Cytoskeleton Protein Defects

Question 1

fragile cytoskeleton of RBCs

Answer 1

hemolytic anemia

Question 2

complete absence of cytoskeletal protein dystrophin

Answer 2

Duchenne’s muscular dystrophy

Question 3

dystrophin protein is present but abnormal

Answer 3

becker’s muscular dystrophy

Question 4

hemolytic anemia characterized by spherical and …….

Answer 4

fragile RBCs that lyse and release hemoglobin

hereditary spherocytosis

Question 5

in types of anemia, bone marrow cannot work fast enough to produce RBCs, so …..

Answer 5

the spleen will begin producing RBCs as well

Question 6

hereditary spherocytosis cause

Answer 6

caused by mutations in genes for the erythrocyte membrane skeleton of RBCs

spectrin

Question 7

osmotic fragility test

Answer 7

test the membrane strength of RBCs in a hypotonic solution

HS RBCs will burst

Question 8

osmotic fragility curve

Answer 8

doing the osmotic fragility test over several trials w/ increasing hypotonic concentrations (decreased [NaCl])

normal RBCs will withstand the tests longer (closer to water) than HS RBCs

Question 9

HS is the most common

Answer 9

most common hemolytic anemia in people of northern European descent

Question 10

HS genes

Answer 10

most are identified but 10% of diseased - we do not know why they have HS

Question 11

treatments for HS

Answer 11

1. blood transfusions
2. splenectomy - which removes spherocytes from circulation
3. increase RBC# and Hb

Question 12

DMD is the most common …..

Answer 12

fatal neuromuscular disorder
no cure
early 20s

Question 13

DMD treatments

Answer 13

1. nothing can alter course of disease

2. treatments to maintain general health and quality of life

Question 14

DMD genetics

Answer 14

• x linked recessive
• dystrophin gene mutations
• genetic defect present at birth but does not show symptoms to ~3 yrs of age

Question 15

function of dystrophin

Answer 15

provide structural stability to muscle cell membranes during contractions

Question 16

dystrophin protein

Answer 16

1. has 4 functional domains
2. N-terminus binding to actin
3. long spectrin like repeats
4. cysteine rich
5. bind to transmembrane proteins at c-terminus

Question 17

dystrophin C-terminus

Answer 17

cysteine rich

binds to dystroglycans and syntrophins - transmembrane proteins

Question 18

dystrophin is localized to

Answer 18

inner surface of muscle membrane

Question 19

loss of dystrophin

Answer 19

results in destabilization of entire actin to membrane complex

Question 20

dystrophic myopathy

Answer 20

progressive muscle degeneration with loss of functional muscle tissue over time w/ resulting weakness

Question 21

clinical presentation of DMD

Answer 21

1. elevated creatine kinase in blood (50-100x normal)
2. slow walking, general weakness
3. age of diagnosis ~5 years
4. wheelchair dependent by 13 yrs

Question 22

physical presentation of DMD

Answer 22

–necrosis of muscle fibers — replaced by fat or CT

leads to pseudohypertrophy

Question 23

gower maneuver

Answer 23

because of weakened leg muscles, boys w/ DMD have a distinct way of rising from the floor

using their hands to walk up their legs

Question 24

EMG

Answer 24

electromyography
test that is used to record the electrical activity of muscles

CRDs

Question 25

CRDs

Answer 25

complex repetitive discharges abnormal/spontaneous firing APs associated w/ membrane instability seen on EMGs

Question 26

significance of CRD presence

Answer 26

indicative of muscle membrane instability and muscle pathology hallmark of testing for dystrophies

Question 27

becker muscular dystrophy

Answer 27

- -milder form than Duchenne - -similar symptoms to dmd but milder - -wheelchair at 16

Question 28

MD etiology

Answer 28

- -x linked recessive - -dmd--dystrophin gone - -bmd--50-80% of protein present

Question 29

associated w/ frameshift mutations

Answer 29

dmd

Question 30

western plot

Answer 30

or protein blot | indicates presence or absence of proteins

Question 31

DMD dystrophin presence

Answer 31

<0.30%

Question 32

BMD phenotype

Answer 32

- -variable in symptoms - -no frameshifts - -dystrophin present and abnormal in quantity or size - -walk till 16 - -lifespan 45 yrs

