<prompt> Essential pentosuria occurs due to defect in the metabolic pathway ofUronic acidHexose-monophosphateGlycogenFructose  <response>: Ans. a Uronic acid Ref. Harpers, Biochemistry, 26th ed., 105, 163, 170; 27th 177; H-18thTable 364-1ESSENTIAL PENTOSURIA In liver, the uronic acid pathway catalyzes the conversion of glucose to glucuronic acid, ascorbic acid, and pentoses. It is also an alternative oxidative pathway for glucose, but--like the pentose phosphate pathway--it does not lead to the generation of ATP. Glucuronic acid is synthesized from glucose via the uronic acid pathway, which is of major significance for the excretion of metabolites and foreign chemicals xenobiotics such as glucuronides. A deficiency in this pathway leads to essential pentosuria. In this rare hereditary disease, considerable quantities of L-xylulose appear in the urine because of absence of the enzyme necessary to reduce L-xylulose to xylitol. Parenteral administration of xylitol may lead to oxalosis, involving calcium oxalate deposition in brain and kidneys. Various drugs markedly increase the rate at which glucose enters the uronic acid pathway.- For example, administration of barbital or of chlorobutanol to rats results in a significant increase in the conversion of glucose to glucuronate, L-gulonate, and ascorbate.ESSENTIAL FRUCTOSURIA The lack of one enzyme of the pathway gulonolactone oxidase in primates and some other animals explains why ascorbic acid is a dietary requirement for humans but not most other mammals. Deficiencies in the enzymes of fructose and galactose metabolism lead to essential fructosuria and the galactosemias.INHERITED DISORDERS OF AMINO ACID METABOLISMAmino acidsConditionEnzyme DefectClinical FindingsInheritancePhenylalaninePhenylketonuriaPhenylalanine hydroxylaseMental retardation, microcephaly, hypopigmented skin and hairs, eczema, mousy odorAR DHPR deficiency hyperphenylalaninemiaDihydropteridine reductaseMental retardation, hypotonia, spasticity, myoclonusAR PTS deficiency hyperphenylalaninemia6-Pyruvoyl-tetrahydropterinsynthaseDystonia, neurologic deterioration, seizures, mental retardationAR GCH1 deficiency hyperphenylalaninemiaGTP cyclohydrolase 1Mental retardation, seizures, dystonia, temperature instabilityAR Carbinolamine dehydratase deficiencyPterin-4-carbinolaminedehydrataseTransient hyperphenylalaninemia benignARTyrosineTyrosinemia type I hepatorenalFumary -lacetoacetatehydrolaseLiver failure, cirrhosis, rickets, failure to thrive, peripheral neuropathy, boiled cabbage odorAR Tyrosinemia type II oculocutaneousTyrosine transaminasePalmoplantar keratosis, painful corneal erosions with photophobia, mental retardation ?AR Tyrosinemia type III4-HydrophenylpyruvateDioxygenaseHypertyrosinemia with normal liver function, occasional mental delayAR Hawkinsinuria4-Hydroxyphenylpyruvate DioxygenaseTransient failure to thrive, metabolic acidosis in infancyAD AlkaptonuriaHomogentisic acid oxidaseOchronosis, arthritis, cardiac valve involvement, coronary artery calcificationAR AlbinismoculocutaneousTyrosinaseHypopigmentation of hair, skin, and optic fundus; visual loss; photophobiaAR Albinism ocularDifferent enzymes or transportersHypopigmentation of optic fundus, visual lossAR, XL DOPA-responsive DystoniaTyrosine hydroxylaseRigidity, truncal