Trisomy 13 is a chromosomal anomaly caused by the presence of an extra chromosome 13 and is characterized by brain malformations (holoprosencephaly), facial dysmorphism, ocular anomalies, postaxial polydactyly, visceral malformations (cardiopathy) and severe psychomotor retardation. The disease is trisomy 13 (MONDO_0018068, a Monarch Disease Ontology term). Also known as: Patau syndrome, Patau's syndrome, Trisomy 13 Syndrome, trisomy type 13.