Fructose metabolism and galactose metabolism

Question 1

essential fructosuria: presentation, symptoms, inheritance, enzyme defect

Answer 1

defect of fructokinase. autosomal recessive. benign, asymptomatic condition b/c fructose is not trapped in cells. fructose in blood and urine.

Question 2

fructose intolerance: presentation, inheritance, enzyme defect, diagnosis

Answer 2

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

Question 3

fructose intolerance: symptoms and treatment

Answer 3

hypoglycemia, jaundice, cirrhosis, vomiting

treat by avoiding fructose and sucrose intake

Question 4

galactokinase deficiency: enzyme deficiency, inheritance,

Answer 4

deficiency of galactokinase (galactose to galactose-1-P).

galacitol accumulates if galactose is present in the diet. realtively mild. autosomal recessive.

Question 5

galactokinase deficiency symptoms

Answer 5

galactose in blood and urine. infantile cataracts. may initially present as a failure to track objects or to develop a social smile

Question 6

classic galactosemia: inherience, enzyme deficiency

Answer 6

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).

Question 7

Symptoms of classic galactosemia

Answer 7

failure to thrive, jaundice, hepatomegaly, infantile cataracts, intellectual disability. tx: exclude galactose and lactose from diet.
can cause E. coli sepsis in neonates.

Question 8

sorbitol

Answer 8

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.

Question 9

findings of lactase deficiency

Answer 9

stool has decr. pH and breath has incr. hydrogen content w/ lactose tolerance test.