The leukodystrophies are rare diseases that affect the cells of the brain. Specifically, the diseases affect the myelin sheath, the material that surrounds and protects nerve cells. Damage to this sheath slows down or blocks messages between the brain and the rest of the body. This leads to problems with Movement Speaking Vision Hearing Mental and physical development Most of the leukodystrophies are genetic . They usually appear during infancy or childhood. They can be hard to detect early because children seem healthy at first. However, symptoms gradually get worse over time. There are no cures for any of the leukodystrophies. Medicines, speech therapy and physical therapy might help with symptoms. Researchers are testing bone marrow transplantation as a treatment for some of the leukodystrophies.