Increased cerebrospinal fluid glycine: a biochemical marker for a leukoencephalopathy with vanishing white matter

Proteomic dissection of vanishing white matter pathogenesis

Vanishing white matter (VWM) is a leukodystrophy caused by biallelic pathogenic variants in eukaryotic translation initiation factor 2B. To date, it remains unclear which factors contribute to VWM pathogenesis. Here, we investigated the basis of VWM pathogenesis using the 2b5ho mouse model. We first mapped the temporal proteome in the cerebellum, corpus callosum, cortex, and brainstem of 2b5ho and wild-type (WT) mice. Protein changes observed in 2b5ho mice were then cross-referenced with published proteomic datasets from VWM patient brain tissue to define alterations relevant to the human disease. By comparing 2b5ho mice with their region- and age-matched WT counterparts, we showed that the proteome in the cerebellum and cortex of 2b5ho mice was already dysregulated prior to pathology development, whereas proteome changes in the corpus callosum only occurred after pathology onset. Remarkably, protein changes in the brainstem were transient, indicating that a compensatory mechanism might occur in this region. Importantly, 2b5ho mouse brain proteome changes reflect features well-known in VWM. Comparison of the 2b5ho mouse and VWM patient brain proteomes revealed shared changes. These could represent changes that contribute to the disease or even drive its progression in patients. Taken together, we show that the 2b5ho mouse brain proteome is affected in a region- and time-dependent manner. We found that the 2b5ho mouse model partly replicates the human disease at the protein level, providing a resource to study aspects of VWM pathogenesis by highlighting alterations from early to late disease stages, and those that possibly drive disease progression.

Startle Seizures and Diffuse Leukoencephalopathy After Resolution of Herpes Simplex Virus 1 Encephalitis in a Child

We describe a unique clinical presentation of a child after the acute phase of herpes simplex virus 1 (HSV1) encephalitis. A 17-month-old boy first presented with HSV1 encephalitis and was promptly treated with antiviral medication. Seven months later, he was re-admitted for startle seizures. Magnetic Resonance Imaging of the brain showed diffuse confluent leukoencephalopathy. This constellation of symptoms has not been previously reported in HSV1 encephalitis. In conclusion, we showed that brain injury due to HSV1 encephalitis can be associated with the development of startle seizures and diffuse white matter injury in the post-acute phase.

Therapy Trial Design in Vanishing White Matter: An Expert Consortium Opinion

Vanishing white matter (VWM) is a leukodystrophy caused by recessive variants in the genes EIF2B1-EIF2B5. It is characterized by chronic neurologic deterioration with superimposed stress-provoked episodes of rapid decline. Disease onset spans from the antenatal period through senescence. Age at onset predicts disease evolution for patients with early onset, whereas disease evolution is unpredictable for later onset; patients with infantile and early childhood onset consistently have severe disease with rapid neurologic decline and often early death, whereas patients with later onset have highly variable disease. VWM is rare, but likely underdiagnosed, particularly in adults. Apart from measures to prevent stressors that could provoke acute deteriorations, only symptomatic care is currently offered. With increased insight into VWM disease mechanisms, opportunities for treatment have emerged. EIF2B1-EIF2B5 encode the 5-subunit eukaryotic initiation factor 2B complex, which is essential for translation of mRNAs into proteins and is a principal regulator of the integrated stress response (ISR). ISR deregulation is central to VWM pathology. Targeting components of the ISR has proven beneficial in mutant VWM mouse models, and several drugs are now in clinical development. However, clinical trials in VWM pose considerable challenges: low numbers of known patients with VWM, unpredictable disease course for patients with onset after early childhood, absence of intermediate biomarkers, and novel first-in-human molecular targets. Given these challenges and considering the critical need to offer therapies, we have formulated recommendations for enhanced diagnosis, drug trial setup, and patient selection, based on our expert evaluation of molecular, laboratory, and clinical data.

