Galactolysis refers to the catabolism of galactose.

In the liver, galactose is converted through the Leloir pathway to glucose 6-phosphate in the following reactions:

       galacto-                uridyl                phosphogluco-
        kinase               transferase                mutase
   gal --------> gal 1 P ------------------> glc 1 P -----------> glc 6 P
                            ^           \
                           /             v
                        UDP-glc       UDP-gal
                           ^             /

Metabolic disorders

There are 3 types of galactosemia or galactose deficiencies:

Name Enzyme Description
galactokinase deficiency Galactokinase Causes cataracts, which are treatable by restricting galactose from the diet.
UDPgalactose-4-epimerase deficiency UDPgalactose-4-epimerase Is extremely rare (only 2 reported cases). It causes nerve deafness.
Galactose-1-phosphate uridyl transferase deficiency Galactose-1-phosphate uridyl transferase Is the most problematic, as galactose-free diets are not effective in treating neurocognitive deficiencies (in particular language disorders such as verbal dyspraxia) and ovarian failure. If a galactose-free diet is administered, cataracts and acute symptoms such as kidney and liver failure respond immediately.