PLP1 Mutations Research Articles

Dört Aileden Pelizaeus-Merzbacher Sendromlu Altı Hastanın Klinik ve Moleküler Sitogenetik Analizleri

Objective: Pelizaeus-Merzbacher Disease is a rare X-linked recessive leukodystrophy caused by a mutation in the proteolipid protein (PLP) gene on chromosome Xq22. PMD is an early-onset neurological disorder characterized by nystagmus, spastic quadriplegia, ataxia, and developmental delay. Genetic analysis has identified Xq22 microduplications (60-70%), point mutations (10–25%), and deletions (5-10%) within the coding region of the PLP genes in Pelizaeus-Merzbacher Disease. This study evaluated six patients with PLP1 deletion and duplication in four Turkish families. Material and Methods: To detect the duplication and deletion of PLP1, chromosomal microarray analysis, and multiplex ligation-related probe amplification assays were performed. Results: In these four families, two brothers had a hemizygous deletion in the PLP1 gene, their carrier mother had a deletion in the PLP1 gene, and another two unrelated boys and one girl had duplication of the PLP1. Also, we identified the rare case of two brother patients who were found to have a hemizygous deletion in the PLP1 gene. Their carrier mother had unexplained dementia. Conclusion: Genotype-phenotype correlations of the PLP1 mutation in these families were identified in this study while trying to elucidate the genetic etiology of six individuals from four different families.

Cytotoxic CNS-associated T cells drive axon degeneration by targeting perturbed oligodendrocytes in PLP1 mutant mice

Myelin defects lead to neurological dysfunction in various diseases and in normal aging. Chronic neuroinflammation often contributes to axon-myelin damage in these conditions and can be initiated and/or sustained by perturbed myelinating glia. We have previously shown that distinct PLP1 mutations result in neurodegeneration that is largely driven by adaptive immune cells. Here we characterize CD8+ CNS-associated Tcells in myelin mutants using single-cell transcriptomics and identify population heterogeneity and disease-associated changes. We demonstrate that early sphingosine-1-phosphate receptor modulation attenuates Tcell recruitment and neural damage, while later targeting of CNS-associated Tcell populations is inefficient. Applying bone marrow chimerism and utilizing random X chromosome inactivation, we provide evidence that axonal damage is driven by cytotoxic, antigen specific CD8+ T cells that target mutant myelinating oligodendrocytes. These findings offer insights into neural-immune interactions and are of translational relevance for neurological conditions associated with myelin defects and neuroinflammation.

In Silico Structural Analysis Predicting the Pathogenicity of PLP1 Mutations in Multiple Sclerosis.

The X chromosome gene PLP1 encodes myelin proteolipid protein (PLP), the most prevalent protein in the myelin sheath surrounding the central nervous system. X-linked dysmyelinating disorders such as Pelizaeus-Merzbacher disease (PMD) or spastic paraplegia type 2 (SPG2) are typically caused by point mutations in PLP1. Nevertheless, numerous case reports have shown individuals with PLP1 missense point mutations which also presented clinical symptoms and indications that were consistent with the diagnostic criteria of multiple sclerosis (MS), a disabling disease of the brain and spinal cord with no current cure. Computational structural biology methods were used to assess the impact of these mutations on the stability and flexibility of PLP structure in order to determine the role of PLP1 mutations in MS pathogenicity. The analysis showed that most of the variants can alter the functionality of the protein structure such as R137W variants which results in loss of helix and H140Y which alters the ordered protein interface. In silico genomic methods were also performed to predict the significance of these mutations associated with impairments in protein functionality and could suggest a better definition for therapeutic strategies and clinical application in MS patients.

