Transcript Document

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