[Familial juvenile hyperuricemic nephropathy]

Familial juvenile hyperuricemic nephropathy is a rare autosomal dominant disease. It is characterized by abnormal handling of urate responsible for hyperuricaemia often complicated of gouty arthritis. Renal failure is due to tubulointerstitial nephritis. Ultrasonography sometimes finds renal cysts of variable size and number. Renal histology, although not specific, shows interstitial fibrosis, atrophic tubules, sometimes enlarged and with irregular membrane thickening. Renal failure progresses to end stage between 30 and 60 years of age. Allopurinol treatment is recommended at the early stages of the disease, its efficacy on slowing down the progression of the disease is however not proven. There is genetic heterogeneity in familial juvenile hyperuricemic nephropathy. Uromodulin encoding Tamm-Horsfall protein is the only gene to date identified, responsible in less than half of the families. The described mutations most often concern a cystein and are clustering in exon 4. These mutations result in abnormal retention of the protein in endoplasmic reticulum of Henle loop cells and in reduction of its urinary excretion. The pathophysiology of the disease is however still dubious. Indeed, Tamm-Horsfall protein functions are not well known (anti-infectious role, cristallisation inhibition, immunomodulating role). Knock-out mice do not develop renal phenotype but are more prone to E. coli urinary infections. Uromodulin gene mutations have also been described in medullary cystic kidney disease, an autosomal dominant tubulointerstitial nephropathy, considered at first as a distinct disorder. Genetic progress allowed us to consider familial juvenile hyperuricemic nephropathy and medullary cystic kidney disease as the two facets of a same disease, we should call uromodulin associated kidney diseases. At least two other genes have been implicated in similar clinical presentation: TCF2 and the gene encoding renin.