New variant in exon 3 of the proteolipid protein (PLP) gene in a family with pelizaeus-merzbacher disease

A C → G transversion has been found in exon 3 of the PLP gene of affected males and their mother in a single sibship with Pelizaeus-Merzbacher disease (PMD). The transversion should not result in an amino acid change in the protein but it does result in the loss of a HaeIII restriction endonuclease cleavage site. It is concordant with the disease in this family. One-hundred-ten unrelated X chromosomes are negative for this mutation. No other sequence defect was found in the PLP exons of the affected males. The cause of disease in this family remains unknown, but the association between this rare mutation and PMD is intriguing. The mutation can serve as a marker for following segregation of the PLP gene.     

Family with Pelizaeus-Merzbacher disease/X-linked spastic paraplegia and a nonsense mutation in exon 6 of the proteolipid protein gene

We report on a C-to-T transition in exon 6 of the PLP gene in a male with Pelizaeus-Merzbacher disease/X-linked spastic paraplegia. The transition changes a glutamine at amino acid residue 233 to a termination codon. This premature stop codon probably results in a truncated protein that is not functional. Six other relatives were analyzed for the mutation and two female carriers were identified. Autopsy data on one male are presented. Am. J. Med. Genet. 71:357–360, 1997. © 1997 Wiley-Liss, Inc.     

Nonsense mutation in exon 3 of the proteolipid protein gene (PLP) in a family with an unusual form of Pelizaeus-Merzbacher disease

We report a G→A transition at nucleotide 431 of the proteolipid protein gene (PLP) results in a nonsense codon in a family with an unusual form of Pelizaeus-Merzbacher disease (PMD). The mutation, which creates a second AluI restriction site, results in a nonsense mutation in PLP. The clinical picture resembles somewhat that of X-linked spastic paraplegia (SPG). It differs from this and both the classical and connatal forms of PMD in that it is relatively mild in form, onset is delayed beyond age 2 years, nystagmus is absent, tremors are prominent, mental retardation is not severe, some patients show dementia or personality disorders, the disease is progressive rather than static in some, and several females show signs of disease. The nonsense mutation, which is in exon 3B, should block the synthesis of normal PLP but spare DM20, the isoform whose persistence has been associated with mild forms of PLP-associated disease in both humans and mice. Am. J. Med Genet. 69:121–125, 1997. © 1997 Wiley-Liss, Inc.     

Prenatal diagnosis in Pelizaeus-Merzbacher disease using RFLP analysis

Pelizaeus-Merzbacher disease (PMD) is a rare X-linked recessive disorder with severe psycho-motor retardation and neurological symptoms due to an inborn abnormality of proteolipid protein (PLP), the major protein component of myelin. A tight linkage between the gene of PLP and PMD locus has been suggested. We have carried out a series of RFLP studies using a cDNA probe for PLP and an anonymous DNA-fragment DXYS12 in a large Finnish family with at least three affected individuals. DNA analysis on chorionic villus specimens allowed us to exclude the disease in a male fetus of a possible carrier mother and, likewise, to demonstrate carrier status in a female fetus in another at-risk pregnancy.     

Different mutations in the same codon of the proteolipid protein gene,PLP, may help in correlating genotype with phenotype in Pelizaeus-Merzbacher disease/X-linked spastic paraplegia (PMD/SPG2)

Pelizaeus-Merzbacher disease/X-linked spastic paraplegia (PMD/SPG2) comprises a spectrum of diseases that range from severe to quite mild. The reasons for the variation in severity are not obvious, but suggested explanations include the extent of disruption of the transmembrane portion of the proteolipid protein caused by certain amino acid substitutions and interference with the trafficking of the PLP molecule in oligodendrocytes. Four codons in which substitution of more than one amino acid has occurred are available for examination of clinical and potential structural manifestations: Valine 165 to either glutamate or glycine, leucine 045 to either proline or arginine, aspartate 202 to asparagine or histidine, and leucine 223 to isoleucine or proline. Three of these mutations, Val165Gly, Leu045Pro, and Leu223Ile have not been described previously in humans. The altered amino acids appear in the A-B loop, C helix, and C-D loop, respectively. We describe clinically patients with the mutations T494G (Val165Gly), T134C (Leu045Pro), and C667A (Leu223Ile). We discuss also the previously reported mutations Asp202Asn and Asp202His. We have calculated the changes in hydrophobicity of short sequences surrounding some of these amino acids and compared the probable results of the changes in transmembrane structure of the proteolipid protein for the various mutations with the clinical data available on the patients. While the Val165Glu mutation, which is expected to produce disruption of a transmembrane loop of the protein, produces more severe disease than does Val165Gly, no particular correlation with hydrophobicity is found for the other mutations. As these are not in transmembrane domains, other factors such as intracellular transport or interaction between protein chains during myelin formation are probably at work. Am. J. Med. Genet. 82:132–139, 1999. © 1999 Wiley-Liss, Inc.     

