The behavioral phenotype of children and adolescents with attenuated non-ketotic hyperglycinemia, intermediate to good subtype.

AIM: We aim to describe the behavioral phenotype of children and adolescents with the good to intermediate attenuated form of non-ketotic hyperglycinemia (NKH) and to explore associations between the behavioral phenotype and age, sex, plasma glycine levels and drug treatment. METHOD: Parents of children with attenuated NKH completed questionnaires assessing maladaptive behavior, adaptive behavior, social communication, speech/language development and motor development in addition to demographic and medical questions. RESULTS AND INTERPRETATION: Twelve children, age 6 to 21y, functioned at mild to severe intellectual disability levels. Their speech/language development was in line with their developmental quotient. Relative to their intellectual functioning, their motor development and communication were weaker in comparison to their general development. Their adaptive behavior, however, appeared a relative strength. There was no evidence for autism spectrum disorder occurring more frequently than expected, rather social skills, except for communication, were rated as a relative strength. Maladaptive behaviors with ADHD-like characteristics were present in more than two thirds of children. Maladaptive behaviors were significantly related to female sex and to taking dextromethorphan, but no significant relation between plasma glycine levels and behavior was found. Future studies will need to evaluate causality in the observed relation between dextromethorphan use and maladaptive behaviors. Clinicians should reconsider the benefit of dextromethorphan when presented with disruptive behaviors in children with attenuated NKH.

Ketogenic diet as a glycine lowering therapy in nonketotic hyperglycinemia and impact on brain glycine levels.

BACKGROUND: Nonketotic hyperglycinemia (NKH) is a severe neurometabolic disorder characterized by increased glycine levels. Current glycine reduction therapy uses high doses of sodium benzoate. The ketogenic diet (KD) may represent an alternative method of glycine reduction. AIM: We aimed to assess clinical and biochemical effects of two glycine reduction strategies: high dose benzoate versus KD with low dose benzoate. METHODS: Six infants with NKH were first treated with high dose benzoate therapy to achieve target plasma glycine levels, and then switched to KD with low dose benzoate. They were evaluated as clinically indicated by physical examination, electroencephalogram, plasma and cerebral spinal fluid amino acid levels. Brain glycine levels were monitored by magnetic resonance spectroscopy (MRS). RESULTS: Average plasma glycine levels were significantly lower with KD compared to benzoate monotherapy by on average 28%. Two infants underwent comparative assessments of brain glycine levels via serial MRS. A 30% reduction of brain glycine levels was observed in the basal ganglia and a 50% reduction in the white matter, which remained elevated above normal, and was equivalent between the KD and high dose benzoate therapies. CSF analysis obtained while participants remained on the KD showed a decrease in glycine, serine and threonine levels, reflecting their gluconeogenetic usage. Clinically, half the patients had seizure reduction on KD, otherwise the clinical impact was variable. CONCLUSION: KD is an effective glycine reduction method in NKH, and may provide a more consistent reduction in plasma glycine levels than high-dose benzoate therapy. Both high-dose benzoate therapy and KD equally reduced but did not normalize brain glycine levels even in the setting of low-normal plasma glycine.

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.

The effect of hyperglycinemic treatment in captive-bred Vervet monkeys (Chlorocebus aethiops).

Nonketotic hyperglycinemia (NKH) is a neuro-metabolic disorder caused by a deficiency in the glycine cleavage system (GCS) and glycine transporter 1 (GlyT1). A case of atypical late onset of NKH has been reported in a colony of captive-bred Vervet monkeys. The purpose of this study was to evaluate the effect of sodium benzoate and dextromethorphan in reducing glycine levels in hyperglycinemic monkeys. Twelve captive-bred Vervet monkeys were assigned into three groups consisting of four animals (control, valproate induced and cataract with spontaneous hyperglycinemia). Valproate was used to elevate glycine levels and the induced group was then treated with sodium benzoate and dextromethorphan together with group three to normalise glycine levels in cerebrospinal fluid (CSF) and plasma. Valproate induction elicited changes in phosphate, alkaline phosphatase and platelet count, however, no significant changes in the glycine levels were observed, and this might be due to the individual variability within the group. The treatment intervention was only obtained in the spontaneous group whereby the glycine levels were normalised in CSF and plasma. Therefore, it can be concluded that sodium benzoate and dextromethorphan treatment was effective and beneficial to the hyperglycinemic group.

