A 9-month-old infant had been in and out of the hospital due to frequent infections. Blood test demonstrated the virtual lack of B and T cells and the almost complete absence of a thymic shadow on a chest X-ray. Measurement of metabolites in the blood would be expected to show elevated levels of which one of the following?
Correct Answer: Deoxyadenosine
Description: The child has inherited a mutation in each copy of the genes for adenosine deaminase and cannot convert adenosine to inosine (and deoxyadenosine to deoxy inosine). The deoxyadenosine is toxic and will accumulate in the blood cells, eventually forming dATP through salvage reactions. The dATP will, in part, inhibit ribonucleotide reductase, and the cells with the high dATP levels will not be able to proliferate when signaled to do so because of the lack of deoxyribonucleotide precursors. This is a form of SCID. Orotic acid builds up in hereditary orotic aciduria, but immune defects are not associated with that condition. Uric acid accumulation leads to gout without affecting the formation of the immune system. NADPH is required for the ribonucleotide reductase reaction, but its levels are not altered, nor is it secreted into the blood in an adenosine deaminase deficiency. dGTP levels do not increase with an adenosine deaminase deficiency.
Category:
Biochemistry
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