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For parents of a child with Down syndrome due to a translocation of chromosome 21, there may be an increased risk of Down syndrome in future pregnancies. This is because one of the two parents may be a balanced translocation carrier.
(Click Translocation and Down Syndrome for more information about balanced translocation.)
A balanced translocation carrier of chromosome 21 is a person that has part of chromosome 21 attached (translocated) to another chromosome. This person does not have Down syndrome, however, because he or she does not have an extra chromosome 21; it is just moved.
When reproduction occurs, if a parent passes on this translocated chromosome along with a normal chromosome 21, the child will develop Down syndrome. If a parent passes on this translocated chromosome along with the chromosome 21 that lost a section due to translocation, then the child will not develop Down syndrome, but will also be a balanced translocation carrier.
Genetic counseling can be sought to find the origin of the translocation.
It is important to realize that not all parents of individuals with translocation trisomy 21 are themselves balanced carriers. In such situations, there is no increased Down syndrome risk in future pregnancies.