Signs and symptoms
Of those fetuses that do survive to gestation and birth, common abnormalities may include:
Nervous system
Intellectual disability and motor disorder
Microcephaly
Holoprosencephaly (failure of the forebrain to divide properly) and associated facial deformities such as cyclopia
Structural eye defects, including microphthalmia, Peters anomaly, cataract, iris or fundus (coloboma), retinal dysplasia or retinal detachment, sensory nystagmus, cortical visual loss, and optic nerve hypoplasia
Meningomyelocele (a spinal defect)
Musculoskeletal and cutaneous
Polydactyly (extra digits)
Proboscis
Congenital trigger digits
Low-set ears
Prominent heel
Deformed feet known as rocker-bottom feet
Omphalocele (abdominal defect)
Abnormal palm pattern
Overlapping of fingers over thumb
Cutis aplasia (missing portion of the skin/hair)
Cleft palate
Urogenital
Abnormal genitalia
Kidney defects
Other
Heart defects (ventricular septal defect) (Patent Ductus Arteriosus)
Dextrocardia
Single umbilical artery

Causes
Patau syndrome is the result of trisomy 13, meaning each cell in the body has three copies of chromosome 13 instead of the usual two. A small percentage of cases occur when only some of the bodys cells have an extra copy; such cases are called mosaic trisomy 13.Patau syndrome can also occur when part of chromosome 13 becomes attached to another chromosome (translocated) before or at conception in a Robertsonian translocation. Affected people have two copies of chromosome 13, plus extra material from chromosome 13 attached to another chromosome. With a translocation, the person has a partial trisomy for chromosome 13 and often the physical signs of the syndrome differ from the typical Patau syndrome.Most cases of Patau syndrome are not inherited, but occur as random events during the formation of reproductive cells (eggs and sperm). An error in cell division called non-disjunction can result in reproductive cells with an abnormal number of chromosomes.
Patau syndrome is a syndrome caused by a chromosomal abnormality, in which some or all of the cells of the body contain extra genetic material from chromosome 13. The extra genetic material disrupts normal development, causing multiple and complex organ defects. This can occur either because each cell contains a full extra copy of chromosome 13 (a disorder known as trisomy 13 or trisomy D or T13), or because each cell contains an extra partial copy of the chromosome, or because there are two different lines of cells—one healthy with the correct number of chromosomes 13 and one that contains an extra copy of the chromosome—mosaic Patau syndrome. Full trisomy 13 is caused by nondisjunction of chromosomes during meiosis (the mosaic form is caused by nondisjunction during mitosis). Like all nondisjunction conditions (such as Down syndrome and Edwards syndrome), the risk of this syndrome in the offspring increases with maternal age at pregnancy, with about 31 years being the average. Patau syndrome affects somewhere between 1 in 10,000 and 1 in 21,700 live births.