Symptoms of congenital Type III Galactosemia are apparent from birth, but vary in severity depending on whether the peripheral or generalized disease form is present.

The recent development of a Drosophila melanogaster GALE mutant exhibiting galactosemic symptoms may yield a promising future animal model.

[6] Functional analysis of these mutant GALE isoforms suggests that reduced catalytic efficiency and increased likelihood of proteolytic digestion act causatively in Type III galactosemia.

High galactose-1-phosphate levels have been shown to interfere with phosphoglucomutase,[7] glycogen phosphorylase,[8] UDP-glycopyrophosphorylase,[9] activity in bacterial models and in vitro, yet in vivo mechanisms toxicity have yet to be confirmed.

[citation needed] Individuals presenting with Type III galactosemia must consume a lactose- and galactose-restricted diet devoid of dairy products and mucilaginous plants.