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Pelizaeus-
 Merzbacher
  Disease

 Chintalagiri
 Shashank,
    chin-
tal@iitk.ac.in                      Pelizaeus-Merzbacher Disease
Outline                      BSE638 - Structural Basis of Protein Function
Introduction
Pelizaeus-
Merzbacher
Disease
Types of PMD                       Chintalagiri Shashank, chintal@iitk.ac.in
Disease
Mechanism

Pathogenesis
Animal Mutants
Molecular                                                April 29, 2010
Pathogenesis
Genotype -
Phenotype
correlation

References




                 Chintalagiri Shashank, chintal@iitk.ac.in   Pelizaeus-Merzbacher Disease
Pelizaeus-
 Merzbacher
  Disease
                 1 Introduction
 Chintalagiri
 Shashank,              Pelizaeus-Merzbacher Disease
    chin-
tal@iitk.ac.in          Types of PMD
Outline
                 2 Disease Mechanism
Introduction
Pelizaeus-
Merzbacher
Disease
Types of PMD
                 3 Pathogenesis
Disease                 Animal Mutants
Mechanism
                        Molecular Pathogenesis
Pathogenesis
Animal Mutants          Genotype - Phenotype correlation
Molecular
Pathogenesis
Genotype -
Phenotype
correlation
                 4 References
References




                 Chintalagiri Shashank, chintal@iitk.ac.in   Pelizaeus-Merzbacher Disease
Pelizaeus-Merzbacher Disease[1]

 Pelizaeus-
 Merzbacher             Rare, progressive, degenerative central nervous system
  Disease
                        disorder
 Chintalagiri
 Shashank,
    chin-
                        Coordination, motor abilities, and intellectual function
tal@iitk.ac.in          deteriorate
Outline                 One of a group of gene-linked disorders known as the
Introduction            leukodystrophies, affects growth of the myelin sheath.
Pelizaeus-
Merzbacher
Disease
                        The disease is caused by a mutation in the gene encoding
Types of PMD
                        a myelin protein called proteolipid protein-1 (PLP1).
Disease
Mechanism               PMD is inherited as an X-linked recessive trait; the
Pathogenesis            affected individuals are male and the mothers are carriers
Animal Mutants
Molecular
Pathogenesis
                        of the PLP1 mutation.
Genotype -
Phenotype
correlation
                        Severity and onset of the disease ranges widely, depending
References              on the type of PLP1 mutation.
                        One of a spectrum of diseases associated with PLP1.
                  Chintalagiri Shashank, chintal@iitk.ac.in   Pelizaeus-Merzbacher Disease
Types of PMD[1]

 Pelizaeus-
 Merzbacher
                 There are 4 general classifications within this spectrum of
  Disease        diseases. In order of severity, they are:
 Chintalagiri
 Shashank,            Connatal PMD, which is the most severe type and involves
    chin-
tal@iitk.ac.in
                      delayed mental and physical development and severe
                      neurological symptoms
Outline
                      Classic PMD, in which the early symptoms include muscle
Introduction
Pelizaeus-
Merzbacher
                      weakness, involuntary movements of the eyes
Disease
Types of PMD
                      (nystagmus), and delays in motor development within the
Disease               first year of life
Mechanism
                      Complicated SPG2, which features motor development
Pathogenesis
Animal Mutants        issues and brain involvement
Molecular
Pathogenesis
Genotype -
                      Pure SPG2, which includes cases of PMD that do not
Phenotype
correlation           have neurologic complications.
References
                 Noticeable changes in the extent of myelination can be
                 detected by MRI analyses of the brain.
                  Chintalagiri Shashank, chintal@iitk.ac.in   Pelizaeus-Merzbacher Disease
Pelizaeus-
 Merzbacher
  Disease

 Chintalagiri
 Shashank,
    chin-
tal@iitk.ac.in
                 Modern morphological, biochemical, and molecular techniques
Outline
                 have made this distinction obsolete, and PMD must now be
Introduction
Pelizaeus-       considered a leukodystrophy with variable clinical and
Merzbacher
Disease
Types of PMD
                 neuropathological phenotypes, although all cases are due to
Disease          mutations of the proteolipid protein (PLP) gene.
Mechanism

Pathogenesis
Animal Mutants
Molecular
Pathogenesis
Genotype -
Phenotype
correlation

References




                  Chintalagiri Shashank, chintal@iitk.ac.in   Pelizaeus-Merzbacher Disease
Disease Mechanism

 Pelizaeus-
 Merzbacher
  Disease

 Chintalagiri
 Shashank,       Proposed roles for PLP1 include mediating interlamellar
    chin-
tal@iitk.ac.in   adhesion in compact myelin, mediating ion flux, and acting as
                 an oligodendrocyte precursor mitogen.
Outline

Introduction
Pelizaeus-
Merzbacher
                 PLP is a major structural component of CNS myelin, whereas
Disease
Types of PMD
                 DM20 which is produced earlier in CNS development may be
Disease          involved in oligodendrocyte differentiation and survival.
Mechanism

Pathogenesis
Animal Mutants   Complete deficiency of PLP1 does not prevent myelination, but
Molecular
Pathogenesis
Genotype -
                 it does result in late-onset axonal degeneration.
Phenotype
correlation

References




                  Chintalagiri Shashank, chintal@iitk.ac.in   Pelizaeus-Merzbacher Disease
Disease Mechanism

 Pelizaeus-
 Merzbacher
  Disease

 Chintalagiri
 Shashank,       In addition to null mutations, mutations that disrupt the
    chin-
tal@iitk.ac.in   PLP1-specific region, a 35-amino-acid region that is spliced out
                 during formation of the DM20 isoform, cause both peripheral
Outline

Introduction
                 neuropathy and central axonal degeneration.
Pelizaeus-
Merzbacher
Disease
Types of PMD     Single amino-acid changes in highly conserved regions of the
Disease          DM20 protein caused the most severe forms of PMD.
Mechanism
                 Substitutions of less conserved amino acids, truncations,
Pathogenesis
Animal Mutants   absence of the protein and PLP-specic mutations cause the
Molecular
Pathogenesis
Genotype -
                 milder forms of PMD and SPG.
Phenotype
correlation

References




                  Chintalagiri Shashank, chintal@iitk.ac.in   Pelizaeus-Merzbacher Disease
Disease Mechanism

 Pelizaeus-
 Merzbacher
  Disease

 Chintalagiri
 Shashank,
    chin-
tal@iitk.ac.in
                 Gow and Lazzarini have suggested a cellular mechanism for
Outline          disease severity in PMD. They reported that classical PMD
Introduction
Pelizaeus-
                 correlates with misfolding and accumulation of PLP1 in the
Merzbacher
Disease          endoplasmic reticulum (ER) and transport of DM20 to the cell
Types of PMD

Disease
                 surface, while connatal PMD correlates with misfolding and
Mechanism        accumulation of both PLP1 and DM20 in the ER.
Pathogenesis
Animal Mutants
Molecular
Pathogenesis
Genotype -
Phenotype
correlation

References




                  Chintalagiri Shashank, chintal@iitk.ac.in   Pelizaeus-Merzbacher Disease
Pathogenesis

