From OMIM
APRT deficiency is an autosomal recessive metabolic disorder that can lead to accumulation of the insoluble purine 2,8-dihydroxyadenine (DHA) in the kidney, which results in crystalluria and the formation of urinary stones. Clinical features include renal colic, hematuria, urinary tract infection, dysuria, and, in some cases, renal failure. The age at onset can range from 5 months to late adulthood; however, as many as 50% of APRT-deficient individuals may be asymptomatic (summary by Sahota et al., 2001). Two types of APRT deficiency have been described based on the level of residual enzyme activity in in vitro studies of erythrocytes. Type I deficiency is characterized by complete enzyme deficiency in intact cells and in cell lysates, whereas type II deficiency is characterized by complete enzyme deficiency in intact cells, but only a partial deficiency in cell lysates. Type II alleles show reduced affinity for phosphoribosyl pyrophosphate (PRPP) compared to wildtype. In both types, APRT activity is not functional in vivo. Type II deficiency is most common among Japanese. Heterozygotes of either type do not appear to have any clinical or biochemical abnormalities (summary by Sahota et al., 2001).  http://www.omim.org/entry/614723

From MedlinePlus Genetics
Adenine phosphoribosyltransferase (APRT) deficiency is an inherited condition that affects the kidneys and urinary tract. The most common feature of this condition is recurrent kidney stones; urinary tract stones are also a frequent symptom. Kidney and urinary tract stones can create blockages in the urinary tract, causing pain during urination and difficulty releasing urine.

Affected individuals can develop features of this condition anytime from infancy to late adulthood. When the condition appears in infancy, the first sign is usually the presence of tiny grains of reddish-brown material in the baby's diaper caused by the passing of stones. Later, recurrent kidney and urinary tract stones can lead to problems with kidney function beginning as early as mid- to late childhood. Approximately half of individuals with APRT deficiency first experience signs and symptoms of the condition in adulthood. The first features in affected adults are usually kidney stones and related urinary problems. Other signs and symptoms of APRT deficiency caused by kidney and urinary tract stones include fever, urinary tract infection, blood in the urine (hematuria), abdominal cramps, nausea, and vomiting.

Without treatment, kidney function can decline, which may lead to end-stage renal disease (ESRD). ESRD is a life-threatening failure of kidney function that occurs when the kidneys are no longer able to filter fluids and waste products from the body effectively.

The features of this condition and their severity vary greatly among affected individuals, even among members of the same family. It is estimated that 15 to 20 percent of people with APRT deficiency do not have any signs or symptoms of the condition.  https://medlineplus.gov/genetics/condition/adenine-phosphoribosyltransferase-deficiency