First two unrelated cases of isolated sedoheptulokinase deficiency: A benign disorder?

We present the first two reported unrelated patients with an isolated sedoheptulokinase (SHPK) deficiency. The first patient presented with neonatal cholestasis, hypoglycemia, and anemia, while the second patient presented with congenital arthrogryposis multiplex, multiple contractures, and dysmorphisms. Both patients had elevated excretion of erythritol and sedoheptulose, and each had a homozygous nonsense mutation in SHPK. SHPK is an enzyme that phosphorylates sedoheptulose to sedoheptulose-7-phosphate, which is an important intermediate of the pentose phosphate pathway. It is questionable whether SHPK deficiency is a causal factor for the clinical phenotypes of our patients. This study illustrates the necessity of extensive functional and clinical workup for interpreting a novel variant, including nonsense variants

Dynamic rerouting of the carbohydrate flux is key to counteracting oxidative stress

<p>Abstract</p> <p>Background</p> <p>Eukaryotic cells have evolved various response mechanisms to counteract the deleterious consequences of oxidative stress. Among these processes, metabolic alterations seem to play an important role.</p> <p>Results</p> <p>We recently discovered that yeast cells with reduced activity of the key glycolytic enzyme triosephosphate isomerase exhibit an increased resistance to the thiol-oxidizing reagent diamide. Here we show that this phenotype is conserved in <it>Caenorhabditis elegans </it>and that the underlying mechanism is based on a redirection of the metabolic flux from glycolysis to the pentose phosphate pathway, altering the redox equilibrium of the cytoplasmic NADP(H) pool. Remarkably, another key glycolytic enzyme, glyceraldehyde-3-phosphate dehydrogenase (GAPDH), is known to be inactivated in response to various oxidant treatments, and we show that this provokes a similar redirection of the metabolic flux.</p> <p>Conclusion</p> <p>The naturally occurring inactivation of GAPDH functions as a metabolic switch for rerouting the carbohydrate flux to counteract oxidative stress. As a consequence, altering the homoeostasis of cytoplasmic metabolites is a fundamental mechanism for balancing the redox state of eukaryotic cells under stress conditions.</p

The difference between rare and exceptionally rare: molecular characterization of ribose 5-phosphate isomerase deficiency

Ribose 5-phosphate isomerase (RPI) deficiency is an enzymopathy of the pentose phosphate pathway. It manifests with progressive leukoencephalopathy and peripheral neuropathy and belongs, with one sole diagnosed case, to the rarest human disorders. The single patient was found compound heterozygous for a RPI frameshift and a missense (RPI(Ala61Val)) allele. Here, we report that two patient-derived cell lines differ in RPI enzyme activity, enzyme concentration, and mRNA expression. Furthermore, we present a transgenic yeast model, which exhibits metabolite- and enzyme-activity changes that correspond to the human syndrome and show that the decrease in RPI activity in patient cells is not fully attributable to the residue exchange. Taken together, our results demonstrate that RPI deficiency is caused by the combination of a RPI null allele with an allele that encodes for a partially active enzyme which has, in addition, cell-type-dependent expression deficits. We speculate that a low probability for comparable traits accounts for the rareness of RPI deficiency

The return of metabolism: biochemistry and physiology of the pentose phosphate pathway.