[A stroke mimic: hemichorea associated with non-ketotic hyperglycaemia].

An 85-year-old man with a history of diabetes was admitted with acute onset hemichorea. Laboratory findings confirmed poorly controlled diabetes. A brain computed tomography (CTC) revealed contralateral striatal hyperdensity. The findings were compatible with hyperglycaemia-induced hemichorea, and antidiabetic and symptomatic treatment was initiated. The symptoms remitted completely after six days, and a follow-up CTC showed partial resolution of the striatal changes. This case illustrates the importance of considering if hyperglycaemia is the cause of hemichorea, as early diagnosis and treatment yield an excellent prognosis.

Neurodevelopmental Outcome and Treatment Efficacy of Benzoate and Dextromethorphan in Siblings with Attenuated Nonketotic Hyperglycinemia.

OBJECTIVE: To evaluate the impact of sodium benzoate and dextromethorphan treatment on patients with the attenuated form of nonketotic hyperglycinemia. STUDY DESIGN: Families were recruited with 2 siblings both affected with attenuated nonketotic hyperglycinemia. Genetic mutations were expressed to identify residual activity. The outcome on developmental progress and seizures was compared between the first child diagnosed and treated late with the second child diagnosed at birth and treated aggressively from the newborn period using dextromethorphan and benzoate at dosing sufficient to normalize plasma glycine levels. Both siblings were evaluated with similar standardized neurodevelopmental measures. RESULTS: In each sibling set, the second sibling treated from the neonatal period achieved earlier and more developmental milestones, and had a higher developmental quotient. In 3 of the 4 sibling pairs, the younger sibling had no seizures whereas the first child had a seizure disorder. The adaptive behavior subdomains of socialization and daily living skills improved more than motor skills and communication. CONCLUSIONS: Early treatment with dextromethorphan and sodium benzoate sufficient to normalize plasma glycine levels is effective at improving outcome if used in children with attenuated disease with mutations providing residual activity and when started from the neonatal period.

[Amplitude-integrated electroencephalography in non-ketotic hyperglycinaemia]. / Electroencefalograma de amplitud integrada en la hiperglicinemia no cetósica.

TITLE: Electroencefalograma de amplitud integrada en la hiperglicinemia no cetosica.

Ketogenic diet in early myoclonic encephalopathy due to non ketotic hyperglycinemia.

Non ketotic hyperglycinemia is a rare inborn error of glycine metabolism due to deficient activity of glycine cleavage system, a multienzymatic complex consisting of four protein subunits: the P-protein, the H-protein, the T-protein and the L-protein. The neonatal form of non ketotic hyperglycinemia presents in the first days of life with encephalopathy, seizures, multifocal myoclonus and characteristic "hiccups". Rapid progression may lead to intractable seizures, coma and respiratory failure requiring mechanical ventilation. Clinical trial with scavenges drugs decreasing glycine levels such as sodium benzoate, and with drugs reducing NMDA receptors excitatory properties, such as ketamine and dextromethorphan, have been tried but the outcome is usually poor; antiepileptic therapy, moreover, is unable to control epileptic seizures. Ketogenic diet has been successfully tried for refractory epilepsy in pediatric patients. We report three cases affected by neonatal non ketotic hyperglycinemia and early myoclonic encephalopathy treated with ketogenic diet. In our patients ketogenic diet, in association with standard pharmacological therapy, determined dramatic reduction of seizures and improved quality of life.

Paradoxical increase in seizure frequency with valproate in nonketotic hyperglycinemia.

Nonketotic hyperglycinemia (NKH), or glycine encephalopathy, is an autosomal recessive disorder caused by a defect in the glycine cleavage enzyme system. In neonatal-onset NKH, patients manifest lethargy, hypotonia, apnea, and intractable epileptic seizures that are not specific to this disease. We experienced a 6-year-old girl with spastic quadriplegia, intractable epilepsy, and mental retardation, all initially regarded as sequelae of neonatal meningitis. The seizure frequency was transiently increased when valproate was started. Head MRI revealed progressive brain atrophy and white matter loss with high intensity signals on T2-weighted and diffusion-weighted images, which prompted us to conduct further metabolic workups. High glycine levels led us to suspect NKH, and we confirmed this diagnosis by the non-invasive, (13)C-glycine breath test. DNA sequencing revealed novel Leu885Pro/Trp897Cys mutations in the glycine decarboxylase gene that were transmitted from both parents. Sodium benzoate and dextromethorphan dramatically decreased her hypertonicity. Our case shows that paradoxical increases in seizure frequency following valproate can be a clue for a diagnosis of NKH, and that a correct diagnosis of NKH can greatly alter the quality of life in such patients.

