What is the role of FISH in the workup of Down syndrome?

Updated: Apr 30, 2018
  • Author: Gratias Tom Mundakel, MBBS, DCH; Chief Editor: Maria Descartes, MD  more...
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Answer

Fluorescence in situ hybridization (FISH) may be used for rapid diagnosis of trisomy 21. It can be successful in both prenatal diagnosis and diagnosis in the neonatal period. A FISH study will detect the presence of trisomy 21; however, it does not provide information about whether trisomy 21 is secondary to a translocation. Therefore, a FISH test must be confirmed by a complete karyotype analysis.

Occult mosaicism for trisomy 21 may partially explain the association between family history of Down syndrome and risk of Alzheimer disease. Screening for mosaicism with FISH is indicated in selected patients with mild developmental delay and those with early onset Alzheimer disease. [55]

Evaluation of the proportion of cells with trisomy 21 in mosaic trisomy 21 includes the following [56] :

  • Lymphocyte preparations

  • Buccal mucosa cellular preparations

  • FISH

  • Scoring frequency of trisomic cells


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