ALD disease is a genetic, or inherited, disorder. If a mother is a carrier of ALD, there is a 50% chance of passing this on to her children. If a father is a carrier of ALD, he will pass this on to his daughters 100% of the time, but never to his sons.
Spontaneous, or de novo, mutations are another way a baby can inherit ALD. This means that the mother and father are not carriers of ALD, but the mutation of the gene causing ALD happens in utero. Spontaneous mutations arise randomly often during DNA replication.