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)