Normal Fetus with two Chromosome 21s

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Triallelic Trisomy,
fetus with Down Syndrome

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Diallelic Trisomy,
fetus with Down Syndrome

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A small amount of amniotic fluid is used for PCR analysis. Using DNA extracted directly from uncultured amniotic fluid cells, selected genomic regions are amplified by the polymerase chain reaction and then quantified using fluorescent markers.

Multiplex tag systems then enable the clear enumeration of the particular chromosomes known to be involved in abnormal fetal outcome. Six DNA markers are used for each of the autosomes 21,18 and 13, five markers for the X-chromosome and two for the Y-chromosome

Definitive results are normally available within 24-48 hours of sample receipt.

To detect other abnormalities such as mosaics, the cytogenetic team may then complement Amnio-PCR with a routine karyotype analysis.