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Specific diagnostic markers are the key to effective diagnosis and treatment of inborn errors of metabolism (IEM). Untargeted metabolomics allows for the identification of potential novel diagnostic biomarkers. Current separation techniques coupled to high-resolution mass spectrometry provide a powerful tool for structural elucidation of unknown compounds in complex biological matrices. This is a proof-of-concept study testing this methodology to determine the molecular structure of as yet uncharacterized m/z signals that were significantly increased in plasma samples from patients with phenylketonuria and 3-hydroxy-3-methylglutaryl-CoA lyase deficiency. A hybrid linear ion trap-orbitrap high resolution mass spectrometer, capable of multistage fragmentation, was used to acquire accurate masses and product ion spectra of the uncharacterized m/z signals. In order to determine the molecular structures, spectral databases were searched and fragmentation prediction software was used. This approach enabled structural elucidation of novel compounds potentially useful as biomarkers in diagnostics and follow-up of IEM patients. Two new conjugates, glutamyl-glutamyl-phenylalanine and phenylalanine-hexose, were identified in plasma of phenylketonuria patients. These novel markers showed high inter-patient variation and did not correlate to phenylalanine levels, illustrating their potential added value for follow-up. As novel biomarkers for 3-hydroxy-3-methylglutaryl-CoA lyase deficiency, three positional isomers of 3-methylglutaconyl carnitine could be detected in patient plasma. Our results highlight the applicability of current accurate mass multistage fragmentation techniques for structural elucidation of unknown metabolites in human biofluids, offering an unprecedented opportunity to gain further biochemical insights in known inborn errors of metabolism by enabling high confidence identification of novel biomarkers.

A reduced response of cystathionine beta-synthase (CBS) to its allosteric activator S-adenosylmethionine (SAM) has been reported to be a cause of CBS dysfunction in homocystinuria patients. In this work we performed a retrospective analysis of fibroblast data from 62 homocystinuria patients and found that 13 of them presented a disturbed SAM activation. Their genotypic background was identified and the corresponding CBS mutant proteins were produced in E. coli. Nine distinct mutations were detected in 22 independent alleles: the novel mutations p.K269del, p.P427L, p.S500L and p.L540Q; and the previously described mutations p.P49L, p.C165Rfs2, p.I278T, p.R336H and p.D444N. Expression levels and residual enzyme activities, determined in the soluble fraction of E. coli lysates, strongly correlated with the localization of the affected amino acid residue. C-terminal mutations lead to activities in the range of the wild-type CBS and to oligomeric forms migrating faster than tetramers, suggesting an abnormal conformation that might be responsible for the lack of SAM activation. Mutations in the catalytic core were associated with low protein expression levels, decreased enzyme activities and a higher content of high molecular mass forms. Furthermore, the absence of SAM activation found in the patients' fibroblasts was confirmed for all but one of the characterized recombinant proteins (p.P49L). Our study experimentally supports a deficient regulation of CBS by SAM as a frequently found mechanism in CBS deficiency, which should be considered not only as a valuable diagnostic tool but also as a potential target for the development of new therapeutic approaches in classical homocystinuria. © 2013 SSIEM and Springer Science+Business Media Dordrecht.

In patients with guanidinoacetate methyltransferase (GAMT) deficiency several parameters may point towards the diagnosis of GAMT deficiency. These include the low levels of creatine and creatinine in urine, the high concentration of guanidinoacetic acid (GAA) in urine and the low levels of creatine and creatinine in the cerebrospinal fluid (CSF). In this study, body fluids from 10 GAMT deficient patients were analysed using (1)H NMR spectroscopy. The urine 1D (1)H NMR spectra of all the patients showed a doublet resonance at 3.98 ppm (pH 2.50) derived from GAA present in high concentration. For this compound, a good recovery and good correlation was found between an LC-MS/MS method and (1)H NMR spectroscopy. In CSF NMR spectra of these patients, the singlet resonances of creatine and creatinine (3.05 and 3.13 ppm, respectively) were absent (normally always present in (1)H NMR spectra of CSF). Due to overlap by other resonances, the doublet of GAA could not be observed. Our data demonstrate that (1)H NMR spectroscopy of urine and CSF can be used to diagnose patients with GAMT deficiency. ispartof: NMR in Biomedicine vol:22 issue:5 pages:538-544 ispartof: location:England status: published

