Observed range of assay values for plasma and cerebrospinal fluid amino acid levels in infants and children aged 3 months to 10 years

Cerebral Metabolic Crisis in Pediatric Cerebral Malaria

Cerebral metabolic energy crisis (CMEC), often defined as a cerebrospinal fluid (CSF) lactate: pyruvate ratio (LPR) >40, occurs in various diseases and is associated with poor neurologic outcomes. Cerebral malaria (CM) causes significant mortality and neurodisability in children worldwide. Multiple factors that could lead to CMEC are plausible in these patients, but its frequency has not been explored. Fifty-three children with CM were enrolled and underwent analysis of CSF lactate and pyruvate levels. All 53 patients met criteria for a CMEC (median CSF LPR of 72.9 [interquartile range [IQR]: 58.5-93.3]). Half of children met criteria for an ischemic CMEC (median LPR of 85 [IQR: 73-184]) and half met criteria for a nonischemic CMEC (median LPR of 60 [IQR: 54-79]. Children also underwent transcranial doppler ultrasound investigation. Cerebral blood flow velocities were more likely to meet diagnostic criteria for low flow (<2 standard deviation from normal) or vasospasm in children with an ischemic CMEC (73%) than in children with a nonischemic CMEC (20%, p  = 0.04). Children with an ischemic CMEC had poorer outcomes (pediatric cerebral performance category of 3-6) than those with a nonischemic CMEC (46 vs. 22%, p  = 0.03). CMEC was ubiquitous in this patient population and the processes underlying the two subtypes (ischemic and nonischemic) may represent targets for future adjunctive therapies.

The Mutation Analysis of the AMT Gene in a Chinese Family With Nonketotic Hyperglycinemia

Background: Nonketotic hyperglycinemia is a metabolic disease with autosomal recessive inheritance due to the glycine cleavage system (GCS) defect leading to the accumulation of glycine that causes severe and fatal neurological symptoms in the neonatal period.

Methods: Genomic DNA was extracted from the peripheral blood of the female proband and her family members. The AMT variation was detected in the patient by whole-exome sequencing (WES), and the variant was validated by Sanger sequencing.

Results: The WES showed that there were novel compound heterozygous frameshift variations c.977delA (p.Glu326Glyfs*12) and c.982_983insG (p.Ala328Glyfs*22) in exon eight of the AMT gene (NM_000481.4) in the proband. Genetic analysis showed that the former was inherited from the mother, and the latter was inherited from the father.

Conclusion: We report the novel compound heterozygous variation of the AMT gene in a Chinese girl with NKH by WES, which has never been reported previously. Our case expanded the AMT gene mutation spectrum, further strengthened the understanding of NKH, and deepened the genetic and clinical heterogeneity of the disease. However, the study of treatment and prognosis is still our future challenge and focus.

Effects of glyphosate and aminomethylphosphonic acid on an isogeneic model of the human blood-brain barrier

Glyphosate is a pesticide used for occupational and non-occupational purposes. Because glyphosate targets a metabolic pathway absent in animals, it is considered safe for humans. Yet, case reports of accidental exposure to concentrated solutions following self-inflicted poisoning documented neurological lesions suggesting a neurotoxicity. In this study, we investigated the effect of acute exposure to glyphosate (GPH) on the blood-brain barrier in vitro based on induced pluripotent stem cells (iPSCs) and compared to two chemical analogs: aminomethylphosphonic acid (AMPA) and glycine (GLY), for concentrations ranging from 0.1 μM to 1000 μM. GPH treatment (1 and 10 μM) for 24 h showed an increase BBB permeability to fluorescein, with similar outcomes for AMPA. In addition to its ability to disrupt the barrier function, GPH show evidence of permeability across the BBB. Although no detrimental effects were observed on neuron differentiation at high doses, we noted changes in neuronal cell metabolic activity and glucose uptake in brain microvascular endothelial cells (BMECs) following treatment with 100 μM GPH or AMPA. Taken together, our data indicates that accidental exposure to high level of GPH may result in neurological damage via an opening of the blood-brain barrier and an alteration of glucose metabolism.