Pelizaeus-Merzbacher disease: a point mutation in exon 6 of the proteolipid protein (PLP) gene

Pelizaeus-Merzbacher disease has been known since 1885. It is characterized by severe dysmyelination of the central nervous system. We describe a new mutation in exon 6 of the proteolipid protein gene in a 9-year-old boy with severe connatal Pelizaeus-Merzbacher disease.     

Connatal Pelizaeus-Merzbacher disease: A missense mutation in exon 4 of the proteolipid protein (PLP) gene

We investigated the proteolipid protein (PLP) gene in two brothers in a Japanese family with a connatal form of Pelizaeus-Merzbacher disease (PMD). Direct sequencing of the PLP gene revealed an A-to-T transition in exon 4, which led to an Asp-to-Val substitution at re-sidue 202. Their mother was confirmed to be heterozygous for the mutation. The mutation was not found in 78 X-chromosomes of normal Japanese individuals. A correlation between the clinical severity of the disease in the brothers and the Asp202-to-Val mutation in the PLP gene was suggested. Received: April 24, 1998 / Accepted: May 29, 1998     

X-linked spastic paraplegia due to a mutation (C506T; Ser169Phe) in exon 4 of the proteolipid protein gene (PLP)

A transition C506T was found in exon 4 of the proteolipid protein gene of a boy with spastic paraplegia. This mutation resulted in the substitution of phenylalanine for serine 169, which is in the third transmembrane domain of the proteolipid protein molecule. The mutation apparently arose de novo, as it was absent from his mother. Am. J. Med. Genet. 75:516–517, 1998. © 1998 Wiley-Liss, Inc.     

Pelizaeus-Merzbacher病的分子遗传学研究进展

Pelizaeus-Merzbacher病(PMD)是罕见的遗传性脑白质营养不良病,是由于蛋白脂蛋白(poteolipid protein 1,PLP1)基因的突变导致髓鞘不能正常形成所致,其中以PLP1基因的重复突变最多见.PLP1基因不同的突变可导致特定的疾病类型,且基因型和表型之间总体上存在对应关系.本文对PMD的分子遗传学特点及近期对该病分子、细胞机制的认识进行综述.     

Novel neuronal proteolipid protein isoforms encoded by the human myelin proteolipid protein 1 gene

The human myelin proteolipid protein 1 gene (hPLP1), which encodes the major structural myelin proteins of the central nervous system (CNS), is classically described as expressed in the oligodendrocytes, the CNS myelinating cells. We identified two new exons in the intron 1 of the hPLP1 gene that lead to the expression of additional mRNA and protein isoforms mainly expressed in neurons instead of oligodendrocytes. Those novel neuronal PLP isoforms are detected as soon as human fetal development and their concomitant expression is specific of the human species. As classical PLP proteins, the novel protein isoforms seem to be addressed to the plasma membrane. These results suggest for the first time that PLP may have functions in humans not only in oligodendrocytes but also in neurons and could be implicated in axono-glial communication. Moreover, this neuronal expression of the hPLP1 gene might explain the neuronal dysfunctions in patients carrying hPLP1 gene mutations.     

Pelizaeus-Merzbacher disease caused by a de novo mutation that originated in exon 2 of the maternal great-grandfather of the propositus

Pelizaeus-Merzbacher disease (PMD) is an X-linked dysmyelinating disorder of the central nervous system. Many cases of PMD can be attributed to defects in the proteolipid protein gene (PLP). To date, with one exception, each family has had either no or a unique mutation in one of the seven exons of PLP. We describe a new missense mutation in exon 2 of the PLP gene of an affected individual. This mutation codes for Ile instead of Thr at codon 42. The point mutation originated in the X chromosome of the maternal great-grandfather of the propositus. This was determined from the pattern of inheritance of the AhaII polymorphism and a series of microsatellite markers that are localized near PLP at Xq22. © 1995 Wiley-Liss, Inc.     

A new mutation in the proteolipid protein (PLP) gene in a German family with pelizaeus-merzbacher disease

A C-to-T transition in exon 4 of the PLP gene was found in 2 affected males and two obligate carriers in a German family with Pelizaeus–Merzbacher disease. The mutation, which causes loss of an HphI site and changes amino acid 155 from threonine to isoleucine, was absent from 108 normal chromosomes. There are 5 concordances and 1 discrepancy between these results and those obtained by magnetic resonance imaging in this family.     

