RESUMO
Severe combined immunodeficiency [SCID] due to adenosine deaminase [ADA] deficiency is a rare autosomal recessive disorder that leads to early demise of the affected child. In this study, we examined the active of ADA in 8 egyptian families with [SCID] be estimating erythrocytic ADA levels in family members as we as 15 healthy subjects as a control. Noreover, we examined the ADA enzyme kinetics [km, thermal stability and ph profile] in residual activity of affected and healthy subjects to characterize its mutations. The erythrocytic ADA activity were low in 2 clinically affected cases and in 11 out of 15 [73%] obligate heterozygotes. Using enzyme kinetics studies, more than one mutation type could be delineated: a] reduced enzyme activity and substrate affinity with normal thermostability b] a thermolabile enzyme with reduced activity, with normal affinity to substrate. c] normal enzyme activity but with reduced affinity to substrate. In sconclusion, we reconfirmed the validity of the assay of erythrocytic ADA in detecting a high percentage of heterozygous state among suspected carriers. In addition, we defined the biochemical criteria of the detected mutations