Publications by authors named "Grace M Hobson"

28 Publications

  • Page 1 of 1

Endocrine and Growth Abnormalities in 4H Leukodystrophy Caused by Variants in POLR3A, POLR3B, and POLR1C.

J Clin Endocrinol Metab 2021 01;106(2):e660-e674

Department of Child Neurology, University Children's Hospital Tübingen, Tübingen, Germany.

Context: 4H or POLR3-related leukodystrophy is an autosomal recessive disorder typically characterized by hypomyelination, hypodontia, and hypogonadotropic hypogonadism, caused by biallelic pathogenic variants in POLR3A, POLR3B, POLR1C, and POLR3K. The endocrine and growth abnormalities associated with this disorder have not been thoroughly investigated to date.

Objective: To systematically characterize endocrine abnormalities of patients with 4H leukodystrophy.

Design: An international cross-sectional study was performed on 150 patients with genetically confirmed 4H leukodystrophy between 2015 and 2016. Endocrine and growth abnormalities were evaluated, and neurological and other non-neurological features were reviewed. Potential genotype/phenotype associations were also investigated.

Setting: This was a multicenter retrospective study using information collected from 3 predominant centers.

Patients: A total of 150 patients with 4H leukodystrophy and pathogenic variants in POLR3A, POLR3B, or POLR1C were included.

Main Outcome Measures: Variables used to evaluate endocrine and growth abnormalities included pubertal history, hormone levels (estradiol, testosterone, stimulated LH and FSH, stimulated GH, IGF-I, prolactin, ACTH, cortisol, TSH, and T4), and height and head circumference charts.

Results: The most common endocrine abnormalities were delayed puberty (57/74; 77% overall, 64% in males, 89% in females) and short stature (57/93; 61%), when evaluated according to physician assessment. Abnormal thyroid function was reported in 22% (13/59) of patients.

Conclusions: Our results confirm pubertal abnormalities and short stature are the most common endocrine features seen in 4H leukodystrophy. However, we noted that endocrine abnormalities are typically underinvestigated in this patient population. A prospective study is required to formulate evidence-based recommendations for management of the endocrine manifestations of this disorder.
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http://dx.doi.org/10.1210/clinem/dgaa700DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7823228PMC
January 2021

Estimating the relative frequency of leukodystrophies and recommendations for carrier screening in the era of next-generation sequencing.

Am J Med Genet A 2020 08 23;182(8):1906-1912. Epub 2020 Jun 23.

Department of Neurology, Children's Hospital of Philadelphia, Philadelphia, Pennsylvania, USA.

Leukodystrophies are a heterogeneous group of heritable disorders characterized by abnormal brain white matter signal on magnetic resonance imaging (MRI) and primary involvement of the cellular components of myelin. Previous estimates suggest the incidence of leukodystrophies as a whole to be 1 in 7,000 individuals, however the frequency of specific diagnoses relative to others has not been described. Next generation sequencing approaches offer the opportunity to redefine our understanding of the relative frequency of different leukodystrophies. We assessed the relative frequency of all 30 leukodystrophies (associated with 55 genes) in more than 49,000 exomes. We identified a relatively high frequency of disorders previously thought of as very rare, including Aicardi Goutières Syndrome, TUBB4A-related leukodystrophy, Peroxisomal biogenesis disorders, POLR3-related Leukodystrophy, Vanishing White Matter, and Pelizaeus-Merzbacher Disease. Despite the relative frequency of these conditions, carrier-screening laboratories regularly test only 20 of the 55 leukodystrophy-related genes, and do not test at all, or test only one or a few, genes for some of the higher frequency disorders. Relative frequency of leukodystrophies previously considered very rare suggests these disorders may benefit from expanded carrier screening.
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http://dx.doi.org/10.1002/ajmg.a.61641DOI Listing
August 2020

Genome sequencing in persistently unsolved white matter disorders.

Ann Clin Transl Neurol 2020 01 7;7(1):144-152. Epub 2020 Jan 7.

Division of Neurology, Children's Hospital of Philadelphia, Philadelphia, Pennsylvania.

Genetic white matter disorders have heterogeneous etiologies and overlapping clinical presentations. We performed a study of the diagnostic efficacy of genome sequencing in 41 unsolved cases with prior exome sequencing, resolving an additional 14 from an historical cohort (n = 191). Reanalysis in the context of novel disease-associated genes and improved variant curation and annotation resolved 64% of cases. The remaining diagnoses were directly attributable to genome sequencing, including cases with small and large copy number variants (CNVs) and variants in deep intronic and technically difficult regions. Genome sequencing, in combination with other methodologies, achieved a diagnostic yield of 85% in this retrospective cohort.
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http://dx.doi.org/10.1002/acn3.50957DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6952322PMC
January 2020

Distinct patterns of complex rearrangements and a mutational signature of microhomeology are frequently observed in PLP1 copy number gain structural variants.

Genome Med 2019 12 9;11(1):80. Epub 2019 Dec 9.

Graduate Program in Diagnostic Genetics, School of Health Professions, The University of Texas MD Anderson Cancer Center, Houston, TX, USA.

Background: We investigated the features of the genomic rearrangements in a cohort of 50 male individuals with proteolipid protein 1 (PLP1) copy number gain events who were ascertained with Pelizaeus-Merzbacher disease (PMD; MIM: 312080). We then compared our new data to previous structural variant mutagenesis studies involving the Xq22 region of the human genome. The aggregate data from 159 sequenced join-points (discontinuous sequences in the reference genome that are joined during the rearrangement process) were studied. Analysis of these data from 150 individuals enabled the spectrum and relative distribution of the underlying genomic mutational signatures to be delineated.

