Contributor: Johannes K. Kristinsson
Trisomy 13 (Patau syndrome, Bartholin-Patau syndrome, D1 trisomy, arhinencephaly, oculocerebral syndrome, encephalo-ophthalmic dysplasia, bilateral retinal dysplasia, Reese-Blodi-­Straatsma syndrome, and mesodermal dysplasia) is a congenital syndrome with severe ocular and systemic anomalies accompanied by mental retardation that results from an extra chromosome 13 caused by meiotic nondisjunction. It is usually lethal <6 month of age. The anomaly affects 1 in 4,000 - 10,000 live births. A characteristic histopathological feature is the presence of cartilage within a coloboma of  the ciliary body [coloboma - ciliary body]. Other ocular abnormalities include a cataract. The embryonic lens nucleus, retains cell nuclei similar to the cataract seen in Lowe syndrome and congenital rubella syndrome. All types of cataracts have been described, as well as microphakia and spherophakia. The most frequent findings in trisomy 13 are colobomas of the iris [coloboma - iris] and ciliary body, cataract, and persistent hyperplastic primary vitreous. Retinal dysplasia is found in ~75% of eyes and is almost always bilateral. Affected infants have numerous profound widespread anomalies including microcephaly, arhinencephaly, agyria, and polydactyly of the hands and feet.