The horse homolog of congenital aniridia conforms to codominant inheritance.

The research examines a common eye disease in Rocky Mountain horses, known as Anterior Segment Dysgenesis Syndrome. It suggests based on pedigree information and ophthalmic examinations that this disease conforms to a codominant inheritance model and could be similar to certain eye abnormalities found in other species like mice, rats, and humans.

Understanding Anterior Segment Dysgenesis Syndrome

• Anterior Segment Dysgenesis Syndrome is a disorder frequently seen in Rocky Mountain horses. It presents two distinctive ocular (related to the eye) characteristics: large cysts that grow from the ciliary body or the peripheral retina, and multiple anomalies in the anterior segment of the eye. These anomalies can include ciliary cysts, iris hypoplasia (underdevelopment of the iris), adhesions between the iris and cornea, opacification (clouding) in the eye, nuclear cataract, and megalocornea (enlarged cornea).

Research Findings

• The researchers carried out ophthalmic examinations on 516 Rocky Mountain horses and collected their pedigree information to assess whether this eye disease could be passed down genetically. From this, a subset of 337 horses was selected, for which the ocular phenotypes of their parents and offspring were known.
• The findings indicated that the disease’s inheritance model fit under codominant inheritance. This suggests that horses with one copy of the disease gene (heterozygous) show the cyst phenotype, while those with two copies (homozygous) exhibit multiple anterior segment anomalies.
• However, instances of nonpenetrance were detected where some horses in one lineage demonstrated the cyst phenotype, despite being expected not to. Nonpenetrance refers to situations where genetic mutation is present but does not result in the associated phenotype.

Comparative Analysis with Other Species

• The research also draws parallels between the disease’s inheritance in horses and similar ocular disorders in the Small eye mice and rats, and in humans with congenital aniridia or anterior segment malformation. This conclusion postulates that this syndrome observed in horses could be homologous (sharing a common ancestry) to these eye abnormalities in other species.