 Pelizaeus-
 Merzbacher
  Disease

 Chintalagiri
 Shashank,
    chin-
tal@iitk.ac.in
                        Gencic et.al.[5] report that the underlying disturbance in
                        myelination of Pelizaeus-Merzbacher patients was
Outline
                        attributed to a failure to form myelin (dys-myelination)
Introduction
Pelizaeus-
                        rather than to a breakdown of preexisting myelin
Merzbacher
Disease                 (demyelination) by a pathogenic analysis by Zeman et.al.
Types of PMD

Disease
                        in 1964.
Mechanism
                        Zeman et.al. also predicted that the defect would involve
Pathogenesis
Animal Mutants          a myelin protein or proteolipid
Molecular
Pathogenesis
Genotype -
Phenotype
correlation

References




                  Chintalagiri Shashank, chintal@iitk.ac.in   Pelizaeus-Merzbacher Disease
Animal Mutants

 Pelizaeus-
 Merzbacher
  Disease

 Chintalagiri
 Shashank,
                 PLP deficiency relates to a X-linked CNS myelin deficiency in
    chin-
tal@iitk.ac.in
                 several animal mutants
                        jimpy mouse (jp) is the oldest and best known
Outline

Introduction            the myelin-deficient rat (md)
Pelizaeus-
Merzbacher
Disease
                        the shaking pup (sh)
Types of PMD

Disease
                        the rumpshaker mouse (rsh)
Mechanism
                        the rabbit with paralytic tremor (pt)
Pathogenesis
Animal Mutants
Molecular
                 The deficiency of PLP protein was commensurate with low
Pathogenesis
Genotype -
                 levels of the matching messenger ribonucleic acid (mRNA).
Phenotype
correlation

References




                  Chintalagiri Shashank, chintal@iitk.ac.in   Pelizaeus-Merzbacher Disease
Implication of PLP

 Pelizaeus-
 Merzbacher
  Disease        Two observations focused attention on the major structural
 Chintalagiri
 Shashank,       protein of myelin, proteolipid protein (PLP), as a candidate for
    chin-
tal@iitk.ac.in
                 mutation in Pelizaeus-Merzbacher disease.
Outline
                        Assignment of the PLP gene to the human X chromosome
Introduction
                        at position Xq22, which supported the X-linked
Pelizaeus-
Merzbacher
                        inheritance of the disease.
Disease
Types of PMD            Discovery that the dysmyelinating mouse mutant jimpy,
Disease
Mechanism               which appears pathologically and genetically similar to
Pathogenesis            Pelizaeus-Merzbacher disease, has a mutation in the PLP
Animal Mutants
Molecular
                        gene that results in aberrantly spliced PLP transcripts
Pathogenesis
Genotype -              (Morello et al. 1986; Nave et al. 1986, 1987; Hudson et
Phenotype
correlation
                        al. 1987; Macklin et al. 1987; Ikenaka et al. 1988).
References




                  Chintalagiri Shashank, chintal@iitk.ac.in   Pelizaeus-Merzbacher Disease
Myelin[8]

 Pelizaeus-
 Merzbacher
  Disease

 Chintalagiri
 Shashank,
    chin-
tal@iitk.ac.in

Outline

Introduction
Pelizaeus-
Merzbacher
Disease
Types of PMD

Disease
Mechanism

Pathogenesis
Animal Mutants
Molecular
Pathogenesis
Genotype -
Phenotype
correlation

References




                  Chintalagiri Shashank, chintal@iitk.ac.in   Pelizaeus-Merzbacher Disease
Structure of PLP

 Pelizaeus-
 Merzbacher
  Disease

 Chintalagiri
 Shashank,
    chin-
tal@iitk.ac.in

Outline

Introduction
Pelizaeus-
Merzbacher
Disease
Types of PMD

Disease
Mechanism

Pathogenesis
Animal Mutants
Molecular
Pathogenesis
Genotype -
Phenotype
correlation

References




                  Chintalagiri Shashank, chintal@iitk.ac.in   Pelizaeus-Merzbacher Disease
Structure of PLP

 Pelizaeus-
 Merzbacher             PLP is a tetraspan protein, with 4 TM α-helices spanning
  Disease
                        the myelin membrane. Both N- and C-terminals are in the
 Chintalagiri
 Shashank,              cytoplasmic side.
    chin-
tal@iitk.ac.in          Immunolabeling studies of PLP and several protein
                        structure prediction algorithms were used to determine the
Outline

Introduction
                        most likely residues making up the α-helices.
Pelizaeus-
Merzbacher
                        The region of PLP that is deleted in DM20 (residues 116
Disease
Types of PMD            150) is shown in yellow.
Disease                 Cysteines involved in the formation of the two disulde
Mechanism
                        bonds in PLP (linking residues 183 227 and 200 219) are
Pathogenesis
Animal Mutants          shown in blue.
Molecular
Pathogenesis
Genotype -
                        6 cysteine residues are thought to be acylated (shown in
Phenotype
correlation             red), with palmitic acid sidechains attached. Alternatively,
References              some of these cysteine residues could be involved in
                        disulde linkages.
                  Chintalagiri Shashank, chintal@iitk.ac.in   Pelizaeus-Merzbacher Disease
Structure of PLP

 Pelizaeus-
 Merzbacher
  Disease

 Chintalagiri
 Shashank,
    chin-        Structural properties of proteins specic to the myelin sheath,
tal@iitk.ac.in
                 Amino Acids (2008)[12]
Outline
                        Some of the myelin proteins, belonging to the family
Introduction
Pelizaeus-              of tetraspanins, are amongst the most hydrophobic
Merzbacher
Disease
Types of PMD
                        proteins known. One of these proteins is the
Disease                 proteolipid protein. This group of proteins is most
Mechanism
                        poorly characterised structurally, and will not be
Pathogenesis
Animal Mutants
                        discussed in this review.
Molecular
Pathogenesis
Genotype -
Phenotype
correlation

References




                  Chintalagiri Shashank, chintal@iitk.ac.in   Pelizaeus-Merzbacher Disease
Mutation of PLP

 Pelizaeus-
 Merzbacher
  Disease

 Chintalagiri
 Shashank,
    chin-
tal@iitk.ac.in          The mutation causing PMD seems to be different for
                        different families.
Outline

Introduction            PMD is always caused by a mutation of PLP.
Pelizaeus-
Merzbacher
Disease
                        A majority of the cases seem to be caused by duplications
Types of PMD
                        involving the entire gene (larger than 100 kb)
Disease
Mechanism               In some families, PMD is caused by the mutation of a
Pathogenesis
Animal Mutants
                        single amino acid.
Molecular
Pathogenesis
Genotype -
Phenotype
correlation

References




                  Chintalagiri Shashank, chintal@iitk.ac.in   Pelizaeus-Merzbacher Disease
Mutations[2]

 Pelizaeus-
 Merzbacher
  Disease

 Chintalagiri
 Shashank,
    chin-
tal@iitk.ac.in
                 Clinical observations and studies of PLP mutations in animals
                 and cell cultures suggest that there at least 3 distinct genetic
Outline
                 mechanisms that cause PMD. [2]
Introduction
Pelizaeus-
Merzbacher
Disease          In addition, spastic paraplegia 2 (SPG2) is allelic to PMD and
Types of PMD

