Defining and categorizing leukoencephalopathies of unknown origin: MR imaging approach

Magnetic resonance imaging pattern recognition in hypomyelinating disorders

Hypomyelination is observed in the context of a growing number of genetic disorders that share clinical characteristics. The aim of this study was to determine the possible role of magnetic resonance imaging pattern recognition in distinguishing different hypomyelinating disorders, which would facilitate the diagnostic process. Only patients with hypomyelination of known cause were included in this retrospective study. A total of 112 patients with Pelizaeus-Merzbacher disease, hypomyelination with congenital cataract, hypomyelination with hypogonadotropic hypogonadism and hypodontia, Pelizaeus-Merzbacher-like disease, infantile GM1 and GM2 gangliosidosis, Salla disease and fucosidosis were included. The brain scans were rated using a standard scoring list; the raters were blinded to the diagnoses. Grouping of the patients was based on cluster analysis. Ten clusters of patients with similar magnetic resonance imaging abnormalities were identified. The most important discriminating items were early cerebellar atrophy, homogeneity of the white matter signal on T(2)-weighted images, abnormal signal intensity of the basal ganglia, signal abnormalities in the pons and additional T(2) lesions in the deep white matter. Eight clusters each represented mainly a single disorder (i.e. Pelizaeus-Merzbacher disease, hypomyelination with congenital cataract, hypomyelination with hypogonadotropic hypogonadism and hypodontia, infantile GM1 and GM2 gangliosidosis, Pelizaeus-Merzbacher-like disease and fucosidosis); only two clusters contained multiple diseases. Pelizaeus-Merzbacher-like disease was divided between two clusters and Salla disease did not cluster at all. This study shows that it is possible to separate patients with hypomyelination disorders of known cause in clusters based on magnetic resonance imaging abnormalities alone. In most cases of Pelizaeus-Merzbacher disease, hypomyelination with congenital cataract, hypomyelination with hypogonadotropic hypogonadism and hypodontia, Pelizaeus-Merzbacher-like disease, infantile GM1 and GM2 gangliosidosis and fucosidosis, the imaging pattern gives clues for the diagnosis.

Leukoencephalopathy with vanishing white matter: a review

Vanishing white matter (VWM) is one of the most prevalent inherited childhood leukoencephalopathies, but this may affect people of all ages, including neonates and adults. It is a progressive disorder clinically dominated by cerebellar ataxia and in which minor stress conditions, such as fever or mild trauma, provoke major episodes of neurologic deterioration. Typical pathological findings include increasing white matter rarefaction and cystic degeneration, oligodendrocytosis with highly characteristic foamy oligodendrocytes, meager astrogliosis with dysmorphic astrocytes, and loss of oligodendrocytes by apoptosis. Vanishing white matter is caused by mutations in any of the genes encoding the 5 subunits of the eukaryotic translation initiation factor 2B (eIF2B), EIF2B1 through EIF2B5. eIF2B is a ubiquitously expressed protein complex that plays a crucial role in regulating the rate of protein synthesis. Vanishing white matter mutations reduce the activity of eIF2B and impair its function to couple protein synthesis to the cellular demands in basal conditions and during stress. Reduced eIF2B activity leads to sustained improper activation of the unfolded protein response, resulting in concomitant expression of proliferation, prosurvival, and proapoptotic downstream effectors. Consequently, VWM cells are constitutively predisposed and hyperreactive to stress. In view of the fact that VWM genes are housekeeping genes, it is surprising that the disease is primarily a leukoencephalopathy. The pathophysiology of selective glial vulnerability in VWM remains poorly understood.

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.

New case of 4H syndrome and a review of the literature

Different pathologic processes (especially demyelination, hypomyelination, and combinations of these) may underlie leukoencephalopathies. Leukoencephalopathies pose a particular diagnostic problem when they occur in children. To seek associated, non-neurologic signs is of fundamental importance in hypomyelinating leukoencephalopathies, because these can help clarify the diagnostic picture. Two new types of leukoencephalopathy have emerged, one classified as ataxia, delayed dentition, and hypomyelination, and the other as hypomyelination with hypogonadotropic hypogonadism and hypodontia. Initially described as distinct entities, they were recently brought together in the Online Mendelian Inheritance in Man database under a single code. However, the literature describes only two patients with the characteristics of both these clinical pictures. We present the extended clinical and neuroradiologic follow-up of a patient with ataxia, delayed dentition, and hypomyelination, as well as hypogonadotropic hypogonadism. This patient reinforces the idea that the two syndromes should actually be considered the same disorder, and prompted us to conduct a critical review of the literature on disorders in which hypomyelinating leukoencephalopathy is associated with cerebellar atrophy or hypogonadism.

Natural history of adult-onset eIF2B-related disorders: a multi-centric survey of 16 cases

