If a baby is born lactose intolerant, what happens during breast-feeding?

Lactose intolerance: Lactose is the main sugar in breast milk. A lactose-intolerant baby will refuse to continue taking it because it will cause abdominal pain, vomiting and diarrhea. However, lactase, the enzyme that splits lactose to simple sugars, maybe added to expressed breast milk in a bottle and fed to the baby instead. The easier way is to feed the baby with lactose-free formula.