From Lowe syndrome to Dent disease: correlations between mutations of the OCRL1 gene and clinical and biochemical phenotypes
Résumé
Mutations of OCRL1 are associated with both the oculocerebrorenal syndrome Lowe, a multi-systemic and Dent-2 disease, a renal tubulopathy. We have identified a mutation in 130 Lowe syndrome families and 6 affected by Dent-2 disease with 51 of these mutations being novel. No founding effect was evidenced for recurrent mutations. Two mutations initially reported as causing Dent-2 disease were identified in patients, including two brothers, presenting with Lowe syndrome thus extending the clinical variability of OCRL1 mutations. mRNA levels, protein content and PiP2-ase activities were analyzed in patient's fibroblasts. Although mRNA levels were normal in cells harbouring a missense mutation, the OCRL1 content was markedly lowered suggesting that enzymatic deficiency resulted mainly from protein degradation rather than a catalytic inactivation as usually reported. Analysis of a splicing mutation that led to the elimination of the initiation codon evidenced the presence of shortened forms of OCRL1 that might result from the use of alternative initiation codons. The specific mapping of the frameshift and nonsense mutations, exclusively identified in exons 1-7 and exons 8-23 respectively for Dent disease and Lowe syndrome together with the possible use of alternative initiation codons might be related to their clinical expression i.e. Lowe syndrome or Dent-2 disease.
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