Mutations in one of the five eukaryotic initiation factor 2B genes (EIF2B1-5) were first described in childhood ataxia with cerebral hypomyelination--vanishing white matter syndrome. The syndrome is characterized by (i) cerebellar and pyramidal signs in children aged 2-5 years; (ii) extensive cavitating leucoencephalopathy; and (iii) episodes of rapid deterioration following stress. Since then a broad clinical spectrum from congenital to adult-onset forms has been reported, leading to the concept of eIF2B-related disorders. Our aim was to describe clinical and brain magnetic resonance imaging characteristics, genetic findings and natural history of patients with adult-onset eIF2B-related disorders (after age 16). The inclusion criteria were based on the presence of eIF2B mutations and a disease onset after the age of 16 years. One patient with an asymptomatic diagnosis (age 16 years) was also included. Clinical and magnetic resonance findings were retrospectively recorded in all patients. All patients were examined to assess clinical evolution, using functional, pyramidal, cerebellar and cognitive scales. This multi-centric study included 16 patients from 14 families. A sex ratio imbalance was noted (male/female = 3/13). The mean age of onset was 31.1 years (range 16-62). Initial symptoms were neurologic (n = 11), psychiatric (n = 2) and ovarian failure (n = 2). Onset of the symptoms was linked to a precipitating factor in 13% of cases that included minor head trauma and delivery. During follow-up (mean: 11.2 years, range 2-22 years) 12.5% of the patients died. Of the 14 survivors, 62% showed a decline in their cognitive functions, and 79% were severely handicapped or bedridden. One case remained asymptomatic. Stress worsened clinical symptoms in 38% of the patients. Magnetic resonance imaging findings consist of constant cerebral atrophy, extensive cystic leucoencephalopathy (81%), corpus callosum (69%) and cerebellar (38%) T2-weighted hyperintensities. All families except one showed mutations in the EIF2B5 gene. The recurrent p.Arg113His-eIF2Bepsilon mutation was found in 79% of the 14 eIF2B-mutated families, mainly at a homozygous state. The family with a mutation in EIF2B2 had the relatively prevalent p.Glu213Gly mutation. eIF2B-related disorder is probably underestimated as an adult-onset inherited leucoencephalopathy. In this late-onset form, presentation ranges from neurologic symptoms to psychiatric manifestations or primary ovarian failure. Cerebral atrophy is constant, whereas the typical vanishing of the white matter can be absent. Functional and/or cognitive prognosis remains severe. Molecular diagnosis is facilitated for these forms by the screening of the two recurrent p.Arg113His-eIF2Bepsilon and p.Glu213Gly-eIF2Bbeta mutations, positive in 86% of cases.

Diffuse cerebral hypomyelination with cerebellar atrophy and hypoplasia of the corpus callosum

Three unrelated Japanese patients who presented with ataxia and mild mental retardation were examined in this study. Early development was normal in two patients and slightly delayed in one. All could walk independently, but were unstable due to cerebellar ataxia. They had mild intellectual retardation and displayed slow, progressive, and mild clinical courses. Two patients lost the ability to walk at 12 and 25 years of age. Brain MRI of the three patients revealed diffuse cerebral hypomyelination, moderate cerebellar cortical atrophy, and hypoplasia of the corpus callosum, which were seen in other diffuse hypomyelination syndrome. No known abnormalities were found in biochemical and genetic studies. Auditory brainstem responses and nerve conduction studies were normal. A definite diagnosis could not be made because of the lack of hypodontia, hypogonadism, cataracts, or basal ganglia atrophy. Based on common MRI findings and the relatively mild clinical courses, we believe that these patients may have another subset form of diffuse hypomyelination syndrome involving the cerebral white matter and cerebellum.

L-2-Hydroxyglutaric aciduria: pattern of MR imaging abnormalities in 56 patients

PURPOSE

To describe the pattern of magnetic resonance (MR) imaging abnormalities in l-2-hydroxyglutaric aciduria (L2HGA) and to evaluate the correlation between imaging abnormalities and disease duration.

MATERIALS AND METHODS

MR images in 56 patients (30 male, 26 female; mean age +/- standard deviation, 11.9 years +/- 8.5) with genetically confirmed L2HGA were retrospectively reviewed, with institutional review board approval and waiver of informed consent. At least one complete series of transverse T2-weighted images was available for all patients. The images were evaluated by using a previously established scoring list. The correlation between MR imaging abnormalities and disease duration was assessed (Mann-Whitney or Kruskal-Wallis test).

RESULTS

The cerebral white matter (WM) abnormalities preferentially affected the frontal and subcortical regions. The abnormal subcortical WM often had a mildly swollen appearance (37 patients). Initially, the WM abnormalities were at least partially multifocal (32 patients). In patients with longer disease duration, the WM abnormalities became more confluent and spread centripetally, but the periventricular rim remained relatively spared (41 patients). The mean disease duration in patients with WM atrophy (14.8 years) was significantly longer (P = .001) than that in patients without atrophy (6.7 years). Bilateral involvement of the globus pallidus (55 patients), caudate nucleus (56 patients), and putamen (56 patients) was seen at all stages. The cerebellar WM was never affected. The dentate nucleus was involved bilaterally in 55 of 56 patients.

CONCLUSION

L2HGA has a distinct highly characteristic pattern of MR imaging abnormalities: a combination of predominantly subcortical cerebral WM abnormalities and abnormalities of the dentate nucleus, globus pallidus, putamen, and caudate nucleus. With increasing disease duration, WM abnormalities and basal ganglia signal intensity abnormalities become more diffuse and cerebral WM atrophy ensues.

Developmental changes in cerebral white matter microstructure in a disorder of lysosomal storage

The goal of this work was to study white matter (WM) integrity in children with cystinosis, a rare lysosomal storage disorder resulting in cystine accumulation in peripheral and central nervous system tissue. Based on previous reports of cystine crystal formation in myelin precursors as well as evidence for specific cognitive deficits in visuospatial functioning, diffusion tensor imaging (DTI) was applied to 24 children with cystinosis (age 3-7 years) and to 24 typically developing age-matched controls. Scalar diffusion indices, fractional anisotropy (FA) and mean diffusivity (MD), were examined in manually defined regions of interest within the parietal and inferior temporal lobes. Diffusion indices were correlated with performance on measures of visuospatial cognition and with white blood cell cystine levels. Bilaterally decreased FA and increased MD were evident in the inferior and superior parietal lobules in children with cystinosis, with comparable FA and MD to controls in inferior temporal WM, and implicate a dissociation of the dorsal and ventral visual pathways. In older cystinosis children (age>5), diminutions in visuospatial performance were associated with reduced FA in the right inferior parietal lobule. In addition, increased MD was found in the presence of high cystine levels in all children with cystinosis. This study provides new information that the average diffusion properties in children with cystinosis deviate from typically developing children. Findings suggest the presence of early microstructural WM changes in addition to a secondary effect of cystine accumulation. These alterations may impact the development of efficient fiber networks important for visuospatial cognition.