Disease
                 typically caused by missense mutations in the second
Mechanism
                 extracellular domain of PLP1 or in the PLP1-specific region
Pathogenesis
Animal Mutants
                 that is spliced out during formation of the DM20 isoform.
Molecular
Pathogenesis
Genotype -
Phenotype
correlation

References




                  Chintalagiri Shashank, chintal@iitk.ac.in   Pelizaeus-Merzbacher Disease
Molecular mechanisms of PMD pathogenesis[3]

 Pelizaeus-
 Merzbacher
  Disease

 Chintalagiri
 Shashank,
    chin-
tal@iitk.ac.in

Outline

Introduction
Pelizaeus-
Merzbacher
Disease
Types of PMD

Disease
Mechanism

Pathogenesis
Animal Mutants
Molecular
Pathogenesis
Genotype -
Phenotype
correlation

References




                  Chintalagiri Shashank, chintal@iitk.ac.in   Pelizaeus-Merzbacher Disease
Pelizaeus-
 Merzbacher
  Disease

 Chintalagiri
 Shashank,
    chin-
                 The first of these mechanisms produces loss of PLP function,
tal@iitk.ac.in   in which PLP does not accumulate in the cell. To date, 4
Outline          so-called null mutations that cause PMD have been identified,
Introduction     including a deletion of the entire PLP gene, all of which
Pelizaeus-
Merzbacher       produce a similar, relatively mild clinical phenotype.
Disease
Types of PMD

Disease
Mechanism
                 Noncoding mutations affecting splicing of PLP1 and deletions
Pathogenesis     have been described in patients with PMD with the lowest
Animal Mutants
Molecular
                 frequency.
Pathogenesis
Genotype -
Phenotype
correlation

References




                  Chintalagiri Shashank, chintal@iitk.ac.in   Pelizaeus-Merzbacher Disease
Pelizaeus-
 Merzbacher
                 The second of these genetic mechanisms produces a
  Disease
                 gain-of-toxic function. Experimental evidence supports this
 Chintalagiri
 Shashank,       mechanism. Gain-of-function mutations, typically amino acid
    chin-
tal@iitk.ac.in
                 substitutions, prevent PLP from reaching the cell surface by
                 disrupting normal PLP folding. The mutant protein then
Outline
                 accumulates in the endoplasmic reticulum, somehow triggering
Introduction
Pelizaeus-       increased oligodendrocyte cell death by apoptosis, with
Merzbacher
Disease
Types of PMD
                 resultant dysmyelination. The clinical phenotype caused by a
Disease          gain-of-function mutation depends on the location of the
Mechanism
                 altered amino acid, as well as on the particular amino acid
Pathogenesis
Animal Mutants   substituted.
Molecular
Pathogenesis
Genotype -
Phenotype
correlation
                 Over 100 point mutations in the PLP1 coding region have been
References       identified, and these account for approximately 15% to 20% of
                 PMD cases.
                  Chintalagiri Shashank, chintal@iitk.ac.in   Pelizaeus-Merzbacher Disease
Pelizaeus-
 Merzbacher
  Disease
                 The third and most common genetic mechanism is duplication
 Chintalagiri
                 of the region of the X chromosome that contains the PLP
 Shashank,
    chin-
                 gene. Since overexpression of PLP and/or DM20 is sufficient to
tal@iitk.ac.in   cause both CNS dysmyelination and subsequent demyelination
Outline          in transgenic mice, the human duplication probably produces
Introduction     PMD for similar reasons. The molecular mechanisms
Pelizaeus-
Merzbacher
Disease
                 underlying the PLP duplication have not yet been elucidated.
Types of PMD     The breakpoints of the PLP duplication often vary between
Disease
Mechanism        patients, and inclusion of flanking genes in addition to PLP
Pathogenesis     and/or disruption of a flanking gene may explain differences in
Animal Mutants
Molecular
                 phenotypic severities among patients with PLP duplication.
Pathogenesis
Genotype -
Phenotype
correlation
                 This mutation probably accounts for 50% to 70% of the cases
References
                 of PMD.

                  Chintalagiri Shashank, chintal@iitk.ac.in   Pelizaeus-Merzbacher Disease
Pelizaeus-
 Merzbacher
  Disease

 Chintalagiri
 Shashank,
    chin-
tal@iitk.ac.in
                 Genotype - phenotype correlation in PLP disease
                 Cailloux et al, 2000
Outline

Introduction
                       52 PMD and 28 SPG families selected for sequencing of
Pelizaeus-
Merzbacher
                       the seven coding regions and the exon/intron junctions of
Disease
Types of PMD
                       the PLP gene
Disease
Mechanism
                       Identied 33 abnormalities (29 in PMD patients, 4 in SPG
Pathogenesis
                       patients)
Animal Mutants
Molecular
Pathogenesis
Genotype -
Phenotype
correlation

References




                 Chintalagiri Shashank, chintal@iitk.ac.in   Pelizaeus-Merzbacher Disease
Type and Position of Mutation

 Pelizaeus-
 Merzbacher
  Disease
                        Twenty-three were missense mutations, three were
 Chintalagiri
 Shashank,              deletion/insertions with frameshifts and seven were
    chin-
tal@iitk.ac.in          splice-site mutations.
Outline
                        Mutations were in
Introduction                1 coding regions in 24 of 29 PMD patients (80%)
Pelizaeus-
Merzbacher
                            2 exons 2 (29%), 4 (29%) and 5 (21%)
Disease
Types of PMD
                            3 2 of the mutations in SPG patients were in the
Disease                       PLP-specific coding region, exon 3B.
Mechanism
                            4 No mutations were observed in exons 1 and 7 of PLP
Pathogenesis
Animal Mutants          Of the 23 aa changes resulting from missense mutations
Molecular
Pathogenesis                1   48% affected the CD loop
Genotype -
Phenotype
correlation
                            2   each of the other locations accounted for only 4 to 13% of
References
                                the mutations.


                  Chintalagiri Shashank, chintal@iitk.ac.in   Pelizaeus-Merzbacher Disease
Correlation between severity and type of mutation

 Pelizaeus-
 Merzbacher
  Disease

 Chintalagiri
 Shashank,
    chin-
tal@iitk.ac.in
                        Missense mutations were observed in two thirds of cases
Outline
                        for the severe forms and in one third of cases for the
Introduction
Pelizaeus-
Merzbacher
                        milder forms .
Disease
Types of PMD            All other types of abnormality were observed almost
Disease
Mechanism
                        exclusively in the mildest forms (80%).
Pathogenesis
Animal Mutants
Molecular
Pathogenesis
Genotype -
Phenotype
correlation

References




                  Chintalagiri Shashank, chintal@iitk.ac.in   Pelizaeus-Merzbacher Disease
Correlation between disease severity and the
                 position of exonic mutations
 Pelizaeus-
 Merzbacher
  Disease
                        Of the 26 mutations in coding regions
 Chintalagiri
 Shashank,                  1 15 were responsible for severe PMD forms (57%)
    chin-
tal@iitk.ac.in              2 9 for mild PMD forms (35%)
                            3 2 for SPG form 4 (8%)
Outline