Isocaloric low protein diet in a mouse model for vanishing white matter does not impact ISR deregulation in brain, but reveals ISR deregulation in liver

Objective: Vanishing white matter (VWM) is a genetic brain white matter disorder caused by mutations in eIF2B. eIF2B is central in the integrated stress response (ISR), during which its activity is inhibited by various cellular stresses. VWM is a chronic progressive disease with episodes of rapid neurological deterioration provoked by stresses. VWM patients and VWM mouse models show ISR deregulation in brain, correlating with chronic disease development. ISR inhibition ameliorates the chronic disease in VWM mice. The subacute deteriorations have not been modeled yet. We hypothesized that ISR activation could worsen disease progression in mice and model the episodic neurological deterioration.Method: We chose to activate the ISR by subjecting wild-type (wt) and VWM mice to an isocaloric low protein diet. This model would allow us to investigate the contribution of ISR activation in subacute decline in VWM.Results: We found that the low protein diet did not significantly affect amino acid levels nor ISR levels in wt and VWM mouse brain. Our study serendipitously led to the discovery of increased levels of glycine, asparagine and Fgf21 mRNA in VWM mouse brain irrespective of the dietary protein content. Strikingly, the ISR was not activated by the low protein diet in the liver of VWM in contrast to wt mice, due to a modest ISR deregulation in this organ.Discussion: A model for subacute neurological deterioration in VWM was not established. Possibly, ISR deregulation in VWM results in reduced ISR responsiveness.

The disappearance of white matter in an adult-onset disease: a case report

BACKGROUND

Vanishing white matter disease (VWMD) is one of the most prevalent hereditary white matter diseases in childhood, but it is increasingly recognised in adulthood with high phenotypic variation and severity.

CASE PRESENTATION

We report a case of an adult female presenting with emotional lability and cognitive impairment, in addition to progressive dystonia, ataxia, postural instability and recurrent falls. Magnetic resonance imaging (MRI) of the brain and genetic testing confirmed the diagnosis of VWMD.

CONCLUSIONS

VWMD has a broad clinical presentation in adulthood, and the age at onset of symptoms is one of its most important prognostic factors. It is crucial to recognize the pathognomonic MRI patterns and consider VWMD as a differential diagnosis when assessing patients presenting with psychiatric, cognitive and non-specific neurological symptoms.

Vanishing white matter: deregulated integrated stress response as therapy target

Objective

Vanishing white matter (VWM) is a fatal, stress‐sensitive leukodystrophy that mainly affects children and is currently without treatment. VWM is caused by recessive mutations in eukaryotic initiation factor 2B (eIF2B) that is crucial for initiation of mRNA translation and its regulation during the integrated stress response (ISR). Mutations reduce eIF2B activity. VWM pathomechanisms remain unclear. In contrast with the housekeeping function of eIF2B, astrocytes are selectively affected in VWM. One study objective was to test our hypothesis that in the brain translation of specific mRNAs is altered by eIF2B mutations, impacting primarily astrocytes. The second objective was to investigate whether modulation of eIF2B activity could ameliorate this altered translation and improve the disease.

Methods

Mice with biallelic missense mutations in eIF2B that recapitulate human VWM were used to screen for mRNAs with altered translation in brain using polysomal profiling. Findings were verified in brain tissue from VWM patients using qPCR and immunohistochemistry. The compound ISRIB (for “ISR inhibitor”) was administered to VWM mice to increase eIF2B activity. Its effect on translation, neuropathology, and clinical signs was assessed.

Results

In brains of VWM compared to wild‐type mice we observed the most prominent changes in translation concerning ISR mRNAs; their expression levels correlated with disease severity. We substantiated these findings in VWM patients’ brains. ISRIB normalized expression of mRNA markers, ameliorated brain white matter pathology and improved motor skills in VWM mice.

Interpretation

The present findings show that ISR deregulation is central in VWM pathomechanisms and a viable target for therapy.

LEUKOENCEPHALOPATHY WITH EVANESCENT WHITE MATTER: A CASE REPORT

Objective:

To describe the case of a child diagnosed with leukoencephalopathy with vanishing white matter (LVWM), a rare genetic disease with autosomal recessive inheritance pattern.

