6.3.8: Gene therapy

Question 1

What is te basic principle of gene therapy?

Answer 1

• A functional allele of a particular gene is inserted into cells that contain only mutated and non-functioning alleles of that gene.
• If the inserted allele is expressed, then the individual will produce a functioning protein and no longer have the symptoms associated with the genetic disorder.

Question 2

Knowledge from the Human genome project has led to further possibilities, such as using interference RNA. What can interference RNA be used for?

Answer 2

• To silence genes by blocking translation.
• Interference RNA has been used to treat cytomegalovirus in AIDS patients by blocking the replication of the cytomegalovirus,

Question 3

What is somatic cell gene therapy?

Answer 3

• Gene therapy by inserting functional alleles into body cells.
• Affects only certain cell types. The alterations made to the patient’s genome in those cells are not passed to the patient’s offspring.

Question 4

What is germ line gene therapy?

Answer 4

Gene therapy by inserting functional alleles into gametes or zygotes.
-The cells of the individual will be altered and their offspring may also inherit the foreign allele(s).

Question 5

Which protein do patients with cystic fibrosis lack?

Answer 5

A functioning CFTR gene.

Question 6

How is gene therapy used to treat cystic fibrosis using liposomes as vectors?

Answer 6

• The alleles, which are lengths of DNA, can be packaged within small spheres of lipid bilayer to make liposomes.
• If these are placed into an aerosol inhaler and sprayed into the noses of patients, some will pass through the plasma membrane of cells lining the respiratory tract.

Question 7

What happens if the liposomes also pass through the nuclear envelope and insert into the host genome

Answer 7

-The host cell will express the CFTR protein - a transmembrane chloride ion channel.

Question 8

Why does gene therapy used to treat cystic fibrosis using liposomes as vectors have to be repeated at regular short intervals?

Answer 8

Because epithelial cells lining the respiratory tract are replaced every 10-14 days.

Question 9

How can viruses be used as vectors in gene therapy?

Answer 9

• A virus that usually infects humans is genetically modified so that it encases a functioning allele to be inserted into the patient.
• At the same time, the virus is made unable to cause disease.
• The virus can enter the recipient cells, taking the allele with it.

Question 10

What are the potential problems with using viruses as gene delivery agents?

Answer 10

• Viruses, even though not virulent, may still provoke an immune or inflammatory response in the patient.
• The patient may become immune to the virus, making subsequent deliveries difficult or impossible.
• The virus may insert the allele into the patient’s genome in a location that disrupts a gene involved in regulating cell division, increasing the risk of cancer.
• The virus may insert the allele into the patient’s genome in a location that disrupts the regulation of the expression of other genes.

Question 11

How could artificial chromosomes be used in gene therapy?

Answer 11

-Research is being carried out into the possibility of inserting genes into an artificial chromosome that would co-exist with the other 46 chromosomes in the target cells.

Question 12

What are the ethical concerns surrounding germ-line therapy?

Answer 12

This type of therapy has the potential to change the genetic makeup of many people, the descendants of the original patient, none of whom would have given consent.
-There are also concerns about how the genes may be inserted- they may find their way into a location that could disrupt the expression or regulation of other genes or increase the risk of cancer.