19.2.4

Gene Therapy

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Gene Therapy

Gene therapy is a genetic engineering technique used to cure disease.

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Procedure

  • Gene therapy involves the introduction of a target gene (the gene that confers a beneficial trait) into the genome.
    • The genome has been transformed.
  • The target gene is then transcribed and translated to produce the desired protein.
  • The protein counteracts the effect of a disease that is caused by a mutation.
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Allele interactions

  • Gene therapy is used to treat diseases that are caused by a mutation in a gene.
  • The way that gene therapy is used depends on the allele interactions of the gene that causes the disease.
    • If the mutation is in the recessive allele, a wild-type (typical of the species) dominant allele is inserted into the genome. The dominant allele counteracts the mutant alleles.
    • If the mutation is in the dominant allele, an allele that 'silences' the mutant allele is inserted in the genome.
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Vectors

  • Gene therapy uses vectors to insert the target gene into the genome.
  • Vectors transport allow the gene to be taken up by the cells of the host. The genome is then transformed.
    • Types of vector include plasmids, bacteriophages, liposomes, & naked DNA.
  • When choosing a vector, you need to consider factors such as the target cell, size of the gene to be inserted, and any immune response that may be caused.
    • For example, bacteriophages are a type of virus so may cause an immune response. They may, however, be able to deliver larger genes than naked DNA. Naked DNA is sensitive and easily broken down.
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Types of gene therapy

  • There are two types of gene therapy -
    • Somatic therapy - altering of alleles in adult body cells. This is a short term therapy and needs repeating.
    • Germline therapy - altering of alleles in sex cells. This is illegal in humans.
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Example - cystic fibrosis

  • Cystic fibrosis is caused by a mutation in the CFTR gene.
  • The CFTR gene codes for a chloride ion channel that or transports Cl- ions out of cells and into mucus.
  • Cl- ions lower the water potential of mucus. This causes water to leaves cells and enter mucus by osmosis.
  • So, when the channel is mutated Cl- ions do not enter mucus. Mucus becomes thick & sticky.
    • This leads to problems such as a build-up of mucus in the lungs, blockage of digestive system ducts, and clogging of the cervical canal with mucus.
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Cystic fibrosis - gene therapy

  • Treating cystic fibrosis with gene therapy would involve delivering a correctly function CFTR protein to affected cells.
  • This therapy is the subject of multiple clinical trials and has shown some promise.

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