Complex chromosomal rearrangements: origin and meiotic behavior

Complex chromosomal rearrangements (CCRs) describe structural rearrangements, essentially translocations, involving at least three breakpoints on two or more chromosomes. Although they are rare in humans, their clinical identification is important since CCR carriers can display various phenotypes which include phenotypically normal subjects, infertile males and patients with mental retardation and/or congenital abnormalities. The rearrangement can be de novo or familial. The use of fluorescent in situ hybridization assays and molecular techniques for the characterization of CCRs have indicated that the rearrangements could be more complex than initially assumed. Accumulating data have revealed that the mechanisms underlying the genesis of CCRs remain elusive.We performed a large PubMed search in order to summarize the current knowledge in this field and address important aspects of CCR formation and meiotic behavior, highlighting the complexity of these rearrangements at the chromosomal and genomic level.The review of published data indicates that the complexity of CCRs is becoming increasingly known, thanks to the application of more and more efficient molecular techniques. These approaches have allowed the precise sequence analysis of breakpoints and the identification of insertions, deletions, inversions and recombination events. New models have been proposed for the formation of CCRs, based on replication-based mechanisms and specific sequence elements. Their meiotic behavior has been discussed in the light of these new molecular data.Despite the increasing understanding of the mechanisms involved in their genesis, CCRs arise as unique, complex events for which the genetic and reproductive counseling of carriers remains a challenge.