Topic Stem Cell and Gene Therapy Essay - Main Points!

Q) Discuss the limitation of gene therapy

Main points
Key idea:	Limitation (1) Target cells
· Difficult to introduce normal gene into correct target cells + integrate normal gene into correct chromosome · Target cells may also be non-dividing + have short life-span
Key idea:	Limitation (2) Incorrect insertion of gene
· Incorrect insertion of gene into a proto-oncogene or tumour suppressor gene · Result: gene mutation, may lead to cancer dev
Key idea:	Limitation (3) Level of gene expression
· Even if gene is correctly integrated into chrom, diff to control level of gene expression · Often, expression of gene is too low to produce sig amount of functional proteins
Key idea:	Limitation (4) Constant risk to patients
· Treatment is short-lived, so patients freq treatment · Hence, constant exposure to risk of treatment
Key idea:	Limitation (5) Disadv of viral delivery sys
· Risk of inducing an immune / allergic response to virus · Virus vector may even regain its virulence in body of patient
Key idea:	Limitation (6) Suitable vector & low transfection efficiency of liposomes
· Lack of suitable vector for a large gene, general low transfection efficiency using liposomes as delivery sys
Key idea:	Limitation (7) Not feasible for complex genetic diseases
· Currently, gene therapy is not useful for complex genetic diseases caused by many defective genes · Reason: diff to introduce many genes into same target cells, at same time
Comments: (i) Visualize the answer with the aid of a labelled diagram. (ii) Verbalize the answer + write down the main points w/o referring to the answer (use abbreviations) (iii) Read again within the next 24h & once more within 72h (do not spend more than 10min) (iv) Do not discuss ethical or social issues in the answer. (v) Transfection is a process that introduce nucleic acids through non-viral methods into eukaryotic cells. It is similar to bacterial transformation which is the uptake of foreign DNA into the bacteria.

Topic Stem Cell and Gene Therapy Essay - Main Points!

Q) Discuss the use of viral and non-viral delivery systems in gene therapy

Main points
Key idea:	What is gene therapy
· Technique for introducing normal copy of the gene into patient suffering fr a genetic disease · Normal gene or allele produces functional proteins; hence restores normal functions of target cells · Two types of delivery sys – (i) viral (ii) non-viral delivery sys
Key idea:	Viral delivery system
· Viral delivery sys: viruses genetically modified (GM) to carry normal human gene · GM viruses then infect target cells - introduce normal gene into them
Key idea:	Named example : (1) Retroviruses
· E.g. Retroviruses carry normal gene coding for adenosine deaminase (ADA) to actively dividing bl stem cells · Adv: ability to integrate the normal gene into lymphocyte chrom for long term treatment of patients w ADA-SCID
Key idea:	Named example : (2) Adenoviruses
· E.g. Adenoviruses carry normal gene coding for cystic fibrosis transmembrane conductance regulator protein (CFTR) to epithelial cells of airways + gut · Adv: treat patients with cystic fibrosis
Key idea:	Non-viral delivery systems
· E.g. Gene gun - introduce DNA directly into target cells · E.g. Liposome - DNA is packaged into synthetic vesicles (liposomes) made up of a lipid bilayer struc which · may be further coated w carbohydrates or peptide chains that bind to specific receptors on surface of target cells
Key idea:	Liposome - process of gene introduction
· Liposomes can introduce normal gene into target cells either by (i) electroporation or by (ii) binding to surf receptors on target cells  · Liposome fuses w cell membrane, then introduces gene into target cell
Comments: (i) Visualize the answer with the aid of a labelled diagram. (ii) Verbalize the answer + write down the main points w/o referring to the answer (use abbreviations) (iii) Read again within the next 24h & once more within 72h (do not spend more than 10min) (iv) To gain maximum marks, explain the term gene therapy before explaining the two delivery systems. (v) Whenever possible, students should use named examples to support their answers (vi) The selection of the type of virus (e.g. adenovirus and retrovirus) depends on the type of cells being targeted. For example, adenoviruses (which are flu viruses) are effective in targeting the slow or non-dividing epithelial cells of the airways and gut. Retroviruses are effective in targeting actively dividing cells

Topic Stem Cell and Gene Therapy Essay - Main Points!

Q) Describe two named genetic diseases and their effects on patients

Main points
Key idea:	What is Severe Combined Immunodeficiency (SCID)
· Genetic disease (of immune sys) - patient lacks cell-mediated immune responses + ability to produce antibodies · Recessive condition · Most common form X-linked; hence more males are affected than females
Key idea:	Molecular basis of X-linked SCID
· Interleukin 2 receptor gamma (IL2RG) gene - codes for common gamma chain subunit (a component of several interleukin receptors including lymphocyte receptor) · Role of functional receptor - normal development of T-lymphocytes crucial for immune sys as they identify foreign pathogenic agents in body, activating other immune cells · Genetics - mutation of gene; hence affects normal function of immune sys
Key idea:	Molecular basis of ADA-SCID
· Adenosine deaminase (ADA) gene - autosomal gene on chrom 20, codes for enz · Role - to break down deoxyadenosine · Genetics - mutation of gene leads to deficiency of functional enzyme; hence, accumulation of metabolites which is toxic to lymphocytes crucial for immune sys
Key idea:	Effects on patient
· Effects The 2 types of single gene disorder compromise immunity of patients who become susceptible to opportunistic infections (e.g. pneumonia, meningitis) · If untreated, patients usu die at an early age
Key idea:	What is cystic fibrosis
· Genetic disease of mucus glands · Autosomal (chrom 7), · Recessive condition
Key idea:	Molecular basis of cystic fibrosis
· Genetics - mutation of gene coding for a CI- channel, cystic fibrosis transmembrane conductance regulator protein (CFTR) · Commonly involves deletion of 3 bp are deleted - loss of codon coding for phenylalanine · Defective chloride channels, not able to transport CI- out of epithelial cells of airways, lung, gut and reprod sys
Key idea:	Effects on patients
· Effects i) Thick, sticky mucus - interferes with gaseous exchange, cause recurrent infections of lungs ii) Digestion (e.g. blocks secretion of pancreatic enz, absorption of digested food products) iii) Infertility (e.g. blocks transport of sperms in vas deferens) · Like SCID, cystic fibrosis reduces life expectancy
Comments: (i) Visualize the answer with the aid of a labelled diagram. (ii) Verbalize the answer + write down the main points w/o referring to the answer (use abbreviations) (iii) Read again within the next 24h & once more within 72h (do not spend more than 10min) (iv) The mutation of the JAK3 gene (on chromosome 19) coding for a relay molecule in the interleukin signaling pathway also result in SCID (v) There are more than 1000 known mutations in the CFTR gene that result in cystic fibrosis. The deletion mutation provided in the answer accounts for more than 70% of the cases (vi) Some immunology background : In cell-mediated immunity, T-lymphocyte cells bind to surface of the infected cells and stimulate other white blood cells (e.g. cytotoxic T cells) to destroy the infected cells. (Note : It is not necessary to study the immune cells involved in cell-mediated immune response or humoral immune response (antibodies production) in detail)