Case description:

A 5-month-old male child started to refuse breast-feeding, showing somnolence and signs of dehydration,with dry mouth, increasing body temperature and adipsy. As days went by, the symptoms got worse. The infant was very sleepy and was transferred to the intensive care unit, where he stayed for one week. At this time, a signal alteration with hyper attenuated T2 predominance was identified in the magnetic resonance imaging, compromising the white matter, which had diffuse and symmetrical aspect. At this time, the infant started to present seizures. When the infant was 11 months old, he was diagnosed with tonsillitis and presented recurrent fever peaks and extreme sleepiness. After hospital admission, the infant progressed to a comatose state and died. The diagnosis of LVWM was confirmed in examinations performed after death. As a late diagnosis, a genetic disease was identified with a mutation in one of the five genes responsible for the codification of complex eukaryotic translation initiation factor 2B (eIF2B), involved with the control of the protein translation and which is described as pathogenic in individuals with LVWM.

Comments:

LVWM is a hereditary brain disease that occurs primarily in children. The disease is chronic and progressive, with additional episodes of rapid deterioration, as shown in the present case report.

Clinical Use of CSF Neurotransmitters

BACKGROUND

Cerebrospinal fluid neurotransmitter collection, analysis, and follow-up are integral to the diagnosis and management of multiple inborn metabolic errors, some of which require prompt identification and intervention to improve outcome. Cerebrospinal fluid pterins and monoamine metabolites are diagnostic in a range of primary neurotransmitter disorders, including disorders of biogenic amine synthesis, metabolism, and transport.

RELEVANT DISORDERS

Recently described mutations of the human dopamine transporter are associated with an elevated cerebrospinal fluid homovanillic acid:hydroxyindoleacetic acid ratio. Disorders of pyridoxine metabolism are also detectable via cerebrospinal fluid quantification of bioamines, amino acids, and pyridoxal-5-phosphate levels. Cerebrospinal fluid amino acids are diagnostic in disorders of gamma aminobutyric acid, glycine, and serine metabolism. A wide range of acquired and genetic disorders has also been associated with secondary alterations in cerebrospinal fluid levels of monoamine metabolites, glycine, and neopterin.

CONCLUSIONS

Lumbar puncture is required to detect abnormal cerebrospinal fluid metabolites in a significant proportion of these disorders, including treatable entities such as dopa-responsive deficiencies of guanosine-5'-triphosphate cyclohydrolase I (Segawa disease), sepiapterin reductase, and tyrosine hydroxylase.

Neurotransmitter signaling in white matter

White matter (WM) tracts are bundles of myelinated axons that provide for rapid communication throughout the CNS and integration in grey matter (GM). The main cells in myelinated tracts are oligodendrocytes and astrocytes, with small populations of microglia and oligodendrocyte precursor cells. The prominence of neurotransmitter signaling in WM, which largely exclude neuronal cell bodies, indicates it must have physiological functions other than neuron-to-neuron communication. A surprising aspect is the diversity of neurotransmitter signaling in WM, with evidence for glutamatergic, purinergic (ATP and adenosine), GABAergic, glycinergic, adrenergic, cholinergic, dopaminergic and serotonergic signaling, acting via a wide range of ionotropic and metabotropic receptors. Both axons and glia are potential sources of neurotransmitters and may express the respective receptors. The physiological functions of neurotransmitter signaling in WM are subject to debate, but glutamate and ATP-mediated signaling have been shown to evoke Ca(2+) signals in glia and modulate axonal conduction. Experimental findings support a model of neurotransmitters being released from axons during action potential propagation acting on glial receptors to regulate the homeostatic functions of astrocytes and myelination by oligodendrocytes. Astrocytes also release neurotransmitters, which act on axonal receptors to strengthen action potential propagation, maintaining signaling along potentially long axon tracts. The co-existence of multiple neurotransmitters in WM tracts suggests they may have diverse functions that are important for information processing. Furthermore, the neurotransmitter signaling phenomena described in WM most likely apply to myelinated axons of the cerebral cortex and GM areas, where they are doubtless important for higher cognitive function.

Multiple sclerosis in children

The onset of multiple sclerosis (MS) in childhood and adolescence is being increasingly recognized. Relative to MS in adults, little is known about the diagnostic evaluation, clinical course, outcome, and management of MS in children. To remedy some of these deficiencies, pediatric MS clinics have been created in several countries to provide specialized care to, and to study, affected children. Research is currently underway to investigate the pathobiologic features of childhood-onset MS, to study the mechanisms of myelin inflammation and repair, to evaluate patient outcomes collaboratively between the different clinics, and to increase knowledge of pediatric MS for children living with the disease. It is hoped that, through an understanding of the earliest aspects of the MS disease process, critical insights will be gained about the genesis of MS.

