A
translocation is when a whole
chromosome, or segment of a chromosome, is attached to another chromosome or interchanged with a segment of another chromosome. When there is no extra or missing
genetic material, it is called a
balanced translocation. A
Robertsonian translocation involving chromosome 13 is when chromosome 13 is attached to another
acrocentric chromosome (usually chromosome 14, 15, 21, or 22).
[1]
An unaffected person with a balanced translocation involving chromosome 13 (Robertsonian or other) has an increased chance with each pregnancy to pass extra material from chromosome 13 to offspring.
[2] However, the exact recurrence risk may depend on which parent is a
carrier, the type of translocation present, as well as the specific chromosome(s) involved. Recurrence is more common when the translocation carrier is the mother.
[3]
For example, it has been estimated that if the mother carries a Robertsonian translocation involving chromosome 13 and either 14, 15, 21, or 22, the mother has a 1% (1 in 100) chance with each pregnancy to have a baby with
trisomy 13. Of note, if it involves chromosomes 13 and 21, there is also a 10-15% risk to have a baby with translocation Down
syndrome (caused by an extra copy of chromosome 21). However, a father who is a Robertsonian translocation carrier has a less than 1% risk of a child being affected.
[4]
If a parent is a carrier of a translocation that involves the two long arms of the
same chromosome (for example, their 2 copies of chromosome 13 are connected), the carrier will always produce eggs or sperm with unbalanced chromosomes - either with two copies of the chromosome or with none. A parent with this type of translocation cannot achieve a normal, full term pregnancy. For these couples, egg or sperm donation may be an option for pregnancy.
[4]
People with questions about personal genetic risks or risks to family members should speak with a genetics professional.
Last updated: 1/20/2015
Last updated: 12/6/2017
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Warm regards,
GARD Information Specialist
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