Methods: Genomic rearrangements in PMD individuals with PLP1 copy number gain events were investigated by high-density customized array or clinical chromosomal microarray analysis and breakpoint junction sequence analysis.

Results: High-density customized array showed that the majority of cases (33/50; ~ 66%) present with single duplications, although complex genomic rearrangements (CGRs) are also frequent (17/50; ~ 34%). Breakpoint mapping to nucleotide resolution revealed further previously unknown structural and sequence complexities, even in single duplications. Meta-analysis of all studied rearrangements that occur at the PLP1 locus showed that single duplications were found in ~ 54% of individuals and that, among all CGR cases, triplication flanked by duplications is the most frequent CGR array CGH pattern observed. Importantly, in ~ 32% of join-points, there is evidence for a mutational signature of microhomeology (highly similar yet imperfect sequence matches).

Conclusions: These data reveal a high frequency of CGRs at the PLP1 locus and support the assertion that replication-based mechanisms are prominent contributors to the formation of CGRs at Xq22. We propose that microhomeology can facilitate template switching, by stabilizing strand annealing of the primer using W-C base complementarity, and is a mutational signature for replicative repair.
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http://dx.doi.org/10.1186/s13073-019-0676-0DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6902434PMC
December 2019

Xq22 deletions and correlation with distinct neurological disease traits in females: Further evidence for a contiguous gene syndrome.

Hum Mutat 2020 01 14;41(1):150-168. Epub 2019 Nov 14.

Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, Texas.

Xq22 deletions that encompass PLP1 (Xq22-PLP1-DEL) are notable for variable expressivity of neurological disease traits in females ranging from a mild late-onset form of spastic paraplegia type 2 (MIM# 312920), sometimes associated with skewed X-inactivation, to an early-onset neurological disease trait (EONDT) of severe developmental delay, intellectual disability, and behavioral abnormalities. Size and gene content of Xq22-PLP1-DEL vary and were proposed as potential molecular etiologies underlying variable expressivity in carrier females where two smallest regions of overlap (SROs) were suggested to influence disease. We ascertained a cohort of eight unrelated patients harboring Xq22-PLP1-DEL and performed high-density array comparative genomic hybridization and breakpoint-junction sequencing. Molecular characterization of Xq22-PLP1-DEL from 17 cases (eight herein and nine published) revealed an overrepresentation of breakpoints that reside within repeats (11/17, ~65%) and the clustering of ~47% of proximal breakpoints in a genomic instability hotspot with characteristic non-B DNA density. These findings implicate a potential role for genomic architecture in stimulating the formation of Xq22-PLP1-DEL. The correlation of Xq22-PLP1-DEL gene content with neurological disease trait in female cases enabled refinement of the associated SROs to a single genomic interval containing six genes. Our data support the hypothesis that genes contiguous to PLP1 contribute to EONDT.
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http://dx.doi.org/10.1002/humu.23902DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6953250PMC
January 2020

Morpholino Antisense Oligomers as a Potential Therapeutic Option for the Correction of Alternative Splicing in PMD, SPG2, and HEMS.

Mol Ther Nucleic Acids 2018 Sep 5;12:420-432. Epub 2018 Jul 5.

Nemours Biomedical Research, Alfred I. duPont Hospital for Children, Wilmington, DE 19803, USA; Department of Biological Sciences, University of Delaware, Newark, DE 19716, USA; Department of Pediatrics, Jefferson Medical College, Thomas Jefferson University, Philadelphia, PA 19107, USA. Electronic address:

DNA variants of the proteolipid protein 1 gene (PLP1) that shift PLP1/DM20 alternative splicing away from the PLP1 form toward DM20 cause the allelic X-linked leukodystrophies Pelizaeus-Merzbacher disease (PMD), spastic paraplegia 2 (SPG2), and hypomyelination of early myelinating structures (HEMS). We designed a morpholino oligomer (MO-PLP) to block use of the DM20 5' splice donor site, thereby shifting alternative splicing toward the PLP1 5' splice site. Treatment of an immature oligodendrocyte cell line with MO-PLP significantly shifted alternative splicing toward PLP1 expression from the endogenous gene and from transfected human minigene splicing constructs harboring patient variants known to reduce the amount of the PLP1 spliced product. Additionally, a single intracerebroventricular injection of MO-PLP into the brains of neonatal mice, carrying a deletion of an intronic splicing enhancer identified in a PMD patient that reduces the Plp1 spliced form, corrected alternative splicing at both RNA and protein levels in the CNS. The effect lasted to post-natal day 90, well beyond the early post-natal spike in myelination and PLP production. Further, the single injection produced a sustained reduction of inflammatory markers in the brains of the mice. Our results suggest that morpholino oligomers have therapeutic potential for the treatment of PMD, SPG2, and HEMS.
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http://dx.doi.org/10.1016/j.omtn.2018.05.019DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6036941PMC
September 2018

Auditory function in Pelizaeus-Merzbacher disease.

J Neurol 2018 Jul 3;265(7):1580-1589. Epub 2018 May 3.

Nemours Biomedical Research, Center for Applied Clinical Genomics, Nemours/Alfred I. duPont Hospital for Children, Wilmington, DE, USA.

