Patau syndrome (trisomy 13) is a type of aneuploidy, in which the individual has three copies of chromosome 13 per cell. Individuals who have an aneuploidy can also be born with one chromosome from a pair—monosomy—or four chromosomes—tetrasomy.

Patau syndrome is the third most common trisomy disease—after Down’s syndrome (trisomy 21) and Edward’s syndrome (trisomy 18)—but is the most severe. 

Chromosome 13 codes for the production of numerous important proteins that are found in nearly every organ in the human body. The absence of these proteins severely restricts fetal development, and will give rise to a vast array of physical and mental difficulties within the individual.