Evidence for further genetic heterogeneity in nephronophthisis

A new type of nephronophthisis (NPH) has been recently identified in a large Venezuelan kindred: adolescent nephronophthisis (NPH3) causes end-stage renal disease (ESRD) at a median age of 19 years. The responsible gene (NPHP3) maps to 3q21-q22. NPH3 shares with juvenile nephronophthisis (NPH1) the same disease manifestations such as polyuria, polydipsia, and secondary enuresis. Histopathological findings consist of tubular basement membrane changes, cysts at the corticomedullary junction, and a chronic sclerosing tubulointerstitial nephropathy. The only difference is a younger age at ESRD in NPH1 (median age of 13 years) when compared with NPH3.

In order to evaluate whether there might be a fourth locus of isolated nephronophthisis, we studied eight NPH families without extrarenal disease manifestations and without linkage to the NPH1 locus (NPHP1) on chromosome 2q12-q13. ESRD was reached at ages ranging from 7 to 33 years. Individuals were haplotyped with microsatellites covering the genetic locus of NPHP3. Infantile NPH (NPH2) was excluded in all families by the clinical history and histological findings.

In four of the examined families haplotype analysis was compatible with linkage to the NPHP3 locus. In one of these families identity by descent was observed. In contrast, in another four families linkage was excluded for NPHP3.

Four NPH-families were neither linked to NPHP1 nor to NPHP3, indicating further genetic heterogeneity within the group of nephronophthisis. The finding of further genetic heterogeneity in NPH has important implications for genetic counselling.