Abstract
A severe deficiency of adenosine deaminase (ADA) is associated with an autosomal recessive form of severe combined immunodeficiency disease, while subjects with partial enzyme activity are immunocompetent. To further our understanding of ADA deficiency, specific mRNA levels and rates of protein turnover were determined in partial. ADA deficient cells and enzyme expression of cloned human ADA cDNA was assessed. Genetic expression of ADA in cultured B lymphoblast cell lines from 4 partially (5-50% activity) ADA deficient subjects showed normal to 2-fold normal ADA mRNA levels (Northern blot). Among these cell lines enzyme synthesis varied from 165% to 15% of normal. ADA degradation rates were 1.5 to almost 3 times faster than normal, consistent with the complete absence of the enzyme in patient erythrocytes. Cloned normal human ADA cDNA inserted into an SV40 based expression vector was shown to generate human ADA activity in monkey kidney (COS) host cells (7-fold over host). An unexpected finding was the identification of another normal human ADA cDNA construct which failed to produce human ADA activity or immunoreactive protein upon transfection. DNA sequence analysis revealed a single nucleotide substitution within this clone that altered the predicted sequence of ADA protein at amino acid 50.
Thus, our studies define transcriptional, translational and post-translational defects in partial ADA deficiency and identify a point mutation in ADA cDNA which mimics the phenotype expressed in severe ADA deficiency.
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Daddono, P., Orkin, S. & Kelley, W. EXPRESSION DEFECTS OF MUTANT HUMAN ADENOSINE DEAMINASE: 42. Pediatr Res 19, 750 (1985). https://doi.org/10.1203/00006450-198507000-00062
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DOI: https://doi.org/10.1203/00006450-198507000-00062