Missense mutation of MAL causes a rare leukodystrophy similar to Pelizaeus-Merzbacher disease

Leukodystrophies are a heterogenous group of genetic disorders, characterised by abnormal development of cerebral white matter. Pelizaeus-Merzbacher disease is caused by mutations in PLP1, encoding major myelin-resident protein required for myelin sheath assembly. We report a missense variant p.(Ala109Asp) in MAL as causative for a rare, hypomyelinating leukodystrophy similar to Pelizaeus-Merzbacher disease. MAL encodes a membrane proteolipid that directly interacts with PLP1, ensuring correct distribution during myelin assembly. In contrast to wild-type MAL, mutant MAL was retained in the endoplasmic reticulum but was released following treatment with 4-phenylbutyrate. Proximity-dependent identification of wild-type MAL interactants implicated post-Golgi vesicle-mediated protein transport and protein localisation to membranes, whereas mutant MAL interactants suggested unfolded protein responses. Our results suggest that mislocalisation of MAL affects PLP1 distribution, consistent with known pathomechanisms for hypomyelinating leukodystrophies.

Novel Insight into the Potential Pathogenicity of Mitochondrial Dysfunction Resulting from PLP1 Duplication Mutations in Patients with Pelizaeus–Merzbacher Disease

Among the hypomyelinating leukodystrophies, Pelizaeus–Merzbacher disease (PMD) is a representative disorder. The disease is caused by different types of PLP1 mutations, among which PLP1 duplication accounts for ∼70% of the mutations. Previous studies have shown that PLP1 duplications lead to PLP1 retention in the endoplasmic reticulum (ER); in parallel, recent studies have demonstrated that PLP1 duplication can also lead to mitochondrial dysfunction. As such, the respective roles and interactions of the ER and mitochondria in the pathogenesis of PLP1 duplication are not clear. In both PLP1 patients’ and healthy fibroblasts, we measured mitochondrial respiration with a Seahorse XF Extracellular Analyzer and examined the interactions between the ER and mitochondria with super-resolution microscopy (spinning-disc pinhole-based structured illumination microscopy, SD-SIM). For the first time, we demonstrated that PLP1 duplication mutants had closer ER-mitochondrion interfaces mediated through structural and morphological changes in both the ER and mitochondria-associated membranes (MAMs). These changes in both the ER and mitochondria then led to mitochondrial dysfunction, as reported previously. This work highlights the roles of MAMs in bridging PLP1 expression in the ER and pathogenic dysfunction in mitochondria, providing novel insight into the pathogenicity of mitochondrial dysfunction resulting from PLP1 duplication. These findings suggest that interactions between the ER and mitochondria may underlie pathogenic mechanisms of hypomyelinating leukodystrophies diseases at the organelle level.

One-step Reprogramming of Human Fibroblasts into Oligodendrocyte-like Cells by SOX10, OLIG2, and NKX6.2.

SummaryLimited access to human oligodendrocytes impairs better understanding of oligodendrocyte pathology in myelin diseases. Here, we describe a method to robustly convert human fibroblasts directly into oligodendrocyte-like cells (dc-hiOLs), which allows evaluation of remyelination-promoting compounds and disease modeling. Ectopic expression of SOX10, OLIG2, and NKX6.2 in human fibroblasts results in rapid generation of O4+ cells, which further differentiate into MBP+ mature oligodendrocyte-like cells within 16 days. dc-hiOLs undergo chromatin remodeling to express oligodendrocyte markers, ensheath axons, and nanofibers in vitro, respond to promyelination compound treatment, and recapitulate in vitro oligodendroglial pathologies associated with Pelizaeus-Merzbacher leukodystrophy related to PLP1 mutations. Furthermore, DNA methylome analysis provides evidence that the CpG methylation pattern significantly differs between dc-hiOLs derived from fibroblasts of young and old donors, indicating the maintenance of the source cells’ “age.” In summary, dc-hiOLs represent a reproducible technology that could contribute to personalized medicine in the field of myelin diseases.

Expanding the Clinical and Mutational Spectrum of the PLP1-Related Hypomyelination of Early Myelinated Structures (HEMS).

