Sometimes, newborns are picked up in newborn screening because the level of galactose-1-phosphate is high. When the level of enzyme is measured, the enzyme activity is usually about 25% of normal. These children do not have galactosaemia. They have what is called the "Duarte Variant".

These 25% of enzyme activity are enough that these children do not need a special diet and do not have any of the problems that people with Galactosaemia have. The only reason for their elevated level of galactose-1-phosphate is because newborns make less enzyme than they will later on.

These newborns are carriers of classical galactosaemia, and on their other copy of the gene there is a mild mistake, which means that a reduced amount of enzyme is made. The only reason why this might matter is that a couple who have had one child with the Duarte variant have a small chance of having a child with galactosaemia. This could happen if one of the parents also has the Duarte variant, and the other is a carrier of galactosaemia. In this case, one in four children born to such a couple would have galactosaemia, one in two would have the Duarte variant, and one in four would carry the gene with the Duarte mistake in it and have one normal copy of the gene.