Protein, proteolipid (PLP)

The most abundant protein of the myelin sheath (the covering of the nerves) in the central nervous system (CNS). The gene that codes for PLP is on the X chromosome. Mutations in PLP cause Pelizaeus-Merzbacher disease (PMD), an X-linked recessive disorder (it affects boys only) characterized by loss of myelin. PMD causes nystagmus (rhythmical oscillation of the eyeballs), psychomotor developmental delay, tremor, spasticity (increased muscular tone), and ataxia (wobbliness). The mutations in PLP result in the loss of myelin that translates into the neurological problems. The severity of myelin loss is dependent on the particular PLP mutation and can range from early lethal forms of PMD to a mild disorder known as spastic paraplegia type 2 (SPG2). Among the mutations in PLP gene that can cause PMD is a duplication of PLP in which the duplicated region may be far away from the original PLP locus in chromosome region Xq22. The PLP duplication is almost always present in the mothers of affected boys and usually can be traced to the maternal grandfather.