Flashcards in Fructose metabolism and galactose metabolism Deck (9):
essential fructosuria: presentation, symptoms, inheritance, enzyme defect
defect of fructokinase. autosomal recessive. benign, asymptomatic condition b/c fructose is not trapped in cells. fructose in blood and urine.
fructose intolerance: presentation, inheritance, enzyme defect, diagnosis
aldolase B deficiency. autosomal recessive. fructose-1-P accumulates. decreases the available phosphate. inhibition of glycogenolysis and gulconeogenesis.
presentation after consumption of fruit juice, honey. urine dipstick is negative (it only tests for glucose). reducing sugar can be detected in the urine
fructose intolerance: symptoms and treatment
hypoglycemia, jaundice, cirrhosis, vomiting
treat by avoiding fructose and sucrose intake
galactokinase deficiency: enzyme deficiency, inheritance,
deficiency of galactokinase (galactose to galactose-1-P).
galacitol accumulates if galactose is present in the diet. realtively mild. autosomal recessive.
galactokinase deficiency symptoms
galactose in blood and urine. infantile cataracts. may initially present as a failure to track objects or to develop a social smile
classic galactosemia: inherience, enzyme deficiency
absence of galactose-1 phosphate uridyltransferase. autosomal recessive. damage caused by accumulation of toxici substances (including galacticol, which accumulates in the eye, like in galactokinase deficiency).
Symptoms of classic galactosemia
failure to thrive, jaundice, hepatomegaly, infantile cataracts, intellectual disability. tx: exclude galactose and lactose from diet.
can cause E. coli sepsis in neonates.
to trap glucose in cells, you can convert it to sorbitol using aldose reductase and NADPH.
some tissues then convert sorbitol to fructose with sorbitol dehydrogenase. if a tissue doesn't have enough sorbitol dehydrogenase, sorbitol may accumulate in the tissue. this causes osmotic damage like cataracts, retinopathy, and peripheral neuropathy (as in DM).
(high levels of galactose also cause conversion to osmotically active galactitol via aldose reductase.