Radioimmunochemical quantitation of human adenosine deaminase

Markedly reduced or absent adenosine deaminase activity in man is associated with an autosomal recessive form of severe combined immunodeficiency disease. To further define the genetic nature of this enzyme defect, we have quantitated immunologically active adenosine deaminase (CRM) in the hemolysate of homozygous deficient patients and their heterozygous parents. A highly specific radioimmunoassay was developed capable of detecting 0.05% of normal erythrocyte adenosine deaminase. Hemolysates from nine heterozygotes (five families) showed a wide range in CRM (32-100% of normal) and variable absolute specific activities with several being at least 1 SD below the normal mean. Hemolysates from four unrelated patients showed < 0.09% adenosine deaminase activity with CRM ranging from < 0.06 to 5.6% of the normal mean. In conclusion, heterozygote and homozygote hemolysates from five of the eight families analyzed revealed variable levels of CRM suggesting heterogeneous genetic alteration or expression of the silent or defective allele(s) of adenosine deaminase.