Trisomy 13

Inheritance

Is Trisomy 13 inherited?

In most cases, trisomy 13 is not inherited. Trisomy 13 most often occurs because of a random mistake in the division of egg or sperm cells. However, trisomy 13 can be inherited if a parent has a rearrangement of chromosome material that involves chromosome 13. This rearrangement can also be called a “balanced translocation”. Humans generally have 46 chromosomes (23 pairs) in every cell in their body. We label them chromosome 1, chromosome 2, chromosome 3, etc. Humans generally have two copies of every chromosome, including chromosome 13. Sometimes bits of chromosomes can swap places. For example, the top of one chromosome 2 and the top of one chromosome 13 could switch places. The swap is called a translocation or a rearrangement. A person with that particular translocation would have a balanced translocation, because they aren’t missing any genetic information. That person’s children would have an increased chance to inherit a chromosome abnormality though, like partial trisomy 13. Analyzing a parent’s chromosomes can determine whether a parent has a balanced translocation. Balanced rearrangements are identified in about 1/1000 individuals, usually through the birth of a baby with an unbalanced chromosome condition.

References
  • http://ghr.nlm.nih.gov/condition/trisomy-13
  • Int J Dev Biol. 2012;56(10-12):841-52. doi: 10.1387/ijdb.120141ue.Oocyte ageing and its cellular basis.Eichenlaub-Ritter U1.
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How is Trisomy 13 most often caused?

What is the chance to have another child with Trisomy 13?

How is Trisomy 13 most often caused?

Trisomy 13 most often occurs randomly as sperm and eggs are created, most commonly due to a process called nondisjunction. Humans generally have 46 chromosomes (23 pairs) in every cell in their body. When a woman’s eggs are made, each egg generally has one copy of each of the 23 chromosomes. The same is true for sperm. The 23 copies from the sperm and the 23 copies from the egg then combine to create an embryo with 46 chromosomes (23 pairs). When nondisjunction happens, an egg or a sperm is created with 2 or 0 copies of a given chromosome instead of the usual 1. If an egg with two copies of chromosome 13 combines with a sperm with 1 copy of chromosome 13, the embryo can develop into a baby who will have trisomy 13.

References
  • http://ghr.nlm.nih.gov/condition/trisomy-13
  • Int J Dev Biol. 2012;56(10-12):841-52. doi: 10.1387/ijdb.120141ue.Oocyte ageing and its cellular basis.Eichenlaub-Ritter U1.
What is the chance to have another child with Trisomy 13?

If neither parent has a chromosome rearrangement, the chance to have a second baby with trisomy 13 is thought to be low, but not impossible. If there is a suspicion of trisomy 13 in a baby, it is important to confirm this with genetic testing so the most accurate recurrence risk (the chance that the couple will have another baby with the same condition) can be provided. There is around a 1% chance to have a second child with trisomy 13 or another trisomy, such as trisomy 21 or trisomy 18. The chance to have a child with trisomy 13 increases as a women ages. Even though trisomy 13 is rare, it is seen more frequently in babies born to women in their late 30s and early 40s, as compared to babies born to younger women. Prenatal testing is available and is generally offered to interested parents through their healthcare providers caring for them during pregnancy. Prenatal genetic counselors can also provide individualized information about the possibility of having another pregnancy with a chromosome problem.

References
  • http://ghr.nlm.nih.gov/condition/trisomy-13
  • Baty, B.J., Blackburn, B.L., and Carey, J.C. Natural History of Trisomy 18 and Trisomy 13: I. Growth, Physical Assessment, Medical Histories, Survival, and Recurrence Risk. American Journal of Medical Genetics. 1994; 49: 175-188

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