An extra copy of chromosome 13 is not the only cause of Patau syndrome.
Other changes in chromosome 13, such as mispositioning (translocation), can also result in the characteristics classified as Patau syndrome.
Due to the severity of these conditions, fewer than 20 percent of those affected with Patau syndrome survive beyond infancy.
As appears to be the case in all trisomies, the risks of Patau syndrome seem to increase with the mother's age, particularly if she is over 30 when pregnant.
The severity and symptoms of Patau syndrome vary with the type of chromosomal anomaly, from extremely serious conditions to nearly normal appearance and functioning.