Identification and functional characterisation of genetic variants in OLFM2 in children with developmental eye disorders.

Anophthalmia, microphthalmia, and coloboma are a genetically heterogeneous spectrum of developmental eye disorders and affect around 30 per 100,000 live births. OLFM2 encodes a secreted glycoprotein belonging to the noelin family of olfactomedin domain-containing proteins that modulate the timing of neuronal differentiation during development. OLFM2 SNPs have been associated with open angle glaucoma in a case-control study, and knockdown of Olfm2 in zebrafish results in reduced eye size. From a cohort of 258 individuals with developmental eye anomalies, we identified two with heterozygous variants in OLFM2: an individual with bilateral microphthalmia carrying a de novo 19p13.2 microdeletion involving OLFM2 and a second individual with unilateral microphthalmia and contralateral coloboma who had a novel single base change in the 5' untranslated region. Dual luciferase assays demonstrated that the latter variant causes a significant decrease in expression of OLFM2. Furthermore, RNA in situ hybridisation experiments using human developmental tissue revealed expression in relevant structures, including the lens vesicle and optic cup. Our study indicates that OLFM2 is likely to be important in mammalian eye development and disease and should be considered as a gene for human ocular anomalies.

New variant and expression studies provide further insight into the genotype-phenotype correlation in YAP1-related developmental eye disorders.

YAP1, which encodes the Yes-associated protein 1, is part of the Hippo pathway involved in development, growth, repair and homeostasis. Nonsense YAP1 mutations have been shown to co-segregate with autosomal dominantly inherited coloboma. Therefore, we screened YAP1 for variants in a cohort of 258 undiagnosed UK patients with developmental eye disorders, including anophthalmia, microphthalmia and coloboma. We identified a novel 1 bp deletion in YAP1 in a boy with bilateral microphthalmia and bilateral chorioretinal coloboma. This variant is located in the coding region of all nine YAP1 spliceforms, and results in a frameshift and subsequent premature termination codon in each. The variant is predicted to result in the loss of part of the transactivation domain of YAP1, and sequencing of cDNA from the patient shows it does not result in nonsense mediated decay. To investigate the role of YAP1 in human eye development, we performed in situ hybridisation utilising human embryonic tissue, and observed expression in the developing eye, neural tube, brain and kidney. These findings help confirm the role of YAP1 and the Hippo developmental pathway in human eye development and its associated anomalies and demonstrate its expression during development in affected organ systems.