My son and his wife were told the baby she carries has Edwards syndrome. Does this mean if she gets pregnant again, any future child will have this condition as well? Will she be able to have a normal child?
Most cases of trisomy 18 are not inherited and occur randomly due to errors in the formation of eggs or sperm. If an egg or sperm gains an extra copy of chromosome 18 during cell division and contributes to a pregnancy, the embryo will have an extra chromosome 18 (trisomy) in each cell of the body.
Mosaic trisomy 18 (when some body cells have trisomy 18 and some have a normal chromosome make-up), is also typically not inherited. Mosaic trisomy 18 is also due to an error in cell division, but the error occurs early in embryonic development. About 5% of affected people have a mosaic form of trisomy 18.
Partial trisomy 18 (when only part of chromosome 18 is present in 3 copies) can be inherited. An unaffected parent can carry a rearrangement of genetic material between chromosome 18 and another chromosome. This rearrangement is called a balanced translocation because there is no extra or missing genetic material. However, a person with a balanced translocation has an increased risk with each pregnancy to have a child with trisomy 18.
Last updated: 7/7/2015
What is the recurrence risk for trisomy 18?
The recurrence risk for trisomy 18 depends on the type of trisomy 18 in an affected family member (full, mosaic, or partial trisomy 18).
The recurrence risk for a family with a child with full trisomy 18 is usually stated as 1% (1 in 100). Therefore, the vast majority of parents with an affected fetus or child go on to have normal children. Parental mosaicism has been reported in a few cases, and recurrence of different trisomies (involving a chromosome other than 18) has also been reported. Experiences have suggested that the recurrence risk seems to be less than 1%, but higher than the maternal age-related risk. The recurrence risk for mosaic trisomy 18 is also thought to be relatively low.
The recurrence risk in families with a child with partial trisomy 18 may be higher than that for full trisomy 18, but the exact risk depends on whether one of the parents has a chromosomal rearrangement (such as a balanced translocation).
People with questions about the recurrence risk of trisomy 18 for themselves or family members are encouraged to speak with a genetics professional.
Last updated: 7/7/2015
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