蛋白脂蛋白在两型星形胶质细胞和少突胶质细胞中的表达

目的:探讨蛋白脂蛋白(PLP)在分化成熟的两型星形胶质细胞和少突胶质细胞中的表达。方法:用激光共聚焦双重免疫荧光标记技术检测PLP在分化成熟的两型星形胶质细胞和少突胶质细胞中的表达情况。结果:在O-2A谱系来源的成熟2型星形胶质细胞和少突胶质细胞中PLP抗体标记为阳性,而在T1A谱系来源的成熟1型星形胶质细胞中则未检测到PLP的表达,从而在蛋白质水平验证本室研究两型星形胶质细胞基因表达谱差异基因芯片结果中PLP mRNA在T2A中高表达,而在T1A中低表达的现象。结论:PLP等脂代谢相关基因可能在O-2A谱系发生和分化过程中起重要作用,O-2A谱系与神经髓鞘发生以及脑内脂质代谢内在机制密切相关。     

High-resolution diffusion tensor imaging of fixed brain in a mouse model of Pelizaeus-Merzbacher disease: comparison with quantitative measures of white matter pathology

Diffusion tensor imaging (DTI) is a powerful technique for the noninvasive assessment of the central nervous system. To facilitate the application of this technique to in vivo studies, we characterised a mouse model of the leukodystrophy, Pelizaeus-Merzbacher disease (PMD), comparing high-resolution ex vivo DTI findings with quantitative histological analysis of selected areas of the brain. The mice used in this study (Plp1-transgenic) carry transgenic copies of the Plp1 gene and are models for PMD as a result of gene duplication. Plp1 transgenic mice display a mild ataxia and experience frequent seizures around the time at which they were imaged. Axial (λ(1) ) and radial (RD) diffusivities and fractional anisotropy (FA) data were analysed using an exploratory whole-brain voxel-based method, a voxel-based approach using tract-based spatial statistics (TBSS), and by application of conventional region of interest (ROI) analyses to selected white matter tracts. Raw t value maps and TBSS analyses indicated widespread changes throughout the brain of Plp1-transgenic mice compared with the wild-type. ROI analyses of the corpus callosum, anterior commissure and hippocampal fimbria showed that FA was reduced significantly, whereas λ(1) and RD were increased significantly, in Plp1-transgenic mice compared with the wild-type. The DTI data derived from ROI analyses were subsequently compared with histological measures taken in the same regions. These revealed an almost complete absence of myelin, preservation of axons, marked astrocytosis and increased or unchanged cell densities. These data contribute to our growing understanding of the basis of anisotropic water diffusion in the normal and diseased nervous system.     

In-frame deletion in the proteolipid protein gene of a family with Pelizaeus-Merzbacher disease

We describe an in-frame deletion of parts of exons 3 and 4 of the proteolipid protein gene (PLP), with all of the intervening sequence, in a 3-generation family with Pelizaeus-Merzbacher disease. The mutation removes 49 amino acids of the PLP. © 1995 Wiley-Liss, Inc.     

Axon-glial interaction in the CNS: what we have learned from mouse models of Pelizaeus-Merzbacher disease

In the central nervous system (CNS) the majority of axons are surrounded by a myelin sheath, which is produced by oligodendrocytes. Myelin is a lipid-rich insulating material that facilitates the rapid conduction of electrical impulses along the myelinated nerve fibre. Proteolipid protein and its isoform DM20 constitute the most abundant protein component of CNS myelin. Mutations in the PLP1 gene encoding these myelin proteins cause Pelizaeus-Merzbacher disease and the related allelic disorder, spastic paraplegia type 2. Animal models of these diseases, particularly models lacking or overexpressing Plp1, have shed light on the interplay between axons and oligodendrocytes, and how one component influences the other.     