Introduction
                        In terms of exons,
Pelizaeus-
Merzbacher
                            1 Mutations causing severe forms of PMD mapped
Disease
Types of PMD
                              essentially to exons 2 (40%) and 4 (33%), more rarely to
Disease                       exons 6 (15%), 5 (7%), and 3A (7%), and never to exons
Mechanism                     1, 3B and 7.
Pathogenesis                2 Mutations causing mild forms of PMD mapped
Animal Mutants
Molecular                     predominantly to exon 5 (44%), more rarely to exons 4
Pathogenesis
Genotype -
Phenotype
                              (22%), 6 (22%) and 2 (12%).
correlation                 3 SPG mutations mapped exclusively to exon 3B.
References




                  Chintalagiri Shashank, chintal@iitk.ac.in   Pelizaeus-Merzbacher Disease
Schematic representation of PLP

 Pelizaeus-
 Merzbacher
  Disease

 Chintalagiri
 Shashank,
    chin-
tal@iitk.ac.in

Outline

Introduction
Pelizaeus-
Merzbacher
Disease
Types of PMD

Disease
Mechanism

Pathogenesis
Animal Mutants
Molecular
Pathogenesis
Genotype -
Phenotype
correlation

References




                  Chintalagiri Shashank, chintal@iitk.ac.in   Pelizaeus-Merzbacher Disease
Severity of the disease

 Pelizaeus-
 Merzbacher
  Disease

 Chintalagiri
 Shashank,
    chin-
tal@iitk.ac.in

Outline

Introduction
Pelizaeus-
Merzbacher
Disease
Types of PMD

Disease
Mechanism

Pathogenesis
Animal Mutants
Molecular
Pathogenesis
Genotype -
Phenotype
correlation

References




                  Chintalagiri Shashank, chintal@iitk.ac.in   Pelizaeus-Merzbacher Disease
Correlation between severity the type of AA
                 substitution resulting from missense mutations
 Pelizaeus-
 Merzbacher             Changes in the PLP-specific BC loop were responsible for
  Disease
                        the SPG phenotype.
 Chintalagiri
 Shashank,
    chin-
                        Ten of the 11 substitutions in the AB extracytoplasmic
tal@iitk.ac.in          loop and the 4 transmembrane segments of the
Outline                 PLP/DM20 protein caused severe forms of PMD.
Introduction            Five of the 11 substitutions in the CD loop caused severe
Pelizaeus-
Merzbacher
Disease
                        PMD and 6 mild PMD.
Types of PMD

Disease
                        3 families had three different exon 4 mutations resulting in
Mechanism               the substitution of the same amino acid, at position 202 in
Pathogenesis
Animal Mutants
                        the PLP/DM20 protein (D202N, D202G,D202E) and had
Molecular
Pathogenesis
                        the most severe form of PMD.
Genotype -
Phenotype
correlation
                        2 families had two different exon 5 mutations resulting in
References              substitution of the same amino acid, at position 215
                        (P215S, P215A).
                  Chintalagiri Shashank, chintal@iitk.ac.in   Pelizaeus-Merzbacher Disease
Correlation between severity the type of AA
                 substitution resulting from missense mutations
 Pelizaeus-
 Merzbacher
  Disease

 Chintalagiri
 Shashank,
    chin-
                        Replacement of a highly conserved amino acid, whatever
tal@iitk.ac.in
                        the new amino acid, caused the most severe forms of
Outline                 PMD, whereas substitutions of less conserved amino acids
Introduction            caused milder forms.
Pelizaeus-
Merzbacher
Disease                 In 2 cases, a severe form of PMD was observed (Y174C
Types of PMD
                        and A247E), despite substitution of a poorly conserved
Disease
Mechanism               amino acid. In two cases, a severe form of PMD was
Pathogenesis            observed (Y174C and A247E), despite substitution of a
Animal Mutants
Molecular
Pathogenesis
                        poorly conserved amino acid.
Genotype -
Phenotype
correlation

References




                  Chintalagiri Shashank, chintal@iitk.ac.in   Pelizaeus-Merzbacher Disease
List of point mutations

 Pelizaeus-
 Merzbacher
  Disease

 Chintalagiri
 Shashank,
    chin-
tal@iitk.ac.in

Outline

Introduction
Pelizaeus-
Merzbacher
Disease
Types of PMD

Disease
Mechanism

Pathogenesis
Animal Mutants
Molecular
Pathogenesis
Genotype -
Phenotype
correlation

References




                  Chintalagiri Shashank, chintal@iitk.ac.in   Pelizaeus-Merzbacher Disease
Distribution of point mutations

 Pelizaeus-
 Merzbacher
  Disease

 Chintalagiri
 Shashank,
    chin-
tal@iitk.ac.in

Outline

Introduction
Pelizaeus-
Merzbacher
Disease
Types of PMD

Disease
Mechanism

Pathogenesis
Animal Mutants
Molecular
Pathogenesis
Genotype -
Phenotype
correlation

References




                  Chintalagiri Shashank, chintal@iitk.ac.in   Pelizaeus-Merzbacher Disease
Myelin Composition[8](2009)

 Pelizaeus-
 Merzbacher
  Disease

 Chintalagiri
 Shashank,
    chin-
tal@iitk.ac.in

Outline

Introduction
Pelizaeus-
Merzbacher
Disease
Types of PMD

Disease
Mechanism

Pathogenesis
Animal Mutants
Molecular
Pathogenesis
Genotype -
Phenotype
correlation

References




                  Chintalagiri Shashank, chintal@iitk.ac.in   Pelizaeus-Merzbacher Disease
References I

 Pelizaeus-
 Merzbacher            NINDS; Pelizaeus-Merzbacher Disease Information Page
  Disease              http://www.ninds.nih.gov/disorders/pelizaeus_merzbacher/pelizaeus_merzbacher.htm.
 Chintalagiri
                       James Garbern et.al.; The Molecular Pathogenesis of Pelizaeus-Merzbacher Disease, Arch. Neurol.,
 Shashank,
    chin-              VOL 56, Oct 1999
tal@iitk.ac.in
                       J. Y. Garbern; Pelizaeus-Merzbacher disease:Genetic and cellular pathogenesis; Cell. Mol. Life Sci. 64
                       (2007) 50 65
Outline

Introduction           Fabrice Cailloux et.al; Genotypephenotype correlation in inherited brain myelination defects due to
Pelizaeus-             proteolipid protein gene mutations; Eur. J. Hum. Genet. (2000) 8, 837845
Merzbacher
Disease
Types of PMD           Simonida Gencic et.al.; Pelizaeus-Merzbacher Disease: An X-linked Neurologic Disorder of Myelin
                       Metabolism with a Novel Mutation in the Gene Encoding Proteolipid Protein, Am. J. Hum. Genet.
Disease
                       45:435-442, 1989
Mechanism

Pathogenesis           Judith M. Greer, Marjorie B. Lees; Myelin proteolipid proteinthe rst 50 years; Int. J. Biochem. & Cell
Animal Mutants         Biol. 34 211215; 2002
Molecular
Pathogenesis           Eun Sil Lee et.al.; A case of complicated spastic paraplegia 2 due to a point mutation in the
Genotype -
Phenotype              proteolipid protein 1 gene; J. Neu. Sci. 224 (2004) 83 87
correlation

