[Nephronophthisis]

Nephronophthisis is an autosomal recessive tubulointerstitial nephropathy leading to end-stage renal failure during adolescence or early adulthood. Initial symptoms of pitressoresistant polyuria and polydipsia start around 3 years of age, increase over the following years and are often responsible for growth retardation. Renal function declines slowly and end-stage renal failure occurs around 12 years of age in most cases. At ultrasound examination, kidneys have a normal or slightly decreased size, parenchymal echogenicity is increased and the differentiation is reduced. When they are present, medullary cysts are an important feature. Renal biopsy shows atropic or dilated tubules, with irregular thickened basal membranes. Interstitial fibrosis and glomerular sclerosis develop progressively. Various extrarenal abnormalities have been reported in association with nephronophthisis; the most frequent is congenital amaurosis. The most recent advance is the localization of a gene (NPH1) on chromosome 2q13. Deletions in this gene have been shown in about 80% of patients with isolated renal involvement. Such deletions have never been reported when nephronophthisis is associated with congenital amaurosis. The evidence of a deletion in NPH1 gene now allows the diagnosis of nephronophthisis to be performed without renal biopsy. When a delation has been demonstrated in one child, the identification of the deletion in siblings allows to determine those who are affected and those who are not, to propose a reliable prenatal diagnosis.