The PLP1 gene, located on chromosome Xq22, encodes the proteolipid protein 1 and its isoform DM20. Mutations in PLP1 cause a spectrum of white matter disorders of variable severity. Here we report on four additional HEMS patients from three families harboring three novel PLP1 mutations in exon 3B detected by targeted next-generation sequencing. Patients experienced psychomotor delay or nystagmus in the first year of age and then developed ataxic–spastic or ataxic syndrome, compatible with a phenotype of intermediate severity in the spectrum of PLP1-related disorders. Regression occurred at the beginning of the third decade of the eldest patient. Extrapyramidal involvement was rarely observed. Brain MRI confirmed the involvement of structures that physiologically myelinate early, although the pattern of abnormalities may differ depending on the age at which the study is performed. These new cases contribute to expanding the phenotypic and genotypic spectrum of HEMS. Additional studies, especially enriched by systematic functional evaluations and long-term follow-up, are welcome to better delineate the natural history of this rare hypomyelinating leukodystrophy.

PLP1 Mutations in Patients with Multiple Sclerosis: Identification of a New Mutation and Potential Pathogenicity of the Mutations.

PLP1 is located on the X-chromosome and encodes myelin proteolipid protein (PLP), the most abundant protein in central nervous system myelin. Generally, point mutations in PLP1 result in X-linked dysmyelinating disorders, such as Pelizaeus-Merzbacher disease (PMD) or spastic paraplegia type 2 (SPG2). However, several case studies have identified patients with missense point mutations in PLP1 and clinical symptoms and signs compatible with a diagnosis of multiple sclerosis (MS). To investigate if PLP1 mutations occur relatively frequently in MS, we sequenced the coding regions of PLP1 in 22 female MS patients who had developed disease after the age of 40 and in 42 healthy women, and identified a missense mutation in exon 2 of PLP1 resulting in a Leu30Val mutation in the protein in one of the MS patients. mCherry-tagged plasmids containing wild type or mutant PLP1 sequences of PLP, including two known PMD/SPG2-related mutations as positive controls, were constructed and transfected into Cos-7 cells. In comparison with cells transfected with wild type PLP1, all mutations caused significant accumulation of PLP in the endoplasmic reticulum of the cells and induction of the unfolded protein response—a mechanism that leads to apoptosis of cells expressing mutant proteins. Additionally, in silico analysis of the binding of peptides containing the Leu30Val mutation to the human leukocyte antigen (HLA) molecules carried by the patient harboring this mutation suggested that the mutation could produce several novel immunogenic epitopes in this patient. These results support the idea that mutations in myelin-related genes could contribute to the development of MS in a small proportion of patients.

Teriflunomide attenuates neuroinflammation-related neural damage in mice carrying human PLP1 mutations

BackgroundGenetically caused neurological disorders of the central nervous system (CNS) are mostly characterized by poor or even fatal clinical outcome and few or no causative treatments are available. Often, these disorders are associated with low-grade, disease-promoting inflammation, another feature shared by progressive forms of multiple sclerosis (PMS). We previously generated two mouse lines carrying distinct mutations in the oligodendrocytic PLP1 gene that have initially been identified in patients diagnosed with MS. These mutations cause a loss of PLP function leading to a histopathological and clinical phenotype common to both PMS and genetic CNS disorders, like hereditary spastic paraplegias. Importantly, neuroinflammation promotes disease progression in these models, suggesting that pharmacological modulation of inflammation might ameliorate disease outcome.MethodsWe applied teriflunomide, an approved medication for relapsing-remitting MS targeting activated T-lymphocytes, in the drinking water (10 mg/kg body weight/day). Experimental long-term treatment of PLP mutant mice was non-invasively monitored by longitudinal optical coherence tomography and by rotarod analysis. Immunomodulatory effects were subsequently analyzed by flow cytometry and immunohistochemistry and treatment effects regarding neural damage, and neurodegeneration were assessed by histology and immunohistochemistry.ResultsPreventive treatment with teriflunomide attenuated the increase in number of CD8+ cytotoxic effector T cells and fostered the proliferation of CD8+ CD122+ PD-1+ regulatory T cells in the CNS. This led to an amelioration of axonopathic features and neuron loss in the retinotectal system, also reflected by reduced thinning of the innermost retinal composite layer in longitudinal studies and ameliorated clinical outcome upon preventive long-term treatment. Treatment of immune-incompetent PLP mutants did not provide evidence for a direct, neuroprotective effect of the medication. When treatment was terminated, no rebound of neuroinflammation occurred and histopathological improvement was preserved for at least 75 days without treatment. After disease onset, teriflunomide halted ongoing axonal perturbation and enabled a recovery of dendritic arborization by surviving ganglion cells. However, neither neuron loss nor clinical features were ameliorated, likely due to already advanced neurodegeneration before treatment onset.ConclusionsWe identify teriflunomide as a possible medication not only for PMS but also for inflammation-related genetic diseases of the nervous system for which causal treatment options are presently lacking.

