During the sixties a sex-specific, hereditary form of congenital tremor type A (CT A) appeared which was classified as CT AIII. The symptoms were the same as in other subtypes and only autopsy and differential diagnosis showed the distinctive signs of this disease. Pigs suffering from CT AIII fail to develop a tight myelin sheath and contain a reduced number of oligodendrocytes in their CNS whereas no pathological changes can be detected in the PNS. The same symptoms as with CT AIII appear in various disorders in animals and humans. The cause for jimpy in mice was traced back to a mutation in the PLP gene. In the course of these findings different mutations in the human PLP gene were identified and shown to be the reason for the rare Pelizaeus-Merzbacher-Disease and the spastic paraplegia type 2. If one considers the clinical and histological similarities between PLP mutants and CT AIII in pigs it is reasonable to assume that this X-linked gene plays a major role in the development of CT AIII. In the following we describe the isolation and characterization of the porcine PLP gene and its possible involvement in congenital tremor type AIII.