartate and glutamate and probably elevated lactate in the upper corticospinal tract but not in the normal-appearing frontal lobe. The spinal cord was thin. Laboratory tests verified Krabbe disease.

CONCLUSIONS

These results indicate early involvement of the upper corticospinal tract in adult-onset Krabbe disease. The cases reported earlier had imaging changes indicating a more advanced disease or no MR findings. Thinning of the spinal cord is a new finding in Krabbe disease.

Adult metachromatic leukodystrophy: a new mutation in the schizophrenia-like phenotype with early neurological signs

OBJECTIVES

The adult type of metachromatic leukodystrophy can manifest itself as motor or as psycho-cognitive form, the latter is very similar to schizophrenia. We report on two sisters with adult metachromatic leukodystrophy who display symptoms of both forms.

METHODS

Presented are genotype analyses and 4-year follow-up data regarding clinical manifestations as well as neurocognitive and neuroimaging results for two adult sisters with metachromatic leukodystrophy.

RESULTS

Whereas the younger sister developed disorganized schizophrenia-like symptoms, the other exhibited schizophrenia-like, negative symptoms. In both sisters, neurological signs were already present at the onset of the disease and progression towards dementia was documented within 1-2 years. In peripheral leukocytes, the activity of arylsulphatase A was reduced to 2 and 5% of the mean normal activity in both women. Genotype analysis revealed compound heterozygosity for a known severe splice site mutation, (c.459+1G>A) together with two known polymorphisms, [(c.937G>T), (p.Trp193Asp)] and [(c.1530C>G), (p.Thr391Ser)], and a novel missense mutation, (c.1194C>T). The latter results in the exchange of a conserved polar amino acid, threonine 279, to hydrophobic isoleucine (Thr279Ileu), which could not be found among >100 control alleles. A family analysis identified T279I as the paternal allele, whereas (c.459+1G>A) as well as the two polymorphisms were inherited from the mother. This is consistent with a disease-causing effect of the novel mutation.

CONCLUSIONS

The novel mutation, T279I detected in our patients, correlates with a specific phenotype with schizophrenia-like symptoms, neurological signs and cognitive impairment early in the course of the disease and a relatively fast progression towards dementia. This is in contrast to previous reports on adult metachromatic leukodystrophy patients with the psycho-cognitive phenotype who did not show any neurological signs for decades, however, most of these patients were heterozygous for another specific missense mutation, I179S.

MR imaging of brain maturation

Magnetic resonance imaging (MRI) is the imaging tool of choice to evaluate brain maturation and especially brain myelination. Magnetic resonance imaging also provides functional insight through diffusion images and proton spectroscopy. In this review the MRI techniques are analyzed for both pre- and postnatal periods. The origin of MR signal changes is also detailed in order to understand normal myelination evolution and the consequences on brain maturation of the different pathologies encountered prior and after birth. Because MRI is "blind" in terms of signal on conventional sequences after 2 years of age, a particular attention is given to diffusion images and proton spectroscopy of the developing brain.

Glial progenitor-based repair of demyelinating neurological diseases

Demyelinating diseases of the brain and spinal cord affect more than one-quarter million of Americans, with numbers reaching more than two million across the world. These patients experience not only the vascular, traumatic, and inflammatory demyelinations of adulthood but the congenital and childhood dysmyelinating syndromes of the pediatric leukodystrophies. Several disease-modifying strategies have been developed that slow disease progression, especially in the inflammatory demyelinations and in multiple sclerosis in particular. Yet, currently available disease modifiers typically influence the immune system and are neither intended to nor competent to reverse the structural neurologic damage attending acquired demyelination. Fortunately, however, the disorders of myelin lend themselves well to attempts at structural repair, because central oligodendrocytes are the primary, and often sole, victims of the underlying disease process. Given the relative availability and homogeneity of human oligodendrocyte progenitor cells, the disorders of myelin formation and maintenance may be especially compelling targets for cell-based neurologic therapy.