Invited article: an MRI-based approach to the diagnosis of white matter disorders

BACKGROUND

There are many different white matter disorders, both inherited and acquired, and consequently the diagnostic process is difficult. Establishing a specific diagnosis is often delayed at great emotional and financial costs. The pattern of brain structures involved, as visualized by MRI, has proven to often have a high diagnostic specificity.

METHODS

We developed a comprehensive practical algorithm that relies mainly on the characteristics of brain MRI.

RESULTS

The initial decision point defines a hypomyelination pattern, in which the cerebral white matter is hyperintense (normal), isointense, or slightly hypointense relative to the cortex on T1-weighted images, vs other pathologies with more prominent hypointensity of the cerebral white matter on T1-weighted images. In all types of pathology, the affected white matter is hyperintense on T2-weighted images, but, as a rule, the T2 hyperintensity is less marked in hypomyelination than in other pathologies. Some hypomyelinating disorders are typically associated with peripheral nerve involvement, while others are not. Lesions in patients with pathologies other than hypomyelination can be either confluent or isolated and multifocal. Among the diseases with confluent lesions, the distribution of the abnormalities is of high diagnostic value. Additional MRI features, such as white matter rarefaction, the presence of cysts, contrast enhancement, and the presence of calcifications, further narrow the diagnostic possibilities.

CONCLUSION

Application of a systematic decision tree in MRI of white matter disorders facilitates the diagnosis of specific etiologic entities.

Classification of childhood white matter disorders using proton MR spectroscopic imaging

BACKGROUND AND PURPOSE

Childhood white matter disorders often show similar MR imaging signal-intensity changes, despite different underlying pathophysiologies. The purpose of this study was to determine if proton MR spectroscopic imaging ((1)H-MRSI) may help identify tissue pathophysiology in patients with leukoencephalopathies.

MATERIALS AND METHODS

Seventy patients (mean age, 6; range, 0.66-17 years) were prospectively examined by (1)H-MRSI; a diagnosis of leukoencephalopathy due to known genetic defects leading to lack of formation, breakdown of myelin, or loss of white matter tissue attenuation (rarefaction) was made in 47 patients. The diagnosis remained undefined (UL) in 23 patients. Patients with definite diagnoses were assigned (on the basis of known pathophysiology) to 3 groups corresponding to hypomyelination, white matter rarefaction, and demyelination. Choline (Cho), creatine (Cr), and N-acetylaspartate (NAA) signals from 6 white matter regions and their intra- and intervoxel (relative to gray matter) ratios were measured. Analysis of variance was performed by diagnosis and by pathophysiology group. Stepwise linear discriminant analysis was performed to construct a model to predict pathophysiology on the basis of (1)H-MRSI, and was applied to the UL group.

RESULTS

Analysis of variance by diagnosis showed 3 main metabolic patterns. Analysis of variance by pathophysiology showed significant differences for Cho/NAA (P < .001), Cho/Cr (P < .004), and NAA/Cr (P < .002). Accuracy of the linear discriminant analysis model was 75%, with Cho/Cr and NAA/Cr being the best parameters for classification. On the basis of the linear discriminant analysis model, 61% of the subjects in the UL group were classified as hypomyelinating.

CONCLUSION

(1)H-MRSI provides information on tissue pathophysiology and may, therefore, be a valuable tool in the evaluation of patients with leukoencephalopathies.

Mitochondrial hsp60 chaperonopathy causes an autosomal-recessive neurodegenerative disorder linked to brain hypomyelination and leukodystrophy

Hypomyelinating leukodystrophies (HMLs) are disorders involving aberrant myelin formation. The prototype of primary HMLs is the X-linked Pelizaeus-Merzbacher disease (PMD) caused by mutations in PLP1. Recently, homozygous mutations in GJA12 encoding connexin 47 were found in patients with autosomal-recessive Pelizaeus-Merzbacher-like disease (PMLD). However, many patients of both genders with PMLD carry neither PLP1 nor GJA12 mutations. We report a consanguineous Israeli Bedouin kindred with clinical and radiological findings compatible with PMLD, in which linkage to PLP1 and GJA12 was excluded. Using homozygosity mapping and mutation analysis, we have identified a homozygous missense mutation (D29G) not previously described in HSPD1, encoding the mitochondrial heat-shock protein 60 (Hsp60) in all affected individuals. The D29G mutation completely segregates with the disease-associated phenotype. The pathogenic effect of D29G on Hsp60-chaperonin activity was verified by an in vivo E. coli complementation assay, which demonstrated compromised ability of the D29G-Hsp60 mutant protein to support E. coli survival, especially at high temperatures. The disorder, which we have termed MitCHAP-60 disease, can be distinguished from spastic paraplegia 13 (SPG13), another Hsp60-associated autosomal-dominant neurodegenerative disorder, by its autosomal-recessive inheritance pattern, as well as by its early-onset, profound cerebral involvement and lethality. Our findings suggest that Hsp60 defects can cause neurodegenerative pathologies of varying severity, not previously suspected on the basis of the SPG13 phenotype. These findings should help to clarify the important role of Hsp60 in myelinogenesis and neurodegeneration.

Pediatric neurodegenerative white matter processes: leukodystrophies and beyond

Pediatric neurodegenerative white matter processes are complex, numerous and result from a vast array of causes ranging from white matter injury or inflammation to congenital metabolic disorders. When faced with a neurodegenerative white matter process on neuroimaging, the first step for the radiologist is to determine whether the findings represent a congenital metabolic leukodystrophy or one of various other white matter processes. In this review we first describe a general approach to neurodegenerative white matter disorders. We will briefly describe a few white matter diseases that mimic metabolic leukodystrophies. In the second half of the review we discuss an approach to distinguishing and classifying white matter leukodystrophies.