hypotonia, tremor, mental retardationARGABA4-Hydroxybutyric AciduriaSuccinic semialdehyde dehydrogenaseSeizures, mental retardation, ataxiaARTryptophanKynurenic aciduriaKynurenine-3-monooxygenaseNiacin deficiency, pellagra, colitisAR Hydroxykynureninuriaxanthurenic aciduriaKynureninaseNiacin deficiency, mental retardation, spasticityARHistidineHistidinemiaHistidine-ammonia lyaseBenignAR Urocanic aciduriaUrocanaseBenignAR Formiminoglutamic aciduriaFormi mi notransferaseOccasional mental retardationARGlycineGlycineencephaiopathyGlycine cleavage 4 enzymesInfantile seizures, lethargy, apnea, profound mental retardationAR SarcosinemiaSarcosine dehydrogenaseBenignAR Hyperoxaluria type IAlanine:glyoxylateaminotransferaseCalcium oxalate nephrolithiasis, renal failureAR Hyperoxaluria type IId-Glyceric acid dehydroge- nase glyoxylate reductaseCalcium oxalate nephrolithiasis, renal failureARSerinePhosphoglycerate dehydrogenase deficiencyPhosphoglycerate dehydrogenaseSeizures, microcephaly, mental retardationARProlineHyperprolinemia type IProline oxidaseBenignAR Hyperprolinemia type IIl-Pyrroline-5-carboxylate dehydrogenaseFebrile seizures, mental retardationAR HyperhydroxyprolinemiaHydroxyproline oxidaseBenignAR Prolidase deficiencyProlidaseMild mental retardation, chronic dermatitisARMethionineHypermethioninemiaMethionine adenosyltransferaseUsually benignAR S-Adenosylhomocysteine hydrolase deficiencyS-Adenosylhomocysteine hydrolaseHypotonia, mental retardation, absent tendon reflexes, delayed myelinationAR Glycine N-methyltrans- ferase deficiencyGlycine N-methyltransferaseElevated liver transaminasesARHomocystineHomocystinuriaCystathionine -synthaseLens dislocation, thrombotic vascular disease, mental retardation, osteoporosisAR Homocystinuria5,10-Methylenetetrahydro- folate reductaseMental retardation, gait and psychiatric abnormalities, recurrent strokesAR HomocystinuriaMethionine synthase cbIE, -GMental retardation, hypotonia, seizures, megaloblastic anemiaAR Homocystinuria and methylmalonic acidemiaVitamin B12 lysosomal efflux and metabolism cbIC, -D, -FMental retardation, lethargy, failure to thrive, hypotonia, seizures, megaloblastic anemiaARCystathionineCystathioninuriaCystathionaseBenignARCystineCystinosisCystinosin CTNS lysosomal effluxRenal Fanconi syndrome, rickets, photophobia, hypotonia, renal failureARS-Sulfo-I- cysteineSulfocysteinuriaSulfate oxidase or molybdenum cofactor deficiencySeizures, mental retardation, dislocated lensesARLysineHyperlysinemia, saccharopinuriaAminoadipic semialdehyde synthaseBenignAR Pyridoxine-dependent seizuresL-l-Piperideine-6-carboxylate dehydrogenaseSeizuresARLysine, tryptophanKetoadipic acidemiaKetoadipic acid dehydrogenaseBenign? Glutaric acidemia type IGlutaryl-CoA dehydrogenaseSevere dystonia and athetosis, mild mental retardationAR Glutaric acidemia type IIElectron transfer flavoprotein ETF or ETF:ubiquinone oxidoreductaseHypoglycemia, metabolic acidosis, sweaty feet odor, hypotonia, cardiomyopathy, exercise-induced myopathyAROrnithineGyrate atrophy of the choroid and retinaOrnithine 5 aminotransferaseMyopia, night blindness, loss of peripheral vision, cataracts, chorioretinal degenerationARUrea cycleCarbamoylphosphate synthase-1 deficiencyCarbamoylphosphate synthase-1Lethargy progressing to coma, protein aversion, mental