Muscular dystrophies Flashcards
How are muscular dystrophies classified?
According to the inheritance pattern, clinical pattern of muscles involved and the genes responsible.
What types of mutations cause severe muscular dystrophy?
Ones resulting in frame shift.
What types of mutations cause moderate to severe muscular dystrophy?
Ones resulting in altered binding.
What types of mutations cause mild muscular dystrophy?
Mutations in the middle rod e.g. Becker.
What pathological features do we see in muscular dystrophy?
Prolonged destruction of single fibres, regeneration and fibrosis/scarring in the muscle.
When does duchenne muscular dystrophy commonly present?
2-4 years of age although some come on later.
What age do DMD sufferers normally survive to?
Usually die by the age of 20.
What serum results do we usually see in DMD?
Raised CK.
What does DMD cause?
Proximal weakness, pseudo hypertrophy of calves. (Look big but actually weak).
What mutation causes DMD?
Mutations in dystrophin gene on long arm of chromosome X.
What does the dystrophin mutation cause in tissues of DMD sufferers?
Alterations in anchorage of actin cytoskeleton to basement membrane. Means that fibres are liable to tear which causes Ca2+ release triggering the apoptopic pathway. Causes uncontrolled calcium entry into cells.
What histological features do we see in DMD?
Muscle fibre necrosis and phagocytosis, regeneration, chronic inflammation and fibrosis and hypertrophy.
What causes BMD (Becker) and how does it differ/is similar with DMD?
Mutation in dystrophin (same as DMD but a different mutation)
Becker has later onset and slower progression.
Both affect type 1 and 2 fibres and cause high CK.
What signs and symptoms does myotonic dystrophy show?
Muscle weakness, myotonia and non muscle features e.g. Cataracts, frontal baldness in men, cardiomyopathy and low intelligence.
What kind of mutation causes myotonic dystrophy?
An autosomal dominant mutation.
What muscles does myotonic dystrophy initially effect?
What are muscles latterly affected?
Face and distal limbs, moving on to respiratory muscles later.
What histological features are seen in myotonic dystrophy?
Atrophy of type 1 muscles, central nuclei, ring fibres, fibre necrosis and fibrofatty replacement.
What features do we see in histological samples of muscle fibres in muscular dystrophy sufferers?
Variability in muscle fibres size. Endomysial fibrosis. Fatty infiltration and replacement Myocyte hypertrophy and fibre splitting Increased central nuclei Segmental necrosis Regeneration Ring fibres
