Patau syndrome, also known as Trisomy 13, is a chromosomal aberration, a disease in which a patient has an additional chromosome 13.

Symptons include:

Most babies suffering from Patau syndrome will not survive infancy; those who do will suffer from a learning disability.

Patients with the so-called mosaic form of Patau syndrome have only some of their cells carrying the additional copy of chromosome 13. The severity of the disease depends on the ratio of affected to unaffected cells.