Adenosine deaminase (enzyme) deficiency is associated with

Ten to 20% of SCID patients exhibit a deficiency in adenosine deaminase (ADA), an enzyme of purinemetabolism that deaminates adenosine (ado) and deoxyadenosine(dAdo). An ADA deficiency results in the accumulation of ado and dAdo metabolites that induce premature cell death of lymphocyte progenitors. The condition results in the absence of B and NK lymphocytesas well as T cells. The clinical expression of complete ADA deficiencytypically occurs very early in life. Since ADA is a ubiquitous enzyme,its deficiency can also cause bone dysplasia with abnormal costochondral junctions and metaphyses (found in 50% of cases) and neurologicdefects. The very rare purine nucleoside phosphorylase (PNP) deficiency causes a profound although incomplete T cell deficiency that isoften associated with severe neurologic impairments Ref - Harrison's internal medicine 20e pg 2392-2493