Galactose Metabolism & Disorders
| Primary Entry Enzyme: | Galactokinase (Galactose → Galactose-1-Phosphate) |
| Core Pathway Key Enzyme: | Galactose-1-Phosphate Uridyltransferase (GALT) |
| Glycolytic Entry Shunt: | Glucose-1-Phosphate (via Phosphoglucomutase → G6P) |
| Alternative Toxic Pathway: | Aldose Reductase (Converts Galactose → toxic Galactitol) |
High-Yield Core Realities:
- Classic Galactosemia (GALT Deficiency): Autosomal recessive. Toxic accumulation of Galactose-1-phosphate in liver, brain, and renal tubules. Symptoms begin **immediately after initiating milk feeding**: hepatomegaly, jaundice, failure to thrive, infantile cataracts, and intellectual disability.
- The Sepsis Clue: Neonates with untreated Classic Galactosemia carry a highly specific, life-threatening predisposition to Escherichia coli (E. coli) neonatal sepsis.
- Galactokinase Deficiency: Far milder, benign variant. Galactose accumulates in blood and urine, shifting into the lens where aldose reductase converts it to galactitol. Presents *solely* as **infantile cataracts** and tracked by a failure to track social cues or develop a social smile. No systemic organ damage.
- Pathophysiology of Cataracts: Aldose reductase traps intracellular galactitol within lens fibers. Galactitol cannot diffuse out, pulling water inward osmotically, leading to fiber swelling, lens cell rupture, and opacity.
- Dietary Management Strategy: Prompt and absolute removal of lactose (glucose + galactose) and galactose from the diet. Breast milk and standard formulas must be replaced immediately with soy-based or sucrose-based alternatives.