Adenine phosphoribosyltransferase deficiency

Adenine phosphoribosyltransferase (APRT) deficiency is an inherited condition that affects the kidneys and urinary tract. Its most common feature is recurrent kidney stones, and urinary tract stones are also frequent; these can block the urinary tract and cause pain on urination and difficulty releasing urine. Features can appear anytime from infancy to late adulthood. In infants the first sign is often tiny grains of reddish-brown material in the diaper caused by passing stones, and about half of affected people first have signs in adulthood. Other signs include fever, urinary tract infection, blood in the urine, abdominal cramps, nausea and vomiting. Without treatment, kidney function can decline and may lead to end-stage renal disease. Severity varies greatly, even within a family, and an estimated 15 to 20 percent of affected people have no signs or symptoms. The condition is caused by mutations in the APRT gene, which reduce or remove the enzyme that converts adenine to adenosine monophosphate; adenine is instead converted to 2,8-dihydroxyadenine, which crystallizes in urine to form brownish stones and is toxic to the kidneys. It is inherited in an autosomal recessive pattern. APRT deficiency is estimated to affect 1 in 27,000 people in Japan and 1 in 50,000 to 100,000 in Europe, and its prevalence elsewhere is unknown.