d-Glyceric aciduria does not cause nonketotic hyperglycinemia: A historic co-occurrence.

Historically, d-glyceric aciduria was thought to cause an uncharacterized blockage to the glycine cleavage enzyme system (GCS) causing nonketotic hyperglycinemia (NKH) as a secondary phenomenon. This inference was reached based on the clinical and biochemical results from the first d-glyceric aciduria patient reported in 1974. Along with elevated glyceric acid excretion, this patient exhibited severe neurological symptoms of myoclonic epilepsy and absent development, and had elevated glycine levels and decreased glycine cleavage system enzyme activity. Mutations in the GLYCTK gene (encoding d-glycerate kinase) causing glyceric aciduria were previously noted. Since glycine changes were not observed in almost all of the subsequently reported cases of d-glyceric aciduria, this theory of NKH as a secondary syndrome of d-glyceric aciduria was revisited in this work. We showed that this historic patient harbored a homozygous missense mutation in AMT c.350C>T, p.Ser117Leu, and enzymatic assay of the expressed mutation confirmed the pathogeneity of the p.Ser117Leu mutation. We conclude that the original d-glyceric aciduria patient also had classic NKH and that this co-occurrence of two inborn errors of metabolism explains the original presentation. We conclude that no evidence remains that d-glyceric aciduria would cause NKH.

Late diagnosis of primary hyperoxaluria type III.

We report the case of a 78-year-old patient with late diagnosis of hyperoxaluria type III (PH3). He developed renal failure after nephrectomy for clear cell papillary renal carcinoma and complained of recurrent urolithiasis for some 30 years, whose aetiology was never identified. Biochemical laboratory investigations of urine and urolithiasis composition revealed marked hyperoxaluria but normal concentrations of urinary glyceric and glycolic acid as well as stones of idiopathic calcium-oxalate appearance. Furthermore, the dietary survey showed excessive consumption of food supplements containing massive amounts of oxalate precursors. However, the persistence of excessive hyperoxaluria after his eating habits was changed leading us to perform molecular genetic testing. We found heterozygous mutations of the recently PH3-associated HOGA1 gene when sequencing PH genes. This is the first description of late diagnosis primary PH3 in a patient with several additional pro-lithogenic factors. This case illustrates the importance of undertaking a complete biological work-up to determine the aetiology of hyperoxaluria. This may reveal underdiagnosed primary hyperoxaluria, even in older patients.

Simultaneous analysis of urinary metabolites for preliminary identification of primary hyperoxaluria.

BACKGROUND: The primary hyperoxalurias are inherited disorders of glyoxylate metabolism, which cause over-production of oxalate leading to urolithiasis and subsequent renal failure. Other metabolites may be produced in excess in the different forms of PH: glycolate in PH1, glycerate in PH2 and 4-hydroxy-2-oxoglutarate and 2,4-dihydroxyglutarate in PH3. The aim of this study was to set up and validate a method for the simultaneous analysis of these metabolites in urine and to evaluate its use for preliminary identification of primary hyperoxaluria prior to definitive diagnosis by genetic testing. METHODS: Urine samples were derivitized by methoximation and silylation and extracted into organic solvent prior to analysis by gas chromatography mass spectrometry. RESULTS: Recovery of the analytes spiked into urine ranged from 91 to 103% and total analytical imprecision ranged from 3.0 to 13.6%. 4-Hydroxy-2-oxoglutarate was unstable in urine at room temperature, and preservation by acidification was required. Mean urinary glycolate, glycerate and 4-hydroxy-2-oxoglutarate or 2,4-dihydroxyglutarate (expressed as a ratio to creatinine) were significantly higher in patients with PH1, PH2 and PH3, respectively. Low 4-hydroxy-2-oxoglutarate was observed in some patients with PH3, probably due to the instability of this analyte, but all PH3 patients had elevated 2,4-dihydroxyglutarate. During five months of routine service, seven cases of PH were identified by this method and subsequently confirmed by gene sequencing including two with novel mutations in HOGA1. CONCLUSIONS: This study confirms that the method is useful in aiding the diagnosis of primary hyperoxaluria and can direct genetic testing.

D-glyceric aciduria.

Inherited metabolic diseases are a heterogeneous group of diseases caused by a punctual defect in cell metabolism, resulting in the accumulation of toxic intermediate metabolites or in the lack of important biomolecules for adequate cell functioning. D-glyceric aciduria is an inherited disease caused by a deficiency of glycerate 2-kinase activity, whose pathophysiological mechanisms remain unknown. The main clinical and neurological symptoms seen in affected patients include progressive encephalopathy, hypotonia, psychomotor and mental retardation, microcephaly, seizures, speech delay, metabolic acidosis, and even death. In this review we shall discuss these clinical and biochemical findings, as well as diagnosis and treatment of affected patients in order to raise awareness about this condition.

A Novel Urinary Metabolite Signature for Non-invasive Post-stroke Depression Diagnosis.

