Galactosemia is a disease caused by a genetic defect that affects an individual's ability to correctly metabolize galactose for use in the glycolytic pathway, but has no effect on metabolism of starch and glycogen, or on glycolysis

Question

Galactosemia results in high galactose levels in the blood and accumulation of galactose-1-phosphate in the tissues.
a) If you were a physician treating a person with this genetic disorder, in addition to galactose, what other dietary sugar would you recommend the patient not consume to avoid high galactose levels in the blood?
b) Why would infants be more likely than adults to have high blood galactose levels associated with galactosemia?
c) Suggest a reason for the observation that galactosemia is more common than fructosemia?
d) Propose possible candidates for the defective enzyme that causes galactosemia.
What will be an ideal response?

Answer 1

Answer:
a) The recommendation would be to also avoid dietary lactose, which is metabolized to glucose and galactose.
b) Infants are more likely than adults to have higher levels of lactose in their diet.
c) There are five enzymes in the pathway that converts galactose to the glycolytic substrate glucose-6-phosphate and only one enzyme in the pathway that converts fructose to the glycolytic substrate fructose-6-phosphate. Mutation of any one of five galactose pathway enzymes, which would cause galactosemia, is much more likely than mutation of the one fructose pathway enzyme that would be required to cause fructosemia.
d) The enzymes most likely to be involved would be the second enzyme uridyl transferase, the third enzyme UDP-galactose epimerase, or the fourth enzyme UDP-glucose pyrophosphorylase in the five-enzyme pathway. The first enzyme galactokinase is not likely involved, because its product, galactose-1-phosphate, is abundant in tissues. The fifth enzyme phosphoglucomutase is not likely involved, because it is required for starch and glycogen metabolism, which is normal in individuals with galactosemia.