Delineation of complex chromosomal rearrangements: evidence for increased complexity.

There is an assumption of parsimony with regard to the number of chromosomes involved in rearrangements and to the number of breaks within those chromosomes. Highly complex chromosome rearrangements are thought to be relatively rare, with the risk for phenotypic abnormalities increasing as the number of chromosomes and chromosomal breaks involved in the rearrangement increases. We report here five cases of de novo complex chromosome rearrangements, each with a minimum of four breaks. Deletions were found in four cases, and in at least one case, a number of genes or potential genes might have been disrupted. This study highlights the importance of the detailed delineation of complex rearrangements, beginning with high-resolution chromosome analysis, and emphasizes the utility of fluorescence in situ hybridization in combination with the data available from the Human Genome Project as a means to delineate such rearrangements.