Family study on the kindred of an adenosine deaminase deficient child with severe combined immunodeficiency.

A study was performed on the family of a child with severe combined immunodeficiency and deficiency of the purine salvage pathway enzyme, adenosine deaminase (ADA). Sixteen relatives over three generations were studied. Erythrocyte ADA levels clearly indicated the heterozygous status of five members. A sixth member, whose erythrocyte ADA level of 48 nmol/hr/ml Hb was within two standard deviations (32) of the mean (76) was shown by ADA determination on platelets to be clearly heterozygous. Similarly, consideration of ADA data of either serum, platelets or lymphocytes only, would have failed to identify all heterozygotes. The survey shows that the identification of phenotype by the indirect means of enzyme level determination is enhanced by the simultaneous study of several tissues.