Epileptic encephalopathy with suppression-bursts and nonketotic hyperglycinemia

Bursts of paroxysmal activity alternating with lack of activity define the suppression-burst (SB) pattern that may be acute, in hypoxic-ischemic encephalopathy and barbiturate intoxication, or chronic in the course of early epileptic and neonatal myoclonic (NME) encephalopathies. Malformations, namely Aicardi syndrome and hemimegalencephaly, gene mutations - of ARX and MUNC18 -, and inborn errors of metabolism, namely glycine encephalopathy, are the main causes, with spasms indicating more likely a malformation whereas myoclonus indicates metabolic disorders. Although glycine encephalopathy has a very severe outcome in its classical expression, it may be transient in the neonatal period, for reasons yet not identified. Although glycine encephalopathy is the main identified cause of NME, the disorder may not cause SB, especially in cases with later onset. The biochemical bases, due to changes in one of the four proteins that compose the enzyme, are well understood, but there is no phenotype-genotype correlation. Prenatal diagnosis is based on villous biopsy. The mechanism of SB partly depends on glutamate - or glycine, the co-neurotransmitter for NMDA transmission - overflow, mainly in the immature brain but also in cases due to barbiturate intoxication. Energy supply defect may also be involved in some inborn errors of metabolism.

Vanishing white matter: the next 10 years

Vanishing white matter (VWM) is an inherited and often severe brain disease. It is caused by mutations in the genes for eIF2B, a protein that plays a key role in mRNA translation. The age of onset and clinical features are highly variable. In severe cases, onset may be antenatal and other organs are affected. The main feature is always a progressive encephalopathy, faster deterioration being provoked by head injury or febrile infections. The myelinating cells, oligodendrocytes, are affected in VWM. Initial studies suggested that VWM mutations decreased eIF2B’s activity. However, recent findings indicate that the situation is more complex. Studies in human brain samples or a mouse model for VWM indicate that development of astroglial cells and oligodendrocytes is impaired. Defects in eIF2B likely affect cell stress pathways and the expression of specific proteins, although their identities remain unknown.

[Case of adult onset vanishing white matter disease developed after minor head trauma]

A 20-year-old previously healthy man presented with prolonged consciousness alteration and severe hypertonia in the extremities after minor head trauma. Laboratory blood tests and cerebrospial fluid (CSF) tests were unremarkable except for an elevated CSF glycine concentratons. Brain MRI revealed hypoplasia of corpus callosum, enlargement of lateral cerebral ventricle and high signal intensity in the bilateral white matter on T(2) weighted images. On fluid attenuated inversion recovery images, the signal intensity resembled that of CSF in the central areas of T(2) alterations, surrounded by a rim of hyperintensity. These characteristic history and the results of brain MRI and CSF, the diagnosis of vanishing white matter disease (VWMD) was made. VWMD is a rare autosomal recessive leukoencephalopathy which typically begins during infancy or early childhood with a chronic progressive neurological deterioration with cerebellar ataxia and spasticity. Recently, milder variants of the disease with adult onset have been reported. VWMD should be included in the differential diagnosis of leucoencephalopathy in young adults.

Late-onset nonketotic hyperglycinemia caused by a novel homozygous missense mutation in the GLDC gene

Nonketotic hyperglycinemia (NKH) is an inborn error of the glycine metabolism. A 9-year-old boy with learning disability and intermittent choreoathetosis during febrile illnesses had elevated plasma glycine level and CSF/plasma glycine ratio (0.044) and a novel homozygous missense mutation (c.605C>T; p.Ala202Val) in the GLDC gene, confirming the diagnosis of NKH. This is the first report of late-onset NKH with a confirmed underlying genetic defect. NKH should be in the differential diagnosis of intermittent choreoathetosis.

