Numerical aberrations of autosomes 13, 18, 21, and sex chromosomes X and Y account for 95% of birth defects in newborns. FISH applied to uncultured amniocytes provides a method to identify those aberrations much faster than conventional chromosome analysis. It has become a standard to provide preliminary results for the detection of anomalies in less than 12 hours.
Duplications of chromosome bands 21q22.13-q22.2 have been shown to define the smallest region implicated in the causation of Down syndrome. Repetitive sequences around the centromeric region of the X and Y chromosomes can reliably determine Klinefelter syndrome (47,XXY), Triple-X syndrome (47,XXX), Turner syndrome (45,X0), and 47,XYY. This probe also allows to differentiate male fetal cells from maternal cells in blood contaminated amniocyte samples.