Type a Niemann-Pick Disease

We describe three patients with type A Niemann-Pick disease (NPD-A). NPD-A is an autosomal recessive neuronal storage disease classified among the sphingolipidoses, characterized by accumulation of sphingomyelin in various tissues and in the brain. Magnetic Resonance imaging (MRI) of our three patients showed a marked delay of myelination with frontal atrophy. Few descriptions of this MRI pattern of delayed myelination have been published to date.

Early onset West syndrome with cerebral hypomyelination and reduced cerebral white matter

Numerous numbers of pre-, peri- and postnatal damages cause West syndrome in early infancy, however, etiology in many cases are not still elucidated despite intensive biochemical and neuroradiologic investigations. We described four patients having early onset epileptic encephalopathy with severe hypomyelination and reduction in cerebral white matter. The clinical symptoms of these patients are impaired visual attention, acquired microcephaly, spastic tetraplegia, profound psychomotor delay and infantile spasms since early infancy. All patients had striking hypomyelination of cerebrum, reduced volume of white matter and cortical atrophy on MRI. Serial MRI investigations in three patients showed absence of myelination of the white matter. On EEG, one patient revealed suppression-burst and other three had hypsarrhythmia. Despite having intractable seizures, no patient showed deterioration of neurological development. The group of these findings is mimicking to clinical manifestations of 3-phosphoglycerate dehydrogenase deficiency, and has some overlap with progressive encephalopathy with edema, hypsarrhythmia, and optic atrophy (PEHO) like syndrome, however it is not compatible with these two conditions. The findings observed in our patients can be regarded as a new clinical condition associated with early onset West syndrome.

Leukoencephalopathy with brainstem and spinal cord involvement and high brain lactate: report of three Brazilian patients

A novel leukoencephalopathy was recently identified based on magnetic resonance imaging (MRI) and proton magnetic resonance spectroscopy ((1)H-MRS) findings. Leukoencephalopathy with brainstem and spinal cord involvement and high lactate (LBSL) is an autosomal recessive disorder characterized by early onset of symptoms and slowly progressive cerebellar, pyramidal and spinal cord dorsal column dysfunction. MRI and (1)H-MRS typically show abnormalities within cerebral and cerebellar white matter, a characteristic involvement of brainstem and spinal cord tracts and elevated lactate in the abnormal white matter. We present three cases with characteristic clinical and neuroimaging findings of this disorder. Some additional unique findings of our patients are discussed, like distal motor neuropathy and elevated creatine kinase in the serum.

Phenotypic characterization of hypomyelination and congenital cataract

OBJECTIVE

To define the clinical and laboratory findings in a novel autosomal recessive white matter disorder called hypomyelination and congenital cataract, recently found to be caused by a deficiency of a membrane protein, hyccin, encoded by the DRCTNNB1A gene located on chromosome 7p21.3-p15.3.

METHODS

We performed neurological examination, neurophysiological, neuroimaging, and neuropathological studies on sural nerve biopsy in 10 hypomyelination and congenital cataract patients from 5 unrelated families.

RESULTS

The clinical picture was characterized by bilateral congenital cataract, developmental delay, and slowly progressive neurological impairment with spasticity, cerebellar ataxia, and mild-to-moderate mental retardation. Neurophysiological studies showed a slightly to markedly slowed motor nerve conduction velocity in 9 of 10 patients, and multimodal evoked potentials indicated increased central conduction times. Neuroimaging studies demonstrated a diffuse supratentorial hypomyelination, with in some patients, additional areas of more prominent signal change in the frontal region. Sural nerve biopsy showed a slight-to-severe reduction in myelinated fiber density, with several axons surrounded by a thin myelin sheath or devoid of myelin.

INTERPRETATION

Hypomyelination and congenital cataract is a novel autosomal recessive white matter disorder characterized by the unique association of congenital cataract and hypomyelination of the central and peripheral nervous system.

Hypomyelination and congenital cataract: neuroimaging features of a novel inherited white matter disorder

BACKGROUND AND PURPOSE

Hypomyelination and congenital cataract (HCC) is an autosomal recessive white matter disease caused by deficiency of hyccin, a membrane protein implicated in both central and peripheral myelination. We aimed to describe the neuroimaging features of this novel entity.

MATERIALS AND METHODS

A systematic analysis of patients with unclassified leukoencephalopathies admitted to our institutions revealed 10 children with congenital cataract, slowly progressive neurologic impairment, and diffuse white matter abnormalities on neuroimaging. Psychomotor developmental delay was evident after the first year of life. Peripheral neuropathy was demonstrated by neurophysiologic studies in 9 children. The available neuroimaging studies were retrospectively reviewed.

RESULTS

In all patients, neuroimaging revealed diffuse involvement of the supratentorial white matter associated with preservation of both cortical and deep gray matter structures. Supratentorial white matter hypomyelination was detected in all patients; 7 patients also had evidence of variably extensive areas of increased white matter water content. Deep cerebellar white matter hypomyelination was found in 6 patients. Older patients had evidence of white matter bulk loss and gliosis. Proton MR spectroscopy showed variable findings, depending on the stage of the disease. Sural nerve biopsy revealed hypomyelinated nerve fibers. Mutations in the DRCTNNB1A gene on chromosome 7p15.3, causing complete or severe deficiency of hyccin, were demonstrated in all patients.

CONCLUSIONS

HCC is characterized by a combined pattern of primary myelin deficiency and secondary neurodegenerative changes. In the proper clinical setting, recognition of suggestive neuroimaging findings should prompt appropriate genetic investigations.

