Explain effect of deletion of gene for ADA in an individual.

Deletion of the gene for ADA results in ADA deficiency in an individual. This enzyme is crucial for the functioning of immune system. Adenosine deaminase (ADA) deficiency causes severe combined immunodeficiency (SCID). People with SCID lack virtually all immune protection from bacteria, viruses, and fungi. They are prone to repeated and persistent infections that can be very serious or life-threatening. These infections are often caused by "opportunistic" organisms that ordinarily do not cause illness in people with a normal immune system.