Adenine phosphoribosyltransferase (APRT) deficiency is characterized by excessive production and renal excretion of 2,8-dihydroxyadenine (DHA), which leads to kidney stone formation and crystal-induced kidney damage (i.e., DHA crystal nephropathy) causing acute kidney injury episodes and progressive chronic kidney disease (CKD). Kidney stones, the most common clinical manifestation of APRT deficiency, can occur at any age; in at least 50% of affected persons symptoms do not occur until adulthood. If adequate treatment is not provided, approximately 20%-25% of affected individuals develop end-stage renal disease (ESRD), usually in adult life.

Renal hypouricemia is characterized by impaired uric acid reabsorption at the apical membrane of proximal renal tubule cells. The syndrome is not lethal and may be asymptomatic. However, it is accompanied by nephrolithiasis and exercise-induced acute renal failure in about 10% of patients (Ichida et al., 2008). Genetic Heterogeneity of Renal Hypouricemia See also RHUC2 (612076), which is caused by mutation in the SLC2A9 gene (606142).

The Finnish type of systemic amyloidosis is characterized clinically by a unique constellation of features including lattice corneal dystrophy, and cranial neuropathy, bulbar signs, and skin changes. Some patients may develop peripheral neuropathy and renal failure. The disorder is usually inherited in an autosomal dominant pattern; however, homozygotes with a more severe phenotype have also been reported (Meretoja, 1973). Finnish hereditary amyloidosis, also known as Meretoja syndrome or AGel amyloidosis, is one of the most common diseases in the Finnish disease heritage. Symptoms commonly appear by age 40, with the first finding usually corneal lattice dystrophy (CLD), diagnosed by an ophthalmologist. Impaired vision, polyneuropathy, facial nerve paresis, and cutis laxa follow. These symptoms may develop slowly and simultaneously, since amyloid accumulates systemically at a constant rate (summary by Nikoskinen et al., 2015). For a discussion of genetic heterogeneity of hereditary systemic amyloidosis, see AMYLD1 (105210).

Phosphoribosylpyrophosphate synthetase (PRS) superactivity comprises two phenotypes, both characterized by hyperuricemia and hyperuricosuria. The mild phenotype (~75% of affected males) with onset in the second or third decade of life is typically limited to these biochemical findings, whereas the severe phenotype (~25% of affected males) with onset in the first decade of life has in addition to these biochemical findings variable combinations of developmental delay (DD) / intellectual disability (ID), sensorineural hearing loss, hypotonia, and ataxia. In the mild phenotype, uric acid crystalluria or a urinary stone is commonly the first clinical finding, followed later by gouty arthritis if serum urate concentration is not controlled.