JOURNAL ARTICLE

Novel OCRL1 mutations in patients with the phenotype of Dent disease

Boris Utsch, Arend Bökenkamp, Marcus R Benz, Nesrin Besbas, Jörg Dötsch, Ingo Franke, Stefan Fründ, Faysal Gok, Bernd Hoppe, Stephanie Karle, Eberhard Kuwertz-Bröking, Guido Laube, Margarita Neb, Matti Nuutinen, Fatih Ozaltin, Wolfgang Rascher, Troels Ring, Velibor Tasic, Joanna A E van Wijk, Michael Ludwig
American Journal of Kidney Diseases 2006, 48 (6): 942.e1-14
17162149

BACKGROUND: Dent disease is an X-linked tubulopathy frequently caused by mutations affecting the voltage-gated chloride channel and chloride/proton antiporter ClC-5. A recent study showed that defects in OCRL1, encoding a phosphatidylinositol 4,5-bisphosphate 5-phosphatase (Ocrl) and usually found mutated in patients with Lowe syndrome, also can provoke a Dent-like phenotype (Dent 2 disease).

METHODS: We investigated 20 CLCN5-negative males from 17 families with a phenotype resembling Dent disease for defects in OCRL1.

RESULTS: In our complete series of 35 families with a phenotype of Dent disease, a mutation in the OCRL1 gene was detected in 6 kindreds. All were novel frameshift (Q70RfsX88 and T121NfsX122, detected twice) or missense mutations (I257T and R476W). None of our patients had cognitive or behavioral impairment or cataracts, 2 classic hallmarks of Lowe syndrome. All patients had mild increases in lactate dehydrogenase and/or creatine kinase levels, which rarely is observed in CLCN5-positive patients, but frequently found in patients with Lowe syndrome. To explain the phenotypic heterogeneity caused by OCRL1 mutations, we performed extensive data-bank mining and extended reverse-transcriptase polymerase chain reaction analysis, which provided no evidence for yet unknown (tissue-specific) alternative OCRL1 transcripts.

CONCLUSION: Mutations in the OCRL1 gene are found in approximately 23% of kindreds with a Dent phenotype. Defective protein sorting/targeting of Ocrl might be the reason for mildly elevated creatine kinase and lactate dehydrogenase serum concentrations in these patients and a clue to suspect Dent disease unrelated to CLCN5 mutations. It remains to be elucidated why the various OCRL1 mutations found in patients with Dent 2 disease do not cause cataracts.

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