References             Olaf Jahn, Stefan Tenzer, Hauke B. Werner;Myelin Proteomics: Molecular Anatomy of an Insulating
                       Sheath; Mol Neurobiol (2009) 40:5572


                  Chintalagiri Shashank, chintal@iitk.ac.in      Pelizaeus-Merzbacher Disease
References II

 Pelizaeus-
 Merzbacher
  Disease

 Chintalagiri
 Shashank,
    chin-
                       Marie-Noelle Bonnet-Dupeyron et.al.;PLP1 Splicing Abnormalities Identified in Pelizaeus-Merzbacher
tal@iitk.ac.in
                       Disease and SPG2 Fibroblasts Are Associated With Different Types of Mutations; Hum. Mut. 29(8),
                       1028 - 1036, 2008
Outline
                       Ken Inoue;PLP1-related inherited dysmyelinating disorders:Pelizaeus-Merzbacher disease and spastic
Introduction
Pelizaeus-
                       paraplegia type 2; Neurogenetics (2005) 6: 1 16
Merzbacher
Disease
                       Olaf Maier et.al.;Polarity Development in Oligodendrocytes: Sorting and Trafficking of Myelin
Types of PMD
                       Components; J Mol Neurosci (2008) 35:35 53
Disease
Mechanism              P. Kursula; Structural properties of proteins specic to the myelin sheath; Amino Acids (2008) 34: 175
Pathogenesis           185
Animal Mutants
Molecular
Pathogenesis
Genotype -
Phenotype
correlation

References




                  Chintalagiri Shashank, chintal@iitk.ac.in     Pelizaeus-Merzbacher Disease

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Pelizaeus–Merzbacher disease