Pelizaeus-Merzbacher disease (PMD; MIM 312080), an inherited defect of central nervous system myelin formation, affects individuals in many ways, including their hearing and language abilities. The aim of this study was to assess the auditory abilities in 18 patients with PMD by examining the functional processes along the central auditory pathways using auditory brainstem responses (ABR) and cortical auditory evoked potentials (CAEP) in response to speech sounds. The significant ABR anomalies confirm the existence of dyssynchrony previously described at the level of the brainstem in patients with PMD. Despite the significant auditory dyssynchrony observed at the level of the brainstem, CAEPs were present in most patients, albeit somehow abnormal in terms of morphology and latency, resembling a type of auditory neuropathy spectrum disorder.
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http://dx.doi.org/10.1007/s00415-018-8884-xDOI Listing
July 2018

Modeling the Mutational and Phenotypic Landscapes of Pelizaeus-Merzbacher Disease with Human iPSC-Derived Oligodendrocytes.

Am J Hum Genet 2017 Apr 30;100(4):617-634. Epub 2017 Mar 30.

Department of Genetics and Genome Sciences, School of Medicine, Case Western Reserve University, Cleveland, OH 44106, USA. Electronic address:

Pelizaeus-Merzbacher disease (PMD) is a pediatric disease of myelin in the central nervous system and manifests with a wide spectrum of clinical severities. Although PMD is a rare monogenic disease, hundreds of mutations in the X-linked myelin gene proteolipid protein 1 (PLP1) have been identified in humans. Attempts to identify a common pathogenic process underlying PMD have been complicated by an incomplete understanding of PLP1 dysfunction and limited access to primary human oligodendrocytes. To address this, we generated panels of human induced pluripotent stem cells (hiPSCs) and hiPSC-derived oligodendrocytes from 12 individuals with mutations spanning the genetic and clinical diversity of PMD-including point mutations and duplication, triplication, and deletion of PLP1-and developed an in vitro platform for molecular and cellular characterization of all 12 mutations simultaneously. We identified individual and shared defects in PLP1 mRNA expression and splicing, oligodendrocyte progenitor development, and oligodendrocyte morphology and capacity for myelination. These observations enabled classification of PMD subgroups by cell-intrinsic phenotypes and identified a subset of mutations for targeted testing of small-molecule modulators of the endoplasmic reticulum stress response, which improved both morphologic and myelination defects. Collectively, these data provide insights into the pathogeneses of a variety of PLP1 mutations and suggest that disparate etiologies of PMD could require specific treatment approaches for subsets of individuals. More broadly, this study demonstrates the versatility of a hiPSC-based panel spanning the mutational heterogeneity within a single disease and establishes a widely applicable platform for genotype-phenotype correlation and drug screening in any human myelin disorder.
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http://dx.doi.org/10.1016/j.ajhg.2017.03.005DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5384098PMC
April 2017

Corrigendum to "GJC2 promoter mutations causing Pelizaeus-Merzbacher-like disease" [Mol. Genet. Metab. 111 (2014) 393-398].

Mol Genet Metab 2016 11;119(3):293

Department of Neurology, Children's National Medical Center, Washington, DC, USA; Department of Pediatrics, Children's National Medical Center, Washington, DC, USA; Jefferson Medical College, Thomas Jefferson University, Philadelphia, PA, USA. Electronic address:

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http://dx.doi.org/10.1016/j.ymgme.2016.06.011DOI Listing
November 2016

Altered PLP1 splicing causes hypomyelination of early myelinating structures.

Ann Clin Transl Neurol 2015 Jun 1;2(6):648-61. Epub 2015 May 1.

Department of Child Neurology, VU University Medical Center Amsterdam, The Netherlands ; Neuroscience Campus Amsterdam, VU University Amsterdam, The Netherlands.

Objective: The objective of this study was to investigate the genetic etiology of the X-linked disorder "Hypomyelination of Early Myelinating Structures" (HEMS).

Methods: We included 16 patients from 10 families diagnosed with HEMS by brain MRI criteria. Exome sequencing was used to search for causal mutations. In silico analysis of effects of the mutations on splicing and RNA folding was performed. In vitro gene splicing was examined in RNA from patients' fibroblasts and an immortalized immature oligodendrocyte cell line after transfection with mutant minigene splicing constructs.

Results: All patients had unusual hemizygous mutations of PLP1 located in exon 3B (one deletion, one missense and two silent), which is spliced out in isoform DM20, or in intron 3 (five mutations). The deletion led to truncation of PLP1, but not DM20. Four mutations were predicted to affect PLP1/DM20 alternative splicing by creating exonic splicing silencer motifs or new splice donor sites or by affecting the local RNA structure of the PLP1 splice donor site. Four deep intronic mutations were predicted to destabilize a long-distance interaction structure in the secondary PLP1 RNA fragment involved in regulating PLP1/DM20 alternative splicing. Splicing studies in fibroblasts and transfected cells confirmed a decreased PLP1/DM20 ratio.

Interpretation: Brain structures that normally myelinate early are poorly myelinated in HEMS, while they are the best myelinated structures in Pelizaeus-Merzbacher disease, also caused by PLP1 alterations. Our data extend the phenotypic spectrum of PLP1-related disorders indicating that normal PLP1/DM20 alternative splicing is essential for early myelination and support the need to include intron 3 in diagnostic sequencing.
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http://dx.doi.org/10.1002/acn3.203DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4479525PMC
June 2015

Complex genomic rearrangements at the PLP1 locus include triplication and quadruplication.

PLoS Genet 2015 Mar 6;11(3):e1005050. Epub 2015 Mar 6.

Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, Texas, United States of America; Department of Pediatrics and Human Genome Sequencing Center, Baylor College of Medicine, Houston, Texas, United States of America; Texas Children's Hospital, Houston, Texas, United States of America.

Inverted repeats (IRs) can facilitate structural variation as crucibles of genomic rearrangement. Complex duplication-inverted triplication-duplication (DUP-TRP/INV-DUP) rearrangements that contain breakpoint junctions within IRs have been recently associated with both MECP2 duplication syndrome (MIM#300260) and Pelizaeus-Merzbacher disease (PMD, MIM#312080). We investigated 17 unrelated PMD subjects with copy number gains at the PLP1 locus including triplication and quadruplication of specific genomic intervals-16/17 were found to have a DUP-TRP/INV-DUP rearrangement product. An IR distal to PLP1 facilitates DUP-TRP/INV-DUP formation as well as an inversion structural variation found frequently amongst normal individuals. We show that a homology-or homeology-driven replicative mechanism of DNA repair can apparently mediate template switches within stretches of microhomology. Moreover, we provide evidence that quadruplication and potentially higher order amplification of a genomic interval can occur in a manner consistent with rolling circle amplification as predicted by the microhomology-mediated break induced replication (MMBIR) model.
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http://dx.doi.org/10.1371/journal.pgen.1005050DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4352052PMC
March 2015

Plp1 gene duplication inhibits airway responsiveness and induces lung inflammation.

Pulm Pharmacol Ther 2015 Feb 4;30:22-31. Epub 2014 Nov 4.

Alfred I. duPont Hospital for Children, Nemours Lung Center, Wilmington, DE 19803, USA; Alfred I. duPont Hospital for Children, Nemours Biomedical Research, Wilmington, DE 19803, USA.

Mice with Plp1 gene duplication model the most common form of Pelizaeus-Merzbacher disease (PMD), a CNS disease in which patients may suffer respiratory complications. We hypothesized that affected mice would lack airway responsiveness compared to wild-type and carrier mice during methacholine challenge. Wild-type (n = 10), carrier female (n = 6) and affected male (n = 8) mice were anesthetized-paralyzed, tracheostomized and ventilated. Respiratory mechanics were recorded at baseline and during escalating doses of nebulized methacholine followed by albuterol. Lung resistance (RL) was the primary endpoint. Lung tissues were assayed for inflammatory and histological differences. At baseline, phase angles were higher in carrier and affected mice than wild-type. Dose-response RL curves in affected and carrier mice indicated a lack of methacholine response. Albuterol reduced RL in wild-type and carrier, but not affected mice. Affected mice exhibited lower interleukin (IL)-6 tissue levels and alveolar inflammatory infiltrates. Affected and carrier mice, compared to wild-type, lacked airway reactivity during methacholine challenge, but only affected mice exhibited decreased lung tissue levels of IL-6 and inflammation.
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http://dx.doi.org/10.1016/j.pupt.2014.10.004DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6874309PMC
February 2015

PMD patient mutations reveal a long-distance intronic interaction that regulates PLP1/DM20 alternative splicing.

Hum Mol Genet 2014 Oct 1;23(20):5464-78. Epub 2014 Jun 1.

Nemours Biomedical Research, Alfred I. duPont Hospital for Children, Wilmington, DE 19803, USA, Department of Biological Sciences, University of Delaware, Newark, DE 19716, USA and Department of Pediatrics, Jefferson Medical College, Thomas Jefferson University, Philadelphia, PA 19107, USA

Alternative splicing of the proteolipid protein 1 gene (PLP1) produces two forms, PLP1 and DM20, due to alternative use of 5' splice sites with the same acceptor site in intron 3. The PLP1 form predominates in central nervous system RNA. Mutations that reduce the ratio of PLP1 to DM20, whether mutant or normal protein is formed, result in the X-linked leukodystrophy Pelizaeus-Merzbacher disease (PMD). We investigated the ability of sequences throughout PLP1 intron 3 to regulate alternative splicing using a splicing minigene construct transfected into the oligodendrocyte cell line, Oli-neu. Our data reveal that the alternative splice of PLP1 is regulated by a long-distance interaction between two highly conserved elements that are separated by 581 bases within the 1071-base intron 3. Further, our data suggest that a base-pairing secondary structure forms between these two elements, and we demonstrate that mutations of either element designed to destabilize the secondary structure decreased the PLP1/DM20 ratio, while swap mutations designed to restore the structure brought the PLP1/DM20 ratio to near normal levels. Sequence analysis of intron 3 in families with clinical symptoms of PMD who did not have coding-region mutations revealed mutations that segregated with disease in three families. We showed that these patient mutations, which potentially destabilize the secondary structure, also reduced the PLP1/DM20 ratio. This is the first report of patient mutations causing disease by disruption of a long-distance intronic interaction controlling alternative splicing. This finding has important implications for molecular diagnostics of PMD.
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http://dx.doi.org/10.1093/hmg/ddu271DOI Listing
October 2014

GJC2 promoter mutations causing Pelizaeus-Merzbacher-like disease.

Mol Genet Metab 2014 03 16;111(3):393-398. Epub 2013 Dec 16.

Department of Neurology, Children's National Medical Center, Washington, DC, USA; Department of Pediatrics, Children's National Medical Center, Washington, DC, USA; Jefferson Medical College, Thomas Jefferson University, Philadelphia, PA, USA. Electronic address:

Objective: Pelizaeus-Merzbacher-like disease is a rare hypomyelinating leukodystrophy caused by autosomal recessive mutations in GJC2, encoding a gap junction protein essential for production of a mature myelin sheath. A previously identified GJC2 mutation (c.-167A>G) in the promoter region is hypothesized to disrupt a putative SOX10 binding site; however, the lack of additional mutations in this region and contradictory functional data have limited the interpretation of this variant.

