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Inherited Disorders and Birth Defects

Trisomy 13

12/08/2006

Question:

On Thanksgiving 2005, my daughter had a chocolate cyst that ruptured. Upon surgery it was found that she had a serious case of endometriosis. In August of 2006, she delivered her first baby who was unexpected diagoised with full trisomy 13. Can endometriosis has any effect on the reproductive eggs? Is it possible that all or other eggs could have been affected by this or anything else in her life that caused this trisomy. If this is possible, is there testing that can be done before she takes the risk of another pregnancy? She is a healthy, intellegent, "clean living" 29 year old woman. Also, with the many, many defects the baby has, why was it not seen or suspected on the multiple untrasounds during pregnancy?Thank you for your time.

Answer:

As you know, trisomy 13 is due to an extra # 13 chromosome. Trisomy happens by a mechanism called non-disjunction. We have 46 chromosomes (the structures that carry our genes that tell us how to develop, grow and function) in each cell of our bodies except for the sex cells - the egg and sperm - they have 23 chromosomes. The egg and sperm only have 23 chromosomes so that at conception, the embryo will have the correct number of chromosomes - 46. You get half of your chromosomes from your mom and half from your dad.

However, when cells go to divide to form eggs or sperm they can mis-divide and the resulting cell - the egg or the sperm ends up with either too many chromosomes or not enough. This is called non-disjunction. If this egg or sperm is fertilized during conception, the embryo will have 47 chromosomes instead of the normal number of 46. In your daughter’s case, the extra chromosome was a number 13.

Researchers do not understand why this occurs. It can occur at any age, however, it is known that non-disjunction occurs more frequently as mothers age. Women over 35 have an increased chance of having a baby with a trisomy. Down syndrome, trisomy 21, is the most common trisomy seen in live births. Trisomy 18 and 13 are much less common. This is an area of intense research. It is highly unlikely that your daughter's endometriosis had anything to do with this happening.

It is highly unlikely that this would happen again, but your daughter could have prenatal diagnosis testing (such as amniocentesis) in a future pregnancy to know for sure whether or not the fetus has a chromosome abnormality. Ultrasound usually can identify major birth defects during pregnancy; I do not know why that did not happen in your daughter’s case.

I would highly recommend that your daughter talk to a geneticist or genetic counselor to discuss why this happened, the chance it could happen again and what options would be available to her in the future. She can locate a genetics center near her through the National Society of Genetic Counselors’ website listed below.

Related Resources:

National Society of Genetic Counselors Resource Center

For more information:

Go to the Inherited Disorders and Birth Defects health topic, where you can:

Response by:

Anne   Matthews, RN, PhD Anne Matthews, RN, PhD
Associate Professor of Genetics
School of Medicine
Case Western Reserve University