Trisomy 13

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.

To find a medical professional who specializes in genetics, you can ask your doctor for a referral or you can search for one yourself. Online directories are provided by the American College of Medical Genetics and the National Society of Genetic Counselors. If you need additional help, contact a GARD Information Specialist. You can also learn more about genetic consultations from Genetics Home Reference.