Pitfalls in measuring cerebrospinal fluid glycine levels in infants with encephalopathy

In encephalopathic infants, cerebrospinal fluid hyperglycinemia and elevated cerebrospinal fluid to plasma glycine ratio are considered pathognomonic of nonketotic hyperglycinemia. To evaluate the significance of cerebrospinal fluid hyperglycinemia and elevated cerebrospinal fluid to plasma glycine ratio in acutely encephalopathic infants, a retrospective chart review of all cases of isolated elevation of cerebrospinal fluid glycine levels at Arkansas Children's Hospital from January 1995 to December 2000 was performed. Twenty-two patients (14 males) were included. The most common diagnosis was hypoxic ischemic encephalopathy (n = 8). Nine patients had elevated cerebrospinal fluid to plasma glycine ratio, which was transient in 7 patients. This study shows that elevated cerebrospinal fluid to plasma glycine ratio can be encountered in a variety of clinical conditions. The significance of this observation in light of the poor prognosis of nonketotic hyperglycinemia and the possible role of glycine in the mechanism of ischemic neuronal injury is addressed.

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.

Vacuolar leucoencephalopathy and pulvinar sign in association with coeliac disease

Several neurological disorders have been associated with coeliac disease, including epilepsy, ataxia and neuropathy. Here we report a rare case of white matter disease in a 55-year-old man with coeliac disease. He presented with anxiety, headache and left upper limb jerking. He subsequently developed epilepsy and brain MRI revealed diffuse white matter abnormality. He died 6 months after presentation due to status epilepticus and sepsis. Brain biopsy demonstrated vacuolar leucoencephalopathy with no evidence of vCJD. An extensive clinical screen excluded infectious, inflammatory and para-neoplastic causes for this condition. Coeliac disease may be causally associated with vacuolar leucoencephalopathy in this case.

Sensitivity and specificity of decreased CSF asialotransferrin for eIF2B-related disorder

OBJECTIVE

This is a study estimating diagnostic accuracy of CSF asialotransferrin to transferrin ratio measurement in eIF2B related disorders by using clinical evaluation and EIF2B mutation analysis as the reference standard. eIF2B-related disorder is a relatively common leukodystrophy with broad phenotypic variation that is caused by mutations in any of the five EIF2B genes. There is a need for a simple and clinically valid screening tool for physicians evaluating patients with an unclassified leukodystrophy.

METHODS

CSF two-dimensional gel (2DG) electrophoresis analyses to measure asialotransferrin to transferrin ratios were performed in 60 subjects including 6 patients with documented EIF2B gene mutations, patients with other types of leukodystrophy, and patients with no leukodystrophy.

RESULTS

All six patients with mutation proven eIF2B-related disease showed low to nearly undetectable amounts of asialotransferrin in their CSF when compared to 54 unaffected controls by CSF 2DG analyses in this study. eIF2B-like patients, with clinically similar presentations but no mutations in EIF2B1-5, were distinguished from patients with mutations in EIF2B1-5 by this biomarker. Patients with mutations in EIF2B1-5 had asialotransferrin/transferrin ratio levels significantly different from the group as a whole (p < 0.001). Using 8% asialotransferrin/transferrin ratio as a cutoff, this biomarker has a 100% sensitivity (95% CI = 52-100%) and 94% specificity (95% CI = 84-99%).

CONCLUSION

Decreased asialotransferrin/transferrin ratio in the CSF of patients with eIF2B-related disorder is highly sensitive and specific. This rapid (<48 hours) and inexpensive diagnostic tool for eIF2B-related disorders has the potential to identify patients with likely eIF2B-related disorder for mutation analysis.

Late-onset nonketotic hyperglycinemia with leukodystrophy and an unusual clinical course

Late-onset nonketotic hyperglycinemia is very rare, presents with varied clinical features, and may be underdiagnosed. A 2-year-old girl with normal development had acute gait disturbance progressing to severe spastic diplegia. Plasma glycine levels were elevated, with a normal cerebrospinal fluid:plasma glycine ratio. Cranial magnetic resonance imaging revealed leukodystrophy. Nonketotic hyperglycinemia was confirmed enzymatically. At age 7 years, she cannot walk, but has borderline normal intelligence. Leukodystrophy and a normal cerebrospinal fluid:plasma glycine ratio were not previously reported in late-onset nonketotic hyperglycinemia.