Update on leukodystrophies

Leukodystrophies, heritable white matter disorders, have long presented significant diagnostic and therapeutic challenges to the practicing neurologist. Recent advances, however, have identified many of the unclassified leukodystrophies, and work in understanding the underlying pathophysiology of these diverse disorders has progressed. Several hypomyelination disorders have been identified, Aicardi–Goutières syndrome-associated genes have been found and autosomal-dominant leukodystrophy has been established as a genetically distinct disorder. In addition, unifying mechanisms in certain leukodystrophies have been found, including an abnormal endoplasmic reticulum stress response and astrocytic dysfunction. Finally, novel diagnostic approaches have established techniques for rapid identification of affected patients. This review provides an update of these changes and discusses the likely impact they will have on the evaluation and management of leukodystrophies.

Magnetic resonance imaging of myelin

The ability to measure myelin in vivo has great consequences for furthering our knowledge of normal development, as well as for understanding a wide range of neurological disorders. The following review summarizes the current state of myelin imaging using MR. We consider five MR techniques that have been used to study myelin: 1) conventional MR, 2) MR spectroscopy, 3) diffusion, 4) magnetization transfer, and 5) T2 relaxation. Fundamental studies involving peripheral nerve and MR/histology comparisons have aided in the interpretation and validation of MR data. We highlight a number of important findings related to myelin development, damage, and repair, and we conclude with a critical summary of the current techniques available and their potential to image myelin in vivo.

Magnetic resonance spectroscopy and metabolic imaging in white matter diseases and pediatric disorders

This review provides the reader with an overview of the magnetic resonance spectroscopy technique and the clinical, pathological, imaging, and metabolic features for select white matter disorders of interest. With this composite summary, the reader should find it easier to implement and interpret spectroscopy in the clinical setting for the diagnosis and monitoring of patients with white matter disorders.

An approach to MRI of metabolic disorders in children

Inborn errors of metabolism are a difficult group of disorders for the neuroradiologist, as there are few good clinical or neuroradiological criteria for differentiating them. In this review, a technique of diagnosis by pattern recognition, supplemented by metabolic data from proton MR spectroscopy and microstructural data, as assessed by diffusion weighted images, is presented. Proper use of these neuroimaging tools can be very useful for separating these disorders into more manageable groups, and sometimes allows a specific diagnosis to be made.

Hypomyelination with atrophy of the basal ganglia and cerebellum: case report

Hypomyelination with atrophy of the basal ganglia and cerebellum (H-ABC) is a rare disease that has been recently described. It must be remembered as a possible etiology of leukoencephalopathies in children. We describe a typical case of H-ABC in a 11-month-old boy. He presents with global development delay, oral dyskinesia, and global dystonia and spasticity. Magnetic resonance imaging disclosed typical features of H-ABC and clinical laboratory tests were all negative. A slow neurological deterioration has been detected with worsening of involuntary movements.

Deficiency of hyccin, a newly identified membrane protein, causes hypomyelination and congenital cataract

We describe a new autosomal recessive white matter disorder ('hypomyelination and congenital cataract') characterized by hypomyelination of the central and peripheral nervous system, progressive neurological impairment and congenital cataract. We identified mutations in five affected families, resulting in a deficiency of hyccin, a newly identified 521-amino acid membrane protein. Our study highlights the essential role of hyccin in central and peripheral myelination.

Leukodystrophies: clinical and genetic aspects

The leukodystrophies comprise an ever-expanding group of rare central nervous system disorders with defined clinical, pathological, and genetic characteristics. The broader term, leukoencephalopathy, is applied to all brain white matter diseases, whether their molecular cause is known. Magnetic resonance imaging has helped to elucidate new forms of leukodystrophy as well as to permit longitudinal studies of disease progression. The white matter abnormality may appear similar in different forms of leukodystrophy so that in most cases, further studies such as magnetic resonance spectroscopy, tissue biopsies, enzyme studies, and molecular DNA analyses are needed to pinpoint the specific diagnosis. The primary inherited leukoencephalopathies include dysmyelinating, hypomyelinative, and vacuolating forms. Metabolic and vascular causes account for most of the secondary forms, but other inherited syndromes are recognized that have their onset in childhood or adult life and are characterized by distinctive clinical and neuropathologic features. This review discusses some of the mechanisms that have been proposed to explain deficiencies of myelin and the molecular genetic bases underlying these disorders.

Vanishing white matter disease

Vanishing white matter disease (VWM) is one of the most prevalent inherited childhood leucoencephalopathies. The classical phenotype is characterised by early childhood onset of chronic neurological deterioration, dominated by cerebellar ataxia. VWM is unusual because of its clinically evident sensitivity to febrile infections, minor head trauma, and acute fright, which may cause rapid neurological deterioration and unexplained coma. Most patients die a few years after onset. The phenotypic variation is extremely wide, including antenatal onset and early demise and adult-onset, slowly progressive disease. MRI findings are diagnostic in almost all patients and are indicative of vanishing of the cerebral white matter. The basic defect of this striking disease resides in either one of the five subunits of eukaryotic translation initiation factor eIF2B. eIF2B is essential in all cells of the body for protein synthesis and its regulation under different stress conditions. Although the defect is in housekeeping genes, oligodendrocytes and astrocytes are predominantly affected, whereas other cell types are surprisingly spared. Recently, undue activation of the unfolded-protein response has emerged as important in the pathophysiology of VWM, but the selective vulnerability of glia for defects in eIF2B is poorly understood.

Childhood ataxia with CNS hypomyelination/vanishing white matter disease--a common leukodystrophy caused by abnormal control of protein synthesis

Mutations in eukaryotic initiation factor 2B (eIF2B) cause one of the most common leukodystrophies, childhood ataxia with CNS hypomyelination/vanishing white matter disease or CACH/VWM. Patients may develop a wide spectrum of neurological abnormalities from prenatal-onset white matter disease to juvenile or adult-onset ataxia and dementia, sometimes with ovarian insufficiency. The pattern of diffuse white matter abnormalities on MRI of the head is often diagnostic. Neuropathological abnormalities indicate a unique and selective disruption of oligodendrocytes and astrocytes with sparing of neurons. Marked decrease of asialo-transferrin in cerebrospinal fluid is the only biochemical abnormality identified thus far. Eukaryotic translation initiation factor 2B (eIF2B) mutations cause a decrease in guanine nucleotide exchange activity on eIF2-GDP, resulting in increased susceptibility to stress and enhanced ATF4 expression during endoplasmic reticulum stress. eIF2B mutations are speculated to lead to increased susceptibility to various physiological stress conditions. Future research will be directed towards understanding why abnormal control of protein translation predominantly affects brain glial cells.

