EPHA2 biallelic disruption causes syndromic complex microphthalmia with iris hypoplasia.

Disruption of any of the ocular development steps can result in ocular defects such as microphthalmia, coloboma and anterior segment dysgeneses including aniridia and cataract. All of these anomalies can be isolated or seen in association with each other. Except for aniridia (almost exclusively due to PAX6 mutations), most of these congenital ocular malformations are related to a wide genetic heterogeneity, as hundreds of genes are implied in ocular development. Here we describe a patient presenting with bilateral microphthalmia, congenital cataract, corneal dystrophy and iris hypoplasia, associated with extra-ocular features, who underwent an analysis of 119 ocular development related genes. Genetic testing revealed the presence of two truncating variants in the EPHA2 gene. While EPHA2 mutations are mainly known to be responsible for isolated dominant congenital cataract, we report here the first case of complex anterior segment dysgenesis caused by a biallelic EPHA2 mutation. This gene should be screened in case of aniridia with a negative PAX6 testing, as the ocular features of our patient clearly mimic those of PAX6 mutated patients. This observation enlarges the phenotype associated with EPHA2 variations and rise the insight of a possible PAX6-EPHA2 interaction that needs further investigations. Moreover, despite a great variability in ocular and extra-ocular phenotypes, mutations type and inheritance pattern, a possible genotype-phenotype correlation can also be drawn for this gene.

First evidence of SOX2 mutations in Peters' anomaly: Lessons from molecular screening of 95 patients.

Peters' anomaly (PA) is a rare anterior segment dysgenesis characterized by central corneal opacity and irido-lenticulo-corneal adhesions. Several genes are involved in syndromic or isolated PA (B3GLCT, PAX6, PITX3, FOXE3, CYP1B1). Some copy number variations (CNVs) have also been occasionally reported. Despite this genetic heterogeneity, most of patients remain without genetic diagnosis. We retrieved a cohort of 95 individuals with PA and performed genotyping using a combination of comparative genomic hybridization, whole genome, exome and targeted sequencing of 119 genes associated with ocular development anomalies. Causative genetic defects involving 12 genes and CNVs were identified for 1/3 of patients. Unsurprisingly, B3GLCT and PAX6 were the most frequently implicated genes, respectively in syndromic and isolated PA. Unexpectedly, the third gene involved in our cohort was SOX2, the major gene of micro-anophthalmia. Four unrelated patients with PA (isolated or with microphthalmia) were carrying pathogenic variants in this gene that was never associated with PA before. Here we described the largest cohort of PA patients ever reported. The genetic bases of PA are still to be explored as genetic diagnosis was unavailable for 2/3 of patients. Nevertheless, we showed here for the first time the involvement of SOX2 in PA, offering new evidence for its role in corneal transparency and anterior segment development.