B6.020 Prework 4: Current and Experimental Therapy for MD

Question 1

primary goal in managing DMD

Answer 1

managing fallout from disease; not much out there for disease process itself

Question 2

drug options in DMD symptom management

Answer 2

heart failure -digoxin
adequate dietary Ca2+ (prevent osteoporosis) and nutrition
physiotherapy to delay contractures
scoliosis braces/surgery

Question 3

exercise recommendations in DMD

Answer 3

NOT beneficial
cannot further strengthen deteriorating muscle
excessive exercise can accelerate fiber degeneration

Question 4

current therapy for DMD

Answer 4

steroids

commonly prednisone and Deflazacort

Question 5

observed benefits of steroids for DMD

Answer 5

cellular: decrease rate of apoptosis of myotubes, can decelerate myofiber necrosis in MD
clinical: some pts have improved long term muscle and myocardial outcome, can keep patients ambulatory longer

Question 6

principles of dystrophin replacement gene therapy

Answer 6

use virus or other means to deliver cDNA of DMD gene
expression of dystrophin protein would theoretically restore normal cellular function
full length dystrophin cDNA is 14 kb (exceeds capacity of viral vectors)

Question 7

micro dystrophin

Answer 7

delete domains of protein (primarily many of the spectrin like repeats) which retaining function to treat DMD
-converts DMD to BMD

Question 8

example viral vectors for DND delivery

Answer 8

engineered to carry DNA of choice and are non-replicative

• RNA genomes: retroviruses, lentiviruses
• DNA genomes: adenovirus, HSV, poxivirus

Question 9

integrating and non-integrating vectors

Answer 9

1. integrating: generally used for actively dividing cells, inherited by daughter cells, risk of insertional mutagenesis
2. nonintegrating vectors used for quiescent/slow dividing cells

Question 10

challenges with gene therapy

Answer 10

sufficient number of myocytes transduced
sustained and sufficient gene expression
immunity against virus and/or dystrophin
cost

Question 11

what is antisense oligonucleotide (ASO) therapy

Answer 11

excludes exon that contains pre-mature termination codon (PTC) from mature mRNA

• prevents nonsense mediated decay, allows translation of truncated proteins
• requires that splicing of exons flanking skipped exon maintains reading frame
• cannot skip exon encoding critical domain
• for DMD, most easily achieved with exons encoding spectrin like repeats

Question 12

discuss snRNPs and the process of splicing

Answer 12

snRNPs U1 and U2 recognize key sites
U1: donor exon/intron boundary
U2: adenosine at the branch point
U4, U5, U6 join to form spliceosome
-proper geometry for splicing
-hold together exons prior to joining
-catalyze cleavage and formation of bonds

Question 13

describe premature termination codon read through therapy

Answer 13

allows insertion of amino acids at PTC rather than termination
selectivity: greater fidelity of ribosome at bone fide stop codon

Question 14

potential problems with PTC read through therapy

Answer 14

may not be enough mRNA surviving
protein made may not work
efficiency of read through depends on nature of PTC and surrounding sequences
read through of physiological stops could be problematic

Question 15

potential benefits with PTC read through therapy

Answer 15

simple pill therapy

could possibly work for any disease with PTC