AAV-mediated expression of mouse or human GLDC normalises metabolic biomarkers in a GLDC-deficient mouse model of Non-Ketotic Hyperglycinemia.

Non-Ketotic Hyperglycinemia (NKH) is a rare inborn error of metabolism caused by impaired function of the glycine cleavage system (GCS) and characterised by accumulation of glycine in body fluids and tissues. NKH is an autosomal recessive condition and the majority of affected individuals carry mutations in GLDC (glycine decarboxylase). Current treatments for NKH have limited effect and are not curative. As a monogenic condition with known genetic causation, NKH is potentially amenable to gene therapy. An AAV9-based expression vector was designed to target sites of GCS activity. Using a ubiquitous promoter to drive expression of a GFP reporter, transduction of liver and brain was confirmed following intra-venous and/or intra-cerebroventricular administration to neonatal mice. Using the same capsid and promoter with transgenes to express mouse or human GLDC, vectors were then tested in GLDC-deficient mice that provide a model of NKH. GLDC-deficient mice exhibited elevated plasma glycine concentration and accumulation of glycine in liver and brain tissues as previously observed. Moreover, the folate profile indicated suppression of folate one­carbon metabolism (FOCM) in brain tissue, as found at embryonic stages, and reduced abundance of FOCM metabolites including betaine and choline. Neonatal administration of vector achieved reinstatement of GLDC mRNA and protein expression in GLDC-deficient mice. Treated GLDC-deficient mice showed significant lowering of plasma glycine, confirming functionality of vector expressed protein. AAV9-GLDC treatment also led to lowering of brain tissue glycine, and normalisation of the folate profile indicating restoration of glycine-derived one­carbon supply. These findings support the hypothesis that AAV-mediated gene therapy may offer potential in treatment of NKH.

Genomic analyses of glycine decarboxylase neurogenic mutations yield a large-scale prediction model for prenatal disease.

Hundreds of mutations in a single gene result in rare diseases, but why mutations induce severe or attenuated states remains poorly understood. Defect in glycine decarboxylase (GLDC) causes Non-ketotic Hyperglycinemia (NKH), a neurological disease associated with elevation of plasma glycine. We unified a human multiparametric NKH mutation scale that separates severe from attenuated neurological disease with new in silico tools for murine and human genome level-analyses, gathered in vivo evidence from mice engineered with top-ranking attenuated and a highly pathogenic mutation, and integrated the data in a model of pre- and post-natal disease outcomes, relevant for over a hundred major and minor neurogenic mutations. Our findings suggest that highly severe neurogenic mutations predict fatal, prenatal disease that can be remedied by metabolic supplementation of dams, without amelioration of persistent plasma glycine. The work also provides a systems approach to identify functional consequences of mutations across hundreds of genetic diseases. Our studies provide a new framework for a large scale understanding of mutation functions and the prediction that severity of a neurogenic mutation is a direct measure of pre-natal disease in neurometabolic NKH mouse models. This framework can be extended to analyses of hundreds of monogenetic rare disorders where the underlying genes are known but understanding of the vast majority of mutations and why and how they cause disease, has yet to be realized.

Why does hyperglycinemia exhibit so grave brain anomalies and so severe neurological symptoms?

Nonketotic-hyperglycinemia (NKH) is an autosomal recessive disorder associated with grave brain malformations and severe neurological symptoms, and also characterized by accumulation of a large amount of glycine in body fluids. NKH is caused by an inherited deficiency of the glycine cleavage system (GCS), which is the main system to degrade glycine in mammalians. These severe symptoms and grave bran malformations are not normally observed in the other amino acid metabolic disorders, suggesting that GCS should have unknown pivotal roles in brain development and function. Interestingly, GCS is indispensable in supplying proliferating cells with 5,10-methylenetetrahydrofolate as a one-carbon donor, which is essential for the synthesis of DNA in cell proliferation. Since GCS is expressed intensely and ubiquitously in the neuroepithelium, the lack of GCS might greatly impair the proliferation of neural stem cells. On the other hand, this system is also very important to regulate extracellular glycine concentrations. Since glycine is an important neurotransmitter, which binds to both glycine receptors and NMDA receptors, high glycine concentrations caused by the deficiency of GCS might cause the aberrant neurotransmission in the patient brains. Considering these unique two faces of GCS functions, proliferation disturbance and aberrant neurotransmission are intricately mixed in the developing brain, leading to the grave brain malformations and sever neurological symptoms.