Exome sequencing reveals a novel PLP1 mutation in a Moroccan family with connatal Pelizaeus-Merzbacher disease: a case report

BackgroundEpilepsy regroups a common and diverse set of chronic neurological disorders that are characterized by spontaneous, unprovoked, and recurrent epileptic seizures. Epilepsies have a highly heterogeneous background with a strong genetic contribution and various mode of inheritance. X-linked epilepsy usually manifests as part of a syndrome or epileptic encephalopathy. The variability of clinical manifestations of X-linked epilepsy may be attributed to several factors including the causal genetic mutation, making diagnosis, genetic counseling and treatment decisions difficult. We report the description of a Moroccan family referred to our genetic department with X-linked epileptic seizures as the only initial diagnosis.Case presentationKnowing the new contribution of Next-Generation Sequencing (NGS) for clinical investigation, and given the heterogeneity of this group of disorders we performed a Whole-Exome Sequencing (WES) analysis and co-segregation study in several members of this large family. We detected a novel pathogenic PLP1 missense mutation c.251C > A (p.Ala84Asp) allowing us to make a diagnosis of Pelizaeus-Merzbacher Disease for this family.ConclusionThis report extends the spectrum of PLP1 mutations and highlights the diagnostic utility of NGS to investigate this group of heterogeneous disorders.

1 - Patterns and modulations of Pendular nystagmus in a family with hereditary spastic paraplegia

Hereditary spastic paraplegia (HSP) is characterized by progressive spasticity and weakness of the lower extremities. Additional findings include ataxia, extrapyramidal signs, and dementia. Pendular nystagmus (PN) has been reported in some subtypes of HSP caused by PLP1 (SPG2) or paraplegin (SPG7) mutation. To describe the patterns and modulation of PN in HSP, we performed eye movement recording using video-oculography in a Korean family with HSP and PN. The PN was convergent-divergent in the oblique plane with a frequency of 6 to 7Hz and maximum amplitude at about 1.5°. The nystagmus diminished briefly after blinks and horizontal saccades, and decreased during eccentric gaze and convergence. Horizontal saccades shifted the phase of the oscillations. During lateral gazes, the PN increased in the abducting eye, but decreased in the adducting eye. Vibratory stimuli decreased the nystagmus mostly in the left but not in the right eye. No pathogenic mutation was found in the genetic loci known for causing spastic paraplegia by whole-exome sequencing. The unusual features and modulation of PN in our patients with HSP emphasize the role of disconjugate and disjunctive capabilities of the brain in ocular motor control, and exemplify what can go wrong.