Contains fulltext : 50036.pdf (Publisher’s version ) (Closed access) A diagnosis of 3-methylglutaconic aciduria type I (OMIM: 250950) based on elevated urinary excretion of 3-methylglutaconic acid (3MGA), 3-methylglutaric acid (3MG) and 3-hydroxyisovaleric acid (3HIVA) was made in a 61-year-old female patient presenting with leukoencephalopathy slowly progressing over more than 30 years. The diagnosis was confirmed at the enzymatic and molecular level. In vivo brain MR spectroscopic imaging (MRSI) was performed at 3.0 T, and one-dimensional and two-dimensional in vitro NMR spectroscopy of body fluids of the patient was performed at 11.7 T. Additionally, we measured 1D (1)H-NMR spectra of urine of seven patients with a total of four different inborn errors of leucine metabolism. Increased concentrations of 3HIVA, 3MGA (cis and trans) and 3MG were observed in the NMR spectra of the patient's urine. In the cerebrospinal fluid, the 3HIVA concentration was 10 times higher than in the plasma of the patient and only the cis isomer of 3MGA was observed. In vivo brain MRSI showed an abnormal resonance at 1.28 ppm that may be caused by 3HIVA. Comparison of (1)H-NMR spectra of urine samples from all eight patients studied, representing five different inborn errors of leucine metabolism, showed that each disease has typical NMR characteristics. Our leukoencephalopathy patient suffers from a late-onset form of 3-methylglutaconic aciduria type I. In the literature, only very few adult patients with this conditions have been described, and 3HIVA accumulation in white matter in the brain has not been presented before in these patients. Our data demonstrate that (1)H-NMR spectroscopy of urine can easily discriminate between the known inborn errors of leucine metabolism and provide the correct diagnosis.

We elucidated the intron-exon boundaries of the 15 coding exons of the human cystathionine β-synthase (CBS) gene in order to establish an improved method based on PCR and direct sequencing for detection of CBS mutations. Using this method we identified the pathogenic mutations in two Danish siblings with CBS deficiency. Patients were compound heterozygotes: we detected the 833T→C mutation and a novel 22 bp deletion of exon 4 (493–514del) that introduces a frameshift and a stop codon immediately after the deletion. The deletion resulted in no detectable mRNA from this allele, as assessed by sequencing of cDNA. The established method represents an improvement of the existing method based on sequencing of cDNA because it permits the detection of mutations within the entire coding region of the CBS gene from a peripheral blood sample, including splice mutations and mutations resulting in the lack or a reduced amount of transcript.

Contains fulltext : 52286.pdf (Publisher’s version ) (Closed access) Cobalamin is an essential cofactor for two mammalian enzymes: methionine synthase and methylmalonyl-CoA mutase. Patients with the cobalamin C (CblC) defect have combined methylmalonic aciduria and homocystinuria. Recently, the gene responsible for the CblC type, MMACHC, was identified, which enables molecular diagnostics. In this study, we describe two siblings, a 16-year-old girl and her 11-year-old brother, of a consanguineous family who presented with a very distinct clinical manifestation. The girl presented at the age of 13 years with macrocytic anaemia, cognitive regression and Marfanoid features such as increased arm-span, arachnodactyly, joint hyperlaxity and scoliosis. Her brother presented at the age of 10 months with developmental delay and behavioural abnormalities. Biochemical analysis showed severely increased homocysteine and methylmalonic acid levels in plasma of both siblings. In addition, plasma cysteine levels were decreased in the girl but not in her brother. The diagnosis of CblC defect was confirmed by genomic sequencing of the coding exons of the MMACHC gene. Two heterozygous mutations were identified in both siblings; the common c.271dupA p.Arg91LysfsX14 and a novel mutation, c.1A > G p.Met1?. Therapy consisting of folic acid, vitamin B6, l-carnitine and intramuscular vitamin B12 resulted in a clear improvement of biochemical parameters and, importantly, resulted in amelioration of the Marfanoid features in the girl. These data might suggest that low cysteine levels account for the Marfanoid features observed in the girl and indicate that the CblC type of combined methylmalonic aciduria and homocystinuria should be considered in the differential diagnosis of patients with Marfanoid features.