MvaI polymorphism in the proteolipid protein (PLP) gene

ER stress and diseases

Proteins synthesized in the endoplasmic reticulum (ER) are properly folded with the assistance of ER chaperones. Malfolded proteins are disposed of by ER-associated protein degradation (ERAD). When the amount of unfolded protein exceeds the folding capacity of the ER, human cells activate a defense mechanism called the ER stress response, which induces expression of ER chaperones and ERAD components and transiently attenuates protein synthesis to decrease the burden on the ER. It has been revealed that three independent response pathways separately regulate induction of the expression of chaperones, ERAD components, and translational attenuation. A malfunction of the ER stress response caused by aging, genetic mutations, or environmental factors can result in various diseases such as diabetes, inflammation, and neurodegenerative disorders including Alzheimer's disease, Parkinson's disease, and bipolar disorder, which are collectively known as 'conformational diseases'. In this review, I will summarize recent progress in this field. Molecules that regulate the ER stress response would be potential candidates for drug targets in various conformational diseases.

Additional copies of the proteolipid protein gene causing Pelizaeus-Merzbacher disease arise by separate integration into the X chromosome

The proteolipid protein gene (PLP) is normally present at chromosome Xq22. Mutations and duplications of this gene are associated with Pelizaeus-Merzbacher disease (PMD). Here we describe two new families in which males affected with PMD were found to have a copy of PLP on the short arm of the X chromosome, in addition to a normal copy on Xq22. In the first family, the extra copy was first detected by the presence of heterozygosity of the AhaII dimorphism within the PLP gene. The results of FISH analysis showed an additional copy of PLP in Xp22.1, although no chromosomal rearrangements could be detected by standard karyotype analysis. Another three affected males from the family had similar findings. In a second unrelated family with signs of PMD, cytogenetic analysis showed a pericentric inversion of the X chromosome. In the inv(X) carried by several affected family members, FISH showed PLP signals at Xp11.4 and Xq22. A third family has previously been reported, in which affected members had an extra copy of the PLP gene detected at Xq26 in a chromosome with an otherwise normal banding pattern. The identification of three separate families in which PLP is duplicated at a noncontiguous site suggests that such duplications could be a relatively common but previously undetected cause of genetic disorders.

Pelizaeus-Merzbacher disease: three novel mutations and implication for locus heterogeneity

We report a mutational and polymorphic analysis of the proteolipid protein gene in members of 27 Japanese families with Pelizaeus-Merzbacher disease. We found causative mutations in 6 members of 27 families (22.2%); 5 of the 6 mutations, including two novel mutations, Leu45Arg and 231 + 2T --> G, resulted in the typically severe clinical symptoms. Paradoxically, the Cys219Tyr mutation, presumed to disrupt the tertiary structure of proteolipid protein by removing the disulfide bond between Cys200 and Cys219, was associated with a mild clinical presentation wherein the patient could walk with assistance and speak. It was inferred that the structural change prevented the toxicity associated with a gain of function mutation. Moreover, in one family 3 patients exhibited a intragenic polymorphism that did not segregate with the disease, suggesting a locus heterogeneity for Pelizaeus-Merzbacher disease.