Trisomy 13, also called Patau syndrome, is a chromosomal condition in which a baby has three copies of chromosome 13 instead of the usual two. It occurs in roughly 1 in 10,000 to 16,000 live births and causes a constellation of structural abnormalities affecting the brain, heart, face, and other organs. Most affected pregnancies end in miscarriage, and among those born alive, the majority do not survive infancy. Yet the clinical picture is more varied than the textbook summary suggests, and a growing body of evidence shows that some children live years or even decades, particularly when their genetic form is mosaic or partial rather than full trisomy.
How the Extra Chromosome Gets There
The overwhelming majority of trisomy 13 cases trace back to the mother’s egg cells. In a study that determined parental origin in every case examined, roughly 89% of the extra chromosomes came from the mother, with an almost equal split between errors in the first and second stages of egg-cell division.1Human Molecular Genetics. Non-disjunction of chromosome 13 A separate analysis found a maternal origin rate above 91% and noted that about 37% of cases arose from errors during the second meiotic division, which is unusually high compared with most other chromosomes.2PubMed. The origin of trisomy 13 This pattern matters because it distinguishes trisomy 13 from, say, Down syndrome, where errors in the first division dominate far more heavily.
A failure of chromosomes to properly separate during cell division, called nondisjunction, is the root cause. When the two copies of chromosome 13 stick together instead of splitting apart, one resulting egg or sperm cell gets two copies and the other gets none. If the cell with two copies is fertilized, the embryo ends up with three. The risk of this happening rises with maternal age, and there is some evidence that the link between older maternal age and trisomy 13 is strongest among liveborn infants with a confirmed meiotic error on the mother’s side.3Human Molecular Genetics. Non-disjunction of chromosome 13
Full Trisomy, Mosaicism, and Translocations
Not every case of trisomy 13 looks the same genetically, and the genetic form has major implications for how severe the condition is and how long a child may live.
- Full trisomy 13: Every cell in the body carries three copies of chromosome 13. This is the most common form, accounting for about 80% of cases, and is associated with the most severe clinical picture.
- Mosaic trisomy 13: Only some cells carry the extra chromosome, while others are normal. Children with mosaicism tend to have milder features and significantly better survival. One reported case involved a boy with just 8% of his blood cells carrying the extra chromosome, inherited through a Robertsonian translocation from his mother.4PubMed. Inheritance of a t(13;14)(q10;q10) Robertsonian translocation with a low level of trisomy 13 mosaicism
- Translocation trisomy 13: The extra chromosome 13 material is physically attached to another chromosome, most often chromosome 14. This can occur as a new event or be inherited from a parent who carries a balanced translocation. Robertsonian translocations involving chromosome 13 are the classic example and can rarely produce trisomy 13 in offspring.5PubMed. Trisomy 13 by robertsonian translocation rob (13;13)(q10;q10) +13: about one case
- Partial trisomy 13: Only a segment of chromosome 13 is present in three copies. The clinical picture depends heavily on which segment is duplicated.
A 2025 study examining long-term outcomes found that children with mosaic or partial trisomy 13 had dramatically better survival than those with full trisomy. About 25% of children with non-full trisomy 13 survived to age 10, compared with roughly 5% of those with full trisomy. The mortality risk for full trisomy was double that of mosaic or partial forms.6JAMA Network Open. Long-Term Survival Among Children With Trisomy 13 and Trisomy 18 by Cytogenetic Status This gap underscores how important it is to determine the exact genetic form early, since it shapes both the medical outlook and the conversations families have about care goals.
What Trisomy 13 Looks Like at Birth
The physical features of Patau syndrome are often recognizable at delivery, even without genetic testing. A large European registry study of 240 liveborn babies with trisomy 13 found that about 57% had a heart defect, 45% had a cleft lip or palate, 44% had extra fingers or toes, 39% had a nervous system anomaly, and 30% had an eye abnormality.7PubMed. Congenital anomalies associated with trisomy 18 or trisomy 13: A registry-based study in 16 European countries, 2000-2011 A case report from a resource-limited setting described a typical presentation: bilateral cleft lip and palate, extra fingers behind the pinky, a scalp defect called aplasia cutis congenita, low muscle tone, and congenital heart disease.8PubMed Central. Recognition of Patau Syndrome (Trisomy 13) Based on Clinical Features in a Resource-Limited Setting: A Case Report
Beyond the visible abnormalities, internal organ problems are common. A pathology study of 12 cases found tissue-level abnormalities in the brain, eyes, pancreas, kidneys, and ovaries, with mild cystic kidney changes present in every case.9PubMed. The pathology of trisomy 13 syndrome. A study of 12 cases Brain malformations, particularly a condition called holoprosencephaly where the forebrain fails to properly divide into two hemispheres, are among the most serious and are strongly associated with trisomy 13.