Reference values of amino acids and of common clinical chemistry in plasma of healthy infants aged 1 and 4 months

OBJECTIVE

To compare plasma levels of amino acids and clinical chemistry parameters in healthy infants at 1 and 4 months of age and to establish corresponding reference limits.

METHODS

Data of three multicenter studies assessing the safety of new infant formulas were used. During these studies infants of both age-groups were either breast-fed or received formulas of low or high protein content. All samples were analyzed centrally in the same accredited laboratory.

RESULTS

Plasma was collected from 521 infants in total, 157 boys and 135 girls aged 1 month and 121 boys and 108 girls aged 4 months. At the age of 1 month, 62 infants had received exclusively breast milk, 198 exclusively formula, and 27 both; in the 4-months age group corresponding numbers were 49, 158 and 18, respectively; for 9 infants, diet was unknown. Concentrations of most amino acids and clinical chemistry parameters differed significantly between both ages. Regardless of age, most plasma amino acid levels were comparable or lower in breast-fed than in formula-fed infants whereas at 1 month of age most clinical chemistry parameters were higher. While in breast-fed infants the plasma urea concentration decreased over 4 months of age, it increased in formula-fed infants. There were significant differences between infants fed a low and high protein formula. At both ages, high protein formulas resulted in significantly higher threonine, 2-aminobutyrate, and urea concentrations.

CONCLUSIONS

For clinical use, age- and diet specific reference limits in infants are warranted.

CSF/plasma ratios of amino acids: reference data and transports in children

OBJECTIVE

We intended to investigate the effects of age, gender, and medications on amino acid cerebrospinal fluid (CSF)/plasma ratios in children, and to determine whether amino acid transports across the blood-CSF barrier in children differ from those in adults.

PATIENTS AND METHODS

Amino acid concentrations measured by ion-exchange high-performance liquid chromatography were used (CSF from 99 children, simultaneously collected plasma from 76 children). Influence of age, gender, and medications on the amino acid CSF concentrations and CSF/plasma ratios were analyzed by linear multiple regression. Interactions of amino acid transports were analyzed by correlation analysis of CSF/plasma ratios.

RESULTS

CSF/plasma ratios of serine, valine, histidine, and arginine were higher in younger children. The glutamate CSF/plasma ratio was higher in older children. Serine, alanine, threonine, valine, and histidine CSF/plasma ratios were lower in females. Glutamine, methionine, tyrosine, and phenylalanine CSF/plasma ratios were elevated with valproate therapy. Serine, threonine, valine, leucine, and tyrosine CSF/plasma ratios were lower with clobazam therapy. The asparagine CSF/plasma ratio was elevated with pyridoxal phosphate therapy. Transports of most essential neutral amino acids interacted with each other, as did neutral amino acids with low molecular weights. Cationic amino acids interacted with each other and some essential neutral amino acids. Acidic amino acids had no interactions with other amino acids.

CONCLUSIONS

Age, gender, and anti-epileptic drugs affect amino acid CSF/plasma ratios in children. Transport interactions between amino acids in children showed no remarkable difference from those of adults and generally followed the substrate specificities of multiple amino acid transport systems.

Amino Acid Profiles in Patients with Urea Cycle Disorders at Admission to Hospital due to Metabolic Decompensation