Methods: We describe two independent Pelizaeus-Merzbacher-like disease families with a novel promoter region mutation and updated in vitro functional assays.

Results: A novel GJC2 mutation (c.-170A>G) in the promoter region was identified in Pelizaeus-Merzbacher-like disease patients. In vitro functional assays using human GJC2 promoter constructs demonstrated that this mutation and the previously described c.-167A>G mutation similarly diminished the transcriptional activity driven by SOX10 and the binding affinity for SOX10.

Interpretation: These findings support the role of GJC2 promoter mutations in Pelizaeus-Merzbacher-like disease. GJC2 promoter region mutation screening should be included in the evaluation of patients with unexplained hypomyelinating leukodystrophies.
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http://dx.doi.org/10.1016/j.ymgme.2013.12.001DOI Listing
March 2014

Gait abnormalities and progressive myelin degeneration in a new murine model of Pelizaeus-Merzbacher disease with tandem genomic duplication.

J Neurosci 2013 Jul;33(29):11788-99

Nemours Biomedical Research, Alfred I. duPont Hospital for Children, Wilmington, Delaware 19803, USA.

Pelizaeus-Merzbacher disease (PMD) is a hypomyelinating leukodystrophy caused by mutations of the proteolipid protein 1 gene (PLP1), which is located on the X chromosome and encodes the most abundant protein of myelin in the central nervous sytem. Approximately 60% of PMD cases result from genomic duplications of a region of the X chromosome that includes the entire PLP1 gene. The duplications are typically in a head-to-tail arrangement, and they vary in size and gene content. Although rodent models with extra copies of Plp1 have been developed, none contains an actual genomic rearrangement that resembles those found in PMD patients. We used mutagenic insertion chromosome engineering resources to generate the Plp1dup mouse model by introducing an X chromosome duplication in the mouse genome that contains Plp1 and five neighboring genes that are also commonly duplicated in PMD patients. The Plp1dup mice display progressive gait abnormalities compared with wild-type littermates. The single duplication leads to increased transcript levels of Plp1 and four of the five other duplicated genes over wild-type levels in the brain beginning the second postnatal week. The Plp1dup mice also display altered transcript levels of other important myelin proteins leading to a progressive degeneration of myelin. Our results show that a single duplication of the Plp1 gene leads to a phenotype similar to the pattern seen in human PMD patients with duplications.
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http://dx.doi.org/10.1523/JNEUROSCI.1336-13.2013DOI Listing
July 2013

Pelizaeus-Merzbacher disease, Pelizaeus-Merzbacher-like disease 1, and related hypomyelinating disorders.

Semin Neurol 2012 Feb 15;32(1):62-7. Epub 2012 Mar 15.

Alfred I. duPont Hospital for Children, Nemours Biomedical Research, RC1-235, 1701 Rockland Road, Wilmington, DE 19803, USA.

The purpose of this article is to present contemporary information on the clinical and molecular diagnosis and the treatment of Pelizaeus-Merzbacher's disease (PMD) and related leukodystrophies. Various types of mutations of the X-linked proteolipid protein 1 gene (PLP1) that include copy number changes, point mutations, and insertions or deletions of a few bases lead to a clinical spectrum from the most severe connatal PMD, to the least severe spastic paraplegia 2 (SPG2). Signs of PMD include nystagmus, hypotonia, tremors, titubation, ataxia, spasticity, athetotic movements and cognitive impairment; the major findings in SPG2 are leg weakness and spasticity. A diffuse pattern of hypomyelination is seen on magnetic resonance imaging (MRI) of PMD/SPG2 patients. A similar constellation of signs and pattern of hypomyelination lead to the autosomal recessive disease called Pelizaeus-Merzbacher-like disease 1 (PMLD1) and the less-severe spastic paraplegia 44 (SPG44), caused by mutations of the gap junction protein, gamma-2 gene (GJC2), formerly known as the gap junction protein, α-12 gene (GJA12). Magnetic resonance spectroscopy (MRS) and brainstem auditory evoked potentials (BAEP) may assist with differential clinical diagnosis of PMD and PMLD1. Supportive therapy for patients with PMD/SPG2 and PMLD1/SPG44 includes medications for seizures and spasticity; physical therapy, exercise, and orthotics for spasticity management; surgery for contractures and scoliosis; gastrostomy for severe dysphagia; proper wheelchair seating, physical therapy, and orthotics to prevent or ameliorate the effects of scoliosis; special education; and assistive communication devices.
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http://dx.doi.org/10.1055/s-0032-1306388DOI Listing
February 2012

A large X-chromosomal deletion is associated with microphthalmia with linear skin defects (MLS) and amelogenesis imperfecta (XAI).

Am J Med Genet A 2009 Aug;149A(8):1698-705

Alfred I. DuPont Hospital for Children, Wilmington, Delaware, USA.

