Treatment of Genetic Diseases Oct 9 Flashcards
What are three complications in treating monogenic disorders?
- we may not know the gene
- we may know the gene but not understand the pathophysiology
- Fetal damage may have occured prior to diagnosis and it may not be reversible
As of now, do most therapies treat symptoms or th eunderlying genetic mutation?
symptoms
What are some additional long term complications in attempting to treat genetic diseases?
- the treatment may be successful, but sublte deficiencys may develop later
- Treatment may be successful in one tissue, but problems may arise in other tissues later
- the treatment doesn’t show harmful affects at first, but they develop later
Why does genetic heterogeneity make treatment more difficult?
If multiple mutations can lead to a certian disease phenotype, you may try to treat the wrong mutation
Agagin, what is allelic heterogeneity
different mutant alleles of the same gene give rise to different disease phenotypes
PKU
Again, what is locus heterogeneity?
Different mutations can result in the same disease
like hyperphenylalaninemia:
defect in PAH or in biopterin
Why has the treatment of metabolic deficiencies been most succesful historically?
You can do diet modification like avoidance
you can do diversion (think ura cycle)
You can inhibit certain enzymes - like using statins against HMG CoA Reductase in familial hypercholesteromeia
What are two ways you can utilize “protein” treatments?
- add a cofactor
- Replace the defective protein (like alpha antitrypsin in emphysema)
What are the main problems with protein treatments?
Proteins have a short half life, so patients need freuquent transfussion - costly and time
Immune responses can develop
risk for viral contamination
sometimes supplies are insufficient
How has Gaucher disease been treated with protein therapy?
Gacher disease is a lysoomal storage disease that is cause by the lack of the enzyme glucocerebrosidase which diegrase glucocerebrosides in the lysosome
the glcocerebrosides build up - especially in macrophages and cause gross enlargment of spleen and liver
the acrophages slowly replace bone marrow, leading to anemia and immune suppression
Protein treatment involves glucocerebrosidase enzyme replacement therapy (expensive and rrequires weekly transfusiosn)
has been super successful - probably because the disease doesn’t affect the brain
What are some ways you can modulate gene expression through treatment?
- increase the mRNA of either the wildtype or (if it still makes a functional protein just not enough) ,the mutant gene
- Induces expression of a different gene that could rescue the mutatnt phenotype (hydroxyurea for fetal Hb in sickle cell)
- Repress expression of a dominal negative mutation using RNAi
What can bone marrow transplantation be used for?
when the disease stems from a defect in the bone marrow stem cells - like hematopoitic cancers, immune disorders, lysoeomal storage diseases, and thalassemias
problem: you have to destroy the patient’s immune system for them to acept the new bone marrow, so they often die of infection
Why is cord blood preferable to a bone marrow transplant in HSC transplantation?
Recipients tend to be more tolerant of histocompatible placental blood than other allogenic donor cells
there’s more cord blood available
risk of host-vs-grat disease greatly reduced
Besides protein replacement therapy, wha tis another way we can treat Gaucher disease?
bone marrow transplants
What’s the goal in gene therapy? why would you do it?
THe goal is to modify cells to produce a therapeutic effect based on recombinant DNA tecnology - it introduces new genes and hopefully removes the damaged genes
this can compensate for a loss of fucntion mutation
it may replace or inactivate a cominant mutant gene
What are some guildelines for gene therapy? What do you need before you can start?
defective gene & biochemistry has been described
cDNA or functional version of the gene exists
substantial disease burden & favorable risk-benefit
confidence that the gene therapy will work based on knowledge of the defect
reliable promoter to regulate gene expression
good target cell
data from model systems (eg., mouse) that gene, vector and delivery system all work
protocol review by government
What are the usual target cells for gene therapy?
You want them to be long-lived so it will last - preferably a stem cell
right now bone marrow is the only current example being used clinically
What’s the difference between ex vivo and in vivo gene transfer strategies?
what are the advantages and disadvantages?
Ex vivo invovles the transfer of stem cells out of the body, modification to remove the mutation and put in the wildtype, amplify, introduce back into the body. This is good because it allows for direct targeting, but it’s difficult and takes time.
in vivo: direct injection into the body using a vector . This is good because it’s quick and easy, but it’s harder to target the right cells, you can get immune responses, and there are safety risks
What is a vector?
It’s what we package the gene into in order to introduce it to the cell
You want them to be safe, easily introduced, and promote expression of the transferred gene for the life of the cell
can be viral and non-viral
What are some examples of viral vectors?
nonviral vectors?
which class has been more successful?
viral vectors include: retroviruses, adenoviruses, adeno-associated viruses, herpesviruses
non-viral vectors: naked DNA, liposomes, protein-DNA conjugates, artificial chromosomes
THe viral vectors have been orme successful
How do the retroviral vectors work?
What are the advantages and disadvantages?
Retroviruses are RNA viruses
Advantages: they will integrate the gene into the host genome, so that if it works it will essentially fix the mutation for the entire lifetime of that cell. THere is very low inflammatory potential. They are easy to make. Can accomodate large trangenes
Disadvantages: they target dividing cells only AND because they integrate into the genome randomly they can turn a cancer gene on (this is what happened with the SCID trial)
Why are lentiviruses considered better than regular retrovirus vectors?
They can targe quiescent cells as well, so they have a broader tropism
However, they can still result in oncogenesis
How do the adenovirus vectors work?
Why don’t we use them anymore?
The Adenovirus vectors were dsDNA
Advantages: they had very broad tropism, can be generated at high titer, can accomodate large genes.
Disadvantages: However, they could not integrate into the host genome, so the fix wasn’t perfect
Also, the biger issue was that they had very high inflammatory potential and people have died because of the immune response tot he vector itself
because of this, they don’t use these anymore
How are adeno-associated vectors different and better than adenovirus vectors?
What’ stheir main fallback?
AAV are ssDNA instead of dsDNA
Advantage: They do not have the inflammatory potential like adenoviral vectors do. They can infect both dividing and nondividing cells.
Disadvantage: although some do, most do not incorporate into the host genome :(
they have VERY low carrying capacity :(
What is the main issue with the Herpes Viral Vectors?
The HSV vectors ar enice because they have CNS tropism and a large packaging capacity, but they can cause severe immune repsonse and neurotoxicity
In what diseases have gene therapy been having some success?
heophilia A
lysosomal storage diseases
Parkinson DIseases
ADA-SCID
What gene therapy is used to treat hemophilia B?
They use gene therapy for Factor 9 replacement in the liver
they use AAV vectors
Why are lysosomal storage diseases comon targets for gene therapies?
Because only low levels of wildtype protein are needed to significantly improve the clinical phenotype