The pentose phosphate pathway (PPP) is a fundamental component of cellular metabolism. The PPP is important to maintain carbon homoeostasis, to provide precursors for nucleotide and amino acid biosynthesis, to provide reducing molecules for anabolism, and to defeat oxidative stress. The PPP shares reactions with the Entner-Doudoroff pathway and Calvin cycle and divides into an oxidative and non-oxidative branch. The oxidative branch is highly active in most eukaryotes and converts glucose 6-phosphate into carbon dioxide, ribulose 5-phosphate and NADPH. The latter function is critical to maintain redox balance under stress situations, when cells proliferate rapidly, in ageing, and for the 'Warburg effect' of cancer cells. The non-oxidative branch instead is virtually ubiquitous, and metabolizes the glycolytic intermediates fructose 6-phosphate and glyceraldehyde 3-phosphate as well as sedoheptulose sugars, yielding ribose 5-phosphate for the synthesis of nucleic acids and sugar phosphate precursors for the synthesis of amino acids. Whereas the oxidative PPP is considered unidirectional, the non-oxidative branch can supply glycolysis with intermediates derived from ribose 5-phosphate and vice versa, depending on the biochemical demand. These functions require dynamic regulation of the PPP pathway that is achieved through hierarchical interactions between transcriptome, proteome and metabolome. Consequently, the biochemistry and regulation of this pathway, while still unresolved in many cases, are archetypal for the dynamics of the metabolic network of the cell. In this comprehensive article we review seminal work that led to the discovery and description of the pathway that date back now for 80 years, and address recent results about genetic and metabolic mechanisms that regulate its activity. These biochemical principles are discussed in the context of PPP deficiencies causing metabolic disease and the role of this pathway in biotechnology, bacterial and parasite infections, neurons, stem cell potency and cancer metabolism.We acknowledge funding from the European Commission (Brussels) Role ofMitochondria in Conserved Mechanisms of Aging (MIMAGE) Project (Contract 512020, to M.B.), the Cancer Research Programme Grant (C197/A3514 to K.M.B.), Cancer Research UK and ERC Grants 322842-METABOp53 (supporting E.C.), the Wellcome Trust (RG 093735/Z/10/Z to M.R.), the ERC (Starting grant 260809 to M.R.), the German Research Foundation DFG (PR 1527/1-1 to A.P.), and the Austrian Science Fund (FWF) S9302-B05 (to M.B.). V.O.-S. is supported by Consejo Nacional de Ciencia y Tecnologia (CONACyT) Mexico postdoctoral fellowship 203450, M.A.K. by the FWF (Austria) by an Erwin Schroedinger postdoctoral fellowship (J 3341). M.R. is a Wellcome-Trust Research career development and Wellcome-Beit prize fellow.This is the final published version. It is also available from Wiley at http://onlinelibrary.wiley.com/doi/10.1111/brv.12140/abstract

Clinical, biochemical, and molecular overview of transaldolase deficiency and evaluation of the endocrine function : Update of 34 patients

BackgroundTransaldolase deficiency (TALDO-D) is a rare autosomal recessive inborn error of the pentose phosphate pathway. Since its first description in 2001, several case reports have been published, but there has been no comprehensive overview of phenotype, genotype, and phenotype-genotype correlation. MethodsWe performed a retrospective questionnaire and literature study of clinical, biochemical, and molecular data of 34 patients from 25 families with proven TALDO-D. In some patients, endocrine abnormalities have been found. To further evaluate these abnormalities, we performed biochemical investigations on blood of 14 patients. Results and conclusionsMost patients (n =22) had an early-onset presentation (prenatally or before 1 month of age); 12 patients had a late-onset presentation (3 months to 9 years). Main presenting symptoms were intrauterine growth restriction, dysmorphic facial features, congenital heart disease, anemia, thrombocytopenia, and hepato(spleno)megaly. An older sib of two affected patients was asymptomatic until the age of 9 years, and only after molecular diagnosis was hepatomegaly noted. In some patients, there was gonadal dysfunction with low levels of testosterone and secondary luteinizing hormone (LH) and follicle-stimulating hormone (FSH) abnormalities later in life. This overview provides information that can be helpful for managing patients and counseling families regarding prognosis. Diagnostic guidelines, possible genotype-phenotype correlations, treatment options, and pathophysiological disease mechanisms are proposed.Peer reviewe

Monitoring phenylalanine concentrations in the follow-up of phenylketonuria patients:An inventory of pre-analytical and analytical variation

