Rare Kidney Stones Consoritum

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Learn More - adenine phosphoribosyltransferase (APRT) deficiency

What is APRT Deficiency?

Adenine phosphoribosyltransferase (APRT) deficiency is an underrecognized genetic form of kidney stones and/or kidney failure. A few patients may have eye complaints. Patients with APRT deficiency are not all affected in the same way. Most untreated patients have repeated episodes of kidney stones and/or impaired kidney function while a subset of patients may be free of symptoms. 

Who gets APRT Deficiency?

APRT deficiency has been reported world-wide in all ethnic groups and affects both children and adults. Most reported cases come from Japan, France and Iceland but an increasing number of patients are being identified in other countries, including the United States.

What causes APRT Deficiency?

APRT deficiency is an inborn error of adenine metabolism causing high levels of 2,8-dihydroxyadenine in the urine, leading to kidney stones and even kidney failure in untreated patients.

How is APRT Deficiency diagnosed?

APRT deficiency should be suspected in all patients with repeated episodes of kidney stones that are not visualized on a regular x-ray (radiolucent stones), in patients with unexplained impairment of kidney function and in young children with a history of reddish-brown diaper stains. The 2,8-dihydroxyadenine crystals should be easily detected by urine microscopy. The diagnosis can also be made with genetic testing or measurement of APRT enzyme activity. Furthermore, analysis of 2,8-DHA crystals and stone material may confirm the diagnosis.

What is/is there treatment for APRT Deficiency?

The drug allopurinol effectively prevents kidney stones and impairment of kidney function in patients with APRT deficiency. Most patients require 300-400 mg of allopurinol daily. The maximum suggested daily dose is 600-800 mg. In patients who do not tolerate allopurinol, treatment with febuxostat (Uloric®) should be considered.

Frequently Asked Questions about adenine phosphoribosyltransferase deficiency (APRT)

I have APRT deficiency. Are my children at risk?

Adenine phosphoribosyltransferase (APRT) deficiency is inherited in an autosomal recessive manner, meaning that individuals who develop the disease have received one defective copy of the APRT gene from each parent. Thus that if both parents have the defective gene, 25% of the children will have the disease, 50% will be asymptomatic but carry the defective gene, and 25% neither carry the defective gene nor have APRT deficiency. If only one parent has the disease the risk for the children is minimal.

I have kidney stone disease. Is it possible that I have APRT deficiency?

If you have kidney stones that are not seen on a regular x-ray film but are detected with ultrasound or computerized tomography (CT) scan, the stones will most likely be composed of uric acid. However,  APRT deficiency and 2,8-dihydroxyadeninuria is also a possible cause of the kidney stones. If you have radiolucent kidney stones you should ask your physician to look for the typical 2,8-dihydroxyadenine crystals in your urine with a microscope (http//: hyperlink to the RKSC website where we will publish a number of photomicrographs of the crystals).

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