Pelizaeus-Merzbacher-like disease, or PMLD, is a slowly progressive disease of myelin, which is the white matter of the central nervous system (brain and spinal cord).
In patients with PMLD, the myelin does not form properly. Myelin insulates the nerves for proper conduction of nerve impulses. When the myelin does not form properly, nerve impulses do not travel properly in the central nervous system
The symptoms of PMLD are: weak muscle tone (hypotonia), involuntary movements of the eyes (nystagmus), and delayed development of speech and motor skills, such as sitting or grasping objects, and muscle stiffness (spasticity), which replaces hypotonia as children get older.