Biochemical and molecular predictors for prognosis in nonketotic hyperglycinemia.

OBJECTIVE: Nonketotic hyperglycinemia is a neurometabolic disorder characterized by intellectual disability, seizures, and spasticity. Patients with attenuated nonketotic hyperglycinemia make variable developmental progress. Predictive factors have not been systematically assessed. METHODS: We reviewed 124 patients stratified by developmental outcome for biochemical and molecular predictive factors. Missense mutations were expressed to quantify residual activity using a new assay. RESULTS: Patients with severe nonketotic hyperglycinemia required multiple anticonvulsants, whereas patients with developmental quotient (DQ) > 30 did not require anticonvulsants. Brain malformations occurred mainly in patients with severe nonketotic hyperglycinemia (71%) but rarely in patients with attenuated nonketotic hyperglycinemia (7.5%). Neonatal presentation did not correlate with outcome, but age at onset ≥ 4 months was associated with attenuated nonketotic hyperglycinemia. Cerebrospinal fluid (CSF) glycine levels and CSF:plasma glycine ratio correlated inversely with DQ; CSF glycine > 230 µM indicated severe outcome and CSF:plasma glycine ratio ≤ 0.08 predicted attenuated outcome. The glycine index correlated strongly with outcome. Molecular analysis identified 99% of mutant alleles, including 96 novel mutations. Mutations near the active cleft of the P-protein maintained stable protein levels. Presence of 1 mutation with residual activity was necessary but not sufficient for attenuated outcome; 2 such mutations conferred best outcome. Divergent outcomes for the same genotype indicate a contribution of other genetic or nongenetic factors. INTERPRETATION: Accurate prediction of outcome is possible in most patients. A combination of 4 factors available neonatally predicted 78% of severe and 49% of attenuated patients, and a score based on mutation severity predicted outcome with 70% sensitivity and 97% specificity.

Diagnosis of glycine encephalopathy in a pediatric patient by detection of a GLDC mutation during initial next generation DNA sequencing.

Early diagnosis for metabolic encephalopathy caused by inborn errors of metabolism is very important for the initiation of early treatment and also for prevention of sequela. Metabolic encephalopathy in the form of seizures can result from many inborn errors of metabolism and considering the large number of disorders causing metabolic encephalopathy, enzyme assays or conventional molecular tests are expensive and take considerably long period of time which results in delayed treatment. In our center we have used next generation DNA sequencing technology as an initial diagnostic test to look for about 700 disorders at the same time for the etiologic diagnosis of a 4-month-old female infant suffering from intractable seizures. The patient was found to have glycine encephalopathy resulting from a previously defined mutation in the GLDC gene. The diagnostic result was obtained much sooner than other conventional investigations. Up to our knowledge, this would be the first case with glycine encephalopathy in the literature who was approached by this novel panel method initially. Although currently, classical evaluation methods such as physical examination, biochemical and conventional molecular investigations are still accepted as the gold standards to clarify the etiology of the metabolic encephalopathy it is obvious that next generation sequence analysis will play a very significant role in the future.

Glycine disrupts myelin, glutamatergic neurotransmission, and redox homeostasis in a neonatal model for non ketotic hyperglycinemia.

Non ketotic hyperglycinemia (NKH) is an inborn error of glycine metabolism caused by mutations in the genes encoding glycine cleavage system proteins. Classic NKH has a neonatal onset, and patients present with severe neurodegeneration. Although glycine accumulation has been implicated in NKH pathophysiology, the exact mechanisms underlying the neurological damage and white matter alterations remain unclear. We investigated the effects of glycine in the brain of neonatal rats and MO3.13 oligodendroglial cells. Glycine decreased myelin basic protein (MBP) and myelin-associated glycoprotein (MAG) in the corpus callosum and striatum of rats on post-natal day (PND) 15. Glycine also reduced neuroglycan 2 (NG2) and N-methyl-d-aspartate receptor subunit 1 (NR1) in the cerebral cortex and striatum on PND15. Moreover, glycine reduced striatal glutamate aspartate transporter 1 (GLAST) content and neuronal nucleus (NeuN), and increased glial fibrillary acidic protein (GFAP) on PND15. Glycine also increased DCFH oxidation and malondialdehyde levels and decreased GSH concentrations in the cerebral cortex and striatum on PND6, but not on PND15. Glycine further reduced viability but did not alter DCFH oxidation and GSH levels in MO3.13 cells after 48- and 72-h incubation. These data indicate that impairment of myelin structure and glutamatergic system and induction of oxidative stress are involved in the neuropathophysiology of NKH.