Intracellular trafficking of the JNCL protein CLN3

Juvenile neuronal ceroid lipofuscinosis is a lysosomal storage disease that causes visual impairment, progressive mental deterioration, and eventually death. A predominant 1.02-kb deletion as well as other mutations have been described in the CLN3 gene. Lacking significant identity with proteins of known function and no overt targeting signals within the primary amino acid sequence, accurate predictions of the intracellular location and function could not be made. Further, recent conflicting reports identified CLN3 as either a lysosomal or a mitochondrial protein. Transfection experiments using native and epitope-tagged fusion proteins were evaluated to help delineate CLN3 localization. We confirmed by immunohistochemistry and brefeldin A treatment that NH2-terminal green fluorescence protein (GFP)-CLN3 fusion proteins were retained in the Golgi apparatus, with no colocalization with mitochondrial markers. Anti-CLN3 antibodies directed against amino acids 67-90 of CLN3 were generated and shown to be specific for a 50-kDa protein in HEK 293 cells and GFP-CLN3 in transfected cells. However, cells transfected with nontagged CLN3 or carboxyl-terminal-tagged CLN3 were not immunoreactive with anti-CLN3 antibodies, suggesting that normally, the amino terminus interacts with other molecules. Thus, tags on the NH2-terminus probably inhibited these interactions and movement of CLN3 from the Golgi to more distal compartments. Also, CLN3 tagged at the COOH-terminus with either GFP or FLAG epitopes were retained in the ER, indicating a role for the COOH-terminus in trafficking. Taken together, these data confirm that CLN3 traffics through the ER and Golgi.     

Cargos and genes: insights into vesicular transport from inherited human disease

Many cellular functions depend on the correct delivery of proteins to specific intracellular destinations. Mutations that alter protein structure and disrupt trafficking of the protein (the "cargo") occur in many genetic disorders. In addition, an increasing number of disorders have been linked to mutations in the genes encoding components of the vesicular transport machinery responsible for normal protein trafficking. We review the clinical phenotypes and molecular pathology of such inherited "protein-trafficking disorders", which provide seminal insights into the molecular mechanisms of protein trafficking. Further characterisation of this expanding group of disorders will provide a basis for developing new diagnostic techniques and treatment strategies and offer insights into the molecular pathology of common multifactorial diseases that have been linked to disordered trafficking mechanisms.     

Phenotypic diversity of Menkes disease in mottled mice is associated with defects in localisation and trafficking of the ATP7A protein

Owing to mutations in the copper-transporting P-type ATPase, ATP7A (or MNK), patients with Menkes disease (MD) have an inadequate supply of copper to various copper-dependent enzymes. The ATP7A protein is located in the trans-Golgi network, where it transports copper via secretory compartments to copper-dependent enzymes. Raised copper concentrations result in the trafficking of ATP7A to the plasma membrane, where it functions in copper export. An important model of MD is the Mottled mouse, which possesses mutations in Atp7A. The Mottled mouse displays three distinct phenotypic severities: embryonic lethal, perinatal lethal and a longer-lived viable phenotype. However, the effects of mutations from these phenotypic classes on the ATP7A protein are unknown. In this study, we found that these classes of mutation differentially affect the copper transport and trafficking functions of the ATP7A protein. The embryonic lethal mutation, Atp7a(mo11H) (11H), caused mislocalisation of the protein to the endoplasmic reticulum, impaired glycosylation, and abolished copper delivery to the secretory pathway. In contrast, the perinatal lethal and viable mutations, Atp7a(moMac) (Macular) and Atp7a(moVbr) (Viable brindle) both resulted in a reduction in copper delivery to the secretory pathway and constitutive trafficking of the ATP7A protein to the plasma membrane in the absence of additional copper. In the case of Viable brindle, this hypertrafficking response was dependent on the catalytic phosphorylation site of ATP7A, whereas no such requirement was found for the Macular mutation. These findings provide evidence that the degree of MD severity in mice is associated with both copper transport and trafficking defects in the ATP7A protein.     

Identification of the encephalitogenic epitopes of CNS proteolipid protein in BALB/c mice

It was previously shown that BALB/c mice were susceptible to experimental autoimmune encephalomyelitis induced by immunization with proteolipid protein (PLP). To determine the encephalitogenic epitopes of PLP in BALB/c mice, mice were immunized with successively smaller pools of 20-mer peptides spanning the PLP molecule from amino acid 30 to amino acid 206. Immunization with PLP(180-199) resulted in clinical EAE in 9/15 mice (mean max clinical score of 3.3), and immunization with PLP(185-206) induced clinical EAE in 7/21 BALB/c mice (mean maximum score of 3.7). No relapses in disease were observed. No EAE was observed in BALB/c mice immunized with PLP(185-199) (n=15), PLP(178-191) (n=13) or other regions of PLP (n=15). Passive transfer of PLP(180-199)-primed lymph node cells into nai;ve BALB/c mice resulted in EAE (2/2 mice, max score of 4.0). One-micron toluidine blue stained sections from the spinal cord of EAE-affected BALB/c mice revealed features typical of EAE in other strains, including mononuclear cell infiltration, myelin loss, and axonal loss.