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Patau syndrome, or trisomy 13, is a life-limiting genetic condition in which there is an extra copy of chromosome 13 in all or some cells. Survival rates are low, and those babies born alive with Patau syndrome will have learning disabilities and a wide range of serious health challenges.

Clinical features


Suggestive ultrasound findings for Patau syndrome are listed below.

  • Intrauterine growth restriction, leading to low birth weight.
  • Severe heart anomalies.
  • Holoprosencephaly (the brain failing to divide into two parts during fetal development), which can be associated with:
    • cleft lip and palate;
    • atypically small eye or eyes (microphthalmia);
    • absence of one or both eyes (anophthalmia);
    • reduced distance between the eyes (hypotelorism); and
    • problems with development of the nasal passages.
  • Other anomalies of the face and head include:
    • smaller-than-normal head size (microcephaly);
    • skin missing from the scalp (cutis aplasia);
    • ear malformations and deafness; and
    • raised, red birthmarks (capillary haemangiomas).
  • Patau syndrome can also cause other problems, such as:
    • abdominal wall anomalies;
    • cysts in the kidneys;
    • small penis in boys; and
    • enlarged clitoris in girls.
  • There may also be anomalies of the hands and feet, such as extra fingers or toes (polydactyly) and a rounded bottom to the feet, known as rocker-bottom feet.


Some of the signs and symptoms of Patau syndrome are listed below.

  • Low birth weight and/or slow growth.
  • Craniofacial features:
    • scalp anomalies, such as missing skin;
    • sloping forehead;
    • close-set eyes;
    • short, flat or atypically shaped nose;
    • cleft palate and/or lip;
    • small jaw; and
    • ears may be small, low set, posteriorly rotated and malformed.
  • Limb anomalies:
    • clenched hands;
    • single palmar crease;
    • extra fingers and toes (polydactyly);
    • nail hypoplasia;
    • smooth, curved sole of the foot with prominent heel; and
    • club feet.
  • Cardiac anomalies (found in 80% of cases):
  • Respiratory symptoms:
    • breathing difficulties, including apnoeas.
  • Neurological symptoms:
    • microcephaly;
    • hypotonia and feeding difficulties;
    • seizures;
    • severe developmental delay;
    • alobar holoprosencephaly; and
    • spinal anomalies.
  • Ophthalmological symptoms:
    • cataracts;
    • retinal dysplasia or detachment;
    • nystagmus;
    • optic nerve hypoplasia;
    • small or absent eyes; and
    • coloboma of the iris.
  • Gastroenterological symptoms:
    • omphalocele;
    • umbilical hernia;
    • malrotation; and
    • Meckel diverticulum.
  • Genital anomalies:
    • undescended testicles;
    • hypospadias;
    • hypertrophy of the clitoris;
    • labia minora hypoplasia; and
    • bicornuate uterus.
  • Renal symptoms:
    • polycystic kidney;
    • hydronephrosis; and
    • horseshoe kidney.
  • Other:
    • hearing loss; and
    • capillary haemangioma.

Individuals with Patau syndrome typically have a short life expectancy (more than 9 in 10 children die during their first year of life). There is a high rate of death in utero. Cardiopulmonary arrest and central apnoeas are leading causes of death in the neonatal period.

Gastro-oesophageal reflux and feeding difficulties are almost universal, and aspiration can lead to decompensation. Survival time is increased for infants treated intensively. Around 1 in 10 babies with less severe forms of the syndrome, such as partial or mosaic trisomy 13, live for more than a year.

Potential genetic causes

Patau syndrome occurs in 1 in 5,000 live births (though it should be noted that these figures will be confounded by the numbers of pregnancy terminations). It usually arises when each cell has three, rather than the usual two, copies of chromosome 13.

Some individuals with Patau syndrome have three copies of chromosome 13 in some of their cells and two in the other cells. This is known as mosaic Patau syndrome. Individuals with mosaic Patau syndrome tend to have milder features.

In up to 1 in 10 cases of Patau syndrome, genetic material is rearranged between chromosome 13 and another chromosome. This is called a chromosomal translocation. Features can vary depending on the level of mosaicism (the number of cells containing an extra copy of chromosome 13) and the tissues involved. This can be difficult to accurately determine, so the prognosis (though often milder) is more unpredictable.

For information about prenatal genomic testing for cases in which Patau syndrome is suspected, see articles:

Inheritance and genomic counselling

Patau syndrome usually arises spontaneously owing to an error in cell division. This is most commonly in the egg, but it occasionally occurs in the sperm. The chance increases with maternal age. Recurrence risk is usually low, though some couples may have an increased recurrence risk owing to parental germline mosaicism. This means that a patch of cells that includes the eggs or sperm has an extra copy of chromosome 13. It is very rare, but it should be considered in the context of two affected pregnancies. Referral to clinical genetics should be considered.

There is a 5% to 10% chance of a Robertsonian translocation. This is a structural rearrangement of the chromosomes in which one copy of chromosome 13 is attached to another chromosome, usually chromosome 14. Cases of Patau syndrome that arise from a translocation result in a different appearance on a karyotype, because the extra copy of chromosome 13 is attached to another chromosome. When this appearance is seen, parental karyotypes are essential to determine the recurrence risk. If this risk is highlighted in your patient’s family, consider a referral to clinical genetics.


Prenatal management

Testing for Patau syndrome can be pre- or postnatal. It is offered, together with screening for trisomies 21 and 18, to all pregnant women in the first trimester. The screening, known as the combined test, uses maternal age, nuchal translucency measurement and blood tests (hCG and PAPP-A). Measuring nuchal translucency calculates the chance of trisomy, and can only be measured from 11 to 14 weeks’ gestation. If the patient’s chance is found to be higher than 1 in 150, the mother is offered either non-invasive prenatal testing (NIPT) or an invasive test.

If a patient presents too late for the combined test, a quadruple test is offered between 14 and 20 weeks’ gestation. This involves combining the results of four blood tests (inhibin A, hCG, AFP and uE3) along with maternal age, to assess the chances of the pregnancy being affected.

Where the chance is found to be higher than 1-in-150, patients will be offered further testing. Where a structurally normal fetus is seen on ultrasound imaging, this testing may be in the form of advanced screening with NIPT; where anomalies are seen on the scan, it may be cytogenetic testing. Formal testing requires an invasive procedure to obtain fetal or placental DNA. See our Knowledge Hub resources on amniocentesis and chorionic villus sampling for further information about invasive testing.

Postnatal management

Management of children with Patau syndrome is complex; it requires sensitive counselling, discussions with the family and shared decision making.

Patient support charity SOFT UK provides some guidance about managing such conversations with families. For some patients, a palliative approach may be pursued; for others, more intensive interventions may be undertaken. Care should be delivered via a multidisciplinary team.


For clinicians


Tagged: Cardiac anomalies, Developmental delay, Chromosomal condition, Trisomy, Differences in sex development

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  • Last reviewed: 21/03/2023
  • Next review due: 21/03/2025
  • Authors: Dr Joanna Kennedy, Heather Longworth
  • Reviewers: Dr Ellie Hay, Dr Emile Hendricks, Dr Jessica Woods