Background: Reliable measurement of phenylalanine (Phe) is a prerequisite for adequate follow-up of phenylketonuria (PKU) patients. However, previous studies have raised concerns on the intercomparability of plasma and dried blood spot (DBS) Phe results. In this study, we made an inventory of differences in (pre-)analytical methodology used for Phe determination across Dutch laboratories, and compared DBS and plasma results. Methods: Through an online questionnaire, we assessed (pre-)analytical Phe measurement procedures of seven Dutch metabolic laboratories. To investigate the difference between plasma and DBS Phe, participating laboratories received simultaneously collected plasma-DBS sets from 23 PKU patients. In parallel, 40 sample sets of DBS spotted from either venous blood or capillary fingerprick were analyzed. Results: Our data show that there is no consistency on standard operating procedures for Phe measurement. The association of DBS to plasma Phe concentration exhibits substantial inter-laboratory variation, ranging from a mean difference of −15.5% to +30.6% between plasma and DBS Phe concentrations. In addition, we found a mean difference of +5.8% in Phe concentration between capillary DBS and DBS prepared from venous blood. Conclusions: The results of our study point to substantial (pre-)analytical variation in Phe measurements, implicating that bloodspot Phe results should be interpreted with caution, especially when no correction factor is applied. To minimize variation, we advocate pre-analytical standardization and analytical harmonization of Phe measurements, including consensus on application of a correction factor to adjust DBS Phe to plasma concentrations

Disorders of glycolysis and the pentose phosphate pathway

Glycolysis which converts each molecule of glucose to two of pyruvate is the most important source of energy in erythrocytes and in some types of skeletal muscle fibres, therefore inherited diseases of glycolysis are mainly characterized by haemolytic anaemia and/or metabolic myopathy. Ten inborn errors of the glycolytic pathway are known. The pentose phosphate pathway consists of two distinct parts: the first part, an oxidative, non-reversible pathway, produces NADPH, and the second part, a non-oxidative, reversible pathway, produces ribose for nucleotide and nucleic acid synthesis and connects intermediates to glycolysis. Four inborn errors in the pentose phosphate pathway (PPP) are known

Confirmation of a Rare Genetic Leukoencephalopathy due to a Novel Bi-allelic Variant in RPIA

Ribose 5-phosphate isomerase deficiency is a rare genetic leukoencephalopathy caused by pathogenic sequence variants in RPIA, that encodes ribose 5-phosphate isomerase, an enzyme in the pentose phosphate pathway. Till date, only three individuals with ribose 5-phosphate isomerase deficiency have been described in literature. We report on a subject with RPIA associated progressive leukoencephalopathy with elevated urine arabitol and ribitol levels and a novel missense variant c.770T > C p.(Ile257Thr) in exon 8 of RPIA. We also compare the phenotypes of all the four subjects. Our report confirms the phenotype and the genetic cause of this condition

Quantification of sugar phosphate intermediates of the pentose phosphate pathway by LC-MS/MS: Application to two new inherited defects of metabolism

We describe a liquid chromatography tandem mass spectrometry (LC-MS/MS) method to quantify pentose phosphate pathway intermediates (triose-3-phosphates, tetrose-4-phosphate, pentose-5-phosphate, pentulose-5-phosphates, hexose-6-phosphates and sedoheptulose-7-phosphate (sed-7P)) in bloodspots, fibroblasts and lymphoblasts. Liquid chromatography was performed using an ion pair loaded C18 HPLC column and detection of the sugar phosphates was carried out by tandem mass spectrometry using an electron ion spray source operating in the negative mode and multiple reaction monitoring. Reference values for the pentose phosphate pathway intermediates in blood spots, fibroblasts and lymphoblasts were established. The method was applied to cells from patients affected with a deficiency of transaldolase. The transaldolase-deficient cells showed an increased concentration of sedoheptulose-7-phosphate. (Bloodspots: 5.19 and 5.43 μmol/L [0.49-3.33 μmol/L]; fibroblasts 7.43 and 26.46 μmol/mg protein [0.31-1.14 μmol/mg protein]; lymphoblasts 16.03 μmol/mg protein [0.61-2.09 μmol/mg protein].) The method was also applied to study enzymes of the pentose phosphate pathway by incubating fibroblasts or lymphoblasts homogenates with ribose-5-phosphate or 6-phosphogluconate and the subsequent analysis of the formed sugar phosphates