Urea cycle disorders (UCDs) result from inherited defects in the ammonia detoxification pathway, leading to episodes of hyperammonaemia and encephalopathy. The purpose of this study was to answer the question, "what is the likely plasma amino acid profile of a patient known to have a UCD presenting with hyperammonaemia during acute metabolic decompensation", in order to support informed decisions regarding management.We analysed the results of plasma ammonia levels and amino acid profiles taken simultaneously or within 30 min of each other during acute admissions of all patients with a UCD at the Royal Children's Hospital, Melbourne, over 28 years. Samples from 96 admissions (79, 9 and 8 admissions for OTC, CPS and ASS deficiencies, respectively) from 14 patients fulfilled these criteria. Amino acid levels were measured by ion exchange chromatography with post-column ninhydrin derivatisation and interpreted in relation to age-related reference ranges.Plasma concentrations of all measured essential amino acids were low or low-normal in almost all samples. There was a strong positive correlation between low plasma branched-chain amino acids and other essential amino acids, and a negative correlation between ammonia and phenylalanine to tyrosine (Phe:Tyr) ratio in patients with OTC deficiency, and between glutamine and Phe:Tyr ratio in all patients, indicating protein deficiency.

CONCLUSION

At admission, protein deficiency is common in patients with a UCD with hyperammonaemia. These results challenge the current guideline of stopping protein intake during acute decompensation in UCDs. Supplementation with essential amino acids (particularly branched-chain amino acids) at these times should be considered.

Eighteen-year follow-up of a patient with cobalamin F disease (cblF): report and review

Cobalamin F disease (cblF) is a rare disorder of intracellular cobalamin metabolism resulting in failure to thrive, recurrent stomatitis, skin rash, megaloblastic anemia, hypotonia, seizures, and intellectual disability. Data on long-term outcomes are not available. We report on the outcome of a patient with cblF disease with a frameshift mutation in the LMBRD1 gene after 18 years of intramuscular hydroxycobalamin treatment.

Multicentre age-related reference intervals for cerebrospinal fluid serine concentrations: implications for the diagnosis and follow-up of serine biosynthesis disorders

The disorders of serine biosynthesis are a group of inborn errors of metabolism characterised by congenital microcephaly, seizures and severe psychomotor retardation. Although these disorders are rare the prompt recognition of serine deficiency is important as these disorders are treatable. The diagnosis is based on decreased concentrations of serine in cerebrospinal fluid (CSF). It has previously been reported that CSF serine concentrations are inversely associated with age. However, accurate age-related reference intervals have not been generated which has contributed to cases not being identified. In a multicentre study involving 9 different laboratories a total of 424 CSF serine results were obtained. Regression based analyses were performed to calculate age-specific reference intervals. Lower reference intervals for subjects aged 1week, 1month, 6months, 1year, 3years and 15years were 35.0, 31.0, 26.0, 24.0, 21.0 and 17.0μmol/L respectively. Assessment of CSF serine concentrations in 11 patients (aged 1day to 13years) previously diagnosed with disorders of serine biosynthesis (serine concentrations ranging from 5 to 18μmol/L) were clearly decreased compared to our age-related reference intervals and would have correctly identified all cases, thus enabling prompt treatment. However, if age had not been taken into consideration a reference interval of 12.6-69.4μmol/L would be obtained for the combined data set and would have resulted in 2 cases being missed. In conclusion, appropriate age-related reference intervals for CSF serine should be used to diagnose patients with inborn errors of serine biosynthesis.

Amino acid cerebrospinal fluid/plasma ratios in children: influence of age, gender, and antiepileptic medication

OBJECTIVE

The purpose of this work was to investigate the influence of age, gender, and antiepileptic therapy on amino acid cerebrospinal fluid/plasma ratios in children.

PATIENTS AND METHODS

Concentrations of 17 amino acids measured by ion-exchange chromatography with ninhydrin detection in plasma and cerebrospinal fluid from 68 patients with neurologic diseases were used to calculate their cerebrospinal fluid/plasma ratios (70 measurements; 28 female patients [29 punctures] and 40 male patients [41 punctures]). Age dependence and the effects of gender and antiepileptic medication on amino acid cerebrospinal fluid/plasma ratios were investigated by linear multiple regression analysis, and nonstandardized predicted mean values for 2 age groups were calculated (cutoff: 3 years old).

