Gene Therapy Flashcards
What is the definition of gene therapy?
The introduction of normal genes into cells in place of missing or defective ones in order to correct genetic disorders
How does gene therapy work for a double recessive genetic disorder?
-a working copy of the dominant allele can be introduced into the cell, which should then mask the 2 faulty recessive genes
How does gene therapy work for a dominant allele genetic disorder?
-this allele is not removed, but it has to be silenced
-this can be done in various que e.g sticking another section of DNA in the middle of the faulty allele so that it no longer functions
Explain using the example of Cystic Fibrosis how vectors are used in gene therapy
-to get new DNA/alleles into a cell a vector must be used
-these could be modified virsues, plasmids or liposomes
Example of Liposome vectors to treat Cystic Fibrosis
-cells in the airway should contain a normal functioning protein carrier (CFTR protein) which transports chloride ions out of the cell into the mucus in the airways
-this lowers the water potential of the mucus, causing water to leave nearby cells into the mucus, making it thin and watery so it can easily be swallowed
-in CF sufferers, this membrane protein does not work (caused by 2 faulty recessive alleles) so their cells can’t transport chloride ions out, so their mucus is much thicker, harder to swallow and stays in the airways
-liposomes can be used to deliver a correctly functioning dominant allele into the airway cell
Why are viruses used as vectors in gene therapy.
-certain viruses are often used as vectors because they can deliver the new gene by infecting the cell
-the viruses are modified so they can’t cause disease when used in people
-some types of viruses integrate their genetic material, including the new gene, into a chromosome in the human cell
What are the potential problems of using viruses as gene vectors?
-may stimulate an immune response in the patient
-patient may then become immune to that virus, so it can’t be used again in the future to deliver that allele
-the virus might insert the allele into the human DNA in a region that disrupts the expression of other genes
-viruses could mutate and become pathogenic
What is somatic gene therapy?
-involves altering the alleles in normal body cells, particularly the specific cells that are affected by the disorder.
-this type of gene therapy doesn’t affect sex cells (egg and sperm) nor the zygote/embryo so CANNOT BE PASSED ON to offspring
-targets genes in specific types of cell
-the edited gene is contained only in the target cell type
-the edited gene is not passed down to future generations
-somatic cell therapies have been researched and tested for many years so are highly regulated
What is germ line gene therapy?
-involves altering the alleles in the sex cells, which means that all of the cells in the offspring would have the genetic modification. IT CAN BE PASSED ON to offspring
-this is possible, but currently illegal
-made so early in development that any change is copied into all of the new cells
-edited gene copied in every cell, including sex cells
-if the person has children the edited gene is passed on to future generations
-human germ line editing is new, presenting legal and societal considerations
Why do you think that germ line gene therapy is current,y banned in humans?
-the potential impact on resulting offspring is unknown
-concerns regarding human rights of the unborn offspring, no consent is given
-it is irreversible
-could enable people to choose desirable characteristics for their unborn children
Why is somatic gene therapy only a temporary cure for disease?
-the newly inserted “correct” allele will be passed on every time the cell divides by mitosis, but somatic cells have a limited lifespan
-they have to be replaced by stem cells (which have the original faulty alleles) so after a while it is expressed again
Evaluate the positives and negatives of the ethics of gene therapy
POSITIVES:
-prolonged life expectancy
-better quality of life with fewer symptoms
-temporary cure, rather than ongoing treatment
NEGATIVES :
-very expensive, NHS resources better spent else where?
-effects only short lived
-difficult to deliver the allele to the specific location where it’s needed
-could trigger immune response (if viral vector used)
