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Cooper A.J.L.,New York Medical College | Kuhara T.,Kanazawa Medical University | Kuhara T.,Japan Clinical Metabolomics Institute
Metabolic Brain Disease | Year: 2014

Glutamine metabolism is generally regarded as proceeding via glutaminase-catalyzed hydrolysis to glutamate and ammonia, followed by conversion of glutamate to α-ketoglutarate catalyzed by glutamate dehydrogenase or by a glutamate-linked aminotransferase (transaminase). However, another pathway exists for the conversion of glutamine to α-ketoglutarate that is often overlooked, but is widely distributed in nature. This pathway, referred to as the glutaminase II pathway, consists of a glutamine transaminase coupled to ω-amidase. Transamination of glutamine results in formation of the corresponding α-keto acid, namely, α-ketoglutaramate (KGM). KGM is hydrolyzed by ω-amidase to α-ketoglutarate and ammonia. The net glutaminase II reaction is: L ‐ Glutamine + α ‐ keto acid + H2O → α ‐ ketoglutarate + L ‐ amino acid + ammonia. In this mini-review the biochemical importance of the glutaminase II pathway is summarized, with emphasis on the key component KGM. Forty years ago it was noted that the concentration of KGM is increased in the cerebrospinal fluid (CSF) of patients with hepatic encephalopathy (HE) and that the level of KGM in the CSF correlates well with the degree of encephalopathy. In more recent work, we have shown that KGM is markedly elevated in the urine of patients with inborn errors of the urea cycle. It is suggested that KGM may be a useful biomarker for many hyperammonemic diseases including hepatic encephalopathy, inborn errors of the urea cycle, citrin deficiency and lysinuric protein intolerance. © 2013, Springer Science+Business Media New York. Source

Akiyama T.,Okayama University | Osaka H.,Jichi Medical University | Shimbo H.,Kanagawa Childrens Medical Center | Kuhara T.,Japan Clinical Metabolomics Institute | And 4 more authors.
Brain and Development | Year: 2016

Background: Succinic semialdehyde dehydrogenase (SSADH) deficiency is a rare autosomal recessive disorder that affects the degradation of gamma-aminobutyric acid and leads to the accumulation of gamma-hydroxybutyric acid (GHB) in body fluids. Diagnosis of SSADH deficiency is challenging, since the neurological symptoms are non-specific. Case: The patient is a nine-year-old Japanese boy who presented with developmental delay, autism, epilepsy, and episodic gait disturbance. Brain magnetic resonance imaging showed hyperintense lesions in the bilateral thalami, globus pallidi, substantia nigra, and dentate nuclei. Urine metabolome analysis revealed elevated GHB, which led to a biochemical diagnosis of SSADH deficiency. Genetic analysis of the ALDH5A1 gene revealed a novel missense mutation c.1586G>A inherited from his father. It also demonstrated three single nucleotide polymorphisms (SNPs) (c.106G>C, c.538C>T, and c.545C>T), all of which were inherited from his mother and are known to reduce SSADH enzyme activity. There were no duplications or deletions in other exons in the patient or his parents. No variants in the upstream, intronic, or downstream regions of the ALDH5A1 gene were found in the patient. Enzymatic assay revealed a marked reduction of SSADH enzyme activity (≈2% of the lower limit of the normal range). Conclusion: Although other mechanisms cannot be fully excluded, the clinical manifestation of SSADH deficiency in this patient may be attributed to the combined effect of the mutation and the three enzyme activity-reducing SNPs. Urine metabolome analysis effectively detected his elevated GHB and is thus considered to be a good screening method for this underdiagnosed and potentially manageable metabolic disorder. © 2016. Source

Nakajima Y.,Metabolic | Nakajima Y.,Nagoya City University | Meijer J.,Metabolic | Dobritzsch D.,Uppsala University | And 16 more authors.
Journal of Inherited Metabolic Disease | Year: 2014

