Patau's syndrome

Patau's syndrome is a rare chromosomal condition in which a baby's cells carry a third copy of chromosome 13. Its other name, the one that usually appears on reports, is trisomy 13. The extra genetic material disturbs development from the earliest weeks of pregnancy, so it is not one organ that goes wrong but several at once: the brain, the face, the heart, the kidneys, the hands and the feet. Most of these pregnancies end on their own, and among babies born alive very few reach their first birthday. It occurs in roughly one in several thousand births. This is one of those conditions where, from day one, parents need fewer new tests and more of a plain conversation about what is happening and what comes next.

Where the extra chromosome comes from

Every human cell holds 23 pairs of chromosomes, half from the mother and half from the father. In Patau's syndrome there are three copies of chromosome 13 instead of two. Almost always this is a chance error while the egg or sperm is maturing, or during the first divisions of the embryo. The parents did nothing and could not have prevented it: diet, medicines, past illnesses and lifestyle have no bearing on trisomy 13.

There are several forms, and the form shapes both the severity and the conversation about any future pregnancy:

• full trisomy 13 — the extra chromosome is in every cell. This accounts for the great majority of cases and the most severe course;
• translocation form — the extra chromosome 13 material is attached to another chromosome. The effects on the baby are the same, but here one parent may be a healthy carrier, which means the situation can recur;
• mosaic form — only some cells carry the extra chromosome. The features can be noticeably milder and these children live longer;
• partial trisomy — only a segment of chromosome 13 is duplicated. What it causes depends on which segment.

The chance of a random trisomy rises with the mother's age, as it does for Down's and Edwards' syndromes. Even so, a baby with Patau's syndrome can be born at any age, and most are born to younger women simply because younger women have more babies.

How the syndrome shows itself in a baby

What sets trisomy 13 apart from many other conditions is the combination of several malformations at once. A cleft lip on its own, or an extra finger on its own, tells you nothing.

• Brain. The hemispheres often fail to separate fully — this is holoprosencephaly. How incompletely they divide shapes both the facial features and the severity of the illness. Seizures and pauses in breathing are common;
• Face. Cleft lip and palate, very small eyes or a missing eyeball, a gap in the iris, closely set eyes, a small head, unusually shaped ears, hearing loss;
• Scalp. Patches where the skin has not formed — a sign particularly characteristic of this syndrome;
• Heart. A defect is found in about eight babies in ten, most often holes in the dividing walls and a patent arterial duct;
• Abdomen and kidneys. An abdominal wall defect in which part of the bowel lies outside the body under a thin membrane; cysts in the kidneys;
• Hands and feet. Extra digits, clenched hands with overlapping fingers, feet with a rounded, convex sole.

Even before birth the baby grows more slowly than expected for the dates and is born small. Those who survive have profound developmental delay, suck and swallow poorly and are prone to chest infections.

What can be seen during pregnancy

The first thing to raise concern is usually not a blood result but a scan. Towards the end of the first trimester the fluid at the back of the baby's neck is measured and, together with a maternal blood test, used to work out the chance of three trisomies: 13, 18 and 21. The exact timing and the make-up of the programme differ a little between countries, but the principle is the same everywhere: first an estimate of chance, then a test that clarifies it.

If the chance comes back high, non-invasive prenatal testing is offered — a blood test that reads fragments of placental DNA circulating in the mother's blood. One point matters here: this is still screening, not a diagnosis. For trisomy 13 the test is wrong more often than for Down's syndrome; a positive result is not rarely a false one, because it can come from mosaicism in the placenta or from features of the mother herself. No decision about a pregnancy is made on a non-invasive test.

The second-trimester scan looks for the malformations themselves: an undivided brain, a facial cleft, heart defects, extra digits, large bright kidneys, an abdominal wall defect, poor growth. Several such findings together argue strongly for a chromosomal condition, but they still do not amount to a diagnosis.

How the diagnosis is confirmed

Only an examination of the baby's chromosomes makes the diagnosis. Before birth, cells are obtained in one of two ways: chorionic villus sampling, usually late in the first trimester, or amniocentesis, drawing off some amniotic fluid, from the second trimester onwards. Both are done with a needle through the abdomen under ultrasound guidance, both carry a small risk of miscarriage, a fraction of one per cent, and this must be discussed with you beforehand.

