What is the expected GALT enzyme activity level in those with the Duarte variant?

In individuals with the Duarte variant of galactose-1-phosphate uridyltransferase (GALT) deficiency, the expected GALT enzyme activity level is reduced but not absent. This variant typically results in approximately 25% of normal enzyme activity. The Duarte variant is often considered a benign variant of classic galactosemia, which is characterized by severe deficiency of GALT leading to the classic symptoms of galactosemia.

Individuals with the Duarte variant can usually metabolize galactose more effectively than those with classic galactosemia due to the presence of some residual enzymatic activity. Therefore, the expectation of around 25% enzyme activity aligns with the understanding of the biochemical properties associated with this variant. This reduced enzyme activity level distinguishes the Duarte variant from classic galactosemia, where activity is typically dramatically lower or absent.