Unfortunately, galactosemia is a contraindication for breastfeeding.  The baby
has a metabolic disease and cannot digest the milk sugar lactose correctly.
Significant neurologic and other damage can result if the baby is continued on
lactose-containing foods.  As far as I know, there is no good way of treating
breastmilk to get rid of the lactose and make it safe for consumption by a
galactosemic baby (treating with Lact-aid tablets would not do the trick).
I'm not sure that even highly limited breastfeeding would be advisable.

If the diagnosis of galactosemia is confirmed, the mom should be grateful that
there are lactose-free products available for the baby.  The baby will need to
be on a special diet all of his/her life.

Mom can (and should) continue to practice attachment parenting.  She can be
sure to hold and cuddle the baby as much as her breastfed children, put
him/her skin-to-skin, and could even consider nursing with a supplementer if
her breastmilk supply were essentially dried up.

Linda L. Shaw MD FAAP