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Biology
Gene Therapy in Practice
Replacing Broken Genes with Working Copies
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Gene therapy is a medical approach that treats disease by adding, replacing, or changing genetic instructions in a patient’s cells. It matters because many serious disorders begin with a faulty gene that leads to a missing or harmful protein. In practice, the goal is to help cells make a functional protein that improves symptoms or slows disease. Gene therapy is already used for conditions such as inherited blindness, spinal muscular atrophy, and some blood disorders.
Key Facts
- Gene therapy pathway: gene problem → therapeutic gene delivered → functional protein made → symptoms may improve.
- AAV vectors are engineered viruses often used to deliver replacement genes into human cells.
- AAV gene therapy usually adds a working gene copy rather than directly editing the original DNA sequence.
- CRISPR is a gene-editing tool, while gene therapy is the broader treatment strategy that may or may not use CRISPR.
- Protein production follows the central dogma: DNA → mRNA → protein.
- Clinical success depends on delivery to the right cells, safe dosing, long-lasting expression, and careful monitoring.
Vocabulary
- Gene therapy
- Gene therapy is a treatment approach that uses genetic material to help cells correct or compensate for a disease-causing problem.
- AAV vector
- An AAV vector is an engineered adeno-associated virus used to carry therapeutic DNA into cells.
- Therapeutic gene
- A therapeutic gene is a working gene copy or genetic instruction introduced to help a cell make a needed protein.
- Nucleus
- The nucleus is the cell compartment that stores most of the cell’s DNA and controls many genetic activities.
- Expression
- Expression is the process by which information in a gene is used to make RNA and often a protein.
Common Mistakes to Avoid
- Calling all gene therapy CRISPR, which is wrong because CRISPR is one possible editing tool and many approved gene therapies use viral delivery without cutting DNA.
- Assuming the new gene always replaces the faulty gene, which is wrong because many AAV therapies add a functional gene copy that works alongside the existing DNA.
- Ignoring the target tissue, which is wrong because a therapy for the eye, liver, blood, or nervous system must reach the correct cells to be effective.
- Thinking gene therapy is automatically permanent and risk-free, which is wrong because expression can change over time and patients must be monitored for immune reactions and side effects.
Practice Questions
- 1 An AAV vector carries a therapeutic gene with 1,200 base pairs. If 3 base pairs code for 1 amino acid, how many amino acids could the protein contain, ignoring start and stop signals?
- 2 In a trial, 48 out of 60 patients show improved protein function after gene therapy. What percentage of patients improved?
- 3 Explain why an AAV gene replacement therapy for inherited blindness is different from using CRISPR to edit a mutation in the genome.