Regulation of protein synthesis in lymphoblasts from vanishing white matter patients

Leukoencephalopathy with vanishing white matter (VWM) is an inherited childhood white matter disorder, caused by mutations in the genes encoding eukaryotic initiation factor 2B (eIF2B). The present study showed that, while the eIF2B activity was reduced in VWM lymphoblasts, the expression levels of the eIF2B subunits were similar to control lymphoblast lines. The mutations in eIF2B did not affect the interaction with eIF2. Strikingly, no apparent differences for the regulation of protein synthesis, measured by [35S]-methionine incorporation, were found between control and VWM lymphoblasts. Western blotting showed that, in some VWM cells, exposure to heat shock caused a decrease in the expression of specific eIF2B subunits. Most importantly, the increase in phosphorylation of eIF2alpha in response to heat shock was lower in VWM lymphoblasts than in control cells. These findings could form part of the explanation for the episodes of rapid and severe deterioration in VWM patients that are precipitated by febrile infections.

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.

Vanishing white matter disease: A review with focus on its genetics

Leukoencephalopathy with vanishing white matter (VWM) is an autosomal recessive brain disorder, most often with a childhood onset. Magnetic resonance imaging and spectroscopy indicate that, with time, increasing amounts of cerebral white matter vanish and are replaced by fluid. Autopsy confirms white matter rarefaction and cystic degeneration. The process of localization and identification of the first two genes related to VWM, EIF2B5 and EIF2B2, was facilitated by two founder effects in the Dutch population. EIF2B5 and EIF2B2 encode the epsilon and beta subunits of translation initiation factor eIF2B. Soon it was shown that mutations in all five eIF2B subunit genes can cause VWM. EIF2B is essential for the initiation of translation of RNA into protein and is involved in regulation of the process, especially under stress conditions, which may explain the sensitivity to stress conditions observed in VWM patients. The pathophysiology of the disease is still poorly understood.

Decreased Asialotransferrin in Cerebrospinal Fluid of Patients with Childhood-Onset Ataxia and Central Nervous System Hypomyelination/Vanishing White Matter Disease

Background: A biomarker for the diagnosis of childhood-onset ataxia and central nervous system hypomyelination (CACH)/vanishing white matter disease (VWM) would have clinical utility and pathophysiologic significance.

Methods: We used 2-dimensional gel electrophoresis/mass spectrometry to compare the cerebrospinal fluid proteome of patients with mutation-confirmed CACH/VWM with that of unaffected controls. We characterized selected spots by in-gel digestion, matrix-assisted laser desorption/ionization time-of-flight tandem mass spectrometry, and nanospray Fourier transform mass spectrometry.

Results: A specific transferrin spot pattern was detected in the CSF samples of the CACH/VWM group (n = 7), distinguishing them from the control group (n = 23) and revealing that patients with CACH/VWM have a deficiency of the asialo form of transferrin usually present in healthy cerebrospinal fluid. The glycopeptide structure, determined from isolated transferrin spots by use of in-gel digestion and extraction, was found to be consistent with earlier reports.

Conclusions: The transferrin isoform abnormality in the cerebrospinal fluid of patients with CACH/VWM appears unique and is a potential clinical diagnostic biomarker. The rapid, efficient diagnosis of this disorder would have a significant impact on clinical studies exploring new strategies for the management and treatment of this disease.

MRI of a family with leukoencephalypathy with vanishing white matter

Leukoencephalopathy with vanishing white matter (VWM) is a newly described entity with characteristic MRI features. We report the cranial MRI findings in three sisters with slowly progressive neurological deterioration. The MRI showed symmetrical diffuse abnormalities of cerebral white matter with hypointensity on FLAIR images. The diagnosis of leukoencephalopathy with VWM was made on the basis of genetic analysis.

Fright is a provoking factor in vanishing white matter disease

Leukoencephalopathy with vanishing white matter is an inherited disorder with a chronic progressive disease course and additional episodes of rapid neurological deterioration. These episodes typically are provoked by febrile infections or minor head trauma. We report on two patients who experienced an episode of rapid neurological deterioration after a fright.

La leucoencéphalopathie mégalencéphalique avec kystes sous-corticaux : étude d’une famille libanaise et revue de la littérature

INTRODUCTION

Megalencephalic leukoencephalopathy with subcortical cysts is a rare disease with autosomal recessive inheritance.

MATERIALS AND METHODS

Two brothers born from a consanguineous marriage, presenting with the phenotype of the disease, their parents, brothers and sisters were examined. Magnetic resonance imaging of the brain was performed for the two patients. Sequence analysis of MLC1 (GenBank mRNA accession no. NM_OI5166) was performed for the patients using intronic primers. PCR restriction fragment length polymorphism analysis was done in patients, their parents and in 100 Lebanese controls in order to exclude gene polymorphism.

RESULTS

The clinical features were characteristic of the disease, consisting of an early-onset macrocephaly followed by slowly progressive ataxia, pyramidal tract involvement and epileptic seizures. In one patient, the clinical manifestations were aggravated by a trivial brain trauma. In his brother and in one female cousin, a status epilepticus was precipitated by a febrile syndrome. The diffuse cerebral white matter lesions and the subcortical temporo-polar and frontal cysts, best seen on MRI, allowed making the diagnosis. Molecular genetics revealed a new mutation involving the MLC1 gene (263G-->T, exon 3). As a consequence, it affects the second transmembrane domain predict (G88V) of the MLC protein (protein sequence NP_055981). The mutation was confirmed by PCR restriction fragment length polymorphism analysis.

