RT Book, Section A1 Hiatt, Howard H. A2 Valle, David L. A2 Antonarakis, Stylianos A2 Ballabio, Andrea A2 Beaudet, Arthur L. A2 Mitchell, Grant A. SR Print(0) ID 1181421043 T1 Pentosuria T2 The Online Metabolic and Molecular Bases of Inherited Disease YR 2019 FD 2019 PB McGraw-Hill Education PP New York, NY SN 9780071459969 LK ommbid.mhmedical.com/content.aspx?aid=1181421043 RD 2024/10/13 AB Essential pentosuria is an inborn error of metabolism in which 1.0 to 4 g of the pentose L-xylulose is excreted in the urine each day. It is a benign disturbance that occurs principally in Jews and behaves genetically as an autosomal-recessive characteristic.This disorder bears no relationship to diabetes mellitus and is easily distinguished from several other varieties of pentosuria in which milligram quantities of a number of pentoses other than L-xylulose appear in the urine.Essential pentosuria is the result of a defect in the glucuronic acid oxidation pathway. In this route of carbohydrate metabolism the carboxyl carbon atom of D-glucuronic acid is removed in a series of reactions, giving rise to the pentose L-xylulose. The latter may then be converted to its stereoisomer, D-xylulose, which, in turn, may be phosphorylated. D-xylulose-5-phosphate may participate in reactions of the pentose phosphate pathway which lead to its conversion to hexose phosphate. (Glucuromic acid→gulonic acid→L-xylulose→xylitol→D-xylulose→ pentose phosphate pathway→hexose phosphate.) The glucuronic acid oxidation pathway serves no essential function in humans.The block results from reduced activity of the nicotinamide adenine dinucleotide phosphate (NADP)-linked xylitol dehydrogenase, the enzyme that catalyzes the conversion of L-xylulose to xylitol.The heterozygote can be recognized by demonstrating either an intermediate level of erythrocyte activity of xylitol dehydrogenase or increased urinary or serum L-xylulose, or both, in a glucuronolactone loading test.Two previously unreported inborn errors of metabolism occur in the reversible part of the pentose phosphate pathway. Deficiency of ribose-5-phosphate isomerase has been described in one patient who suffered from a progressive leukoencephalopathy and developmental delay. Transaldolase deficiency has been diagnosed in two unrelated families in whiupdt the proband presented in the newborn period with liver problems.(See Supplement: Ribose-5-Phosphate Isomerase Deficiency and Transaldolase Deficiency.)