Alternative Names
Bartholin-Patau syndrome; Chromosomal imbalance syndrome, pair 13, trisomy; chromosome 13 trisomy syndrome; Complete trisomy 13 syndrome; D1 Trisomy; Patau syndrome
Symptoms & Characteristics
Trisomy 13 (also known as Patau syndrome) is associated with mental retardation and certain physical abnormalities. Some common physical abnormalities can include:
- small eyes (microphthalmia) that can be widely set apart (hypertelorism)
- a split in the iris of the eye (coloboma)
- undescended testes (cryptorchidism) in males
- extra fingers and toes (polydactyly).
- small head (microcephaly)
- failure to grow and gain weight at the expected rate (failure to thrive)
- severe feeding difficulties
- an opening in the roof of the mouth (cleft palate) and/or a cleft lip
- low muscle tone (hypotonia)
The majority of pregnancies affected with Trisomy 13 will spontaneously miscarry during the pregnancy. For the pregnancies that do survive until birth, there is an extremely high mortality rate in infancy.
Treatment
There is currently no cure for Trisomy 13. Treatment involves managing the symptoms.
How Common Is It?
Trisomy 13 affects about 1 in 10,000 newborns worldwide.
Genetics & Inheritance
All of our genes are packaged together on chromosomes. People typically have 46 chromosomes in total, which are grouped into 23 pairs. The first 22 pairs are numbered largest to smallest (1-22) and are called autosomes. The last pair are called the sex chromosomes and determine gender, either XX (female) or XY (male). We typically inherit 23 chromosomes (one of each pair) from our mother (in an egg cell) and the other 23 from father (in a sperm cell).
Trisomy 13 is caused by the presence of an extra copy of chromosome 13 in every cell of a person's body.
In most cases, the extra copy is caused by a random "non-disjunction event" in either the egg or the sperm cell.
- Non-disjunction occurs when chromosomes in the developing egg or sperm fail to separate during cell division. The result is a sperm or egg cell with either an additional chromosome or one that lacks a chromosome. When this sperm or egg cell combines with one from the opposite sex, the resulting embryo will have cells with an extra chromosome (47) or cells that have a missing chromosome (45).
- The chance for a "non-disjunction event" to occur in an egg increases with age of the biological mother (maternal age). As a consequence, so does the risk for Trisomy 13 and other chromosome trisomies.
In some cases, the extra copy is caused by a chromosome translocation.
- This type of chromosome rearrangement can be inherited from a parent. 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 or missing genetic material from chromosome 13. Although they do not have signs of Trisomy 13, people who carry this type of balanced translocation are at an increased risk to have children with Trisomy 13. People who carry this type of balanced translocation may also be at increased risk to have pregnancy losses, stillbirths, and children with other chromosome abnormalities.
- Parents and family members of an affected person may want to consider chromosome analyses themselves. This testing should be discussed with a qualified health care professional.
In a few cases, the extra copy is caused by a random error during cell division early in fetal development (after conception has already occurred). As a result, only some (not all) of the body's cells have the usual two copies of chromosome 13, and other cells have three copies of chromosome 13. This is called Mosaic Trisomy 13.
In rare cases, only part of chromosome 13 will be duplicated. This will lead to extra copies of some, but not all, of the genes on chromosome 13.
There are other genetic conditions that have symptoms that overlap with Trisomy 13. A genetic consultation with a trained genetic professional is important for a complete evaluation, accurate diagnosis, as well as discussion of the benefits and limitations of chromosome testing and recurrence risk.
Genetic Testing
Trisomy 13 can be diagnosed by a chromosome analysis, which is available through an in person genetic consultation for people who are considered at risk. Use our find a genetic professional directory to locate a trained genetic professional in your area.
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