All material is copyrighted and the property of mehlmanmedical.
Copyright © 2020 mehlmanmedical.
Privacy Policy and Terms and Conditions
The fructose disorders on the USMLE are presented in vignettes as an infant who has just been introduced to fruit, honey, or juice.
Essential fructosuria = deficiency of fructokinase = asymptomatic presentation
Hereditary fructose intolerance = deficiency of aldolase B = severe presentation
| A USMLE question assessing you on essential fructosuria will give you a completely normal/asymptomatic infant who has reducing sugar in the urine. This is due to fructokinase deficiency.
When aldolase B is deficient, there is a buildup of fructose-1-phosphate, which leads to jaundice, cirrhosis, and hypoglycemia. |
Questions also like you to know that the reason the Sx are so severe with hereditary fructose intolerance is because of trapping of hepatic phosphate as fructose-1-phosphate.
| For the fructose (and galactose) disorders, deficiency of the more downstream (second) enzyme causes the severe presentation. This is because of phosphate trapping in the liver. Buildup of fructose-1-phosphate means more phosphate is tied up in the form of that intermediate. |
A patient with a fructose disorder needs to avoid table sugar, since this is sucrose, which is catabolized to glucose + fructose.
—
