Expanding CEP290 mutational spectrum in ciliopathies

Abstract

Ciliopathies are an expanding group of rare conditions characterized by multiorgan involvement, that are caused by mutations in genes encoding for proteins of the primary cilium or its apparatus. Among these genes, CEP290 bears an intriguing allelic spectrum, being commonly mutated in Joubert syndrome and related disorders (JSRD), Meckel syndrome (MKS), Senior-Loken syndrome and isolated Leber congenital amaurosis (LCA). Although these conditions are recessively inherited, in a subset of patients only one CEP290 mutation could be detected. To assess whether genomic rearrangements involving the CEP290 gene could represent a possible mutational mechanism in these cases, exon dosage analysis on genomic DNA was performed in two groups of CEP290 heterozygous patients, including five JSRD/MKS cases and four LCA, respectively. In one JSRD patient, we identified a large heterozygous deletion encompassing CEP290 C-terminus that resulted in marked reduction of mRNA expression. No copy number alterations were identified in the remaining probands. The present work expands the CEP290 genotypic spectrum to include multiexon deletions. Although this mechanism does not appear to be frequent, screening for genomic rearrangements should be considered in patients in whom a single CEP290 mutated allele was identified.

Fig. 1

Characterization of the CEP290 gene deletion in COR001 family. a: CEP290 exon dosage in the proband showing the heterozygous deletion of exons 42 to 54. b: Measurement of CEP290 mRNA expression levels showing a reduction of about 50% in the father and 80% in the proband compared with those of normal control. [Color figure can be viewed in the online issue, which is available at www.interscience.wiley.com].

Fig. 2

Characterization of the deletion breakpoints in COR001 family. a: Dosage analysis of CEP290 neighbouring genes showing the heterozygous deletion of all C12orf29 exons and of C12orf50 exons 1 to 3. b: schematic representation of the genomic region enclosing CEP290, C12orf29 and C12orf50 genes: open and solid triangles represent exons with ratio < 0.6 and between 0.8 and 1.2, respectively. c: agarose gel electrophoresis showing the ~700 bp fragment obtained with genomic primers located adjacent to the supposed deletion breakpoints. d: top schematic representation of the breakpoints. Bottom electropherogram of the fragment across the breakpoints, showing the newly generated junction between C12orf50 intron 3 and CEP290 intron 41 sequences. [Color figure can be viewed in the online issue, which is available at www.interscience.wiley.com]