RESULTS

The cerebrospinal fluid/plasma ratios ranged between 0.02 for glycine and 0.93 for glutamine. Age had a significant influence on cerebrospinal fluid/plasma ratios for valine, isoleucine, leucine, and tyrosine, with higher ratios in younger children. Gender had a significant influence only on the glutamine cerebrospinal fluid/plasma ratio (female patients had lower ratios). Cerebrospinal fluid/plasma ratios of glutamine and tyrosine were significantly elevated by valproate therapy and those of serine, asparagine, glutamine, valine, methionine, and phenylalanine by phenobarbital therapy. No significant influence of age, gender, and antiepileptic drugs was detectable on cerebrospinal fluid/plasma ratios of threonine, proline, glycine, alanine, histidine, ornithine, lysine, and arginine.

CONCLUSIONS

Cerebrospinal fluid/plasma ratios, especially for essential neutral amino acids and for serine, asparagine, and glutamine were influenced to different degrees by age, gender, and antiepileptic therapy.

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.

Plasma glutamine levels and falciparum malaria

Glutamine deficiency is associated with increased rates of sepsis and mortality, which can be prevented by glutamine supplementation. Changes in glutamine concentration were examined in Ghanaian children with acute falciparum malaria and control cases. The mean (SD) plasma glutamine concentration was lower in patients with acute malaria (401 (82) mumol/L, n = 50) than in control patients (623 (67) mumol/L, n = 7; P < 0.001). Plasma glutamine concentrations all rose in convalescence. The mean (SD) increase in plasma glutamine was 202 (123) mumol/L (n = 18; P < 0.001) compared with acute infection. We conclude that acute falciparum malaria is associated with large decreases in plasma glutamine and these falls may increase susceptibility to sepsis and dyserythropoeisis.

Cerebrospinal fluid amino acid levels in newborn infants with intracranial hemorrhage

Cerebrospinal fluid (CSF) amino acid levels including excitatory amino acids (i.e. glutamate and aspartate) in 25 preterm and 18 full-term newborn infants with no serious disease except intracranial hemorrhage (ICH) were measured. ICH was detected in 13 preterm and six full-term infants on the basis of the clinical, lumbar puncture (LP) and cranial ultrasonography (CraUSG) findings. Twelve preterm and 12 full-term infants who were neurologically healthy comprised the control group. The mean concentration of CSF amino acids did not differ between preterm and full-term infants. The CSF concentrations of taurine, threonine, glycine, alanine, valine, isoleucine, leucine, tyrosine and phenylalanine in preterm infants, and threonine, aspartic acid and alanine in full-term infants were significantly elevated in infants with ICH. These abnormalities, especially in preterm infants, are probably related to cerebral hypoxia in CSF amino acid concentrations in newborn infants with ICH.

Nutrition support for glutaric acidemia type I

Glutaric acidemia type I is a rare, autosomal recessive, inborn error of lysine and tryptophan metabolism. This disorder is caused by a defect in the mitochondrial enzyme glutaryl-coenzyme A dehydrogenase, resulting in permanent or episodic elevations of glutaric acid. Despite clinical variability, untreated children often experience progressive neurologic damage that frequently leads to death. Recent evidence suggests that a lysine- and tryptophan-restricted diet and pharmacologic therapy with oral riboflavin and L-carnitine may arrest the neurologic deterioration. Several cases of normal growth and development have been reported in children diagnosed and treated before neurologic insult. In this article, we review previously published experience with dietary and pharmacologic therapy and provide guidelines for nutrition support based on our experience of treating four affected children. We suggest that dietary restriction of lysine and tryptophan is a safe and potentially effective therapy for individuals with glutaric acidemia type I.

