How does the type of translocation affect recurrence risk in Down syndrome?

Updated: Apr 30, 2018
  • Author: Gratias Tom Mundakel, MBBS, DCH; Chief Editor: Maria Descartes, MD  more...
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The recurrence risk depends on the type of translocation. In most cases, the recurrence risk for de novo translocations is similar to that of the general population but may be slightly higher in some situations; it is estimated to be 2-3%. [101]

In any trisomy 21 patient with a translocation, karyotype testing must be recommended to both parents to look for a translocation. If a translocation is found in one of the parents, the recurrence risk is significantly higher, and further genetic counseling is crucial.

The theoretic recurrence risk for a Robertsonian carrier parent to have a liveborn offspring with Down syndrome is 1 in 3. However, only 10-15% of the progeny of carrier mothers and only 2-3% of the progeny of carrier fathers have Down syndrome. The reason for this difference is not clear. In a carrier parent with a 21q21q translocation or isochromosome, the recurrence risk is 100%.

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