The XA 13/18/21 mix of specific probes allows detecting copy number variations of chromosomes 13, 18, and 21. The green labeled probe hybridizes to a region at 13q14 including the RB1 locus, the blue (aqua) labeled probe hybridizes to a locus at 18q21, and the orange labeled probe hybridizes to a region at 21q22 including the DSCR4 (Down syndrome critical region 4).

Probe maps are created in accordance with the intended purpose of the product. Solid colored bars do not necessarily indicate that the probe fully covers the indicated genomic region. Therefore, caution is advised when interpreting results generated through off-label use. Probe map details based on UCSC Genome Browser GRCh37/hg19. Map components not to scale. Further information is available on request.

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. Trisomy 13 syndrome is a rare chromosomal disorder in which all or a portion of chromosome 13 appears three times (trisomy). Based on molecular results, a region ranging from from 13q14-13qter has been found to be critically involved in Patau syndrome. Most of the features of Edwards syndrome have been shown to be associated with duplication of the region 18q12.3-q22.1. A locus-specific probe for 18q21 gives clearer signals and provides less ambiguous results compared to a centromeric probe for chromosome 18.

XA 13/18/21 hybridized to cultured amniocytes. A normal signal constellation is observed for 13q14 and 21q22, two green and two orange signals, respectively. For the 18q21 locus-specific probe three blue signals are shown.

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• Tepperberg et al (2001) Prenat Diagn 21:293-301
• Stumm et al (2006) Cytogenet Genome Res 114:296-301