Severe Combined Immunodeficiency (SCID) - Adenosine Deaminase (ADA) Deficiency

Severe Combined Immunodeficiency (SCID) - Adenosine Deaminase (ADA) Deficiency is a rare genetic disorder that affects the body's immune system, which normally protects against infections. This condition results from a lack of the enzyme adenosine deaminase, leading to a buildup of toxic substances that damage immune cells. As a result, people with this disorder have a severely weakened immune system and are highly vulnerable to frequent and severe infections. The disease primarily affects the lymphocytes, a type of white blood cell essential for fighting infections. Without treatment, infants with this condition often suffer from life-threatening infections early in life. The disorder impacts the body's ability to defend itself, making even common germs dangerous.

Severe Combined Immunodeficiency (SCID) - Adenosine Deaminase (ADA) Deficiency is a form of SCID caused by mutations in the ADA gene leading to deficient activity of the adenosine deaminase enzyme. This enzyme deficiency results in accumulation of toxic metabolites such as deoxyadenosine and dATP, which are particularly harmful to developing T cells, B cells, and NK cells, causing profound lymphopenia and impaired adaptive immunity. The condition manifests as a combined immunodeficiency with severe defects in both cellular and humoral immunity. Clinically, it presents in infancy with recurrent, severe infections, failure to thrive, and opportunistic infections including Pneumocystis jirovecii pneumonia. Without intervention, the disease is fatal due to overwhelming infections. It is a classic example of a primary immunodeficiency with a well-defined enzymatic defect.