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.

Determination of benzoic acid in serum or plasma by gas chromatography-mass spectrometry (GC/MS).

Nonketotic hyperglycinemia (NKH), a metabolic disorder due to defects in the glycine cleavage system, leads to the accumulation of toxic levels of glycine. Glycine levels in these patients may be lowered by sodium benzoate treatment. Benzoic acid binds to glycine to form hippurate, which is subsequently eliminated through the kidneys. At high concentrations, hippuric acid can crystallize in the kidneys and cause renal failure. Therefore, it is desirable to have benzoic acids concentrations within a therapeutic range. In the gas chromatography method described, the drug from the acidified serum or plasma sample is extracted using ethyl acetate. The organic phase containing drug is separated and dried under a stream of nitrogen. After trimethylsilyl derivatization, benzoic acid analysis is done on a gas chromatograph mass spectrometer. Quantitation of the drug in a sample is achieved by comparing responses of the unknown sample to the responses of the calibrators using selected ion monitoring. Benzoic acid D(5) is used as an internal standard.

High-frequency rhythmic cortical myoclonus in a long-surviving patient with nonketotic hypergylcemia.

An 11-year-old girl with nonketotic hyperglycinemia who typically presented with a picture of early myoclonic encephalopathy in the neonatal period is presented in this article. Treated early with sodium benzoate and dextromethorphan, she became seizure-free, while myoclonus persisted. During examination, multifocal rhythmic myoclonic jerks in gamma frequency enhanced by motor activity were noted. Coherence analysis of the electroencephalography-electromyography relationship indicated a cortical origin of the myoclonic jerks. Observation of this case suggests that rhythmic cortical myoclonus may represent a late evolution of this rare disorder.

Valproate-induced chorea and encephalopathy in atypical nonketotic hyperglycinemia.

Nonketotic hyperglycinemia is a disorder of amino acid metabolism in which a defect in the glycine cleavage system leads to an accumulation of glycine in the brain and other body compartments. In the classical form it presents as neonatal apnea, intractable seizures, and hypotonia, followed by significant psychomotor retardation. An important subset of children with nonketotic hyperglycinemia are atypical variants who present in a heterogeneous manner. This report describes a patient with mild language delay and mental retardation, who was found to have nonketotic hyperglycinemia following her presentation with acute encephalopathy and chorea shortly after initiation of valproate therapy.

Treatment from birth of nonketotic hyperglycinemia due to a novel GLDC mutation.

OBJECTIVE: To determine whether the devastating outcome of neonatal-onset glycine encephalopathy (NKH) could be improved by instituting treatment immediately at birth rather than after symptoms are already well established. METHODS: A newborn with NKH diagnosed prenatally following the neonatal death of a previous affected sibling was treated from birth with oral sodium benzoate (250 mg/kg/day) and the NMDA receptor antagonist ketamine (15 mg/kg/day) immediately after sampling cord blood and cerebrospinal fluid (CSF) for glycine determination. Glycine cleavage system (CGS) activity was determined in placental tissue. Mutation analysis was performed by sequencing all GLDC, GCSH and AMT exons. RESULTS: CSF glycine (99 micromol/L, reference 3.8-8.0) was already markedly elevated at birth. GCS activity in placental tissue was severely reduced (2.6% of controls). A novel homozygous GLDC c.482A-->G(Y161C) missense mutation was identified. Neonatal hypotonia and apnea did not occur but the long-term outcome was poor, with intractable seizures and severe psychomotor retardation. This contrasts with the favorable outcome with early treatment in variant NKH with mild GCS deficiency (Ann Neuol 2004;56:139-143). INTERPRETATION: Prospective treatment with this regimen can favorably modify the early neonatal course of severe NKH but does not prevent the poor long-term outcome, suggesting glycine-induced prenatal injury and/or ongoing postnatal damage.