CONCLUSION

Megalencephalic leucoencephalopathy with subcortical cysts may be individualized on clinical and radiological basis and confirmed by molecular genetics. In this Lebanese family, a new mutation of the MLC1 gene is reported.

A neuroimaging approach to inborn errors of metabolism

There are numerous neurodegenerative and neurometabolic disorders of childhood. Individually, however, they are quite rare. Some may be seen only once in a lifetime at a given medical center, even one devoted to the specialized care of children. This article presents the classic neuroimaging features of some of the more commonly seen entities and of some of the more recently described metabolic disorders.

Severe hypomyelination associated with increased levels of N-acetylaspartylglutamate in CSF

BACKGROUND

Two unrelated girls had early onset of nystagmus and epilepsy, absent psychomotor development, and almost complete absence of myelin on cerebral MRI. The clinical features and MR images of both patients resembled the connatal form of Pelizaeus-Merzbacher disease (PMD), which is an X-linked recessive disorder caused by duplications or mutations of the proteolipid protein gene (PLP).

OBJECTIVE

To define a unique neurometabolic disorder with failure of myelination.

METHOD

S AND RESULTS: 1H-NMR of CSF in both girls was performed repeatedly, and both showed highly elevated concentrations of N-acetylaspartylglutamate (NAAG). The coding sequence of the gene coding for glutamate carboxypeptidase II, which converts NAAG to N-acetylaspartate (NAA) and glutamate, was entirely sequenced but revealed no mutations. Even though both patients are girls, the authors sequenced the PLP gene and found no abnormality.

CONCLUSIONS

NAAG is an abundant peptide neurotransmitter whose exact role is unclear. NAAG is implicated in two cases of unresolved severe CNS disorder. Its elevated concentration in CSF may be the biochemical hallmark for a novel neurometabolic disorder. The cause of its accumulation is still unclear.

Neuroimaging in leukodystrophies

The application of techniques based on in vivo magnetic resonance to the study of leukodystrophies is evaluated. Magnetic resonance imaging (MRI), the most important neuroimaging modality for patients with leukodystrophies, has proven invaluable for the detection of the extent and etiology of white-matter involvement, diagnosis, and monitoring of disease progression. Proton magnetic resonance spectroscopy, which can detect several brain metabolites, including those related to axonal function and myelination, can provide additional diagnostic and prognostic information and, in some cases, allows a rare insight into the biochemical pathology of leukodystrophies. The potential of other advanced magnetic resonance techniques, including diffusion tensor imaging, magnetization transfer contrast, and molecular imaging, is also discussed. In the future, anatomic and physiologic magnetic resonance techniques are expected to be integrated into a single examination that will provide a detailed characterization of white-matter diseases in children.

Ribose-5-phosphate isomerase deficiency: new inborn error in the pentose phosphate pathway associated with a slowly progressive leukoencephalopathy

The present article describes the first patient with a deficiency of ribose-5-phosphate isomerase (RPI) (Enzyme Commission number 5.3.1.6) who presented with leukoencephalopathy and peripheral neuropathy. Proton magnetic resonance spectroscopy of the brain revealed highly elevated levels of the polyols ribitol and D-arabitol, which were subsequently also found in high concentrations in body fluids. Deficient activity of RPI, one of the pentose-phosphate-pathway (PPP) enzymes, was demonstrated in fibroblasts. RPI gene-sequence analysis revealed a frameshift and a missense mutation. Recently, we described a patient with liver cirrhosis and abnormal polyol levels in body fluids, related to a deficiency of transaldolase, another enzyme in the PPP. RPI is the second known inborn error in the reversible phase of the PPP, confirming that defects in pentose and polyol metabolism constitute a new area of inborn metabolic disorders.

Pattern of White Matter Abnormalities at MR Imaging: Use of Polymerase Chain Reaction Testing of Guthrie Cards to Link Pattern with Congenital Cytomegalovirus Infection

PURPOSE

To define a magnetic resonance (MR) imaging pattern suggestive of congenital cytomegalovirus (CMV) infection by using polymerase chain reaction (PCR) testing to detect CMV DNA in neonatal blood on Guthrie cards for validation.

MATERIALS AND METHODS

On the basis of findings in eight patients with documented congenital CMV infection, the authors developed MR imaging inclusion criteria, including multifocal lesions predominantly located in the deep parietal white matter. If gyral abnormalities were present, white matter lesions were either multifocal or diffuse. The criteria were applied to 152 patients with static leukoencephalopathy of unknown etiology. Guthrie cards for 22 of the 43 patients fulfilling the MR imaging criteria, 20 patients not fulfilling them, and 300 control subjects were analyzed. Fisher exact testing was used to evaluate the association between MR imaging characteristics and CMV status, and backward elimination linear discriminant analysis was used to identify MR imaging characteristics predictive of CMV infection in addition to the initial criteria.

RESULTS

PCR test results were positive in 12 of 22 patients suspected of having congenital CMV infection, in no patient not suspected of having infection (P <.001), and in two of 300 control subjects (negative predictive value [NPV] of MR imaging criteria, 100% [95% CI: 83%, 100%]; positive predictive value [PPV], 55% [95% CI: 32%, 76%]). The most important additional MR imaging finding predicting a positive PCR result was abnormality of the anterior part of the temporal lobe, including abnormal white matter, cysts, and enlargement of inferior horns. Including this finding in the MR imaging criteria enhanced the PPV (89%; 95% CI: 52%, 99%) at the expense of the NPV (88%; 95% CI: 72%, 97%).

