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, while others are caused by mosaic Patau syndrome. The extra chromosome 13 disrupts the normal course of development, causing heart and kidney defects, amongst other features characteristic of Patau syndrome. 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.
Patau’s syndrome is most often 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 body’s cells have an extra copy; such cases are called mosaic Patau.
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. For example, an egg or sperm cell may gain an extra copy of the chromosome. If one of these atypical reproductive cells contributes to the genetic makeup of a child, the child will have an extra chromosome 13 in each of the body’s cells. Mosaic Patau syndrome is also not inherited. It occurs as a random error during cell division early in fetal development.
Patau syndrome due to a translocation can be inherited. An unaffected person can carry a rearrangement of genetic material between chromosome 13 and another chromosome. This rearrangement is called a balanced translocation because there is no extra material from chromosome 13. Although they do not have signs of Patau syndrome, people who carry this type of balanced translocation are at an increased risk of having children with the condition.
Manifestations and physical findings
Of those fetuses that do survive to gestation and subsequent birth, common abnormalities include:
- Nervous system
- Mental and motor challenged
- Holoprosencephaly (failure of the forebrain to divide properly).
- Structural eye defects, including microphthalmia, Peters anomaly (a type of eye abnormality), cataract, iris and/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)
- 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
- Abnormal genitalia
- Kidney defects
- Heart defects (ventricular septal defect)
- Single umbilical artery
Unless one of the parents is a carrier of a translocation the chances of a couple having another trisomy 13 affected child is less than 1% (less than that of Down Syndrome).
Trisomy 13 was first observed by Thomas Bartholin in 1657, but the chromosomal nature of the disease was ascertained by Dr. Klaus Patau in 1960. The disease is named in his honor. Patau syndrome was also described in Pacific island tribes. These reports were thought to have been caused by radiation from atomic bomb tests. The tribes were temporarily moved before and during the test by an x amount of distance. They were then put back where they had been taken; all of this occurred before it was known how long, or even if, radiation still lingered on after a nuclear explosion.
In England and Wales during 2008–09 there were 172 diagnoses of Patau’s syndrome (trisomy 13), with 91% of diagnoses made prenatally. There were 111 elective abortions, 14 stillbirth/miscarriage/fetal deaths, 30 outcomes unknown, and 17 live births. Approximately 4% of Patau’s syndrome with unknown outcomes are likely to result in a live birth, therefore the total number of live births is estimated to be 18. The small percentage of babies with the full Patau’s syndrome who survive birth and early infancy may live to adulthood, and children with mosaic or partial forms of this trisomy may have a completely different and much more hopeful prognosis.
Medical management of children with Trisomy 13 is planned on a case-by-case basis and depends on the individual circumstances of the patient. Treatment of Patau syndrome focuses on the particular physical problems with which each child is born. Many infants have difficulty surviving the first few days or weeks due to severe neurological problems or complex heart defects. Surgery may be necessary to repair heart defects or cleft lip and cleft palate. Physical, occupational, and speech therapy will help individuals with Patau syndrome reach their full developmental potential.
More than 80% of children with Patau syndrome die within the first year of life.