Benzoate treatment and the glycine index in nonketotic hyperglycinaemia.

High-dose benzoate treatment aimed at reducing plasma glycine levels to normal reduces seizures and increases wakefulness in patients with nonketotic hyperglycinaemia (NKH). Since benzoate metabolism is dependent on the available glycine pool, and since the glycine pool is variably affected by the deficiency in the glycine cleavage enzyme system, we examined the importance of interpatient variability in benzoate requirement. To correct for the dietary glycine contribution, the glycine index was introduced as the molar requirement of benzoate dose necessary to normalize plasma glycine levels and subtracting from that the dietary glycine intake, both corrected for weight. The glycine index varied between 3.62 and 4.87 mmol/kg per day in five patients with a poor neurodevelopmental outcome and between 0.92 and 1.90 mmol/kg per day in four patients with a better neurodevelopmental outcome, and was 2.54 mmol/kg per day in a single patient with an intermediate outcome. The glycine index was stable over time within each patient. Exceeding the balance by either increasing food glycine intake or decreasing the benzoate dose resulted in increased glycine levels. Exceeding the glycine tolerance by increasing benzoate resulted in elevated and toxic levels of benzoate. The glycine index is a stable, individually specific parameter in patients with NKH. It has clinical consequences for the dose of benzoate required and the role of dietary management. Through its correlation with neurodevelopmental outcome, the glycine index points to potential genetic factors that could contribute to the psychomotor retardation in NKH.

[Clinical progress of neonatal non-ketotic hyperglycinemia under treatment]. / Evolución de la hiperglicinemia no cetósica neonatal en tratamiento.

INTRODUCTION: Non-ketotic hyperglycinemia is a congenital error in the breakdown of glycine. The most common type is the classical neonatal form, which begins at the age of a few days with symptoms of lethargy, hypotonia, myoclonia, convulsions, apneas and, frequently, ends in death. Survivors usually develop intractable epilepsy and mental retardation. There is no effective treatment for this condition, but trials have been carried out with a therapy that diminishes the levels of glycine, benzoate (BZ), and another that blocks the excitatory effect in N-methyl-D-aspartate receptors: dextromethorphan (DTM). CASE REPORT: We report on the progress of a classical neonatal case, which began at the age of a few hours with hypotonia and stupor, without myoclonias or seizures, but with a suppression wave trace on the electroencephalogram (EEG). Cerebrospinal fluid (CSF) showed glycine levels of 141 micromol/L (the normal level is 6.66 +/- 2.66 micromol/L), with a CSF/plasma ratio of 0.19 (the normal ratio is < 0.02). Treatment was started on the thirteenth day with BZ and DTM, and alertness and eye fixation improved in just three days; at the same time the EEG readings become normal. The glycine level in plasma returned to normal at two months and that in CSF was considerably reduced, although with CSF/plasma levels that were still high. At present the patient is 4 years old, has never had convulsions, EEG results have always been normal, and continues with BZ, DTM, carnitine and diet. The patient has presented a high degree of hypermotoric behaviour, but is currently more attentive and more sociable, has been walking from the age of 35 months and has a quotient in the different areas of development of 40-50. CONCLUSIONS: The clinical progress made by our patient could be said to be anything but negligible, and we therefore recommend that treatment should be started as early as possible after diagnosis.

Poor outcome for neonatal-type nonketotic hyperglycinemia treated with high-dose sodium benzoate and dextromethorphan.

Neonatal-type nonketotic hyperglycinemia treatment remains unsatisfactory, even if started early. A review of six patients who underwent treatment for neonatal-type nonketotic hyperglycinemia in our hospital is presented. All patients were treated with a standardized protocol. Medical histories were retrieved from case notes. All six patients had elevated cerebrospinal fluid plasma glycine levels initially. All but one had received sodium benzoate and dextromethorphan from 1 month of age. All suffered from intractable seizures and severe mental retardation, and only two patients remain alive. One patient died at 5 days of age. No resuscitation was attempted in accordance with the family's wish after genetic counseling. The prognosis of neonatal nonketotic hyperglycinemia remains poor with current treatment. Genetic counseling helps parents cope with this devastating genetic disease.