  • 1. Pelizaeus- Merzbacher Disease Chintalagiri Shashank, chin- tal@iitk.ac.in Pelizaeus-Merzbacher Disease Outline BSE638 - Structural Basis of Protein Function Introduction Pelizaeus- Merzbacher Disease Types of PMD Chintalagiri Shashank, chintal@iitk.ac.in Disease Mechanism Pathogenesis Animal Mutants Molecular April 29, 2010 Pathogenesis Genotype - Phenotype correlation References Chintalagiri Shashank, chintal@iitk.ac.in Pelizaeus-Merzbacher Disease
  • 2. Pelizaeus- Merzbacher Disease 1 Introduction Chintalagiri Shashank, Pelizaeus-Merzbacher Disease chin- tal@iitk.ac.in Types of PMD Outline 2 Disease Mechanism Introduction Pelizaeus- Merzbacher Disease Types of PMD 3 Pathogenesis Disease Animal Mutants Mechanism Molecular Pathogenesis Pathogenesis Animal Mutants Genotype - Phenotype correlation Molecular Pathogenesis Genotype - Phenotype correlation 4 References References Chintalagiri Shashank, chintal@iitk.ac.in Pelizaeus-Merzbacher Disease
  • 3. Pelizaeus-Merzbacher Disease[1] Pelizaeus- Merzbacher Rare, progressive, degenerative central nervous system Disease disorder Chintalagiri Shashank, chin- Coordination, motor abilities, and intellectual function tal@iitk.ac.in deteriorate Outline One of a group of gene-linked disorders known as the Introduction leukodystrophies, affects growth of the myelin sheath. Pelizaeus- Merzbacher Disease The disease is caused by a mutation in the gene encoding Types of PMD a myelin protein called proteolipid protein-1 (PLP1). Disease Mechanism PMD is inherited as an X-linked recessive trait; the Pathogenesis affected individuals are male and the mothers are carriers Animal Mutants Molecular Pathogenesis of the PLP1 mutation. Genotype - Phenotype correlation Severity and onset of the disease ranges widely, depending References on the type of PLP1 mutation. One of a spectrum of diseases associated with PLP1. Chintalagiri Shashank, chintal@iitk.ac.in Pelizaeus-Merzbacher Disease
  • 4. Types of PMD[1] Pelizaeus- Merzbacher There are 4 general classifications within this spectrum of Disease diseases. In order of severity, they are: Chintalagiri Shashank, Connatal PMD, which is the most severe type and involves chin- tal@iitk.ac.in delayed mental and physical development and severe neurological symptoms Outline Classic PMD, in which the early symptoms include muscle Introduction Pelizaeus- Merzbacher weakness, involuntary movements of the eyes Disease Types of PMD (nystagmus), and delays in motor development within the Disease first year of life Mechanism Complicated SPG2, which features motor development Pathogenesis Animal Mutants issues and brain involvement Molecular Pathogenesis Genotype - Pure SPG2, which includes cases of PMD that do not Phenotype correlation have neurologic complications. References Noticeable changes in the extent of myelination can be detected by MRI analyses of the brain. Chintalagiri Shashank, chintal@iitk.ac.in Pelizaeus-Merzbacher Disease
  • 5. Pelizaeus- Merzbacher Disease Chintalagiri Shashank, chin- tal@iitk.ac.in Modern morphological, biochemical, and molecular techniques Outline have made this distinction obsolete, and PMD must now be Introduction Pelizaeus- considered a leukodystrophy with variable clinical and Merzbacher Disease Types of PMD neuropathological phenotypes, although all cases are due to Disease mutations of the proteolipid protein (PLP) gene. Mechanism Pathogenesis Animal Mutants Molecular Pathogenesis Genotype - Phenotype correlation References Chintalagiri Shashank, chintal@iitk.ac.in Pelizaeus-Merzbacher Disease
  • 6. Disease Mechanism Pelizaeus- Merzbacher Disease Chintalagiri Shashank, Proposed roles for PLP1 include mediating interlamellar chin- tal@iitk.ac.in adhesion in compact myelin, mediating ion flux, and acting as an oligodendrocyte precursor mitogen. Outline Introduction Pelizaeus- Merzbacher PLP is a major structural component of CNS myelin, whereas Disease Types of PMD DM20 which is produced earlier in CNS development may be Disease involved in oligodendrocyte differentiation and survival. Mechanism Pathogenesis Animal Mutants Complete deficiency of PLP1 does not prevent myelination, but Molecular Pathogenesis Genotype - it does result in late-onset axonal degeneration. Phenotype correlation References Chintalagiri Shashank, chintal@iitk.ac.in Pelizaeus-Merzbacher Disease
  • 7. Disease Mechanism Pelizaeus- Merzbacher Disease Chintalagiri Shashank, In addition to null mutations, mutations that disrupt the chin- tal@iitk.ac.in PLP1-specific region, a 35-amino-acid region that is spliced out during formation of the DM20 isoform, cause both peripheral Outline Introduction neuropathy and central axonal degeneration. Pelizaeus- Merzbacher Disease Types of PMD Single amino-acid changes in highly conserved regions of the Disease DM20 protein caused the most severe forms of PMD. Mechanism Substitutions of less conserved amino acids, truncations, Pathogenesis Animal Mutants absence of the protein and PLP-specic mutations cause the Molecular Pathogenesis Genotype - milder forms of PMD and SPG. Phenotype correlation References Chintalagiri Shashank, chintal@iitk.ac.in Pelizaeus-Merzbacher Disease
  • 8. Disease Mechanism Pelizaeus- Merzbacher Disease Chintalagiri Shashank, chin- tal@iitk.ac.in Gow and Lazzarini have suggested a cellular mechanism for Outline disease severity in PMD. They reported that classical PMD Introduction Pelizaeus- correlates with misfolding and accumulation of PLP1 in the Merzbacher Disease endoplasmic reticulum (ER) and transport of DM20 to the cell Types of PMD Disease surface, while connatal PMD correlates with misfolding and Mechanism accumulation of both PLP1 and DM20 in the ER. Pathogenesis Animal Mutants Molecular Pathogenesis Genotype - Phenotype correlation References Chintalagiri Shashank, chintal@iitk.ac.in Pelizaeus-Merzbacher Disease
  • 9. Pathogenesis Pelizaeus- Merzbacher Disease Chintalagiri Shashank, chin- tal@iitk.ac.in Gencic et.al.[5] report that the underlying disturbance in myelination of Pelizaeus-Merzbacher patients was Outline attributed to a failure to form myelin (dys-myelination) Introduction Pelizaeus- rather than to a breakdown of preexisting myelin Merzbacher Disease (demyelination) by a pathogenic analysis by Zeman et.al. Types of PMD Disease in 1964. Mechanism Zeman et.al. also predicted that the defect would involve Pathogenesis Animal Mutants a myelin protein or proteolipid Molecular Pathogenesis Genotype - Phenotype correlation References Chintalagiri Shashank, chintal@iitk.ac.in Pelizaeus-Merzbacher Disease
  • 10. Animal Mutants Pelizaeus- Merzbacher Disease Chintalagiri Shashank, PLP deficiency relates to a X-linked CNS myelin deficiency in chin- tal@iitk.ac.in several animal mutants jimpy mouse (jp) is the oldest and best known Outline Introduction the myelin-deficient rat (md) Pelizaeus- Merzbacher Disease the shaking pup (sh) Types of PMD Disease the rumpshaker mouse (rsh) Mechanism the rabbit with paralytic tremor (pt) Pathogenesis Animal Mutants Molecular The deficiency of PLP protein was commensurate with low Pathogenesis Genotype - levels of the matching messenger ribonucleic acid (mRNA). Phenotype correlation References Chintalagiri Shashank, chintal@iitk.ac.in Pelizaeus-Merzbacher Disease
  • 11. Implication of PLP Pelizaeus- Merzbacher Disease Two observations focused attention on the major structural Chintalagiri Shashank, protein of myelin, proteolipid protein (PLP), as a candidate for chin- tal@iitk.ac.in mutation in Pelizaeus-Merzbacher disease. Outline Assignment of the PLP gene to the human X chromosome Introduction at position Xq22, which supported the X-linked Pelizaeus- Merzbacher inheritance of the disease. Disease Types of PMD Discovery that the dysmyelinating mouse mutant jimpy, Disease Mechanism which appears pathologically and genetically similar to Pathogenesis Pelizaeus-Merzbacher disease, has a mutation in the PLP Animal Mutants Molecular gene that results in aberrantly spliced PLP transcripts Pathogenesis Genotype - (Morello et al. 1986; Nave et al. 1986, 1987; Hudson et Phenotype correlation al. 1987; Macklin et al. 1987; Ikenaka et al. 1988). References Chintalagiri Shashank, chintal@iitk.ac.in Pelizaeus-Merzbacher Disease
