Genetic architecture of retinoic-acid signaling-associated ocular developmental defects.

Ocular developmental anomalies are among the most common causes of severe visual impairment in newborns (combined incidence 1-2:10,000). They comprise a wide range of inborn errors of eye development with a spectrum of overlapping phenotypes and they are frequently associated with extraocular malformations, neuropsychomotor developmental delay and/or intellectual disabilities. Many studies from model organisms have demonstrated the role of retinoic acid (RA) during organogenesis, including eye development, and have revealed the wide spectrum of malformations that can arise from defective RA signaling. However, genes coding for homeobox proteins and morphogenetic factors were implicated in anomalies of ocular development long before genes coding for RA-signaling proteins. The purpose of this review is to discuss current knowledge about the highly complex genetic architecture of RA-signaling-associated ocular developmental anomalies in humans. Despite less than a dozen genes identified thus far, all steps of RA-signaling, from vitamin A transport to target cells to transcriptional activation of RA targets, have been implicated. Furthermore, the majority of these genetic disorders are associated with both dominant and recessive inheritance patterns and a wide spectrum of ocular malformations, which can dominate the phenotype or represent one of many features. Although some genotype-phenotype correlations are described, in many cases, the variability of clinical expression cannot be accounted for by the genotype alone. This observation and the large number of unsolved cases suggest that the relationship between RA signaling and eye development deserves further investigation.

Implication of non-coding PAX6 mutations in aniridia.

There is an increasing implication of non-coding regions in pathological processes of genetic origin. This is partly due to the emergence of sophisticated techniques that have transformed research into gene expression by allowing a more global understanding of the genome, both at the genomic, epigenomic and chromatin levels. Here, we implemented the analysis of PAX6, whose coding loss-of-function variants are mainly implied in aniridia, by studying its non-coding regions (untranslated regions, introns and cis-regulatory sequences). In particular, we have taken advantage of the development of high-throughput approaches to screen the upstream and downstream regulatory regions of PAX6 in 47 aniridia patients without identified mutation in the coding sequence. This was made possible through the use of custom targeted resequencing and/or CGH array to analyze the entire PAX6 locus on 11p13. We found candidate variants in 30 of the 47 patients. 9/30 correspond to the well-known described 3' deletions encompassing SIMO and other enhancer elements. In addition, we identified numerous different variants in various non-coding regions, in particular untranslated regions. Among these latter, most of them demonstrated an in vitro functional effect using a minigene strategy, and 12/21 are thus considered as causative mutations or very likely to explain the phenotypes. This new analysis strategy brings molecular diagnosis to more than 90% of our aniridia patients. This study revealed an outstanding mutation pattern in non-coding PAX6 regions confirming that PAX6 remains the major gene for aniridia.

Abnormal respiratory cilia in non-syndromic Leber congenital amaurosis with CEP290 mutations.

BACKGROUND: Leber congenital amaurosis (LCA) is the earliest and most severe inherited retinal degeneration. Isolated forms of LCA frequently result from mutation of the CEP290 gene which is expressed in various ciliated tissues. METHODS: Seven LCA patients with CEP290 mutations were investigated to study otorhinolaryngologic phenotype and respiratory cilia. Nasal biopsies and brushing were performed to study cilia ultrastructure using transmission electron microscopy and ciliary beating using high-speed videomicroscopy, respectively. CEP290 expression in normal nasal epithelium was studied using real-time RT-PCR. RESULTS: When electron microscopy was feasible (5/7), high levels of respiratory cilia defects were detected. The main defects concerned dynein arms, central complex and/or peripheral microtubules. All patients had a rarefaction of ciliated cells and a variable proportion of short cilia. Frequent but moderate and heterogeneous clinical and ciliary beating abnormalities were found. CEP290 was highly expressed in the neural retina and nasal epithelial cells compared with other tissues. DISCUSSION: These data provide the first clear demonstration of respiratory cilia ultrastructural defects in LCA patients with CEP290 mutations. The frequency of these findings in LCA patients along with the high expression of CEP290 in nasal epithelium suggest that CEP290 has an important role in the proper development of both the respiratory ciliary structures and the connecting cilia of photoreceptors. The presence of respiratory symptoms in patients could represent additional clinical criteria to direct CEP290 genotyping of patients affected with the genetically heterogeneous cone-rod dystrophy subtype of LCA.

Application of intron 9 and intron 25 dinucleotide repeats of the factor VIII gene for carrier diagnosis in haemophilia A.

We describe the usefulness of two dinucleotide repeats located in intron 9 and in intron 25 of the factor VIII gene for carrier diagnosis of haemophilia A. We analyzed 100 unrelated Spanish women and 34 women from haemophilia A (HA) families in whom known intragenic markers were unhelpful in determining their carrier status. The heterozygosity rate of intron 9 and intron 25 markers in the 100 control women was lower (0.28 and 0.38, respectively) than the values obtained with common markers routinely used in our laboratory. However, the application of intron 9 and intron 25 markers was effective in identifying the at-risk X chromosome in 11 of 34 (32%) of the uninformative women from HA families. The combined use of these repeats with current markers may facilitate the identification of the X chromosome in HA families for application in carrier, prenatal and pre-implantation diagnoses.