High-affinity glycine and glutamate transport in pig forebrain white and gray matter: A quantitative study

High-affinity uptake of glycine and glutamate modulates glutamatergic neurotransmission in gray matter. N-Methyl-D-aspartate (NMDA) receptors were recently described on white matter oligodendrocytes, therefore uptake of glutamate and glycine in white matter may also modulate NMDA receptor function. We found that glycine uptake in white structures of pig forebrain (corpus callosum, fimbria, subcortical pyramidal tracts, and occipital subcortical white matter) was similar to that in gray structures (frontal and temporal cortices and hippocampus), and that it was sensitive to sarcosine, a GLYT1 inhibitor (IC(50) 15 microM). Glutamate uptake in white matter was approximately 10% of that in gray; it was sensitive to dihydrokainate, an EAAT2 inhibitor. The levels of glycine and its precursor serine were similar in white and gray matter: approximately 2 and 1 nmol/mg tissue, respectively. The white matter level of glutamate was approximately 7.6 nmol/mg tissue, or approximately 74% of gray matter levels. The activity of serine hydroxymethyl transferase, which converts serine into glycine, was similar in white and gray matter (11-18 pmol/(mg tissue)min), whereas the white matter activity of phosphate-activated glutaminase, which converts glutamine into glutamate, was approximately 100 pmol/(mg tissue)min, or approximately 34% of gray matter activity. The white matter activity of glutamine synthetase, the glial enzyme that converts glutamate into glutamine, was 20-40 nmol/(mg tissue)min in neocortex and 5-6 nmol/(mg tissue)min in white matter. The data show that forebrain white matter is equipped to regulate extracellular levels of glycine and glutamate, functions that may modulate white matter NMDA receptor function.

Progressive vacuolating glycine leukoencephalopathy with pulmonary hypertension

To report two unrelated patients with a new phenotype of nonketotic hyperglycinemia associated with idiopathic pulmonary hypertension. Clinical findings included rapidly progressive neurological deterioration with onset in the first year of life characterized by developmental regression without seizures or electroencephalogram abnormalities during follow-up. Both patients died before the age of 18 months. Glycine cleavage system deficiency was confirmed by enzymatic studies in frozen liver. Molecular analysis in the related genes showed no pathogenic mutation. Radiological and pathological findings were consistent with progressive vacuolating encephalopathy. Our patients with biochemical and enzymatic parameters consistent with atypical nonketotic hyperglycinemia. The clinical and radiological evolution, as progressive vacuolating leukoencephalopathy and the association with pulmonary hypertension constitute a previously unrecognized variant.

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.

Comprehensive mutation analysis ofGLDC,AMT, andGCSHin nonketotic hyperglycinemia

Nonketotic hyperglycinemia (NKH) is an inborn error of metabolism characterized by accumulation of glycine in body fluids and various neurological symptoms. NKH is caused by deficiency of the glycine cleavage multi-enzyme system with three specific components encoded by GLDC, AMT, and GCSH. We undertook the first comprehensive screening for GLDC, AMT, and GCSH mutations in 69 families (56, six, and seven families with neonatal, infantile, and late-onset type NKH, respectively). GLDC or AMT mutations were identified in 75% of neonatal and 83% of infantile families, but not in late-onset type NKH. No GCSH mutation was identified in this study. GLDC mutations were identified in 36 families, and AMT mutations were detected in 11 families. In 16 of the 36 families with GLDC mutations, mutations were identified in only one allele despite sequencing of the entire coding regions. The GLDC gene consists of 25 exons. Seven of the 32 GLDC missense mutations were clustered in exon 19, which encodes the cofactor-binding site Lys754. A large deletion involving exon 1 of the GLDC gene was found in Caucasian, Oriental, and black families. Multiple origins of the exon 1 deletion were suggested by haplotype analysis with four GLDC polymorphisms. This study provides a comprehensive picture of the genetic background of NKH as it is known to date.

MR Spectroscopy of Metabolic Disorders

The application of MR spectroscopy (MRS) in pediatric brain disorders yields valued information on pathologic processes, such as ischemia, demyelination, gliosis, and neurodegeneration. Because these processes manifest in inborn errors of metabolism, the purposes of this article are to (1) describe the spectral changes that are associated with the relatively common metabolic disorders, with summaries of known spectroscopic features of these disorders; (2) offer suggestions for recognition and distinction of disorders; and (3) provide general guidelines for MRS implementation. Although many conditions have a similar presentation, MRS offers valuable information for the individual patient in diagnosis and therapy when integrated fully into the clinical setting.

