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 (a-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 -

Gene therapy

The correct answer is Option (1) → Gene therapy 

In 1990, the first clinical gene therapy was administered to a 4-year-old girl who had adenosine deaminase (ADA) deficiency, a condition essential for the proper functioning of the immune system. This deficiency arises due to the deletion of the gene responsible for producing ADA. Mutations in the ADA gene lead to a deficiency or absence of this enzyme, causing a buildup of harmful substances like deoxyadenosine, which can be toxic to lymphocytes and other cells. This can result in severe combined immunodeficiency (SCID), a condition where the body's ability to fight off infections is severely impaired.

While bone marrow transplantation and enzyme replacement therapy can partially address ADA deficiency in some cases, they are not fully curative.

As an initial step toward gene therapy, lymphocytes from the patient's blood are cultured outside the body. Functional ADA complementary DNA (cDNA) is then introduced into these lymphocytes using a retroviral vector. Subsequently, the modified lymphocytes are infused back into the patient. However, since these cells are not immortal, the patient requires periodic infusions of genetically engineered lymphocytes to maintain the effect.

Alternatively, for a more permanent cure, if the gene responsible for producing ADA is introduced into cells during early embryonic stages, it could result in a lasting solution. This approach aims to correct the genetic defect early in development, offering the potential for a lifelong and complete cure for ADA deficiency through gene therapy.