Heterozygous deletions of noncoding parts of the gene cause retinitis pigmentosa via reduced gene expression.

PURPOSE

Heterozygous mutations in the gene , encoding a pre-mRNA splicing factor, cause autosomal dominant retinitis pigmentosa (adRP) with reduced penetrance. At the molecular level, pathogenicity results from haploinsufficiency, as the largest majority of such mutations trigger nonsense-mediated mRNA decay or involve large deletions of coding exons. We investigated genetically two families with a history of adRP, one of whom showed incomplete penetrance.

METHODS

All patients underwent thorough ophthalmological examination, including electroretinography (ERG) and Goldmann perimetry. Array-based comparative genomic hybridization (aCGH) and multiplex ligation-dependent probe amplification (MLPA) were used to map heterozygous deletions, while real-time PCR on genomic DNA and long-range PCR allowed resolving the mutations at the base-pair level. transcripts were quantified with real-time PCR on patient-derived lymphoblastoid cell lines.

RESULTS

We identified two independent deletions affecting the promoter and the 5' untranslated region (UTR) of but leaving its coding sequence completely unaltered. Analysis of mRNA from lymphoblastoid cell lines from one of these families showed reduced levels of expression in patients versus controls, probably due to the heterozygous ablation of its promoter sequences.

CONCLUSIONS

In addition to reporting the identification of two novel noncoding deletions in , this study provides strong additional evidence that mRNA-mediated haploinsufficiency is the primary cause of pathogenesis for -linked adRP.