Patau Syndrome or Trisomy 13 is a chromosome condition resulting in most cases, from three copies of chromosome 13 in every cell in their body rather than the usual 2 copies.  This extra copy disrupts the normal pattern of fetal development causing severe abnormalities.

Trisomy 13 can become attached to another chromosome during very early fetal development. Babies affected with Patau Syndrome will have two normal copies of chromosome 13 with an extra chromosome 13 attached to another chromosome.

Very occasionally, babies with Trisomy 13 have the extra copy in only some of the cells. This is called mosaic Trisomy 13.  The severity of the condition depends on the type of cell affected and the number of cells affected. Physical features of a mosaic trisomy are often more mild than those of a full trisomy 13.

Features of Patau Syndrome

Severe intellectual disability with physical abnormalities.
Heart defects, brain and spinal cord abnormalities.
Very small, poorly developed eyes, extra fingers and toes.
Cleft lip and palate.
Weak muscle tone.

Generally infants with Trisomy 13 will die within a few days of life, with only 5-10% living past their first birthday.  Approximately 1 in 16,000 babies are affected by Patau Syndrome. It is not inherited.