PAX6 helps to control expression of other key genes in differentiation of structures of the eye and plays a direct role in the establishment of eye fields and formation of the lens. PAX6 is one of the main regulatory molecules in optic development. OTX2 genes have considerable variable expressivity in phenotypic presentation.Įxtraocular manifestations associated with OTX2 mutations include learning disability, developmental delay, and structural abnormalities of brain structures. OTX2 encodes a transcription factor that is implicated in differentiation of the optic vesicle and formation of the retina and assists in the development of pigmentation. Mutations in the OTX2 gene are also commonly implicated in a wide range of ocular malformations and occurs in 3% of patients with bilateral anophthalmia. Extraocular manifestations of SOX2 anophthalmia syndrome include learning disabilities, growth and motor delays, seizures, and malformation of CNS structures such as the hippocampus, pituitary gland, and corpus callosum. Ĭases of anophthalmia with identified SOX2 mutations are characteristically bilateral and may occur as part of SOX2 anophthalmia syndrome. The SOX2 gene encodes a transcription factor that plays a central role in differentiation of lens tissue from surface ectoderm. These are most commonly de novo, loss of function mutations with a heterozygous genotype. Mutations in SOX2 are the most common genetic cause of anophthalmia and are present in up to 40% of cases of anophthalmia. Mutations in SOX2, OTX2, PAX6, STRA6, ALDH1A3, RARB, VSX2, RAX, FOXE3, BMP4, BMP7, GDF3, GDF6, ABCB6, ATOH7, C12orf57, TENM3 (ODZ3), and VAX1 have all been implicated in abnormal ocular development and the pathogenesis of anophthalmia. Several genes are implicated in the development of anophthalmia. Anophthalmia results from failed development of optic structures, which can occur due to a defect in neural tube induction, formation of the optic vesicle and/or cup, or by secondary breakdown of previously formed optic tissues. Possible contributing environmental factors include infections (such as several TORCH infections including CMV, rubella, Parvovirus B19, and toxoplasmosis), nutritional deficiencies (vitamin A), and in utero exposure to toxins (alcohol, thalidomide, warfarin). The genetics of anophthalmia are discussed below. EtiologyĪnophthalmia has a complex etiology that is not fully elucidated, but is thought to include both genetic and environmental components.
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