Patau’s syndrome is a serious rare genetic disorder caused by having an additional copy of chromosome 13 in some or all of the body’s cells. It’s also called trisomy 13. A baby with Patau’s syndrome has 3 copies of chromosome 13, instead of 2. This severely disrupts normal development and, in many cases, results in miscarriage, stillbirth or the baby dying shortly after birth. Babies with Patau’s syndrome grow slowly in the womb and have a low birth weight, along with a number of other serious medical problems. Patau’s syndrome affects about 1 in every 5,000 births. The risk of having a baby with the syndrome increases with the mother’s age. More than 9 out of 10 children born with Patau’s syndrome die during the first year. About 1 in 10 babies with less severe forms of the syndrome, such as partial or mosaic trisomy 13, live for more than a year.
Symptoms and features
Babies with Patau’s syndrome can have a wide range of health problems. Their growth in the womb is often restricted, resulting in a low birth weight, and 8 out of 10 will be born with severe heart defects. The brain often does not divide into 2 halves. This is known as holoprosencephaly. When this happens, it can affect facial features and cause defects such as:
- cleft lip and palate
- an abnormally small eye or eyes (microphthalmia)
- absence of 1 or both eyes (anophthalmia)
- reduced distance between the eyes (hypotelorism)
- problems with the development of the nasal passages
Other abnormalities of the face and head include:
- smaller than normal head size (microcephaly)
- skin missing from the scalp (cutis aplasia)
- ear malformations and deafness
- raised, red birthmarks (capillary haemangiomas)
Patau’s syndrome can also cause other problems, such as:
- an abdominal wall defect where the abdomen does not develop fully in the womb, resulting in the intestines being outside the body, covered only by a membrane.
- abnormal cysts in the kidneys.
- an abnormally small penis in boys .
- an enlarged clitoris in girls.
- abnormalities of the hands and feet, such as extra fingers or toes (polydactyly) and a rounded bottom to the feet, known as rocker-bottom feet.
Causes of Patau’s syndrome
An error occurs when the cells divide i.e non-disjunction, resulting in an additional copy, or part of a copy, of chromosome 13, which severely affects the baby’s development in the womb. In many cases, the baby dies before reaching full term (miscarriage) or is dead at birth (stillbirth). In most cases of Patau’s syndrome, a baby has a whole extra copy of chromosome number 13 in their body’s cells. This is sometimes known as trisomy 13 or simple trisomy 13. In up to 1 in 10 cases of Patau’s syndrome, genetic material is rearranged between chromosome 13 and another chromosome. This is called a chromosomal translocation. Patau’s syndrome that arises because of this can be inherited.
Screening for Patau’s syndrome
A screening test for Patau’s syndrome, as well as Down’s syndrome (trisomy 21) and Edwards’ syndrome (trisomy 18), from 10 to 14 weeks of pregnancy. The test assesses chances of having a baby with these syndromes. The screening test offered at 10 to 14 weeks of pregnancy is called the combined test because it involves a blood test and an ultrasound scan. If the screening tests show that you have a higher risk of having a baby with Patau’s syndrome, you’ll be offered a diagnostic test to find out for certain whether your baby has the syndrome. This test will check baby’s chromosomes in a sample of cells taken from him or her. Two techniques can be used to obtain the cell sample: amniocentesis or chorionic villus sampling (CVS). These are invasive tests to remove a sample of tissue or fluid so it can be tested for the presence of the extra copy of chromosome 13.
