Special Topic: Cytoskeletal Protein Defects Flashcards
What is a hemolytic anemia?
result from abnormally shortened red blood cell lifespan
What is hereditary spherocytosis?
hemolytic anemia is characterized by spherical and fragile red blood cells that lyse and release hemoglobin
What are symptoms of heredity spherocytosis?
hemolysis, anemia, splenomegaly
What causes heredity spherocytosis?
mutations in genes for the erythrocyte membrane skeleton of red blood cells
What is the osmotic fragility test?
- place few drops of blood into slightly hypotonic saline
- Water rushes in by osmosis
- normal cells will swell but not break
- heredity spherocytosis cells will swell and break releasing hemoglobin due to being so fragile
What is the top EMS mutation for heredity spherocytosis?
spectrin/ankyrin defet
Nan ______ a mutation in cytoskeletal protein
is not
What is Nan a mutation for?
DNA binding protein called Kruppel like factor 1 or Klf1
What does Klf1 target?
EMS genes
What changes a WT mouse to a Nan mouse in Klf1 DNA binding motif?
glutamic acid to aspartic acid
What are treatments for heredity spherocytosis?
blood tranfusions
splenectomy- removal of spleen
increase RBC # and Hb
What are some characteristics of Duchenne Muscular dystrophy (DMD)?
- severe, progressive muscle degeneration
- loss of ability to walk
- loss of cardiac and lung function
- scoliosis
- premature death
- no cure
What is the treatment for DMD?
no actual treatment, just to improve quality of life
glucocorticoids slow decline in muscle strength but do not alter course of clinical disease
What causes death in DMD?
abnormal hearts and/or respiratory failure
DMD is ______ linked and _____
x; recessive
DMD defect present at birth but does not show symptoms until _____
about 3 years of age
What is the main function of the dystrophin protein?
provide structural stability to the muscle cell membrane during cycles of contraction and relaxation
What are the four functional domains of the dystrophin protein?
n-terminus
long spectrin like repeats domain
cysteine rich and c-terminus domain
What does the n-terminal of dystrophin bind to?
actin
What does the cys rich and c-terminal domains bind to?
dystroglycans and syntrophins
Where is dystrophin localized?
inner surface of muscle membrane
Loss of dystrophin results in _____
destabilization of entire dystrophin-glycoprotein complex
What is dystrophic myopathy?
progressive muscle degeneration with loss of functional muscle tissue over time with resulting weakness
what is at an elevated level in DMD?
creatine kinase
DMD causes necrosis of muscles fibers, occurs with
replacement of fat or connective tissue
What is pseudohypertrophy?
replacement of muscle with adipose and fibrous connective tissue (enlarged calves)
What is lordosis?
excessive inward curvature
What is kyphosis?
upward back curvature outward
What is a Gower maneuver?
due to weakened leg muscles, people with DMD will get on hands and renews then elevate the posterior then walk hands up legs
What are CRDs?
complex repetitive discharges-abnormal spontaneous firing action potentials associated with membrane instability
What are CRDs indicative of?
muscle membrane instability and muscle pathology
What is Beck muscular dystrophy (BMD)?
milder form of duchenne
loss of walking at 16 years of age
muscle pain, dilated cardiomyopathy
What leads to death in BMD?
increased workload on left ventricle leads to let ventricular enlargement, severity results in heart failure and death
What is the incidence of DMD?
1/3 de novo mutations
2/3 familial
What is the case of DMD vs BMD?
DMD: missing dystrophin protein to weaken muscle membrane
BMD: some dystrophin protein, abnormal quantity and size
What type of mutation is DMD associated with?
frameshift mutations
What type of mutation is BMD associated with?
in frame deletions
What is a manifesting female carrier for DMD?
mild form slightly elevated CK weaker muscles of back, arms, legs fatigue easily heart problems/shortness of breath
How do you diagnosis DMD?
EMG to measure muscle response to nervous stimulation
blood test: elevated creatine kinase levels
muscle biopsy
DNA gene deletion studies: PCR
quantitative dystrophin analysis: western blot
How do you prenatal diagnose DMD?
fetal DNA: amniocentesis, chorionic villus sampling
molecular analysis: PCR
preimplantation genetics: remove single cell following IVF and see if they have bad gene
What are some treatment strategies to DMD?
use of growth factors to make more muscles
use of gene therapy
strategy of exon skipping
strategy of nonsense (stop) codon read through
What does myostatin do? What happens if you knock it out?
inhibits muscle growth.
if knocked out, it can lead to very large muscles
What is the problem with replacing the dystrophin gene in gene therapy?
too large for adeno associated viruses
What is the problem with microdystrophins for BMD treatment?
you can make a functional dystrophin protein and will generate protein with n terminus, some spectrin like repeats, and cya-rich and c-terminus
but issues with immunogenicity
What is the issue with immunogenicity for microdystrophins?
T-cells mediated immunity against dystrophin proteins
What is the problem with trying to treat DMD with exon skipping and skipping stop codon?
problems with immunogenicity
What is eye dystrophin?
similar to muscle dystrophin but smaller in the eye
What domains do eye dystrophin have?
spectrin, cys, c-terminus
and an actin binding site
Would expression of Dp260 in muscle rescue DMD?
yes
What happens when you use a natural isoform of dystrophin?
removes immunogenicity barrier
A 17 year old male exhibiting muscle weakness is examined for a dystrophinopathy. The patient is not restricted to a wheelchair but is easily fatigued. A western blot of protein, taken from a needle biopsy of muscle, shows 50% of the expected level of dystrophin protein which is slightly smaller than normal dystrophin. Multiplex PCR of exons from the dystrophin gene indicates a deletion from exon 50 to 51. What is the most likely diagnosis for this patient? A. Duchenne muscular dystrophy B. Listeria infection C. Hereditary Spherocytosis D. Becker’s muscular dystrophy E. Cystic Fibrosis
D. Becker’s muscular dystrophy
