Pelizaeus-Merzbacher disease is a rare, progressive, degenerative central nervous system disorder in which coordination, motor abilities, and intellectual function deteriorate. The disease is one of a group of genetic disorders called the leukodystrophies that affect growth of the myelin sheath, the fatty covering--which acts as an insulator--on nerve fibers in the brain. It is usually caused by a mutation of the gene that codes for a myelin protein called proteolipid protein or PLP. There are several forms of Pelizaeus-Merzbacher disease including classic, connatal, transitional, adult variants. Except for the adult form of the disease, onset of Pelizaeus-Merzbacher disease is usually in early infancy. Early symptoms may include slow growth, nystagmus (rapid, involuntary, rhythmic jerking of the eyes and the head), and failure to develop normal control of head movement. In adult-onset cases, deteriorating speech may be an early sign. Other symptoms may include tremor, various involuntary movements, grimacing, weakness, unsteady gait, and muscle contractures (shrinkage or shortening of a muscle). Over time, legs and arms may become spastic, and mental functions may deteriorate. Some patients may have convulsions and skeletal deformation, resulting from abnormal muscular stress on bones.
There is no cure for Pelizaeus-Merzbacher disease, nor is there a standard course of treatment. Treatment, which is symptomatic and supportive, may include medication for seizures and movement disorders. The prognosis for those with Pelizaeus-Merzbacher disease is poor. The course of the disorder is usually progressive deterioration until death.
