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MS 1 Unit 7 MCP > Emerging Clinical Technologies > Flashcards

Flashcards in Emerging Clinical Technologies Deck (32):

Level of intervention and treatment

-mutant gene- modify somatic genotype: transplantation, gene therapy
-Mutant mRNA- RNAi
-Mutant protein- protein replacement, enhancement of residual function
-Metabolic or biochemical dysfunction- disease specific compensation
-clinical phenotype- medical or surgical intervention
-the family- genetic counseling, carrier screening, prenatal testing



-prenatal/carrier testing
-provide information
-planning and education
-provides opportunity for patients to obtain data about potential genetic disorders or carrier status and to discuss their concerns with someone who understands genetic principles


Medical or Surgical intervention

-Drug therapy: usually treats the symptoms
-Surgery: transplantation (heart, liver, etc); Repair (cleft lip/palate, aorta, bone fusion)


Treatment of Metabolic Disorders- dietary modification

-Dietary modification/restriction: amino acid catabolic pathway disorders (PKU), life long, can be difficult for patient and family


Treatment of Metabolic Disorders- Replacement

-add back something that is missing
-BH4 hyperphenylalanemia


Treatment of Metabolic Disorders- diversion

-use other pathways to avoid accumulation of a metabolite
-redirect to breakdown substances to harmless compounds
-example: defect in the urea pathway where the block prevents degradation of NH3 to urea which can be eliminated from the body
-NH3 will accumulate which can be toxic
-diet is partial solution but does not solve the entire problem
-it was found that administering sodium benzoate will push the excess ammonia to combine with glycine, and this is converted to hippurate which can be excreted in the urine


Treatment of Metabolic Disorders- Inhibition/Depletion

-Inhibition: modifying the rate of synthesis by using a drug or other agent that slows or blocks a critical step in the pathway
-Depletion: Removal of a substance that is in excess, hereditary hemochromatosis- accumulation of iron be controlled by regular phlebotomy


Treatment at the Protein Levels- Replacement Extracellular

-if a protein is absent- add it back
-Hemophilia A- factor VII
-alpha 1 antitrypsin deficiency- treat with alpha 1 antitrypsin

-Problems: cost, availability, antibody production in patient (pigs, cows), contamination


Treatment at Protein Level- Replacement Intracellular

-must target a specific cell type
-Example: Gaucher disease: lysosomal storage disease, deficiency of glucocerebrosidase
-there is modification of the glucosidase by mannose 6-phosphate. This is picked up by the macrophages. The enzyme can then cross the lysosomal membrane to begin to digest the stored macromolecules
-response in patients has been positive, with overall improvement in function and phenotype


Treatment at Protein level- enhancing genetic expression

-enhancing genetic expression: use of one gene to compensate for the mutation in another
-Sickle cell anemia
-treatment with decitabine increases levels of y-globin in the blood (hypomethylates DNA by inhibiting methyltransferase)
-Hb F functions as a replacement oxygen carrier and inhibits polymerization of deoxyhemoglobin S


Transplantation- Bone Marrow for Hematologic disorders

-hematologic disorders
-remove the disease clone and replace it with unaffected cells
-collect bone marrow stem cells from the patient (autologous) or from a matched donor (allogenic)
-transplanted cells with re-establish in the new host, and hopefully cure the disease
-possibility that not all of the disease related cells will be removed, and they could re-establish the disease


Transplantation of Bone Marrow 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 other cells
-acts as a source of mononuclear phagocytes
-can reduce the size of various internal organs
-if done within the first 2 years of life, will limit the negative neurological impact of the disease


Stem Cells

-self renewing, undifferentiated cells
-can proliferate and produce a wide variety of different types of differentiated cells
-Embryonic stem cells (ESC)-which are pluripotent and capable of differentiating into any cell type in the body
-Somatic stem cells (SSC) which are self renewing but can only differentiate into the cell types present in the tissue of origin- for example hematopoetic stem cells can differentiate into lymphocytes, neutrophils, basophils, red blood cells but could not generate skin or nerve cells


Embryonic Stem Cells

-Potential therapy for : Parkinson disease, Alzheimer disease
-Potential source of cells for: tissue grafting, organ transplants
-attract option because they provide the possibility of creating multiple types of cells from a single source
-furthermore, they offer the possibility of generating normal cells from tissues that may not be normally accessible- such as brain cells


Downside of Embryonic Stem Cells

-what about the source of cells?
-should embryos be used in this way?
-do the potential benefits outweigh other considerations?
-will the embryos be destroyed during the harvesting process?
-if ESC are an important commodity, will this become a commercial endeavor?


