Dent disease is an X-linked renal proximal tubulopathy associated with mutations in the chloride channel gene CLCN5. Lowe syndrome, a multisystem disease characterized by renal tubulopathy, congenital cataracts, and mental retardation, is associated with mutations in the gene OCRL1, which encodes a phosphatidylinositol 4,5-bisphosphate (PIP(2)) 5-phosphatase. Genetic heterogeneity has been suspected in Dent disease, but no other gene for Dent disease has been reported. We studied male probands in 13 families, all of whom met strict criteria for Dent disease but lacked mutations in CLCN5. Linkage analysis in the one large family localized the gene to a candidate region at Xq25-Xq27.1. Sequencing of candidate genes revealed a mutation in the OCRL1 gene. Of the 13 families studied, OCRL1 mutations were found in 5. PIP(2) 5-phosphatase activity was markedly reduced in skin fibroblasts cultured from the probands of these five families, and protein expression, measured by western blotting, was reduced or absent. Slit-lamp examinations performed in childhood or adulthood for all five probands showed normal results. Unlike patients with typical Lowe syndrome, none of these patients had metabolic acidosis. Three of the five probands had mild mental retardation, whereas two had no developmental delay or behavioral disturbance. These findings demonstrate that mutations in OCRL1 can occur with the isolated renal phenotype of Dent disease in patients lacking the cataracts, renal tubular acidosis, and neurological abnormalities that are characteristic of Lowe syndrome. This observation confirms genetic heterogeneity in Dent disease and demonstrates more-extensive phenotypic heterogeneity in Lowe syndrome than was previously appreciated. It establishes that the diagnostic criteria for disorders resulting from mutations in the Lowe syndrome gene OCRL1 need to be revised.

This kindred manifested an X-linked recessive nephrolithiasis with renal failure, a new form of hereditary renal disease. Most of the identifiable physiologic abnormalities occurred after the development of nephrolithiasis and renal insufficiency and may not be of pathogenetic importance.

These findings suggest that mutation in other gene(s) may be responsible for the phenotype of Dent's disease in some patients.

Background/Aims: Dent disease is an X-linked renal proximal tubulopathy associated with mutations in CLCN5 (Dent 1) or OCRL1 (Dent 2). OCRL1 mutations also cause the oculocerebrorenal syndrome of Lowe. Methods: Dent patients with normal sequence for CLCN5 were sequenced for mutations in OCRL1. By analyzing these and all other OCRL1 mutations reported, a model relating OCRL1 mutations to the resulting disease (Dent 2 or Lowe’s) was developed. Results: Six boys with Dent disease had novel OCRL1 mutations: two missense (R301H, G304E) and four mutations predicted to produce premature termination codons (L56DfsX1, S149X, P161PfsX3, and M170IfsX1). These include one of the original patients reported by Dent and Friedman. Slit lamp examinations revealed early cataracts in only one boy with normal vision. None of these Dent 2 patients had metabolic acidosis; 3 had mild mental retardation. Analysis of all known OCRL1 mutations show that Dent 2 mutations fall into two classes that do not overlap with Lowe mutations. Bioinformatics analyses identified expressed OCRL1 splice variants that help explain the variability of those clinical features that distinguish Dent disease from Lowe syndrome. Conclusions:OCRL1 mutations can cause the renal phenotype of Dent disease, without acidosis or the dramatic eye abnormalities typical of Lowe syndrome. We propose a model to explain the phenotypic variability between Dent 2 and Lowe’s based on distinctly different classes of mutations in OCRL1 producing splice variants.

These studies expand the range of mutations identified in this disease, and broaden the phenotypic range to include clinically affected women and the first North American case with severe rickets.