  • 12. Myelin[8] Pelizaeus- Merzbacher Disease Chintalagiri Shashank, chin- tal@iitk.ac.in Outline Introduction Pelizaeus- Merzbacher Disease Types of PMD Disease Mechanism Pathogenesis Animal Mutants Molecular Pathogenesis Genotype - Phenotype correlation References Chintalagiri Shashank, chintal@iitk.ac.in Pelizaeus-Merzbacher Disease
  • 13. Structure of PLP Pelizaeus- Merzbacher Disease Chintalagiri Shashank, chin- tal@iitk.ac.in Outline Introduction Pelizaeus- Merzbacher Disease Types of PMD Disease Mechanism Pathogenesis Animal Mutants Molecular Pathogenesis Genotype - Phenotype correlation References Chintalagiri Shashank, chintal@iitk.ac.in Pelizaeus-Merzbacher Disease
  • 14. Structure of PLP Pelizaeus- Merzbacher PLP is a tetraspan protein, with 4 TM α-helices spanning Disease the myelin membrane. Both N- and C-terminals are in the Chintalagiri Shashank, cytoplasmic side. chin- tal@iitk.ac.in Immunolabeling studies of PLP and several protein structure prediction algorithms were used to determine the Outline Introduction most likely residues making up the α-helices. Pelizaeus- Merzbacher The region of PLP that is deleted in DM20 (residues 116 Disease Types of PMD 150) is shown in yellow. Disease Cysteines involved in the formation of the two disulde Mechanism bonds in PLP (linking residues 183 227 and 200 219) are Pathogenesis Animal Mutants shown in blue. Molecular Pathogenesis Genotype - 6 cysteine residues are thought to be acylated (shown in Phenotype correlation red), with palmitic acid sidechains attached. Alternatively, References some of these cysteine residues could be involved in disulde linkages. Chintalagiri Shashank, chintal@iitk.ac.in Pelizaeus-Merzbacher Disease
  • 15. Structure of PLP Pelizaeus- Merzbacher Disease Chintalagiri Shashank, chin- Structural properties of proteins specic to the myelin sheath, tal@iitk.ac.in Amino Acids (2008)[12] Outline Some of the myelin proteins, belonging to the family Introduction Pelizaeus- of tetraspanins, are amongst the most hydrophobic Merzbacher Disease Types of PMD proteins known. One of these proteins is the Disease proteolipid protein. This group of proteins is most Mechanism poorly characterised structurally, and will not be Pathogenesis Animal Mutants discussed in this review. Molecular Pathogenesis Genotype - Phenotype correlation References Chintalagiri Shashank, chintal@iitk.ac.in Pelizaeus-Merzbacher Disease
  • 16. Mutation of PLP Pelizaeus- Merzbacher Disease Chintalagiri Shashank, chin- tal@iitk.ac.in The mutation causing PMD seems to be different for different families. Outline Introduction PMD is always caused by a mutation of PLP. Pelizaeus- Merzbacher Disease A majority of the cases seem to be caused by duplications Types of PMD involving the entire gene (larger than 100 kb) Disease Mechanism In some families, PMD is caused by the mutation of a Pathogenesis Animal Mutants single amino acid. Molecular Pathogenesis Genotype - Phenotype correlation References Chintalagiri Shashank, chintal@iitk.ac.in Pelizaeus-Merzbacher Disease
  • 17. Mutations[2] Pelizaeus- Merzbacher Disease Chintalagiri Shashank, chin- tal@iitk.ac.in Clinical observations and studies of PLP mutations in animals and cell cultures suggest that there at least 3 distinct genetic Outline mechanisms that cause PMD. [2] Introduction Pelizaeus- Merzbacher Disease In addition, spastic paraplegia 2 (SPG2) is allelic to PMD and Types of PMD Disease typically caused by missense mutations in the second Mechanism extracellular domain of PLP1 or in the PLP1-specific region Pathogenesis Animal Mutants that is spliced out during formation of the DM20 isoform. Molecular Pathogenesis Genotype - Phenotype correlation References Chintalagiri Shashank, chintal@iitk.ac.in Pelizaeus-Merzbacher Disease
  • 18. Molecular mechanisms of PMD pathogenesis[3] Pelizaeus- Merzbacher Disease Chintalagiri Shashank, chin- tal@iitk.ac.in Outline Introduction Pelizaeus- Merzbacher Disease Types of PMD Disease Mechanism Pathogenesis Animal Mutants Molecular Pathogenesis Genotype - Phenotype correlation References Chintalagiri Shashank, chintal@iitk.ac.in Pelizaeus-Merzbacher Disease
  • 19. Pelizaeus- Merzbacher Disease Chintalagiri Shashank, chin- The first of these mechanisms produces loss of PLP function, tal@iitk.ac.in in which PLP does not accumulate in the cell. To date, 4 Outline so-called null mutations that cause PMD have been identified, Introduction including a deletion of the entire PLP gene, all of which Pelizaeus- Merzbacher produce a similar, relatively mild clinical phenotype. Disease Types of PMD Disease Mechanism Noncoding mutations affecting splicing of PLP1 and deletions Pathogenesis have been described in patients with PMD with the lowest Animal Mutants Molecular frequency. Pathogenesis Genotype - Phenotype correlation References Chintalagiri Shashank, chintal@iitk.ac.in Pelizaeus-Merzbacher Disease
  • 20. Pelizaeus- Merzbacher The second of these genetic mechanisms produces a Disease gain-of-toxic function. Experimental evidence supports this Chintalagiri Shashank, mechanism. Gain-of-function mutations, typically amino acid chin- tal@iitk.ac.in substitutions, prevent PLP from reaching the cell surface by disrupting normal PLP folding. The mutant protein then Outline accumulates in the endoplasmic reticulum, somehow triggering Introduction Pelizaeus- increased oligodendrocyte cell death by apoptosis, with Merzbacher Disease Types of PMD resultant dysmyelination. The clinical phenotype caused by a Disease gain-of-function mutation depends on the location of the Mechanism altered amino acid, as well as on the particular amino acid Pathogenesis Animal Mutants substituted. Molecular Pathogenesis Genotype - Phenotype correlation Over 100 point mutations in the PLP1 coding region have been References identified, and these account for approximately 15% to 20% of PMD cases. Chintalagiri Shashank, chintal@iitk.ac.in Pelizaeus-Merzbacher Disease
  • 21. Pelizaeus- Merzbacher Disease The third and most common genetic mechanism is duplication Chintalagiri of the region of the X chromosome that contains the PLP Shashank, chin- gene. Since overexpression of PLP and/or DM20 is sufficient to tal@iitk.ac.in cause both CNS dysmyelination and subsequent demyelination Outline in transgenic mice, the human duplication probably produces Introduction PMD for similar reasons. The molecular mechanisms Pelizaeus- Merzbacher Disease underlying the PLP duplication have not yet been elucidated. Types of PMD The breakpoints of the PLP duplication often vary between Disease Mechanism patients, and inclusion of flanking genes in addition to PLP Pathogenesis and/or disruption of a flanking gene may explain differences in Animal Mutants Molecular phenotypic severities among patients with PLP duplication. Pathogenesis Genotype - Phenotype correlation This mutation probably accounts for 50% to 70% of the cases References of PMD. Chintalagiri Shashank, chintal@iitk.ac.in Pelizaeus-Merzbacher Disease
  • 22. Pelizaeus- Merzbacher Disease Chintalagiri Shashank, chin- tal@iitk.ac.in Genotype - phenotype correlation in PLP disease Cailloux et al, 2000 Outline Introduction 52 PMD and 28 SPG families selected for sequencing of Pelizaeus- Merzbacher the seven coding regions and the exon/intron junctions of Disease Types of PMD the PLP gene Disease Mechanism Identied 33 abnormalities (29 in PMD patients, 4 in SPG Pathogenesis patients) Animal Mutants Molecular Pathogenesis Genotype - Phenotype correlation References Chintalagiri Shashank, chintal@iitk.ac.in Pelizaeus-Merzbacher Disease
