Q. If you already have a child with Down syndrome, what are the chances that your next child will have Down syndrome?
A. The risk of recurrence in a subsequent pregnancy for a family that has had one child with Down syndrome is dependent on several factors. First, the results of the chromosome analysis are important and one needs to know if the karyotype is a translocation, nondisjunction or mosaicism. The most common is non-disjunction and the recurrence risk is usually quoted as about 1%. This, however, is also dependent on the mother’s age so for mother’s over 35-40, the risk is affected according to her age as well.
For translocation, the risk of recurrence is dependent on whether one of the parents is a carrier or if the translocation was de novo and occurs only in the baby. If the parent is a carrier, the recurrence risk is dependent on which parent is the carrier and to which chromosome the 21 is translocated.
Clearly, this can be complicated and we always recommend the family be seen by a genetic counselor for a complete explanation that is pertinent to their situation.
Dr. Marilyn Bull, Pediatrician
Riley Children’s Hospital