Introduction - what is aniridia: Epidemiology, clinical features and genetic implications

Aniridia is characterized by congenital hypoplasia of the iris and alterations of other structures of the eye, including cornea, crystalline lens, optic nerve, and retina. Patients suffer from early onset of nystagmus, photophobia, amblyopia, and severely decreased visual acuity. In 70 % of cases, aniridia is inherited in an autosomal dominant fashion, while it is sporadic in about 30 % of cases. In the great majority of patients, this disease is caused by heterozygous mutations in the PAX6 gene, which encodes for a transcription factor, very well conserved along phylogeny and critical for eye morphogenesis. Aniridia-causing mutations can be of various types, from single base substitution to large chromosomal deletions. All of them determine a loss of function of the gene. When chromosomal deletions are large and involve the WT1 gene, subjects suffer from the WAGR (Wilm's tumor, Aniridia, Genitourinary abnormalities, mental Retardation) syndrome. Both prenatal or postnatal genetic test is available. It is indicated when isolated or WAGR is present, as well as other eye disorders potentially associated with PAX6 mutations. Genetic testing is useful for differentiating aniridia caused by mutations only in the PAX6 gene from those forms associated with the deletion of contiguous genes.