A female patient is described with clinical symptoms of both microphthalmia with linear skin defects (MLS or MIDAS) and dental enamel defects, having an appearance compatible with X-linked amelogenesis imperfecta (XAI). Genomic DNA was purified from the patient's blood and semiquantitative multiplex PCR revealed a deletion encompassing the amelogenin gene (AMELX). Because MLS is also localized to Xp22, genomic DNA was subjected to array comparative genomic hybridization, and a large heterozygous deletion was identified. Histopathology of one primary and one permanent molar tooth showed abnormalities in the dental enamel layer, and a third tooth had unusually high microhardness measurements, possibly due to its ultrastructural anomalies as seen by scanning electron microscopy. This is the first report of a patient with both of these rare conditions, and the first description of the phenotype resulting from a deletion encompassing the entire AMELX gene. More than 50 additional genes were monosomic in this patient.
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http://dx.doi.org/10.1002/ajmg.a.32968DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2760392PMC
August 2009

Neuronal loss in Pelizaeus-Merzbacher disease differs in various mutations of the proteolipid protein 1.

Acta Neuropathol 2009 Oct 27;118(4):531-9. Epub 2009 Jun 27.

Department of Pathology, School of Medicine, Wayne State University, Detroit, MI, USA.

Mutations affecting proteolipid protein 1 (PLP1), the major protein in central nervous system myelin, cause the X-linked leukodystrophy Pelizaeus-Merzbacher disease (PMD). We describe the neuropathologic findings in a series of eight male PMD subjects with confirmed PLP1 mutations, including duplications, complete gene deletion, missense and exon-skipping. While PLP1 mutations have effects on oligodendrocytes that result in mutation-specific degrees of dysmyelination, our findings indicate that there are also unexpected effects in the central nervous system resulting in neuronal loss. Although length-dependent axonal degeneration has been described in PLP1 null mutations, there have been no reports on neuronal degeneration in PMD patients. We now demonstrate widespread neuronal loss in PMD. The patterns of neuronal loss appear to be dependent on the mutation type, suggesting selective vulnerability of neuronal populations that depends on the nature of the PLP1 disturbance. Nigral neurons, which were not affected in patients with either null or severe misfolding mutations, and thalamic neurons appear particularly vulnerable in PLP1 duplication and deletion patients, while hippocampal neuronal loss was prominent in a patient with complete PLP1 gene deletion. All subjects showed cerebellar neuronal loss. The patterns of neuronal involvement may explain some clinical findings, such as ataxia, being more prominent in PMD than in other leukodystrophies. While the precise pathogenetic mechanisms are not known, these observations suggest that defective glial functions contribute to neuronal pathology.
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http://dx.doi.org/10.1007/s00401-009-0562-8DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3876935PMC
October 2009

Variable expression of a novel PLP1 mutation in members of a family with Pelizaeus-Merzbacher disease.

J Child Neurol 2009 May 16;24(5):618-24. Epub 2009 Jan 16.

Institute for Child Development and Pediatric Neurology Unit, Tel Aviv Sourasky Medical Center, Sackler Faculty of Medicine, Tel Aviv University, Tel Aviv, Israel.

Pelizaeus-Merzbacher disease is a rare X-linked disorder caused by mutations of the proteolipid protein 1 gene that encodes a structural component of myelin. It is characterized by progressive psychomotor delay, nystagmus, spastic quadriplegia, and cerebellar ataxia. Variable clinical expression was seen in 5 members of a family bearing a novel missense mutation in proteolipid protein 1, c.619T>C. Symptomatic patients included a 6-year-old girl, her younger brother, and their maternal uncle, a 29-year-old college graduate initially diagnosed with cerebral palsy; their brain magnetic resonance imaging studies showed diffuse dysmyelination. The mother had a history of delayed walking, achieved independently by age 3; she and the maternal grandmother were asymptomatic on presentation. Review of clinical information and family history led to consideration of Pelizaeus-Merzbacher disease. Subsequent identification of the causal mutation enabled preimplantation genetic diagnosis and the birth of an unaffected child.
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http://dx.doi.org/10.1177/0883073808327833DOI Listing
May 2009

Deletion of a splicing enhancer disrupts PLP1/DM20 ratio and myelin stability.

Exp Neurol 2008 Dec 18;214(2):322-30. Epub 2008 Sep 18.

Department of Neurology, University of Kentucky, Lexington, KY 40536, USA.

PLP1 and DM20, major myelin proteins, are generated by developmentally regulated alternative splicing. In the post-natal brain, PLP1 is the predominant product. Deletion of a splicing enhancer in PLP1 intron 3 causes a mild form of Pelizaeus-Merzbacher disease and reduces PLP1 specific splicing in vitro (Hobson, G. M., Huang, Z., Sperle, K., Stabley, D. L., Marks, H. G., and Cambi, F., 2002. A PLP splicing abnormality is associated with an unusual presentation of PMD. Ann. Neurol. 52, 477-488). We sought to investigate the pathogenic role of the mutation and to determine the consequences on the developmental regulation of PLP1 alternative splicing and myelin stability and function in vivo. We have generated a knockin mouse that carries deletion of the intronic splicing enhancer and have characterized the PLP1/DM20 ratio by Real Time RT-PCR and Western blot analysis in the developing and mature brain and examined the clinical and pathological phenotype by motor testing and electron microscopy. The deletion impairs the increase in the PLP1/DM20 transcript and protein ratio at the time of myelination and in adulthood and results in a PLP1 hypomorph. Electron microscopy shows abnormal myelin wraps with fragmented myelin whorls, which are progressive with age, suggesting a defect in myelin stability. Phenotypic characterization of the knockin mouse shows a defect in motor coordination. The data indicate that the intronic splicing enhancer is necessary for the developmental increase in PLP1/DM20 ratio and that full PLP1 dosage is necessary for myelin stability and brain function. This knockin mouse represents a useful model to investigate the mechanisms of disease in human disorders in which PLP1 expression is reduced.
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http://dx.doi.org/10.1016/j.expneurol.2008.09.001DOI Listing
December 2008

Heterogeneous duplications in patients with Pelizaeus-Merzbacher disease suggest a mechanism of coupled homologous and nonhomologous recombination.