Heart Defects and the Surgery Question
Cardiac anomalies are the leading cause of death in trisomy 13 and are present in more than half of affected newborns. The most common defect is a hole between the lower heart chambers (ventricular septal defect), found in about 39% of children with trisomy 13 who underwent cardiac evaluation, followed by problems with the pulmonary valve or the outflow tract connecting the heart to the lungs, seen in about 20%.10PubMed Central. Long Term Outcomes of Children with Trisomy 13 and 18 After Congenital Heart Disease Interventions
For decades, the standard approach was to withhold cardiac surgery for children with trisomy 13, on the grounds that the prognosis was too poor to justify the risks. That view has shifted. A national analysis using the Kids’ Inpatient Database found that congenital heart surgery was associated with a 45% reduction in in-hospital mortality for trisomy 13, and the survival benefit persisted through at least 24 months of follow-up.11Pediatrics. Congenital Heart Surgery on In-Hospital Mortality in Trisomy 13 and 18 Surgery is not without risk, though. An analysis of the Society of Thoracic Surgeons database reported an operative mortality rate of 15% and a complication rate of 56%. Babies who needed a breathing machine before surgery had far worse odds, with a mortality risk more than eight times higher.12PubMed Central. Cardiac Surgery in Patients With Trisomy 13 and 18: An Analysis of The Society of Thoracic Surgeons Congenital Heart Surgery Database
These findings don’t mean every child with trisomy 13 and a heart defect should have surgery. They mean the blanket refusal that once prevailed is harder to justify. The decision now depends on the specific defect, the child’s overall condition, what the family wants, and how the care team weighs the potential benefit against the real surgical risks.
Detecting Trisomy 13 Before Birth
Trisomy 13 can be suspected through ultrasound and confirmed through genetic testing during pregnancy. On ultrasound, the condition tends to show a cluster of recognizable abnormalities. In the first trimester, a fluid-filled sac at the back of the neck called a cystic hygroma is one of the earliest signs. By the second trimester, heart defects, brain abnormalities, facial clefts, hand anomalies, and urinary tract problems become visible. One study found that 49 of 54 second-trimester cases were detected by ultrasound, with heart defects and brain anomalies being the most commonly identified.13PubMed. Sonographic detection of trisomy 13 in the first and second trimesters of pregnancy
Cell-free DNA screening, sometimes called noninvasive prenatal testing (NIPT), analyzes fragments of fetal DNA circulating in the mother’s blood. A systematic review and meta-analysis of microarray-based cell-free DNA testing found a sensitivity of 100% for trisomy 13, meaning it caught every true case in the study populations, with a specificity above 99.9%.14PubMed. Antenatal screening for fetal trisomies using microarray-based cell-free DNA testing: A systematic review and meta-analysis A validation study confirmed these strong performance numbers.15PubMed Central. Clinical validation of a novel automated cell-free DNA screening assay for trisomies 21, 13, and 18 in maternal plasma
However, screening is not the same as diagnosis. A positive screen still needs to be confirmed by amniocentesis or chorionic villus sampling, which analyze fetal cells directly. The positive predictive value of cell-free DNA screening for trisomy 13 has been reported at roughly 63% in low-risk pregnancies and about 83% in high-risk pregnancies.16American Journal of Obstetrics and Gynecology. Cell-free DNA screening for trisomies 21, 18, and 13 in pregnancies at low and high risk for aneuploidy with genetic confirmation In practical terms, if you’re in a low-risk group and get a positive screen for trisomy 13, there’s still about a one-in-three chance it’s a false alarm. That’s why diagnostic confirmation matters before making any decisions based on the result.
Survival and What Shapes It
The statistics on trisomy 13 survival are among the starkest in pediatric medicine. A multi-state population study of 693 children identified with trisomy 13 found that 5-year survival was about 9.7%.17PubMed Central. Survival of children with trisomy 13 and trisomy 18: A multi-state population-based study Most deaths cluster in the first two months of life, with the rate declining rapidly before reaching a steadier plateau.18JAMA Network Open. Long-Term Survival Among Children With Trisomy 13 and Trisomy 18 by Cytogenetic Status That plateau is significant: children who survive the initial newborn period have a meaningfully different trajectory from those who don’t.
As noted earlier, the genetic form matters enormously. A quarter of children with mosaic or partial trisomy 13 were still alive at age 10 in the 2025 study, compared with about 5% of those with full trisomy. Children with full trisomy faced double the mortality risk of those with non-full forms.19JAMA Network Open. Long-Term Survival Among Children With Trisomy 13 and Trisomy 18 by Cytogenetic Status Whether a child receives surgical intervention for heart defects and other correctable problems also influences survival, as does the overall intensity of medical support.
Neurological and Developmental Outlook
Trisomy 13 causes severe intellectual disability. A study examining psychomotor development across standardized skill areas found that children with trisomy 13 had an average developmental quotient of 0.25, meaning their developmental age was roughly a quarter of their chronological age. Despite functioning in the severe to profound range, these children did achieve milestones. Some learned to walk, and some acquired basic toileting skills. Researchers emphasized that individuals with trisomy 13 “always continued to learn,” even if progress was slow.20PubMed. Natural history of trisomy 18 and trisomy 13: II. Psychomotor development
Epilepsy is a common neurological complication. An electroencephalography study of children with Patau syndrome found that nearly 40% had photosensitive myoclonic epilepsy, a seizure type triggered by flickering light. Other seizure types, including tonic spasms, were also documented. Some children had non-epileptic jerking movements that could be confused with seizures but had a different underlying mechanism.21PubMed. Epileptic spasms and early-onset photosensitive epilepsy in Patau syndrome: An EEG study Recognizing these different movement patterns matters for choosing the right treatment, since anti-seizure medications help epileptic spasms but don’t change non-epileptic jerks.
