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61 Cards in this Set
- Front
- Back
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Duchenne muscular distrophy and Becker muscular distrophy are examples of what type of inheritance?
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X-linked
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what inheritance pattern is most often seen with limb girdle?
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autosomal dominant or recessive
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what is the pathogenesis of Duchenne MD?
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absence of dystrophin which normally functions to link the cell membrane to actin -> leads to muscle damage and eventually necrosis -> replaced by fat and fibrocytes -> remaining muscle hypertrophies
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A definitive diagnosis of duchennes MD can be made with what tissue observation?
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flourescent staining of skeletal muscle shopwing an absence of dystrophin
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when do most people with duchennes MD die?
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early 20's from cardiac or respiratory failure
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what is the name of the unique method by which these patients stand and why does it occur?
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Gower sign, occurs because of weakness in the pelvic girdle
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what is the disorder in which dystrophin is diminished, is X-linked, and patients can live a normal lifespan?
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beckers
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A 45 year old female with a pattern of muscle weakness is most at risk for which of these?
Duchennes MD Beckers MD Pelvic girdle |
pelvic girdle because it is the only autosomal inheritance option (being female an X-linked disorder would not effect her)
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by which age to patients with Duchennes MD become wheelchair dependent?
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10-12
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what is the pathogenesis of myotonic dystrophy?
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trinucleotide (CTG) repeat mutation which occurs in chromosome 19 during meiosis
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describe the concept of genetic anticipation and how it applies to myotonic muscular dystrophy?
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each generation with the disease has earlier onset and more severe progression
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what enzyme does the defective mRNA in myotonic dystrophy cause to be abnormal?
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dystrophila myotonia-protein kinase (DMPK)
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what are the clinical signs of myotonic dystrophy?
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1. skeletal muscle atrophy
2. cataracts in the lens of the eye |
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what are the 3 histological findings with myotonic dystrophy?
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1. variation in fiber size
2. increase in connective tissue 3. internalized nuclei in muscle fibers |
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what is a ring fiber?
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sub-plasmalemmal band of myofibrils arranged in rings around normal longitudinal myofibrils
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when looking at a crossection of skeletal muscle from a person with myotonic dystrophy, what is the striking and distincitve feature seen involving muscle fibers?
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ring fibers which are perpendicular to the orientation of normal longitudinal fibers
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what is the "cardinal" sign of myotonic dystrophy?
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myotonia
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what is the inheritance pattern of myotonic dystrophy?
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autosomal dominant
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mitochondrial DNA encodes proteins for which important process in the human cell?
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oxidative phorphorylation protiens for ATP generation
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which has a higher replication error, mitochondrial or nuclear DNA?
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mitochondrial (20x greater mutation rate)
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"ragged red fibers" are a hallmark sing of?
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mitochondrial myopathies
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what causes the ragged red fiber appearance in cellls of mitochondrial myopathy?
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accumulations of mitochondria beneath the sarcolemma
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what are the special features which can be seen inside the mitochondria of patients with a mitochondrial myopathy?
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"parking lot inclusions"
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when does mitochondrial myopathy usually appear?
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young adult years
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what are the clinical signs of mitochondrial myopathy?
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proximal muscle weakness along with external opthalmoplegia
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why would people with mitochondrial myopathy develope lactic acidosis?
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they have to rely on anaerobic glycolysis because they lake oxidative enzymes
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why are muscular symptoms the first to show up with mitochondrial myopathy?
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they are highly dependent on oxidative phosphorylation for lots of ATP generation
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infantile motor neuron disease is officially called what?
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spinal muscular atrophy
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what is the pathogenesis of spinal muscular dystrophy?
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autosomal-recessive inheritance of mutation results in selective loss of anterior horn motor neurons and cranial nerve motor neurons
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what is the genetic mutation that is found in greater than 90% of spinal muscular dystrophy patients?
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homozygous deletion of survival motor neuron gene on chromosome 5
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what genetic mutation is associated with the most severe form of spinal muscular dystrophy?
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neuronal apoptosis inhibitory protein gene
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what does a loss in the SMN gene result in?
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loss of motor neurons in the anterior horn of the spinal cord
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what does loss in NAIP gene cause to happen in spinal muscular dystrophy?
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loss of motor neurons in the anterior horn of the spinal cord
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what is the distinctive histological presentation of spinal muscular dystrophy?
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group atrophy
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what is panfascicular atrophy?
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atrophy involving the entire fascicle after loss of spinal cord motor neurons
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what is the name of spinal muscular dystrophy type 1
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Werdnig-Hoffman disease or floppy infant syndrome
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what is the age of onset for spinal muscular dystrophy?
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3 months
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what is the age of death for spinal muscular dystrophy type 1?
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3 years of age (mean of 8 months)
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whichs is the most severe form of spinal muscular dystrophy?
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type 1 or Werdnig-Hoffman
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what is the most common form of spinal muscular dystrophy?
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type 1 or Werdnig-Hoffman
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what is the age of onset for spinal muscular dystrophy type 2?
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3-15 months
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what is the prognosis for spinal muscular dystrophy type 2?
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live into late childhood depending on the condition of respiratory muscles
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what is the age of onset for spinal muscular dystrophy type 3?
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2 years of age or later
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what is the prognosis for spinal muscular dystrophy type 3?
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survive into adulthood with some living a normal lifespan
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what causes hyperkalemic periodic hypotonic paralysis?
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a mutation in the SCN4A gene encoding Na+ channel
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hyperkalemic periodic hypotonic paralysis is an example of which type of myopathy?
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ION channel Myopathy
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what causes the paralytic attacks seen with hyperkalemic periodic hypotonic paralysis
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vigorous exercise or cold
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describe abnormal serum findings and a hyperkalemic periodic hypotonic paralysis attack?
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increased serum K+ (5-7 mg/dl)
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what is the rare but serious disorder characterized by tachycardia, tachypnea, muscle spasms, & hyperpyrexia after induction of anesthesia by a halogenated agent?
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malignant hyperthermia
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what is the pathogenesis of malignant hyperthermia?
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mutation in genes encoding Ca++ channels
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what are nemaline rods?
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subsarcolemmal aggregates derived from alpha-actinin (Z band) material
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what type of muscle fibers does nemaline myopathy occur in?
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type 1
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what is arthogryposis and which disorder is it associated with?
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contracture of joints in extremities due to static muscle shortening, characteristic of nemaline myopathy
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describe the pathogenesis of type V or McArdles glycogen storage disease?
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the enzyme phosphorylase is deficient resulting in a decreased break down of glycogen to glucose in muscles
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describe the pathogenesis of type VII glycogenosis?
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deficiency in phosphofructokinase halting glycolysis and causing excess production of of glycogen
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subsarcolemmal vacuoles or "blebs" are characteristic of which disorder?
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glycogen storage disease
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what is the age of onset for glycogen storage disease?
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20
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what is the clinical presentation?
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painful cramps upon vigorous exercise
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what is the prognosis for patients with glycogen storage disease?
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good, live normal lifespan but are limited in physical activity
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how is glycogen storage disease diagnosed?
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exercise fails to raise serum lactate levels
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50% of glycogen storage disease patients also have which disorder?
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myogobinuria
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