Leucoencefalopatia megalencefálica com substância branca evanescente e cistos subcorticais

Apresentamos três casos de leucoencefalopatia megalencefálica com substancia branca evanescente e cistos subcorticais, diagnosticados através da ressonância nuclear magnética.Os casos estudados apresentam quadro clinico e radiológico de acordo com os critérios diagnósticos estabelecidos na descrição inicial desta enfermidade. São discutidos os aspectos clínicos e neuroradiológicos.

The glycine peak in brain diseases

Glycine is an excitatory amino acid, a neurotransmitter for the brain. A recent experimental study by a 9.3T laboratory spectrometer identified the peak of pure glycine at 3.52 ppm, and in a clinical case this peak was demonstrated at 3.50 ppm by a 1.5 T clinical scanner. This study was undertaken to investigate the brain diseases having the glycine peak. An experiment with a 1.5 T clinical MRI unit was performed. Two grams of pure glycine was dissolved in 200 cc of distilled water and the solution was frozen, and proton MR spectroscopy (TR=1500 ms, TE=20 ms) was obtained. Nine patients with various diseases studied by two-dimensional chemical shift spectroscopy (hybrid CSI) with TR=1500 ms, and TE=40 ms are included in the study. Ten normal cases were available for comparison. In the experiment with the clinical MRI unit, the glycine peak was centered at 3.50 ppm. The disease processes associated with distinct glycine peaks at 3.50 ppm included infarction, high-grade astrocytoma, megalencephalic leukoencephalopathy with cysts, Leigh's disease, adrenoleukodystrophy, congenital muscular dystrophy, Rasmussen's encephalitis, gliosis in neuronal migrational disorder, and hamartoma in tuberous sclerosis. None of the control cases displayed a glycine peak. In conclusion, glycine has a peak centered at 3.50 ppm in in vivo environments. It is distinct from the myoinositol peak. Detection of glycine in a wide variety of brain diseases ranging from infarction, tumor, leukoencephalopathies, infection to gliosis likely reflects presence of excitotoxic brain damage or a disturbance of neurotransmitting mechanisms in these conditions.

Proton MR spectroscopy demonstration of taurine peaks in megalencephalic leukoencephalopathy with cysts

Taurine is an amino acid. It has roles in neurotransmitter activities, facilitates synaptic connections, and possesses cyto-protective properties. Normally, it is invisible on proton MR spectroscopy acquired at low field strengths (i.e. 1.5T). In a patient with megalencephalic leukoencephalopathy with cysts (MLC), distinct taurine peaks centered at 3.35ppm were found on hybrid-CSI spectroscopy obtained at 1.5T with a long TE value (i.e. TE=135ms). This suggested increased concentrations of this metabolite in MLC. In this leukoencephalopathy taurine may be linked to a metabolic disturbance related with neurotransmitters associated with a disturbance in synaptic connections, and cyto-protective mechanisms. Further spectroscopic and clinical studies are required to evaluate this observation.

Leukoencephalopathy with patchy lesions, temporal cystic degeneration, and normal head size

A 5 yr old girl is reported with patchy white matter lesions, cystic degeneration of the temporal tips, normal cortex, and normal cerebellum, documented by FLAIR, and diffusion-weighted MRI. This condition differed from the entity megalencephalic leukoencephalopathy with cysts by lack of diffuse involvement of the white matter and cortical thinning, by presence of a normal head size, and existence of a non-progressive, severe clinical condition. Occurrence of cystic degeneration in the temporal tips distinguished the condition from other leukoencephalopathies. This leukoencephalopathy appears to be a new distinct entity.

Diagnosis and treatment of neurotransmitter-related disorders

Neurotransmitter disorders constitute a spectrum of neurologic conditions that share several clinical features depending on the severity and pattern of neurotransmitter deficiency or excess. These uncommon conditions can be suspected based on their clinical features, and several can be confirmed by cerebrospinal fluid analysis of neurotransmitters and their metabolites. Certain disorders, such as autosomal dominant dopa-responsive dystonia caused by GTP cyclohydrolase deficiency, or Segawa syndrome, respond dramatically to medical therapy. This article summarizes current knowledge regarding the clinical manifestations, diagnosis, and treatment of these important disorders.