The Role of Excitotoxicity, Oxidative Stress and Bioenergetics Disruption in the Neuropathology of Nonketotic Hyperglycinemia.

Nonketotic hyperglycinemia (NKH) is an inherited disorder of amino acid metabolism biochemically characterized by the accumulation of glycine (Gly) predominantly in the brain. Affected patients usually manifest with neurological symptoms including hypotonia, seizures, epilepsy, lethargy, and coma, the pathophysiology of which is still not completely understood. Treatment is limited and based on lowering Gly levels aiming to reduce overstimulation of N-methyl-D-aspartate (NMDA) receptors. Mounting in vitro and in vivo animal and human evidence have recently suggested that excitotoxicity, oxidative stress, and bioenergetics disruption induced by Gly are relevant mechanisms involved in the neuropathology of NKH. This brief review gives emphasis to the deleterious effects of Gly in the brain of patients and animal models of NKH that may offer perspectives for the development of novel adjuvant treatments for this disorder.

Paracetamol prevents hyperglycinemia in vervet monkeys treated with valproate.

Valproate administration increases the level of the inhibitory transmitter, glycine, in the urine and plasma of patients and experimental animals. Nonketotic hyperglycinemia (NKH), an autosomal recessive disorder of glycine metabolism, causes increased glycine concentrations in blood, urine, and cerebrospinal fluid (CSF), most likely due to a defect in the glycine cleavage enzyme or possibly deficits in glycine transport across cell membranes. We investigated the relationship between the hyperglycinemic effect of valproate and induced pyroglutamic aciduria via paracetamol in the vervet monkey. Firstly it was determined if valproate could induce hyperglycinemia in the monkey. The second aim was to increase glutamic acid (oxoproline) urine excretion using paracetamol as a pre-treatment and to assess whether valproate has an influence on the γ-glutamyl cycle. Hyperglycinemia was induced in healthy vervet monkeys when treated with a single oral dose of 50 mg/kg valproate. An acute dose of 50 mg/kg paracetamol increased oxoproline in the urine. Pre-treatment with paracetamol opposed the hyperglycinemic effect of valproate. However, the CSF:serum glycine ratio in a nonketotic monkey increased markedly after paracetamol treatment and remained high following valproate treatment. These results indicate that the γ-glutamyl cycle does indeed play a role in the hyperglycinemic effect of valproate treatment, and that paracetamol may have value in preventing and/or treating valproate-induced NKH.

Elevated preoptic brain activity in zebrafish glial glycine transporter mutants is linked to lethargy-like behaviors and delayed emergence from anesthesia.

Delayed emergence from anesthesia was previously reported in a case study of a child with Glycine Encephalopathy. To investigate the neural basis of this delayed emergence, we developed a zebrafish glial glycine transporter (glyt1 - / -) mutant model. We compared locomotor behaviors; dose-response curves for tricaine, ketamine, and 2,6-diisopropylphenol (propofol); time to emergence from these anesthetics; and time to emergence from propofol after craniotomy in glyt1-/- mutants and their siblings. To identify differentially active brain regions in glyt1-/- mutants, we used pERK immunohistochemistry as a proxy for brain-wide neuronal activity. We show that glyt1-/- mutants initiated normal bouts of movement less frequently indicating lethargy-like behaviors. Despite similar anesthesia dose-response curves, glyt1-/- mutants took over twice as long as their siblings to emerge from ketamine or propofol, mimicking findings from the human case study. Reducing glycine levels rescued timely emergence in glyt1-/- mutants, pointing to a causal role for elevated glycine. Brain-wide pERK staining showed elevated activity in hypnotic brain regions in glyt1-/- mutants under baseline conditions and a delay in sensorimotor integration during emergence from anesthesia. Our study links elevated activity in preoptic brain regions and reduced sensorimotor integration to lethargy-like behaviors and delayed emergence from propofol in glyt1-/- mutants.

Magnetic resonance findings in a neonate with nonketotic hyperglycinemia: case report.

We present brain imaging and spectroscopy data in a neonate with a confirmed classic form of nonketotic hyperglycinemia (NKH), an autosomal-recessive metabolic disorder characterized by accumulation of glycine. To our knowledge, this is the first report of such complete analysis of the changes seen on conventional magnetic resonance imaging, diffusion-weighted imaging, and magnetic resonance spectroscopy at such an early age. The findings in a neonate are consistent with reports in older children with NKH, confirming that pathological changes typical for NKH can be seen in the first postnatal week.

