Fructose & Galactose

Question 1

Essential Fructosuria

Answer 1

• Fructokinase def.
• Benign
• Fructosuria
• No glucose or galactose in urine
• No liver enlargement

Question 2

Heriditary Fructose Intolerance (HFI)

Answer 2

• Aldolase B def.
• 1st Sx appear when baby is weaned and begins to ingest sucrose or fructose
• Accumulation of F1-P in aldolase B deficient tissues
• Accumulation of free fructose in blood which is excreted in urine; urine analysis detects a reducing sugar that is NOT glucose.
• Drop in ATP levels activates the enzyme AMP deaminase leading to hyperurecemia and further depletion of ATP.
• Decreased ATP stimulates glycolysis & lactate production, which can lead to lactic acidosis.
• Protein synthesis in liver compromised; production of essential proteins, e.g. albumin, clotting factors drops. Pt often present with Jaundice, icterus & hepatosplenomegaly.
• If untreated liver & kidney damage can occur, resulting in jaundice, vomiting, mental retardation, seizures & death

Question 3

Dietary Galactose intestinal absorption?

Answer 3

• Lactose -> glucose + galactose
• Luminal transport: SGLT1
• Contra-luminal: GLUT2

Question 4

Classic Galactosemia

Answer 4

• Galactose-1-P Uridyl Transferase Defect
• Stores of Pi & ATP depleted
• Sx.: similar to HFI but a wider spectrum of tissues affected, i.e. Liver damage & Mental retardation
• Rx: Infants cannot break feed; soy milk replacement

Question 5

Lactose synthesis in mammary tissue?

Answer 5

• Lactose Synthase converts UDP-Galactose + Glucose into Lactose
• Lactose Synthase consists of:
  
  • Protein A: Beta-D-Galactosyltransferase
  • Protein B: alpha-Lactalbumin
  • Together aka UDP-galactose-glucose galactosyltransferase