Gene therapy

• recombinant DNA technology could be used to treat human diseases - gene therapy
• gene therapy involves altering the defective genes (mutated alleles) inside cells to treat genetic disorders and cancer

  how you do this depends on whether the disorder is caused by a mutated allele or 2 mutated recessive alleles
• • if its caused by two mutated recessive alleles you can add a working dominant allele to make up for them - 'supplement' the faulty ones
• • if it is caused by a mutated dominant allele you can 'silence' the dominant allele e.g. by sticking a bit of DNA in the middle of the allele so it doesn't work any more
• both of these processes involve inserting a DNA fragment into the person's original DNA

  just like in recombinant DNA technology - need a vector to get the DNA into the cell

  a range of different vectors can be used e.g. altered viruses, plasmids or liposomes (spheres made of lipids)
• there are 2 types of gene therapy:

  • somatic
  • germ line
• somatic:

  • involves altering the alleles in body cells, particularly the cells that are most affected by the disorder
  • e.g. cystic fibrosis is a genetic disorder that if very damaging to the respiratory system
  • somatic therapy for CF targets the epithelial cells lining the lungs
  • somatic therapy does not affect the individual's sex cells (sperm or eggs) though, so any offspring could still inherit the disease
• germ line therapy:

  • involves altering the alleles in the sex cells
  • this means that every cell of any offspring produced from these cells will be affected by the gene therapy and won't suffer from the disease
  • currently illegal in humans
• Ethical issues surrounding gene therapy:

  • some people are worried that the technology could be used in ways other than for medical treatment e.g. for treating the cosmetic effects of ageing
  • others worry there is potential to do more harm than good by using the technology e.g. risk of overexpression of genes - genes produce too much of the missing protein
• gene therapy is not being used widely yet, but there is a form of somatic gene therapy available to treat some people with a genetic disease called LPLD - treatments for other diseases such as cystic fibrosis are undergoing clinical trials