Molecular Basis for

1
Molecular Basis for Relationship between Genotype
and Phenotype
DNA
genotype
DNA sequence
transcription
RNA
translation
amino acid sequence
protein
function
organism
phenotype
2
Gene Therapy
Germ-line Therapy vs Somatic Therapy
3
Gene Therapy in Mammals
4
Human Gene Therapy

• Approaches to treatment of diseases
• DNA transfer into afflicted individual

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1990 First Clinical Trial Severe Combined
Immunodeficiency (SCID) - defective adenosine
deaminase (ADA) gene. - afflicted patients
express no functional T or B lymphocytes. -
Bubble Boy Disease
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Delivery Approaches to Somatic Therapy

• Direct Administration
• Introduction of normal gene using a virus
• retrovirus
• adenovirus
• Indirect Administration
• Reintroduction of cells that have been made
  transgenic

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Criteria for Gene Therapy Candidacy of a
Disease for Consideration
1. Mendelian inheritance 2. One gene product for
the gene 3. Knowledge of function of gene
product 4. Availability of normal gene
sequence 5. Localized symptoms for the
disease 6. Availability of delivery system
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25,000 genes in humans are potential candidates
for gene therapy.
9
Candidates for Gene Therapy ?
10
25,000 genes in humans are potential candidates
for gene therapy.
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Cystic Fibrosis
Disease is usually fatal. Lungs, other organs
are clogged with mucus. repeated bouts of
pneumonia heart stressed by decreased lung
capacity delivery failure of pancreatic
enzymes Life expectancy of 20-25 years 1 of
29 Caucasians are carriers 1 of 1600
Caucasians are affected 30,000 Americans are
affected
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Cystic Fibrosis

• Caused by recessive mutation (chromosome 7)
• Failure to pump Cl- ions across cell membrane
• Missing Cl- ion channel protein (cystic
  fibrosis
• transmembrane protein or CFTR)
• Normal gene sequence available (cloned in
  1989)
• Normal gene 250 kb in size
• Transcript of 6 kb in size
• Gene product of 1480 amino acids in length
• Over 1500 mutations documented

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Cystic Fibrosis as Candidate for Gene Therapy
1. Recessive gene on chromosome 7. 2. CFTR is
the gene product. 3. CFTR is an ion channel
protein. 4. Normal gene sequence has been
cloned. 5. Symptoms are localized to specific
organs. 6. Adenovirus (cold virus) can be used
to deliver normal sequence to lung cells.
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Human DNA Information Ethical Concerns
Who should have access to your DNA information?