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medium difficulty9 min

Gene Therapy

Gene therapy is a biotechnological approach in which a functional gene is introduced into a person's cells to compensate for a defective or missing gene responsible for a disorder.

In one line: Gene therapy: give the cell a working instruction copy.

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Understand it

  • Gene therapy aims to correct a disorder at the genetic expression level by supplying a functional copy of a gene.
  • The Class 12 focus is ADA deficiency, a disorder affecting immune function due to lack of adenosine deaminase enzyme.
  • In ex-vivo gene therapy, cells are removed from the patient, genetically modified outside the body, and returned.
  • In in-vivo gene therapy, the therapeutic gene is delivered directly into the body.
  • The first clinical gene therapy example commonly tested is ADA deficiency.
  • Students should also mention limitations: treatment may need repeated cell infusion unless stem cells are corrected, and gene delivery must be carefully controlled.

Example

In ADA deficiency, lymphocytes can be taken from the patient, cultured, supplied with a functional ADA gene using a vector, and returned to the patient's body to provide temporary immune support.

Rule to remember

Key biological rule: gene therapy works by adding a functional gene copy to restore or improve production of a missing protein, but success depends on delivery, expression, and cell survival.

See it worked out

Follow the example line by line, then use the same method on new questions.

Worked example

Question: Explain ex-vivo gene therapy for ADA deficiency.

  1. 1Answer: Lymphocytes are taken from the patient and grown in culture.
  2. 2A functional ADA gene is introduced using a vector.
  3. 3The genetically corrected lymphocytes are returned to the patient, where they produce ADA for a limited period.

Method you can reuse

Name the disorder, identify the defective gene or missing enzyme, state whether the method is ex-vivo or in-vivo, describe gene delivery using a vector, explain return or expression in cells, and mention limitation if asked.

Visual tip

A useful diagram can show ex-vivo therapy: patient cells removed, functional gene inserted with vector, corrected cells cultured, and cells returned. Labels: patient lymphocyte, ADA gene, vector, corrected cell, reinfusion.

Check yourself

Answer the question in your head before opening the answer.

Try it yourself

Why may gene therapy for ADA deficiency need repeated treatment when lymphocytes are used?

Think first, then show answer
Lymphocytes have a limited life span, so corrected lymphocytes may not remain in the body permanently. Repeated infusion may be needed unless the functional gene is introduced into long-lived stem cells.

Common wrong answer

Gene therapy means replacing every defective gene in every body cell at once.

Don't mix this up

Students often write that gene therapy always gives a permanent cure. Some approaches are temporary unless long-lived stem cells are corrected successfully.

Exam tip

For ADA deficiency, include defective gene, missing enzyme, patient lymphocytes, vector-mediated gene insertion, and return of corrected cells.

Write it in the exam

Each point is worth about one mark. Write point 1 for a 1-mark question and keep adding points as the marks go up.

How CBSE asks it

Asked as a short answer on ADA deficiency, an assertion-reason question on temporary treatment, or a comparison between ex-vivo and in-vivo gene therapy.

Answer plan

Define gene therapy, name ADA deficiency, describe the ex-vivo sequence, mention functional ADA gene and vector, then add why repeated treatment may be required.
  1. 1

    Enough for 1 mark

    Gene therapy is a biotechnological approach in which a functional gene is introduced into a person's cells to compensate for a defective or missing gene responsible for a disorder.

  2. 2

    Add for 2 marks

    Example: In ADA deficiency, lymphocytes can be taken from the patient, cultured, supplied with a functional ADA gene using a vector, and returned to the patient's body to provide temporary immune support.

  3. 3

    Add for 3 marks

    Gene therapy aims to correct a disorder at the genetic expression level by supplying a functional copy of a gene.

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