Chapter 2 : Gene Therapy

Topics covered in this snack-sized chapter:



Gene Therapy arrow_upward


  • Genes, who are carried on chromosomes, are the basic physical and functional units of heredity.
  • Genes are specific sequences of bases that encode instructions on how to make proteins.
  • Although genes get a lot of attention, it’s the proteins that perform most life functions and even make up the majority of cellular structures.
  • Gene therapy is a technique for correcting defective genes responsible for disease development.
  • Several approaches may use for correcting faulty genes:
    • A normal gene may be inserted into a nonspecific location within the genome to replace a nonfunctional gene; this approach is most common
    • An abnormal gene could be swapped for a normal gene through homologous recombination
    • The abnormal gene could be repaired through selective reverse mutation, which returns the gene to its normal function
    • The regulation of a particular gene could be altered

    Types of Gene Therapy arrow_upward


  • Somatic gene therapy:
    • The therapeutic genes are transferred into the somatic cells of a patient
    • Any modifications and effects will be restricted to the individual patient only, and will not be inherited by the patient's offspring or later generations
  • Germ line gene therapy:
    • Germ cells, that is sperms or eggs, are modified by the introduction of functional genes, which are ordinarily integrated into their genomes
    • Therefore, the change due to therapy is heritable and passed onto the later generations

    How Does Gene Therapy Work? arrow_upward


  • In most gene therapy studies, a "normal" gene is inserted into the genome to replace an "abnormal," disease-causing gene.
  • A carrier molecule called a “vector” must be used to deliver the therapeutic gene to the patient's target cells.
  • Currently, the most common vector is a virus that has been genetically altered to carry genetic material into the cells “genes.”
  • Researchers are trying to take advantage of this unique capability.
    • They remove the original disease causing genes from the viruses
    • Replace them with the genes needed to stop disease
    •  Insert the altered viruses into a person's diseased cells to deliver their genetic material


    Vectors Used in Gene Therapy arrow_upward


  • Retroviruses:
    • A class of viruses that can create double-stranded DNA copies of their RNA genomes
    • These copies of its genome can be integrated into the chromosomes of host cells
    • Human immunodeficiency virus (HIV) is a retrovirus
  • Adenoviruses:
    • A class of viruses with double-stranded DNA genomes that cause respiratory, intestinal, and eye infections in humans
    • The virus that causes the common cold is an “adenovirus”
  • Adeno-associated viruses:
    • A class of small, single-stranded DNA viruses that can insert their genetic material at a specific site on chromosome 19
  • Herpes simplex viruses:
    • A class of double-stranded DNA viruses that infect a particular cell type, neurons
    • Herpes simplex virus type 1 is a common human pathogen that causes cold sores

    Clinical Implications of Gene Therapy arrow_upward


  • Gene therapy can be used to fix defective genes or to replace missing genes.
  • Many diseases are the result of just one gene malfunctioning; sickle cell anemia, cystic fibrosis, SCID, are all caused by one defective gene.
  • To correct the problem, gene therapy is used to deliver genes that function correctly.
  • A cancer patient can also get advantage of this technique by insertion of genetically altered vectors into human genome.


    • Thank You from Kimavi arrow_upward


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