Trisomy 21 (Down’s Syndrome), Fluorescent In Situ Hybridisation


Trisomy 21 (Down’s syndrome) is the most frequent of the autosomal trisomies in liveborns and is the most common chromosomal abnormality among children. The condition is usually the result of malsegregation (non-disjunction) of chromosome 21 in meiosis in either oogenesis (the risk of which increases with maternal age) or spermatogenesis. However, in 80 – 95 % of trisomy 21 cases the source of the extra chromosome is maternal. In about 5% of trisomy 21 cases, the condition is probably due to mitotic non-disjunction of a chromosome 21 in the early embryo.


Trisomy 21 by FISH is used to confirm the diagnosis of Down’s syndrome in suspected individuals. This test is also used as a prenatal diagnostic tool, (when performed on amniotic fluid), to confirm or rule out Down’s syndrome pregnancies, especially after triple or quadruple test results suggestive of high-risk pregnancy. This test offers an advantage over traditional chromosomal Karyotyping as it is rapid, results are usually reported within 24 hours, allowing for enough time to consider the future of a given pregnancy.

Sample Type, Quantity & Conditions

7 ml Heparin Whole Blood / Amniotic Fluid Room Temperature

Special Precautions

Normal Range

By Report

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