THE MOLECULAR BASIS FOR THE HEREDITARY OVERPRODUCTION OF ADENOSINE DEAMINASE: 32

Abstract

A marked increase in erythrocyte adenosine deaminase (ADA) activity has been associated with chronic hemolytic anemia and decreased erythrocyte ATP levels (Valentine et al., Science 1977). This defect is inherited as an autosomal dominant trait specific for erythroid cells. The kinetic and physicochemical properties of ADA are normal, suggesting the cell line-specific overproduction of a normal enzyme. We have investigated the molecular basis of this defect in erythrocytes and lymphoid cells from an affected individual. The proband's erythrocytes had a 70-fold increase in ADA specific activity and a 30-fold increase in immunologic cross-reacting material (CRM) as measured by a solid-phase radioimmunoassay. Southern blot analysis of genomic DNA using a full-length ADA cDNA probe revealed no evidence of ADA gene amplification or rearrangement. Northern blots of reticulocyte RNA did not demonstrate correspondingly increased levels of ADA-specific RNA. RNA from control reticulocytes hybridized with the ADA cDNA probe in three distinct bands at 5.8 kb, 3.0 kb, and 2.0 kb. The proband's reticulocyte RNA differed from controls in that the 3.0 kb band was replaced by a 2.0 kb band. Lymphoblast ADA specific activity, CRM, and RNA were similar to those in normal B lymphoblast controls. We conclude that there is a true overproduction of ADA protein which is specific for red cells and which may be mediated at the translational rather than the transcriptional level.