TY - CHAP M1 - Book, Section TI - Pentosuria A1 - Hiatt, Howard H. A2 - Valle, David L. A2 - Antonarakis, Stylianos A2 - Ballabio, Andrea A2 - Beaudet, Arthur L. A2 - Mitchell, Grant A. PY - 2019 T2 - The Online Metabolic and Molecular Bases of Inherited Disease 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.) SN - PB - McGraw-Hill Education CY - New York, NY Y2 - 2024/10/13 UR - ommbid.mhmedical.com/content.aspx?aid=1181421043 ER -