Am J Hum Genet 2005 Dec 19;77(6):966-87. Epub 2005 Oct 19.

Clinical and Molecular Genetics, Institute of Child Health, London.

We describe genomic structures of 59 X-chromosome segmental duplications that include the proteolipid protein 1 gene (PLP1) in patients with Pelizaeus-Merzbacher disease. We provide the first report of 13 junction sequences, which gives insight into underlying mechanisms. Although proximal breakpoints were highly variable, distal breakpoints tended to cluster around low-copy repeats (LCRs) (50% of distal breakpoints), and each duplication event appeared to be unique (100 kb to 4.6 Mb in size). Sequence analysis of the junctions revealed no large homologous regions between proximal and distal breakpoints. Most junctions had microhomology of 1-6 bases, and one had a 2-base insertion. Boundaries between single-copy and duplicated DNA were identical to the reference genomic sequence in all patients investigated. Taken together, these data suggest that the tandem duplications are formed by a coupled homologous and nonhomologous recombination mechanism. We suggest repair of a double-stranded break (DSB) by one-sided homologous strand invasion of a sister chromatid, followed by DNA synthesis and nonhomologous end joining with the other end of the break. This is in contrast to other genomic disorders that have recurrent rearrangements formed by nonallelic homologous recombination between LCRs. Interspersed repetitive elements (Alu elements, long interspersed nuclear elements, and long terminal repeats) were found at 18 of the 26 breakpoint sequences studied. No specific motif that may predispose to DSBs was revealed, but single or alternating tracts of purines and pyrimidines that may cause secondary structures were common. Analysis of the 2-Mb region susceptible to duplications identified proximal-specific repeats and distal LCRs in addition to the previously reported ones, suggesting that the unique genomic architecture may have a role in nonrecurrent rearrangements by promoting instability.
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http://dx.doi.org/10.1086/498048DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1285180PMC
December 2005

Spastic paraplegia type 2 associated with axonal neuropathy and apparent PLP1 position effect.

Ann Neurol 2006 Feb;59(2):398-403

Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, TX, USA.

Objective: To report an association between spastic paraplegia type 2 with axonal peripheral neuropathy and apparent proteolipid protein gene (PLP1) silencing in a family.

Methods: Pulsed-field gel electrophoresis, custom array comparative genomic hybridization, and semi-quantitative multiplex polymerase chain reaction analyses were used to examine the PLP1 genomic region.

Results: Electrodiagnostic studies and a sural nerve biopsy showed features of a dystrophic axonal neuropathy. Molecular studies identified a small duplication downstream of PLP1.

Interpretation: We propose the duplication to result in PLP1 gene silencing by virtue of a position effect. Our observations suggest that genomic rearrangements that do not include PLP1 coding sequences should be considered as yet another potential mutational mechanism underlying PLP1-related dysmyelinating disorders.
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http://dx.doi.org/10.1002/ana.20732DOI Listing
February 2006

PLP1 alternative splicing in differentiating oligodendrocytes: characterization of an exonic splicing enhancer.

J Cell Biochem 2006 Apr;97(5):999-1016

Department of Neurology, University of Kentucky, Lexington, Kentucky 40536-0284, USA.

Proteolipid protein (PLP) and DM20 are generated by alternative splicing of exon 3B of PLP1 transcript in differentiating oligodendrocytes. We investigated the role of exonic splicing enhancers (ESE) in the selection of PLP 5' donor site, focusing on putative ASF/SF2, and SC35 binding motifs in exon 3B on the basis of mutations that cause disease in humans. Mutations in a putative ASF/SF2 binding motif (nucleotides 406-412) reduced PLP 5' donor site selection, whereas a mutation in a putative SC35 binding motif (nucleotides 382-389) had no effect. UV crosslinking and immunoprecipitation (IP) assays using an antibody to ASF/SF2 showed that the ASF/SF2 protein specifically binds to the ESE (nucleotides 406-412). The single nucleotide mutations that reduced PLP splice site selection greatly diminished ASF/SF2 protein binding to this motif. We next tested the effect of overexpressed ASF/SF2 on PLP 5'splice selection in differentiating oligodendrocytes. ASF/SF2 positively regulates PLP splice site selection in a concentration-dependent manner. Disruption of the putative ASF/SF2 binding site in exon 3B reduced the positive effect of ASF/SF2 on PLP splicing. We conclude that an ESE in exon3B regulates PLP 5' donor site selection and that ASF/SF2 protein participates in the regulation of PLP alternative splicing in oligodendrocytes.
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http://dx.doi.org/10.1002/jcb.20692DOI Listing
April 2006

Splice-site contribution in alternative splicing of PLP1 and DM20: molecular studies in oligodendrocytes.

Hum Mutat 2006 Jan;27(1):69-77

Nemours Biomedical Research, Alfred I. duPont Hospital for Children, Nemours Children's Clinic, Wilmington, Delaware, USA.

