The document discusses Pelizaeus-Merzbacher Disease (PMD), a rare degenerative neurological disorder caused by mutations in the proteolipid protein 1 (PLP1) gene. PMD affects the growth of the myelin sheath and causes deterioration of motor and intellectual abilities. There are different types of PMD classified by severity, from the most severe connatal PMD to pure spastic paraplegia 2. Animal studies showed that PLP deficiency relates to myelin deficiencies in mutants like the jimpy mouse. The disease mechanism involves PLP1's role in myelin structure and how various mutations affect its function.
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
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
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
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
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