Expression patterns of MLC1 protein in the central and peripheral nervous systems

Mutations in MLC1 cause megalencephalic leukoencephalopathy with subcortical cysts (MLC), a disorder characterized clinically by macrocephaly, deterioration of motor functions, epilepsy and mental decline. Recent studies have detected MLC1 mRNA and protein in astroglial processes. In addition, our group previously reported MLC1 expression in some neurons in the adult mouse brain. Here we performed an exhaustive study of the expression pattern of MLC1 in the developing mouse brain by means of optic and electron microscopy. In the central nervous system, MLC1 was detected mainly in axonal tracts early in development. In addition, MLC1 was also observed in the peripheral nervous system and in several sensory epithelia, as retina or saccula maculae. Post-embedding immunogold experiments indicated that MLC1 is localized in astrocyte-astrocyte junctions, but not in the perivascular membrane, indicating that MLC1 is not a component of the dystrophin-glycoprotein complex. In neurons, MLC1 is located at the plasma membrane and vesicular structures. Our data provide a mouse MLC1 expression map that could be useful to understand the phenotype of MLC patients, and suggested that MLC disease is caused by an astrocytic and a neuronal dysfunction.

Hypomyelinating leukoencephalopathy with paroxysmal tonic upgaze and absence of psychomotor development

Hypomyelinating leukoencephalopathies are characterized by a substantial and permanent deficit in myelin deposition in the brain. Although our knowledge and understanding of the etiology of white matter diseases has progressively increased, many cases with this disorder remain undiagnosed, despite extensive evaluations. Recently, new disease entities have been defined by combining magnetic resonance imaging pattern recognition and clinical features. We describe a 1-year-old Ashkenazi Jewish girl with a hypomyelinating leukoencephalopathy, who presented in the neonatal period with episodes of sustained paroxysmal tonic upward gaze, roving eye movements, pendular nystagmus, and severe hypotonia, with the later appearance of pyramidal and extrapyramidal signs and no development. In addition, she has dysmorphic signs. This clinical picture is not consistent with any of the previously described hypomyelinating leukoencephalopathies and may represent a new entity.

Cell replacement therapy in neurological disease

Diseases of the brain and spinal cord represent especially daunting challenges for cell-based strategies of repair, given the multiplicity of cell types within the adult central nervous system, and the precision with which they must interact in both space and time. Nonetheless, a number of diseases are especially appropriate for cell-based therapy, in particular those in which single phenotypes are lost, and in which the re-establishment of vectorially specific connections is not entirely requisite for therapeutic benefit. We review here a set of potential therapeutic indications that meet these criteria as potentially benefiting from the transplantation of neural stem and progenitor cells. These include: (i) transplantation of phenotypically restricted neuronal progenitor cells into diseases of a single neuronal phenotype, such as Parkinson's disease; (ii) implantation of mixed progenitor pools into diseases characterized by the loss of a limited number of discrete phenotypes, such as spinal cord injury and the motor neuronopathies; (iii) transplantation of glial and nominally oligodendrocytic progenitor cells as a means of treating disorders of myelin; and (iv) transplantation of neural stem cells as a means of treating lysosomal storage disorders and other diseases of enzymatic deficiency. Among the diseases potentially approachable by these strategies, the myelin disorders, including the paediatric leucodystrophies as well as adult traumatic and inflammatory demyelinations, may present the most compelling targets for cell-based neurological therapy.

Myoclonic seizures in Krabbe disease: a unique presentation in late-onset type

Krabbe disease is a rare, recessively inherited degenerative disorder of myelin, caused by a deficiency of the lysosomal enzyme galactocerebroside beta-galactosidase. Ninety-five percent of cases begin in early infancy, typically presenting with irritability, hypertonicity, tonic spasms, visual loss with optic atrophy, and occasionally seizures. In 5% of cases, symptoms begin late, between 15 months and 10 years, usually presenting with spastic paralyses, cerebellar ataxia, visual failure, and peripheral neuropathy. Seizures occasionally develop months to years after symptom onset. In a review of 50 such cases from the world literature, in only two did seizures signal the onset. This report describes an 18-month-old male with late-onset Krabbe disease who is the first such reported patient presenting with myoclonic seizures, an epileptic encephalopathy normally thought to reflect gray matter disease.