Cerebrospinal fluid amino acids, purines and pyrimidines as a tool in the study of metabolic brain diseases

After establishing more extended reference values for amino acids, purines and pyrimidines in cerebrospinal fluid (CSF) in infancy and childhood, we studied 1250 CSF-aliquots from patients who were undergoing a diagnostic lumbar puncture for diverse clinical indications. Our primary aim was to answer the question whether determination of the concentration of amino acids, purines and pyrimidines in CSF is a useful tool in screening for metabolic disorders in children with unexplained mental retardation. In unexplained mental retardation (95 patients) we observed varying abnormalities of CSF. These were reproducible in only 2 patients (a decrease of homocarnosine in combination with two unidentified compounds). Striking abnormalities in pyrimidine content which are limited to CSF are found in argininosuccinic aciduria and uraemia. In uraemia a general decrease in amino acids in CSF and increase of gamma-aminobutyric acid (GABA) was observed. The results obtained indicate that determination of amino acids, purines and pyrimidines in CSF is only of limited value in the diagnosis of unexplained mental retardation.

Serotonin release varies with brain tryptophan levels

This study examines directly the effects on serotonin release of varying brain tryptophan levels within the physiologic range. It also addresses possible interactions between tryptophan availability and frequency of membrane depolarization in controlling serotonin release. We demonstrate that reducing tryptophan levels in rat hypothalamic slices (by superfusing them with medium supplemented with 100 microM leucine) decreases tissue serotonin levels as well as both spontaneous and electrically-evoked serotonin release. Conversely, elevating tissue tryptophan levels (by superfusing slices with medium supplemented with 2 microM tryptophan) increases both tissue serotonin levels and serotonin release. Serotonin release was found to be affected independently by tryptophan availability and frequency of electrical field-stimulation (1-5 Hz), since increasing both variables produced nearly additive increases in release. These observations demonstrate for the first time that both precursor-dependent elevations and reductions in brain serotonin levels produce proportionate changes in serotonin release, and that the magnitude of the tryptophan effect is unrelated to neuronal firing frequency. The data support the hypothesis that serotonin release is proportionate to intracellular serotonin levels.

Recurrent, familial Reye-like syndrome with a new complex amino and organic aciduria

Five of 13 siblings from a Jewish-Ashkenazi family suffered from recurrent Reye-like episodes. During attacks, these patients excreted alpha-keto-adipic, alpha-hydroxy-adipic, and alpha-aminoadipic acids, branched-chain keto acids and saccharopine in addition to lactic, pyruvic, and dicarboxylic acids characteristic of Reye syndrome. The serum concentrations of citrulline and alpha-amino-adipic acid were elevated and carnitine was at the upper limit of the normal range. Serum acetoacetate level was 4-5 times the beta-hydroxybutyrate level, but the pyruvate/lactate ratio was normal. Notably, plasma ketone bodies were lower than expected from the degree of catabolism. When the patients were symptom-free, no abnormal amino or organic acids in serum or urine were detected. These findings might be interpreted as a functional impairment at three different biochemical sites: fatty acid beta-oxidation, dehydrogenase complexes of the pyruvic, alpha-ketoglutaric, alpha-ketoadipic, and branched-chain keto acids, and pyruvate carboxylase. We suggest that in this hereditary disorder a toxic substance, exogenously or endogenously derived, interfered at multiple sites in different metabolic pathways.

Reference values for amino acids in cerebrospinal fluid of children determined using ion-exchange chromatography with fluorimetric detection

One thousand specimens of CSF were collected from subjects ranging in age from newborn to 18 yr, who were undergoing a diagnostic lumbar puncture. Sixty-two samples were judged retrospectively as being suitable for calculating reference age-related values. The analyses were performed by an amino acid analyser using ion-exchange chromatography with fluorimetric detection giving a tenfold increase in sensitivity, thereby enhancing the diagnostic capabilities. As many as 36 known compounds could be detected, additionally 10 we could not identify. In children older than 3 yr nine of the identified compounds showed age-dependency. We found 22 amino acids to be significantly higher in infants younger than 1 yr, with only gamma-aminobutyric acid being significantly lower in infants. Alpha-aminoadipic acid showed a sex difference, being slightly higher in girls.

