Oneliner_1428

OneLiner

Severe combined immunodeficiency (SCID) due to adenosine deaminase (ADA) deficiency presents very early in life with Pneumocystis pneumonia, thrush, and failure to thrive. ADA deficiency inhibits metabolism of deoxyadensine resulting in accumulation of this metabolite. In turn, there is an increase in the levels of deoxyadenosine triphosphate and S-adenosylhomocystine, which are toxic to lymphocytes and inhibit DNA synthesis in these actively replicating cells. A lymphopenic state results in the SCID phenotype. As macrophages are still functional in these patients, mycobacterial infections are not common.