Problems with Allogenic Stem Cell Use

-graft vs host disease
-the ideal situation is for stem cells to be collected from one individual and reimplanted in the same person which avoids the problems of immune reaction (autologous transplantation)
-even with matched donors (allogenic transplantation), there are likely to be negative consequences of a transplant or infusion of "foreigh" cells
-thus patients will be at risk for graft vs host disease and will require immunosuppressive drugs throughout the remainder of their lives


Induced Pluripotent Stem Cells

-cells collected from an individual are treated in vitro using reprogramming factors that have been shown to reverse the differentiation in the cells and revert them to a state of pluripotency
-these cells are able to function in much the same way as embryonic stem cells with the capability of being stimulated to re-differentiate into any desired cell type
-the newly established cells can be transplanted back into the patient
-as they are his/her own cells, there should not be a problem with immune rejection


Cloning/ Nuclear Transfer

-taking a cell from one individual and growing up another identical individual
-a single cell is obtained from a donor and a unfertilized egg (oocyte) is obtained from another individual
-the oocyte is enucleated, and the nuclear from the donor cell is inserted into the oocyte
-the reconstituted cell has the nuclear contents of one individual and the cytoplasm from another
-this cell is now implanted into a surrogate mother who will carry it to term and hopefully produce a healthy newborn


Effects of cloning

-Dolly only lived 6 years of an expected 12
-telomere shortening was evident and even as a young sheep her cells and body processes often resembled those of an older individual
-there was also a question of inappropriate imprinting
-positive: creating a herd of cows or other animals that display the most positive characteristics (high milk production, thick wool)
-for crop plants, higher productivity, heat and insect resistance, my be possible


Nuclear transfer in humans

-nuclear transfer involving a diploid nucleus derived from a somatic cells does not occur in humans
-however it is possible to transfer a nucleus (haploid) from one egg to another
-this is useful when the patient's egg cytoplasm carries deleterious mutations (mitochondrial disorders)
-if a normal donor egg can be obtained, the nucleus can be removed and replaced by the nucleus from the patient's egg
-in vitro fertilization or ICSI with the patient's husband's sperm follows to create a fertilized egg that can be reimplanted into the patient


Cloning pets

-it will not be an exact duplicate
-color might be different because of the X inactivation which is random
-size differences are possible, because this is an environmentally related feature
-and personality can be totally different as this is a learned behavior


Gene therapy

-the deliberate introduction of genetic material into human somatic cells for therapeutic, prophylactic or diagnostic purposes
-general classes of therapy:
-correct a loss of function mutation by incorporating a functional gene into the genome
-compensate for a deleterious dominant allele by replacing or inactivating the 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 the gene of interest
-identification of target tissue
-ability to deliver gene to target
-understanding of gene biochemistry
-understand of expression


Major limitation- Delivery of Gene to Target

-vector must be able to carry the DNA
-must be able to insert DNA into the target cell
-viruses tend to be favored but there are other options
-most permanent if the therapy DNA is incorporated into the host cell's own DNA
-temporary incorporation in cytoplasm requires repeated therapy sessions: artificial liposome that carries DNA of interest, the lipid bilayer membrane of the liposome will fuse with the cell membrane and the DNA will be released into the cytoplasm


In vivo vs Ex vivo

-in vivo: genes are incorporated into vectors and targeted to specific cells in the body
-ex vivo: cells are extracted from the patient and genetically modified. The altered cells are returned to the patient


ADA Deficiency

-ADA Deficiency- Immunodeficiency disorder, 15% of severe combined immunodeficiency (SCID)
-Deoxyadenosine -> Deoxyinosine (with ADA) -> Xanthine Oxidase (with PNP) -> Uric Acid (excretion in urine)
-lack of adenosine deaminase results in a block in the metabolic pathway leading to an accumulation of dATP in the cells which prevents DNA synthesis and cell division
-T and B cells are highly susceptibile and the immune system is compromised


First successful gene therapy

-T cells were collected, grown in vitro and stimulated to proliferate with interleukin 2 and monoclonal antibody OKT3
-about 10 days later retroviral vectors carrying the non-mutant adenine deaminase cDNA are added to the cultures
-some cells will be infected by the virus particles
-the cells were sorted and amplified then reinfused into the patients
-significant improvement was seen as measured by improved T cell function
-First Ashanti, then Cindy, began to produce antibodies and grow tonsils
-they no longer needed to be isolated but could go to school, play with others their age, and begin a normal life


Who should be subjects for gene therapy

-only patients who had failed conventional therapies and who had less than 3 months to live were accepted onto new protocols
-therapies were carefully tested in other animals before being offered to human


Back to Gene Therapy Success

-an adenoviral vector was created carrying the CFTR. The vectors are suspended in solution in an inhaler often used by CF patients
-when inhaled the solution deposits the vector in the lungs where they are incorportated into surface cells
-the modified cells function normally, reducing the mucus in the lungs
-unfortunately the short term fix as the benefit is lost when the cells die
-also things used to treat DMD, melanoma, hemophilia, Leber's congenital amaurosis (eye disease), adrenoleukodystropy


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
by prevent binding of ribosomes


RNA interference

-targeted degradation of mRNA
-destroy mRNA from negative dominant mutations while leaving the second allele alone
-reduce the concentration of an mRNA that is over expressed


Adeno-associated virus

-non-pathogenic vector
-reduces the likelikhood of an immune reaction
-is found in many serotypes- so the proper vector can be matched to a particular cell type
-non-integrative, so will not disrupt cancer genes