SPG2 mimicking multiple sclerosis in a family identified using next generation sequencing

Several single gene disorders can potentially be overlooked in the differential diagnostic evaluation of patients with multiple sclerosis (MS). Pelizaeus-Merzbacher disease and spastic paraplegia type 2 are allelic X-linked disorders associated with defective myelination of the central nervous system and mutations in PLP1. Neurological symptoms are occasionally observed in female carriers of these mutations.Two women – the proposita (Pt1) and her mother (Pt2) – reported walking difficulties since adolescence and showed progressive cognitive decline. Their neurological examinations revealed spastic gait, pyramidal tract involvement and distal muscle atrophy in the legs. Peripheral neuropathy and diffuse white matter (WM) changes on brain MRI were also observed. Both patients had a preliminary diagnosis of primary progressive MS. Using a targeted method in next generation sequencing, the novel heterozygous c.210T>G/p.Y70* in PLP1 was identified in Pt2. The same mutation was also found in Pt1 but not in five healthy relatives. The mutation showed moderate-to-severe skewed X inactivation in tissues, and Western blotting revealed a significant reduction of PLP1 and DM20 in the sural nerve of Pt2. In conclusion a mother and daughter presented an X-linked dominant disorder with skewed X inactivation. The authors suggest that PLP1 testing might be considered in the evaluation of women with spastic paraparesis, cognitive decline and WM changes.

A novel PLP1 mutation F240L identified in a patient with connatal type Pelizaeus-Merzbacher disease

Pelizaeus-Merzbacher disease (PMD) is an X-linked recessive hypomyelination disorder caused by mutations in the proteolipid protein 1 gene (PLP1) located on chromosome Xq22. A male patient showed severe developmental delay, pendular nystagmus and laryngeal wheezing. The auditory brain stem response showed only the first wave and brain magnetic resonance imaging showed white matter hypomyelination, suggesting typical PMD. A novel PLP1 mutation, F240L, which was inherited from his mother, was identified.

A microdeletion at Xq22.2 implicates a glycine receptor GLRA4 involved in intellectual disability, behavioral problems and craniofacial anomalies.

BackgroundAmong the 21 annotated genes at Xq22.2, PLP1 is the only known gene involved in Xq22.2 microdeletion and microduplication syndromes with intellectual disability. Using an atypical microdeletion, which does not encompass PLP1, we implicate a novel gene GLRA4 involved in intellectual disability, behavioral problems and craniofacial anomalies.Case presentationWe report a female patient (DGDP084) with a de novo Xq22.2 microdeletion of at least 110 kb presenting with intellectual disability, motor delay, behavioral problems and craniofacial anomalies. While her phenotypic features such as cognitive impairment and motor delay show overlap with Pelizaeus-Merzbacher disease (PMD) caused by PLP1 mutations at Xq22.2, this gene is not included in our patient’s microdeletion and is not dysregulated by a position effect. Because the microdeletion encompasses only three genes, GLRA4, MORF4L2 and TCEAL1, we investigated their expression levels in various tissues by RT-qPCR and found that all three genes were highly expressed in whole human brain, fetal brain, cerebellum and hippocampus. When we examined the transcript levels of GLRA4, MORF4L2 as well as TCEAL1 in DGDP084′s family, however, only GLRA4 transcripts were reduced in the female patient compared to her healthy mother. This suggests that GLRA4 is the plausible candidate gene for cognitive impairment, behavioral problems and craniofacial anomalies observed in DGDP084. Importantly, glycine receptors mediate inhibitory synaptic transmission in the brain stem as well as the spinal cord, and are known to be involved in syndromic intellectual disability.ConclusionWe hypothesize that GLRA4 is involved in intellectual disability, behavioral problems and craniofacial anomalies as the second gene identified for X-linked syndromic intellectual disability at Xq22.2. Additional point mutations or intragenic deletions of GLRA4 as well as functional studies are needed to further validate our hypothesis.Electronic supplementary materialThe online version of this article (doi:10.1186/s12883-016-0642-z) contains supplementary material, which is available to authorized users.

Severe Hypotonia, Nystagmus and Hypomyelination in A 9-Month Female Infant: Diagnosing Pelizaeus–Merzbacher Disease Outside the Usual Inheritance Patterns

Pelizaeus-Merzbacher disease is a rare X-linked recessive disorder regarding the defective myelin sheath formation in the CNS neurons due to mutations of the proteolipid protein 1 gene (PLP1). Even though it is predominant in males, affected females have been found to represent a small proportion in the medical literature 1. A wide variety of PLP1 mutations have been reported as a cause. Herein, we describe the case of a 9-month-old female with (bearing) the typical features of the disease who was found to have a rare mutation.

