APRT

APRT refers to adenine phosphoribosyltransferase, an enzyme that catalyzes the transfer of ribose-5-phosphate from PRPP to adenine, producing AMP and pyrophosphate. This reaction is part of the purine salvage pathway, allowing cells to reuse adenine rather than synthesizing it de novo. In humans, the APRT enzyme is encoded by the APRT gene and is located in the cytoplasm.

Mutations in the APRT gene cause APRT deficiency, a rare autosomal recessive metabolic disorder. The deficiency impairs adenine salvage, leading to excess adenine that is oxidized by xanthine oxidoreductase to 2,8-dihydroxyadenine (2,8-DHA). 2,8-DHA is poorly soluble and can crystallize in the urine, forming kidney stones and potentially causing crystalline nephropathy and renal impairment if not treated.

Clinical presentation varies but can include recurrent kidney stones, urinary crystals, or progressive kidney damage. Diagnosis is based on reduced or absent APRT enzyme activity in erythrocytes or other cells, supported by identification of biallelic APRT mutations. Urine analysis or stone analysis showing 2,8-DHA crystals can also aid diagnosis, and genetic testing confirms the cause.

Management focuses on preventing 2,8-DHA formation and its consequences. Allopurinol or febuxostat is used to inhibit the production of 2,8-DHA; maintaining hydration and, in some cases, urinary alkalinization may be recommended to reduce crystal formation. Regular monitoring by metabolic or renal specialists is advised.