Question 33

DMD phenotype

Answer 33

- -frameshifts - -no dystrophin - -wheelchair by 12 - -lifespan up to 25 yrs

Question 34

inheritance risk for MD

Answer 34

50% risk for affected sons 50% risk for daughters to be carriers when mother is carrier

Question 35

MD manifestation in females

Answer 35

1. mild 2. slight elevation of CK 3. weak back, arms, legs 4. fatigue easily 5. heart problems/shortness of breath

Question 36

cellular pathophysiology of MD

Answer 36

1. sarcolemmas sustain mechanical injury 2. Ca influx/oxidative stress 3. reduced resting potential (close to threshold) 4. fiber degeneration 5. irreversible necrosis -- replaced by fat or CT

Question 37

How does MD result in fatality?

Answer 37

progressive respiratory weakness chronic hypoxia result in cardiac and respiratory failure

Question 38

diagnostic tools for MD

Answer 38

1. EMG 2. blood test 3. biopsy 4. DNA study 5. quantitative dystrophin analysis

Question 39

prenatal MD diagnosis

Answer 39

1. use fetal DNA -- molecular analysis | 2. preimplantation genetics -- checking blastomere in IVF -- transfer only healthy embryos

Question 40

treatments for DMD

Answer 40

1. use growth factors 2. use gene therapy 3. gene therapy microdystrophins 4. exon skipping 5. nonsense stop codon read-thru

Question 41

describe DMD option 1 gene therapy

Answer 41

1. replace dystrophin gene but is too large for adeno-associated viruses also try utrophin ultimately does not work --- immune issues

Question 42

DMD usage of growth factors

Answer 42

1. myostatin inhibits muscle cell growth 2. knockout myostatin 3. muscles grow very large 4. but does not change that we are just making more DMD compromised muscle

Question 43

utrophin

Answer 43

homologous dystrophin like protein

Question 44

DMD option 2 gene therapy

Answer 44

1. use microdystrophins generate a protein like dystrophin but w/ less spectrin like repeats works little but still immune issues

Question 45

problem of dystrophin immunity

Answer 45

immune system has never seen this protein before so generates a response T-cell mediated immunity against dystrophin proteins

Question 46

DMD exon skipping

Answer 46

--in dmd deletions in gene cause frameshift mutations therapy to skip the exons to get back into frame works little but still immune issues

Question 47

DMD stop codon skipping

Answer 47

--premature stop codon mutations which result in single nuc substitution use a drug to skip or suppress the stop codon --read-thru stop codon works little but still immune issues

Question 48

overall treatment strategies for DMD conclusions

Answer 48

all approaches have problems, typically immune responses KCU investigating the dystrophin gene itself

Question 49

dystrophin gene

Answer 49

has several different products by different promoters dif. dystrophin sizes depending on where in the body it is ex. muscle vs. retinal dystrophin

Question 50

Dp260

Answer 50

retinal dystrophin similar but basically smaller

Question 51

DMD treatment w/ dp260

Answer 51

works in mice | but do not know the promoter for dp260 yet

Question 52

describe how the osmotic fragility test indicates a patient has hereditary spherocytosis

Answer 52

--using this test we subject RBCs to a hypotonic solution to test the strength of their membranes --in hs RBC membranes are weakened and will show up much weaker in a of test

Question 53

describe the function of the erythrocyte membrane cytoskeleton and how defects in the EMS cause hereditary spherocytosis

Answer 53

--the cytoskeleton is responsible for giving RBCs their biconcave shape which gives them structural integrity which is important for them to survive the mechanical stress of passing thru the circulatory system defects in ems result in deformed shapes of RBCs, which weakens them and greatly shortens their lifespan

Question 54

EMS

Answer 54

erythrocyte membrane cytoskeleton

Question 55

differentiate Duchenne muscular dystrophy vs. becker muscular dystrophy

Answer 55

Duchenne --- dystrophin protein is absent becker --- dystrophin protein is abnormal in quantity or size

Question 56

describe 2 therapeutic strategies to attempt to treat Duchenne muscular dystrophy

Answer 56

1. treat patient with growth factors to knockout myostatin (which prevents muscle cell growth) to allow muscles to grow large but the muscles are still weakened by dmd 2. gene therapy by using microdystrophins, creating a dystrophin-like protein, treating patient with this. works a little bit but the patient will have an immune response since the immune system has never encountered this protein before