89 HEREDITARY RED BLOOD CELL ADENOSINE DEAMINASE OVERPRODUCTION: ASSOCIATION WITH INCREASED LEVELS OF STRUCTURALLY NORMAL ADA mRNA

Abstract

A marked tissue-specific increase in erythrocyte adenosine deaminase activity is associated with an autosomal dominantly inherited hemolytic anemia. Preliminary studies suggested that the defect lay at the level of ADA mRNA translation in red blood cells. We have directly analyzed reticulocyte ADA mRNA from affected individuals. Sequencing of seven proband reticulocyte ADA cDNA clones did not reveal any base changes in coding or non-coding regions. RNase mapping demonstrated that the 5′- and 3′-untranslated regions of reticulocyte and B lymphoblast ADA mRNAs from affected individuals were identical to those of normal B lymphoblasts. However, RNase mapping failed to detect any comparable bands in RNA from control reticulocytes. Northern blot analysis performed under stringent hybridization and washing conditions confirmed a markedly increased amount of reticulocyte ADA mRNA in affected individuals compared to controls. These findings were obscured in the previous study by non-specific hybridization of the ADA cDNA probe to 18s ribosomal RNA. We conclude that the red cell-specific overexpression of ADA probably occurs at the level of transcription in erythroid precursors.