Contributor: Gordon K. Klintworth
Aniridia is congenital developmental anomaly of the iris. Most cases are bilateral and have an autosomal dominant mode of inheritance and are caused by mutations in the PAX6 gene. Sporadic cases of aniridia are occasionally associated with Wilms tumor, microcephaly, mental retardation, hemihypertrophy, and genital abnormalities (WAGR syndrome). Aniridia may also be associated with Peters anomaly, synophthalmia, and cyclopia. Glaucoma develops in <50% of cases. In some cases it is an open angle glaucoma [glaucoma - open angle]; in others the anterior chamber angle is closed [glaucoma - closed angle]. The glaucoma tends to become apparent >age 5 years, but before the patient is 20 years old. The onset is later than in primary infantile glaucoma [glaucoma - primary infantile] and in contrast to primary infantile glaucoma the cornea does not usually enlarge. The glaucoma seems to be progressive and its severity correlates with the degree of the adhesions between the peripheral iris and the trabecular meshwork. Aside from glaucoma several other lesions seem to contribute to decreased visual acuity (macular abnormalities, nystagmus, cataracts [cataract], as well corneal opacification and corneal vascularization [neovascularization - cornea]). Aniridia is associated with a variety of ocular abnormalities (including ciliary body hypoplasia, cataract, secondary angle closure glaucoma [glaucoma - secondary closed angle], optic nerve hypoplasia [hypoplasia - optic nerve], macular hypoplasia [hypoplasia - macula]). The sporadic type is associated with deletion of the short arm of chromosome 11 (aniridia-2 locus of 11p13).
While 1-3% of patients with Wilms tumor have aniridia, ~25-33% of children with aniridia develop Wilms tumor. This relationship of Wilms tumor and aniridia has also been reported in the familial, autosomal dominant mode of inheritance. A locus on chromosome 1 linked to the Rh Duffy locus has been documented. Several years ago aniridia -1 was thought to be linked to chromosome 2 (2p) near the acid phosphatase-1 locus, but these cases were later shown to be linked to the site as aniridia-2. Aniridia and deafness have been reported.