Lactose metabolism

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.