Galactosemia is often times a heretic genetic disorder where a simple sugar called galactose becomes a poisonous substance its commonly found in lactose which is milk sugar so if your aiming to help a friend id say the best way is to
1. make sure your friend stays away from milk
2. treat your friend if he/she ingests galactose
3. provide replacements for milk and other things with glacatose in it
4. checkup on your friend every day to make sure his/her sugar levels are normal