Download 6.4 Manipulating the Genome - Hutchison

6.5 Gene Therapy
Pages 249-251
Gene therapy
• Defective genes are corrected using a normal
copy of the gene.
How gene therapy works:
• Replacing a mutated gene that causes disease
with a healthy copy of the gene.
• Inactivating, or “knocking out,” a mutated
gene that is functioning improperly.
• Introducing a new gene into the body to help
fight a disease.
Target cell
• One of the cells that contain the faulty gene to
be corrected.
Vector
• Any agent, such as a plasmid or a virus,
capable of inserting a piece of foreign DNA
into a cell.
Limitations
• Viruses vectors are a good choice for
mammals, but plasmid vectors are not.
• A cold virus is a good choice to target lung
cells but not bone cells.
Process
Step 1: Remove or alter viral DNA
Step 2: Human DNA coding for the normal gene
are inserted into virus and incorporated into the
viral DNA.
Step 3: Large numbers of virus infect human
cells.
Tragedies
• A teenager died in 1999 when he had an
unexpected severe immune response to the
virus serving as the vector.
• Leukemia has developed in two children who
were treated with gene therapy.
The hurdles:
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Multiple treatments are required.
No control over where gene is inserted.
The body may attack the virus.
The virus may attack the cell.
Many disorders have multiple genes at play.
Regulation of genes such as insulin
Ability of vector to reach target cells
Successes
• Restoring vision
• Restoring hearing
• Repairing gene causing Duchenne Muscular
Dystrophy.
Inherited Blindness
• Added photoreceptors to dogs to correct
vision
• Children regain sight after pigment layer cells
are repaired.
Duchenne Muscular Dystrophy
Deafness
• Up to 80% of Guinea pigs’ hearing was
restored when genes were added to promote
the growth of hairs in the cochlea.