Glycine provokes lipid oxidative damage and reduces the antioxidant defenses in brain cortex of young rats.

Patients affected by nonketotic hyperglycinemia (NKH) usually present severe neurological symptoms and suffer from acute episodes of intractable seizures with leukoencephalopathy. Although excitotoxicity seems to be involved in the brain damage of NKH, the mechanisms underlying the neuropathology of this disease are not fully established. The objective of the present study was to investigate the in vitro effects of glycine (GLY), that accumulate at high concentrations in the brain of patients affected by this disorder, on important parameters of oxidative stress, such as lipid peroxidation (thiobarbituric acid-reactive substances (TBA-RS) and chemiluminescence) and the most important non-enzymatic antioxidant defense reduced glutathione (GSH) in cerebral cortex from 30-day-old rats. GLY significantly increased TBA-RS and chemiluminescence values, indicating that this metabolite provokes lipid oxidative damage. Furthermore, the addition of high doses of the antioxidants melatonin, trolox (soluble vitamin E) and GSH fully prevented GLY-induced increase of lipid peroxidation, indicating that free radicals were involved in this effect. GLY also decreased GSH brain concentrations, which was totally blocked by melatonin treatment. Finally, GLY significantly reduced sulfhydryl group content from a commercial GSH solution, but did not oxidize reduced cytochrome C. Our data indicate that oxidative stress elicited in vitro by GLY may possibly contribute at least in part to the pathophysiology of the neurological dysfunction in NKH.

Hyperglycaemic hyperosmolar nonketotic state as a cause of low gonadotrophin levels in postmenopausal diabetic women: a role for severe hypernatraemia.

Hypogonadotrophic hypogonadism is associated with uncontrolled diabetes mellitus. Hyperglycaemia is a unique metabolic abnormality of the hyperglycaemic hyperosmolar nonketotic state (HHNKS) and, as glucose availability regulates gonadotrophin release, we investigated whether gonadotrophin release is inhibited in diabetic women with HHNKS, and whether hyperglycaemia, hypernatraemia or both inhibit in vitro gonadotrophin-releasing hormone (GnRH) expression in GT1-7 neurones. Three groups of postmenopausal women were studied: nine diabetics with HHNKS, nine hospitalised ill nondiabetics and 15 healthy women. In addition, the effects of glucose (5.55, 33.3, 66.6 mmol/l) and sodium chloride (150 and 170 mmol/l) on GnRH expression were investigated using GT1-7 neurones. Postmenopausal diabetics with HHNKS showed a decrease in serum levels of luteinising hormone (diabetic HHNKS 2.2 +/- 0.9 IU/l versus ill nondiabetic 21.0 +/- 2.3 IU/l and healthy controls 20.9 +/- 2.8 IU/l, P < 0.01), follicle-stimulating hormone (diabetic HHNKS 8.2 +/- 2.1 IU/l versus ill nondiabetic 50.4 +/- 9.1 IU/l and controls 60.2 +/- 6.9 IU/l, P < 0.01) and free 3,5,3'-triiodothyronine (diabetic HHNKS 1.48 +/- 0.57 pmol/l versus ill nondiabetic 4.28 +/- 0.26 pmol/l and controls 3.88 +/- 0.11 pmol/l, P < 0.01). The plasma cortisol level was higher in both diabetic (985 +/- 130 nmol/l) and ill nondiabetic (726 +/- 52 nmol/l) women than in healthy women (512 +/- 47 nmol/l), but no differences were observed in plasma oestradiol, thyroid-stimulating hormone or free thyroxine. In vitro GT1-7 neurones expressed three-fold less GnRH at 170 mmol/l than at 150 mmol/l NaCl, whereas changing glucose concentrations in the culture medium did not affect GnRH expression. In conclusion, postmenopausal diabetic women with HHNKS show decreased serum gonadotrophin levels, and severe hypernatraemia may participate in the hypogonadotropism observed in HHNKS.

Clinical heterogeneity of glycine encephalopathy in three Palestinian siblings: A novel mutation in the glycine decarboxylase (GLDC) gene.

