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Human Therapeutics Applications of DNA technology Unit 1 Cell and Molecular Biology Advanced Higher Biology Arrangements • Detecting genetic disorders. – The use of DNA probes and hybridisation to locate specific sequences, genes and gene mutations as illustrated by cystic fibrosis and Duchennes muscular dystrophy. – The discovery of a defective gene and the development of a screening test. – The importance of counselling. Arrangements • Gene therapy: the replacement of a faulty gene with a normal gene; the insertion of an extra gene with the intention that the gene product will play a therapeutic role. • Difficulty of gene therapy in practical terms. Suggested Activities • Analyse data and discuss case studies of cystic fibrosis and Duchennes muscular dystrophy. • Analyse the results of gene therapy trials on cystic fibrosis and discuss the legal, moral and ethical issues for the future. Learning Objective • To describe how DNA technology is being used to detect genetic disorders • To explain how DNA technology can be used to add “normal” genes to cells of patients with genetic disorders • To explain the technical difficulties of gene therapy Learning Objective • To explain how the genes responsible for genetic disorders are identified and used in diagnostic testing • To demonstrate an understanding of DNA profiling and the genetics of CF • To understand the sorts of problems associated with diagnostic testing for genetic disorders Learning Objective • To understand the theory behind gene therapy • To understand the practical difficulties of gene therapy Higher Revision • Mutations – Mutagenic agents – Chromosomal mutations • Deletion • Duplication • Translocation • inversion – Gene mutations • Substitution • Inversion • Deletion • insertion Key Terms • Genetic diseases • Monogenic traits • Polygenic traits • Autosomal dominant • Autosomal recessive • X-linked • Cystic fibrosis • Duchenne muscular dystrophy Cystic Fibrosis Human Therapeutics Cystic Fibrosis • Cystic Fibrosis (CF) is the UK’s most common, life-threatening, inherited disease. • CF affects vital organs in the body, especially the lungs and pancreas, by literally clogging them with thick, sticky mucus. • There is currently no cure for Cystic Fibrosis. • 7,500 babies, children and young adults have Cystic Fibrosis in the UK. – Of the 7,500 Cystic Fibrosis patients, 6,000 are aged 25 or under, Only 1,500 are aged over 25. Cystic Fibrosis • One person in 25 is carrier of the faulty Cystic Fibrosis gene – more than 2.3 million people in the UK. • The average life-expectancy has risen from 5 years to just over 30 years. • The defective gene that causes Cystic Fibrosis was found in 1989. CFTR (1,480 aa) • Cystic fibrosis • transmembrane • conductance • regulator F508 – 3bp deletion • – Deletion •F – Phenylalanine • 508 – Position in protein • Defective protein does not fold up and reach it’s membrane location. Duchenne muscular dystrophy Human Therapeutics Duchenne muscular dystrophy • X-linked • Affects 1 in 3,300 boys • Progressive wasting of muscles, resulting in wheel chair confinement in teenage years. • Life expectancy – 30 yrs • Gene found in 1987 Dystrophin (3,685 aa) • Function – Link cytoskeleton to the sarcolemma in muscle cells Detecting Genetic Disorders Human Therapeutics Detecting genetic disorders • Presentation of disease symptoms • Pedigree analysis • Genetic counselling • Identify as monogenetic trait – Genetic markers – Meiotic recombination frequencies – Genetic and physical mapping Screening Tests • First line tests – CF = salty sweat – DMD = high level creatine kinase Screening tests • F508 – Identified by amplifying a 100bp DNA fragment that spans the area of deletion. • Use PCR • Separation using gel electrophoresis Larger smaller +/+ +/ F508 F508/ F508 Gene Therapy Human Therapeutics Gene Therapy • Target cause of disease not just symptoms • 1990 ASA deficiency – 4 yr old girl – Condition was improved • CF and DMD obvious candidates Factors for consideration • Nature of gene defect • Target cells in patient • Method of delivery of normal gene • Expression and stability of normal gene in target cells • Ethics – Somatic cells vs germ cell gene therapy