Muscle Dystrophy

Question 1

Dys?

Answer 1

suggests abnormal function

Question 2

which muscle does muscle dystrophy typically occur in?

Answer 2

Skeletal muscle

Question 3

Dystrophy?

Answer 3

degeneration of muscles (not r/t to aging, can happen early in life)

Question 4

Does MD get worse and worse from onset?

Answer 4

YES it is progressive

Question 5

what does MD involve?

Answer 5

• Atrophy (loss of muscle components/fibres), necrosis & pseudo hypertrophy

Question 6

Pseudohypertrophy?

Answer 6

Replacing lost muscular components with non-muscular tissue

Question 7

How do MD’s typically differ from one another?

Answer 7

• age of onset
• muscle groups affected
• mode of inheritance
• rate of progression

Question 8

What is the most common type of MD?

Answer 8

Duchenne MD

Question 9

Rate of Incidence for Duchenne MD?

Answer 9

1 in 3500 live births

Question 10

Etiology of Duchenne MD?

Answer 10

• mutated dystrophin gene on the short-arm of the X-chromosome
• recessive trait - MOI: X-linked recessive
• gender bias -> mostly impacts males

Question 11

Dystrophin gene?

Answer 11

codes for the membrane protein dystrophin on the sarcolemma of the muscle

Question 12

Explain the MOI: X-linked recessive?

Answer 12

females have 2 X chromosomes so if one is defective, the other X chromosome will compensate. Males only have 1 X chromosome, so a defective X will result in manifestations. The defective X chromosome is most often carried by the mother and passed to her offspring. This is why Duchenne MD is found more so in males.

Question 13

Function of dystrophin?

Answer 13

Attaches contractile filaments to each other, to the sacrolemma and to the matrix of the fiber.

Question 14

Patho?

Answer 14

Mutated gene -> decreased dystrophin function -> improper attachment of contractile filaments (fibres will move but more improperly, resulting in damage) -> fibre necrosis with use -> poor repair and regeneration -> more necrosis (muscle fibre cells die) -> calcium influx (sacrolemmas selective permeability is altered) and enzymes released when cells die (eg. CK) -> contractile fibres are lost and CT is deposited where the muscle cells were -> fibrofatty CT replaces muscle = “PSEUDOHYPERTROPHY”

Question 15

Which enzymes are released?

Answer 15

Creatine Kinase (CK)

Question 16

Manifestations?

Answer 16

• initially asymptomatic until ~2-6 years of age (bc there is not that much muscle use occurring to cause muscle damage)
• progressive muscle weakness
• respiratory problems
• cardiac problems
• death usually from resp and cardiac problems

Question 17

What is the average life span for pt with Duchenne MD?

Answer 17

20-25 years

Question 18

Dx?

Answer 18

• Hx, px (focusing on voluntary movement such as walking)
• biopsy
• blood sample -> serum creatine kinase d/t damage to the muscle cells
• prenatal testing
• carrier screening

Question 19

Treatment?

Answer 19

• supportive & symptomatic management
• increase comfort and function
  NO CURE

Question 20

how can you increase comfort and function?

Answer 20

Breathing exercises, braces for support, surgery may be required