Expression of the PLP Gene: Studies Ondiagnosi and Treatment of PMD

Leukodystrophies represent a heterogeneous group of genetic disorders characterized by pathology in the white matter of the central nervous system and caused by alteration in myelin. The etiology remains often undetennined. The gene for PLP codes for the major proteins of CNS myelin, PLP and DM20. We have characterized the role that this gene has in the hypomyelinating leukodystrophies (Pelizaeus-Merzbacher Disease, Spastic Paraparesis type 2). The majority of mutations are duplications of large chromosomal region containing the PLP gene, others are deletions and point mutations. From these mutations phenotype-genotype correlations were established. Of the 443 patients affected by leukodystroghies of unknown etiologY recruited by our laboratory, 291 did not have any mutations typical for mutations in the PLP gene, i.e. either duplication/deletion of the entire gene or exonic mutations or mutations of the splicing sites. To better and fully characterize the role of PLP mutations in these patients, we have assessed other mutations that may potentially be pathogenic. We have looked for partial duplication/deletion of the PLP gene by utilizing MAPH (Multiplex Amplifiable Probe Hybridization) IN each exon and the regulatory promoter region and intron I, which is thought to contain regulatory regions and potentials exons. We have begun the characterization of levels of expression of PLP/DM20 at the RNA level in patients with mutations in the PLP/DM20 gene and in patients who do not carry any mutations in the PLP gene. These studies will allow to detennine whether mechanisms of gene regulation may play a role in the disease. We plan to sequence the genes encoding for two transcription factors that early in development control PLP expression: MyTI and Olig2. In parallel, with the goal of devising novel therapeutic strategies that modify PLP expression, we propose to test in oligodendrocytes in vitro: The role of non coding PLP/DM20m transcripts containing parts of intron I that we have identified in human brains. The efficacy of Short interfering (Si) RNA in order to reduce the PLP expression. Results obtained from these studies should have a major diagnostic and therapeutic impact on leukodystrophies caused by alterations in myelination, especially PMD.