Adenosine Deaminase Deficiency - Pathophysiology

Pathophysiology

ADA deficiency is due to a lack of the enzyme adenosine deaminase. This deficiency results in an accumulation of deoxyadenosine, which, in turn, leads to:

• a build up of dATP in all cells, which inhibits ribonucleotide reductase and prevents DNA synthesis, so cells are unable to divide. Since developing T cells and B cells are some of the most mitotically active cells, they are highly susceptible to this condition.
• an increase in S-adenosylhomocysteine since the enzyme adenosine deaminase is important in the purine salvage pathway; both substances are toxic to immature lymphocytes, which thus fail to mature.

Because T cells undergo proliferation and development in the thymus, affected individuals typically have a small, underdeveloped thymus. As a result, the immune system is severely compromised or completely lacking.