Galactose is converted into glucose by the action of three enzymes, known as the leoloir pathway. There are diseases associated with deficiencies of each of these three enzymes-
1. Classic galactosemia (Galactosemia Type I):
• Due to galactose-1-phosphate uridylyltransferase (GALT) enzyme deficiency
• GALT converts galactose-1-phosphate to UDP-galactose, exchanging it with UDP-glucose.
• Diagnosis: Elevated levels of galactose-1-phosphate in red blood cells.
2. Galactokinase deficiency (Galactosemia Type II):
• Due to galactokinase enzyme deficiency
• Galactokinase converts galactose to galactose-1-phosphate.
• Diagnosis: Elevated levels of galactose in blood and urine.
3. UDP-galactose-4-epimerase deficiency (Galactosemia Type III):
• Due to UDP-galactose-4-epimerase enzyme deficiency
• UDP-galactose-4-epimerase converts UDP-galactose to UDP-glucose.
• Diagnosis: Elevated levels of galactose and galactose-1-phosphate.
|
Disorder |
Enzyme deficiency |
Diagnosis |
|
Classic Galactosemia (Type I) |
Galactose-1-phosphate uridylyltransferase (GALT) |
Elevated galactose-1-phosphate in RBC |
|
Galactokinase Deficiency (Type II) |
Galactokinase (GALK) |
Elevated galactose in blood and urine |
|
UDP-galactose-4-epimerase Deficiency (Type III) |
UDP-galactose-4-epimerase (GALE) |
Elevated galactose and galactose-1-phosphate |