Q.One of the applications of biotechnology is 'gene therapy' to treat a person born with a hereditary disease. i) What does "gene therapy" mean? ii) Name the hereditary disease for which the first clinical gene therapy was used. iii) Mention the steps involved in gene therapy to treat this disease.

Step 1. Explain what 'gene therapy' means: it is the process of transferring a normal gene into the cells of a person who carries one or more mutant alleles, using a vector for delivery, so that expression of the normal gene restores a functional gene product and a normal phenotype. Step 2. Name the hereditary disease treated in the first clinical gene therapy: adenosine deaminase (ADA) deficiency, a form of Severe Combined Immunodeficiency (SCID), treated by French Anderson in 1990 in a four-year-old girl. Step 3. Describe the steps involved in that treatment: lymphocytes are removed from the patient's blood and grown in a nutrient culture medium; a healthy, functional human ADA cDNA is introduced into these lymphocytes using a genetically disabled retrovirus as the vector; the genetically engineered lymphocytes are then returned (reinfused) into the patient, where they can now produce ADA enzyme. Step 4. Note the follow-up detail: since these transduced lymphocytes are not immortal, the patient requires periodic repeat inf …

Answer the three sub-parts in order — definition, the named disease, and the specific treatment steps — drawing di …

• Naming a different disease (e.g. cystic fibrosis) instead of the ADA-deficiency SCID case actually described as the FIRST clinical trial. …