Screening for GFAP rearrangements in a cohort of Alexander disease and undetermined leukoencephalopathy patients

Alexander disease (AxD), a fatal degenerative leukoencephalopathy, is caused by de novo heterozygous missense mutations in the Glial Fibrillary Acidic Protein (GFAP) gene. The pathological hallmark of the disease is the presence of Rosenthal fibers, cytoplasmic inclusions in astrocytes, composed mainly of GFAP, αB-crystallin and HSP27.To date, several patients with a typical presentation of the disease or displaying characteristic Rosenthal fibers in brain material have been reported with no GFAP mutation. Recently, several studies have demonstrated a correlation between Rosenthal fiber formation and wild-type GFAP overexpression, despite the absence of mutations.We tested the hypothesis that a GFAP gene rearrangement could modulate AxD severity or promote GFAP overexpression and aggregation, resulting in leukoencephalopathy. A QMPSF assay was validated for 11 exonic fragments: 3 in control genes (CFTR, DSCR1, F9) and 8 corresponding to GFAP exons. A total of 97 patients suspected of AxD were analyzed: 28 with a GFAP mutation; 69 with clinical and magnetic resonance imaging criteria compatible with the disease. Neither duplications nor deletions of GFAP were found, suggesting that GFAP coding-region rearrangements may not be involved in AxD or Alexander-related leukoencephalopathies.In addition, 80 patients with undetermined leukodystrophies, and negative for PLP1, GJA12, Sox10 and MCT8 mutations and PLP1 and Lamin B1 rearrangements, were tested. These patients were also negative for GFAP rearrangements.Other hypotheses should be investigated for a molecular diagnosis in patients with undetermined leukoencephalopathy: mutations in GFAP isoforms, splicing sites or regulatory regions, or defaults in genes encoding molecular partners of GFAP.

OP49 – 2560: PLP1 mutations affecting PLP1/DM20 alternative splicing causes hypomyelination of early myelinating structures

Objectives Inherited leukodystrophies represent a diagnostic challenge, as many patients remain without definitive diagnosis. In this study we investigated the genetic etiology of the recently described X-linked childhood disorder “Hypomyelination of Early Myelinating Structures” (HEMS). In HEMS, brain structures normally myelinating early, are hypomyelinated, which is in contrast to known hypomyelination disorders, like Pelizaeus-Merzbacher disease (PMD). Methods We included patients diagnosed with HEMS by brain MRI criteria and affected siblings. Exome sequencing was used to search for causal mutations in 16 patients of 10 families. In silico analysis of effects of the mutations on splicing and secondary RNA folding was performed. Also, gene splicing was examined in RNA prepared from patients' fibroblasts and an immortalized immature oligodendrocyte cell line after transfection with mutant minigene splicing constructs. Results All patients had unusual hemizygous mutations in a specific region of the PLP1 gene. These mutations were located in exon 3B (2 silent, 1 missense and 1 deletion), which is splice out in isoform DM20 or in intron 3 outside the splice donor sequence (5 mutations). Four mutations are located deep in intron 3; a region that is not sequenced with Sanger sequencing. These mutations effect the secondary PLP1 RNA structure and decreased the PLP1/DM20 ratio. The other mutations, except for the deletion that truncated PLP1 but not DM20, were also predicted to alter PLP1/DM20 alternative splicing. Splicing studies in fibroblasts' and transfected cells confirmed a decreased PLP1/DM20 ratio. Conclusions We show that specific mutations in the PLP1 gene cause a hypomyelination pattern which contrasts the pattern seen in PMD, also caused by PLP1 mutations. This indicates that the PLP1/DM20 ratio influences early myelination. The mutations present in HEMS patients provide a challenge for PLP1 diagnostic sequencing and support the need to include intron 3.

