Prenatal detection of isochromosome 21 by QF-PCR. A comparison between FISH and traditional karyotyping.
OBJECTIVE
To compare rapid aneuploidy diagnostic tests with traditional karyotyping in the prenatal detection of Down syndrome due to isochromosome 21.


METHODS
Quantitative fluorescence PCR (QF-PCR) and fluorescent in situ hybridization (FISH) for chromosomes 13, 18, 21, X and Y were performed on uncultured amniotic fluid, followed by routine karyotyping. chromosomal and microsatellite analysis of peripheral blood from parents was also carried out.


RESULTS
The QF-PCR screening showed a trisomic diallelic pattern for 5 of 6 markers spanning the long arm of chromosome 21. FISH showed 3 signals in the interphase cells for the region 21q22.13-q22 during LSI 21 probe mapping. Cultured amniotic fluid revealed an isochromosome 21 resulting in a 46,XX,i(21)(q10),+21 karyotype. Parental microsatellite analysis proved that the isochromosome was paternal in origin.


CONCLUSIONS
The most informative analytical tool in this case appears to be QF-PCR, although a combination of QF-PCR and karyotyping provided the most evidence.
Gole
Leena
L
Department of Obstetrics and Gynaecology, National University Hospital, National University of Singapore, Singapore. leenagole@gmail.com
Lian
Ng Bee
NB
Lian
Ng Poh
NP
Rauff
Mary
M
Biswas
Arijit
A
Choolani
Mahesh
M
D000328:Adult; D000649:Amniocentesis; D002891:Chromosomes, Human, Pair 21; D004314:Down Syndrome / Q000175:diagnosis* / Q000235:genetics; D005260:Female; D005819:Genetic Markers; D006801:Humans; D017404:In Situ Hybridization, Fluorescence / Q000379:methods*; D018404:Isochromosomes; D007621:Karyotyping / Q000379:methods*; D016133:Polymerase Chain Reaction / Q000379:methods*; D011247:Pregnancy
D005819:Genetic Markers