Patau syndrome, also known as trisomy 13 and trisomy D, is a chromosomal abnormality, a syndrome in which a patient has an additional chromosome 13 due to a nondisjunction of chromosomes during meiosis. Some are caused by Robertsonian translocations. The extra chromosome 13 disrupts the normal course of development, causing heart and kidney defects amongst other features characteristic of Patau syndrome.