We compiled 104 constitutional de novo or sporadic rearranged chromosomes mimicking recombinants from a parental pericentric inversion in order to comment on their occurrence and parental derivation, meiotic or postzygotic origin, mean parental ages, and underlying pathways. Chromosomes involved were 1-9, 13-18, 20-22, and X (64 autosomes and 40 X chromosomes). In the whole series, mean paternal and maternal ages in cases of paternal (proved or possible; n = 29) or maternal (proved or possible; n = 36) descent were 31.14 and 28.31 years, respectively. Rearranged X chromosomes appeared to be of paternal descent and to arise through intrachromosomal non-allelic homologous recombination (NAHR), whereas rec-like autosomes were of either maternal or paternal origin and resulted from mechanisms proper of non-recurrent rearrangements. Except for some mosaic cases, most rearranged chromosomes apparently had a meiotic origin. Except for 8 rearranged X chromosomes transmitted maternally, all other cases compiled here were sporadic. Hence, the recurrence risk for sibs of propositi born to euploid parents is virtually zero, regardless of the imbalance's size. In brief, recombinant-like or rea chromosomes are not related to advanced parental age, may (chromosome X) or may not (autosomes) have a parent-of-origin bias, arise in meiosis or postzygotically, and appear to be mediated by NAHR, nonhomologous end joining, and telomere transposition. Because rearranged chromosomes 10, 11, and Y are also on record, albeit just in abstracts or listed in large series, we remark that all chromosomes can undergo this distinct rearrangement, even if it is still to be described for pairs 12 and 19.
