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Muscular Dystrophies

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All characterized by escalating muscle weakness and deterioration, usually ... accounts for 0.002% of proteins in striated muscle ... – PowerPoint PPT presentation

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Title: Muscular Dystrophies


1
Muscular Dystrophies
  • Robert Yarnall
  • Rachel Hanson
  • Dustin Jensen-Reiber

2
What is Muscular Dystrophy?
  • A category of over 30 genetic diseases
  • Duchenne MD (most common)
  • Becker MD
  • Emery-Dreifuss MD
  • Oculopharyngeal MD
  • All characterized by escalating muscle weakness
    and deterioration, usually occurring in proximal
    to distal direction due to muscle protein
    abnormality
  • DIFFERENTIATION
  • muscles affected
  • extent of weakness
  • onset age
  • progression rate
  • inheritance pattern

3
Who is affected?
  • INHERITANCE PATTERNS
  • Recessive e.g. Mm x Mm
  • Dominant e.g. Mm x mm
  • X-linked e.g. XMXm x XMY
  • The most common two forms, Duchenne and Becker,
    are X-linked, so males are almost exclusively
    affected by these two forms
  • DUCHENNE MD
  • 1 case per 3,500 live male birth -- 121,000 per
    year
  • BECKER MD
  • 1 case per 30,000 live male births

4
What causes the protein abnormality?
  • Muscular dystrophy is a genetic disease
  • The root of the problems lies with a defective
    gene. The gene responsible for the production of
    a certain protein
  • Transcription
  • Transfer of information coded in DNA to mRNA
  • Translation
  • Conversion of mRNA message to a protein
  • If a gene is defective, it will not be able to
    produce the appropriate mRNA strand
  • The inappropriate mRNA strand will not produce
    the appropriate protein

5
Common Signs and Symptoms
  • Difficulty taking first steps
  • Difficulty getting up from sitting or supine
    position
  • Gower sign
  • Unusual gait
  • may walk on toes or balls of feet
  • belly pushed out and shoulders back
  • Weak muscular strength tests
  • Scoliosis

6
Common signs and symptoms
  • Loss of ambulation (walking)
  • usually occurs between ages of 7-13
  • can occur as early as age 6
  • Wheel chair needed
  • Contractures (often permanent muscle shortening)
  • Pseudohypertrophy of muscle
  • dead cells replaced by fibro-fatty pad
  • High creatine phosphokinase blood levels
  • enzyme leaks out of damaged muscle

7
Why do the muscle cells die?
  • The muscle cells either completely lack, are
    insufficient in, or have an abnormality relating
    to some form of vital sarcolemma protein
  • Dystrophin, Merosin, Fukutin, Caveolin, etc
  • Dystrophin
  • 3,685 amino acid protein
  • accounts for 0.002 of proteins in striated
    muscle
  • This abnormality in muscle fiber membrane
    proteins disrupts the structural integrity of the
    cell
  • Dystrophin links with actin proteins and DAG
    complex (dystrophin associated glycoproteins) to
    create a stable complex that interacts with
    extracellular matrix
  • Cell contents leak out, eventually causing cell
    death

8
Analogy
  • The whole muscle cell is a building
  • contains many different components
  • One component being bolts
  • dystrophin (or another structural protein) are a
    certain type of bolt in the building
  • If this bolt is nonexistent or lacking in number,
    the structural integrity of the building suffers
  • the cell membrane suffers
  • The building may even collapse
  • the cell dies
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