Idiopathic renal hypouricaemia (IRH), an autosomal recessive disorder, is an uncommon disease that presents with an increase in uric acid excretion. Most patients with IRH have homozygous deleterious mutations in the SLC22A12 gene that encodes for URAT1 protein. Gout is a multifactorial metabolic disease caused by the deposition of urate crystals. This study describes a patient with high levels of uric acid, primary gout and a novel SLC22A12 gene mutation, which is associated to IRH. The patient showed a 1 bp homozygous insertion (680insG) that resulted in substitution of threonine instead of alanine and in a premature stop codon. This finding provides information about the influence of environmental and/or epigenetic factors in Mendelian inheritance.

Idiopathic renal hypouricaemia (IRH) is an autosomal recessive disorder characterised by increased uric acid excretion.¹ The main biochemical defect is abnormal uric acid transport at the proximal tubule. URAT protein seems to be the major mechanism regulating blood urate levels.^2,3 Most patients with IRH (Online Mendelian Inheritance in Man 607 096) harbour homozygous deleterious mutations in the SLC22A12 gene, which encodes for URAT1 protein.² The major clinical manifestation of IRH is the presence of uric acid stones in the urinary tract.⁴ Around 50% of patients with IRH are Japanese.

Gout is a multifactorial metabolic disease caused by the deposition of urate crystals that produce characteristic joint inflammation. Hyperuricaemia is the most important risk factor for gout and, in 90% of patients, is secondary to renal uric acid under-excretion. SLC22A12 has been studied in patients with gout, the mutation W258X is observed in a healthy population but in none of …