  • 23. Type and Position of Mutation Pelizaeus- Merzbacher Disease Twenty-three were missense mutations, three were Chintalagiri Shashank, deletion/insertions with frameshifts and seven were chin- tal@iitk.ac.in splice-site mutations. Outline Mutations were in Introduction 1 coding regions in 24 of 29 PMD patients (80%) Pelizaeus- Merzbacher 2 exons 2 (29%), 4 (29%) and 5 (21%) Disease Types of PMD 3 2 of the mutations in SPG patients were in the Disease PLP-specific coding region, exon 3B. Mechanism 4 No mutations were observed in exons 1 and 7 of PLP Pathogenesis Animal Mutants Of the 23 aa changes resulting from missense mutations Molecular Pathogenesis 1 48% affected the CD loop Genotype - Phenotype correlation 2 each of the other locations accounted for only 4 to 13% of References the mutations. Chintalagiri Shashank, chintal@iitk.ac.in Pelizaeus-Merzbacher Disease
  • 24. Correlation between severity and type of mutation Pelizaeus- Merzbacher Disease Chintalagiri Shashank, chin- tal@iitk.ac.in Missense mutations were observed in two thirds of cases Outline for the severe forms and in one third of cases for the Introduction Pelizaeus- Merzbacher milder forms . Disease Types of PMD All other types of abnormality were observed almost Disease Mechanism exclusively in the mildest forms (80%). Pathogenesis Animal Mutants Molecular Pathogenesis Genotype - Phenotype correlation References Chintalagiri Shashank, chintal@iitk.ac.in Pelizaeus-Merzbacher Disease
  • 25. Correlation between disease severity and the position of exonic mutations Pelizaeus- Merzbacher Disease Of the 26 mutations in coding regions Chintalagiri Shashank, 1 15 were responsible for severe PMD forms (57%) chin- tal@iitk.ac.in 2 9 for mild PMD forms (35%) 3 2 for SPG form 4 (8%) Outline Introduction In terms of exons, Pelizaeus- Merzbacher 1 Mutations causing severe forms of PMD mapped Disease Types of PMD essentially to exons 2 (40%) and 4 (33%), more rarely to Disease exons 6 (15%), 5 (7%), and 3A (7%), and never to exons Mechanism 1, 3B and 7. Pathogenesis 2 Mutations causing mild forms of PMD mapped Animal Mutants Molecular predominantly to exon 5 (44%), more rarely to exons 4 Pathogenesis Genotype - Phenotype (22%), 6 (22%) and 2 (12%). correlation 3 SPG mutations mapped exclusively to exon 3B. References Chintalagiri Shashank, chintal@iitk.ac.in Pelizaeus-Merzbacher Disease
  • 26. Schematic representation of PLP Pelizaeus- Merzbacher Disease Chintalagiri Shashank, chin- tal@iitk.ac.in Outline Introduction Pelizaeus- Merzbacher Disease Types of PMD Disease Mechanism Pathogenesis Animal Mutants Molecular Pathogenesis Genotype - Phenotype correlation References Chintalagiri Shashank, chintal@iitk.ac.in Pelizaeus-Merzbacher Disease
  • 27. Severity of the disease Pelizaeus- Merzbacher Disease Chintalagiri Shashank, chin- tal@iitk.ac.in Outline Introduction Pelizaeus- Merzbacher Disease Types of PMD Disease Mechanism Pathogenesis Animal Mutants Molecular Pathogenesis Genotype - Phenotype correlation References Chintalagiri Shashank, chintal@iitk.ac.in Pelizaeus-Merzbacher Disease
  • 28. Correlation between severity the type of AA substitution resulting from missense mutations Pelizaeus- Merzbacher Changes in the PLP-specific BC loop were responsible for Disease the SPG phenotype. Chintalagiri Shashank, chin- Ten of the 11 substitutions in the AB extracytoplasmic tal@iitk.ac.in loop and the 4 transmembrane segments of the Outline PLP/DM20 protein caused severe forms of PMD. Introduction Five of the 11 substitutions in the CD loop caused severe Pelizaeus- Merzbacher Disease PMD and 6 mild PMD. Types of PMD Disease 3 families had three different exon 4 mutations resulting in Mechanism the substitution of the same amino acid, at position 202 in Pathogenesis Animal Mutants the PLP/DM20 protein (D202N, D202G,D202E) and had Molecular Pathogenesis the most severe form of PMD. Genotype - Phenotype correlation 2 families had two different exon 5 mutations resulting in References substitution of the same amino acid, at position 215 (P215S, P215A). Chintalagiri Shashank, chintal@iitk.ac.in Pelizaeus-Merzbacher Disease
  • 29. Correlation between severity the type of AA substitution resulting from missense mutations Pelizaeus- Merzbacher Disease Chintalagiri Shashank, chin- Replacement of a highly conserved amino acid, whatever tal@iitk.ac.in the new amino acid, caused the most severe forms of Outline PMD, whereas substitutions of less conserved amino acids Introduction caused milder forms. Pelizaeus- Merzbacher Disease In 2 cases, a severe form of PMD was observed (Y174C Types of PMD and A247E), despite substitution of a poorly conserved Disease Mechanism amino acid. In two cases, a severe form of PMD was Pathogenesis observed (Y174C and A247E), despite substitution of a Animal Mutants Molecular Pathogenesis poorly conserved amino acid. Genotype - Phenotype correlation References Chintalagiri Shashank, chintal@iitk.ac.in Pelizaeus-Merzbacher Disease
  • 30. List of point mutations Pelizaeus- Merzbacher Disease Chintalagiri Shashank, chin- tal@iitk.ac.in Outline Introduction Pelizaeus- Merzbacher Disease Types of PMD Disease Mechanism Pathogenesis Animal Mutants Molecular Pathogenesis Genotype - Phenotype correlation References Chintalagiri Shashank, chintal@iitk.ac.in Pelizaeus-Merzbacher Disease
  • 31. Distribution of point mutations Pelizaeus- Merzbacher Disease Chintalagiri Shashank, chin- tal@iitk.ac.in Outline Introduction Pelizaeus- Merzbacher Disease Types of PMD Disease Mechanism Pathogenesis Animal Mutants Molecular Pathogenesis Genotype - Phenotype correlation References Chintalagiri Shashank, chintal@iitk.ac.in Pelizaeus-Merzbacher Disease
  • 32. Myelin Composition[8](2009) Pelizaeus- Merzbacher Disease Chintalagiri Shashank, chin- tal@iitk.ac.in Outline Introduction Pelizaeus- Merzbacher Disease Types of PMD Disease Mechanism Pathogenesis Animal Mutants Molecular Pathogenesis Genotype - Phenotype correlation References Chintalagiri Shashank, chintal@iitk.ac.in Pelizaeus-Merzbacher Disease
  • 33. References I Pelizaeus- Merzbacher NINDS; Pelizaeus-Merzbacher Disease Information Page Disease http://www.ninds.nih.gov/disorders/pelizaeus_merzbacher/pelizaeus_merzbacher.htm. Chintalagiri James Garbern et.al.; The Molecular Pathogenesis of Pelizaeus-Merzbacher Disease, Arch. Neurol., Shashank, chin- VOL 56, Oct 1999 tal@iitk.ac.in J. Y. Garbern; Pelizaeus-Merzbacher disease:Genetic and cellular pathogenesis; Cell. Mol. Life Sci. 64 (2007) 50 65 Outline Introduction Fabrice Cailloux et.al; Genotypephenotype correlation in inherited brain myelination defects due to Pelizaeus- proteolipid protein gene mutations; Eur. J. Hum. Genet. (2000) 8, 837845 Merzbacher Disease Types of PMD Simonida Gencic et.al.; Pelizaeus-Merzbacher Disease: An X-linked Neurologic Disorder of Myelin Metabolism with a Novel Mutation in the Gene Encoding Proteolipid Protein, Am. J. Hum. Genet. Disease 45:435-442, 1989 Mechanism Pathogenesis Judith M. Greer, Marjorie B. Lees; Myelin proteolipid proteinthe rst 50 years; Int. J. Biochem. & Cell Animal Mutants Biol. 34 211215; 2002 Molecular Pathogenesis Eun Sil Lee et.al.; A case of complicated spastic paraplegia 2 due to a point mutation in the Genotype - Phenotype proteolipid protein 1 gene; J. Neu. Sci. 224 (2004) 83 87 correlation References Olaf Jahn, Stefan Tenzer, Hauke B. Werner;Myelin Proteomics: Molecular Anatomy of an Insulating Sheath; Mol Neurobiol (2009) 40:5572 Chintalagiri Shashank, chintal@iitk.ac.in Pelizaeus-Merzbacher Disease
  • 34. References II Pelizaeus- Merzbacher Disease Chintalagiri Shashank, chin- Marie-Noelle Bonnet-Dupeyron et.al.;PLP1 Splicing Abnormalities Identified in Pelizaeus-Merzbacher tal@iitk.ac.in Disease and SPG2 Fibroblasts Are Associated With Different Types of Mutations; Hum. Mut. 29(8), 1028 - 1036, 2008 Outline Ken Inoue;PLP1-related inherited dysmyelinating disorders:Pelizaeus-Merzbacher disease and spastic Introduction Pelizaeus- paraplegia type 2; Neurogenetics (2005) 6: 1 16 Merzbacher Disease Olaf Maier et.al.;Polarity Development in Oligodendrocytes: Sorting and Trafficking of Myelin Types of PMD Components; J Mol Neurosci (2008) 35:35 53 Disease Mechanism P. Kursula; Structural properties of proteins specic to the myelin sheath; Amino Acids (2008) 34: 175 Pathogenesis 185 Animal Mutants Molecular Pathogenesis Genotype - Phenotype correlation References Chintalagiri Shashank, chintal@iitk.ac.in Pelizaeus-Merzbacher Disease