Mutations in the proteolipid protein 1 (PLP1) gene cause the X-linked dysmyelinating diseases Pelizaeus-Merzbacher disease (PMD) and spastic paraplegia 2 (SPG2). We examined the severity of the following mutations that were suspected of affecting levels of PLP1 and DM20 RNA, the alternatively spliced products of PLP1: c.453G>A, c.453G>T, c.453G>C, c.453+2T>C, c.453+4A>G, c.347C>A, and c.453+28_+46del (the old nomenclature did not include the methionine codon: G450A, G450T, G450C, IVS3+2T>C, IVS3+4A>G, C344A, and IVS3+28-+46del). These mutations were evaluated by information theory-based analysis and compared with mRNA expression of the alternatively spliced products. The results are discussed relative to the clinical severity of disease. We conclude that the observed PLP1 and DM20 splicing patterns correlated well with predictions of information theory-based analysis, and that the relative strength of the PLP1 and DM20 donor splice sites plays an important role in PLP1 alternative splicing.
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http://dx.doi.org/10.1002/humu.20276DOI Listing
January 2006

Three or more copies of the proteolipid protein gene PLP1 cause severe Pelizaeus-Merzbacher disease.

Brain 2005 Apr 2;128(Pt 4):743-51. Epub 2005 Feb 2.

Clinical and Molecular Genetics, Institute of Child Health, London, UK.

We describe five boys from different families with an atypically severe form of Pelizaeus-Merzbacher disease (PMD) who have three, and in one case, five copies of the proteolipid protein (PLP1) gene. This is the first report of more than two copies of PLP1 in PMD patients and clearly demonstrates that severe clinical symptoms are associated with increased PLP1 gene dosage. Previously, duplications, deletions and mutations of the PLP1 gene were reported to give rise to this X-linked disorder. Patients with PLP1 duplication are usually classified as having either classical or transitional PMD rather than the more rare severe connatal form. The clinical symptoms of the five patients in this study included lack of stable head control and severe mental retardation, with three having severe paroxysmal disorder and two dying before the first year of life. Gene dosage was determined using interphase FISH (fluorescence in situ hybridization) and the novel approach of multiple ligation probe amplification (MLPA). We found FISH unreliable for dosage detection above the level of a duplication and MLPA to be more accurate in determination of specific copy number. Our finding that three or more copies of the gene give rise to a more severe phenotype is in agreement with observations in transgenic mice where severity of disease increased with Plp1 gene dosage and level of overexpression. The patient with five copies of PLP1 was not more affected than those with a triplication, suggesting that there is possibly a limit to the level of severity or that other genetic factors influence the phenotype. It highlights the significance of PLP1 dosage in CNS myelinogenesis as well as the importance of accurate determination of PLP1 gene copy number in the diagnosis of PMD and carrier detection.
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http://dx.doi.org/10.1093/brain/awh409DOI Listing
April 2005

A case of complicated spastic paraplegia 2 due to a point mutation in the proteolipid protein 1 gene.

J Neurol Sci 2004 Sep;224(1-2):83-7

Department of Pediatrics, Yeungnam University Hospital, Daegu, South Korea.

Pelizaeus-Merzbacher disease (PMD) is a rare X-linked dysmyelinating disorder resulting from mutation of the proteolipid protein gene (PLP1). Clinical features of PMD include progressive psychomotor developmental delay, nystagmus, spastic quadriplegia, dystonia, and cerebellar ataxia. PMD is clinically classified into three subtypes according to the severity of the disease: connatal, transitional, and classic forms. Patients with PMD have been identified with duplication, point mutations, and deletion of PLP1. In addition, spastic paraplegia 2 (SPG2) is allelic to PMD and typically caused by missense mutations in the second extracellular domain of PLP1 or in the PLP1-specific region that is spliced out during formation of the DM20 isoform. The authors describe a Korean boy diagnosed with SPG2 caused by a mutation that results in a Pro215Leu substitution in the second extracellular domain. Analysis of phenotypes resulting from mutations affecting PLP1 has been valuable in identifying functional domains of this still incompletely understood major myelin protein. Null mutations and mutations affecting the PLP1-specific domain cause peripheral neuropathy. The PLP1-specific domain also is important in the long-term maintenance of axonal integrity. This patient's phenotype was relatively mild, in contrast with other mutations at position 215 of PLP1 that cause severe PMD. One of these severe mutations is also a missense mutation substituting an aliphatic residue, alanine, for proline. The distinct severity difference between the Pro215Leu and Pro215Ala substitutions suggests that this region of the protein is very sensitive to subtle structural changes and likely plays a critical role in PLP1 function.
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http://dx.doi.org/10.1016/j.jns.2004.05.015DOI Listing
September 2004

A PLP splicing abnormality is associated with an unusual presentation of PMD.

Ann Neurol 2002 Oct;52(4):477-88

Department of Research, Alfred I. duPont Hospital for Children, Wilmington, DE, USA.

We report that a deletion of 19 base pairs (bp) in intron 3 of the proteolipid protein (PLP/DM20) gene causes a neurological disease characterized by mild developmental delay, followed by progressive decline of acquired motor and cognitive milestones. The clinical features are associated with mild delay in myelination demonstrated by magnetic resonance imaging studies and with ongoing demyelination and axonal loss demonstrated by magnetic resonance spectroscopy. We demonstrate that the purine-rich 19bp element regulates PLP-specific splice site selection in transient transfections of chimeric constructs into cultured oligodendrocytes. Runs of 4 and 5 Gs centered in the 19bp element are critical for efficient PLP-specific splicing. The intronic element is sequence specific in oligodendrocytes and is not a repressor of PLP-specific splicing in nonglial cells. These data support the conclusion that deletion of the 19bp purine-rich region in PLP intron 3 causes a reduction in PLP message and protein, which affects myelin stability and axonal integrity.
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http://dx.doi.org/10.1002/ana.10320DOI Listing
October 2002
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