The horse homolog of congenital aniridia conforms to codominant inheritance

Anterior segment dysgenesis syndrome occurs frequently in Rocky Mountain ho rses and has two distinct ocular phenotypes: (1) large cysts originating fr om the temporal ciliary body or peripheral retina and (2) multiple anterior segment anomalies including ciliary cysts, iris hypoplasia, iridocorneal a dhesions and opacification, nuclear cataract, and megalocornea, To determin e if anterior segment dysgenesis syndrome is heritable in horses we perform ed ophthalmic examinations and collected pedigree information on horses (n = 516) in an extended Rocky Mountain horse pedigree, Logistic regressive se gregation analysis of a subset of animals (n = 337) in which the ocular phe notypes of progeny and both parents were known indicated that the codominan t inheritance model best fit the data. This model predicted cyst phenotype expression in heterorygous animals and multiple anterior segment anomalies in homozygous animals. Several cases of nonpenetrance of the cyst phenotype were detected in one lineage. The close resemblance between the inheritanc e and lesions observed in Small eye mice and rats, humans with congenital a niridia or anterior segment malformation, and horses with anterior segment dysgenesis syndrome supported the conclusion that anterior segment dysgenes is syndrome in the horse may be homologous to similar ophthalmic anomalies in other species.