PLP1 mutations in patients with multiple sclerosis: Identification of a new mutation and analysis of in vitro effects of PLP1 mutations

PLP1 is located on the X-chromosome and encodes myelin proteolipid protein (PLP), which is produced by oligodendrocytes and is the most abundant protein of central nervous system (CNS) myelin. Generally, mutations in PLP1 result in the X-linked dysmyelinating disorders Pelizaeus–Merzbacher disease (PMD) or spastic paraplegia type 2. However, 2 case studies (Warshawsky et al., 2005; Gorman et al., 2007) identified 2 patients with clinical symptoms and signs indistinguishable from multiple sclerosis (MS) who had missense point mutations in PLP1 (resulting in changes Leu30Arg and Arg136Trp in the protein). To investigate whether PLP1 mutations might occur relatively frequently in MS, we sequenced the coding regions of PLP1 in 22 female MS patients who had developed MS after the age of 40 and in 51 healthy females, and identified a missense mutation in exon 2 of PLP1 (resulting in a Leu30Val mutation in the protein) in one of the MS patients. mCherry-tagged plasmids containing wild type or mutant PLP1 sequences encoding the 7 exons of PLP (including two known PMD-related mutations as positive controls) were constructed and transfected into COS-7 cells. In the cells transfected with wild type PLP1, PLP was expressed throughout the cells and at the cell surface by 12 h post-transfection. In contrast, the two PMD-related mutations and one of the 3 MS-related PLP1 mutations (Leu30Arg) caused accumulation of PLP in the endoplasmic reticulum of the cells and induction of the unfolded protein response, leading to apoptosis of the cells. While the Leu30Val mutation identified in the current study did not adversely affect the distribution of PLP in the COS-7 cells or induce the unfolded protein response, in silico analysis of HLA binding for the HLA molecules carried by the patient harbouring this mutation suggested that the mutation would produce a novel immunogenic PLP epitope in this patient. These results suggest that PLP1 mutations can occur in patients who meet clinical criteria for MS, and that some of these mutations have the potential to induce oligodendrocyte apoptosis. Other PLP1 mutations may produce novel epitopes of PLP that could become targets of autoreactivity in MS. The results support the idea that mutations in myelin-related genes could underlie development of MS in some patients.

Pelizaeus-Merzbacher disease: cellular pathogenesis and pharmacologic therapy.

Pelizaeus-Merzbacher disease (PMD) is a rare leukodystrophy that causes severe dysmyelination in the central nervous system in infancy and early childhood. Many previous studies showed that various proteolipid protein 1 (plp1) mutations, including duplications, point mutations, and deletions, lead to oligodendrocyte dysfunction in patients with PMD. PMD onset and clinical severity range widely, depending on the type of plp1 mutation. Patients with PMD exhibit a delayed mental and physical development phenotype, but specific pharmacological therapy and clinical treatment for PMD are not yet well established. This review describes PMD pathology and establishment of new clinical treatment for PMD. These findings support the development of a new therapy for PMD and these treatments may improve the quality of life in patients with PMD.

Brain magnetic resonance imaging findings and auditory brainstem response in a child with spastic paraplegia 2 due to a PLP1 splice site mutation

A boy with spastic paraplegia type 2 (SPG2) due to a novel splice site mutation of PLP1 presented with progressive spasticity of lower limbs, which was first observed during late infancy, when he gained the ability to walk with support. His speech was slow and he had dysarthria. The patient showed mildly delayed intellectual development. Subtotal dysmyelination in the central nervous system was revealed, which was especially prominent in structures known to be myelinated during earlier period, whereas structures that are myelinated later were better myelinated. These findings on the brain magnetic resonance imaging were unusual for subjects with PLP1 mutations. Peaks I and II of the auditory brainstem response (ABR) were normally provoked, but peaks III-V were not clearly demarcated, similarly to the findings in Pelizaeus-Merzbacher disease. These findings of brain MRI and ABR may be characteristic for a subtype of SPG2 patients.