Read the Passage carefully and answer the questions.
Insulin consists of two short polypeptide chains: chain A and chain B, that are linked together by disulphide bridges. The first clinical gene therapy was given in 1990 to a 4-year old girl with adenosine deaminase (ADA) deficiency. This enzyme is crucial for the immune system to function. Recombinant DNA technology, Polymerase Chain Reaction (PCR) and Enzyme Linked Immuno-sorbent Assay (ELISA) are some of the techniques that serve the purpose of early diagnosis of diseases. Transgenic animals that produce useful biological products can be created by the introduction of the portion of DNA (or genes) which codes for a particular product such as human protein (α-1-antitrypsin) used to treat emphysema. Biopiracy is the term used to refer to the use of bio-resources by multinational companies and other organisations without proper authorisation from the countries and people concerned without compensatory payment.
Deficiency of adenosine deaminase (ADA) can be permanently cured by -
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → Gene therapy
In ADA deficiency the gene for adenosine deaminase is deleted, so the immune system fails. Gene therapy puts a working ADA gene into the patient’s cells. If the gene is put into cells at an early embryonic stage, it could be a permanent cure.
Option (1) Gene therapy — Correct. Only gene therapy can put the missing gene back; introduced at an early embryonic stage, it could cure the disease permanently.
Option (2) Bone marrow transplantation — Incorrect. It can help some patients, but NCERT says it is not completely curative.
Option (3) Periodic infusion of genetically engineered lymphocytes. — Incorrect. Lymphocytes do not live for ever, so the patient needs these infusions again and again; it is not a permanent cure.
Option (4) Enzyme replacement therapy — Incorrect. Giving the enzyme by injection also works only as long as it is given.
Note: The passage is taken from NCERT. NTA has put lines of the NCERT text together to make it. Most CUET (UG) questions come straight from NCERT, so study the book line by line, including figures and their titles.
NCERT Extract:
Gene Therapy – “… In some children ADA deficiency can be cured by bone marrow transplantation; in others it can be treated by enzyme replacement therapy, in which functional ADA is given to the patient by injection. But the problem with both of these approaches that they are not completely curative. As a first step towards gene therapy, lymphocytes from the blood of the patient are grown in a culture outside the body. A functional ADA cDNA (using a retroviral vector) is then introduced into these lymphocytes, which are subsequently returned to the patient. However, as these cells are not immortal, the patient requires periodic infusion of such genetically engineered lymphocytes. However, if the gene isolate from marrow cells producing ADA is introduced into cells at early embryonic stages, it could be a permanent cure.”