POLY-FISH - A TECHNIQUE OF REPEATED HYBRIDIZATIONS THAT IMPROVES CYTOGENETIC ANALYSIS OF FETAL CELLS IN MATERNAL BLOOD

Prenatal diagnosis of fetal chromosomal abnormalities using interphase fetal nucleated erythrocytes (FNRBCs) separated from maternal periphe ral blood can be technically challenging due to the limited number of FNRBCs available for analysis, the limited number of probes that can b e used simultaneously, and low FISH efficiency on the formaldehyde-fix ed and immunohistochemically stained interphase FNRBCs. We developed a technique of sequential FISH analysis that involves removal of the pr evious hybridized probe under denaturing conditions, and rehybridizati on with different probes to improve FISH efficiency. This technique fa cilitates the analysis of multiple chromosome-specific probes on the s ame nuclei. Results from our experiments show that FISH can be perform ed at least nine times on the same interphase nucleus and at least thr ee different probes can be used simultaneously. Thus, theoretically, a t least 24 different chromosomes can be analysed on a single interphas e fetal cell isolated from maternal blood. We have termed this techniq ue 'Poly-FISH', and have successfully diagnosed trisomy 21, triploidy, and other chromosome abnormalities in FNRBCs using this technique. (C ) 1998 John Wiley & Sons, Ltd.