Post-stroke depression (PSD) is the most common psychiatric complication in stroke survivors that has been associated with increased physical disability, distress, poor rehabilitation, and suicidal ideation. However, there are still no biomarkers available to support objective laboratory testing for this disorder. Here, a GC-MS-based urinary metabolomics approach was used to characterize the urinary metabolic profiling of PSD (stroke) subjects and non-PSD (health controls) subjects in order to identify and validate urinary metabolite biomarkers for PSD. Six metabolites, azelaic acid, glyceric acid, pseudouridine, 5-hydroxyhexanoic acid, tyrosine, and phenylalanine, were defined as biomarkers. A combined panel of these six urinary metabolites could effectively discriminate between PSD subjects and non-PSD subjects, achieving an area under the receiver-operating characteristic curve (AUC) of 0.961 in a training set (n = 72 PSD subjects and n = 146 non-PSD subjects). Moreover, this urinary biomarker panel was capable of discriminating blinded test samples (n = 58 PSD patients and n = 109 non-PSD subjects) with an AUC of 0.954. These findings suggest that a urine-based laboratory test using these biomarkers may be useful in the diagnosis of PSD.

Untargeted metabolome quantitative trait locus mapping associates variation in urine glycerate to mutant glycerate kinase.

With successes of genome-wide association studies, molecular phenotyping systems are developed to identify genetically determined disease-associated biomarkers. Genetic studies of the human metabolome are emerging but exclusively apply targeted approaches, which restricts the analysis to a limited number of well-known metabolites. We have developed novel technical and statistical methods for systematic and automated quantification of untargeted NMR spectral data designed to perform robust and accurate quantitative trait locus (QTL) mapping of known and previously unreported molecular compounds of the metabolome. For each spectral peak, six summary statistics were calculated and independently tested for evidence of genetic linkage in a cohort of F2 (129S6xBALB/c) mice. The most significant evidence of linkages were obtained with NMR signals characterizing the glycerate (LOD10-42) at the mutant glycerate kinase locus, which demonstrate the power of metabolomics in quantitative genetics to identify the biological function of genetic variants. These results provide new insights into the resolution of the complex nature of metabolic regulations and novel analytical techniques that maximize the full utilization of metabolomic spectra in human genetics to discover mappable disease-associated biomarkers.

D-glyceric aciduria in a six-month-old boy presenting with West syndrome and autistic behaviour.

D-Glyceric aciduria is a disease with a very heterogeneous group of symptoms, with D-glyceric acid excretion as the chief common characteristic. Findings described in previous patients include progressive neurological impairment, hypotonia, seizures, failure to thrive and metabolic acidosis. However, there are also asymptomatic patients with mild neurological impairment. A six-month-old boy was admitted to our clinic with the complaints of dullness to his environment, seizures and autistic behaviour. EEG revealed multifocal generalized epileptic activity in a hypsarrhythmia pattern. Organic acid analysis (GC-MS) in urine revealed increased glyceric acid excretion. Analysis of the optical form of glyceric acid by a polarimetric method supported the diagnosis of D-glyceric aciduria. MRI showed white matter lesions with cerebral atrophy, particularly in the frontotemporal regions, and reversible abnormalities in the mesencephalon, thalami and globus pallidium resolving after fructose restriction in the diet. To our knowledge, this is the first case report of a patient with D-glyceric aciduria who presented with West syndrome and autistic behaviour in whom serial MRI findings are also defined.

Chiral liquid chromatography tandem mass spectrometry in the determination of the configuration of glyceric acid in urine of patients with D-glyceric and L-glyceric acidurias.

Glyceric acid is a highly polar chiral carboxylic acid that is usually not detected during routine organic acid analysis. Increased excretion is observed in two phenotypically distinct and rare inherited metabolic diseases, D-glyceric aciduria, and L-glyceric aciduria (also known as primary hyperoxaluria type 2). The determination of the exact configuration of the excreted glyceric acid is necessary for the accurate diagnosis of D-glyceric aciduria and for the differentiation between type 1 and type 2 primary hyperoxaluria. The separation of the two stereoisomers was achieved using a narrow-bore ristocetin A glycopeptide antibiotic silica gel bonded column. Triethylamine acetate at pH 4.1 with 10% methanol was used as mobile phase. The column was directly interfaced to a triple quadrupole tandem mass spectrometer and the electrospray ion source was operated in the negative ion mode. Three parent-to-daughter transitions were employed to specifically detect eluting glyceric enantiomers from essentially untreated urine samples. The two forms of glyceric acid were satisfactorily separated at 3.6 and 4.5 min. Application of the method led to the confirmation of three cases of D-glyceric aciduria from three different families. Two other cases are suspected to be L-glyceric aciduria but further confirmation is needed. The method allowed the detection of the glyceric acid stereoisomers in control urine where it was found without exception that L-glyceric was the predominate metabolite.