Patau Syndrome (Trisomy 13)

What causes trisomy 13

Humans normally have 23 pairs of chromosomes. In trisomy 13, there are three copies of chromosome 13 instead of two.

The risk of full trisomy 13 rises with maternal age. It is not caused by anything the parents did during pregnancy.

Features

Not every baby has every feature. Common findings include:

Brain and nervous system

• holoprosencephaly: the front of the brain does not divide properly into two halves
• small head (microcephaly)
• seizures, low muscle tone, and severe developmental delay

Heart

• congenital heart defects in about 80%: ventricular or atrial septal defects, patent ductus arteriosus and more complex defects

Face and head

• cleft lip and palate
• small or absent eyes (microphthalmia), closely spaced eyes, coloboma
• scalp defects (cutis aplasia)
• low-set, malformed ears

Limbs and body

• extra fingers or toes (polydactyly)
• clenched hands, rocker-bottom feet
• kidney abnormalities, umbilical hernia or omphalocele
• genital differences
• low birth weight

Other issues

• feeding difficulties and reflux
• breathing pauses (central apnea)
• hearing and vision loss

Diagnosis

During pregnancy

• Cell-free DNA screening from the mother's blood, from about 10 weeks, estimates the risk of trisomy 13. It is a screening test, and positive results must be confirmed.
• First-trimester combined screening and ultrasound may show heart defects, holoprosencephaly, cleft lip, extra digits or growth restriction.
• Diagnostic tests: chorionic villus sampling (10 to 13 weeks) or amniocentesis (from 15 weeks) confirm the diagnosis.

After birth

A karyotype or chromosomal microarray from a blood sample confirms trisomy 13 and identifies the type. Babies are evaluated with echocardiography, brain imaging, kidney ultrasound and eye and hearing exams.

Care and treatment

There is no cure. Care is individualized and shaped by the baby's specific problems and the family's values:

• Comfort-focused (palliative) care: feeding support, warmth, pain relief and time together, with hospice or palliative care teams.
• Active medical care: treatment of breathing problems, seizures, infections and reflux; feeding tubes.
• Surgery: some families and centers choose heart surgery, cleft repair or other operations, and studies show this can extend survival in selected children.
• Developmental support: physical, occupational and speech therapy for children who survive infancy.

Early, honest conversations between families and the medical team, including perinatal palliative care, help families make informed choices.

Outlook

Many pregnancies with full trisomy 13 end in miscarriage or stillbirth. Of babies born alive, median survival is about 1 to 2 weeks, and roughly 1 in 10 live beyond the first year. Children with mosaic trisomy 13 often have milder features and longer survival. Children who live longer have significant intellectual disability but can recognize family, smile and interact, and they often bring great joy to their families.

Recurrence and genetic counseling

For full trisomy 13, the chance of recurrence in a future pregnancy is low, about 1% or less. For translocation trisomy 13, parental chromosome testing is recommended, because a parent carrying a balanced translocation has a higher chance of recurrence. Genetic counseling is recommended after a diagnosis. Related conditions include Down syndrome (trisomy 21) and Edwards syndrome (trisomy 18).

Frequently asked questions

What is Patau syndrome?

Patau syndrome, or trisomy 13, is a chromosomal condition where a person has an extra copy of chromosome 13. It causes severe intellectual disability and physical differences such as heart defects, brain malformations, cleft lip and palate and extra fingers or toes.

What causes trisomy 13?

Most cases are caused by a random error in cell division when the egg or sperm forms, resulting in an extra chromosome 13. The risk rises with maternal age. About a fifth of cases involve a translocation, which can occasionally be inherited from a parent.

What is the life expectancy for Patau syndrome?

Most babies with full trisomy 13 live only days to weeks, and about 1 in 10 survive past the first year. Some children, especially those with mosaic trisomy 13 or who receive intensive care and surgery, live for many years.

Can trisomy 13 be detected before birth?

Yes. Cell-free DNA screening and ultrasound can indicate a high chance of trisomy 13. The diagnosis is confirmed by chorionic villus sampling or amniocentesis, which examine the baby's chromosomes directly.

Is trisomy 13 inherited?

Usually not. Most cases happen by chance and are not inherited. Translocation trisomy 13 can occasionally be inherited from a parent who carries a balanced chromosome rearrangement, so parental testing is recommended in that case.