16.5 Gene Therapy Flashcards
Cystic fibrosis is caused by…
a mutant recessive allele in which three bases (AAA) are missing
it is a deletion mutation
The cystic fibrosis deletion results in…
CFTR proteins being unable to transport Cl- ions across epithelial membranes
Cystic fibrosis faulty CTFR leads to…
Water doesn’t follow the Cl- ions so membranes are not moistened
Viscous mucus in cystic fibrosis suffers leads to…
mucus congestion
breathing difficulties and less efficient gas exchange
accumulation of mucus in ducts (sperm, enzymes)
Two ways gene therapy may be used to treat cystic fibrosis
Gene replacement
Gene supplmentation
Gene replacement can be used to treat genetic disorders by…
replacing the defective gene with a healthy gene
Gene supplementation can be used to treat genetic disorders by
adding a healthy, dominant copy of the gene alongside the defective to mask the recessive alleles.
Germ-line therapy involves…
replacing/supplementing the defective gene in the fertilised egg
is currently prohibited
Somatic-cell therapy involves…
targeting just the affected tissues
isn’t passed onto future generations
must be repeated often
Delivering cloned CTFR genes could be done by…
viral delivery
lipid delivery
Use of viruses in CTFR gene transfer
- Viruses made harmless by altering genes for replication
- Grown in epithelial cells with plasmids for CTFR gene
- CTFR is incorporated
- Adenoviruses isolated and purified
- Adenoviruses introduced into nostrils of patients
- DNA injected by viruses into lung epithelial cells
Genes can be wrapped in lipid molecules as…
lipid molecules easily pass through the phospholipid bilayer
Lipid CTFR delivery
- CTFR isolated and inserted into bacterial vector
- Plasmid reintroduced to host cells and gene markers used to identify successful ones
- Bacteria cloned to produce copies
- Plasmids extracted and wrapped in lipid to form lysosome
- Liposomes sprayed into nostrils
- Pass across phospholipid membrane into lung epithelial cells
Viral/lipid delivery not always effective as…
- adenoviruses may cause infection
- patients may develop immunity
- liposome aerosol may not be fine enough to pass through bronchioles
- CTFR gene may not be expressed properly
Treatment of SCID with normal ADA gene
- ADA gene is isolated from human tissue using restriction endonucleases
- ADA gene inserted into a retrovirus
- Viruses grown with host cells to increase numbers
- Viruses mixed with patient’s T cells, injecting the ADA gene into them
- T cells are reintroduced into blood