Leukoencephalopathy with bilateral anterior temporal lobe cysts

Recently, several reports describing patients with a nonprogressive clinical course, increased signal in the cerebral white matter, and cystic changes in the anterior temporal lobes on magnetic resonance imaging (MRI) have appeared. To date, 25 patients with this very distinctive condition have been described. We report four new cases of this newly recognized entity. All have been identified primarily because of the distinctive MRI features consisting of the very unusual anterior temporal lobe cystic changes. The clinical features are characterized by severe, disabling, but nonprogressive mental and motor retardation. Magnetic resonance spectroscopy has shown increased myo-inositol and decreased N-acetylaspartate in the cerebral white matter. This is a distinctive, probably genetic, condition with characteristic neuroimaging and clinical features. In the appropriate clinical situation, the neuroimaging features are diagnostic.

[Adult onset hereditary leukoencephalopathies]

In clinical practice, the term "genetic leukoencephalopathy" refers to a group of genetic diseases whose common point is to give an aspect of diffuse leukoencephalopathy on MRI. With progress in diagnostic techniques including radiology, biochemistry or genetics, a large number of hereditary diseases causing leukoencephalopathy have been identified. Although generally beginning in childhood, these diseases often have more insidious clinical forms which can begin in adulthood. These forms remain poorly known. Some are accessible to treatment so their diagnosis appears essential. The diagnostic steps must be guided by clinical examination (neurological, ophthalmological and systemic), electromyography and MRI. The purpose of this review is to propose a classification of the genetic leukoencephalopathies and to give a progress report applicable in neurological practice.

Nonprogressive familial leukoencephalopathy with porencephalic cyst and focal seizures

Two siblings with a similar white-matter disease but different clinical symptoms are described. The first sibling suffers from nonprogressive spastic hemiparesis secondary to a congenital periventricular porencephalic cyst. Her brother has focal epilepsy. On magnetic resonance imaging, both patients show diffuse white-matter involvement predominantly of the posterior periventricular area. We suggest that this is a familial white-matter disorder with minimal symptoms and no progression in early childhood.

Progenitor cell-based myelination as a model for cell-based therapy of the central nervous system

Diseases of the brain and spinal cord are especially daunting challenges for cell-based strategies of repair, given the multiplicity of cell types within the adult central nervous system, and the precision with which they must interact in both space and time. Nonetheless, a number of diseases are especially appropriate for cell-based therapy, in particular those in which single phenotypes are lost. Foremost among these are the disorders of myelin, in which oligodendrocytes are the specific and often sole victims of the underlying disease process. These include not only the vascular, traumatic, and inflammatory demyelinations of adulthood, but also the congenital and childhood dysmyelinating syndromes of the pediatric leukodystrophies. These congenital disorders of myelin formation and maintenance may present especially compelling targets for cell-based neurological therapy.

eIF2B, a mediator of general and gene-specific translational control

eIF2B (eukaryotic initiation factor 2B) is a multisubunit protein that is required for protein synthesis initiation and its regulation in all eukaryotic cells. Mutations in eIF2B have also recently been found to cause a fatal human disease called CACH (childhood ataxia with central nervous system hypomyelination) or VWM (vanishing white matter disease). This review provides a general background to translation initiation and mechanisms known to control eIF2B function, before describing molecular genetic and biochemical analysis of eIF2B structure and function, integrating work from studies of the yeast and mammalian eIF2B proteins.

Stem and progenitor cell-based therapy of the human central nervous system

Multipotent neural stem cells, capable of giving rise to both neurons and glia, line the cerebral ventricles of all adult animals, including humans. In addition, distinct populations of nominally glial progenitor cells, which also have the capacity to generate several cell types, are dispersed throughout the subcortical white matter and cortex. A number of approaches have evolved for using neural progenitor cells in cell therapy. Four strategies are especially attractive for clinical translation: first, transplantation of oligodendrocyte progenitor cells as a means of treating the disorders of myelin; second, transplantation of phenotypically restricted neuronal progenitor cells to treat diseases of discrete loss of a single neuronal phenotype, such as Parkinson disease; third, implantation of mixed progenitor pools to treat diseases characterized by the loss of several discrete phenotypes, such as spinal cord injury; and fourth, mobilization of endogenous neural progenitor cells to restore neurons lost as a result of neurodegenerative diseases, in particular Huntington disease. Together, these may present the most compelling strategies and near-term disease targets for cell-based neurological therapy.