CONCLUSION

In patients with static encephalopathy, an MR imaging pattern of multifocal lesions predominantly involving deep parietal white matter, with or without gyral abnormalities, is predictive of congenital CMV infection. When gyral abnormalities are present, leukoencephalopathy may also be diffuse. The presence of abnormalities in the anterior part of the temporal lobe increases the likelihood that CMV infection is present.

Aicardi-Goutières syndrome: neuroradiological findings after nine years of follow-up

The main radiological features of Aicardi-Goutières syndrome include basal ganglia calcification, cerebral atrophy and white matter alterations. We present a case where progress of cerebral calcifications demonstrated on consecutive CT-scans later on was followed by a decrease. The MRI showed a progressive and significant loss of white matter and severe signal changes of the remaining myelin. The aetiology of the myelin changes and the transient worsening of the cerebral calcifications remains to be elucidated. It has previously been shown that the spinal fluid level of interferon-alpha decreases with age and we suggest that the biphasic course of the calcifications and the ventricular size as well as the clinical course shown in many patients with Aicardi-Goutières might favor a causal role of interferon-alpha in the disease leading to a transient microangiopathy.

eIF2B-related disorders: antenatal onset and involvement of multiple organs

Leukoencephalopathy with vanishing white matter, also called "childhood ataxia with central nervous system hypomyelination," is the first human disease related to mutations in any of the five genes encoding subunits of eukaryotic initiation factor eIF2B or any translation factor at all. eIF2B is essential in all cells of the body for protein synthesis and the regulation of this protein synthesis under different stress conditions. It is surprising that mutations in the eIF2B genes have been reported to lead to abnormalities of the white matter of the brain only, although it has been shown recently that ovarian failure may accompany the leukoencephalopathy. Another surprising observation is that the onset of the disease varies from early childhood to adulthood, with the exception of Cree leukoencephalopathy, a disease related to a particular mutation in one of the eIF2B genes, which invariably has its onset within the first year of life. We analyzed the eIF2B genes of nine patients with an antenatal- or early-infantile-onset encephalopathy and an early demise and found mutations in eight of the patients. In addition to signs of a serious encephalopathy, we found oligohydramnios, intrauterine growth retardation, cataracts, pancreatitis, hepatosplenomegaly, hypoplasia of the kidneys, and ovarian dysgenesis. Until now, no evidence had been found for a genotype-phenotype correlation, but the consistently severe phenotype in affected siblings among our patients and in Cree encephalopathy patients suggests an influence of the genotype on the phenotype.

A new leukoencephalopathy with brainstem and spinal cord involvement and high lactate

We identified eight patients with a distinct magnetic resonance imaging pattern of inhomogeneous cerebral white matter abnormalities and selective involvement of brainstem and spinal tracts. Proton magnetic resonance imaging showed increased lactate in the abnormal white matter. Clinically, the patients had slowly progressive pyramidal, cerebellar, and dorsal column dysfunction. The uniform, highly characteristic magnetic resonance imaging pattern and the similarities in clinical and magnetic resonance spectroscopy findings provide evidence for a new disease entity. Autosomal recessive inheritance is likely.

Neuroradiology of the central nervous system in childhood

The purpose of this article is to familiarize readers with new imaging applications, identify the relative strengths of imaging modalities, and emphasize practical applications of imaging the child's nervous system. Because of recent advances in MRI, the article emphasizes the expanding role of MRI in evaluating children with neurologic disease.

Infantile spongiform leukoencephalopathy: clinical and neuropathologic findings

A 10-month-old male with spongy leukoencephalopathy is presented. Neurologic manifestations included feeding difficulties, horizontal nystagmus, and spasticity at 5 months of age. His head circumference was within the normal range. Radiologic examination demonstrated a diffuse white matter disorder. There was no detectable biochemical abnormality. He followed a neurologically progressive course. Neuropathologic findings revealed characteristic vacuolar changes in the white matter located immediately under the cortex with spongy alterations of the entire subcortical white matter, including intense astrocytic gliosis and marked vascular hyperplasia. Tissue of the matrix was destroyed in the deep white matter to form cystic areas of degeneration. White matter myelin development was severely disturbed compared with that of a normal infant of the same age. Cortical neuronal cells were preserved and did not reveal any specific abnormalities. Electron microscopic examination revealed that each vacuole in the white matter was covered by several layers of myelin structures, and intralamellar splits of white matter myelin were observed. These neuropathologic findings are also observed in some known inherent metabolic disorders. The present patient, however, did not demonstrate any metabolic abnormalities. These findings suggested a new genetic disorder of myelin metabolism.

Mutations in each of the five subunits of translation initiation factor eIF2B can cause leukoencephalopathy with vanishing white matter

Leukoencephalopathy with vanishing white matter is a recently defined autosomal recessive disorder. The course is chronic progressive with additional episodes of rapid deterioration, provoked by fever and minor head trauma. A previous study showed that mutations in the genes encoding the epsilon- or the beta-subunit of the eukaryotic translation initiation factor eIF2B, a complex consisting of five subunits, cause the disease in most patients. Seven unsolved patients remained. The unsolved patients were investigated by mutation analysis of the genes encoding the alpha-, gamma-, and delta-subunit of eIF2B and the gene encoding the alpha-subunit of eIF2, because phosphorylation of this latter subunit regulates eIF2B activity. Mutations were found in the genes encoding the alpha- (1 patient), gamma- (2 patients), and delta-subunits (2 patients) of eIF2B, but no mutations were found in the gene encoding the alpha-subunit of eIF2. In 2, both less typical patients, no mutations were found. Mutations in all five genes eIF2B subunit genes can cause VWM. eIF2B is essential for the initiation of translation of RNA into protein and is involved in regulation of the process, especially under circumstances of stress, such as fever. A defect in eIF2B may explain the sensitivity to stress factors in vanishing white matter patients.