retardation, hyperammonemiaAR N-Acetylglutamate synthase deficiencyN-Acetylglutamate synthaseLethargy progressing to coma, protein aversion, mental retardation, hyperammonemiaAR Ornithine transcar- bamylase deficiencyOrnithine transcarbamylaseLethargy progressing to coma, protein aversion, mental retardation, hyperammonemiaXL Citrullinemia type 1Argininosuccinate synthaseLethargy progressing to coma, protein aversion, mental retardation, hyperammonemiaAR Argininosuccinic acidemiaArgininosuccinate lyaseLethargy progressing to coma, protein aversion, mental retardation, hyperammonemia, trichorrhexis nodosaAR Arginase deficiencyArginaseSpastic tetraparesis, mental retardation, mild hyperammonemiaAR Hyperornithinemia, hyperammonemia, homocitrullinuriaMitochondrial ornithine carrier ORNT1Vomiting, lethargy, failure to thrive, mental retardation, episodic confusion, hyperammonemia, protein intoleranceAR Citrullinemia type 2Mitochondrial aspartate glutamate carrier CTLN2Neonatal intrahepatic cholestasis, adult presentation with sudden behavioral changes and stupor, coma, hyperammonemiaARProline, ornithine, argininel-pyrroline-5-carboxylate synthase deficiencyl-pyrroline-5-carboxylate synthaseHypotonia, seizures, hyperammo- nemia, neurodegenerationARGlutamineGlutamine synthase deficiencyGlutamine synthaseBrain malformations, pachygyria, seizures, hypotonia, dysmorphic featuresARValineIsobutyryl-CoA dehydro- genase deficiencyIsobutyryl-CoA dehydrogenaseFailure to thrive, anemia, and dilated cardiomyopathy?ARValine, leucine, isoleucineMaple syrup urine diseaseBranched chain ketoacid dehydrogenaseLethargy, vomiting, encephalopathy, seizures, mental retardation, maple syrup odor, protein intoleranceARLeucineIsovaleric acidemiaIsovaleryl-CoA dehydrogenaseAcidosis, ketosis, vomiting, coma, hyperammonemia, sweaty feet odor, protein intoleranceAR 3-Methylcrotonyl glycinuria3-Methylcrotonyl-CoA carboxylaseStress-induced metabolic acidosis, hypotonia, hypoglycemia, cats urine odorAR 3-Methyfglutaconic aciduria type 13-Methylglutaconyl-CoA hydratase deficiencyStress-induced acidosis, leukoencephalopathyAR 3-Hydroxy-3-methylglutaricaciduria3-Hydroxy-3-methylglutaryl- CoA lyaseStress-induced hypoketotic hypoglycemia and acidosis, encephalopathy, hyperammonemiaARIsoleucine2-Methylbutyryl-glycinuria2-Methylbutyryl-CoA dehydrogenaseFasting-induced metabolic acidosishypoglycemiaAR 2-Methyl-3-hydroxybutyryl- CoA dehydrogenase deficiency2-Methyl-3-hydroxybutyryl- CoA dehydrogenaseDevelopmental regression, seizures, and rigidity sometimes triggered by illnessesXL 3-Oxothiolase deficiency3-OxothiolaseFasting-induced acidosis and ketosis, vomiting, lethargyARValine, isoleucine, methionine, threoninePropionic academia pccA,-B,-CPropionyl-CoA carboxylaseMetabolic ketoacidosis, hyperammonemia, hypotonia, lethargy, coma, protein intolerance, mental retardation, hyperglycinemiaAR Multiple carboxylase biotinidase deficiencyHolocarboxylase synthase or biotinidaseMetabolic ketoacidosis, diffuse rash, alopecia, seizures, mental retardationAR Methylmalonic acidemia mutase, racemase, CbIA, -B, -DMethylmalonyl-CoA mutase racemase or cobalamin reductase adenosy transferaseMetabolic ketoacidosis, hyperammonemia, hypertonia, lethargy, coma, protein intolerance, mental retardation, hyperglycinemia 