1. We have compared urinary purine excretion by two different methods in three separate paediatric disorders of purine metabolism: purine nucleoside phosphorylase deficiency, adenosine deaminase deficiency and adenine phosphoribosyltransferase deficiency.

2. The abnormal purines identified in each case were specific for the defect and directly related to it: adenine in adenine phophoribosyltransferase deficiency; the abnormal nucleosides inosine, guanosine and their corresponding deoxyribosides in purine nucleoside phosphorylase deficiency; deoxyadenosine in adenosine deaminase deficiency, the latter having previously been identified erroneously as adenine after degradation in the acidic conditions used.

3. Deoxyriboside excretion was specific for the two defects associated with immunodeficiency; adenine for adenine phosphoribosyltransferase deficiency and 2,8-dihydroxyadenine urolithiasis. The results obtained by a quantitative method were reflected in a simple rapid qualitative technique, isotachophoresis of the urine.

4. Purine overexcretion (principally inosine) was evident only in purine nucleoside phosphorylase deficiency, which emphasizes the importance of hypoxanthine salvage for the overall control of purine production in man. In none of these disorders was any inhibition of pyrimidine biosynthesis as reflected by oroticaciduria noted. Orotic acid excretion was within normal limits in all cases.

5. From these results it is suggested that the associated immunodeficiency in adenosine deaminase deficiency and purine nucleoside phosphorylase deficiency relates directly to the intracellular accumulation of 2′-deoxyribosides and not indirectly to an inhibitory effect on pyrimidine metabolism.

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