Adenosine deaminase (ADA) is an enzyme that plays a crucial role in the metabolism of nucleotides, specifically in the conversion of adenosine to inosine. This process is essential for maintaining the balance of nucleotides in the body, which is important for cellular function and energy production. Deficiency in adenosine deaminase can lead to severe combined immunodeficiency (SCID), a genetic disorder that affects the immune system. Individuals with ADA deficiency have difficulty fighting infections due to a lack of functional T cells and B cells, making early diagnosis and treatment vital for their health.