The cells are then used for a full chromosome analysis — a karyotype — alongside rapid methods that count specific chromosomes within a day or two. A chromosomal microarray will additionally pick up partial duplications and losses. It is the karyotype that answers the second important question: chance trisomy or translocation.

If the baby has already been born and the syndrome is suspected from their appearance, the karyotype is done on a blood sample from the newborn. A scan, an examination and images on their own neither prove nor rule out trisomy 13.

What else it can look like

Several other conditions produce a similar picture, and genetic testing is what tells them apart:

• Edwards' syndrome (trisomy 18) — also multiple malformations, poor growth, clenched hands and rounded soles, but without holoprosencephaly and usually without extra digits;
• triploidy — a triple set of every chromosome, with severe growth restriction and an abnormal placenta;
• Meckel-Gruber syndrome — inherited from both parents, combining cystic kidneys, extra digits and a skull defect with protruding brain tissue, outwardly very close to trisomy 13;
• Smith-Lemli-Opitz syndrome — a disorder of cholesterol metabolism with malformations and fused toes;
• isolated holoprosencephaly without any trisomy — it can follow faults in single genes or severe, poorly controlled diabetes in the mother;
• rearrangements of chromosome 13 itself — loss or duplication of part of it.

The distinction is not academic: what is found determines both the outlook and the risk of the same thing happening again in the family.

The first days after birth

There is no medicine that removes the extra chromosome. Care of the newborn is aimed at keeping the baby free of pain and distress and able to feed: warmth, pain relief, tube feeding, oxygen if it is needed, anticonvulsants if seizures begin. How far to go with each intervention is discussed with the parents point by point, not decided for them.

Babies who get through the first weeks are followed by a team of specialists covering the heart, vision, hearing, seizures and feeding. Whether to operate on the heart or to repair a cleft is not answered the same way for everyone; it is weighed case by case, against what the operation would give the child.

Call an ambulance — in Spain, Italy, Portugal, Poland and Ukraine the single number is 112 — if the baby stops breathing or breathes with long pauses, turns blue, becomes floppy and unresponsive, starts fitting, refuses all feeds or stops passing urine. Families taking such a baby home are taught in advance what to do if breathing stops; ask for that teaching if it has not been offered.

The decisions parents have to make

A diagnosis made before birth brings a choice nobody can make on the family's behalf: whether to continue the pregnancy or end it and, if it continues, how much treatment the baby will receive after birth. Care can go in two directions here: intensive, aimed at prolonging life, or palliative, aimed at comfort. The choice does not have to be made once and for all — the plan can be revisited.

Ask people to be specific: what exactly has been found, how certain they are, what is known about the outlook in this particular form, what is realistically available in your hospital. It helps to record the conversation or to bring someone with you; in that state half of what is said does not stay in the memory. Counselling and groups of parents who have been through the same thing are not a formality — more often than not they are what carries a family through the first year, whatever decision was taken.

Will it happen again in another pregnancy?

If the baby had a chance full trisomy, the likelihood of it recurring is low — only a little above the background chance for your age — and there is no reason to test the parents. If the karyotype showed a translocation, both parents have their own chromosomes analysed. Sometimes one of them turns out to be a healthy carrier of the rearrangement; the recurrence risk is then higher and differs between types of rearrangement, to the point that with some rare variants an unaffected pregnancy is not possible. Other blood relatives may also be worth testing.

This conversation belongs with a clinical geneticist, and it is better held before the next pregnancy rather than during it: that leaves time to discuss early diagnosis and the other routes to having a child.

Online consultation

An online appointment suits going through paperwork, and this diagnosis generates a great deal of it. The doctor can read the scan report, the screening result, the non-invasive test printout or the karyotype with you and explain in plain words what each says: how a probability differs from a diagnosis, why one test does not cancel out another, and which form of the syndrome the report actually names.

Online you can also work out in advance what to ask the geneticist, what the proposed test involves and how chorionic villus sampling differs from amniocentesis. If the baby has already been born, the doctor can help make sense of the prescriptions and the feeding plan and of which specialists to approach first. And there is a separate, entirely reasonable reason to book: to ask what there was no time to ask in hospital.

What cannot be done online: a scan, taking blood or amniotic fluid, and examining a newborn. And if any of the signs in the emergency section appear, do not send a message — call an ambulance.

This material is for information only and does not replace medical advice.