β-ureidopropionase (βUP) deficiency is an autosomal recessive disease characterized by N-carbamyl-β-amino aciduria. To date, only 16 genetically confirmed patients with βUP deficiency have been reported. Here, we report on the clinical, biochemical and molecular findings of 13 Japanese βUP deficient patients. In this group of patients, three novel missense mutations (p.G31S, p.E271K, and p.I286T) and a recently described mutation (p.R326Q) were identified. The p.R326Q mutation was detected in all 13 patients with eight patients being homozygous for this mutation. Screening for the p.R326Q mutation in 110 Japanese individuals showed an allele frequency of 0.9 %. Transient expression of mutant βUP enzymes in HEK293 cells showed that the p.E271K and p.R326Q mutations cause profound decreases in activity (≤ 1.3 %). Conversely, βUP enzymes containing the p.G31S and p.I286T mutations possess residual activities of 50 and 70 %, respectively, suggesting we cannot exclude the presence of additional mutations in the non-coding region of the UPB1 gene. Analysis of a human βUP homology model revealed that the effects of the mutations (p.G31S, p.E271K, and p.R326Q) on enzyme activity are most likely linked to improper oligomer assembly. Highly variable phenotypes ranging from neurological involvement (including convulsions and autism) to asymptomatic, were observed in diagnosed patients. High prevalence of p.R326Q in the normal Japanese population indicates that βUP deficiency is not as rare as generally considered and screening for βUP deficiency should be included in diagnosis of patients with unexplained neurological abnormalities. © 2014 The Author(s). Source

Kuhara T.,Japan Clinical Metabolomics Institute
Nihon eiseigaku zasshi. Japanese journal of hygiene | Year: 2014

In Japan, screening for six diseases including four inborn errors of metabolism has been performed since 1977 for all neonates to prevent severe mental handicaps or death. A rapid screening procedure for analysis of several amino acids and acylcarnitines in blood spots by tandem mass spectrometry was developed by Millington DS et al. in the early 1990s. Although it is called expanded (or extended) newborn screening, the procedure is insufficiently sensitive to or specific for several diseases. Screening for all diseases that can be screened using this procedure is suggested to be cost-ineffective. Many European countries target only two diseases: medium-chain acyl-CoA dehydrogenase deficiency and phenylketonuria; their prevalence in Caucasian populations is very high, but some countries target more than twenty diseases and others an intermediate number. A pilot study targeting 22 diseases suggests that the combined incidence is one per 9,000 (0.01%) in Japan. This primary screening requires secondary screening to confirm the disease using urine, and either organic acids with solvent extraction or metabolome without fractionation are analyzed by gas chromatography-mass spectrometry. There is no need for primary or secondary screening tests to be performed at the same laboratory because the skills required are quite different. Understanding of the methodological problems of tandem mass screening and amelioration of variation and false positivity rate of this screening method among laboratories are critical to the success of the screening system in Japan. GC/MS-based urine metabolomics is expected to become one of the primary screening methodologies for neonates/infants who are already ill. Source

Takayama T.,Hamamatsu University School of Medicine | Takaoka N.,Hamamatsu University School of Medicine | Nagata M.,Hamamatsu University School of Medicine | Johnin K.,Shiga University of Medical Science | And 11 more authors.
Clinical Genetics | Year: 2014

The objective of this study was to investigate ethnic differences in the glyoxylate reductase/hydroxypyruvate reductase (GRHPR) gene in patients with primary hyperoxaluria type 2 (PH2). GRHPR was genotyped in Japanese patients with PH2 and all GRHPR mutations described to date were reviewed in terms of geographic and ethnic association. We identified a novel mutation, a two-nucleotide deletion (c.248_249delTG) in exon 3 creating a premature 'stop' at codon 91. Also, we found that the c.864_865delTG mutation was associated with the rs35891798 single-nucleotide polymorphism. The allelic frequencies of the c.103delG, c.494G>A, c.403_404+2 delAAGT, and c.864_865delTG mutations in PH2 patients were 37.8%, 15.6%, 10.0%, and 10.0%, respectively. All patients with the c.103delG mutation were Caucasian. Patients with the c.494G>A mutation and 78% (7/9) of those with the c.403_404+2 delAAGT mutation were from the Indian subcontinent, whereas those with the c.864_865delTG mutation were Chinese or Japanese. Molecular analysis of GRHPR of four Japanese PH2 patients identified a novel mutation (c.248_249delTG in exon 3). Caucasians with PH2 should be screened for the c.103delG mutation; patients from the Indian subcontinent for c.494G>A; and patients of East Asian origin (particularly) for c.864_865delTG. The prevalence of the latter mutation in PH2 patients from East Asia was 75.0%. © 2013 John Wiley & Sons A/S. Source

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