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Gene therapy: the ADA deficiency case sheet
3-mark answer frame

What is gene therapy? Describe how it has been used to treat ADA deficiency.

How to lay out the answer. Follow the frame, then write it in your own words.

  1. 1 · Define in one line. Gene therapy corrects a gene defect by delivering a normal gene into the person's cells or tissues.
  2. 2 · Explain the disease. ADA deficiency is caused by deletion of the gene for adenosine deaminase, an enzyme crucial for immunity.
  3. 3 · Mention other treatments. Bone marrow transplant and enzyme replacement therapy help but are not completely curative.
  4. 4 · Describe the gene therapy.
    • Lymphocytes taken from the patient's blood and cultured.
    • Functional ADA cDNA added using a retroviral vector.
    • Engineered lymphocytes returned to the patient.
  5. 5 · State the limitation. Lymphocytes are not immortal, so infusions are repeated; adding the gene at an early embryonic stage could be a permanent cure.
  6. 6 · Close in one line. So gene therapy treats the cause of the disease, not only its symptoms.

Scoring tip: Write 'adenosine deaminase' in full once, and say why the infusions are repeated.