A new approach to detection of heterozygotes for adenosine deaminase deficiency: a hypothetical method.

In a second and third families with ADA deficiency found in Japan, we tried a new approach to evaluate heterozygote detection. This is based on the hypothesis that ADA activity of red blood cell is the quantitative sum of the activities of ADA proteins expressed by two allelic genes at the ADA autosomal locus, and that these activities are not changed by the gene transmission from parents to children. We have detected red blood cell-ADA activities expressed by the one normal allelic gene in heterozygotes (including parents and paternal or maternal grandfather or grandmother) and from these values have determined combinations for the pair of ADA activities expressed by the two allelic genes of other family members. These combinations were consistently made in all relatives examined in the two families, and we conclude that several members of each family who were judged to have nil activity in the combinations were heterozygotes for ADA deficiency.