Genomic duplications in anophthalmia, microphthalmia and coloboma

PROJECT SUMMARY Microphthalmia, anophthalmia and coloboma (MAC) is a group of severe ocular phenotypes characterized by a reduction in size or absence of the eye or a gap (hole) involving various ocular structures. The success rate for identifying a genetic diagnosis for MAC spectrum remains incomplete, making the discovery of novel mechanisms an important priority. Copy number variations (CNVs) are deletions or duplications of genomic segments that can be inherited or occur as dominant de novo variants. There is a growing list of developmental phenotypes associated with CNVs, indicating that dosage imbalance represents an important factor in human disease. Within this group, the contribution of dosage gain variants remains underappreciated due to many factors including the involvement of multiple genes necessitating complex functional studies. In this proposal, we will combine our expertise in MAC and the zebrafish model to reveal novel mechanisms of these debilitating human phenotypes. We present evidence for the association of dosage gain at two different genomic regions, 20q11 and 3q29, with isolated and syndromic MAC, with multiple affected families identified in our cohort for both loci. We will utilize our extensive collection of DNA samples from individuals affected with MAC to further define the contribution of these and other candidate regions to human disease, as well as to discover novel disease-causing dosage-sensitive loci. Specifically, we will: 1) identify the driver gene(s) and pathway(s) involved in phenotypes associated with 20q11 dosage variation by generating and studying dosage gain/loss models for the zebrafish id1, bcl2l1 and tpx2 genes, identified as top candidates within the region; 2) reveal driver gene(s) and pathway(s) involved in phenotypes associated with 3q29 dosage variation by exploring dosage gain/loss models for zebrafish rubcn, dlg1 and/or bdh1 genes, located in the affected human region; and 3) uncover critical dosage-sensitive regions involved in human MAC spectrum by additional mapping of previously identified CNVs as well as exploring a large cohort (760 samples from affected individuals and their relatives) of extensively tested but unexplained MAC families, followed by dissection of novel candidate regions in zebrafish. The successful completion of this project will identify novel factors in human ocular development, both genomic regions/genes and affected pathways, and generate robust animal models of these complex human phenotypes.