Biotechnological Applications In Medicine

The first clinical application of gene therapy, carried out in 1990, treated a girl suffering from adenosine deaminase (ADA) deficiency, as recorded in NCERT Class 12, Chapter 11 (Biotechnology and its Applications). ADA is essential for the proper functioning of the immune system, and its absence, caused by deletion of the gene, leads to severe combined immunodeficiency. In the therapy, lymphocytes from the patient's blood were grown outside the body, a functional ADA gene was introduced into them using a retroviral vector, and these cells were reintroduced into the patient. Because mature lymphocytes are short-lived, the treatment had to be repeated periodically. DNA ligase is an enzyme that joins DNA fragments during cloning and is not linked to this disorder. Restriction endonucleases cut DNA at specific sites and are tools of genetic engineering rather than a deficiency disease. Reverse transcriptase synthesises DNA from RNA and is associated with retroviruses, not the condition treated. A plausibility check confirms the answer: gene therapy targets a missing functional gene, and only ADA deficiency among the options is a heritable enzyme disorder.