Q.A child is born with ADA-deficiency.

(a) The permanent cure for ADA deficiency involves gene therapy using a bone marrow stem cell approach. First, lymphocytes (white blood cells) are taken from the child's bone marrow. In the lab, a functional ADA gene is inserted into these cells using a retrovirus as a vector. The genetically corrected cells are then re-infused into the child's body. Because these are stem cells, they multiply and produce a continuous supply of ADA enzyme, providing a lifelong cure. …

Adenosine deaminase (ADA) deficiency is a severe inherited disorder that cripples the immune system. Children born with this condition lack a functional ADA enzyme, which leads to a toxic buildup of metabolites that destroy T-lymphocytes. Without treatment, the child cannot fight even minor infections and typically does not survive early childhood. The NCERT textbook discusses this disease as a landmark case in gene therapy, so let us walk through the two approaches it describes.

1. The procedure for a permanent cure: Gene therapy using the patient's own stem cells The only method that offers a lifelong cure is gene therapy. The idea is straightforward: give the child's cells a working copy of the ADA gene so they can produce the missing enzyme permanently. But the execution is delicate and precise. First, blood is drawn from the child to isolate bone marrow stem cells — these are the parent cells that give rise to all blood cells, including the immune system's T-lymphocytes. These stem cells are then grown in a culture dish. Into these cells, a functional ADA gene is inserted using a disabled retrovirus as a vector. The retrovirus has been engineered so it cannot cause disease; it merely acts as a delivery vehicle, carrying the normal ADA gene into the stem cells' DNA. Once the stem cells have taken up and integrated the gene, they are infused back into the child's bloodstream. Because these are the child's own cells, there is no risk of immune rejection. The corrected stem cells settle in the bone marrow and begin producing healthy T-lymphocytes that now carry the functional ADA gene. Over time, these cells multiply and repopulate the immune system, providing a permanent cure.
   Important

   The NCERT textbook specifically states that this procedure was first successfully performed in 1990 on a four-year-old girl in the United States. The stem cells used were her own, and the retroviral vector carried the normal ADA gene. This remains the classic example of gene therapy in the Indian curriculum.

2. Another possible treatment: Enzyme replacement therapy (PEG-ADA) …