Lecture 5 - human genome editing Flashcards
(18 cards)
EXAM TIP - if it says chose 3 - what should you do?
Rank them and justify your choice
Communicating with MPs:
- be impartial and non-directive
- use clear, accessible language
- acknowledge nuance and complexity
(low scientific jargon, bit can still communicate complex ideas)
What can CRISPR/Cas9 be used for?
Can be used to locate genes using fluorescence
- the Cas9 nuclease creates a double strand break at a (hopefully) unique site in the genome.
- The sequence specificity is determined by the synthetic guide RNA (sgRNA)
- the host cell repairs the break
- if a repair template is provided, the break is frequently repaired by HDR (homology-directed repair), allowing for gene replacement.
What are the 2 repair mechanisms used?
HDR - homologous directed repair
NHEJ - non-homologous end joining
What is NHEJ?
Non-homologous end joining
(sticking it together)
- it is error prone and can lead to the addition or removal of a number of bases
What is HDR (Homology-directed repair)?
Provide the cell with the DNA that is homologous to the sides of the break point. You can then choose the sequence of the repair template - precise gene editing.
Can you choose which repair mechanism is adopted? (NHEJ or HDR)
No - diploid organisms may use other strand to repair, not necessarily the template. Both mechanisms likely to be used and have variations.
What is metachromatic leukodystrophy?
Caused by mutation leading lack of production of enzyme ARSA, which is important for metabolism.
Sulphatides build up and gradually destroy the protective layer around cells - particularly around the brain and the neurosystem - dissolve fatty sheets.
How is gene therapy used to treat metachromatic leukodystrophy?
- Teddi (girl) is connected to a machine to remove stem cells from her blood
- Virus is used to place a working copy of the gene into the cells.
- The gene-modified cells are returned to Teddi
- They make blood cells which contain the missing enzyme
Modification occurs outside the body - allows for it to be checked before being inserted back into host.
What did He Jiankui do?
Created genetically-modified human
- aimed to make HIV-resistant humans by altering a gene called CCR5 - cell surface protein. Some people that have a certain allele are more HIV resistant - but not all strains. Attempted to reproduce mutation (32bp deletion) - offspring would be HIV resistant, despite having HOV- mother and HIV+ father.
NO evidence he got the base-pair deletion correct - as you cannot control the repair mechanism
Need both copies
He didn’t get any ethical approval - from parents or governments
Didn’t do a good job of looking for off-targets. CCR5 encodes transmembrane receptors - meaning these could’ve been affected
Ended up in prison
3 female babies born
What are the different categories of the potential applications of Heritable Genome Editing
Category A - F
What is Category A?
Cases of serious monogenic diseases which ALL children would inherit the disease genotype (e.g. Huntington’s disease (very rare))
What is Category B?
Serious monogenic diseases with some not all of a couple’s children would inherit the disease-causing genotype (e.g. Cystic fibrosis)
What is Category C?
Other diseases with less serious impact that those in A or B (familial hypercholesterolemia)
What is Category D?
Polygenic diseases (Type II diabetes/schizophrenia/some cancers)
What is Category E?
Other applications (not heritable diseases) - e.g. EPO gene for endurance sports, thousands of genes linked to intelligence
What is Category F?
Genetic conditions that result in infertility
Compare Category A vs Category F
A = best suited to heritable genome editing
F = least suited to heritable genome editing
All about likelihood of getting disease
Explain a therapy
Therapy name - GSK237
Gene - RPGR
Disease name - Chorioderemia
Description of disease - Rare genentic condition causing progressive vision loss
Pharmaceutical - GSK & Orchard Therapeutics
