Lecture 20

Question 1

what is the basic concept of an osmotic fragility test? what is it usually used to identify?

Answer 1

a few drops of a patient’s blood are added to a slightly hypotonic solution, which causes H2O to rush into the RBC’s

Healthy RBC’s swell but wont break, while HS patient’s RBC’s will swell, burst, and release hemoglobin. (the solution turns pink)

Question 2

What is the function of the erythrocyte membrane skeleton (EMS)?

Answer 2

to provide a membrane that is durable, yet flexible enough to withstand the mechanical stresses that occur during circulation (like cardiac contraction and passing through small capillaries)

Question 3

what is the cause of Hereditary Spherocytosis (HS)? give specific percentages for the top 3 most common causes.

Answer 3

mutations in the proteins that make up the EMS

Spectrin/Ankrin defect: 63%
Band 3 defect: 22%
unknown: 10%

Question 4

what are the main differences between Duchenne muscular dystrophy and Becker muscular dystrophy? (in terms of dystrophin, mutations, wheelchair need, and lifespan)

Answer 4

DMD: no dystrophin protein
frameshift mutations leading to stop codons
wheelchair by age 12
25 yr lifespan

BMD: some/defective dystrophin
no frameshift mutations
may still walk at 16 yrs
45 yr lifespan

Question 5

List some therapeutic strategies for DMD

Answer 5

use growth factors

replace dystrophin gene w/ gene therapy

induce microdystrophin production

skipping exons back into the frame to create “BMD” dystrophin

skip/suppress the premature stop codons

turn on the promoter forHuman Retinal dystrophin in muscles

Question 6

What is the clinical presentation of hereditary spherocytosis?

Answer 6

hemolysis, anemia, and/or splenomegaly at varying severities

Question 7

Describe the structure of spectrin. what alignment is it in?

Answer 7

it is an alpha and beta chain heterodimer of chains formed by AA repeats.

head-to-head alignment (tetramers)

Question 8

what is the most common hemolytic anemia cause in people of northern european decent?

Answer 8

hereditary spherocytosis

Question 9

What gene does the “Nan mutation” cause a defect in?

Answer 9

a mutation in Klf1, which is a DNA binding protein (NOT a cytoskeletal protein)

Question 10

What is the “nan mutation” in terms of it’s association with HS?

Answer 10

the Klf1 mutation it causes targets all the EMS genes

could be the cause of the unknown 10% of HS cases

Question 11

What do “zinc finger domains” and RER DNA binding motif’s have to do with one another?

Answer 11

they both are targets of the KlF1 gene mutation that can become the nan mutation

Zinc instead of Iron as the hemoglobin carrier

RER mutates to RDR

Question 12

name 3 treatments for HS

Answer 12

Blood transfusions

Splenectomy (leaves spherocytes in circulation longer)

Increase the # of RBC’s and Hb

Question 13

what is the usual cause of lethality in DMD and BMD?

Answer 13

respiratory failure or cardiomyopathy

left ventricular enlargement is common in BMD

Question 14

What are the 4 domains of the dystrophin protein and what do they do?

Answer 14

N-terminal: actin binding

Spectrin-like repeats

Cys-rich and C-terminal domains: bind to dytroglycans and syntropins

(all of these provide structural stability in some way)

Question 15

what does dystrophin bind to?

Answer 15

glycoproteins

Question 16

What is dystrophic myopathy?

Answer 16

progressive muscle degeneration and loss of functional muscle tissue

Question 17

What is pseudohypertrophy in DMD?

Answer 17

necrosis of muscle fibers with replacement by fat/CT tissue (commonly seen by enlarged calves)

Question 18

What is the Gower maneuver?

Answer 18

“walking up your legs in order to stand up” common identifier for DMD

Question 19

True or false: DMD is x-linked recessive, while BMD is Y linked recessive.

Answer 19

False

both DMD and BMD are X-linked recessive

Question 20

identify the mutation types that are associated with DMD and BMD.

Answer 20

DMD: frameshift mutations

BMD: in-frame deletions

Question 21

What are Electromyography and complex repetitive discharges? why are they useful for DMD?

Answer 21

EMG: test that records electrical activity of muscles

CRD’s: abnormal spontaneous discharges associated with membrane instability

they indicate the membrane issues caused by DMD

Question 22

What is more common, DMD or BMD?

Answer 22

DMD

Question 23

Where is the dystrophin protein localized?

Answer 23

the inner surface of the muscle membrane

Question 24

when attempting to diagnose DMD/BMD, what 2 options can you use collect the fetal DNA? What do you do with the fetal DNA sample after you acquire it so that you have enough of the DNA sample to make the diagnosis?

Answer 24

Amniocentesis

CVS (Chorionic Villus Sampling)

use Multiplex PCR to amplify the genes so you can study them