INTRODUCTION: Glycine encephalopathy (GE), also known as non-ketotic hyperglycinemia (NKH), is a rare inborn error of glycine metabolism caused by a defect in glycine cleavage system, a multi-enzyme complex located in mitochondrial membrane. This defect results in elevated glycine concentration in plasma and cerebrospinal fluid (CSF). Clinical manifestations vary from severe lethargy, hypoactivity and apneic episodes in the neonatal form, mild or moderate psychomotor delay and seizures in the infantile form, and abnormal behaviors, ataxia and choreoathetoid movements in late onset form. More than 50 GLDC mutations were found, reflecting large heterogeneity of the gene. METHODS: We describe the clinical, biochemical and molecular characteristics of three Palestinian siblings who have distinct clinical phenotypes. Molecular study was performed utilizing standard Polymerase Chain Reaction (PCR) amplification then direct DNA sequencing for the affected family members. RESULTS: Their phenotypes included severe symptoms in neonatal period, infantile onset of seizure and psychomotor delay and a mild late-onset form with speech delay at age 20months. All siblings were homozygous for a novel mutation Y164H in exon 4 of GLDC gene. The described novel homozygous variant in our study is predicted deleterious and pathogenic. CONCLUSIONS: This article further expands the genetic spectrum of glycine encephalopathy and adds an evidence of the clinical heterogeneity of glycine encephalopathy even in siblings with identical mutation.

Crystal structure of human T-protein of glycine cleavage system at 2.0 A resolution and its implication for understanding non-ketotic hyperglycinemia.

T-protein, a component of the glycine cleavage system, catalyzes the formation of ammonia and 5,10-methylenetetrahydrofolate from the aminomethyl moiety of glycine attached to the lipoate cofactor of H-protein. Several mutations in the human T-protein gene cause non-ketotic hyperglycinemia. To gain insights into the effect of disease-causing mutations and the catalytic mechanism at the molecular level, crystal structures of human T-protein in free form and that bound to 5-methyltetrahydrofolate (5-CH3-H4folate) have been determined at 2.0 A and 2.6 A resolution, respectively. The overall structure consists of three domains arranged in a cloverleaf-like structure with the central cavity, where 5-CH3-H4folate is bound in a kinked shape with the pteridine group deeply buried into the hydrophobic pocket and the glutamyl group pointed to the C-terminal side surface. Most of the disease-related residues cluster around the cavity, forming extensive hydrogen bonding networks. These hydrogen bonding networks are employed in holding not only the folate-binding space but also the positions and the orientations of alpha-helix G and the following loop in the middle region, which seems to play a pivotal role in the T-protein catalysis. Structural and mutational analyses demonstrated that Arg292 interacts through water molecules with the folate polyglutamate tail, and that the invariant Asp101, located close to the N10 group of 5-CH3-H4folate, might play a key role in the initiation of the catalysis by increasing the nucleophilic character of the N10 atom of the folate substrate for the nucleophilic attack on the aminomethyl lipoate intermediate. A clever mechanism of recruiting the aminomethyl lipoate arm to the reaction site seems to function as a way of avoiding the release of toxic formaldehyde.

Transient nonketotic hyperglycinemia and defective serotonin metabolism in a child with neonatal seizures.

Neonatal nonketotic hyperglycinemia is usually fatal or, less commonly, severely developmentally disabling, whereas transient nonketotic hyperglycinemia has usually been followed by normal development. We report a boy who had transient neonatal nonketotic hyperglycinemia but a coexistent disorder of serotonin metabolism manifested by initially low cerebrospinal fluid 5-hydroxyindoleacetic acid (which later normalized), low whole blood serotonin, and decreased platelet serotonin uptake. He survived the neonatal period but was neurodevelopmentally delayed and developed an autistic-like disorder. Later, his positron emission tomographic (PET) scans with alpha[(11)C] methyl-l-tryptophan revealed a pattern characteristic of autistic children. Although we know of no link between glycine and serotonin metabolism, and our patient had low, rather than high, central and peripheral serotonin, this case might represent a novel infantile disorder that affects both the glycine and serotonin neurotransmitter systems.

Lessons from the knocked-out glycine transporters.

