47,XX,+13: What the Trisomy 13 Karyotype Means
Last updated: October 22, 2026
47,XX,+13
47,XX,+13 is the karyotype of a female with trisomy 13, the cause of Patau syndrome. This page explains the notation, how to pick out chromosome 13 from the other D-group acrocentrics, and the translocation form of the condition.
What 47,XX,+13 means
| Part | Meaning |
|---|---|
| 47 | 47 chromosomes in each cell analyzed, one more than the usual 46 |
| XX | Two X chromosomes: the person is chromosomally female |
| +13 | An extra whole chromosome 13, giving three copies (trisomy 13) |
The male equivalent is 47,XY,+13. Both are the karyotype of Patau syndrome caused by a free trisomy.
What to look for in the karyotype
- A count of 47.
- Seven D-group acrocentrics instead of six: three 13s, two 14s and two 15s.
- Telling the D group apart. On chromosome 13 the long arm gets darker toward its end. On 15 the darkest bands are in the proximal half and the end is paler. Chromosome 14 has dark bands near the centromere and near the end, with a paler region between.
A count of 46 does not rule it out. If you see three copies of 13q with only 46 chromosomes, look for a Robertsonian translocation such as rob(13;14), where the extra 13q is joined to another acrocentric.
How trisomy 13 happens
Most trisomy 13 is free trisomy from nondisjunction, usually in the mother's egg, and its likelihood rises with maternal age. A minority of cases come from a Robertsonian translocation, most often between chromosomes 13 and 14. In those families a parent may carry the balanced translocation, so the parents' chromosomes are usually checked. A small share of cases are mosaic.
Related karyotypes
| Karyotype | Meaning |
|---|---|
| 47,XY,+13 | Male with free trisomy 13 |
| 46,XY,rob(13;14)(q10;q10),+13 | Translocation trisomy 13: 46 chromosomes, but three copies of 13q |
| 45,XX,rob(13;14)(q10;q10) | A balanced carrier of the 13;14 translocation, the most common Robertsonian translocation |
| mos 47,XX,+13[9]/46,XX[21] | Mosaic trisomy 13: 9 trisomic cells and 21 normal cells |
About Patau syndrome
Patau syndrome occurs in roughly 1 in 10,000 to 16,000 live births, and many affected pregnancies end in miscarriage. It typically involves severe brain malformations such as holoprosencephaly, cleft lip and palate, extra fingers or toes, small or absent eyes, and heart defects. It is a severe condition, and many affected babies do not survive their first year, although mosaic and translocation cases can differ.
Common questions
Is 47,XX,+13 the same as Patau syndrome?
Yes. Full trisomy 13 in all cells is the chromosomal cause of Patau syndrome.
Is trisomy 13 inherited?
Free trisomy 13 is almost always a new event. Translocation trisomy 13 can be inherited from a parent who carries a balanced Robertsonian translocation, which is why the parents are tested in those cases.
Keep learning
This page is for education and training. It is not medical advice and must not be used to diagnose or treat anyone. Laboratory results should be interpreted by qualified professionals following current standards.