Treatment of Genetic Disease Flashcards
mutant gene
-modify somatic genotype- transplantation or gene therapy
mutant mRNA
-RNAi
mutant protein
- protein replacement
- enhancement of residual function
metabolic/biochemical dysfunction
-disease specific compensation
clinical phenotype
-medical or surgical intervention
family
-genetic counseling, carrier screening, pre natal testing
counseling
- prenatal or carrier testing
- provide information
- planning and education
medical or surgical intervention
- drug therapy- usually treats symptoms
- surgery- transplant
- repair
treatment of metabolic disorders
- dietary modification/restriction
- aa catabolic pathway disorders
- life long
- PKU
- can be difficult for patient and family
- replacement- adding back something thats missing (BH4)
- diversion- use other pathways to avoid accumulation of metabolite
- redirect breakdown substances to harmless compounds
- inhibition- modifying rate of synthesis by using drug or other gent that slows or blocks critical step
- depletion-removes excess
hereditarty hemochromatosis
-accumulation of iron can be controlled by regular phlebotomy
treatment at protein level
- replacement-extracellular
- VIII hemophilia and a1 antitrypsin
- cost
- availability
- antibody production in patient
- contamination
replacement- intracellular
- must target cell type
- gaucher- lysosomal storage, deficiency of glucocerebrosidase
enhancing genetic expression
- protein level
- using gene to compensate for the mutation in another
- sickle cell anemia- treat with decitabine increases gamma globin
- functions as replacement oxygen carrier and inhibits polymerization of HbS
bone marrow transplant
- hematologic disorders
- remove the disease clone and replace it with unaffected cells
- collect bone marrow stem cells from the patient for from matched donor (autologous vs allogenic)
- transplanted cells will re establish in the new host and hopefully cure disease
bone marrow transplant for lysosomal storage diseases
- bone marrow is about 10% of the body’s cell mass and extracellular transfer from the normal marrow may stimulate function in the other cells
- acts as a source of mono-nuclear phagocytes
- can reduce the size of various internal organs
- if done within the first 2 years of life, will limit negative neuro impact
stem cells
- self renewing, undifferentiated cells
- can proliferate and produce a wide variety of different types of differentiated cells
- embryonic are pluripotent and can make all things
- somatic stem cells are limited to tissue or origin
embryonic stem cells
- potential therapy for parkinsons/alzheimers
- potential source of cells for tissue grafting and organ transplants
- source of cells?
- should embryos be used?
- do potential benefits outweigh other considerations?
problems with allogenic stem cell use
- immunosuppresion
- GVHD
induced pluripotent stem cells
-can take cells from adult and revert them to stem cells and transplant them back in
cloning/nuclear transfer
- take donor egg and remove nucleus
- take nucleus from thing to be cloned and insert it into donor egg to be carried and birthed
- potential ill effects of procedure
- negative impact on genes, chromosomes, normal cell processes like aging
- benefits from agriculture-improving crops, herds, etc
donor egg
- removing mother’s nucleus
- removing nucleus from donors egg
- inserting mothers nucleus in donor egg
- fertilizing egg
companies for cloning
- offering nuclear transfer for other animals
- closed in sept 2009 by parent company due to patent infringement by other entities and anomalies identified in some of their attempts
gene therapy
- deliberate introduction of genetic material into human somatic cells for therapeutic, prophylactic, or diagnostics purposes
- correct a loss of function mutation by incorporating functional gene
- compensate for deleterious dominant allele by replacing or inactivating mutant allele
- adding genetic material that has a pharmacological effect
requirements for successful gene therapy
- identification of gene
- availability of gene sequence or cloned DNA from gene of interest
- identification of target tissue
- ability to deliver gene to target
- understanding of gene biochem
- understanding of expression
major limitation of gene therapy
- delivery of gene to target
- vector must be able to carry DNA
- must be able to insert DNA into the target cell
delivery of gene to target
- most permanent if the therapy DNA is incorporated into the host cells own DNA
- viral vectors
- temporary incorporation in cytoplasm requires repeated therapy sessions
in vivo vs ex vivo
- can put man made cloned gene in patient or
- can take pt cells, fix them, and put them back
first successful gene therapy
- 1990
- ADA deficiency
- immunodeficiency disorfer
- 15% of SCIDs
- pathway thats disrupted causes increase in dATP and lymphocyte cell death
- ashanti de silva and cindy kisik
- took cells, corrected them, and put them back
clinical trials
-1999- Jesse Gelsinger, 18 dies from liver complications- he had OTC and an immune response to adenovirus gene therapy
-2002- two French patients die of cancer
-retroviral vector
-insertion of therapy gene into another active gene lead to loss of function
2003- gene therapy with retroviral vectors is banned in US
who should be subjects?
- when to the benefits outweigh the risks?
- who should participate?
- an individual known to have a disease causing mutation but is currently not showing symptoms?
- an individual with clinical symptoms of a disease by whom has received no standard therapies?
- an individual who has failed standard therapies?
- be sure that the protocol and risks are clearly described and an informed consent is executed
2004
-adenovirus vector carrying CFTR gene is used in an inhaler for CF pts
2006
- clinical trials start for DMD intramuscular injection using a plasmid vector
- possible immunity complication in 2010
2006 2
- first successful use of gene therapy to treat a melanoma
- T cells targeting to attack cancer cells
2007
- proposal for intramuscular injection for hemophilia
- 1st ADA patient (Ashanti) doing well, treated at 4, now 20-25% normal population of T cells, attending college
- 3 year old with X-SCID dies of leukemia- received retroviral gene therapy at birth in the UK
- death in chicago due to immunosuppression caused by gene therapy (adenovirus)- for arthritis and died of fungal infection
2008
-8 patients with rare immunological diseases were cured
2009
- 5 children with Lebers congenital amaurosis had partial restoration of sight
- 2 kids with adrenoleukodystrophy responded to therapy and stable after 2 years- used HIV as vector
2010
-gene therapy in dogs to treat color blindness
additional approaches
- antisense DNA therapy
- useful to down regulate protein production
- cancer characterized by overproduction of a protein
- incorporate an antisense strand into the cells to block translation
RNA interference
- targeted degradation of mRNA
- destroy mRNA from negative dominant mutations while leaving second allele alone
- reduce the concentration of an mRNA that is over expressed
other vectors
- AAC- adeno associated virus
- non-pathogenic
- reduces likelihood of an immune reaction
- found in many serotyoes- so proper vector can be matched to a particular cell type
- non integrative, won’t disrupt cancer
germ line gene therapy?
currently only on somatic cells
- modification of germ line could end certain diseases
- tampering with evolution?
- designer babies?
conclusions
- there are many different options, and it is important to assess the disease and best choice
- use the technology wisely
- be aware of possible ethical issues for different treatments
