IDENTIFICATION OF THE ORIGIN OF DOUBLE MINUTES IN NORMAL HUMAN-CELLS BY LASER-BASED CHROMOSOME MICRODISSECTION APPROACH

Single copies of tiny chromosome fragments, appearing as double minute s, were observed in a high proportion of cells from amniotic fluid cul tures of two mothers;undergoing prenatal testing because of advanced a ge. We applied a laser-based chromosome microdissection method to diag nose the origin of the double minutes. The diagnostic procedures consi sted of microdissection of double minutes from a single cell, polymera se chain reaction (PCR) amplification of the dissected DNA, and subseq uent fluorescence in situ hybridization (FISH) using the PCR products as a probe pool. Metaphase chromosomes from the patients' cells and fr om a karyotypically normal individual were probed. Using this strategy , we were able to determine that the double minutes originated from th e centromere of chromosome 13 or 21 in one case, and from the chromoso me 12 centromere in the other. The characterization of such double min utes helps both in the delineation of the nature of these epichromosom al bodies in normal individuals as well as in the clarification of gen etic counselling issues.