COMPLEX CHROMOSOMAL REARRANGEMENTS - SOME BREAKPOINTS MAY HAVE CELLULAR ADAPTIVE SIGNIFICANCE

Cytogenetic study of a 3-year-old girl with developmental delay and so me minor abnormalities revealed a complex chromosome rearrangement (CC R) involving seven chromosomes with eight breakpoints, leading to mono somy of segment 5q15-q22. According to breakpoint distribution, CCRs m ay be classified as those with primary intrachromosomal abnormalities (including inversions, insertions, duplications, etc.) and those witho ut them. Only the latter group of CCRs was used in this analysis. Comp arison of theoretical and observed breakpoint distributions in 33 case s demonstrated that recurrent involvement of some chromosome(s) (''re- entry'') occurs more frequently than expected. One possible explanatio n for this observation suggests that the initial event leads to an uns table provisional rearrangement, and subsequent breaks are necessary t o stabilize the karyotype.