Which Genes Drive Which Features
Not all regions of chromosome 13 contribute equally to the Patau syndrome picture. Researchers have tried to map specific features to specific chromosomal segments by studying people with partial trisomy 13, where only a piece of the chromosome is duplicated. An early analysis of 41 cases found that having three copies of the region from 13q22 to the tip of the chromosome was enough to produce most of the classic features of the syndrome, including some, like cleft palate, that appeared in non-overlapping partial duplications.22PubMed. The phenotype in partial 13q trisomies, apropos of a familial (13;15)(q22;q26) translocation
More recent work using high-resolution chromosome analysis has refined the map. A study comparing partial trisomy 13 patients with published literature indicated that the 13q22-q31 region is particularly critical for cleft lip and palate, while the far end of chromosome 13 appears responsible for seizures.23PubMed Central. Identification of partial trisomy 13q in two unrelated patients using single-nucleotide polymorphism array and literature overview This kind of genotype-phenotype mapping is still imprecise, but it has practical value: when a prenatal test shows a partial duplication of chromosome 13, knowing which segment is involved can give families and clinicians a better idea of what to expect.
When a Parent Carries a Balanced Translocation
In a small percentage of trisomy 13 cases, one parent carries a balanced Robertsonian translocation, most commonly between chromosomes 13 and 14. The parent is healthy because they have the right amount of genetic material, just rearranged. But when their chromosomes sort into egg or sperm cells, there’s a chance the resulting cell will get an unbalanced set, potentially producing a child with trisomy 13.
The actual recurrence risk tends to be lower than the theoretical maximum. A segregation analysis of 86 families where a parent carried a 13;14 translocation found that none of the chromosomal conditions (including trisomy 13) recurred after the birth of the first affected child.24PubMed. Reproductive risk of t(13q14q) carriers: case report and review This doesn’t mean the risk is zero, but it is reassuringly low in practice. Genetic counseling is recommended for any couple where a translocation has been identified, since the specific translocation type and which parent carries it both influence the numbers.
Comfort Care, Active Treatment, and Everything in Between
One of the hardest questions families face after a trisomy 13 diagnosis is how aggressively to pursue medical treatment. For decades, many hospitals treated the condition as “incompatible with life” and offered only comfort-focused care. That framing has softened, partly because survival data shows that some children do live for years, and partly because families have pushed back against being told their child’s life isn’t worth treating.
A study comparing children with complete trisomy 13 or 18 whose families pursued life-prolonging therapies versus comfort-directed care found that the parents’ goals of care did not significantly affect how long children with complete trisomy survived. What changed was treatment intensity, not lifespan.25PubMed. Clinical Course for Patients With Trisomy 13 and 18 Pursuing Life-Prolonging Therapies Versus Comfort-Directed Care That finding is both humbling and clarifying: it suggests that for full trisomy 13, the trajectory is heavily shaped by the condition’s biology regardless of what medical teams do. But it also means that choosing comfort care does not condemn a child to die sooner, which is a fear many parents carry.
In practice, most families end up somewhere between the poles. They may agree to surgery for a heart defect but decline resuscitation if the heart stops again. They may accept tube feeding but not mechanical ventilation. These decisions are deeply personal, and the medical literature increasingly argues that they belong to the family, not to a hospital ethics committee applying a one-size-fits-all standard.
What Families Actually Report
Surveys of parents who have raised a child with trisomy 13 or 18 paint a picture that clashes with the clinical literature’s emphasis on mortality statistics. In a study of families participating in social support networks, 97% of parents described their child as happy. Half said caring for a child with severe disabilities was harder than expected, but parents consistently reported that their child enriched their family and their relationship, regardless of how long the child lived.26PubMed. The experience of families with children with trisomy 13 and 18 in social networks Among families with full trisomy 13 or 18 whose children were still alive at the time of the study, the median age of the children was 4 years.
A scoping review of the moral experiences of these families highlighted a recurring theme: parents who continued pregnancies after a trisomy 13 diagnosis often faced significant pushback from healthcare professionals who questioned whether the decision was truly in the child’s best interest. Many parents found this opposition distressing, but multiple studies noted that it also spurred a kind of resilience that later helped them navigate the medical system and advocate for their child. Parents described fighting for their child’s personhood to be recognized and found value in connecting with other families who had been through the same experience.27PubMed Central. “She was finally mine”: the moral experience of families in the context of trisomy 13 and 18– a scoping review with thematic analysis
The tension between clinical prognosis and lived family experience is real and probably irreducible. The numbers are what they are: most children with full trisomy 13 do not survive their first year, and those who do face profound disability. But the families living inside those numbers report something the statistics don’t capture. Any clinician counseling a family after a diagnosis needs to hold both realities at once.