Adenine phosphoribosyltransferase (APRT) deficiency is a rare form of nephrolithiasis. The outcome can be good if diagnosed early and treated properly.
Inheritance: autosomal recessive
The prevalence is high in people of Icelandic descent.
Mechanism: formation of 2,8-dihydroxyadenine (2,8-DHA) which is poorly soluble in the urine. APRT is involved in the formation of adenosine monosphosphate from adenine. In the absence of APRT activity adenine accumulates and is metabolized by xanthine dehydrogenase to 2,8-DHA.
Clinical features:
(1) recurrent episodes of nephrolithiasis
(2) variable risk for urinary tract infections
(3) development of chronic renal insufficiency
Laboratory findings:
(1) brown spheres in the urine
(2) stones a birefingent with pseudo-Maltese cross under polarized light
(3) reduced APRT enzyme activity in red blood cell lysate
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