To our knowledge, there is no difference in prognosis
between fetuses with full trisomy
13 and those with translocation
trisomy 13 involving a Robertsonian translocation
13 is one of the acrocentric chromosomes (the others are 14, 15, 21 and 22). A chromosome is acrocentric if the centromere
(a part needed for chromosome separation during cell
division) is very near one end of the chromosome. The position of the centromere is how we distinguish a chromosome's "long arm" from its "short arm." When there is a Robertsonian translocation, 2 of the acrocentric chromosomes are broken at the beginning of the short arm (at the centromere). The long arms are then fused together, so the resulting chromosome has 2 long arms only. While the short arms of the 2 chromosome involved are lost, the lost material causes no health problems because the genes
usually present are available on the short arms of the other acrocentric chromosomes. In other words, the acrocentric chromosomes have no "unique" genes on their short arms.
This means that having an extra full copy of chromosome 13 and having an extra copy of only the long arm of chromosome 13 are thought to cause the same condition. You can view detailed information about Robertsonian translocations from Unique
, an organization that provides information and support to families affected by rare chromosome disorders
However, the prognosis may differ for a fetus or baby with mosaic
trisomy 13 or partial trisomy 13. In mosaic trisomy 13, there is an extra chromosome 13 in some of the cells of the body - but not all. The prognosis in this case may depend on the proportion of cells that have the extra genetic material
, as well as the body parts or systems in which the trisomy cell line is present. In partial trisomy 13, only part of the unique genetic material from chromosome 13 is present in 3 copies (in all the cells of the body). In this case, the prognosis may depend on how much of chromosome 13 is present in 3 copies, as well as the specific genes involved.
People with questions about genetic risks, or prognosis relating to a specific genetic condition, should speak with a genetics professional.
Last updated: 5/4/2015
Last updated: 12/6/2017
We hope this information is helpful. We strongly recommend you discuss this information with your doctor. If you still have questions, please
GARD Information Specialist
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