Glycine has multiple neurotransmitter functions in the central nervous system (CNS). In the spinal cord and brainstem of vertebrates, it serves as a major inhibitory neurotransmitter. In addition, it participates in excitatory neurotransmission by modulating the activity of the N-methyl-D-aspartate (NMDA) subtype of glutamate receptors. The extracellular concentrations of glycine are regulated by Na+/Cl(-)-dependent glycine transporters (GlyTs), which are expressed in neurons and adjacent glial cells. Considerable progress has been made recently towards elucidating the in vivo roles of GlyTs in the CNS. The generation and analysis of animals carrying targeted disruptions of GlyT genes (GlyT knockout mice) have allowed investigators to examine the different contributions of individual GlyT subtypes to synaptic transmission. In addition, they have provided animal models for two hereditary human diseases, glycine encephalopathy and hyperekplexia. Selective GlyT inhibitors have been shown to modulate neurotransmission and might constitute promising therapeutic tools for the treatment of psychiatric and neurological disorders such as schizophrenia and pain. Therefore, pharmacological and genetic studies indicate that GlyTs are key regulators of both glycinergic inhibitory and glutamatergic excitatory neurotransmission. This chapter describes our present understanding of the functions of GlyTs and their involvement in the fine-tuning of neuronal communication.

Structure and expression of the glycine cleavage system in rat central nervous system.

The glycine cleavage system (GCS) is a mitochondrial multienzyme system consisting of four individual proteins, three specific components (P-, T-, and H-proteins) and one house-keeping enzyme, dihydrolipoamide dehydrogenase. Inherited deficiency of the GCS causes nonketotic hyperglycinemia (NKH), an inborn error of glycine metabolism. NKH is characterized by massive accumulation of glycine in serum and cerebrospinal fluids and severe neuronal dysfunction in neonates. To elucidate the neuropathogenesis of NKH, we cloned cDNAs encoding three specific components of the GCS and studied the gene expression in rat central nervous system. P-, T-, and H-protein cDNAs encoded 1024, 403, and 170 amino acids, respectively. In situ hybridization analysis revealed that P-protein mRNA was expressed mainly in glial-like cells, including Bergmann glias in the cerebellum, while T- and H-protein mRNAs were detected in both glial-like cells and neurons. T- and H-protein mRNAs, but not P-protein mRNA, were expressed in the spinal cord. Primary astrocyte cultures established from cerebral cortex had higher GCS activities than hepatocytes whereas those from spinal cord expressed only H-protein mRNA and had no enzymatic activity. An important role of glycine as inhibitory neurotransmitter has been established in the brainstem and spinal cord and another role of glycine as an excitation modulator of N-methyl-D-aspartate receptor is suggested in the hippocampus, cerebral cortex, olfactory bulbus, and cerebellum. Our results suggest that the GCS plays a major role in the forebrain and cerebellum rather than in the spinal cord, and that N-methyl-D-aspartate receptor may participate in neuropathogenesis of NKH.

Atypical nonketotic hyperglycinemia with normal cerebrospinal fluid to plasma glycine ratio.

The diagnosis of nonketotic hyperglycinemia is considered to depend upon the presence of increased cerebrospinal fluid glycine and an increased cerebrospinal fluid to plasma glycine ratio. We studied two siblings who have the neurologic and peripheral biochemical features of the atypical variant of nonketotic hyperglycinemia but have normal cerebrospinal fluid glycine and cerebrospinal fluid to plasma glycine ratios. The proband had reduced liver glycine cleavage system activity of 17% and 21% of mean normal values, confirmed in two independent laboratories. Her lymphoblast glycine cleavage system activity was normal. Nonketotic hyperglycinemia can be present in the absence of increased cerebrospinal fluid glycine. Measurement of liver glycine cleavage system activity is indicated when nonketotic hyperglycinemia is suggested by clinical features and peripheral glycine levels but cerebrospinal fluid glycine is normal.

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

Recently, a new disease entity has been defined: the disease of vanishing white matter. This leukoencephalopathy has an autosomal-recessive mode of inheritance. No cause or biochemical marker is known. We studied cerebrospinal fluid amino acids in five patients with the disease and found a consistent, moderate elevation of cerebrospinal fluid glycine in all. The ratio of cerebrospinal fluid to plasma glycine was elevated in four patients, in two patients reaching the level considered diagnostic for nonketotic hyperglycinemia. The activity of the glycine cleavage system was found to be normal in lymphoblasts in two patients. The elevation of cerebrospinal fluid glycine in the disease of vanishing white matter is either caused by a primary disturbance of glycine metabolism or is secondary to excitotoxic brain damage.

Transient nonketotic hyperglycinemia in an asphyxiated patient with pyridoxine-dependent seizures.

An asphyxiated neonate with pyridoxine-dependent seizures and associated transient nonketotic hyperglycinemia is reported. Frequent seizures and their resultant hypoxic-ischemic insult may have led to the elevation of the cerebrospinal fluid glycine level in this patient. Early diagnosis and treatment of pyridoxine-dependent seizures is essential for an improved neurologic outcome.