A rare genetic optic nerve disorder characterized by visual impairment or blindness resulting from varying degrees of underdevelopment of the optic nerve or even complete absence of the optic nerve, ganglion cells, and central retinal vessels. It may be unilateral, typically with otherwise normal brain development, or bilateral with accompanying severe and widespread congenital malformations of the central nervous system.

The phenotypic spectrum of SOX2 disorder includes anophthalmia and/or microphthalmia, brain malformations, developmental delay / intellectual disability, esophageal atresia, hypogonadotropic hypogonadism (manifest as cryptorchidism and micropenis in males, gonadal dysgenesis infrequently in females, and delayed puberty in both sexes), pituitary hypoplasia, postnatal growth delay, hypotonia, seizures, and spastic or dystonic movements.

Coloboma is an ocular birth defect resulting from abnormal development of the eye during embryogenesis. It is defined as a congenital defect in any ocular tissue, typically presenting as absent tissue or a gap, at a site consistent with aberrant closure of the optic fissure. Failure of fusion can lead to coloboma of one or multiple regions of the inferior portion of the eye affecting any part of the globe traversed by the fissure, from the iris to the optic nerve, including the ciliary body, retina, and choroid. Coloboma is also frequently associated with small (microphthalmic) or absent (anophthalmic) eyes as part of an interrelated spectrum of developmental eye anomalies, and can affect either one or both eyes (summary by Kelberman et al., 2014). Microphthalmia/coloboma-12 (MCOPCB12) is characterized by inter- and intrafamilial variability. In addition to microphthalmia and coloboma, other ocular anomalies include iris hypoplasia, aphakia or small lens, lens subluxation, congenital cataract, microcornea, and sclerocornea. Some patients also exhibit neurodevelopmental anomalies (Deml et al., 2016; Williamson et al., 2020). For a discussion of genetic heterogeneity of colobomatous microphthalmia, see MCOPCB1 (300345).