Leukoencephalopathy with vanishing white matter: report of four cases from three unrelated Brazilian families

Four patients with leukoencephalopathy with vanishing white matter from three unrelated Brazilian families are reported. In all cases the initial symptoms occurred in the three first years of life. In three cases the onset was acute and at least in two patients the involvement of the white matter preceded the clinical symptoms. Only cerebellar and pyramidal signs were present and persisted throughout the evolution. An episodic course with worsening of the symptoms during febrile illnesses was noted in one patient. In three patients a significant deceleration of the head growth was noted. In one family, brother and sister were affected but the twin brother of the boy was free from the disease. In another family, the patient had a sister who died at 13 years of age from an identical disease not diagnosed at that time. In one family, the parents were first cousins. In all patients, serial magnetic resonance imaging and magnetic resonance spectroscopy showed the characteristic picture of the involvement of the white matter with increasing signal intensity close to that of the cerebrospinal fluid.

Nonketotic hyperglycinemia (glycine encephalopathy): laboratory diagnosis

Nonketotic hyperglycinemia (NKH) is an autosomal recessive disorder of glycine metabolism caused by a defect in the glycine cleavage enzyme complex (GCS). GCS is a complex of four proteins encoded on four different chromosomes. In classical neonatal NKH, levels of cerebrospinal fluid (CSF) glycine and CSF/plasma glycine ratio are very high but the CSF results, in particular, may be more difficult to interpret in later-onset, milder, or otherwise atypical NKH. Enzymatic confirmation of NKH requires a liver sample. Delineation of which protein of the complex is defective is necessary to screen for mutations in the appropriate gene. Except for Finnish NKH patients, few recurrent mutations have yet been found, although analysis of the P-protein gene (the site of the defect in the majority of patients) is at an early stage. Prenatal diagnosis by GCS assay in chorionic villus biopsies is not completely reliable and will be replaced by molecular analysis in families where the mutations are known.

A Japanese girl with leukoencephalopathy with vanishing white matter

A Japanese girl with peculiar leukoencephalopathy was reported. Following normal development until 1 year of age, she showed progressive neurological deterioration with ataxia, epilepsy, pyramidal tract signs and choreic movement. Serial brain computed tomographies (CTs) revealed markedly low density and progressive volume loss in whole white matter. In extensive laboratory investigations, the level of glycine in the urine was elevated. She died at the age of 4 years, and the neuropathological findings were comprised of severe extensive changes in cerebral and cerebellar white matter, such as marked rarefaction or cystic degeneration with axonal loss. The pontine central tegmental tracts were also affected. Neuronal loss was seen in the cerebellar cortex. These features were compatible with leukoencephalopathy with vanishing white matter, which was recently established as a clinical entity. To our knowledge, this is the first report of a non-Caucasian patient with this new type of leukoencephalopathy.

Update on genetic disorders affecting white matter

The classification of diseases affecting white matter has changed dramatically with the use of magnetic resonance imaging. Classical leukodystrophies, such as metachromatic leukodystrophy and Krabbe's disease, account for only a small number of inherited diseases that affect white matter. Magnetic resonance imaging has clarified genetic disorders that result in white matter changes or leukoencephalopathies. The term leukoencephalopathy is used to reflect the broader number of diseases that may cause as either primary or secondary changes in myelin development. This review attempts to categorize white matter disorders into classes such as lipid, myelin protein, organic acids, and defects in energy metabolism, in addition to other causes.

MR spectroscopy: a powerful tool for investigating brain function and neurological diseases

Magnetic resonance spectroscopy (MRS) has attracted much attention in recent years and has become an important tool to study in vivo particular biochemical aspects of brain disorders. Since the proton is the most sensitive stable nucleus for MRS, and since almost all metabolites contain hydrogen atoms, investigation by in vivo 1H MRS provides chemical information on tissue metabolites, thus enabling a non-invasive assessment of changes in brain metabolism underlying several brain diseases. In this review a brief description of the basic principles of MRS is given. Moreover, we provide some explanations on the techniques and technical problems related to the use of 1H MRS in vivo including water suppression, localization, editing, quantitation and interpretation of 1H spectra. Finally, we discuss the more recent advancement in three major areas of neurological diseases: brain tumors, multiple sclerosis, and inborn errors of metabolism.