Free amino acids in cerebrospinal fluid from patients with infantile spasms

Profiles of free amino acids in cerebrospinal fluid (CSF) were determined by high-performance liquid chromatography for 20 nonneurologic control patients and 12 patients with infantile spasms. Statistical comparisons showed significantly elevated levels of lysine (p less than 0.001) and the excitatory neurotransmitter, glutamate, (p less than 0.01) for the infantile spasms group as compared to the nonneurologic control group. When the infantile spasms patients were subdivided according to the presence or absence of etiologic associations, highly elevated amino acid levels were observed only in CSF from patients of the symptomatic subgroup. The idiopathic subgroup showed levels of free amino acids that were not statistically different from those of the nonneurologic control group. These results indicate that while abnormalities of amino acid metabolism often accompany infantile spasms, no specific pattern of the major free amino acids in CSF appears to be directly related to this seizure disorder. Elevated levels of the excitatory amino acids, aspartate and glutamate, do not necessarily accompany infantile spasms, and in this study were only observed in symptomatic patients.

Plasma free amino acid values in normal children and adolescents

We measured plasma free amino acids in 52 children (mean age 8 years) and 80 adolescents (mean age 16 years); conditions of diet and time of day were similar in the two groups. The protocols allowed us to compare their interindividual variation with values previously reported by us for adults. In children, the values for all but seven amino acids were normally distributed; in adolescents there were only six exceptions. Effects of age were apparent: values for only two amino acids were higher in children than adolescents. Values were significantly lower for ten amino acids in children v adolescents and for 11 amino acids in younger children (1 to 6 years) v older children (7 to 12 years). An effect of sex was apparent for five amino acids in adolescents; such differences were not apparent in children. All differences were quasicontinuous and occurred within the global distributions that define values for plasma amino acids in normal children and adolescents. Two artifacts (choice of anticoagulant and delay in deproteinization) affected values for taurine and cystine, respectively.

Analysis of aspartate and glutamate in human cerebrospinal fluid by high-performance liquid chromatography with automated precolumn derivatization

A method is described for the analysis of the neuroexcitatory amino acids, aspartate and glutamate, in human cerebrospinal fluid (CSF) by reverse-phase, high-performance liquid chromatography. Fluorescent isoindole derivatives of the amino acids were prepared by reacting the amino acids with ortho-phthalaldehyde in an automated, precolumn procedure. Chromatographic conditions were developed that resolve the isoindole derivatives of aspartate and glutamate from those of at least 10 unidentified components of CSF. Amino acids were reliably quantified in 5-microliter samples of CSF, and deproteinization of the specimens was not required. Furthermore, it was found that deproteinization by precipitation with strong acid can lead to artifactually high measurements of glutamate. The concentrations of free aspartate and glutamate in lumbar CSF from 15 neurologically normal children were 0.30 +/- 0.11 and 0.48 +/- 0.26 microM (mean +/- SD), respectively. The value for glutamate is considerably lower than has been reported in any previous study of human CSF.

Difficulties in assessing the effect of strychnine on the outcome of non-ketotic hyperglycinaemia. Observations on sisters with a mild T-protein defect

Sisters with a mild variant of non-ketotic hyperglycinaemia resulting from a defect in the T-protein of the glycine cleavage system had different clinical outcomes. The older sister was ascertained at 6 months of age because of mental retardation. She received only brief treatment with sodium benzoate from 11-15 months and at 15 years of age is profoundly retarded and has epilepsy. The younger sister was diagnosed 36 h after birth, was treated with strychnine, sodium benzoate and arginine from the neonatal period and at 27 months of age is only moderately retarded and free of seizures. The possible role of strychnine in the improved outcome is discussed.

The influence of anticonvulsants on fasting plasma ammonia and amino acid levels

We examined fasting levels of plasma ammonia, glutamine, glycine, and ornithine in patients taking three anticonvulsants - phenobarbital, carbamazepine and valproic acid. Contrary to previous reports no striking abnormalities were seen.