Genetic causes of optic nerve hypoplasia
Optic nerve hypoplasia (ONH) is the most common congenital optic nerve anomaly and a leading cause of blindness in the USA. Although most cases of ONH occur as isolated cases within their respective families, the advancement in molecular diagnostic technology has made us realise that a substantial fraction of cases has identifiable genetic causes, typically de novo mutations. An increasing number of genes has been reported, mutations of which can cause ONH. Many of the genes involved serve as transcription factors, participating in an intricate multistep process critical to eye development and neurogenesis in the neural retina. This review will discuss the respective genes and mutations, human phenotypes, and animal models that have been created to gain a deeper understanding of the disorders. The identification of the underlying gene and mutation provides an important step in diagnosis, medical care and counselling for the affected individuals and their families. We envision that future research will lead to further disease gene identification, but will also teach us about gene–gene and gene–environment interactions relevant to optic nerve development. How much of the functional impairment of the various forms of ONH is a reflection of altered morphogenesis versus neuronal homeostasis will determine the prospect of therapeutic intervention, with the ultimate goal of improving the quality of life of the individuals affected with ONH.