Question

Which one of the following can be used as a permanent cure for ADA deficiency?

• A. Bone marrow transplantation upon detection of disorder in adult
• B. Enzyme replacement therapy at any point in life
• C. Both a and b
• D. Gene therapy at early embryonic stages

Answer 1

The correct option is D Gene therapy at early embryonic stages

A permanent cure for ADA deficiency is gene therapy at early embryonic stages. ADA or adenosine deaminase deficiency causes a rare genetic disorder of the immune system known as Severe Combined Immunodeficiency. It is caused due to a deletion mutation in the gene that codes for ADA enzyme which is essential for the proper functioning of the immune system.
There can be three approaches to the treatment of ADA deficiency:

• Transplantation of bone marrow with the cells containing normal ADA gene
• Enzyme replacement therapy by injecting functional ADA enzyme
• Gene therapy by introducing functional ADA gene into the lymphocytes followed by their infusion into the patient

Gene therapy involves treatment of a genetic disorder caused by a single defective gene by replacing the defective gene by a normal one.
In ADA gene therapy, lymphocytes from the patient’s body are grown in a culture medium outside the body. A functional ADA cDNA is introduced into the lymphocytes using a retroviral vector. The advantage of this is that retrovirus vectors are capable of transforming their ssRNA genome into a dsDNA molecule that stably integrates itself into the host cell’s genome.
The genetically modified lymphocytes are returned to the patient’s blood. If the genes isolated from the marrow cells of a healthy individual can be introduced into early embryonic cells, a permanent cure for ADA deficiency can be achieved.