Gene therapy Flashcards
What is genetic counselling?
They advise patients who believe they may be at risk of developing a genetic disease or transmitting a genetic disease to their children. Go through the consequences of the condition and the chances of transmitting it to their offspring.
They consider:
Number of people in either family with condition.
Whether the parents are closely related.
Genetic counsellor can then advise if genetic screening is appropriate.
What is genetic screening?
It involves identifying chromosome or gene mutations in the cells of an individual. Results of genetic screening can confirm or rule out suspected genetic condition or help determine whether they may get it.
Advantages to genetic screening?
- Determine if a person is a carrier for recessive.
- Can be used to screen unborn children for genetic diseases, e.g. blood tests, amniocentesis..
- Used to test for conditions in children or adults that have not developed yet.
- Used to detect genes associated with cancer or Alzheimer (family history).
- Forensic science to determine identity.
Disadvantages to genetic screening?
- Genetic screening for genes associated with cancer only indicates potential; anxiety.
- Concerns that test results may be used to discriminate against, e.g. employment.
- Risks of social stigmatisation.
- Risk of false positives or non-diagnosis of a condition, due to lab error.
What is gene therapy?
Process of inserting a correct/normal functioning version of a gene into the cells of an organism.
Faulty gene causing disease still present, new gene can correctly code for the protein.
What are the two types of gene therapy??
- Somatic cell gene therapy.
2. Germ-line therapy.
What is somatic cell gene therapy?
Inserting normal gene in cell.
- Certain tissue with faulty gene are targeted.
- For therapy to work, correct gene must be introduced to cells, transcription and translation must occur and normal protein produced.
- Main problem is inserting the gene into patients cells using a vector.
What is duchenne muscular dystrophy (DMD)?
A recessive sex-linked condition. It is a muscle wasting condition caused by the lack of a structural protein called dystrophin. Can be caused by a deletion in the dystrophin gene. The gene has 79 exons and deletions in any of them alters the reading frame of dystrophin mRNA, ribosome meets stop codon too soon and dystrophin protein not produced.
Usually only affects boys.
There is no cure, usually need a wheelchair by age 11.
Muscle weakness increases and complications develop, breathing or heart problems become more serious in teens.
What is the treatment for DMD?
The drug drisapersen is an antisense oligonucleotide. It is a 50 nucleotide sequence that is complementary to the mutated sequence and acts as a molecular patch. Binds to the mRNA over the exon with deletion, becomes double so ribosome cannot translate. Restores frame so a shorter dystrophin is synthesised.
Called EXON SKIPPING..
It is delivered to patients in subcutaneous injections.
Also, gene therapy (shortened version of a healthy gene) or stem cells.
What is cystic fibrosis (CF)?
People who have it are homozygous for an autosomal recessive allele. Normal allele codes for CFTR trans-membrane regulator, mem containing Cl ions, Na ions follow and water leaves by osmosis so mucus is watery.
Mutant CFTR cannot transport ions and so water does not move and mucus remains thick and sticky.
What happens during CF is mucus thick and sticky?
Mucus is present in all linings of the body:
- Bronchioles + alveoli become clogged, causing congestion and difficulty in breathing, mucus does not move and leads to infection.
- Pancreatic duct becomes blocked and pancreatic enzymes cannot reach duodenum so food digestion is incomplete, have large appetites.
- Vas deferens in males may become blocked, reducing fertility.
Using liposomes to deliver a gene?
These are hollow phospholipids spheres containing the gene preparation. They are inhaled with an aerosol and fuse with the phospholipid bilayer of the lung epithelial cell membranes. The DNA enters the cells, which transcribe the inserted gene and make the CTFR protein. Gene remains functional and relieves from CF symptoms, as soon as replaced treatment has to be repeated, not a cure.
Steps for using liposomes?
- Gene for normal CFTR protein identified using gene probe.
- The probe is complementary to DNA sequence in correct allele of CTFR gene.
- Correct allele is cut out using restriction enzymes.
- Many copies of allele are made by PCR.
- Allele is placed into a liposome which is used as the vector.
- Aerosol inhaler is used to deliver liposomes to system.
- Fuse with bilayer of lung cell membrane and gene travels to nucleus.
- New gene will hopefully incroporate into the cell DNA.
Using a virus to deliver a gene?
Same process but virus used.
- Virus made harmless.
- Virus is cultured inside epithelial cells along with plasmids with normal CFTR gene inserted in them.
- Viruses take up plasmids.
- Normal CTR becomes incorporated into viral DNA.
- Viruses are extracted from the cells and introduced into patient by inhaler.
- Virus injects DNA into cells of lungs.
What is germ-line therapy?
Introduces the correct genes into germ-line cells, the oocyte, genetic correction is inherited. Genes interact with eachother. Influences such genes in the oocyte has unpredictable effects in future generations.
