The recent detection of mutations in the myelin proteolipid protein (PLP) gene in several PMD patients offers the opportunity both to design DNA-based tests that would be useful in diagnosing a proportion of PMD cases and, in particular, to evaluate the diagnostic utility of single-strand conformation polymorphism (SSCP) analysis for this disease.
Carrier detection and prenatal diagnosis of Pelizaeus-Merzbacher disease using a combination of anonymous DNA polymorphisms and the proteolipid protein (PLP) gene cDNA.
The specificity of this protein deficiency in Pelizaeus-Merzbacher disease gains additional support from the recent mapping of the lipophilin gene to the human X chromosome.
Comparison of the gene maps of the human and mouse X chromosomes suggests that myelin proteolipid protein may be involved in X-linked mutations at the mouse jimpy locus and has implications for Pelizaeus-Merzbacher disease, a human inherited X-linked myelin disorder.
Findings in our patients support that this form of spastic paraplesia is allelic to Pelizaeus-Merzbacher disease and that the mild clinical phenotype of this disorder may be related to a mutation within exon 3B of the PLP gene.
Single-strand conformational polymorphism analysis of an affected male with Pelizaeus-Merzbacher disease (PMD) showed a slight change in mobility of amplified exon 5 of the proteolipid protein (PLP) gene.
We report a dinucleotide polymorphism in the first intron of the proteolipid protein (PLP) gene with a heterozygosity frequency of 0.69 useful for molecular analysis of families with X-linked neurologic disorders characterized by dysmyelination of the central nervous system, Pelizaeus-Merzbacher Disease (PMD) and X-linked Spastic Paraplegia (SPG2).
As the proteolipid protein gene (PLP) is within this region and mutations have been shown to be associated with non-classical PMD (Pelizaeus-Merzbacher disease), such as complex X linked hereditary spastic paraplegia, PLP may represent a candidate gene for this disorder.
Direct sequencing of the PLP gene and PLP mRNAs from the brain of the PMD patient revealed a G to T transition in exon V of the PLP gene, which leads to a glycine to cysteine substitution at residue 220.
In an attempt to identify molecular defects of this genomic region that are responsible for PMD, these results meant that RFLP analysis could be used to improve genetic counseling for the numerous affected families in which a PLP exon mutation could not be demonstrated.
The X chromosome-linked PLP/DM-20 gene is the CNS myelin gene most frequently associated with mutations, resulting in dysmyelination in several species including man (Pelizaeus-Merzbacher disease, X-linked Spastic Paraplegia).
Because a homologous myelin protein gene, PMP22, is duplicated in the majority of patients with Charcot-Marie-Tooth 1A, PLP gene overdosage may be a important genetic abnormality in PMD and affect myelin formation.
Although this patient might be heterozygous for a mutation of the extraexonic PLP gene sequences or of other unknown X-linked PLP associated genes, we speculate that this case had a dysmyelinating disease with an autosomal recessive trait characterized by the same phenotype as that of PMD.